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Öğe Angular Analysis of the decay B+?K+?+?? in Proton-proton Collisions at ?s=8??TeV(American Physical Society, 2018) Bilki, Burak; ., ve digerThe angular distribution of the flavor-changing neutral current decay B+?K+?+?? 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.Öğe Azimuthal Correlations For İnclusive 2-Jet, 3-Jet, And 4-Jet Events İn Pp Collisions At S?=13 Tev(The European Physical Journal C, 2018) Bilki, Burak; ., ve digerAzimuthal correlations between the two jets with the largest transverse momenta pTpT in inclusive 2-, 3-, and 4-jet events are presented for several regions of the leading jet pTpT up to 4TeVTeV. For 3- and 4-jet scenarios, measurements of the minimum azimuthal angles between any two of the three or four leading pTpT jets are also presented. The analysis is based on data from proton–proton collisions collected by the CMS Collaboration at a centre-of-mass energy of 13TeVTeV, corresponding to an integrated luminosity of 35.9fb?1fb?1. Calculations based on leading-order matrix elements supplemented with parton showering and hadronization do not fully describe the data, so next-to-leading-order calculations matched with parton shower and hadronization models are needed to better describe the measured distributions. Furthermore, we show that azimuthal jet correlations are sensitive to details of the parton showering, hadronization, and multiparton interactions. A next-to-leading-order calculation matched with parton showers in the MC@NLO method, as implemented in HERWİG 7, gives a better overall description of the measurements than the POWHEG method.Öğe Bose-Einstein Correlations İn Pp, Ppb, And Pbpb Collisions At ? Snn = 0.9–7 Tev(American Physical Society, 2018) Bilki, Burak; ., ve digerQuantum-statistical (Bose-Einstein) two-particle correlations are measured in pp collisions at ? s = 0.9, 2.76, and 7 TeV, as well as in pPb and peripheral PbPb collisions at nucleon-nucleon center-of-mass energies of 5.02 and 2.76 TeV, respectively, using the CMS detector at the Large Hadron Collider. Separate analyses are performed for same-sign unidentified charged particles as well as for same-sign pions and kaons identified via their energy loss in the silicon tracker. The characteristics of the one-, two-, and three-dimensional correlation functions are studied as functions of the pair average transverse momentum (kT) and the charged-particle multiplicity in the event. For all systems, the extracted correlation radii steadily increase with the event multiplicity, and decrease with increasing kT. The radii are in the range 1–5 fm, the largest values corresponding to very high multiplicity pPb interactions and to peripheral PbPb collisions with multiplicities similar to those seen in pPb data. It is also observed that the dependencies of the radii on multiplicity and kT largely factorize. At the same multiplicity, the radii are relatively independent of the colliding system and center-of-mass energy.Öğe Charged-Particle Nuclear Modification Factors in XeXe Collisions at sNN????=5.44sNN=5.44 TeV(Springer Link, 2018) Bilki, Burak; ., ve digerThe differential yields of charged particles having pseudorapidity within |?| < 1 are measured using xenon-xenon (XeXe) collisions at sNN????=5.44sNN=5.44 TeV. The data, corresponding to an integrated luminosity of 3.42 ?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 s?=5.02s=5.02TeV 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 ?6 GeV, the XeXe data show a notably smaller suppression than previous results for lead-lead (PbPb) collisions at sNN????=5.02sNN=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.Öğe Combination Of Searches For Heavy Resonances Decaying To WW, WZ, ZZ, WH, And ZH Boson Pairs İn Proton-Proton Collisions At Root S=8 And 13 Tev(ScienceDirect, 2017) Bilki, Burak; ., ve digerA 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 13 TeV, 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 W0 and Z0 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 W0 and Z0 singlets at 2.3 TeV, and for a triplet at 2.4 TeV. The limits on the production cross section of a narrow bulk graviton resonance with the curvature scale of the warped extra dimension ˜k = 0.5, in the mass range of 0.6 to 4.0 TeV, are the most stringent published to date.Öğe Combined Search For Electroweak Production Of Charginos And Neutralinos İn Proton-Proton Collisions At S?=13s=13TeV(Springer Link, 2018) Bilki, Burak; ., ve digerA statistical combination of several searches for the electroweak production of charginos and neutralinos is presented. All searches use 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. In addition to the combination of previous searches, a targeted analysis requiring three or more charged leptons (electrons or muons) is presented, focusing on the challenging scenario in which the difference in mass between the two least massive neutralinos is approximately equal to the mass of the Z boson. The results are interpreted in simplified models of chargino-neutralino or neutralino pair production. For chargino-neutralino production, in the case when the lightest neutralino is massless, the combination yields an observed (expected) limit at the 95% confidence level on the chargino mass of up to 650 (570) GeV, improving upon the individual analysis limits by up to 40 GeV. If the mass difference between the two least massive neutralinos is approximately equal to the mass of the Z boson in the chargino-neutralino model, the targeted search requiring three or more leptons obtains observed and expected exclusion limits of around 225 GeV on the second neutralino mass and 125 GeV on the lightest neutralino mass, improving the observed limit by about 60 GeV in both masses compared to the previous CMS result. In the neutralino pair production model, the combined observed (expected) exclusion limit on the neutralino mass extends up to 650–750 (550–750) GeV, depending on the branching fraction assumed. This extends the observed exclusion achieved in the individual analyses by up to 200 GeV. The combined result additionally excludes some intermediate gaps in the mass coverage of the individual analyses.Öğe Comparing Transverse Momentum Balance of b Jet Pairs in pp and PbPb Collisions at sNN????=5.02sNN=5.02 TeV(Springer Link, 2018) Bilki, Burak; ., ve digerThe transverse momentum balance of pairs of back-to-back b quark jets in PbPb and pp collisions recorded with the CMS detector at the LHC is reported. The center-of-mass energy in both collision systems is 5.02 TeV per nucleon pair. Compared to the pp collision baseline, b quark jets have a larger imbalance in the most central PbPb collisions, as expected from the jet quenching effect. The data are also compared to the corresponding measurement with inclusive dijets. In the most central collisions, the imbalance of b quark dijets is comparable to that of inclusive dijets.Öğe Constraining Gluon Distributions in Nuclei Using Dijets in Proton-Proton and Proton-Lead Collisions at ?sNN=5.02??TeV(American Physical Society, 2018) Bilki, Burak; ., ve digerThe pseudorapidity distributions of dijets as functions of their average transverse momentum (paveT) 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 paveT 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.Öğe Constraints On Models Of Scalar And Vector Leptoquarks Decaying To A Quark And A Neutrino At ?S=13??TeV(American Physical Society, 2018) Bilki, Burak; ., ve digerThe 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 t?, and 50% to b?, has been proposed as part of an explanation of anomalous flavor physics results. In such a model, using only the decays to t?, LQ masses below 1530 GeV are excluded assuming the Yang-Mills case with coupling ?=1, or 1115 GeV in the minimal coupling case ?=0, placing the most stringent constraint to date from pair production of vector LQs.Öğe Constraints On The Chiral Magnetic Effect Using Charge-Dependent Azimuthal Correlations İn Ppb And Pbpb Collisions At The Cern Large Hadron Collider(American Physical Society, 2018) Bilki, Burak; ., ve digerCharge-dependent azimuthal correlations of same- and opposite-sign pairswith respect to the second- and thirdorder event planes have been measured in pPb collisions at ? sNN = 8.16 TeV and PbPb collisions at 5.02 TeV with the CMS experiment at the LHC. The measurement is motivated by the search for the charge separation phenomenon predicted by the chiral magnetic effect (CME) in heavy ion collisions. Three- and two-particle azimuthal correlators are extracted as functions of the pseudorapidity difference, the transverse momentum (pT) difference, and the pT average of same- and opposite-charge pairs in various event multiplicity ranges. The data suggest that the charge-dependent three-particle correlators with respect to the second- and third-order event planes share a common origin, predominantly arising from charge-dependent two-particle azimuthal correlations coupled with an anisotropic flow. The CME is expected to lead to a v2-independent three-particle correlation when the magnetic field is fixed. Using an event shape engineering technique, upper limits on the v2-independent fraction of the three-particle correlator are estimated to be 13% for pPb and 7% for PbPb collisions at 95% confidence level. The results of this analysis, both the dominance of two-particle correlations as a source of the three-particle results and the similarities seen between PbPb and pPb, provide stringent constraints on the origin of charge-dependent three-particle azimuthal correlations and challenge their interpretation as arising from a chiral magnetic effect in heavy ion collisions.Öğe Constraints On The Double-Parton Scattering Cross Section From Same-Sign W Boson Pair Production İn Proton-Proton Collisions At S?=8s=8 TeV(Springer Link, 2018) Bilki, Burak; ., ve digerA first search for same-sign WW production via double-parton scattering is performed based on proton-proton collision data at a center-of-mass energy of 8 TeV using dimuon and electron-muon final states. The search is based on the analysis of data corresponding to an integrated luminosity of 19.7 fb?1. No significant excess of events is observed above the expected single-parton scattering yields. A 95% confidence level upper limit of 0.32 pb is set on the inclusive cross section for same-sign WW production via the double-parton scattering process. This upper limit is used to place a 95% confidence level lower limit of 12.2 mb on the effective double-parton cross section parameter, closely related to the transverse distribution of partons in the proton. This limit on the effective cross section is consistent with previous measurements as well as with Monte Carlo event generator predictions.Öğe Electroweak Production Of Two Jets İn Association With A Z Boson İn Proton–Proton Collisions At S?=S= 13TeV(Springer Link, 2018) Bilki, Burak; ., ve digerA measurement of the electroweak (EW) production of two jets in association with a ZZ boson in proton-proton collisions at s?=13TeVs=13TeV is presented, based on data recorded in 2016 by the CMS experiment at the LHC corresponding to an integrated luminosity of 35.9fb--1fb--1. The measurement is performed in the ??jj??jj final state with ?? including electrons and muons, and the jets j corresponding to the quarks produced in the hard interaction. The measured cross section in a kinematic region defined by invariant masses m??>50GeVm??>50GeV, mjj>120GeVmjj>120GeV, and transverse momenta pTj>25GeVpTj>25GeV is ?EW(??jj)=534±20(stat)±57(syst) fb?EW(??jj)=534±20(stat)±57(syst) fb, in agreement with leading-order standard model predictions. The final state is also used to perform a search for anomalous trilinear gauge couplings. No evidence is found and limits on anomalous trilinear gauge couplings associated with dimension-six operators are given in the framework of an effective field theory. The corresponding 95% confidence level intervals are ?2.6Öğe Elliptic Flow of Charm and Strange Hadrons in High-Multiplicity p+Pb Collisions at ?sNN=8.16??TeV(American Physical Society, 2018) Bilki, Burak; ., ve digerThe elliptic azimuthal anisotropy coefficient (v2) is measured for charm (D0) and strange (K0S, ?, ??, and ??) 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+Pbcollisions. 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.Öğe Event Shape Variables Measured Using Multijet Final States İn Proton-Proton Collisions At S?=13s=13 Tev(Springer Link, 2018) Bilki, Burak; ., ve digerThe study of global event shape variables can provide sensitive tests of predictions for multijet production in proton-proton collisions. This paper presents a study of several event shape variables calculated using jet four momenta in proton-proton collisions at a centre-of-mass energy of 13 TeV and uses data recorded with the CMS detector at the LHC corresponding to an integrated luminosity of 2.2 fb?1. After correcting for detector effects, the resulting distributions are compared with several theoretical predictions. The agreement generally improves as the energy, represented by the average transverse momentum of the two leading jets, increases.Öğe Evidence For Associated Production Of A Higgs Boson With A Top Quark Pair İn Final States With Electrons, Muons, And Hadronically Decaying ? Leptons At S?=13s=13 TeV(Springer Link, 2018) Bilki, Burak; ., ve digerResults of a search for the standard model Higgs boson produced in association with a top quark pair (tt¯Htt¯H) in final states with electrons, muons, and hadronically decaying ? leptons are presented. The analyzed data set corresponds to an integrated luminosity of 35.9 fb?1 recorded in proton-proton collisions at s?=13s=13 TeV by the CMS experiment in 2016. The sensitivity of the search is improved by using matrix element and machine learning methods to separate the signal from backgrounds. The measured signal rate amounts to 1.23 ??0.43 +?0.45 times the production rate expected in the standard model, with an observed (expected) significance of 3.2? (2.8?), which represents evidence for tt¯Htt¯H production in those final states. An upper limit on the signal rate of 2.1 times the standard model production rate is set at 95% confidence levelÖğe Evidence for the Associated Production of a Single Top Quark and a Photon in Proton-Proton Collisions at ?s=13??TeV(American Physical Society, 2018) Bilki, Burak; ., ve digerThe first evidence of events consistent with the production of a single top quark in association with a photon is reported. The analysis is based on proton-proton collisions at ?s=13??TeV and recorded by the CMS experiment in 2016, corresponding to an integrated luminosity of 35.9??fb?1. Events are selected by requiring the presence of a muon (?), a photon (?), an imbalance in transverse momentum from an undetected neutrino (?), and at least two jets (j) of which exactly one is identified as associated with the hadronization of a b quark. A multivariate discriminant based on topological and kinematic event properties is employed to separate signal from background processes. An excess above the background-only hypothesis is observed, with a significance of 4.4 standard deviations. A fiducial cross section is measured for isolated photons with transverse momentum greater than 25 GeV in the central region of the detector. The measured product of the cross section and branching fraction is ?(pp?t?j)B(t???b)=115±17(stat)±30(syst)??fb, which is consistent with the standard model prediction.Öğe Evidence For The Higgs Boson Decay To A Bottom Quark–Antiquark Pair(Elsevier, 2018) Bilki, Burak; ., ve digersearch for the standard model (SM) Higgs boson (H) decaying to bbwhen produced in association with an electroweak vector boson is reported for the following processes: Z(??)H, W(??)H, W(e?)H, Z(??)H, and Z(ee)H. The search is performed in data samples corresponding to an integrated luminosity of 35.9fb?1at ?s=13 TeVrecorded by the CMS experiment at the LHC during Run2 in 2016. An excess of events is observed in data compared to the expectation in the absence of a H ?bbsignal. The significance of this excess is 3.3 standard deviations, where the expectation from SM Higgs boson production is 2.8. The signal strength corresponding to this excess, relative to that of the SM Higgs boson production, is 1.2 ±0.4. When combined with the Run1 measurement of the same processes, the signal significance is 3.8 standard deviations with 3.8 expected. The corresponding signal strength, relative to that of the SM Higgs boson, is 1.06+0.31?0.29.Öğe Inclusive Search for a Highly Boosted Higgs Boson Decaying to a Bottom Quark-Antiquark Pair(American Physical Society, 2018) Bilki, Burak; ., ve digerAn inclusive search for the standard model Higgs boson (H) produced with large transverse momentum (pT) and decaying to a bottom quark-antiquark pair (b¯b) is performed using a data set of ppcollisions at ?s=13??TeV collected with the CMS experiment at the LHC. The data sample corresponds to an integrated luminosity of 35.9??fb?1. A highly Lorentz-boosted Higgs boson decaying to b¯b is reconstructed as a single, large radius jet, and it is identified using jet substructure and dedicated b tagging techniques. The method is validated with Z?b¯b decays. The Z?b¯b process is observed for the first time in the single-jet topology with a local significance of 5.1 standard deviations (5.8 expected). For a Higgs boson mass of 125 GeV, an excess of events above the expected background is observed (expected) with a local significance of 1.5 (0.7) standard deviations. The measured cross section times branching fraction for production via gluon fusion of H?b¯b with reconstructed pT>450??GeV and in the pseudorapidity range ?2.5Öğe Jet Properties in PbPb and pp Collisions at sNN?????=5.02sNN=5.02TeV(Springer Link, 2018) Bilki, Burak; ., ve digerModifications of the properties of jets in PbPb collisions, relative to those in pp collisions, are studied at a nucleon-nucleon center-of-mass energy of sNN?????=5.02sNN=5.02 TeV via correlations of charged particles with the jet axis in relative pseudorapidity (??), relative azimuth (??), and relative angular distance from the jet axis ?r=(??)2+(??)2??????????????r=(??)2+(??)2. This analysis uses data collected with the CMS detector at the LHC, corresponding to integrated luminosities of 404 ?b?1 and 27.4 pb?1 for PbPb and pp collisions, respectively. Charged particle number densities, jet fragmentation functions, and jet shapes are presented as a function of PbPb collision centrality and charged-particle track transverse momentum, providing a differential description of jet modifications due to interactions with the quark-gluon plasmaÖğe Measurement of Angular Parameters From the Decay B0?K?0?+??in Proton–proton Collisions at ?s=8TeV(Elsevier, 2018) Bilki, Burak; ., ve digerAngular distributions of the decay B0?K?0?+??are studied using a sample of proton–proton collisions at ?s=8TeVcollected with the CMS detector at the LHC, corresponding to an integrated luminosity of 20.5fb?1. An angular analysis is performed to determine the P1and P 5parameters, where the P 5parameter is of particular interest because of recent measurements that indicate a potential discrepancy with the standard model predictions. Based on a sample of 1397 signal events, the P1and P 5parameters are determined as a function of the dimuon invariant mass squared. The measurements are in agreement with predictions based on the standard model.
