Browsing by Author "Sirunyan, A. M."
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ArticlePublication Open Access Angular analysis of the decay B + → K + μ + μ − in proton-proton collisions at √s =8 TeV(American Physical Society, 2018-12-01) Sirunyan, A. M.; Işıldak, Bora; The CMS Collaboration; Natural and Mathematical Sciences; IŞILDAK, BoraThe angular distribution of the flavor-changing neutral current decay B+→K+μ+μ- is studied in proton-proton collisions at a center-of-mass energy of 8 TeV. The analysis is based on data collected with the CMS detector at the LHC, corresponding to an integrated luminosity of 20.5 fb-1. The forward-backward asymmetry AFB of the dimuon system and the contribution FH from the pseudoscalar, scalar, and tensor amplitudes to the decay width are measured as a function of the dimuon mass squared. The measurements are consistent with the standard model expectations.ArticlePublication Open Access Angular analysis of the decay B + → K ∗ (892) +µ +µ − in proton-proton collisions at √s = 8 TeV(Springer, 2021-01-14) Sirunyan, A. M.; Işıldak, Bora; The CMS Collaboration; Natural and Mathematical Sciences; IŞILDAK, BoraAngular distributions of the decay B+→ K∗(892)+μ+μ− are studied using events collected with the CMS detector in s = 8 TeV proton-proton collisions at the LHC, corresponding to an integrated luminosity of 20.0 fb−1. The forward-backward asymmetry of the muons and the longitudinal polarization of the K∗(892)+ meson are determined as a function of the square of the dimuon invariant mass. These are the first results from this exclusive decay mode and are in agreement with a standard model prediction.ArticlePublication Open Access Azimuthal anisotropy of charged particles with transverse momentum up to 100 GeV/c in PbPb collisions at √sNN= 5.02 TeV(Elsevier, 2018-01) Sirunyan, A. M.; Işıldak, Bora; The CMS Collaboration; Natural and Mathematical Sciences; IŞILDAK, BoraThe 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.ArticlePublication Open Access Azimuthal separation in nearly back-to-back jet topologies in inclusive 2- and 3-jet events in pp collisions at s√=13TeV(Springer Nature, 2019-09) Sirunyan, A. M.; Işıldak, Bora; The CMS Collaboration; Natural and Mathematical Sciences; IŞILDAK, BoraA measurement for inclusive 2- and 3-jet events of the azimuthal correlation between the two jets with the largest transverse momenta, Delta phi(12), is presented. The measurement considers events where the two leading jets are nearly collinear ("back-to-back") in the transverse plane and is performed for several ranges of the leading jet transverse momentum. Proton-proton collision data collected with the CMS experiment at a center-of-mass energy of 13 TeV and corresponding to an integrated luminosity of 35.9 fb(-1) are used. Predictions based on calculations using matrix elements at leading-order and next-to-leading-order accuracy in perturbative quantum chromodynamics supplemented with leading-log parton showers and hadronization are generally in agreement with themeasurements. Discrepancies between the measurement and theoretical predictions are as large as 15%, mainly in the region 177 degrees < Delta phi(12) < 180 degrees. The 2- and 3-jet measurements are not simultaneously described by any of models.ArticlePublication Open Access Beyond nPDFs effects: prompt J/ψ and ψ(2S) production in pPb and pp collisions(Elsevier, 2019-02) Oh, G.; Sirunyan, A. M.; Işıldak, Bora; The CMS Collaboration; Natural and Mathematical Sciences; IŞILDAK, BoraA multi-dimensional analysis of prompt charmonia in pp and pPb collisions at root s(NN) = 5.02 TeV with the CMS detector is presented. The pPb differential cross-sections of prompt J/psi are shown in a wide kinematic region, for transverse momentum p(T) spanning from 2 to 30 GeV/c and a rapidity interval between -2.4 to 1.93 in the center of mass of the collision. The final results on prompt psi/(2S) meson production cross section in pp and pPb collisions at 5.02 TeV are also reported as a function of p(T) and rapidity, for p(T) from 4 to 30 GeV/c. The nuclear modification factor is found to be smaller than that of prompt J/psi in all measured bins, especially at low p(T) and at backward rapidity. Such a different behaviour between the ground and excited states cannot be reproduced considering nPDF effects alone.ArticlePublication Open Access Bose-Einstein correlations of charged hadrons in proton-proton collisions at s√ = 13 TeV(Springer Nature, 2020-03-03) Sirunyan, A. M.; Işıldak, Bora; The CMS Collaboration; Natural and Mathematical Sciences; IŞILDAK, BoraBose-Einstein correlations of charged hadrons are measured over a broad multiplicity range, from a few particles up to about 250 reconstructed charged hadrons in proton-proton collisions at s = 13 TeV. The results are based on data collected using the CMS detector at the LHC during runs with a special low-pileup configuration. Three analysis techniques with different degrees of dependence on simulations are used to remove the non-Bose-Einstein background from the correlation functions. All three methods give consistent results. The measured lengths of homogeneity are studied as functions of particle multiplicity as well as average pair transverse momentum and mass. The results are compared with data from both CMS and ATLAS at s = 7 TeV, as well as with theoretical predictions.ArticlePublication Open Access Calibration of the CMS hadron calorimeters using proton-proton collision data at √s = 13 TeV(IOP Publishing, 2020-05) Sirunyan, A. M.; Işıldak, Bora; The CMS Collaboration; Natural and Mathematical Sciences; IŞILDAK, BoraMethods are presented for calibrating the hadron calorimeter system of theCMSetector at the LHC. The hadron calorimeters of the CMS experiment are sampling calorimeters of brass and scintillator, and are in the form of one central detector and two endcaps. These calorimeters cover pseudorapidities vertical bar eta vertical bar < 3 and are positioned inside the solenoidal magnet. An outer calorimeter, outside the magnet coil, covers vertical bar eta vertical bar < 1.26, and a steel and quartz-fiber Cherenkov forward calorimeter extends the coverage to vertical bar eta vertical bar < 5.19. The initial calibration of the calorimeters was based on results from test beams, augmented with the use of radioactive sources and lasers. The calibration was improved substantially using proton-proton collision data collected at root s = 7, 8, and 13 TeV, as well as cosmic ray muon data collected during the periods when the LHC beams were not present. The present calibration is performed using the 13 TeV data collected during 2016 corresponding to an integrated luminosity of 35.9 fb(-1). The intercalibration of channels exploits the approximate uniformity of energy collection over the azimuthal angle. The absolute energy scale of the central and endcap calorimeters is set using isolated charged hadrons. The energy scale for the electromagnetic portion of the forward calorimeters is set using Z -> ee data. The energy scale of the outer calorimeters has been determined with test beam data and is confirmed through data with high transverse momentum jets. In this paper, we present the details of the calibration methods and accuracy.ArticlePublication Open Access Centrality and pseudorapidity dependence of the transverse energy density in pPb collisions at √sNN = 5.02 TeV(American Physical Society, 2019-08-01) Sirunyan, A. M.; Işıldak, Bora; The CMS Collaboration; Natural and Mathematical Sciences; IŞILDAK, BoraThe almost hermetic coverage of the CMS detector is used to measure the distribution of transverse energy, E-T, over 13.2 units of pseudorapidity, eta, for pPb collisions at a center-of-mass energy per nucleon pair of root s(NN) = 5.02 TeV. The huge angular acceptance exploits the fact that the CASTOR calorimeter at -6.6 < eta < -5.2 is effectively present on both sides of the colliding system because of a switch in the proton-going and lead-going beam directions. This wide acceptance enables the study of correlations between well-separated angular regions and makes the measurement a particularly powerful test of event generators. For minimum bias pPb collisions the maximum value of dE(T)/d eta is 22 GeV, which implies an E-T per participant nucleon pair comparable to that of peripheral PbPb collisions at root s(NN) 7 = 2.76 TeV. The increase of dE(T)/d eta with centrality is much stronger for the lead-going side than for the proton-going side. The i dependence of dE(T)/d eta is sensitive to the eta range in which the centrality variable is defined. Several modern generators are compared to these results but none is able to capture all aspects of the eta and centrality dependence of the data and the correlations observed between different eta regions.ArticlePublication Open Access Charged-particle angular correlations in XeXe collisions at √sNN = 5.44 TeV(American Physical Society, 2019-10-03) Sirunyan, A. M.; Işıldak, Bora; The CMS Collaboration; Natural and Mathematical Sciences; IŞILDAK, BoraAzimuthal correlations of charged particles in xenon-xenon collisions at a center-of-mass energy per nucleon pair of root s(NN) = 5.44 TeV are studied. The data were collected by the CMS experiment at the LHC with a total integrated luminosity of 3.42 mu b(-1). The collective motion of the system formed in the collision is parametrized by a Fourier expansion of the azimuthal particle density distribution. The azimuthal anisotropy coefficients v(2), v(3), and v(4) are obtained by the scalar-product, two-particle correlation, and multiparticle correlation methods. Within a hydrodynamic picture, these methods have different sensitivities to noncollective and fluctuation effects. The dependence of the Fourier coefficients on the size of the colliding system is explored by comparing the xenon-xenon results with equivalent lead-lead data. Model calculations that include initial-state fluctuation effects are also compared to the experimental results. The observed angular correlations provide new constraints on the hydrodynamic description of heavy ion collisions.ArticlePublication Open Access Charged-particle nuclear modification factors in XeXe collisions at √sNN=5.44 TeV(Springer Nature, 2018-10) Sirunyan, A. M.; Işıldak, Bora; The CMS Collaboration; Natural and Mathematical Sciences; IŞILDAK, BoraThe differential yields of charged particles having pseudorapidity within vertical bar eta vertical bar < 1 are measured using xenon-xenon (XeXe) collisions at root S-NN = 5.44 TeV. The data, corresponding to an integrated luminosity of 3.42 mu b(-1), were collected in 2017 by the CMS experiment at the LHC. The yields are reported as functions of collision centrality and transverse momentum, pT, from 0.5 to 100 GeV. A previously reported pT spectrum from proton-proton collisions at root S = 5.02 TeV is used for comparison after correcting for the difference in center-of-mass energy. The nuclear modification factors using this reference, R-AA*, are constructed and compared to previous measurements and theoretical predictions. In head-on collisions, the R-AA* has a value of 0.17 in the pT range of 6-8 GeV, but increases to approximately 0.7 at 100 GeV. Above approximate to 6 GeV, the XeXe data show a notably smaller suppression than previous results for lead-lead (PbPb) collisions at root S-NN = 5.02 TeV when compared at the same centrality (i.e., the same fraction of total cross section). However, the XeXe suppression is slightly greater than that for PbPb in events having a similar number of participating nucleons.ArticlePublication Open Access Combination of CMS searches for heavy resonances decaying to pairs of bosons or leptons(Elsevier, 2019-11-10) Sirunyan, A. M.; Işıldak, Bora; The CMS Collaboration; Natural and Mathematical Sciences; Doser, M.; IŞILDAK, BoraA statistical combination of searches for heavy resonances decaying to pairs of bosons or leptons is presented. The data correspond to an integrated luminosity of 35.9 fb(-1) collected during 2016 by the CMS experiment at the LHC in proton-proton collisions at a center-of-mass energy of 13 TeV. The data are found to be consistent with expectations from the standard model background. Exclusion limits are set in the context of models of spin-1 heavy vector triplets and of spin-2 bulk gravitons. For mass degenerate W' and Z' resonances that predominantly couple to the standard model gauge bosons, the mass exclusion at 95% confidence level of heavy vector bosons is extended to 4.5 TeV as compared to 3.8 TeV determined from the best individual channel. This excluded mass increases to 5.0 TeV if the resonances couple predominantly to fermions.ArticlePublication Open Access Combination of searches for higgs boson pair production in proton-proton collisions at √ s = 13 TeV(American Physical Society, 2019-03-29) Sirunyan, A. M.; Işıldak, Bora; The CMS Collaboration; Natural and Mathematical Sciences; IŞILDAK, BoraThis Letter describes a search for Higgs boson pair production using the combined results from four final states: bb gamma gamma, bb tau tau, bbbb, and bbVV, where V represents a W or Z boson. The search is performed using data collected in 2016 by the CMS experiment from LHC proton-proton collisions at root s = 13 TeV, corresponding to an integrated luminosity of 35.9 fb(-1). Limits are set on the Higgs boson pair production cross section. A 95% confidence level observed (expected) upper limit on the non-resonant production cross section is set at 22.2 (12.8) times the standard model value. A search for narrow resonances decaying to Higgs boson pairs is also performed in the mass range 250-3000 GeV. No evidence for a signal is observed, and upper limits are set on the resonance production cross section.ArticlePublication Open Access Combined measurements of Higgs boson couplings in proton–proton collisions at √s = 13 TeV(Springer Nature, 2019-05-20) Sirunyan, A. M.; Işıldak, Bora; The CMS Collaboration; Natural and Mathematical Sciences; IŞILDAK, BoraCombined measurements of the production and decay rates of the Higgs boson, as well as its couplings to vector bosons and fermions, are presented. The analysis uses the LHC proton-proton collision data set recorded with the CMS detector in 2016 at fb-1. The combination is based on analyses targeting the five main Higgs boson production mechanisms (gluon fusion, vector boson fusion, and associated production with a W or Z boson, or a top quark-antiquark pair) and the following decay modes: H, ZZ, WW, , bb, and . Searches for invisible Higgs boson decays are also considered. The best-fit ratio of the signal yield to the standard model expectation is measured to be =1.17 +/- 0.10, assuming a Higgs boson mass of 125.09. Additional results are given for various assumptions on the scaling behavior of the production and decay modes, including generic parametrizations based on ratios of cross sections and branching fractions or couplings. The results are compatible with the standard model predictions in all parametrizations considered. In addition, constraints are placed on various two Higgs doublet models.ArticlePublication Open Access Combined search for supersymmetry with photons in proton-proton collisions at √s=13 TeV(Elsevier, 2020-02-10) Sirunyan, A. M.; Işıldak, Bora; The CMS Collaboration; Natural and Mathematical Sciences; IŞILDAK, BoraA combination of four searches for new physics involving signatures with at least one photon and large missing transverse momentum, motivated by generalized models of gauge-mediated supersymmetry (SUSY) breaking, is presented. All searches make use of proton-proton collision data at root s = 13 TeV, which were recorded with the CMS detector at the LHC in 2016, and correspond to an integrated luminosity of 35.9 fb(-1). Signatures with at least one photon and large missing transverse momentum are categorized into events with two isolated photons, events with a lepton and a photon, events with additional jets, and events with at least one high-energy photon. No excess of events is observed beyond expectations from standard model processes, and limits are set in the context of gauge-mediated SUSY. Compared to the individual searches, the combination extends the sensitivity to gauge-mediated SUSY in both electroweak and strong production scenarios by up to 100GeV in neutralino and chargino masses, and yields the first CMS result combining various SUSY searches in events with photons at root s = 13 TeV.ArticlePublication Open Access Constraining gluon distributions in nuclei using dijets in proton-proton and proton-lead collisions at √sNN = 5.02 TeV(American Physical Society, 2018-08-07) Sirunyan, A. M.; Işıldak, Bora; The CMS Collaboration; Natural and Mathematical Sciences; IŞILDAK, BoraThe pseudorapidity distributions of dijets as functions of their average transverse momentum (p(T)(ave)) are measured in proton-lead (pPb) and proton-proton (pp) collisions. The data samples were collected by the CMS experiment at the CERN LHC, at a nucleon-nucleon center-of-mass energy of 5.02 TeV. A significant modification of the pPb spectra with respect to the pp spectra is observed in all p(T)(ave) intervals investigated. The ratios of the pPb and pp distributions are compared to next-to-leading order perturbative quantum chromodynamics calculations with unbound nucleon and nuclear parton distribution functions (PDFs). These results give the first evidence that the gluon PDF at large Bjorken x in lead ions is strongly suppressed with respect to the PDF in unbound nucleons.ArticlePublication Open Access Constraints on anomalous Higgs boson couplings to vector bosons and fermions in its production and decay using the four-lepton final state(American Physical Society, 2021-09-17) Sirunyan, A. M.; Işıldak, Bora; The CMS Collaboration; Natural and Mathematical Sciences; IŞILDAK, BoraStudies of CP violation and anomalous couplings of the Higgs boson to vector bosons and fermions are presented. The data were acquired by the CMS experiment at the LHC and correspond to an integrated luminosity of 137 fb-1 at a proton-proton collision energy of 13 TeV. The kinematic effects in the Higgs boson's four-lepton decay H→4ℓ and its production in association with two jets, a vector boson, or top quarks are analyzed, using a full detector simulation and matrix element techniques to identify the production mechanisms and to increase sensitivity to the tensor structure of the Higgs boson interactions. A simultaneous measurement is performed of up to five Higgs boson couplings to electroweak vector bosons (HVV), two couplings to gluons (Hgg), and two couplings to top quarks (Htt). The CP measurement in the Htt interaction is combined with the recent measurement in the H→γγ channel. The results are presented in the framework of anomalous couplings and are also interpreted in the framework of effective field theory, including the first study of CP properties of the Htt and effective Hgg couplings from a simultaneous analysis of the gluon fusion and top-associated processes. The results are consistent with the standard model of particle physics.ArticlePublication Open Access Constraints on anomalous HVV couplings from the production of Higgs bosons decaying to τ lepton pairs(American Physical Society, 2019-12-04) Sirunyan, A. M.; Işıldak, Bora; The CMS Collaboration; Natural and Mathematical Sciences; IŞILDAK, BoraA study is presented of anomalous HVV interactions of the Higgs boson, including its CP properties. The study uses Higgs boson candidates produced mainly in vector boson fusion and gluon fusion that subsequently decay to a pair of tau leptons. The data were recorded by the CMS experiment at the LHC in 2016 at a center-of-mass energy of 13 TeV and correspond to an integrated luminosity of 35.9 fb(-1). A matrix element technique is employed for the analysis of anomalous interactions. The results are combined with those from the H -> 4l decay channel presented earlier, yielding the most stringent constraints on anomalous Higgs boson couplings to electroweak vector bosons expressed as effective cross section fractions and phases: the CP-violating parameter f(a3) cos(phi(a3)) = (0.00 +/- 0.27) x 10(-3) and the CP-conserving parameters f(a2) cos(phi(a2)) = (0.08)(-0.21)(+1.04)) x 10(-3), f(Lambda 1) cos(phi(Lambda 1)) = (0.00)(-0.09)(+0.53)) x 10(-3), and f(Lambda 1)(Z gamma) cos(phi(Z gamma)(Lambda 1)) = (0.0(-1.3)(+1.1)) x 10(-3). The current dataset does not allow for precise constraints on CP properties in the gluon fusion process. The results are consistent with standard model expectations.ArticlePublication Open Access Constraints on models of scalar and vector leptoquarks decaying to a quark and a neutrino at √s = 13 TeV(American Physical Society, 2018-08-10) Sirunyan, A. M.; Işıldak, Bora; The CMS Collaboration; Natural and Mathematical Sciences; IŞILDAK, BoraThe results of a previous search by the CMS Collaboration for squarks and gluinos are reinterpreted to constrain models of leptoquark (LQ) production. The search considers jets in association with a transverse momentum imbalance, using the MT2 variable. The analysis uses proton-proton collision data at s=13 TeV, recorded with the CMS detector at the LHC in 2016 and corresponding to an integrated luminosity of 35.9 fb-1. Leptoquark pair production is considered with LQ decays to a neutrino and a top, bottom, or light quark. This reinterpretation considers higher mass values than the original CMS search to constrain both scalar and vector LQs. Limits on the cross section for LQ pair production are derived at the 95% confidence level depending on the LQ decay mode. A vector LQ decaying with a 50% branching fraction to tν, and 50% to bτ, has been proposed as part of an explanation of anomalous flavor physics results. In such a model, using only the decays to tν, LQ masses below 1530 GeV are excluded assuming the Yang-Mills case with coupling κ=1, or 1115 GeV in the minimal coupling case κ=0, placing the most stringent constraint to date from pair production of vector LQs.ArticlePublication Open Access Constraints on the initial state of Pb-Pb collisions via measurements of Z -Boson yields and azimuthal anisotropy at √ sNN = 5.02 TeV(American Physical Society, 2021-08-31) Sirunyan, A. M.; Işıldak, Bora; The CMS Collaboration; Natural and Mathematical Sciences; IŞILDAK, BoraThe CMS experiment at the LHC has measured the differential cross sections of Z bosons decaying to pairs of leptons, as functions of transverse momentum and rapidity, in lead-lead collisions at a nucleon-nucleon center-of-mass energy of 5.02 TeV. The measured Z boson elliptic azimuthal anisotropy coefficient is compatible with zero, showing that Z bosons do not experience significant final-state interactions in the medium produced in the collision. Yields of Z bosons are compared to Glauber model predictions and are found to deviate from these expectations in peripheral collisions, indicating the presence of initial collision geometry and centrality selection effects. The precision of the measurement allows, for the first time, for a data-driven determination of the nucleon-nucleon integrated luminosity as a function of lead-lead centrality, thereby eliminating the need for its estimation based on a Glauber model.ArticlePublication Open Access Constraints on the χ c1 versus χ c2 polarizations in proton-proton collisions at √s = 8 TeV(American Physical Society, 2020-04-24) Sirunyan, A. M.; Işıldak, Bora; The CMS Collaboration; Natural and Mathematical Sciences; IŞILDAK, BoraThe polarizations of promptly produced chi(c1) and chi(c2) mesons are studied using data collected by the CMS experiment at the LHC, in proton-proton collisions at root s = 8 TeV. The chi(c) states are reconstructed via their radiative decays chi(c) -> J/psi gamma, with the photons being measured through conversions to e(+)e(-), which allows the two states to be well resolved. The polarizations are measured in the helicity frame, through the analysis of the chi(c2) to chi(c1) yield ratio as a function of the polar or azimuthal angle of the positive muon emitted in the J/psi -> mu(+)mu(-) decay, in three bins of J/psi transverse momentum. While no differences are seen between the two states in terms of azimuthal decay angle distributions, they are observed to have significantly different polar anisotropies. The measurement favors a scenario where at least one of the two states is strongly polarized along the hclicity quantization axis, in agreement with nonrelativistic quantum chromodynamics predictions. This is the first measurement of significantly polarized quarkonia produced at high transverse momentum.