nan Khachatryan

Measurement of the elliptic anisotropy of charged particles produced in PbPb collisions at square root of sNN equals to 2.76 TeV

The anisotropy of the azimuthal distributions of charged particles produced in √ sNN = 2.76 TeV PbPb collisions is studied with the CMS experiment at the LHC. The elliptic anisotropy parameter, v2, defined as the second coefficient in a Fourier expansion of the particle invariant yields, is extracted using the event-plane method, twoand four-particle cumulants, and Lee–Yang zeros. The anisotropy is presented as a function of transverse momentum (pT), pseudorapidity (η) over a broad kinematic range: 0.3 < pT < 20 GeV/c, |η| < 2.4, and in 12 classes of collision centrality from 0 to 80%. The results are compared to those obtained at lower center-of-mass energies, and various scaling behaviors are examined. When scaled by the geometric eccentricity of the collision zone, the elliptic anisotropy is found to obey a universal scaling with the transverse particle density for different collision systems and center-of-mass energies. Submitted to Physical Review C ∗See Appendix A for the list of collaboration members ar X iv :1 20 4. 14 09 v2 [ nu cl -e x] 1 5 Ja n 20 13

Search for supersymmetry in events with photons and low missing transverse energy in pp collisions at (square root) s (equivalent) 7 TeV

Many models of new physics, including versions of supersymmetry (SUSY), predict production of events with low missing transverse energy, electroweak gauge bosons, and many energetic final-state particles. The stealth SUSY model yields this signature while conserving R-parity by means of a new hidden sector in which SUSY is approximately conserved. The results of a general search for new physics, with no requirement on missing transverse energy, in events with two photons and four or more hadronic jets are reported. The study is based on a sample of proton-proton collisions at √ s = 7 TeV corresponding to 4.96 fb−1 of integrated luminosity collected with the CMS detector in 2011. Based on good agreement between the data and the standard model expectation, the data are used to determine model-independent cross-section limits and a limit on the squark mass in the framework of stealth SUSY. With this first study of its kind, squark masses less than 1430 GeV are excluded at the 95% confidence level. Submitted to Physics Letters B c

Search for anomalous production of highly boosted Z bosons decaying to mu positive mu negative in proton-proton collisions at square root s equals to 7 TeV

Results are reported from a search for the anomalous production of highly boosted Z bosons with large transverse momentum and decaying to μ+μ−. Such Z bosons may be produced in the decays of new heavy particles. The search uses pp collision data at √ s = 7 TeV, corresponding to an integrated luminosity of 5.0 fb−1 recorded with the CMS detector. The shape of the observed transverse momentum distribution of Z bosons is consistent with standard model expectations. Constraints are obtained on models predicting the production of excited quarks decaying via electroweak processes. Assuming a compositeness scale that is equal to the excited quark mass as well as transition coupling strengths between Z bosons and excited quarks that are equal to standard model couplings to quarks, masses of excited quarks below 1.94 TeV are excluded at the 95% confidence level. For excited quark production via a novel contact interaction, masses below 2.22 TeV are excluded, even if the excited quarks do not couple to gluons. Submitted to Physics Letters B c

Search for a narrow, spin-2 resonance decaying to a pair of Z bosons in the qq negative l positive l negative final state

Article history: Received 17 September 2012 Received in revised form 12 November 2012 Accepted 28 November 2012 Available online 5 December 2012 Editor: M. Doser

Measurement of the tt production cross section in pp collisions at square root of s equals to 7 TeV with lepton positive jets final states

A measurement of the tt production cross section in pp collisions at √ s = 7 TeV is presented. The results are based on data corresponding to an integrated luminosity of 2.3 fb−1 collected by the CMS detector at the LHC. Selected events are required to have one isolated, high transverse momentum electron or muon, large missing transverse energy, and hadronic jets, at least one of which must be consistent with having originated from a b quark. The measured cross section is 158.1± 2.1 (stat.)± 10.2 (syst.)± 3.5 (lum.) pb, in agreement with standard model predictions. Submitted to Physics Letters B c

Search for fractionally charged particles in pp collisions at (square root) s (equivalent to) 7 TeV

A search is presented for free heavy long-lived fractionally charged particles produced in pp collisions at √ s = 7 TeV. The data sample was recorded by the CMS detector at the LHC and corresponds to an integrated luminosity of 5.0 fb−1. Candidate fractionally charged particles are identified by selecting tracks with associated low charge measurements in the silicon tracking detector. Observations are found to be consistent with expectations for background processes. The results of the search are used to set upper limits on the cross section for pair production of fractionally charged, massive spin-1/2 particles that are neutral under SU(3)C and SU(2)L. We exclude at 95% confidence level such particles with electric charge±2e/3 with masses below 310 GeV, and those with charge ±e/3 with masses below 140 GeV. Submitted to Physical Review D c

Measurement of differential top-quark-pair production cross sections in pp collisions at square root of s equals to 7TeV

Normalised differential top-quark-pair production cross sections are measured in pp collisions at a centre-of-mass energy of 7 TeV at the LHC with the CMS detector using data recorded in 2011 corresponding to an integrated luminosity of 5.0 fb−1. The measurements are performed in the lepton+jets decay channels (e+jets and μ+jets) and the dilepton decay channels (e+e−, μ+μ−, and μ±e∓). The tt differential cross section is measured as a function of kinematic properties of the final-state charged leptons and jets associated to b quarks, as well as those of the top quarks and the tt system. The data are compared with several predictions from perturbative QCD calculations up to approximate next-to-next-to-leading-order precision. No significant deviations from the standard model are observed. Submitted to the European Physical Journal C c

Search for exotic resonances decaying into WZ/ZZ in pp collisions at (square root) s (equivalent to)7 TeV

A bstractA search for new exotic particles decaying to the VZ final state is performed, where V is either a W or a Z boson decaying into two overlapping jets and the Z decays into a pair of electrons, muons or neutrinos. The analysis uses a data sample of pp collisions corresponding to an integrated luminosity of 5 fb−1 collected by the CMS experiment at the LHC at

Search for heavy Majorana neutrinos in \mu 'plus\minus' \mu 'plus\minus' + jets and e 'plus\minus' e 'plus\minus' + jets events in pp collisions at sqrt(s)=7TeV

\sqrt{s}=7

Search for three-jet resonances in pp collisions at sqrt(s)=7TeV

TeV in 2011. No significant excess is observed in the mass distribution of the VZ candidates compared with the background expectation from standard model processes. Model-dependent upper limits at the 95% confidence level are set on the product of the cross section times the branching fraction of hypothetical particles decaying to the VZ final state as a function of mass. Sequential standard model W′ bosons with masses between 700 and 940 GeV are excluded. In the Randall-Sundrum model for graviton resonances with a coupling parameter of 0.05, masses between 750 and 880 GeV are also excluded.