R-3 Repository :: Browsing by Author "Akgun, B."

Browsing by Author "Akgun, B."

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Alignment of the CMS tracker with LHC and cosmic ray data
(IOP Publishing, 2014) Adair, A.; Akgun, B.; Ecklund, K.M.; Geurts, F.J.M.; Li, W.; Michlin, B.; Padley, B.P.; Redjimi, R.; Roberts, J.; Zabel, J.
The central component of the CMS detector is the largest silicon tracker ever built. The precise alignment of this complex device is a formidable challenge, and only achievable with a significant extension of the technologies routinely used for tracking detectors in the past. This article describes the full-scale alignment procedure as it is used during LHC operations. Among the specific features of the method are the simultaneous determination of up to 200 000 alignment parameters with tracks, the measurement of individual sensor curvature parameters, the control of systematic misalignment effects, and the implementation of the whole procedure in a multi-processor environment for high execution speed. Overall, the achieved statistical accuracy on the module alignment is found to be significantly better than 10μm.
Angular analysis and branching fraction measurement of the decay B0→K*0μ+μ−
(Elsevier, 2013) Adair, A.; Akgun, B.; Ecklund, K.M.; Geurts, F.J.M.; Li, W.; Padley,B.P.; Redjimi, R.; Roberts, J.; Zabel, J.
The angular distributions and the differential branching fraction of the decay B0→K*(892)0μ+μ− are studied using a data sample corresponding to an integrated luminosity of 5.2 fb−1collected with the CMS detector at the LHC in pp collisions at √s=7 TeV. From more than 400 signal decays, the forward–backward asymmetry of the muons, the K*(892)0 longitudinal polarization fraction, and the differential branching fraction are determined as a function of the square of the dimuon invariant mass. The measurements are in good agreement with standard model predictions.
Combined Measurement of the Higgs Boson Mass in pp Collisions at √s=7 and 8 TeV with the ATLAS and CMS Experiments
(American Physical Society, 2015) Adair, A.; Akgun, B.; Chen, Z.; Ecklund, K.M.; Geurts, F.J.M.; Guilbaud, M.; Li, W.; Michlin, B.; Northup, M.; Padley, B.P.; Redjimi, R.; Roberts, J.; Rorie, J.; Tu, Z.; Zabel, J.
A measurement of the Higgs boson mass is presented based on the combined data samples of the ATLAS and CMS experiments at the CERN LHC in the H→γγ and H→ZZ→4ℓ decay channels. The results are obtained from a simultaneous fit to the reconstructed invariant mass peaks in the two channels and for the two experiments. The measured masses from the individual channels and the two experiments are found to be consistent among themselves. The combined measured mass of the Higgs boson is mH=125.09±0.21 (stat)±0.11 (syst) GeV.
Constraints on the Higgs boson width from off-shell production and decay to Z-boson pairs
(Elsevier, 2014) Adair, A.; Akgun, B.; Ecklund, K.M.; Geurts, F.J.M.; Li, W.; Michlin, B.; Padley, B.P.; Redjimi, R.; Roberts, J.; Zabel, J.
Constraints are presented on the total width of the recently discovered Higgs boson, ΓH, using its relative on-shell and off-shell production and decay rates to a pair of Z bosons, where one Z boson decays to an electron or muon pair, and the other to an electron, muon, or neutrino pair. The analysis is based on the data collected by the CMS experiment at the LHC in 2011 and 2012, corresponding to integrated luminosities of 5.1 fb−1 at a center-of-mass energy √s=7 TeV and 19.7 fb−1 at √s=8 TeV. A simultaneous maximum likelihood fit to the measured kinematic distributions near the resonance peak and above the Z-boson pair production threshold leads to an upper limit on the Higgs boson width of ΓH<22 MeV at a 95% confidence level, which is 5.4 times the expected value in the standard model at the measured mass of mH=125.6 GeV.
Description and performance of track and primary-vertex reconstruction with the CMS tracker
(IOP Publishing, 2014) Adair, A.; Akgun, B.; Ecklund, K.M.; Geurts, F.J.M.; Li, W.; Michlin, B.; Padley, B.P.; Redjimi, R.; Roberts, J.; Zabel, J.
A description is provided of the software algorithms developed for the CMS tracker both for reconstructing charged-particle trajectories in proton-proton interactions and for using the resulting tracks to estimate the positions of the LHC luminous region and individual primary-interaction vertices. Despite the very hostile environment at the LHC, the performance obtained with these algorithms is found to be excellent. For tbar t events under typical 2011 pileup conditions, the average track-reconstruction efficiency for promptly-produced charged particles with transverse momenta of pT > 0.9GeV is 94% for pseudorapidities of |η| < 0.9 and 85% for 0.9 < |η| < 2.5. The inefficiency is caused mainly by hadrons that undergo nuclear interactions in the tracker material. For isolated muons, the corresponding efficiencies are essentially 100%. For isolated muons of pT = 100GeV emitted at |η| < 1.4, the resolutions are approximately 2.8% in pT, and respectively, 10μm and 30μm in the transverse and longitudinal impact parameters. The position resolution achieved for reconstructed primary vertices that correspond to interesting pp collisions is 10–12μm in each of the three spatial dimensions. The tracking and vertexing software is fast and flexible, and easily adaptable to other functions, such as fast tracking for the trigger, or dedicated tracking for electrons that takes into account bremsstrahlung.
Determination of the top-quark pole mass and strong coupling constant from the tt production cross section in pp collisions at √s = 7 TeV
(Elsevier, 2014) Adair, A.; Akgun, B.; Ecklund, K.M.; Geurts, F.J.M.; Li, W.; Michlin, B.; Padley, B.P.; Redjimi, R.; Roberts, J.; Zabel, J.
The inclusive cross section for top-quark pair production measured by the CMS experiment in proton–proton collisions at a center-of-mass energy of 7 TeV is compared to the QCD prediction at next-to-next-to-leading order with various parton distribution functions to determine the top-quark pole mass, View the MathML sourcemtpole, or the strong coupling constant, αSαS. With the parton distribution function set NNPDF2.3, a pole mass of 176.7 +3.8 −3.4 GeV is obtained when constraining αS at the scale of the Z boson mass, mZ, to the current world average. Alternatively, by constraining mtpole to the latest average from direct mass measurements, a value of αS(mZ)=0.1151−0.0032+0.0033 is extracted. This is the first determination of αS using events from top-quark production.
Differential cross section measurements for the production of a W boson in association with jets in proton–proton collisions at √s=7 eV
(Elsevier, 2015) Adair, A.; Akgun, B.; Ecklund, K.M.; Geurts, F.J.M.; Li, W.; Michlin, B.; Padley, B.P.; Redjimi, R.; Roberts, J.; Zabel, J.
Measurements are reported of differential cross sections for the production of a W boson, which decays into a muon and a neutrino, in association with jets, as a function of several variables, including the transverse momenta (pT) and pseudorapidities of the four leading jets, the scalar sum of jet transverse momenta (HT), and the difference in azimuthal angle between the directions of each jet and the muon. The data sample of pp collisions at a centre-of-mass energy of 7 TeV was collected with the CMS detector at the LHC and corresponds to an integrated luminosity of 5.0 fb−1. The measured cross sections are compared to predictions from Monte Carlo generators, MADGRAPH + PYTHIA and SHERPA, and to next-to-leading-order calculations from BLACKHAT + SHERPA. The differential cross sections are found to be in agreement with the predictions, apart from the pT distributions of the leading jets at high pT values, the distributions of the HT at high-HT and low jet multiplicity, and the distribution of the difference in azimuthal angle between the leading jet and the muon at low values
Energy calibration and resolution of the CMS electromagnetic calorimeter in pp collisions at √s = 7 TeV
(IOP Publishing, 2013) Adair, A.; Akgun, B.; Ecklund, K.M.; Geurts, F.J.M.; Li, W.; Padley, B.P.; Redjimi, R.; Roberts, J.; Zabel, J.
The energy calibration and resolution of the electromagnetic calorimeter (ECAL) of the CMS detector have been determined using proton-proton collision data from LHC operation in 2010 and 2011 at a centre-of-mass energy of √s = 7 TeV with integrated luminosities of about 5\fbinv. Crucial aspects of detector operation, such as the environmental stability, alignment, and synchronization, are presented. The in-situ calibration procedures are discussed in detail and include the maintenance of the calibration in the challenging radiation environment inside the CMS detector. The energy resolution for electrons from Z-boson decays is better than 2% in the central region of the ECAL barrel (for pseudorapidity |η| < 0.8) and is 2–5% elsewhere. The derived energy resolution for photons from 125 GeV Higgs boson decays varies across the barrel from 1.1% to 2.6% and from 2.2% to 5% in the endcaps. The calibration of the absolute energy is determined from Z→e+e− decays to a precision of 0.4% in the barrel and 0.8% in the endcaps.
Erratum to: Search for new physics in events with same-sign dileptons and jets in pp collisions at √s = 8 TeV
(Springer, 2015) Adair, A.; Akgun, B.; Ecklund, K.M.; Geurts, F.J.M.; Li, W.; Michlin, B.; Padley, B.P.; Redjimi, R.; Roberts, J.; Zabel, J.
Event shapes and azimuthal correlations in Z+jets events in pp collisions at √s=7 TeV
(Elsevier, 2013) Adair, A.; Akgun, B.; Boulahouache, C.; Ecklund, K.M.; Geurts, F.J.M.; Li, W.; Padley, B.P.; Redjimi, R.; Roberts, J.; Zabel, J.
Measurements of event shapes and azimuthal correlations are presented for events where a Z boson is produced in association with jets in proton–proton collisions. The data collected with the CMS detector at the CERN LHC at √s=7 TeV correspond to an integrated luminosity of 5.0 fb−1. The analysis provides a test of predictions from perturbative QCD for a process that represents a substantial background to many physics channels. Results are presented as a function of jet multiplicity, for inclusive Z boson production and for Z bosons with transverse momenta greater than 150 GeV, and compared to predictions from Monte Carlo event generators that include leading-order multiparton matrix-element (with up to four hard partons in the final state) and next-to-leading-order simulations of Z+1-jet events. The experimental results are corrected for detector effects, and can be compared directly with other QCD models.
Evidence of b-Jet Quenching in PbPb Collisions at √sNN=2.76 TeV
(American Physical Society, 2014) Adair, A.; Akgun, B.; Ecklund, K.M.; Geurts, F.J.M.; Li, W.; Michlin, B.; Padley, B.P.; Redjimi, R.; Roberts, J.; Zabel, J.
The production of jets associated to bottom quarks is measured for the first time in PbPb collisions at a center-of-mass energy of 2.76 TeV per nucleon pair. Jet spectra are reported in the transverse momentum (pT) range of 80–250 GeV/c, and within pseudorapidity |η|<2. The nuclear modification factor (RAA) calculated from these spectra shows a strong suppression in the b-jet yield in PbPb collisions relative to the yield observed in pp collisions at the same energy. The suppression persists to the largest values of pT studied, and is centrality dependent. The RAA is about 0.4 in the most central events, similar to previous observations for inclusive jets. This implies that jet quenching does not have a strong dependence on parton mass and flavor in the jet pT range studied.
Interpretation of searches for supersymmetry with simplified models
(American Physical Society, 2013) Adair, A.; Akgun, B.; Boulahouache, C.; Ecklund, K.M.; Geurts, F.J.M.; Li, W.; Padley, B.P.; Redjimi, R.; Roberts, J.; Zabel, J.
The results of searches for supersymmetry by the CMS experiment are interpreted in the framework of simplified models. The results are based on data corresponding to an integrated luminosity of 4.73 to 4.98 fb−1. The data were collected at the LHC in proton–proton collisions at a center-of-mass energy of 7 TeV. This paper describes the method of interpretation and provides upper limits on the product of the production cross section and branching fraction as a function of new particle masses for a number of simplified models. These limits and the corresponding experimental acceptance calculations can be used to constrain other theoretical models and to compare different supersymmetry-inspired analyses.
Measurement of associated production of vector bosons and top quark-antiquark pairs in pp collisions at s =7 TeV
(American Physical Society, 2013-04) Adair, A.; Akgun, B.; Boulahouache, C.; Ecklund, K.M.; Geurts, F.J.M.; Li, W.; Padley, B.P.
Measurement of differential cross sections for the production of a pair of isolated photons in pp collisions at √s=7TeV
(Springer, 2014) Adair, A.; Akgun, B.; Ecklund, K.M.; Geurts, F.J.M.; Li, W.; Michlin, B.; Padley, B.P.; Redjimi, R.; Roberts, J.; Zabel, J.
A measurement of differential cross sections for the production of a pair of isolated photons in proton–proton collisions at √s=7TeV is presented. The data sample corresponds to an integrated luminosity of 5.0 fb−1 collected with the CMS detector. A data-driven isolation template method is used to extract the prompt diphoton yield. The measured cross section for two isolated photons, with transverse energy above 40 and 25 GeV respectively, in the pseudorapidity range |η|<2.5 , |η|∉[1.44,1.57] and with an angular separation ΔR>0.45 , is 17.2±0.2(stat)±1.9(syst)±0.4(lumi) \,pb . Differential cross sections are measured as a function of the diphoton invariant mass, the diphoton transverse momentum, the azimuthal angle difference between the two photons, and the cosine of the polar angle in the Collins–Soper reference frame of the diphoton system. The results are compared to theoretical predictions at leading, next-to-leading, and next-to-next-to-leading order in quantum chromodynamics.
Measurement of J/ψ and ψ(2S) Prompt Double-Differential Cross Sections in pp Collisions at √s=7 TeV
(American Physical Society, 2015) Adair, A.; Akgun, B.; Ecklund, K.M.; Geurts, F.J.M.; Li, W.; Michlin, B.; Padley, B.P.; Redjimi, R.; Roberts, J.; Zabel, J.
The double-differential cross sections of promptly produced J/ψ and ψ(2S) mesons are measured in pp collisions at √s=7 TeV, as a function of transverse momentum pT and absolute rapidity |y|. The analysis uses J/ψ and ψ(2S) dimuon samples collected by the CMS experiment, corresponding to integrated luminosities of 4.55 and 4.90 fb−1, respectively. The results are based on a two-dimensional analysis of the dimuon invariant mass and decay length, and extend to pT=120 and 100 GeV for the J/ψ and ψ(2S), respectively, when integrated over the interval |y|<1.2. The ratio of the ψ(2S) to J/ψ cross sections is also reported for |y|<1.2, over the range 10
Measurement of neutral strange particle production in the underlying event in proton-proton collisions at √s=7TeV
(American Physical Society, 2013) Adair, A.; Akgun, B.; Ecklund, K.M.; Geurts, F.J.M.; Li, W.; Padley, B.P.; Redjimi, R.; Roberts, J.; Zabel, J.; CMS Collaboration
Measurements are presented of the production of primary K0S and particles in proton-proton collisions at ffisffiffi p ¼ 7 TeV in the region transverse to the leading charged-particle jet in each event. The average multiplicity and average scalar transverse momentum sum of K0S and particles measured at pseudorapidities j j < 2 rise with increasing charged-particle jet pT in the range 1–10 GeV=c and saturate in the region 10–50 GeV=c. The rise and saturation of the strange-particle yields and transverse momentum sums in the underlying event are similar to those observed for inclusive charged particles, which confirms the impact-parameter picture of multiple parton interactions. The results are compared to recent tunes of the PYTHIA Monte Carlo event generator. The PYTHIA simulations underestimate the data by 15%–30% for K0S mesons and by about 50% for baryons, a deficit similar to that observed for the inclusive strange-particle production in non-single-diffractive proton-proton collisions. The constant strange- to charged-particle activity ratios with respect to the leading jet pT and similar trends for mesons and baryons indicate that the multiparton-interaction dynamics is decoupled from parton hadronization, which occurs at a later stage.
Measurements of differential jet cross sections in proton-proton collisions at √s=7 TeV with the CMS detector
(American Physical Society, 2013) Adair, A.; Akgun, B.; Boulahouache, C.; Ecklund, K.M.; Geurts, F.J.M.; Li, W.; Padley, B.P.; Redjimi, R.; Roberts, J.; Zabel, J.
Measurements of inclusive jet and dijet production cross sections are presented. Data from LHC proton-proton collisions at √s=7 TeV, corresponding to 5.0 fb−1 of integrated luminosity, have been collected with the CMS detector. Jets are reconstructed up to rapidity 2.5, transverse momentum 2 TeV, and dijet invariant mass 5 TeV, using the anti-kT clustering algorithm with distance parameter R=0.7. The measured cross sections are corrected for detector effects and compared to perturbative QCD predictions at next-to-leading order, using five sets of parton distribution functions.
Rapidity distributions in exclusive Z+jet and γ+jet events in pp collisions at √s=7 TeV
(American Physical Society, 2013) Adair, A.; Akgun, B.; Ecklund, K.M.; Geurts, F.J.M.; Li, W.; Padley, B.P.; Redjimi, R.; Roberts, J.; Zabel, J.
Rapidity distributions are presented for events containing either a Z boson or a photon with a single jet in proton-proton collisions produced at the CERN LHC. The data, collected with the CMS detector at √s=7 TeV, correspond to an integrated luminosity of 5.0 fb−1. The individual rapidity distributions of the boson and the jet are consistent within 5% with expectations from perturbative QCD. However, QCD predictions for the sum and the difference in rapidities of the two final-state objects show discrepancies with CMS data. In particular, next-to-leading-order QCD calculations, and two common Monte Carlo event generators using different methods to match matrix-element partons with parton showers, appear inconsistent with the data as well as with each other.
Search for anomalous production of events with three or more leptons in pp collisions at √s=8 TeV
(American Physical Society, 2014) Adair, A.; Akgun, B.; Ecklund, K.M.; Geurts, F.J.M.; Li, W.; Michlin, B.; Padley, B.P.; Redjimi, R.; Roberts, J.; Zabel, J.
A search for physics beyond the standard model in events with at least three leptons is presented. The data sample, corresponding to an integrated luminosity of 19.5 fb−1 of proton-proton collisions with center-of-mass energy √s=8 TeV, was collected by the CMS experiment at the LHC during 2012. The data are divided into exclusive categories based on the number of leptons and their flavor, the presence or absence of an opposite-sign, same-flavor lepton pair (OSSF), the invariant mass of the OSSF pair, the presence or absence of a tagged bottom-quark jet, the number of identified hadronically decaying τ leptons, and the magnitude of the missing transverse energy and of the scalar sum of jet transverse momenta. The numbers of observed events are found to be consistent with the expected numbers from standard model processes, and limits are placed on new-physics scenarios that yield multilepton final states. In particular, scenarios that predict Higgs boson production in the context of supersymmetric decay chains are examined. We also place a 95% confidence level upper limit of 1.3% on the branching fraction for the decay of a top quark to a charm quark and a Higgs boson (t→cH), which translates to a bound on the left- and right-handed top-charm flavor-violating Higgs Yukawa couplings, λHtc and λHct, respectively, of √|λHtc|2+|λHct|2−−−−−−−−−−−<0.21.
Search for narrow resonances using the dijet mass spectrum in pp collisions at √s=8 TeV
(American Physical Society, 2013) Adair, A.; Akgun, B.; Boulahouache, C.; Ecklund, K.M.; Geurts, F.J.M.; Li, W.; Padley, B.P.; Redjimi, R.; Roberts, J.; Zabel, J.
Results are presented of a search for the production of new particles decaying to pairs of partons (quarks, antiquarks, or gluons), in the dijet mass spectrum in proton-proton collisions at √s=8 TeV. The data sample corresponds to an integrated luminosity of 4.0 fb−1, collected with the CMS detector at the LHC in 2012. No significant evidence for narrow resonance production is observed. Upper limits are set at the 95% confidence level on the production cross section of hypothetical new particles decaying to quark-quark, quark-gluon, or gluon-gluon final states. These limits are then translated into lower limits on the masses of new resonances in specific scenarios of physics beyond the standard model. The limits reach up to 4.8 TeV, depending on the model, and extend previous exclusions from similar searches performed at lower collision energies. For the first time mass limits are set for the Randall–Sundrum graviton model in the dijet channel.

Browsing by Author "Akgun, B."

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