ORCID Profile
0000-0002-2761-485X
Current Organisation
University of Illinois at Chicago
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Applied statistics | Statistics | Statistical theory
Publisher: Statistica Sinica (Institute of Statistical Science)
Date: 2021
Publisher: Springer Science and Business Media LLC
Date: 07-2021
DOI: 10.1038/S41567-021-01225-Z
Abstract: Leptons with essentially the same properties apart from their mass are grouped into three families (or flavours). The number of leptons of each flavour is conserved in interactions, but this is not imposed by fundamental principles. Since the formulation of the standard model of particle physics, the observation of flavour oscillations among neutrinos has shown that lepton flavour is not conserved in neutrino weak interactions. So far, there has been no experimental evidence that this also occurs in interactions between charged leptons. Such an observation would be a sign of undiscovered particles or a yet unknown type of interaction. Here the ATLAS experiment at the Large Hadron Collider at CERN reports a constraint on lepton-flavour-violating effects in weak interactions, searching for Z -boson decays into a τ lepton and another lepton of different flavour with opposite electric charge. The branching fractions for these decays are measured to be less than 8.1 × 10 −6 ( e τ ) and 9.5 × 10 −6 ( μ τ ) at the 95% confidence level using 139 fb −1 of proton–proton collision data at a centre-of-mass energy of $$\\sqrt{s}=13\\,{\\rm{TeV}}$$ s = 13 TeV and 20.3 fb −1 at $$\\sqrt{s}=8\\,{\\rm{TeV}}.$$ s = 8 TeV . These results supersede the limits from the Large Electron–Positron Collider experiments conducted more than two decades ago.
Publisher: Institute of Mathematical Statistics
Date: 2021
DOI: 10.1214/21-EJS1862
Publisher: Institute of Mathematical Statistics
Date: 08-2019
DOI: 10.1214/19-STS711
Publisher: Wiley
Date: 05-07-2016
DOI: 10.1111/BIOM.12552
Abstract: Comparing large covariance matrices has important applications in modern genomics, where scientists are often interested in understanding whether relationships (e.g., dependencies or co-regulations) among a large number of genes vary between different biological states. We propose a computationally fast procedure for testing the equality of two large covariance matrices when the dimensions of the covariance matrices are much larger than the s le sizes. A distinguishing feature of the new procedure is that it imposes no structural assumptions on the unknown covariance matrices. Hence, the test is robust with respect to various complex dependence structures that frequently arise in genomics. We prove that the proposed procedure is asymptotically valid under weak moment conditions. As an interesting application, we derive a new gene clustering algorithm which shares the same nice property of avoiding restrictive structural assumptions for high-dimensional genomics data. Using an asthma gene expression dataset, we illustrate how the new test helps compare the covariance matrices of the genes across different gene sets athways between the disease group and the control group, and how the gene clustering algorithm provides new insights on the way gene clustering patterns differ between the two groups. The proposed methods have been implemented in an R-package HDtest and are available on CRAN.
Publisher: Informa UK Limited
Date: 02-10-2015
Publisher: Bernoulli Society for Mathematical Statistics and Probability
Date: 05-2017
DOI: 10.3150/15-BEJ766
Publisher: The R Foundation
Date: 2020
DOI: 10.32614/RJ-2021-023
Publisher: American Physical Society (APS)
Date: 27-07-2021
Publisher: IOP Publishing
Date: 07-2021
DOI: 10.1088/1748-0221/16/07/P07029
Abstract: The ATLAS experiment at the Large Hadron Collider (LHC) employs a trigger system consisting of a first-level hardware trigger (L1) and a software-based high-level trigger. The L1 muon trigger system selects muon candidates, assigns them to the correct LHC bunch crossing and classifies them into one of six transverse-momentum threshold classes. The L1 muon trigger system uses resistive-plate chambers (RPCs) to generate the muon-induced trigger signals in the central (barrel) region of the ATLAS detector. The ATLAS RPCs are arranged in six concentric layers and operate in a toroidal magnetic field with a bending power of 1.5 to 5.5 Tm. The RPC detector consists of about 3700 gas volumes with a total surface area of more than 4000 m 2 . This paper reports on the performance of the RPC detector and L1 muon barrel trigger using 60.8 fb -1 of proton-proton collision data recorded by the ATLAS experiment in 2018 at a centre-of-mass energy of 13 TeV. Detector and trigger performance are studied using Z boson decays into a muon pair. Measurements of the RPC detector response, efficiency, and time resolution are reported. Measurements of the L1 muon barrel trigger efficiencies and rates are presented, along with measurements of the properties of the selected s le of muon candidates. Measurements of the RPC currents, counting rates and mean avalanche charge are performed using zero-bias collisions. Finally, RPC detector response and efficiency are studied at different high voltage and front-end discriminator threshold settings in order to extrapolate detector response to the higher luminosity expected for the High Luminosity LHC.
Publisher: Springer Science and Business Media LLC
Date: 30-10-2021
Abstract: A search for pair production of third-generation scalar leptoquarks decaying into a top quark and a τ -lepton is presented. The search is based on a dataset of pp collisions at $$ \\sqrt{s} $$ s = 13 TeV recorded with the ATLAS detector during Run 2 of the Large Hadron Collider, corresponding to an integrated luminosity of 139 fb − 1 . Events are selected if they have one light lepton (electron or muon) and at least one hadronically decaying τ -lepton, or at least two light leptons. In addition, two or more jets, at least one of which must be identified as containing b -hadrons, are required. Six final states, defined by the multiplicity and flavour of lepton candidates, are considered in the analysis. Each of them is split into multiple event categories to simultaneously search for the signal and constrain several leading backgrounds. The signal-rich event categories require at least one hadronically decaying τ -lepton candidate and exploit the presence of energetic final-state objects, which is characteristic of signal events. No significant excess above the Standard Model expectation is observed in any of the considered event categories, and 95% CL upper limits are set on the production cross section as a function of the leptoquark mass, for different assumptions about the branching fractions into tτ and bν . Scalar leptoquarks decaying exclusively into tτ are excluded up to masses of 1 . 43 TeV while, for a branching fraction of 50% into tτ , the lower mass limit is 1 . 22 TeV.
Publisher: Elsevier BV
Date: 08-2021
Publisher: Springer Science and Business Media LLC
Date: 07-2021
Abstract: This article presents a new set of proton parton distribution functions, ATLASepWZVjet20, produced in an analysis at next-to-next-to-leading order in QCD. The new data sets considered are the measurements of W + and W − boson and Z boson production in association with jets in pp collisions at $$ \\sqrt{s} $$ s = 8 TeV performed by the ATLAS experiment at the LHC with integrated luminosities of 20 . 2 fb − 1 and 19 . 9 fb − 1 , respectively. The analysis also considers the ATLAS measurements of differential W ± and Z boson production at $$ \\sqrt{s} $$ s = 7 TeV with an integrated luminosity of 4 . 6 fb − 1 and deep-inelastic-scattering data from e ± p collisions at the HERA accelerator. An improved determination of the sea-quark densities at high Bjorken x is shown, while confirming a strange-quark density similar in size to the up- and down-sea-quark densities in the range x ≲ 0 . 02 found by previous ATLAS analyses.
Publisher: The Hong Kong University of Science and Technology Library
Publisher: Statistica Sinica (Institute of Statistical Science)
Date: 2023
Publisher: Springer Science and Business Media LLC
Date: 06-2021
DOI: 10.1140/EPJC/S10052-021-09192-8
Abstract: The paper presents a measurement of the Standard Model Higgs Boson decaying to b -quark pairs in the vector boson fusion (VBF) production mode. A s le corresponding to 126 $$\\hbox {fb}^{-1}$$ fb - 1 of $$\\sqrt{s} = 13\\,\\text {TeV}$$ s = 13 TeV proton–proton collision data, collected with the ATLAS experiment at the Large Hadron Collider, is analyzed utilizing an adversarial neural network for event classification. The signal strength, defined as the ratio of the measured signal yield to that predicted by the Standard Model for VBF Higgs production, is measured to be $$0.95^{+0.38}_{-0.36}$$ 0 . 95 - 0.36 + 0.38 , corresponding to an observed (expected) significance of 2.6 (2.8) standard deviations from the background only hypothesis. The results are additionally combined with an analysis of Higgs bosons decaying to b -quarks, produced via VBF in association with a photon.
Publisher: Springer Science and Business Media LLC
Date: 05-2021
Abstract: The results of a search for new phenomena in final states with b -jets and missing transverse momentum using 139 fb − 1 of proton-proton data collected at a centre-of-mass energy $$ \\sqrt{s} $$ s = 13 TeV by the ATLAS detector at the LHC are reported. The analysis targets final states produced by the decay of a pair-produced supersymmetric bottom squark into a bottom quark and a stable neutralino. The analysis also seeks evidence for models of pair production of dark matter particles produced through the decay of a generic scalar or pseudoscalar mediator state in association with a pair of bottom quarks, and models of pair production of scalar third-generation down-type leptoquarks. No significant excess of events over the Standard Model background expectation is observed in any of the signal regions considered by the analysis. Bottom squark masses below 1270 GeV are excluded at 95% confidence level if the neutralino is massless. In the case of nearly mass-degenerate bottom squarks and neutralinos, the use of dedicated secondary-vertex identification techniques permits the exclusion of bottom squarks with masses up to 660 GeV for mass splittings between the squark and the neutralino of 10 GeV. These limits extend substantially beyond the regions of parameter space excluded by similar ATLAS searches performed previously.
Publisher: Institute of Mathematical Statistics
Date: 06-2020
DOI: 10.1214/19-AOS1863
Publisher: American Physical Society (APS)
Date: 10-06-2021
Publisher: Bernoulli Society for Mathematical Statistics and Probability
Date: 08-2018
DOI: 10.3150/16-BEJ912
Publisher: American Physical Society (APS)
Date: 07-06-2021
Publisher: Institute of Mathematical Statistics
Date: 10-2016
DOI: 10.1214/16-AOS1442
Publisher: Springer Science and Business Media LLC
Date: 08-2021
DOI: 10.1140/EPJC/S10052-021-09402-3
Abstract: Jet energy scale and resolution measurements with their associated uncertainties are reported for jets using 36–81 fb $$^{-1}$$ - 1 of proton–proton collision data with a centre-of-mass energy of $$\sqrt{s}=13$$ s = 13 $${\text {Te}}{\text {V}}$$ TeV collected by the ATLAS detector at the LHC. Jets are reconstructed using two different input types: topo-clusters formed from energy deposits in calorimeter cells, as well as an algorithmic combination of charged-particle tracks with those topo-clusters, referred to as the ATLAS particle-flow reconstruction method. The anti- $$k_t$$ k t jet algorithm with radius parameter $$R=0.4$$ R = 0.4 is the primary jet definition used for both jet types. This result presents new jet energy scale and resolution measurements in the high pile-up conditions of late LHC Run 2 as well as a full calibration of particle-flow jets in ATLAS. Jets are initially calibrated using a sequence of simulation-based corrections. Next, several in situ techniques are employed to correct for differences between data and simulation and to measure the resolution of jets. The systematic uncertainties in the jet energy scale for central jets ( $$|\eta | .2$$ | η | 1.2 ) vary from 1% for a wide range of high- $$p_{{\text {T}}}$$ p T jets ( $$250 _{{\text {T}}} ~{\text {Ge}}{\text {V}}$$ 250 p T 2000 GeV ), to 5% at very low $$p_{{\text {T}}}$$ p T ( $$20~{\text {Ge}}{\text {V}}$$ 20 GeV ) and 3.5% at very high $$p_{{\text {T}}}$$ p T ( $$ .5~{\text {Te}}{\text {V}}$$ 2.5 TeV ). The relative jet energy resolution is measured and ranges from ( $$24 \pm 1.5$$ 24 ± 1.5 )% at 20 $${\text {Ge}}{\text {V}}$$ GeV to ( $$6 \pm 0.5$$ 6 ± 0.5 )% at 300 $${\text {Ge}}{\text {V}}$$ GeV .
Publisher: Informa UK Limited
Date: 22-04-2020
Publisher: Bernoulli Society for Mathematical Statistics and Probability
Date: 11-2016
DOI: 10.3150/15-BEJ719
Publisher: Springer Science and Business Media LLC
Date: 21-02-2022
Publisher: Wiley
Date: 13-11-2018
Publisher: Springer Science and Business Media LLC
Date: 06-2021
Abstract: A search for charged Higgs bosons decaying into W ± W ± or W ± Z bosons is performed, involving experimental signatures with two leptons of the same charge, or three or four leptons with a variety of charge combinations, missing transverse momentum and jets. A data s le of proton-proton collisions at a centre-of-mass energy of 13 TeV recorded with the ATLAS detector at the Large Hadron Collider between 2015 and 2018 is used. The data correspond to a total integrated luminosity of 139 fb − 1 . The search is guided by a type-II seesaw model that extends the scalar sector of the Standard Model with a scalar triplet, leading to a phenomenology that includes doubly and singly charged Higgs bosons. Two scenarios are explored, corresponding to the pair production of doubly charged H ±± bosons, or the associated production of a doubly charged H ±± boson and a singly charged H ± boson. No significant deviations from the Standard Model predictions are observed. H ±± bosons are excluded at 95% confidence level up to 350 GeV and 230 GeV for the pair and associated production modes, respectively.
Publisher: Springer Science and Business Media LLC
Date: 06-2021
Abstract: A search for charged Higgs bosons decaying into a top quark and a bottom quark is presented. The data analysed correspond to 139 fb − 1 of proton-proton collisions at $$ \\sqrt{s} $$ s = 13 TeV, recorded with the ATLAS detector at the LHC. The production of a heavy charged Higgs boson in association with a top quark and a bottom quark, pp → tbH + → tbtb , is explored in the H + mass range from 200 to 2000 GeV using final states with jets and one electron or muon. Events are categorised according to the multiplicity of jets and b -tagged jets, and multivariate analysis techniques are used to discriminate between signal and background events. No significant excess above the background-only hypothesis is observed and exclusion limits are derived for the production cross-section times branching ratio of a charged Higgs boson as a function of its mass they range from 3.6 pb at 200 GeV to 0.036 pb at 2000 GeV at 95% confidence level. The results are interpreted in the hMSSM and $$ {M}_h^{125} $$ M h 125 scenarios.
Publisher: Springer Science and Business Media LLC
Date: 30-05-2017
Publisher: Oxford University Press (OUP)
Date: 11-05-2020
Abstract: This paper establishes non-asymptotic concentration bound and Bahadur representation for the quantile regression estimator and its multiplier bootstrap counterpart in the random design setting. The non-asymptotic analysis keeps track of the impact of the parameter dimension $d$ and s le size $n$ in the rate of convergence, as well as in normal and bootstrap approximation errors. These results represent a useful complement to the asymptotic results under fixed design and provide theoretical guarantees for the validity of Rademacher multiplier bootstrap in the problems of confidence construction and goodness-of-fit testing. Numerical studies lend strong support to our theory and highlight the effectiveness of Rademacher bootstrap in terms of accuracy, reliability and computational efficiency.
Publisher: Wiley
Date: 31-03-2201
DOI: 10.1111/BIOM.12695
Abstract: In this article, we study the problem of testing the mean vectors of high dimensional data in both one-s le and two-s le cases. The proposed testing procedures employ maximum-type statistics and the parametric bootstrap techniques to compute the critical values. Different from the existing tests that heavily rely on the structural conditions on the unknown covariance matrices, the proposed tests allow general covariance structures of the data and therefore enjoy wide scope of applicability in practice. To enhance powers of the tests against sparse alternatives, we further propose two-step procedures with a preliminary feature screening step. Theoretical properties of the proposed tests are investigated. Through extensive numerical experiments on synthetic data sets and an human acute lymphoblastic leukemia gene expression data set, we illustrate the performance of the new tests and how they may provide assistance on detecting disease-associated gene-sets. The proposed methods have been implemented in an R-package HDtest and are available on CRAN.
Publisher: Springer Science and Business Media LLC
Date: 09-2017
Publisher: Informa UK Limited
Date: 27-10-2023
Publisher: Elsevier BV
Date: 05-2022
Publisher: American Physical Society (APS)
Date: 12-07-2021
Publisher: Oxford University Press (OUP)
Date: 15-06-2023
Abstract: Expected shortfall (ES), also known as superquantile or conditional value-at-risk, is an important measure in risk analysis and stochastic optimisation and has applications beyond these fields. In finance, it refers to the conditional expected return of an asset given that the return is below some quantile of its distribution. In this paper, we consider a joint regression framework recently proposed to model the quantile and ES of a response variable simultaneously, given a set of covariates. The current state-of-the-art approach to this problem involves minimising a non-differentiable and non-convex joint loss function, which poses numerical challenges and limits its applicability to large-scale data. Motivated by the idea of using Neyman-orthogonal scores to reduce sensitivity to nuisance parameters, we propose a statistically robust and computationally efficient two-step procedure for fitting joint quantile and ES regression models that can handle highly skewed and heavy-tailed data. We establish explicit non-asymptotic bounds on estimation and Gaussian approximation errors that lay the foundation for statistical inference, even with increasing covariate dimensions. Finally, through numerical experiments and two data applications, we demonstrate that our approach well balances robustness, statistical, and numerical efficiencies for expected shortfall regression.
Publisher: Institute of Mathematical Statistics
Date: 2016
DOI: 10.1214/16-EJS1147
Publisher: Springer Science and Business Media LLC
Date: 07-2021
DOI: 10.1038/S41567-021-01236-W
Abstract: The standard model of particle physics encapsulates our best current understanding of physics at the smallest scales. A fundamental axiom of this theory is the universality of the couplings of the different generations of leptons to the electroweak gauge bosons. The measurement of the ratio of the decay rate of W bosons to τ leptons and muons, R ( τ / μ ), constitutes an important test of this axiom. Using 139 fb −1 of proton–proton collisions recorded with the ATLAS detector at a centre-of-mass energy of 13 TeV, we report a measurement of this quantity from di-leptonic $$t\\overline{t}$$ t t ¯ events where the top quarks decay into a W boson and a bottom quark. We can distinguish muons originating from W bosons and those originating from an intermediate τ lepton through the muon transverse impact parameter and differences in the muon transverse momentum spectra. The measured value of R ( τ / μ ) is 0.992 ± 0.013 [± 0.007(stat) ± 0.011(syst)] and is in agreement with the hypothesis of universal lepton couplings as postulated in the standard model. This is the only such measurement from the Large Hadron Collider, so far, and obtains twice the precision of previous measurements.
Publisher: Institute of Mathematical Statistics
Date: 06-2018
DOI: 10.1214/17-AOS1575
Publisher: Springer Science and Business Media LLC
Date: 07-2021
Abstract: A search for long-lived particles, which have come to rest within the ATLAS detector, is presented. The subsequent decays of these particles can produce high-momentum jets, resulting in large out-of-time energy deposits in the ATLAS calorimeters. These de- cays are detected using data collected during periods in the LHC bunch structure when collisions are absent. The analysed dataset is composed of events from proton-proton collisions produced by the Large Hadron Collider at a centre-of-mass energy of $$ \\sqrt{s} $$ s = 13 TeV and recorded by the ATLAS experiment during 2017 and 2018. The dataset used for this search corresponds to a total live time of 579 hours. The results of this search are used to derive lower limits on the mass of gluino R -hadrons, assuming a branching fraction $$ \\mathcal{B}\\left(\\overset{\\sim }{g}\\to q\\overline{q}{\\chi}_1^0\\right) $$ B g ~ → q q ¯ χ 1 0 = 100%, with masses of up to 1 . 4 TeV excluded for gluino lifetimes of 10 − 5 to 10 3 s.
Publisher: Oxford University Press (OUP)
Date: 16-12-2021
DOI: 10.1111/RSSB.12485
Abstract: ℓ 1 -penalized quantile regression (QR) is widely used for analysing high-dimensional data with heterogeneity. It is now recognized that the ℓ1-penalty introduces non-negligible estimation bias, while a proper use of concave regularization may lead to estimators with refined convergence rates and oracle properties as the signal strengthens. Although folded concave penalized M-estimation with strongly convex loss functions have been well studied, the extant literature on QR is relatively silent. The main difficulty is that the quantile loss is piecewise linear: it is non-smooth and has curvature concentrated at a single point. To overcome the lack of smoothness and strong convexity, we propose and study a convolution-type smoothed QR with iteratively reweighted ℓ1-regularization. The resulting smoothed empirical loss is twice continuously differentiable and (provably) locally strongly convex with high probability. We show that the iteratively reweighted ℓ1-penalized smoothed QR estimator, after a few iterations, achieves the optimal rate of convergence, and moreover, the oracle rate and the strong oracle property under an almost necessary and sufficient minimum signal strength condition. Extensive numerical studies corroborate our theoretical results.
Publisher: Informa UK Limited
Date: 20-03-2019
Publisher: Springer Science and Business Media LLC
Date: 07-2021
Abstract: A search for supersymmetry in events with four or more charged leptons (electrons, muons and τ -leptons) is presented. The analysis uses a data s le corresponding to 139 fb − 1 of proton-proton collisions delivered by the Large Hadron Collider at $$ \\sqrt{s} $$ s = 13 TeV and recorded by the ATLAS detector. Four-lepton signal regions with up to two hadronically decaying τ -leptons are designed to target several supersymmetric models, while a general five-lepton signal region targets any new physics phenomena leading to a final state with five charged leptons. Data yields are consistent with Standard Model expectations and results are used to set upper limits on contributions from processes beyond the Standard Model. Exclusion limits are set at the 95% confidence level in simplified models of general gauge-mediated supersymmetry, excluding higgsino masses up to 540 GeV. In R -parity-violating simplified models with decays of the lightest supersymmetric particle to charged leptons, lower limits of 1 . 6 TeV, 1 . 2 TeV, and 2 . 5 TeV are placed on wino, slepton and gluino masses, respectively.
Publisher: Institute of Mathematical Statistics
Date: 10-2018
DOI: 10.1214/17-AOS1606
Publisher: Springer Science and Business Media LLC
Date: 07-2021
Abstract: Measurements of four-lepton differential and integrated fiducial cross-sections in events with two same-flavour, opposite-charge electron or muon pairs are presented. The data correspond to 139 fb − 1 of $$ \\sqrt{s} $$ s = 13 TeV proton-proton collisions, collected by the ATLAS detector during Run 2 of the Large Hadron Collider (2015–2018). The final state has contributions from a number of interesting Standard Model processes that dominate in different four-lepton invariant mass regions, including single Z boson production, Higgs boson production and on-shell ZZ production, with a complex mix of interference terms, and possible contributions from physics beyond the Standard Model. The differential cross-sections include the four-lepton invariant mass inclusively, in slices of other kinematic variables, and in different lepton flavour categories. Also measured are dilepton invariant masses, transverse momenta, and angular correlation variables, in four regions of four-lepton invariant mass, each dominated by different processes. The measurements are corrected for detector effects and are compared with state-of-the-art Standard Model calculations, which are found to be consistent with the data. The Z → 4 ℓ branching fraction is extracted, giving a value of (4 . 41 ± 0 . 30) × 10 − 6 . Constraints on effective field theory parameters and a model based on a spontaneously broken B − L gauge symmetry are also evaluated. Further reinterpretations can be performed with the provided information.
Publisher: Institute of Mathematical Statistics
Date: 03-2014
DOI: 10.1214/13-AOP837
Publisher: Elsevier BV
Date: 02-2021
Publisher: Institute of Mathematical Statistics
Date: 10-2016
DOI: 10.1214/15-AOS1375
Publisher: Elsevier BV
Date: 2016
Publisher: Institute of Mathematical Statistics
Date: 10-2022
DOI: 10.1214/22-AOS2214
Location: United States of America
Start Date: 03-2023
End Date: 03-2026
Amount: $425,000.00
Funder: Australian Research Council
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