Mathematics / Matematik
Permanent URI for this collectionhttps://hdl.handle.net/11147/8
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Article Citation - WoS: 9Citation - Scopus: 15Constraints on the Initial State of Pb-Pb Collisions Via Measurements of Z-Boson Yields and Azimuthal Anisotropy at Root S(nn)=5.02 Tev(Amer Physical Soc, 2021) Karapınar, Güler; CMS CollaborationThe 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.Article Citation - WoS: 4Citation - Scopus: 9Observation of the Z -> Psi L(+)l(-) Decay in Pp Collisions at Root S= 13 Tev(American Physical Society, 2018) CMS Collaboration; Karapınar, GülerThis Letter presents the observation of the rare Z boson decay Z→ψ + -. Here, ψ represents contributions from direct J/ψ and ψ(2S)→J/ψX, + - is a pair of electrons or muons, and the J/ψ meson is detected via its decay to μ+μ-. The sample of proton-proton collision data, collected by the CMS experiment at the LHC at a center-of-mass energy of 13 TeV, corresponds to an integrated luminosity of 35.9 fb-1. The signal is observed with a significance in excess of 5 standard deviations. After subtraction of the ψ(2S)→J/ψX contribution, the ratio of the branching fraction of the exclusive decay Z→J/ψ + - to the decay Z→μ+μ-μ+μ- within a fiducial phase space is measured to be B(Z→J/ψ + -)/B(Z→μ+μ-μ+μ-)=0.67±0.18(stat)±0.05(syst).Article Citation - WoS: 187Citation - Scopus: 313Observation of Higgs Boson Decay To Bottom Quarks(American Physical Society, 2018) CMS Collaboration; Karapınar, GülerThe observation of the standard model (SM) Higgs boson decay to a pair of bottom quarks is presented. The main contribution to this result is from processes in which Higgs bosons are produced in association with a W or Z boson (VH), and are searched for in final states including 0, 1, or 2 charged leptons and two identified bottom quark jets. The results from the measurement of these processes in a data sample recorded by the CMS experiment in 2017, comprising 41.3 fb-1 of proton-proton collisions at s=13 TeV, are described. When combined with previous VH measurements using data collected at s=7, 8, and 13 TeV, an excess of events is observed at mH=125 GeV with a significance of 4.8 standard deviations, where the expectation for the SM Higgs boson is 4.9. The corresponding measured signal strength is 1.01±0.22. The combination of this result with searches by the CMS experiment for H→bb in other production processes yields an observed (expected) significance of 5.6 (5.5) standard deviations and a signal strength of 1.04±0.20.Article Citation - WoS: 38Citation - Scopus: 30Observation of the Chi(b1)(3p) and Chi(b2)(3p) and Measurement of Their Masses(American Physical Society, 2018) CMS Collaboration; Karapınar, GülerThe χb1(3P) and χb2(3P) states are observed through their (3S)γ decays, using an event sample of proton-proton collisions collected by the CMS experiment at the CERN LHC. The data were collected at a center-of-mass energy of 13 TeV and correspond to an integrated luminosity of 80.0 fb-1. The (3S) mesons are identified through their dimuon decay channel, while the low-energy photons are detected after converting to e+e- pairs in the silicon tracker, leading to a χb(3P) mass resolution of 2.2 MeV. This is the first time that the J=1 and 2 states are well resolved and their masses individually measured: 10513.42±0.41(stat)±0.18(syst) MeV and 10524.02±0.57(stat)±0.18(syst) MeV; they are determined with respect to the world-average value of the ~(3S) mass, which has an uncertainty of 0.5 MeV. The mass splitting is measured to be 10.60±0.64(stat)±0.17(syst) MeV.Article Citation - WoS: 76Citation - Scopus: 96Elliptic Flow of Charm and Strange Hadrons in High-Multiplicity P + Pb Collisions at ? S Nn = 8.16 Tev(American Physical Society, 2018) CMS Collaboration; Karapınar, GülerThe elliptic azimuthal anisotropy coefficient (v2) is measured for charm (D0) and strange (KS0, Λ, Ξ-, and Ω-) hadrons, using a data sample of p+Pb collisions collected by the CMS experiment, at a nucleon-nucleon center-of-mass energy of sNN=8.16 TeV. A significant positive v2 signal from long-range azimuthal correlations is observed for all particle species in high-multiplicity p+Pb collisions. The measurement represents the first observation of possible long-range collectivity for open heavy flavor hadrons in small systems. The results suggest that charm quarks have a smaller v2 than the lighter quarks, probably reflecting a weaker collective behavior. This effect is not seen in the larger PbPb collision system at sNN=5.02 TeV, also presented.Article Citation - WoS: 28Citation - Scopus: 46Constraining Gluon Distributions in Nuclei Using Dijets in Proton-Proton and Proton-Lead Collisions at ?s Nn = 5.02 Tev(American Physical Society, 2018) CMS Collaboration; Karapınar, GülerThe pseudorapidity distributions of dijets as functions of their average transverse momentum (pTave) 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 pTave 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.Article Citation - WoS: 11Citation - Scopus: 23Search for Physics Beyond the Standard Model in Events With High-Momentum Higgs Bosons and Missing Transverse Momentum in Proton-Proton Collisions at 13 Tev(American Physical Society, 2018) CMS Collaboration; Karapınar, GülerA search for physics beyond the standard model in events with one or more high-momentum Higgs bosons, H, decaying to pairs of b quarks in association with missing transverse momentum is presented. The data, corresponding to an integrated luminosity of 35.9 fb-1, were collected with the CMS detector at the LHC in proton-proton collisions at the center-of-mass energy s=13 TeV. The analysis utilizes a new b quark tagging technique based on jet substructure to identify jets from H→bb. Events are categorized by the multiplicity of H-tagged jets, jet mass, and the missing transverse momentum. No significant deviation from standard model expectations is observed. In the context of supersymmetry (SUSY), limits on the cross sections of pair-produced gluinos are set, assuming that gluinos decay to quark pairs, H (or Z), and the lightest SUSY particle, LSP, through an intermediate next-to-lightest SUSY particle, NLSP. With large mass splitting between the NLSP and LSP, and 100% NLSP branching fraction to H, the lower limit on the gluino mass is found to be 2010 GeV.Article Citation - WoS: 182Citation - Scopus: 288Observation of T¯th Production(American Physical Society, 2018) CMS Collaboration; Karapınar, GülerThe observation of Higgs boson production in association with a top quark-antiquark pair is reported, based on a combined analysis of proton-proton collision data at center-of-mass energies of s=7, 8, and 13 TeV, corresponding to integrated luminosities of up to 5.1, 19.7, and 35.9 fb-1, respectively. The data were collected with the CMS detector at the CERN LHC. The results of statistically independent searches for Higgs bosons produced in conjunction with a top quark-antiquark pair and decaying to pairs of W bosons, Z bosons, photons, τ leptons, or bottom quark jets are combined to maximize sensitivity. An excess of events is observed, with a significance of 5.2 standard deviations, over the expectation from the background-only hypothesis. The corresponding expected significance from the standard model for a Higgs boson mass of 125.09 GeV is 4.2 standard deviations. The combined best fit signal strength normalized to the standard model prediction is 1.26-0.26+0.31.Article Citation - WoS: 92Citation - Scopus: 211Search for Heavy Neutral Leptons in Events With Three Charged Leptons in Proton-Proton Collisions at ?s = 13 Tev(American Physical Society, 2018) CMS Collaboration; Karapınar, GülerA search for a heavy neutral lepton N of Majorana nature decaying into a W boson and a charged lepton is performed using the CMS detector at the LHC. The targeted signature consists of three prompt charged leptons in any flavor combination of electrons and muons. The data were collected in proton-proton collisions at a center-of-mass energy of 13 TeV, with an integrated luminosity of 35.9 fb-1. The search is performed in the N mass range between 1 GeV and 1.2 TeV. The data are found to be consistent with the expected standard model background. Upper limits are set on the values of |VeN|2 and |VμN|2, where V N is the matrix element describing the mixing of N with the standard model neutrino of flavor. These are the first direct limits for N masses above 500 GeV and the first limits obtained at a hadron collider for N masses below 40 GeV.Article Citation - WoS: 47Citation - Scopus: 70Search for the X (5568) State Decaying Into B-s(0)pi(+/-) in Proton-Proton Collisions at Root S=8 Tev(American Physical Society, 2018) CMS Collaboration; Karapınar, GülerA search for resonancelike structures in the Bs0π± invariant mass spectrum is performed using proton-proton collision data collected by the CMS experiment at the LHC at s=8 TeV, corresponding to an integrated luminosity of 19.7 fb-1. The Bs0 mesons are reconstructed in the decay chain Bs0→J/ψφ, with J/ψ→μ+μ- and φ→K+K-. The Bs0π± invariant mass distribution shows no statistically significant peaks for different selection requirements on the reconstructed Bs0 and π± candidates. Upper limits are set on the relative production rates of the X(5568) and Bs0 states times the branching fraction of the decay X(5568)±→Bs0π±. In addition, upper limits are obtained as a function of the mass and the natural width of possible exotic states decaying into Bs0π±.