Person:
IŞILDAK, Bora

First Name

Bora

Last Name

IŞILDAK

Organizational Unit

Natural and Mathematical Sciences

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Publication Search Results

Now showing 1 - 10 of 941

Open Access
Search for charged-lepton flavor violation in top quark production and decay in pp collisions at s√ = 13 TeV
(Springer, 2022-06-15) Tumasyan, A.; Işıldak, Bora; The CMS Collaboration; Natural and Mathematical Sciences; IŞILDAK, Bora
Results are presented from a search for charged-lepton flavor violating (CLFV) interactions in top quark production and decay in pp collisions at a center-of-mass energy of 13 TeV. The events are required to contain one oppositely charged electron-muon pair in the final state, along with at least one jet identified as originating from a bottom quark. The data correspond to an integrated luminosity of 138 fb−1, collected by the CMS experiment at the LHC. This analysis includes both the production (q → eμt) and decay (t → eμq) modes of the top quark through CLFV interactions, with q referring to a u or c quark. These interactions are parametrized using an effective field theory approach. With no significant excess over the standard model expectation, the results are interpreted in terms of vector-, scalar-, and tensor-like CLFV four-fermion effective interactions. Finally, observed exclusion limits are set at 95% confidence levels on the respective branching fractions of a top quark to an eμ pair and an up (charm) quark of 0.13 × 10−6 (1.31 × 10−6), 0.07 × 10−6 (0.89 × 10−6), and 0.25 × 10−6 (2.59 × 10−6) for vector, scalar, and tensor CLFV interactions, respectively.
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Measurement of the triple-differential dijet cross section in proton-proton collisions at √s = 8 TeV and constraints on parton distribution functions
(Springer International Publishing, 2017-11-07) Sirunyan, A. M.; Işıldak, Bora; The CMS Collaboration; Natural and Mathematical Sciences; IŞILDAK, Bora
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.
Open Access
Search for long-lived heavy neutral leptons with displaced vertices in proton-proton collisions at s√ =13 TeV
(Springer, 2022-07-14) Tumasyan, A.; Işıldak, Bora; The CMS Collaboration; Natural and Mathematical Sciences; IŞILDAK, Bora
A search for heavy neutral leptons (HNLs), the right-handed Dirac or Majorana neutrinos, is performed in final states with three charged leptons (electrons or muons) using proton-proton collision data collected by the CMS experiment at s = 13 TeV at the CERN LHC. The data correspond to an integrated luminosity of 138 fb−1. The HNLs could be produced through mixing with standard model neutrinos ν. For small values of the HNL mass (<20 GeV) and the square of the HNL-ν mixing parameter (10−7–10−2), the decay length of these particles can be large enough so that the secondary vertex of the HNL decay can be resolved with the CMS silicon tracker. The selected final state consists of one lepton emerging from the primary proton-proton collision vertex, and two leptons forming a displaced, secondary vertex. No significant deviations from the standard model expectations are observed, and constraints are obtained on the HNL mass and coupling strength parameters, excluding previously unexplored regions of parameter space in the mass range 1–20 GeV and squared mixing parameter values as low as 10−7.
Open Access
Measurement of tt¯ normalised multi-differential cross sections in pp collisions at s√=13 TeV, and simultaneous determination of the strong coupling strength, top quark pole mass, and parton distribution functions
(Springer Nature, 2020-07-22) Sirunyan, A. M.; Işıldak, Bora; The CMS Collaboration; Natural and Mathematical Sciences; IŞILDAK, Bora
Normalised multi-differential cross sections for top quark pair (t (t) over bar) production are measured in proton-proton collisions at a centre-of-mass energy of 13 TeV using events containing two oppositely charged leptons. The analysed data were recorded with the CMS detector in 2016 and correspond to an integrated luminosity of 35.9 fb(-1). The doubledifferential t (t) over bar cross section is measured as a function of the kinematic properties of the top quark and of the t (t) over bar system at parton level in the full phase space. A triple-differential measurement is performed as a function of the invariant mass and rapidity of the t (t) over bar system and the multiplicity of additional jets at particle level. The data are compared to predictions of Monte Carlo event generators that complement next-to-leading-order (NLO) quantum chromodynamics (QCD) calculations with parton showers. Together with a fixed-order NLO QCD calculation, the triple-differential measurement is used to extract values of the strong coupling strength alpha(S) and the top quark pole mass (m(t)(pole)) using several sets of parton distribution functions (PDFs). The measurement of m(t)(pole) exploits the sensitivity of the t (t) over bar invariant mass distribution to m(t)(pole) near the production threshold. Further-more, a simultaneous fit of the PDFs, aS, and m(t)(pole) is performed at NLO, demonstrating that the new data have significant impact on the gluon PDF, and at the same time allow an accurate determination of alpha(S) and m(t)(pole). The values alpha S(mZ) = 0.1135+0.0021-0.0017 and m(t)(pole) = 170.5 +/- 0.8GeV are extracted, which account for experimental and theoretical uncertainties, the latter being estimated from NLO scale variations. Possible effects from Coulomb and soft-gluon resummation near the t (t) over bar production threshold are neglected in these parameter extractions. A rough estimate of these effects indicates an expected correction of m(t)(pole) of the order of +1 GeV, which can be regarded as additional theoretical uncertainty in the current m(t)(pole) extraction.
Open Access
Search for resonances decaying to a pair of Higgs bosons in the b b ¯ q q ¯ ’ℓν final state in proton-proton collisions at √s = 13 TeV
(Springer Nature, 2019-10-09) Sirunyan, A. M.; Işıldak, Bora; The CMS Collaboration; Natural and Mathematical Sciences; IŞILDAK, Bora
A search for new massive particles decaying into a pair of Higgs bosons in proton-proton collisions at a center-of-mass energy of 13 TeV is presented. Data were collected with the CMS detector at the LHC, corresponding to an integrated luminosity of 35.9 fb−1. The search is performed for resonances with a mass between 0.8 and 3.5 TeV using events in which one Higgs boson decays into a bottom quark pair and the other decays into two W bosons that subsequently decay into a lepton, a neutrino, and a quark pair. The Higgs boson decays are reconstructed with techniques that identify final state quarks as substructure within boosted jets. The data are consistent with standard model expectations. Exclusion limits are placed on the product of the cross section and branching fraction for generic spin-0 and spin-2 massive resonances. The results are interpreted in the context of radion and bulk graviton production in models with a warped extra spatial dimension. These are the best results to date from searches for an HH resonance decaying to this final state, and they are comparable to the results from searches in other channels for resonances with masses below 1.5 TeV.
Open Access
Measurement of the single top quark and antiquark production cross sections in the tchannel and their ratio in proton-proton collisions at √s=13 TeV
(Elsevier, 2020-01-10) Sirunyan, A. M.; Işıldak, Bora; The CMS Collaboration; Natural and Mathematical Sciences; IŞILDAK, Bora
Measurements of the cross sections for the production of single top quarks and antiquarks in the t channel, and their ratio, are presented for proton-proton collisions at a center-of-mass energy of 13 TeV. The data set used was recorded in 2016 by the CMS detector at the LHC and corresponds to an integrated luminosity of 35.9 fb(-1). Events with one muon or electron are selected, and different categories of jet and b jet multiplicity and multivariate discriminators are applied to separate the signal from the background. The cross sections for the t-channel production of single top quarks and antiquarks are measured to be 130 +/- 1(stat) +/- 19(syst) pb and 77 +/- 1(stat) +/- 12(syst) pb, respectively, and their ratio is 1.68 +/- 0.02(stat) +/- 0.05(syst). The results are in agreement with the predictions from the standard model.
Open Access
Measurements of the differential cross sections of the production of Z + jets and γ + jets and of Z boson emission collinear with a jet in pp collisions at s√ = 13 TeV
(Springer, 2021-05-31) Sirunyan, A. M.; Işıldak, Bora; The CMS Collaboration; Natural and Mathematical Sciences; IŞILDAK, Bora
Measurements of the differential cross sections of Z + jets and γ + jets production, and their ratio, are presented as a function of the boson transverse momentum. Measurements are also presented of the angular distribution between the Z boson and the closest jet. The analysis is based on pp collisions at a center-of-mass energy of 13 TeV corresponding to an integrated luminosity of 35.9 fb−1 recorded by the CMS experiment at the LHC. The results, corrected for detector effects, are compared with various theoretical predictions. In general, the predictions at higher orders in perturbation theory show better agreement with the measurements. This work provides the first measurement of the ratio of the differential cross sections of Z + jets and γ + jets production at 13 TeV, as well as the first direct measurement of Z bosons emitted collinearly with a jet.
Open Access
Pileup mitigation at CMS in 13 TeV data
(IOP Publishing, 2020-09) Sirunyan, A. M.; Işıldak, Bora; The CMS Collaboration; Natural and Mathematical Sciences; IŞILDAK, Bora
With increasing instantaneous luminosity at the LHC come additional reconstruction challenges. At high luminosity, many collisions occur simultaneously within one proton-proton bunch crossing. The isolation of an interesting collision from the additional "pileup" collisions is needed for effective physics performance. In the CMS Collaboration, several techniques capable of mitigating the impact of these pileup collisions have been developed. Such methods include charged-hadron subtraction, pileup jet identification, isospin-based neutral particle "delta beta" correction, and, most recently, pileup per particle identification. This paper surveys the performance of these techniques for jet and missing transverse momentum reconstruction, as well as muon isolation. The analysis makes use of data corresponding to 35.9 fb(-1) collected with the CMS experiment in 2016 at a center-of-mass energy of 13 TeV. The performance of each algorithm is discussed for up to 70 simultaneous collisions per bunch crossing. Significant improvements are found in the identification of pileup jets, the jet energy, mass, and angular resolution, missing transverse momentum resolution, and muon isolation when using pileup per particle identification.
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Suppression and azimuthal anisotropy of prompt and nonprompt J/psi production in PbPb collisions at root S-NN=2.76 TeV
(Springer International Publishing, 2017-04) Khachatryan, V.; Işıldak, Bora; The CMS Collaboration; Natural and Mathematical Sciences; IŞILDAK, Bora
The nuclear modification factor R-AA and the azimuthal anisotropy coefficient v(2) ofprompt and nonprompt (i.e. those from decays of b hadrons) J/psi mesons, measured from PbPb and pp collisions at root S-NN = 2.76 rfeV at itheLHC, are reported. The results are presented in several event centrality intervals and several kinematic regions, for transverse momenta p(T) > 6.5 GeV/c and rapidity vertical bar y vertical bar < 2.4, extending down to p(T) = 3 GeV/c in the 1.6 < vertical bar y vertical bar < 2.4 range. The v(2) of prompt J/psi is found to be nonzero, but with no strong dependence on centrality, rapidity, or p(T) over the full kinematic range studied. The measured v(2) of nonprompt J/psi is consistent with zero. The R-AA of prompt J/psi exhibits a suppression that increases from peripheral to central collisions but does not vary strongly as a function of either y or pT in the fiducial range. The nonprompt J/psi RAA shows a suppression which becomes stronger as rapidity or p(T) increases. The v(2) and R-AA of open and hidden charm, and of open charm and beauty, are compared.
Metadata only
Recent results from the CMS experiment at the LHC
(EDP Sciences, 2014) Işıldak, Bora; Natural and Mathematical Sciences; IŞILDAK, Bora
Numerous studies on Jet Production, Vector Boson Production, V+Jets Production and Multi-Boson Production have been carried out by the Compact Muon Solenoid (CMS) Collaboration to test perturbative quantum chromodynamics (QCD) predictions, and to put more stringent constraints on PDFs (Parton Distribution Functions). In this paper, some of these experimental results will be presented, and their possible impacts on Higgs physics and new physics searches will be discussed.