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Azimuthal anisotropy of charged particles with transverse momentum up to 100GeV/c in PbPb collisions at ?SNN=5.02 TeV
(Elsevier, 2018) Sirunyan, A. M.; Tumasyan, A.; Adam, W.; Asilar, E.; Bergauer, T.; Brandstetter, J.; The CMS Collaboration
The Fourier coefficients v(2) and v(3) characterizing the anisotropy of the azimuthal distribution of charged particles produced in PbPb collisions at root S-NN = 5.02 TeV are measured with data collected by the CMS experiment. The measurements cover a broad transverse momentum range, 1 < p(T) < 100 GeV/c. The analysis focuses on the p(T) > 10 GeV/c range, where anisotropic azimuthal distributions should reflect the path-length dependence of parton energy loss in the created medium. Results are presented in several bins of PbPb collision centrality, spanning the 60% most central events. The v(2) coefficient is measured with the scalar product and the multiparticle cumulant methods, which have different sensitivities to initial-state fluctuations. The values from both methods remain positive up to p(T) similar to 60-80 GeV/c, in all examined centrality classes. The v(3) coefficient, only measured with the scalar product method, tends to zero for p(T) greater than or similar to 20 GeV/c. Comparisons between theoretical calculations and data provide new constraints on the path-length dependence of parton energy loss in heavy ion collisions and highlight the importance of the initial-state fluctuations. (C) 2017 The Author. Published by Elsevier B.V.
Combination of searches for heavy resonances decaying to WW, WZ, ZZ, WH, and ZH boson pairs in proton-proton collisions at ?s=8 and 13 TeV
(Elsevier, 2017) Sirunyan, A. M.; Tumasyan, A.; Adam, W.; Asilar, E.; Bergauer, T.; Brandstetter, J.; The CMS Collaboration
A statistical combination of searches is presented for massive resonances decaying to WW, WZ, ZZ, WH, and ZH boson pairs in proton-proton collision data collected by the CMS experiment at the LHC. The data were taken at centre-of-mass energies of 8 and 13TeV, corresponding to respective integrated luminosities of 19.7 and up to 2.7 fb(-1). The results are interpreted in the context of heavy vector triplet and singlet models that mimic properties of composite-Higgs models predicting W' and Z' bosons decaying to WZ, WW, WH, and ZH bosons. A model with a bulk graviton that decays into WW and ZZ is also considered. This is the first combined search for WW, WZ, WH, and ZH resonances and yields lower limits on masses at 95% confidence level for W' and Z' singlets at 2.3 TeV, and for a triplet at 2.4TeV. The limits on the production cross section of a narrow bulk graviton resonance with the curvature scale of the warped extra dimension (K)over-tilde = 0.5, in the mass range of 0.6 to 4.0TeV, are the most stringent published to date. (c) 2017 The Author(s). Published by Elsevier B.V.
Combined search for anomalous pseudoscalar HW couplings in VH(H ? b(b)over-bar) production and H ? VV decay
(Elsevier, 2016) Adam, W.; Asilar, E.; Bergauer, T.; Brandstetter, J.; Brondolin, E.; Dragicevic, M.; Ero, J.
A search for anomalous pseudoscalar couplings of the Higgs boson H to electroweak vector bosons V (= W or Z) in a sample of proton-proton collision events corresponding to an integrated luminosity of 18.9 fb(-1) at a center-of-mass energy of 8 TeV is presented. Events consistent with the topology of associated VH production, where the Higgs boson decays to a pair of bottom quarks and the vector boson decays leptonically, are analyzed. The consistency of data with a potential pseudoscalar contribution to the HVV interaction, expressed by the effective pseudoscalar cross section fractions f(a3), is assessed by means of profile likelihood scans. Results are given for the VH channels alone and for a combined analysis of the VH and previously published H -> VV channels. Under certain assumptions, f(a3)(ZZ) > 0.0034 is excluded at 95% confidence level in the combination. Scenarios in which these assumptions are relaxed are also considered. (C) 2016 The Author. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
Cross section measurement of t-channel single top quark production in pp collisions at ?s=13 TeV
(Elsevier, 2017) Sirunyan, A. M.; Tumasyan, A.; Adam, W.; Asilar, E.; Bergauer, T.; Brandstetter, J.; The CMS Collaboration
The cross section for the production of single top quarks in the t channel is measured in proton- proton collisions at 13TeV with the CMS detector at the LHC. The analyzed data correspond to an integrated luminosity of 2.2fb(-1). The event selection requires one muon and two jets where one of the jets is identified as originating from a bottom quark. Several kinematic variables are then combined into a multivariate discriminator to distinguish signal from background events. A fit to the distribution of the discriminating variable yields a total cross section of 238 +/- 13 (stat)+/- 29(syst) pband a ratio of top quark and top antiquark production of Rt-ch.= 1.81 +/- 0.18 (stat)+/- 0.15(syst). From the total cross section the absolute value of the CKM matrix element Vtbis calculated to be 1.05 +/- 0.07 (exp)+/- 0.02(theo). All results are in agreement with the standard model predictions. (C) 2017 The Author(s). Published by Elsevier B.V.
Measurement of charged pion, kaon, and proton production in proton-proton collisions at ?s=13 TeV
(Amer Physical Soc, 2017) Sirunyan, A. M.; Tumasyan, A.; Adam, W.; Asilar, E.; Bergauer, T.; Brandstetter, J.; The CMS Collaboration
Transverse momentum spectra of charged pions, kaons, and protons are measured in proton-proton collisions at root s = 13 TeV with the CMS detector at the LHC. The particles, identified via their energy loss in the silicon tracker, are measured in the transverse momentum range of p(T) approximate to 0.1-1.7 GeV/c and rapidities vertical bar y vertical bar < 1. The pT spectra and integrated yields are compared to previous results at smaller ffiffiffi root s and to predictions of Monte Carlo event generators. The average pT increases with particle mass and charged particle multiplicity of the event. Comparisons with previous CMS results at root s = 0.9, 2.76, and 7 TeV show that the average pT and the ratios of hadron yields feature very similar dependences on the particle multiplicity in the event, independently of the center-of-mass energy of the pp collision.
Measurement of double-differential cross sections for top quark pair production in pp collisions at ?s=8 TeV and impact on parton distribution functions
(Springer, 2017) Sirunyan, A. M.; Tumasyan, A.; Adam, W.; Asilar, E.; Bergauer, T.; Brandstetter, J.; The CMS Collaboration
Normalized double-differential cross sections for top quark pair (t (t) over bar) production are measured in pp collisions at a centre-of-mass energy of 8 TeV with the CMS experiment at the LHC. The analyzed data correspond to an integrated luminosity of 19.7 fb(-1). The measurement is performed in the dilepton e(+/-)mu(+/-) final state. The tt cross section is determined as a function of various pairs of observables characterizing the kinematics of the top quark and tt system. The data are compared to calculations using perturbative quantum chromodynamics at next-to-leading and approximate next-to-next-to-leading orders. They are also compared to predictions of Monte Carlo event generators that complement fixed-order computations with parton showers, hadronization, and multiple-parton interactions. Overall agreement is observed with the predictions, which is improved when the latest global sets of proton parton distribution functions are used. The inclusion of the measured tt cross sections in a fit of parametrized parton distribution functions is shown to have significant impact on the gluon distribution.
Measurement of prompt and nonprompt J/? production in pp and pPb collisions at ?sNN=5.02 TeV
(Springer, 2017) Sirunyan, A. M.; Tumasyan, A.; Adam, W.; Asilar, E.; Bergauer, T.; Brandstetter, J.; The CMS Collaboration
This paper reports the measurement of J/psi meson production in proton proton (pp) and proton lead (pPb) collisions at a center-of-mass energy per nucleon pair of 5.02 TeV by the CMS experiment at the LW. The data samples used in the analysis correspond to integrated luminosities of 28 ph(-1) and 35 nb(-1) for pp and pPb collisions, respectively. Prompt and nonprompt J/psi mesons, the latter produced in the decay of B hadrons, are measured in their dilution decay channels, Differential cross sections are measured in the transverse momentum range of 2 < p(T) < 30 GeV/c, and center-of-mass rapidity ranges of vertical bar y(CM)vertical bar < 2.4 (pp) and -2.87 < y(CM) < 1.93 (pPb). The nuclear modification factor, R-pPb, is measured as a function of both p(T) and y(CM). Small modifications to the J/psi cross sections are observed in pPb relative to pp collisions. The ratio of J/psi production cross sections in p-going and Pb-going directions, R-FB, studied as functions of p(T) and y(CM), shows a significant decrease for increasing transverse energy deposited at large pseudorapidities. These results, which cover a wide kinematic range, provide new insight on the role of cold nuclear matter effects on prompt and nonprompt J/psi production.
Measurement of the B± Meson Nuclear Modification Factor in Pb-Pb Collisions at ?sNN=5.02 TeV
(Amer Physical Soc, 2017) Sirunyan, A. M.; Tumasyan, A.; Adam, W.; Asilar, E.; Bergauer, T.; Brandstetter, J.; The CMS Collaboration
The differential production cross sections of B-+/- mesons are measured via the exclusive decay channels B-+/- -> J/psi K-+/- -> mu(+)mu K--(+/-) as a function of transverse momentum in pp and Pb-Pb collisions at a center-of-mass energy root s(NN) = 5.02 TeV per nucleon pair with the CMS detector at the LHC. The pp(Pb - Pb) data set used for this analysis corresponds to an integrated luminosity of 28.0 pb(-1) (351 mu b(-1)). The measurement is performed in the B-+/- meson transverse momentum range of 7 to 50 GeV/c, in the rapidity interval vertical bar y vertical bar < 2.4. In this kinematic range, a strong suppression of the production cross section by about a factor of 2 is observed in the Pb-Pb system in comparison to the expectation from pp reference data. These results are found to be roughly compatible with theoretical calculations incorporating beauty quark diffusion and energy loss in a quark-gluon plasma.
Measurement of the inclusive energy spectrum in the very forward direction in proton-proton collisions at ?s=13 TeV
(Springer, 2017) Sirunyan, A. M.; Tumasyan, A.; Adam, W.; Asilar, E.; Bergauer, T.; Brandstetter, J.; The CMS Collaboration
The differential cross section for inclusive particle production as a function of energy in proton-proton collisions at a center-of-mass energy of 13 TeV is measured in the very forward region of the CMS detector. The measurement is based on data collected with the CMS apparatus at the LHC, and corresponds to an integrated luminosity of 0.34 mu b(-1). The energy is measured in the CASTOR calorimeter, which covers the pseudorapidity region -6.6 < eta < -5.2. The results are given as a function of the total energy deposited in CASTOR, as well as of its electromagnetic and hadronic components. The spectra are sensitive to the modeling of multiparton interactions in pp collisions, and provide new constraints for hadronic interaction models used in collider and in high energy cosmic ray physics.
Measurement of the jet mass in highly boosted t(t)over-bar events from pp collisions at ?s=8TeV
(Springer, 2017) Sirunyan, A. M.; Tumasyan, A.; Adam, W.; Asilar, E.; Bergauer, T.; Brandstetter, J.; The CMS Collaboration
The first measurement of the jet mass m(jet) of top quark jets produced in t (t) over bar events from pp collisions at root s = 8 TeV is reported for the jet with the largest transverse momentum p(T) in highly boosted hadronic top quark decays. The data sample, collected with the CMS detector, corresponds to an integrated luminosity of 19.7 fb(-1). The measurement is performed in the lepton+jets channel in which the products of the semileptonic decay t -> bW with W -> l nu where l is an electron or muon, are used to select t (t) over bar events with large Lorentz boosts. The products of the fully hadronic decay t -> bW with W -> q (q) over bar ' are reconstructed using a single Cambridge-Aachen jet with distance parameter R = 1.2, and pT > 400 GeV. The t (t) over bar cross section as a function of m(jet) is unfolded at the particle level and is used to test the modelling of highly boosted top quark production. The peak position of the m(jet) distribution is sensitive to the top quark mass m(t), and the data are used to extract a value of m(t) to assess this sensitivity.
Measurement of the semileptonic t(t)over-bar plus ? production cross section in pp collisions at ?s=8 TeV
(Springer, 2017) Sirunyan, A. M.; Tumasyan, A.; Adam, W.; Asilar, E.; Bergauer, T.; Brandstetter, J.; The CMS Collaboration
A measurement of the cross section for top quark-antiquark (t (t) over bar) pairs produced in association with a photon in proton-proton collisions at root s = 8TeV is presented. The analysis uses data collected with the CMS detector at the LHC, corresponding to an integrated luminosity of 19.7 fb(1). The signal is de fined as the production of a t (t) over bar pair in association with a photon having a transverse energy larger than 25 GeV and an absolute pseudorapidity smaller than 1.44. The measurement is performed in the fiducial phase space corresponding to the semileptonic decay chain of the t (t) over bar pair, and the cross section is measured relative to the inclusive t (t) over bar pair production cross section. The fiducial cross section for associated t (t) over bar pair and photon production is found to be 127 +/- 27 (stat + syst) fb per semileptonic final state. The measured value is in agreement with the theoretical prediction.
Measurement of the t(t)over-bar production cross section using events with one lepton and at least one jet in pp collisions at ?s=13 TeV
(Springer, 2017) Sirunyan, A. M.; Tumasyan, A.; Adam, W.; Asilar, E.; Bergauer, T.; Brandstetter, J.; The CMS Collaboration
A measurement of the t (t) over bar production cross section at root s = 13 TeV is presented using proton-proton collisions, corresponding to an integrated luminosity of 2.2 fb(-1), collected with the CMS detector at the LHC. Final states with one isolated charged lepton (electron or muon) and at least one jet are selected and categorized according to the accompanying jet multiplicity. From a likelihood fit to the invariant mass distribution of the isolated lepton and a jet identified as coming from the hadronization of a bottom quark, the cross section is measured to be sigma(tt) = 888 +/- 2; (stat) (+26)(-28) (syst) +/- 20 (lumi) pb, in agreement with the standard model prediction. Using the expected dependence of the cross section on the pole mass of the top quark (m(t)), the value of m(t) is found to be 170:6 +/- 2:7 GeV.
Measurement of the triple-differential dijet cross section in proton-proton collisions at ?s=8 TeV and constraints on parton distribution functions
(Springer, 2017) Sirunyan, A. M.; Tumasyan, A.; Adam, W.; Asilar, E.; Bergauer, T.; Brandstetter, J.; The CMS Collaboration
A measurement is presented of the triple-differential dijet cross section at a centre-of-mass energy of 8 TeV using 19.7 fb(-1) of data collected with the CMS detector in proton-proton collisions at the LHC. The cross section is measured as a function of the average transverse momentum, half the rapidity separation, and the boost of the two leading jets in the event. The cross section is corrected for detector effects and compared to calculations in perturbative quantum chromodynamics at next-to-leading order accuracy, complemented with electroweak and nonperturbative corrections. New constraints on parton distribution functions are obtained and the inferred value of the strong coupling constant is alpha(S)(M-Z) = 0.1199 +/- 0.0015 (exp)(-0.0020)(+0.0031) (theo), where M-Z is the mass of the Z boson.
Measurements of jet charge with dijet events in pp collisions at ? s=8 TeV
(Springer, 2017) Sirunyan, A. M.; Tumasyan, A.; Adam, W.; Asilar, E.; Bergauer, T.; Brandstetter, J.; The CMS Collaboration
Jet charge is an estimator of the electric charge of a quark, antiquark, or gluon initiating a jet. It is based on the momentum-weighted sum of the electric charges of the jet constituents. Measurements of three charge observables of the leading jet in transverse momentum pT are performed with dijet events. The analysis is carried out with data collected by the CMS experiment at the CERN LHC in proton-proton collisions at root s = 8 TeV corresponding to an integrated luminosity of 19.7 fb(-1). The results are presented as a function of the pT of the leading jet and compared to predictions from leading and next-to-leading-order event generators combined with parton showers. Measured jet charge distributions, unfolded for detector effects, are reported, which expand on previous measurements of the jet charge average and standard deviation in pp collisions.
Measurements of t(t)over-bar cross sections in association with b jets and inclusive jets and their ratio using dilepton final states in pp collisions at ?s=13 TeV
(Elsevier, 2018) Sirunyan, A. M.; Tumasyan, A.; Adam, W.; Asilar, E.; Bergauer, T.; Brandstetter, J.; The CMS Collaboration
The cross sections for the production of t (t) over bar b (b) over bar and t (t) over bar jj events and their ratio sigma(t (t) over bar b (b) over bar)/sigma(t (t) over bar jj) are measured using data corresponding to an integrated luminosity of 2.3 fb(-1) collected in pp collisions at root s = 13 TeV with the CMS detector at the LHC. Events with two leptons (e or mu) and at least four reconstructed jets, including at least two identified as b quark jets, in the final state are selected. In the full phase space, the measured ratio is 0.022 +/- 0.003 (stat) +/- 0.006 (syst), the cross section sigma(t (t) over bar b (b) over bar) bis 4.0 +/- 0.6 (stat)+/- 1.3 (syst) pb and sigma(t (t) over bar jj) is 184 +/- 6 (stat)+/- 33 (syst) pb. The measurements are compared with the standard model expectations obtained from a POWHEG simulation at next-to-leading-order interfaced with PYTHIA. (c) 2017 The Author. Published by Elsevier B.V.
Measurements of the charm jet cross section and nuclear modification factor in pPb collisions at ?sNN=5.02TeV
(Elsevier, 2017) Sirunyan, A. M.; Tumasyan, A.; Adam, W.; Asilar, E.; Bergauer, T.; Brandstetter, J.; The CMS Collaboration
The CMS Collaboration presents the first measurement of the differential cross section of jets from charm quarks produced in proton-lead (pPb) collisions at a nucleon-nucleon center-of-mass energy of root sNN= 5.02 TeV, as well as results from charm quark jets in proton-proton (pp) collisions at root s=2.76and 5.02TeV. By comparing the yields of the pPb and pp collision systems at the same energy, a nuclear modification factor for charm jets from 55 to 400GeV/cin pPb collisions at root sNN=5.02 TeV of R-pA= 0.92 +/- 0.07 (stat) +/- 0.11(syst) is obtained. This is consistent with an absence of final-state energy loss for charm quarks in pPb collisions. In addition, the fraction of jets coming from charm quarks is found to be consistent with that predicted by PYTHIA 6 for pp collisions at root s=2.76 and 5.02TeV, and is independent of the jet transverse momentum from 55 to 400 GeV/c. (C) 2017 The Author(s). Published by Elsevier B.V.
Measurements of the pp ? W?? and pp ? Z?? cross sections and limits on anomalous quartic gauge couplings at ?s=8 TeV
(Springer, 2017) Sirunyan, A. M.; Tumasyan, A.; Adam, W.; Asilar, E.; Bergauer, T.; Brandstetter, J.; The CMS Collaboration
Measurements are presented of W gamma gamma and Z gamma gamma production in proton-proton collisions. Fiducial cross sections are reported based on a data sample corresponding to an integrated luminosity of 19.4 fb(-1) collected with the CMS detector at a center-of-mass energy of 8 TeV. Signal is identified through the W -> lv and Z -> ll decay modes, where l is a muon or an electron. The production of W gamma gamma and Z gamma gamma, measured with significances of 2.6 and 5.9 standard deviations, respectively, is consistent with standard model predictions. In addition, limits on anomalous quartic gauge couplings in W gamma gamma production are determined in the context of a dimension-8 effective field theory.
Mechanical stability of the CMS strip tracker measured with a laser alignment system
(Iop Publishing Ltd, 2017) Sirunyan, A. M.; Tumasyan, A.; Adam, W.; Asilar, E.; Bergauer, T.; Brandstetter, J.; The CMS Collaboration
The CMS tracker consists of 206m(2) of silicon strip sensors assembled on carbon fibre composite structures and is designed for operation in the temperature range from -25 to + 25 degrees C. The mechanical stability of tracker components during physics operation was monitored with a few mu m resolution using a dedicated laser alignment system as well as particle tracks from cosmic rays and hadron-hadron collisions. During the LHC operational period of 2011-2013 at stable temperatures, the components of the tracker were observed to experience relative movements of less than 30 mu m. In addition, temperature variations were found to cause displacements of tracker structures of about 2 mu m/degrees C, which largely revert to their initial positions when the temperature is restored to its original value.
Particle-flow reconstruction and global event description with the CMS detector
(Iop Publishing Ltd, 2017) Sirunyan, A. M.; Tumasyan, A.; Adam, W.; Asilar, E.; Bergauer, T.; Brandstetter, J.; The CMS Collaboration
The CMS apparatus was identified, a few years before the start of the LHC operation at CERN, to feature properties well suited to particle-flow (PF) reconstruction: a highly-segmented tracker, a fine-grained electromagnetic calorimeter, a hermetic hadron calorimeter, a strong magnetic field, and an excellent muon spectrometer. A fully-fledged PF reconstruction algorithm tuned to the CMS detector was therefore developed and has been consistently used in physics analyses for the first time at a hadron collider. For each collision, the comprehensive list of final-state particles identified and reconstructed by the algorithm provides a global event description that leads to unprecedented CMS performance for jet and hadronic tau decay reconstruction, missing transverse momentum determination, and electron and muon identification. This approach also allows particles from pileup interactions to be identified and enables efficient pileup mitigation methods. The data collected by CMS at a centre-of-mass energy of 8 TeV show excellent agreement with the simulation and confirm the superior PF performance at least up to an average of 20 pileup interactions.
Relative Modification of Prompt ?(2S) and J/? Yields from pp to PbPb Collisions at ?SNN=5.02 TeV
(Amer Physical Soc, 2017) Sirunyan, A. M.; Tumasyan, A.; Adam, W.; Asilar, E.; Bergauer, T.; Brandstetter, J.; The CMS Collaboration
The relative modification of the prompt psi(2S) and J/psi yields from pp to PbPb collisions, at the center-of- mass energy of 5.02 TeV per nucleon pair, is presented. The analysis is based on pp and PbPb data samples collected by the CMS experiment at the LHC in 2015, corresponding to integrated luminosities of 28.0 pb(-1) and 464 mu b(-1), respectively. The double ratio of measured yields of prompt charmonia reconstructed through their decays into muon pairs,(N-psi(2S)/N J/psi )(PbPb)/(N-psi((2S))/N (J/psi) )(pp),is determined as a function of PbPb collision centrality and charmonium transverse momentum p(T), in two kinematic intervals: broken vertical bar y vertical bar < 1.6 covering 6.5 < pT < 30 GeV/c and 1.6 < broken vertical bar y vertical bar < 2.4 covering 3 < pT < 30 GeV/c. The centrality-integrated double ratios are 0.36 +/- 0.08(stat) +/- 0.05(syst) in the first interval and 0.24 +/- 0.22(stat) +/- 0.09(syst) in the second. The double ratio is lower than unity in all the measured bins, suggesting that the psi(2S) yield is more suppressed than the J/psi yield in the explored phase space.

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