ORCID Profile
0000-0003-1609-3515
Current Organisations
University of Helsinki
,
Helsinki Institute of Physics
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Publisher: Springer Science and Business Media LLC
Date: 2022
Abstract: Measurements of jet substructure describing the composition of quark- and gluon-initiated jets are presented. Proton-proton (pp) collision data at $$ \\sqrt{s} $$ s = 13 TeV collected with the CMS detector are used, corresponding to an integrated luminosity of 35.9 fb − 1 . Generalized angularities are measured that characterize the jet substructure and distinguish quark- and gluon-initiated jets. These observables are sensitive to the distributions of transverse momenta and angular distances within a jet. The analysis is performed using a data s le of dijet events enriched in gluon-initiated jets, and, for the first time, a Z+jet event s le enriched in quark-initiated jets. The observables are measured in bins of jet transverse momentum, and as a function of the jet radius parameter. Each measurement is repeated applying a “soft drop” grooming procedure that removes soft and large angle radiation from the jet. Using these measurements, the ability of various models to describe jet substructure is assessed, showing a clear need for improvements in Monte Carlo generators.
Publisher: Springer Science and Business Media LLC
Date: 26-04-2022
Abstract: The top quark pair production cross section is measured in proton-proton collisions at a center-of-mass energy of 5.02 TeV. The data were collected in a special LHC low-energy and low-intensity run in 2017, and correspond to an integrated luminosity of 302 pb − 1 . The measurement is performed using events with one electron and one muon of opposite charge, and at least two jets. The measured cross section is 60 . 7 ± 5 . 0 (stat) ± 2 . 8 (syst) ± 1 . 1 (lumi) pb. A combination with the result in the single lepton + jets channel, based on data collected in 2015 at the same center-of-mass energy and corresponding to an integrated luminosity of 27.4 pb − 1 , is then performed. The resulting measured value is 63 . 0 ± 4 . 1 (stat) ± 3 . 0 (syst+lumi) pb, in agreement with the standard model prediction of $$ {66.8}_{-3.1}^{+2.9} $$ 66.8 − 3.1 + 2.9 pb.
Publisher: American Physical Society (APS)
Date: 05-10-2021
Publisher: American Physical Society (APS)
Date: 26-04-2022
Publisher: Springer Science and Business Media LLC
Date: 11-04-2022
Abstract: A search for long-lived particles decaying into muon pairs is performed using proton-proton collisions at a center-of-mass energy of 13 TeV, collected by the CMS experiment at the LHC in 2017 and 2018, corresponding to an integrated luminosity of 101 fb − 1 . The data sets used in this search were collected with a dedicated dimuon trigger stream with low transverse momentum thresholds, recorded at high rate by retaining a reduced amount of information, in order to explore otherwise inaccessible phase space at low dimuon mass and nonzero displacement from the primary interaction vertex. No significant excess of events beyond the standard model expectation is found. Upper limits on branching fractions at 95% confidence level are set on a wide range of mass and lifetime hypotheses in beyond the standard model frameworks with the Higgs boson decaying into a pair of long-lived dark photons, or with a long-lived scalar resonance arising from a decay of a b hadron. The limits are the most stringent to date for substantial regions of the parameter space. These results can be also used to constrain models of displaced dimuons that are not explicitly considered in this paper.
Publisher: Springer Science and Business Media LLC
Date: 07-2022
Abstract: A search for physics beyond the standard model (SM) in final states with an electron or muon and missing transverse momentum is presented. The analysis uses data from proton-proton collisions at a centre-of-mass energy of 13 TeV, collected with the CMS detector at the LHC in 2016–2018 and corresponding to an integrated luminosity of 138 fb − 1 . No significant deviation from the SM prediction is observed. Model-independent limits are set on the production cross section of W’ bosons decaying into lepton-plus-neutrino final states. Within the framework of the sequential standard model, with the combined results from the electron and muon decay channels a W’ boson with mass less than 5.7 TeV is excluded at 95% confidence level. Results on a SM precision test, the determination of the oblique electroweak W parameter, are presented using LHC data for the first time. These results together with those from the direct W’ resonance search are used to extend existing constraints on composite Higgs scenarios. This is the first experimental exclusion on compositeness parameters using results from LHC data other than Higgs boson measurements.
Publisher: Springer Science and Business Media LLC
Date: 11-2021
Abstract: A search is presented for new particles produced at the LHC in proton-proton collisions at $$ \\sqrt{s} $$ s = 13 TeV, using events with energetic jets and large missing transverse momentum. The analysis is based on a data s le corresponding to an integrated luminosity of 101 fb − 1 , collected in 2017–2018 with the CMS detector. Machine learning techniques are used to define separate categories for events with narrow jets from initial-state radiation and events with large-radius jets consistent with a hadronic decay of a W or Z boson. A statistical combination is made with an earlier search based on a data s le of 36 fb − 1 , collected in 2016. No significant excess of events is observed with respect to the standard model background expectation determined from control s les in data. The results are interpreted in terms of limits on the branching fraction of an invisible decay of the Higgs boson, as well as constraints on simplified models of dark matter, on first-generation scalar leptoquarks decaying to quarks and neutrinos, and on models with large extra dimensions. Several of the new limits, specifically for spin-1 dark matter mediators, pseudoscalar mediators, colored mediators, and leptoquarks, are the most restrictive to date.
Publisher: Springer Science and Business Media LLC
Date: 12-2021
Abstract: A search for new top quark interactions is performed within the framework of an effective field theory using the associated production of either one or two top quarks with a Z boson in multilepton final states. The data s le corresponds to an integrated luminosity of 138 fb − 1 of proton-proton collisions at $$ \\sqrt{s} $$ s = 13 TeV collected by the CMS experiment at the LHC. Five dimension-six operators modifying the electroweak interactions of the top quark are considered. Novel machine-learning techniques are used to enhance the sensitivity to effects arising from these operators. Distributions used for the signal extraction are parameterized in terms of Wilson coefficients describing the interaction strengths of the operators. All five Wilson coefficients are simultaneously fit to data and 95% confidence level intervals are computed. All results are consistent with the SM expectations.
Publisher: Springer Science and Business Media LLC
Date: 11-2021
Abstract: A measurement of the cross section of the associated production of a single top quark and a W boson in final states with a muon or electron and jets in proton-proton collisions at $$ \\sqrt{s} $$ s = 13 TeV is presented. The data correspond to an integrated luminosity of 36 fb − 1 collected with the CMS detector at the CERN LHC in 2016. A boosted decision tree is used to separate the tW signal from the dominant t $$ \\overline{\\mathrm{t}} $$ t ¯ background, whilst the subleading W+jets and multijet backgrounds are constrained using data-based estimates. This result is the first observation of the tW process in final states containing a muon or electron and jets, with a significance exceeding 5 standard deviations. The cross section is determined to be 89 ± 4 (stat) ± 12 (syst) pb, consistent with the standard model.
Publisher: Springer Science and Business Media LLC
Date: 26-04-2022
Abstract: A direct search for electroweak production of charginos and neutralinos is presented. Events with three or four leptons, with up to two hadronically decaying τ leptons, or two same-sign light leptons are analyzed. The data s le consists of 137 fb − 1 of proton-proton collisions with a center of mass energy of 13 TeV, recorded with the CMS detector at the LHC. The results are interpreted in terms of several simplified models. These represent a broad range of production and decay scenarios for charginos and neutralinos. A parametric neural network is used to target several of the models with large backgrounds. In addition, results using orthogonal search regions are provided for all the models, simplifying alternative theoretical interpretations of the results. Depending on the model hypotheses, charginos and neutralinos with masses up to values between 300 and 1450 GeV are excluded at 95% confidence level.
Publisher: Springer Science and Business Media LLC
Date: 12-2021
Abstract: A measurement of the top quark mass is performed using a data s le enriched with single top quark events produced in the t channel. The study is based on proton- proton collision data, corresponding to an integrated luminosity of 35.9 fb − 1 , recorded at $$ \\sqrt{s} $$ s = 13 TeV by the CMS experiment at the LHC in 2016. Candidate events are selected by requiring an isolated high-momentum lepton (muon or electron) and exactly two jets, of which one is identified as originating from a bottom quark. Multivariate discriminants are designed to separate the signal from the background. Optimized thresholds are placed on the discriminant outputs to obtain an event s le with high signal purity. The top quark mass is found to be $$ {172.13}_{-0.77}^{+0.76} $$ 172.13 − 0.77 + 0.76 GeV, where the uncertainty includes both the statistical and systematic components, reaching sub-GeV precision for the first time in this event topology. The masses of the top quark and antiquark are also determined separately using the lepton charge in the final state, from which the mass ratio and difference are determined to be $$ {0.9952}_{-0.0104}^{+0.0079} $$ 0.9952 − 0.0104 + 0.0079 and $$ {0.83}_{-1.35}^{+1.79} $$ 0.83 − 1.35 + 1.79 GeV, respectively. The results are consistent with CPT invariance.
Publisher: IOP Publishing
Date: 07-2022
DOI: 10.1088/1748-0221/17/07/P07023
Abstract: A new algorithm is presented to discriminate reconstructed hadronic decays of tau leptons ( τ h ) that originate from genuine tau leptons in the CMS detector against τ h candidates that originate from quark or gluon jets, electrons, or muons. The algorithm inputs information from all reconstructed particles in the vicinity of a τ h candidate and employs a deep neural network with convolutional layers to efficiently process the inputs. This algorithm leads to a significantly improved performance compared with the previously used one. For ex le, the efficiency for a genuine τ h to pass the discriminator against jets increases by 10–30% for a given efficiency for quark and gluon jets. Furthermore, a more efficient τ h reconstruction is introduced that incorporates additional hadronic decay modes. The superior performance of the new algorithm to discriminate against jets, electrons, and muons and the improved τ h reconstruction method are validated with LHC proton-proton collision data at √ s = 13 TeV.
Publisher: IOP Publishing
Date: 18-02-2020
Publisher: Elsevier BV
Date: 11-2022
Publisher: American Physical Society (APS)
Date: 25-06-2021
Publisher: Springer Science and Business Media LLC
Date: 13-09-2022
Abstract: A search is presented for a heavy W′ boson resonance decaying to a B or T vector-like quark and a t or a b quark, respectively. The analysis is performed using proton-proton collisions collected with the CMS detector at the LHC. The data correspond to an integrated luminosity of 138 fb − 1 at a center-of-mass energy of 13 TeV. Both decay channels result in a signature with a t quark, a Higgs or Z boson, and a b quark, each produced with a significant Lorentz boost. The all-hadronic decays of the Higgs or Z boson and of the t quark are selected using jet substructure techniques to reduce standard model backgrounds, resulting in a distinct three-jet W′ boson decay signature. No significant deviation in data with respect to the standard model background prediction is observed. Upper limits are set at 95% confidence level on the product of the W′ boson cross section and the final state branching fraction. A W′ boson with a mass below 3.1 TeV is excluded, given the benchmark model assumption of democratic branching fractions. In addition, limits are set based on generalizations of these assumptions. These are the most sensitive limits to date for this final state.
Publisher: American Physical Society (APS)
Date: 09-03-2022
Publisher: American Physical Society (APS)
Date: 20-05-2022
Publisher: Springer Science and Business Media LLC
Date: 10-2021
Abstract: Double-parton scattering is investigated using events with a Z boson and jets. The Z boson is reconstructed using only the dimuon channel. The measurements are performed with proton-proton collision data recorded by the CMS experiment at the LHC at $$ \sqrt{s} $$ s = 13 TeV, corresponding to an integrated luminosity of 35.9 fb − 1 collected in the year 2016. Differential cross sections of Z+ ≥ 1 jet and Z+ ≥ 2 jets are measured with transverse momentum of the jets above 20 GeV and pseudorapidity |η| 2 . 4. Several distributions with sensitivity to double-parton scattering effects are measured as functions of the angle and the transverse momentum imbalance between the Z boson and the jets. The measured distributions are compared with predictions from several event generators with different hadronization models and different parameter settings for multiparton interactions. The measured distributions show a dependence on the hadronization and multiparton interaction simulation parameters, and are important input for future improvements of the simulations.
Publisher: American Physical Society (APS)
Date: 17-09-2021
Publisher: Springer Science and Business Media LLC
Date: 10-2021
Abstract: The cross section for W or Z boson production in association with two photons is measured in proton-proton collisions at a centre-of-mass energy of 13 TeV. The data set corresponds to an integrated luminosity of 137 fb − 1 collected by the CMS experiment at the LHC. The W → ℓν and Z → ℓℓ decay modes (where ℓ = e , μ ) are used to extract the W γγ and Z γγ cross sections in a phase space defined by electron (muon) with transverse momentum larger than 30 GeV and photon transverse momentum larger than 20 GeV. All leptons and photons are required to have absolute pseudorapidity smaller than 2.5. The measured cross sections in this phase space are σ (W γγ ) = $$ {13.6}_{-1.9}^{+1.9}{\\left(\\mathrm{stat}\\right)}_{-4.0}^{+4.0} $$ 13.6 − 1.9 + 1.9 stat − 4.0 + 4.0 (syst) ± 0 . 08 (PDF + scale) fb and σ (Z γγ ) = $$ {5.41}_{-0.55}^{+0.58}{\\left(\\mathrm{stat}\\right)}_{-.070}^{+0.64} $$ 5.41 − 0.55 + 0.58 stat − .070 + 0.64 (syst) ± 0 . 06 (PDF + scale) fb. Limits on anomalous quartic gauge couplings are set in the framework of an effective field theory with dimension-8 operators.
Publisher: Springer Science and Business Media LLC
Date: 03-2022
Abstract: A search for long-lived particles (LLPs) produced in association with a Z boson is presented. The study is performed using data from proton-proton collisions with a center-of-mass energy of 13 TeV recorded by the CMS experiment during 2016–2018, corresponding to an integrated luminosity of 117 fb − 1 . The LLPs are assumed to decay to a pair of standard model quarks that are identified as displaced jets within the CMS tracker system. Triggers and selections based on Z boson decays to electron or muon pairs improve the sensitivity to light LLPs (down to 15 GeV). This search provides sensitivity to beyond the standard model scenarios which predict LLPs produced in association with a Z boson. In particular, the results are interpreted in the context of exotic decays of the Higgs boson to a pair of scalar LLPs (H → SS). The Higgs boson decay branching fraction is constrained to values less than 6% for proper decay lengths of 10–100 mm and for LLP masses between 40 and 55 GeV. In the case of low-mass ( ≈ 15 GeV) scalar particles that subsequently decay to a pair of b quarks, the search is sensitive to branching fractions $$ \\mathcal{B} $$ B (H → SS) 20% for proper decay lengths of 10–50 mm. The use of associated production with a Z boson increases the sensitivity to low-mass LLPs of this analysis with respect to gluon fusion searches. In the case of 15 GeV scalar LLPs, the improvement corresponds to a factor of 2 at a proper decay length of 30 mm.
Publisher: Springer Science and Business Media LLC
Date: 2022
Abstract: A measurement of inclusive four-jet production in proton-proton collisions at a center-of-mass energy of 13 TeV is presented. The transverse momenta of jets within |η| 4 . 7 are required to exceed 35, 30, 25, and 20 GeV for the first-, second-, third-, and fourth-leading jet, respectively. Differential cross sections are measured as functions of the jet transverse momentum, jet pseudorapidity, and several other observables that describe the angular correlations between the jets. The measured distributions show sensitivity to different aspects of the underlying event, parton shower modeling, and matrix element calculations. In particular, the interplay between angular correlations caused by parton shower and double-parton scattering contributions is shown to be important. The double-parton scattering contribution is extracted by means of a template fit to the data, using distributions for single-parton scattering obtained from Monte Carlo event generators and a double-parton scattering distribution constructed from inclusive single-jet events in data. The effective double-parton scattering cross section is calculated and discussed in view of previous measurements and of its dependence on the models used to describe the single- parton scattering background.
Publisher: American Physical Society (APS)
Date: 05-07-2022
Publisher: Springer Science and Business Media LLC
Date: 02-2022
Abstract: Inclusive and differential cross sections of single top quark production in association with a Z boson are measured in proton-proton collisions at a center-of-mass energy of 13 TeV with a data s le corresponding to an integrated luminosity of 138 fb − 1 recorded by the CMS experiment. Events are selected based on the presence of three leptons, electrons or muons, associated with leptonic Z boson and top quark decays. The measurement yields an inclusive cross section of $$ {87.9}_{-7.3}^{+7.5}{\\left(\\mathrm{stat}\\right)}_{-6.0}^{+7.3}\\left(\\mathrm{syst}\\right) $$ 87.9 − 7.3 + 7.5 stat − 6.0 + 7.3 syst fb for a dilepton invariant mass greater than 30 GeV, in agreement with standard model (SM) calculations and represents the most precise determination to date. The ratio between the cross sections for the top quark and the top antiquark production in association with a Z boson is measured as $$ {2.37}_{-0.42}^{+0.56}{\\left(\\mathrm{stat}\\right)}_{-0.13}^{+0.27}\\left(\\mathrm{syst}\\right) $$ 2.37 − 0.42 + 0.56 stat − 0.13 + 0.27 syst . Differential measurements at parton and particle levels are performed for the first time. Several kinematic observables are considered to study the modeling of the process. Results are compared to theoretical predictions with different assumptions on the source of the initial-state b quark and found to be in agreement, within the uncertainties. Additionally, the spin asymmetry, which is sensitive to the top quark polarization, is determined from the differential distribution of the polarization angle at parton level to be 0 . 54 ± 0 . 16 (stat) ± 0 . 06 (syst), in agreement with SM predictions.
Publisher: Springer Science and Business Media LLC
Date: 02-05-2012
Abstract: A search for new heavy resonances decaying to a pair of Higgs bosons (HH) in proton-proton collisions at a center-of-mass energy of 13 TeV is presented. Data were collected with the CMS detector at the LHC in 2016–2018, corresponding to an integrated luminosity of 138 fb − 1 . Resonances with a mass between 0.8 and 4.5 TeV are considered using events in which one Higgs boson decays into a bottom quark pair and the other into final states with either one or two charged leptons. Specifically, the single-lepton decay channel $$ \\mathrm{HH}\\to \\mathrm{b}\\overline{\\mathrm{b}}{\\mathrm{WW}}^{\\ast}\\to \\mathrm{b}\\overline{\\mathrm{b}}\\ell v\\mathrm{q}{\\overline{\\mathrm{q}}}^{\\prime } $$ HH → b b ¯ WW ∗ → b b ¯ ℓ v q q ¯ ′ and the dilepton decay channels $$ \\mathrm{HH}\\to \\mathrm{b}\\overline{\\mathrm{b}}{\\mathrm{WW}}^{\\ast}\\to \\mathrm{b}\\overline{\\mathrm{b}}\\ell v\\ell v $$ HH → b b ¯ WW ∗ → b b ¯ ℓ v ℓ v and $$ \\mathrm{HH}\\to \\mathrm{b}\\overline{\\mathrm{b}}\\uptau \\uptau \\to \\mathrm{b}\\overline{\\mathrm{b}}\\ell vv\\ell vv $$ HH → b b ¯ ττ → b b ¯ ℓ vv ℓ vv are examined, where ℓ in the final state corresponds to an electron or muon. The signal is extracted using a two-dimensional maximum likelihood fit of the $$ \\mathrm{H}\\to \\mathrm{b}\\overline{\\mathrm{b}} $$ H → b b ¯ jet mass and HH invariant mass distributions. No significant excess above the standard model expectation is observed in data. Model-independent exclusion limits are placed on the product of the cross section and branching fraction for narrow spin-0 and spin-2 massive bosons decaying to HH. The results are also interpreted in the context of radion and bulk graviton production in models with a warped extra spatial dimension. The results provide the most stringent limits to date for X → HH signatures with final-state leptons and at some masses provide the most sensitive limits of all X → HH searches.
Publisher: IOP Publishing
Date: 03-2022
DOI: 10.1088/1748-0221/17/03/P03014
Abstract: Many measurements at the LHC require efficient identification of heavy-flavour jets, i.e. jets originating from bottom (b) or charm (c) quarks. An overview of the algorithms used to identify c jets is described and a novel method to calibrate them is presented. This new method adjusts the entire distributions of the outputs obtained when the algorithms are applied to jets of different flavours. It is based on an iterative approach exploiting three distinct control regions that are enriched with either b jets, c jets, or light-flavour and gluon jets. Results are presented in the form of correction factors evaluated using proton-proton collision data with an integrated luminosity of 41.5 fb -1 at √s = 13 TeV, collected by the CMS experiment in 2017. The closure of the method is tested by applying the measured correction factors on simulated data sets and checking the agreement between the adjusted simulation and collision data. Furthermore, a validation is performed by testing the method on pseudodata, which emulate various mismodelling conditions. The calibrated results enable the use of the full distributions of heavy-flavour identification algorithm outputs, e.g. as inputs to machine-learning models. Thus, they are expected to increase the sensitivity of future physics analyses.
Publisher: Elsevier BV
Date: 08-2022
Publisher: Springer Science and Business Media LLC
Date: 16-05-2022
Abstract: A search is presented for single production of a vector-like T quark with charge 2 / 3 e , in the decay channel featuring a top quark and a Z boson, with the top quark decaying hadronically and the Z boson decaying to neutrinos. The search uses data collected by the CMS experiment in proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 137 fb − 1 recorded at the CERN LHC in 2016–2018. The search is sensitive to a T quark mass between 0.6 and 1.8 TeV with decay widths ranging from negligibly small up to 30% of the T quark mass. Reconstruction strategies for the top quark are based on the degree of Lorentz boosting of its final state. At 95% confidence level, the upper limit on the product of the cross section and branching fraction for a T quark of small decay width varies between 15 and 602 fb, depending on its mass. For a T quark with decay widths between 10 and 30% of its mass, this upper limit ranges between 16 and 836 fb. For most of the studied range, the results provide the best limits to date. This is the first search for single T quark production based on the full Run 2 data set of the LHC.
Publisher: Springer Science and Business Media LLC
Date: 16-05-2022
Abstract: The production cross section of a top quark pair in association with a photon is measured in proton-proton collisions in the decay channel with two oppositely charged leptons ( e ± μ ∓ , e + e − , or μ + μ − ). The measurement is performed using 138 fb − 1 of proton-proton collision data recorded by the CMS experiment at $$ \\sqrt{s} $$ s = 13 TeV during the 2016–2018 data-taking period of the CERN LHC. A fiducial phase space is defined such that photons radiated by initial-state particles, top quarks, or any of their decay products are included. An inclusive cross section of 175 . 2 ± 2 . 5(stat) ± 6 . 3(syst) fb is measured in a signal region with at least one jet coming from the hadronization of a bottom quark and exactly one photon with transverse momentum above 20 GeV. Differential cross sections are measured as functions of several kinematic observables of the photon, leptons, and jets, and compared to standard model predictions. The measurements are also interpreted in the standard model effective field theory framework, and limits are found on the relevant Wilson coefficients from these results alone and in combination with a previous CMS measurement of the t $$ \\overline{t} $$ t ¯ γ production process using the lepton+jets final state.
Publisher: Springer Science and Business Media LLC
Date: 07-2021
Abstract: Measurements of Higgs boson production cross sections and couplings in events where the Higgs boson decays into a pair of photons are reported. Events are selected from a s le of proton-proton collisions at $$ \\sqrt{s} $$ s = 13 TeV collected by the CMS detector at the LHC from 2016 to 2018, corresponding to an integrated luminosity of 137 fb − 1 . Analysis categories enriched in Higgs boson events produced via gluon fusion, vector boson fusion, vector boson associated production, and production associated with top quarks are constructed. The total Higgs boson signal strength, relative to the standard model (SM) prediction, is measured to be 1 . 12±0 . 09. Other properties of the Higgs boson are measured, including SM signal strength modifiers, production cross sections, and its couplings to other particles. These include the most precise measurements of gluon fusion and vector boson fusion Higgs boson production in several different kinematic regions, the first measurement of Higgs boson production in association with a top quark pair in five regions of the Higgs boson transverse momentum, and an upper limit on the rate of Higgs boson production in association with a single top quark. All results are found to be in agreement with the SM expectations.
Publisher: Springer Science and Business Media LLC
Date: 20-10-2022
DOI: 10.1038/S41567-022-01682-0
Abstract: Since the discovery of the Higgs boson in 2012, detailed studies of its properties have been ongoing. Besides its mass, its width—related to its lifetime—is an important parameter. One way to determine this quantity is to measure its off-shell production, where the Higgs boson mass is far away from its nominal value, and relating it to its on-shell production, where the mass is close to the nominal value. Here we report evidence for such off-shell contributions to the production cross-section of two Z bosons with data from the CMS experiment at the CERN Large Hadron Collider. We constrain the total rate of the off-shell Higgs boson contribution beyond the Z boson pair production threshold, relative to its standard model expectation, to the interval [0.0061, 2.0] at the 95% confidence level. The scenario with no off-shell contribution is excluded at a p -value of 0.0003 (3.6 standard deviations). We measure the width of the Higgs boson as $${{{\\varGamma }}}_{{{{{{\\rm{H}}}}}}}={3.2}_{-1.7}^{+2.4}\\,{{{{{\\rm{MeV}}}}}}$$ Γ H = 3.2 − 1.7 + 2.4 MeV , in agreement with the standard model expectation of 4.1 MeV. In addition, we set constraints on anomalous Higgs boson couplings to W and Z boson pairs.
Publisher: Elsevier BV
Date: 12-2022
Publisher: Springer Science and Business Media LLC
Date: 19-01-2023
DOI: 10.1038/S41567-022-01838-Y
Abstract: Protons consist of three valence quarks, two up-quarks and one down-quark, held together by gluons and a sea of quark-antiquark pairs. Collectively, quarks and gluons are referred to as partons. In a proton-proton collision, typically only one parton of each proton undergoes a hard scattering – referred to as single-parton scattering – leaving the remainder of each proton only slightly disturbed. Here, we report the study of double- and triple-parton scatterings through the simultaneous production of three J/ ψ mesons, which consist of a charm quark-antiquark pair, in proton-proton collisions recorded with the CMS experiment at the Large Hadron Collider. We observed this process – reconstructed through the decays of J/ ψ mesons into pairs of oppositely charged muons – with a statistical significance above five standard deviations. We measured the inclusive fiducial cross-section to be $$27{2}_{-104}^{+141}\\,{{{\\rm{(stat)}}}}\\,\\pm 17\\,{{{\\rm{(syst)}}}}\\,{{{\\rm{fb}}}}\\,$$ 27 2 − 104 + 141 (stat) ± 17 (syst) fb , and compared it to theoretical expectations for triple-J/ ψ meson production in single-, double- and triple-parton scattering scenarios. Assuming factorization of multiple hard-scattering probabilities in terms of single-parton scattering cross-sections, double- and triple-parton scattering are the dominant contributions for the measured process.
Publisher: Springer Science and Business Media LLC
Date: 05-2022
DOI: 10.1140/EPJC/S10052-022-10315-Y
Abstract: Using a data s le of $$\\sqrt{s}=13\\,\\text {TeV}$$ s = 13 TeV proton-proton collisions collected by the CMS experiment at the LHC in 2017 and 2018 with an integrated luminosity of $$103\\text {~fb}^{-1}$$ 103 fb - 1 , the $$\\text {B}^{0}_{\\mathrm{s}} \\rightarrow \\uppsi (\\text {2S})\\text {K}_\\mathrm{S}^{0}$$ B s 0 → ψ ( 2S ) K S 0 and $$\\text {B}^{0} \\rightarrow \\uppsi (\\text {2S})\\text {K}_\\mathrm{S}^{0} \\uppi ^+\\uppi ^-$$ B 0 → ψ ( 2S ) K S 0 π + π - decays are observed with significances exceeding 5 standard deviations. The resulting branching fraction ratios, measured for the first time, correspond to $${\\mathcal {B}}(\\text {B}^{0}_{\\mathrm{s}} \\rightarrow \\uppsi (\\text {2S})K_\\mathrm{S}^{0})/{\\mathcal {B}}(\\text {B}^{0}\\rightarrow \\uppsi (\\text {2S})K_\\mathrm{S}^{0}) = (3.33 \\pm 0.69 (\\text {stat})\\, \\pm 0.11\\,(\\text {syst}) \\pm 0.34\\,(f_{\\mathrm{s}}/f_{\\mathrm{d}})) \\times 10^{-2}$$ B ( B s 0 → ψ ( 2S ) K S 0 ) / B ( B 0 → ψ ( 2S ) K S 0 ) = ( 3.33 ± 0.69 ( stat ) ± 0.11 ( syst ) ± 0.34 ( f s / f d ) ) × 10 - 2 and $${\\mathcal {B}}(\\text {B}^{0} \\rightarrow \\uppsi (\\text {2S})\\text {K}_\\mathrm{S}^{0} \\uppi ^{+} \\uppi ^{-})/ {\\mathcal {B}}(\\text {B}^{0} \\rightarrow \\uppsi (\\text {2S})\\text {K}^{0}_{\\mathrm{S}}) = 0.480 \\pm 0.013\\,(\\text {stat}) \\pm 0.032\\,(\\text {syst})$$ B ( B 0 → ψ ( 2S ) K S 0 π + π - ) / B ( B 0 → ψ ( 2S ) K S 0 ) = 0.480 ± 0.013 ( stat ) ± 0.032 ( syst ) , where the last uncertainty in the first ratio is related to the uncertainty in the ratio of production cross sections of $$\\hbox {B}^{0}_{\\mathrm{s}}$$ B s 0 and $$\\hbox {B}^{0}$$ B 0 mesons, $$f_{\\mathrm{s}}/f_{\\mathrm{d}}$$ f s / f d .
Publisher: American Physical Society (APS)
Date: 02-11-2021
Publisher: American Physical Society (APS)
Date: 14-06-2022
Publisher: American Physical Society (APS)
Date: 30-11-2021
Publisher: Springer Science and Business Media LLC
Date: 10-2021
Abstract: A search for electroweak production of supersymmetric (SUSY) particles in final states with one lepton, a Higgs boson decaying to a pair of bottom quarks, and large missing transverse momentum is presented. The search uses data from proton-proton collisions at a center-of-mass energy of 13 TeV collected using the CMS detector at the LHC, corresponding to an integrated luminosity of 137 fb − 1 . The observed yields are consistent with backgrounds expected from the standard model. The results are interpreted in the context of a simplified SUSY model of chargino-neutralino production, with the chargino decaying to a W boson and the lightest SUSY particle (LSP) and the neutralino decaying to a Higgs boson and the LSP. Charginos and neutralinos with masses up to 820 GeV are excluded at 95% confidence level when the LSP mass is small, and LSPs with mass up to 350 GeV are excluded when the masses of the chargino and neutralino are approximately 700 GeV.
Publisher: Springer Science and Business Media LLC
Date: 03-06-2022
Abstract: The first measurement of the CP structure of the Yukawa coupling between the Higgs boson and τ leptons is presented. The measurement is based on data collected in proton-proton collisions at $$ \\sqrt{s} $$ s = 13 TeV by the CMS detector at the LHC, corresponding to an integrated luminosity of 137 fb − 1 . The analysis uses the angular correlation between the decay planes of τ leptons produced in Higgs boson decays. The effective mixing angle between CP -even and CP -odd τ Yukawa couplings is found to be − 1 ± 19°, compared to an expected value of 0 ± 21° at the 68.3% confidence level. The data disfavour the pure CP -odd scenario at 3.0 standard deviations. The results are compatible with predictions for the standard model Higgs boson.
Publisher: American Physical Society (APS)
Date: 23-02-2022
Publisher: Springer Science and Business Media LLC
Date: 14-04-2022
Abstract: A search has been performed for heavy resonances decaying to ZZ or ZW and for axion-like particles (ALPs) mediating nonresonant ZZ or ZH production, in final states with two charged leptons ( ℓ = e , μ) produced by the decay of a Z boson, and two quarks produced by the decay of a Z, W, or Higgs boson H. The analysis is sensitive to resonances with masses in the range 450 to 2000 GeV. Two categories are defined corresponding to the merged or resolved reconstruction of the hadronically decaying boson. The search is based on data collected during 2016–2018 by the CMS experiment at the LHC in proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 138 fb − 1 . No significant excess is observed in the data above the standard model background expectation. Upper limits on the production cross section of heavy, narrow spin-2 and spin-1 resonances are derived as functions of the resonance mass, and exclusion limits on the production of bulk graviton particles and W′ bosons are calculated in the framework of the warped extra dimensions and heavy vector triplet models, respectively. In addition, upper limits on the ALP-mediated diboson production cross section and ALP couplings to standard model particles are obtained in the framework of linear and chiral effective field theories. These are the first limits on nonresonant ALP-mediated ZZ and ZH production obtained by the LHC experiments.
Publisher: American Physical Society (APS)
Date: 18-08-2022
Publisher: Springer Science and Business Media LLC
Date: 03-05-2022
Abstract: Results are presented from a search for physics beyond the standard model in proton-proton collisions at $$ \\sqrt{s} $$ s = 13 TeV in channels with two Higgs bosons, each decaying via the process H → b $$ \\overline{\\mathrm{b}} $$ b ¯ , and large missing transverse momentum. The search uses a data s le corresponding to an integrated luminosity of 137 fb − 1 collected by the CMS experiment at the CERN LHC. The search is motivated by models of supersymmetry that predict the production of neutralinos, the neutral partners of the electroweak gauge and Higgs bosons. The observed event yields in the signal regions are found to be consistent with the standard model background expectations. The results are interpreted using simplified models of supersymmetry. For the electroweak production of nearly mass-degenerate higgsinos, each of whose decay chains yields a neutralino $$ \\left({\\overset{\\sim }{\\upchi}}_1^0\\right) $$ χ ~ 1 0 that in turn decays to a massless goldstino and a Higgs boson, $$ \\left({\\overset{\\sim }{\\upchi}}_1^0\\right) $$ χ ~ 1 0 masses in the range 175 to 1025 GeV are excluded at 95% confidence level. For the strong production of gluino pairs decaying via a slightly lighter $$ \\left({\\overset{\\sim }{\\upchi}}_2^0\\right) $$ χ ~ 2 0 to H and a light $$ \\left({\\overset{\\sim }{\\upchi}}_1^0\\right) $$ χ ~ 1 0 , gluino masses below 2330 GeV are excluded.
Publisher: Springer Science and Business Media LLC
Date: 11-2021
Abstract: A search for a heavy Higgs boson H decaying into the observed Higgs boson h with a mass of 125 GeV and another Higgs boson h S is presented. The h and h S bosons are required to decay into a pair of tau leptons and a pair of b quarks, respectively. The search uses a s le of proton-proton collisions collected with the CMS detector at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 137 fb −1 . Mass ranges of 240–3000 GeV for m H and 60–2800 GeV for $$ {m}_{{\\mathrm{h}}_{\\mathrm{S}}} $$ m h S are explored in the search. No signal has been observed. Model independent 95% confidence level upper limits on the product of the production cross section and the branching fractions of the signal process are set with a sensitivity ranging from 125 fb (for m H = 240 GeV) to 2 . 7 fb (for m H = 1000 GeV). These limits are compared to maximally allowed products of the production cross section and the branching fractions of the signal process in the next-to-minimal supersymmetric extension of the standard model.
Publisher: Springer Science and Business Media LLC
Date: 12-2021
Abstract: The production cross section of a top quark pair in association with a photon is measured in proton-proton collisions at a center-of-mass energy of 13 TeV. The data set, corresponding to an integrated luminosity of 137 fb − 1 , was recorded by the CMS experiment during the 2016–2018 data taking of the LHC. The measurements are performed in a fiducial volume defined at the particle level. Events with an isolated, highly energetic lepton, at least three jets from the hadronization of quarks, among which at least one is b tagged, and one isolated photon are selected. The inclusive fiducial t $$ \overline{\mathrm{t}} $$ t ¯ γ cross section, for a photon with transverse momentum greater than 20 GeV and pseudorapidity |η| 1 . 4442, is measured to be 798 ± 7(stat) ± 48(syst) fb, in good agreement with the prediction from the standard model at next-to-leading order in quantum chromodynamics. The differential cross sections are also measured as a function of several kinematic observables and interpreted in the framework of the standard model effective field theory (EFT), leading to the most stringent direct limits to date on anomalous electromagnetic dipole moment interactions of the top quark and the photon.
Publisher: Springer Science and Business Media LLC
Date: 08-04-2022
Abstract: A search for a heavy resonance decaying into a top quark and a W boson in proton-proton collisions at $$ \\sqrt{s} $$ s = 13 TeV is presented. The data analyzed were recorded with the CMS detector at the LHC and correspond to an integrated luminosity of 138 fb − 1 . The top quark is reconstructed as a single jet and the W boson, from its decay into an electron or muon and the corresponding neutrino. A top quark tagging technique based on jet clustering with a variable distance parameter and simultaneous jet grooming is used to identify jets from the collimated top quark decay. The results are interpreted in the context of two benchmark models, where the heavy resonance is either an excited bottom quark b ∗ or a vector-like quark B. A statistical combination with an earlier search by the CMS Collaboration in the all-hadronic final state is performed to place upper cross section limits on these two models. The new analysis extends the lower range of resonance mass probed from 1.4 down to 0.7 TeV. For left-handed, right-handed, and vector-like couplings, b ∗ masses up to 3.0, 3.0, and 3.2 TeV are excluded at 95% confidence level, respectively. The observed upper limits represent the most stringent constraints on the b ∗ model to date.
Publisher: Springer Science and Business Media LLC
Date: 08-04-2022
Abstract: A search is presented for a right-handed W boson (W R ) and a heavy neutrino (N), in a final state consisting of two same-flavor leptons (ee or μμ) and two quarks. The search is performed with the CMS experiment at the CERN LHC using a data s le of proton-proton collisions at a center-of-mass energy of 13 TeV corresponding to an integrated luminosity of 138 fb − 1 . The search covers two regions of phase space, one where the decay products of the heavy neutrino are merged into a single large-area jet, and one where the decay products are well separated. The expected signal is characterized by an excess in the invariant mass distribution of the final-state objects. No significant excess over the standard model background expectations is observed. The observations are interpreted as upper limits on the product of W R production cross sections and branching fractions assuming that couplings are identical to those of the standard model W boson. For N masses m N equal to half the W R mass $$ {m}_{{\\mathrm{W}}_{\\mathrm{R}}} $$ m W R ( m N = 0 . 2 TeV), $$ {m}_{{\\mathrm{W}}_{\\mathrm{R}}} $$ m W R is excluded at 95% confidence level up to 4.7 (4.8) and 5.0 (5.4) TeV for the electron and muon channels, respectively. This analysis provides the most stringent limits on the W R mass to date.
Publisher: American Physical Society (APS)
Date: 13-07-2022
Publisher: American Physical Society (APS)
Date: 23-12-2021
Publisher: Springer Science and Business Media LLC
Date: 04-08-2022
Abstract: A measurement of the forward-backward asymmetry of pairs of oppositely charged leptons (dimuons and dielectrons) produced by the Drell-Yan process in proton-proton collisions is presented. The data s le corresponds to an integrated luminosity of 138 fb − 1 collected with the CMS detector at the LHC at a center-of-mass energy of 13 TeV. The asymmetry is measured as a function of lepton pair mass for masses larger than 170 GeV and compared with standard model predictions. An inclusive measurement across both channels and the full mass range yields an asymmetry of 0 . 612 ± 0 . 005 (stat) ± 0 . 007 (syst). As a test of lepton flavor universality, the difference between the dimuon and dielectron asymmetries is measured as well. No statistically significant deviations from standard model predictions are observed. The measurements are used to set limits on the presence of additional gauge bosons. For a Z′ boson in the sequential standard model the observed (expected) 95% confidence level lower limit on the Z′ mass is 4.4 TeV (3.7 TeV).
Publisher: American Physical Society (APS)
Date: 21-06-2022
Publisher: Springer Science and Business Media LLC
Date: 03-2022
Abstract: The cross sections for inclusive and Mueller-Navelet dijet production are measured as a function of the rapidity separation between the jets in proton-proton collisions at $$ \sqrt{s} $$ s = 2 . 76 TeV for jets with transverse momentum p T 35 GeV and rapidity | y | 4 . 7. Various dijet production cross section ratios are also measured. A veto on additional jets with p T 20 GeV is introduced to improve the sensitivity to the effects of the Balitsky-Fadin-Kuraev-Lipatov (BFKL) evolution. The measurement is compared with the predictions of various Monte Carlo models based on leading-order and next-to-leading-order calculations including the Dokshitzer-Gribov-Lipatov-Altarelli-Parisi leading-logarithm (LL) parton shower as well as the LL BFKL resummation.
Publisher: Springer Science and Business Media LLC
Date: 14-04-2022
Abstract: A search for supersymmetry in events with two or three low-momentum leptons and missing transverse momentum is performed. The search uses proton-proton collisions at $$ \\sqrt{s} $$ s = 13 TeV collected in the three-year period 2016–2018 by the CMS experiment at the LHC and corresponding to an integrated luminosity of up to 137 fb − 1 . The data are found to be in agreement with expectations from standard model processes. The results are interpreted in terms of electroweakino and top squark pair production with a small mass difference between the produced supersymmetric particles and the lightest neutralino. For the electroweakino interpretation, two simplified models are used, a wino-bino model and a higgsino model. Exclusion limits at 95% confidence level are set on $$ {\\overset{\\sim }{\\upchi}}_2^0/{\\overset{\\sim }{\\upchi}}_1^{\\pm } $$ χ ~ 2 0 / χ ~ 1 ± masses up to 275 GeV for a mass difference of 10 GeV in the wino-bino case, and up to 205(150) GeV for a mass difference of 7.5 (3) GeV in the higgsino case. The results for the higgsino are further interpreted using a phenomenological minimal supersymmetric standard model, excluding the higgsino mass parameter μ up to 180 GeV with the bino mass parameter M 1 at 800 GeV. In the top squark interpretation, exclusion limits are set at top squark masses up to 540 GeV for four-body top squark decays and up to 480 GeV for chargino-mediated decays with a mass difference of 30 GeV.
Publisher: American Physical Society (APS)
Date: 06-07-2022
Publisher: American Physical Society (APS)
Date: 31-08-2021
Publisher: Springer Science and Business Media LLC
Date: 07-2022
Abstract: The associated production of a W and a Z boson is studied in final states with multiple leptons produced in proton-proton (pp) collisions at a centre-of-mass energy of 13 TeV using 137 fb − 1 of data collected with the CMS detector at the LHC. A measurement of the total inclusive production cross section yields σ tot (pp → WZ) = 50 . 6 ± 0 . 8 (stat) ± 1 . 5 (syst) ± 1 . 1 (lumi) ± 0 . 5 (theo) pb. Measurements of the fiducial and differential cross sections for several key observables are also performed in all the final-state lepton flavour and charge compositions with a total of three charged leptons, which can be electrons or muons. All results are compared with theoretical predictions computed up to next-to-next-to-leading order in quantum chromodynamics plus next-to-leading or- der in electroweak theory and for various sets of parton distribution functions. The results include direct measurements of the charge asymmetry and the W and Z vector boson polarization. The first observation of longitudinally polarized W bosons in WZ production is reported. Anomalous gauge couplings are searched for, leading to new constraints on beyond-the-standard-model contributions to the WZ triple gauge coupling.
Publisher: Springer Science and Business Media LLC
Date: 15-06-2022
Abstract: Results are presented from a search for charged-lepton flavor violating (CLFV) interactions in top quark production and decay in pp collisions at a center-of-mass energy of 13 TeV. The events are required to contain one oppositely charged electron-muon pair in the final state, along with at least one jet identified as originating from a bottom quark. The data correspond to an integrated luminosity of 138 fb − 1 , collected by the CMS experiment at the LHC. This analysis includes both the production (q → e μ t) and decay (t → e μ q) modes of the top quark through CLFV interactions, with q referring to a u or c quark. These interactions are parametrized using an effective field theory approach. With no significant excess over the standard model expectation, the results are interpreted in terms of vector-, scalar-, and tensor-like CLFV four-fermion effective interactions. Finally, observed exclusion limits are set at 95% confidence levels on the respective branching fractions of a top quark to an e μ pair and an up (charm) quark of 0 . 13 × 10 − 6 (1 . 31 × 10 − 6 ), 0 . 07 × 10 − 6 (0 . 89 × 10 − 6 ), and 0 . 25 × 10 − 6 (2 . 59 × 10 − 6 ) for vector, scalar, and tensor CLFV interactions, respectively.
Publisher: American Physical Society (APS)
Date: 25-02-2022
Publisher: American Physical Society (APS)
Date: 06-07-2022
Publisher: Elsevier BV
Date: 09-2022
Publisher: American Physical Society (APS)
Date: 31-05-2022
Publisher: Springer Science and Business Media LLC
Date: 07-2019
Abstract: A search for heavy neutral leptons (HNLs), the right-handed Dirac or Majorana neutrinos, is performed in final states with three charged leptons (electrons or muons) using proton-proton collision data collected by the CMS experiment at $$ \\sqrt{s} $$ s = 13 TeV at the CERN LHC. The data correspond to an integrated luminosity of 138 fb − 1 . The HNLs could be produced through mixing with standard model neutrinos ν . For small values of the HNL mass ( 20 GeV) and the square of the HNL- ν mixing parameter (10 − 7 –10 − 2 ), the decay length of these particles can be large enough so that the secondary vertex of the HNL decay can be resolved with the CMS silicon tracker. The selected final state consists of one lepton emerging from the primary proton-proton collision vertex, and two leptons forming a displaced, secondary vertex. No significant deviations from the standard model expectations are observed, and constraints are obtained on the HNL mass and coupling strength parameters, excluding previously unexplored regions of parameter space in the mass range 1–20 GeV and squared mixing parameter values as low as 10 − 7 .
Publisher: Springer Science and Business Media LLC
Date: 29-06-2022
Abstract: The first collider search for dark matter arising from a strongly coupled hidden sector is presented and uses a data s le corresponding to 138 fb −1 , collected with the CMS detector at the CERN LHC, at $$ \\sqrt{s} $$ s = 13 TeV. The hidden sector is hypothesized to couple to the standard model (SM) via a heavy leptophobic Z′ mediator produced as a resonance in proton-proton collisions. The mediator decay results in two “semivisible” jets, containing both visible matter and invisible dark matter. The final state therefore includes moderate missing energy aligned with one of the jets, a signature ignored by most dark matter searches. No structure in the dijet transverse mass spectra compatible with the signal is observed. Assuming the Z′ boson has a universal coupling of 0.25 to the SM quarks, an inclusive search, relevant to any model that exhibits this kinematic behavior, excludes mediator masses of 1.5–4.0 TeV at 95% confidence level, depending on the other signal model parameters. To enhance the sensitivity of the search for this particular class of hidden sector models, a boosted decision tree (BDT) is trained using jet substructure variables to distinguish between semivisible jets and SM jets from background processes. When the BDT is employed to identify each jet in the dijet system as semivisible, the mediator mass exclusion increases to 5.1 TeV, for wider ranges of the other signal model parameters. These limits exclude a wide range of strongly coupled hidden sector models for the first time.
Publisher: Springer Science and Business Media LLC
Date: 02-2022
Abstract: A search for flavor-changing neutral current interactions of the top quark (t) and the Higgs boson (H) is presented. The search is based on a data s le corresponding to an integrated luminosity of 137 fb − 1 recorded by the CMS experiment at the LHC in proton-proton collisions at $$ \\sqrt{s} $$ s = 13 TeV. Events containing exactly one lepton (muon or electron) and at least three jets, among which at least two are identified as originating from the hadronization of a bottom quark, are analyzed. A set of deep neural networks is used for kinematic event reconstruction, while boosted decision trees distinguish the signal from the background events. No significant excess over the background predictions is observed, and upper limits on the signal production cross sections are extracted. These limits are interpreted in terms of top quark decay branching fractions ( $$ \\mathcal{B} $$ B ) to the Higgs boson and an up (u) or a charm quark (c). Assuming one nonvanishing extra coupling at a time, the observed (expected) upper limits at 95% confidence level are $$ \\mathcal{B} $$ B (t → Hu) 0 . 079 (0 . 11)% and $$ \\mathcal{B} $$ B (t → Hc) 0 . 094 (0 . 086)%.
No related grants have been discovered for Laura Martikainen.