ORCID Profile
0000-0002-2691-7963
Current Organisation
Stanford University
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Publisher: American Physical Society (APS)
Date: 05-10-2020
Publisher: Elsevier BV
Date: 09-2020
Publisher: American Physical Society (APS)
Date: 14-06-2019
Publisher: Springer Science and Business Media LLC
Date: 06-2018
DOI: 10.1140/EPJC/S10052-018-5950-6
Abstract: The nuclear modification factors of $${\mathrm {J}/\psi }$$ J / ψ and $$\psi \text {(2S)}$$ ψ (2S) mesons are measured in $$\text {PbPb}$$ PbPb collisions at a centre-of-mass energy per nucleon pair of $$\sqrt{\smash [b]{s_{_{\text {NN}}}}} = 5.02\,\text {Te}\text {V} $$ s NN = 5.02 TeV . The analysis is based on $$\text {PbPb}$$ PbPb and $$\mathrm {p}\mathrm {p}$$ p p data s les collected by CMS at the LHC in 2015, corresponding to integrated luminosities of 464 $$\,\mu \mathrm {b}^{-1}$$ μ b - 1 and 28 $$\,\text {pb}^\text {-1}$$ pb -1 , respectively. The measurements are performed in the dimuon rapidity range of $$|y | 2.4$$ | y | 2.4 as a function of centrality, rapidity, and transverse momentum ( $$p_{\mathrm {T}}$$ p T ) from $$p_{\mathrm {T}} =3$$ p T = 3 $${\,\text {Ge}\text {V}/}\text {c}$$ GeV / c in the most forward region and up to 50 $${\,\text {Ge}\text {V}/}\text {c}$$ GeV / c . Both prompt and nonprompt (coming from b hadron decays) $${\mathrm {J}/\psi }$$ J / ψ mesons are observed to be increasingly suppressed with centrality, with a magnitude similar to the one observed at $$\sqrt{\smash [b]{s_{_{\text {NN}}}}} = 2.76\,\text {Te}\text {V} $$ s NN = 2.76 TeV for the two $${\mathrm {J}/\psi }$$ J / ψ meson components. No dependence on rapidity is observed for either prompt or nonprompt $${\mathrm {J}/\psi }$$ J / ψ mesons. An indication of a lower prompt $${\mathrm {J}/\psi }$$ J / ψ meson suppression at $$p_{\mathrm {T}} 25$$ p T 25 $${\,\text {Ge}\text {V}/}\text {c}$$ GeV / c is seen with respect to that observed at intermediate $$p_{\mathrm {T}}$$ p T . The prompt $$\psi \text {(2S)}$$ ψ (2S) meson yield is found to be more suppressed than that of the prompt $${\mathrm {J}/\psi }$$ J / ψ mesons in the entire $$p_{\mathrm {T}}$$ p T range.
Publisher: IOP Publishing
Date: 28-02-2020
Publisher: American Physical Society (APS)
Date: 22-06-2020
Publisher: Springer Science and Business Media LLC
Date: 06-2018
Abstract: A search for flavor-changing neutral currents (FCNC) in events with the top quark and the Higgs boson is presented. The Higgs boson decay to a pair of b quarks is considered. The data s le corresponds to an integrated luminosity of 35.9 fb −1 recorded by the CMS experiment at the LHC in proton-proton collisions at $$ \\sqrt{s}=13 $$ s = 13 TeV. Two channels are considered: single top quark FCNC production in association with the Higgs boson (pp → tH), and top quark pair production with FCNC decay of the top quark (t → qH). Final states with one isolated lepton and at least three reconstructed jets, among which at least two are associated with b quarks, are studied. No significant deviation is observed from the predicted background. Observed (expected) upper limits at 95% confidence level are set on the branching fractions of top quark decays, ℬ(t → uH) 0.47% (0.34%) and ℬ(t → cH) 0.47% (0.44%), assuming a single nonzero FCNC coupling.
Publisher: American Physical Society (APS)
Date: 09-11-2020
Publisher: Springer Science and Business Media LLC
Date: 06-2020
Publisher: American Physical Society (APS)
Date: 16-11-2020
Publisher: IOP Publishing
Date: 15-09-2020
Publisher: American Physical Society (APS)
Date: 24-04-2020
Publisher: American Physical Society (APS)
Date: 05-08-2020
Publisher: American Physical Society (APS)
Date: 24-12-2020
Publisher: IOP Publishing
Date: 03-06-2020
Publisher: Elsevier BV
Date: 09-2020
Publisher: IOP Publishing
Date: 08-06-2020
DOI: 10.1088/1748-0221/15/06/P06009
Abstract: Measurements are presented of the reduction of signal output due to radiation damage for two types of plastic scintillator tiles used in the hadron endcap (HE) calorimeter of the CMS detector. The tiles were exposed to particles produced in proton-proton (pp) collisions at the CERN LHC with a center-of-mass energy of 13 TeV, corresponding to a delivered luminosity of 50 fb −1 . The measurements are based on readout channels of the HE that were instrumented with silicon photomultipliers, and are derived using data from several sources: a laser calibration system, a movable radioactive source, as well as hadrons and muons produced in pp collisions. Results from several irradiation c aigns using 60 Co sources are also discussed. The damage is presented as a function of dose rate. Within the range of these measurements, for a fixed dose the damage increases with decreasing dose rate.
Publisher: Springer Science and Business Media LLC
Date: 05-2020
Publisher: Springer Science and Business Media LLC
Date: 04-2020
Publisher: Springer Science and Business Media LLC
Date: 05-2020
DOI: 10.1140/EPJC/S10052-020-7858-1
Abstract: A measurement is presented of differential cross sections for t -channel single top quark and antiquark production in proton–proton collisions at a centre-of-mass energy of 13 $$\\,\\text {Te}\\text {V}$$ Te by the CMS experiment at the LHC. From a data set corresponding to an integrated luminosity of 35.9 $$\\,\\text {fb}^{-1}$$ fb - 1 , events containing one muon or electron and two or three jets are analysed. The cross section is measured as a function of the top quark transverse momentum ( $$p_{\\mathrm{T}} $$ p T ), rapidity, and polarisation angle, the charged lepton $$p_{\\mathrm{T}} $$ p T and rapidity, and the $$p_{\\mathrm{T}} $$ p T of the $$\\text {W}{}{}$$ W boson from the top quark decay. In addition, the charge ratio is measured differentially as a function of the top quark, charged lepton, and $$\\text {W}{}{}$$ W boson kinematic observables. The results are found to be in agreement with standard model predictions using various next-to-leading-order event generators and sets of parton distribution functions. Additionally, the spin asymmetry, sensitive to the top quark polarisation, is determined from the differential distribution of the polarisation angle at parton level to be $$0.440 \\pm 0.070$$ 0.440 ± 0.070 , in agreement with the standard model prediction.
Publisher: American Physical Society (APS)
Date: 12-08-2020
Publisher: American Physical Society (APS)
Date: 30-11-2020
Publisher: Springer Science and Business Media LLC
Date: 06-2020
Publisher: American Physical Society (APS)
Date: 30-11-2020
Publisher: American Physical Society (APS)
Date: 30-11-2020
Publisher: IOP Publishing
Date: 10-2020
Publisher: American Physical Society (APS)
Date: 25-03-2020
Publisher: Springer Science and Business Media LLC
Date: 07-2020
Abstract: The momentum-weighted sum of the electric charges of particles inside a jet, known as jet charge, is sensitive to the electric charge of the particle initiating the parton shower. This paper presents jet charge distributions in $$ \\sqrt{s_{\\mathrm{NN}}} $$ s NN = 5 . 02 TeV lead-lead (PbPb) and proton-proton (pp) collisions recorded with the CMS detector at the LHC. These data correspond to integrated luminosities of 404 μ b − 1 and 27.4 pb − 1 for PbPb and pp collisions, respectively. Leveraging the sensitivity of the jet charge to fundamental differences in the electric charges of quarks and gluons, the jet charge distributions from simulated events are used as templates to extract the quark- and gluon-like jet fractions from data. The modification of these jet fractions is examined by comparing pp and PbPb data as a function of the overlap of the colliding Pb nuclei (centrality). This measurement tests the color charge dependence of jet energy loss due to interactions with the quark-gluon plasma. No significant modification between different centrality classes and with respect to pp results is observed in the extracted quark- and gluon-like jet fractions.
Publisher: Elsevier BV
Date: 03-2019
Publisher: Springer Science and Business Media LLC
Date: 07-2020
Abstract: The transverse energy ( $$ {E}_{\mathrm{T}}^{\upgamma} $$ E T γ ) spectra of photons isolated from other particles are measured using proton-proton (pp) and lead-lead (PbPb) collisions at the LHC at $$ \sqrt{s_{\mathrm{NN}}} $$ s NN = 5 . 02 TeV with integrated luminosities of 27.4 pb − 1 and 404 μ b − 1 for pp and PbPb data, respectively. The results are presented for photons with 25 $$ {E}_{\mathrm{T}}^{\upgamma} $$ E T γ 200 GeV in the pseudorapidity range |η| 1 . 44, and for different centrality intervals for PbPb collisions. Photon production in PbPb collisions is consistent with that in pp collisions scaled by the number of binary nucleon-nucleon collisions, demonstrating that photons do not interact with the quark-gluon plasma. Therefore, isolated photons can provide information about the initial energy of the associated parton in photon+jet measurements. The results are compared with predictions from the next-to-leading-order jetphox generator for different parton distribution functions (PDFs) and nuclear PDFs (nPDFs). The comparisons can help to constrain the nPDFs global fits.
Publisher: Elsevier BV
Date: 03-2018
Publisher: American Physical Society (APS)
Date: 19-08-2020
Publisher: American Physical Society (APS)
Date: 07-12-2020
Publisher: Elsevier BV
Date: 12-2020
Publisher: Elsevier BV
Date: 07-2020
Publisher: Springer Science and Business Media LLC
Date: 08-2020
Abstract: The combination of measurements of the W boson polarization in top quark decays performed by the ATLAS and CMS collaborations is presented. The measurements are based on proton-proton collision data produced at the LHC at a centre-of-mass energy of 8 TeV, and corresponding to an integrated luminosity of about 20 fb − 1 for each experiment. The measurements used events containing one lepton and having different jet multiplicities in the final state. The results are quoted as fractions of W bosons with longitudinal ( F 0 ), left-handed ( F L ), or right-handed ( F R ) polarizations. The resulting combined measurements of the polarization fractions are F 0 = 0 . 693 ± 0 . 014 and F L = 0 . 315 ± 0 . 011. The fraction F R is calculated from the unitarity constraint to be F R = − 0 . 008 ± 0 . 007. These results are in agreement with the standard model predictions at next-to-next-to-leading order in perturbative quantum chromodynamics and represent an improvement in precision of 25 (29)% for F 0 ( F L ) with respect to the most precise single measurement. A limit on anomalous right-handed vector ( V R ), and left- and right-handed tensor ( g L , g R ) tWb couplings is set while fixing all others to their standard model values. The allowed regions are [ − 0 . 11 , 0 . 16] for V R , [ − 0 . 08 , 0 . 05] for g L , and [ − 0 . 04 , 0 . 02] for g R , at 95% confidence level. Limits on the corresponding Wilson coefficients are also derived.
Publisher: IOP Publishing
Date: 19-10-2020
Publisher: Springer Science and Business Media LLC
Date: 06-2020
Publisher: American Physical Society (APS)
Date: 21-05-2020
Publisher: Springer Science and Business Media LLC
Date: 11-2020
Abstract: The ratios of the production cross sections between the excited ϒ(2S) and ϒ(3S) mesons and the ϒ(1S) ground state, detected via their decay into two muons, are studied as a function of the number of charged particles in the event. The data are from proton-proton collisions at $$ \\sqrt{s} $$ s = 7 TeV, corresponding to an integrated luminosity of 4.8 fb − 1 , collected with the CMS detector at the LHC. Evidence of a decrease in these ratios as a function of the particle multiplicity is observed, more pronounced at low transverse momentum $$ {p}_{\\mathrm{T}}^{\\upmu \\upmu} $$ p T μμ . For ϒ(nS) mesons with $$ {p}_{\\mathrm{T}}^{\\upmu \\upmu} $$ p T μμ 7 GeV, where most of the data were collected, the correlation with multiplicity is studied as a function of the underlying event transverse sphericity and the number of particles in a cone around the ϒ(nS) direction. The ratios are found to be multiplicity independent for jet-like events. The mean $$ {p}_{\\mathrm{T}}^{\\upmu \\upmu} $$ p T μμ values for the ϒ(nS) states as a function of particle multiplicity are also measured and found to grow more steeply as their mass increases.
Publisher: Springer Science and Business Media LLC
Date: 07-2020
Abstract: A search for charged Higgs bosons (H ± ) decaying into a top and a bottom quark in the all-jet final state is presented. The analysis uses LHC proton-proton collision data recorded with the CMS detector in 2016 at $$ \\sqrt{s} $$ s = 13 TeV, corresponding to an integrated luminosity of 35.9 fb − 1 . No significant excess is observed above the expected background. Model-independent upper limits at 95% confidence level are set on the product of the H ± production cross section and branching fraction in two scenarios. For production in association with a top quark, limits of 21.3 to 0.007 pb are obtained for H ± masses in the range of 0.2 to 3 TeV. Combining this with a search in leptonic final states results in improved limits of 9.25 to 0.005 pb. The complementary s -channel production of an H ± is investigated in the mass range of 0.8 to 3 TeV and the corresponding upper limits are 4.5 to 0.023 pb. These results are interpreted using different minimal supersymmetric extensions of the standard model.
Publisher: Springer Science and Business Media LLC
Date: 07-2020
Abstract: Measurements of the cross section for the production of top quark pairs in association with a pair of jets from bottom quarks $$ \\left({\\sigma}_{\\mathrm{t}\\overline{\\mathrm{t}}\\mathrm{b}\\overline{\\mathrm{b}}}\\right) $$ σ t t ¯ b b ¯ and in association with a pair of jets from quarks of any flavor or gluons $$ \\left({\\sigma}_{\\mathrm{t}\\overline{\\mathrm{t}}\\mathrm{jj}}\\right) $$ σ t t ¯ jj and their ratio are presented. The data were collected in proton-proton collisions at a center-of-mass energy of 13 TeV by the CMS experiment at the LHC in 2016 and correspond to an integrated luminosity of 35.9 fb − 1 . The measurements are performed in a fiducial phase space and extrapolated to the full phase space, separately for the dilepton and lepton+jets channels, where lepton corresponds to either an electron or a muon. The results of the measurements in the fiducial phase space for the dilepton and lepton+jets channels, respectively, are $$ {\\sigma}_{\\mathrm{t}\\overline{\\mathrm{t}}\\mathrm{jj}} $$ σ t t ¯ jj = 2 . 36 ± 0 . 02 (stat) ± 0 . 20 (syst) pb and 31 . 0 ± 0 . 2 (stat) ± 2 . 9 (syst) pb, and for the cross section ratio 0 . 017 ± 0 . 001 (stat) ± 0 . 001 (syst) and 0 . 020 ± 0 . 001 (stat) ± 0 . 001 (syst). The values of $$ {\\sigma}_{\\mathrm{t}\\overline{\\mathrm{t}}\\mathrm{b}\\overline{\\mathrm{b}}} $$ σ t t ¯ b b ¯ are determined from the product of the $$ {\\sigma}_{\\mathrm{t}\\overline{\\mathrm{t}}\\mathrm{jj}} $$ σ t t ¯ jj and the cross section ratio, obtaining, respectively, 0 . 040 ± 0 . 002 (stat) ± 0 . 005 (syst) pb and 0 . 62 ± 0 . 03 (stat) ± 0 . 07 (syst) pb. These measurements are the most precise to date and are consistent, within the uncertainties, with the standard model expectations obtained using a matrix element calculation at next-to-leading order in quantum chromodynamics matched to a parton shower.
Publisher: Elsevier BV
Date: 10-2020
Publisher: Springer Science and Business Media LLC
Date: 07-2020
DOI: 10.1140/EPJC/S10052-020-7917-7
Abstract: Normalised multi-differential cross sections for top quark pair ( $$\\hbox {t}{\\bar{\\hbox {t}}}$$ t t ¯ ) production are measured in proton-proton collisions at a centre-of-mass energy of 13 $$\\,{\\text {TeV}}$$ TeV using events containing two oppositely charged leptons. The analysed data were recorded with the CMS detector in 2016 and correspond to an integrated luminosity of $$35.9{\\,{\\text {fb}}^{-1}} $$ 35.9 fb - 1 . The double-differential $$\\hbox {t}{\\bar{\\hbox {t}}}$$ t t ¯ cross section is measured as a function of the kinematic properties of the top quark and of the $$\\hbox {t}{\\bar{\\hbox {t}}}$$ t t ¯ system at parton level in the full phase space. A triple-differential measurement is performed as a function of the invariant mass and rapidity of the $$\\hbox {t}{\\bar{\\hbox {t}}}$$ t t ¯ system and the multiplicity of additional jets at particle level. The data are compared to predictions of Monte Carlo event generators that complement next-to-leading-order (NLO) quantum chromodynamics (QCD) calculations with parton showers. Together with a fixed-order NLO QCD calculation, the triple-differential measurement is used to extract values of the strong coupling strength $$\\alpha _{S}$$ α S and the top quark pole mass ( $$m_{{\\text {t}}}^{{\\text {pole}}}$$ m t pole ) using several sets of parton distribution functions (PDFs). The measurement of $$m_{{\\text {t}}}^{{\\text {pole}}}$$ m t pole exploits the sensitivity of the $$\\hbox {t}{\\bar{\\hbox {t}}}$$ t t ¯ invariant mass distribution to $$m_{{\\text {t}}}^{{\\text {pole}}}$$ m t pole near the production threshold. Furthermore, a simultaneous fit of the PDFs, $$\\alpha _{S}$$ α S , and $$m_{{\\text {t}}}^{{\\text {pole}}}$$ m t pole is performed at NLO, demonstrating that the new data have significant impact on the gluon PDF, and at the same time allow an accurate determination of $$\\alpha _{S}$$ α S and $$m_{{\\text {t}}}^{{\\text {pole}}}$$ m t pole . The values $$\\alpha _{S}(m_{{\\text {Z}}}) = 0.1135{}^{+0.0021}_{-0.0017}$$ α S ( m Z ) = 0.1135 - 0.0017 + 0.0021 and $$m_{{\\text {t}}}^{{\\text {pole}}} = 170.5 \\pm 0.8 \\,{\\text {GeV}} $$ m t pole = 170.5 ± 0.8 GeV are extracted, which account for experimental and theoretical uncertainties, the latter being estimated from NLO scale variations. Possible effects from Coulomb and soft-gluon resummation near the $$\\hbox {t}{\\bar{\\hbox {t}}}$$ t t ¯ production threshold are neglected in these parameter extractions. A rough estimate of these effects indicates an expected correction of $$m_{{\\text {t}}}^{{\\text {pole}}}$$ m t pole of the order of $$+1 \\,{\\text {GeV}} $$ + 1 GeV , which can be regarded as additional theoretical uncertainty in the current $$m_{{\\text {t}}}^{{\\text {pole}}}$$ m t pole extraction.
Publisher: Springer Science and Business Media LLC
Date: 04-2020
Publisher: Springer Science and Business Media LLC
Date: 05-2020
Publisher: Springer Science and Business Media LLC
Date: 05-2020
Publisher: American Physical Society (APS)
Date: 03-09-2020
Publisher: Springer Science and Business Media LLC
Date: 08-2020
Abstract: A search for a light pseudoscalar Higgs boson (a) decaying from the 125 GeV (or a heavier) scalar Higgs boson (H) is performed using the 2016 LHC proton-proton collision data at $$ \\sqrt{s} $$ s = 13 TeV, corresponding to an integrated luminosity of 35 . 9 fb − 1 , collected by the CMS experiment. The analysis considers gluon fusion and vector boson fusion production of the H, followed by the decay H → aa → μμττ , and considers pseudoscalar masses in the range 3 . 6 m a 21 GeV. Because of the large mass difference between the H and the a bosons and the small masses of the a boson decay products, both the μμ and the ττ pairs have high Lorentz boost and are collimated. The ττ reconstruction efficiency is increased by modifying the standard technique for hadronic τ lepton decay reconstruction to account for a nearby muon. No significant signal is observed. Model-independent limits are set at 95% confidence level, as a function of m a , on the branching fraction (ℬ) for H → aa → μμττ , down to 1 . 5 (2 . 0) × 10 − 4 for m H = 125 (300) GeV. Model-dependent limits on ℬ(H → aa) are set within the context of two Higgs doublets plus singlet models, with the most stringent results obtained for Type-III models. These results extend current LHC searches for heavier a bosons that decay to resolved lepton pairs and provide the first such bounds for an H boson with a mass above 125 GeV.
Publisher: IOP Publishing
Date: 05-05-2020
Publisher: Springer Science and Business Media LLC
Date: 12-2020
Abstract: A search for standard model Higgs bosons (H) produced with transverse momentum ( p T ) greater than 450 GeV and decaying to bottom quark-antiquark pairs ( $$ \\mathrm{b}\\overline{\\mathrm{b}} $$ b b ¯ ) is performed using proton-proton collision data collected by the CMS experiment at the LHC at $$ \\sqrt{s} $$ s = 13 TeV. The data s le corresponds to an integrated luminosity of 137 fb − 1 . The search is inclusive in the Higgs boson production mode. Highly Lorentz-boosted Higgs bosons decaying to $$ \\mathrm{b}\\overline{\\mathrm{b}} $$ b b ¯ are reconstructed as single large-radius jets, and are identified using jet substructure and a dedicated b tagging technique based on a deep neural network. The method is validated with Z → $$ \\mathrm{b}\\overline{\\mathrm{b}} $$ b b ¯ decays. For a Higgs boson mass of 125 GeV, an excess of events above the background assuming no Higgs boson production is observed with a local significance of 2.5 standard deviations ( σ ), while the expectation is 0.7. The corresponding signal strength and local significance with respect to the standard model expectation are μ H = 3 . 7 ± 1 . 2(stat) $$ {}_{-0.7}^{+0.8} $$ − 0.7 + 0.8 (syst) $$ {}_{-0.5}^{+0.8} $$ − 0.5 + 0.8 (theo) and 1 . 9 σ . Additionally, an unfolded differential cross section as a function of Higgs boson p T for the gluon fusion production mode is presented, assuming the other production modes occur at the expected rates.
Publisher: Springer Science and Business Media LLC
Date: 09-2018
DOI: 10.1140/EPJC/S10052-018-6242-X
Abstract: A search is presented for physics beyond the standard model, based on measurements of dijet angular distributions in proton–proton collisions at $$\\sqrt{s}=13\\hbox {TeV}$$ s = 13 TeV . The data collected with the CMS detector at the LHC correspond to an integrated luminosity of 35.9 $$\\,\\text {fb}^{-1}$$ fb - 1 . The observed distributions, corrected to particle level, are found to be in agreement with predictions from perturbative quantum chromodynamics that include electroweak corrections. Constraints are placed on models containing quark contact interactions, extra spatial dimensions, quantum black holes, or dark matter, using the detector-level distributions. In a benchmark model where only left-handed quarks participate, contact interactions are excluded at the 95% confidence level up to a scale of 12.8 or 17.5TeV, for destructive or constructive interference, respectively. The most stringent lower limits to date are set on the ultraviolet cutoff in the Arkani–Hamed–Dimopoulos–Dvali model of extra dimensions. In the Giudice–Rattazzi–Wells convention, the cutoff scale is excluded up to 10.1TeV. The production of quantum black holes is excluded for masses below 5.9 and 8.2TeV, depending on the model. For the first time, lower limits between 2.0 and 4.6TeVare set on the mass of a dark matter mediator for (axial-)vector mediators, for the universal quark coupling $$g_{\\mathrm {\\mathrm {q}}} =1.0$$ g q = 1.0 .
Publisher: Springer Science and Business Media LLC
Date: 09-2020
Abstract: A search for new physics in events with two highly Lorentz-boosted Z bosons and large missing transverse momentum is presented. The analyzed proton-proton collision data, corresponding to an integrated luminosity of 137 fb − 1 , were recorded at $$ \\sqrt{s} $$ s = 13 TeV by the CMS experiment at the CERN LHC. The search utilizes the substructure of jets with large radius to identify quark pairs from Z boson decays. Backgrounds from standard model processes are suppressed by requirements on the jet mass and the missing transverse momentum. No significant excess in the event yield is observed beyond the number of background events expected from the standard model. For a simplified supersymmetric model in which the Z bosons arise from the decay of gluinos, an exclusion limit of 1920 GeV on the gluino mass is set at 95% confidence level. This is the first search for beyond-standard-model production of pairs of boosted Z bosons plus large missing transverse momentum.
Publisher: Springer Science and Business Media LLC
Date: 11-2020
Abstract: Decays of the 125 GeV Higgs boson into a Z boson and a ρ 0 (770) or ϕ(1020) meson are searched for using proton-proton collision data collected by the CMS experiment at the LHC at $$ \\sqrt{s} $$ s = 13 TeV. The analysed data set corresponds to an integrated luminosity of 137 fb − 1 . Events are selected in which the Z boson decays into a pair of electrons or a pair of muons, and the ρ and ϕ mesons decay into pairs of pions and kaons, respectively. No significant excess above the background model is observed. As different polarization states are possible for the decay products of the Z boson and ρ or ϕ mesons, affecting the signal acceptance, scenarios in which the decays are longitudinally or transversely polarized are considered. Upper limits at the 95% confidence level on the Higgs boson branching fractions into Zρ and Zϕ are determined to be 1.04–1.31% and 0.31–0.40%, respectively, where the ranges reflect the considered polarization scenarios these values are 740–940 and 730–950 times larger than the respective standard model expectations. These results constitute the first experimental limits on the two decay channels.
Publisher: American Physical Society (APS)
Date: 05-10-2020
Publisher: Springer Science and Business Media LLC
Date: 08-2020
DOI: 10.1140/EPJC/S10052-020-8166-5
Abstract: Central exclusive and semiexclusive production of "Equation missing" pairs is measured with the CMS detector in proton-proton collisions at the LHC at center-of-mass energies of 5.02 and 13TeV. The theoretical description of these nonperturbative processes, which have not yet been measured in detail at the LHC, poses a significant challenge to models. The two pions are measured and identified in the CMS silicon tracker based on specific energy loss, whereas the absence of other particles is ensured by calorimeter information. The total and differential cross sections of exclusive and semiexclusive central "Equation missing" production are measured as functions of invariant mass, transverse momentum, and rapidity of the "Equation missing" system in the fiducial region defined as transverse momentum "Equation missing" and pseudorapidity "Equation missing" . The production cross sections for the four resonant channels "Image missing" , "Equation missing" , "Image missing" , and "Image missing" are extracted using a simple model. These results represent the first measurement of this process at the LHC collision energies of 5.02 and 13TeV.
Publisher: Springer Science and Business Media LLC
Date: 12-2020
Abstract: The dependence of inclusive jet production in proton-proton collisions with a center-of-mass energy of 13 TeV on the distance parameter R of the anti- k T algorithm is studied using data corresponding to integrated luminosities up to 35.9 fb − 1 collected by the CMS experiment in 2016. The ratios of the inclusive cross sections as functions of transverse momentum p T and rapidity y , for R in the range 0.1 to 1.2 to those using R = 0 . 4 are presented in the region 84 p T 1588 GeV and | y | 2 . 0. The results are compared to calculations at leading and next-to-leading order in the strong coupling constant using different parton shower models. The variation of the ratio of cross sections with R is well described by calculations including a parton shower model, but not by a leading-order quantum chromodynamics calculation including nonperturbative effects. The agreement between the data and the theoretical predictions for the ratios of cross sections is significantly improved when next-to-leading order calculations with nonperturbative effects are used.
Location: India
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