Armen Tumasyan

Bio: Armen Tumasyan is an academic researcher from Yerevan Physics Institute. The author has contributed to research in topics: Large Hadron Collider & Lepton. The author has an hindex of 128, co-authored 1189 publications receiving 79408 citations. Previous affiliations of Armen Tumasyan include CERN & Austrian Academy of Sciences.

Measurement of Prompt D0 Meson Azimuthal Anisotropy in Pb-Pb Collisions at sNN =5.02 TeV

Abstract: The prompt D0 meson azimuthal anisotropy coefficients, v2 and v3, are measured at midrapidity (|y|<1.0) in Pb-Pb collisions at a center-of-mass energy sNN=5.02 TeV per nucleon pair with data collected by the CMS experiment. The measurement is performed in the transverse momentum (pT) range of 1 to 40 GeV/c, for central and midcentral collisions. The v2 coefficient is found to be positive throughout the pT range studied. The first measurement of the prompt D0 meson v3 coefficient is performed, and values up to 0.07 are observed for pT around 4 GeV/c. Compared to measurements of charged particles, a similar pT dependence, but smaller magnitude for pT<6 GeV/c, is found for prompt D0 meson v2 and v3 coefficients. The results are consistent with the presence of collective motion of charm quarks at low pT and a path length dependence of charm quark energy loss at high pT, thereby providing new constraints on the theoretical description of the interactions between charm quarks and the quark-gluon plasma.

Search for supersymmetry in pp collisions at √s = 7 TeV in events with a single lepton, jets, and missing transverse momentum

Abstract: Results are reported from a search for physics beyond the standard model in proton-proton collisions at a center-of-mass energy of 7 TeV, focusing on the signature with a single, isolated, high-transverse-momentum lepton (electron or muon), energetic jets, and large missing transverse momentum The data sample comprises an integrated luminosity of 36 inverse picobarns, recorded by the CMS experiment at the LHC The search is motivated by models of new physics, including supersymmetry The observed event yields are consistent with standard model backgrounds predicted using control samples obtained from the data The characteristics of the event sample are consistent with those expected for the production of t t-bar and W +jets events The results are interpreted in terms of limits on the parameter space for the constrained minimal supersymmetric extension of the standard model

Search for massive resonances decaying into WW, WZ, ZZ, qW, and qZ with dijet final states at √s =13 TeV

Abstract: Results are presented from a search in the dijet final state for new massive narrow resonances decaying to pairs of W and Z bosons or to a W/Z boson and a quark. Results are based on data recorded in proton-proton collisions at √s = 13 TeV with the CMS detector at the CERN LHC. The data correspond to an integrated luminosity of 35.9 fb^(−1). The mass range investigated extends upwards from 1.2 TeV. No excess is observed above the estimated standard model background and limits are set at 95% confidence level on cross sections, which are interpreted in terms of various models that predict gravitons, heavy spin-1 bosons, and excited quarks. In a heavy vector triplet model, W′ and Z′ resonances, with masses below 3.2 and 2.7 TeV, respectively, and spin-1 resonances with degenerate masses below 3.8 TeV are excluded at 95% confidence level. In the case of a singlet W′resonance masses between 3.3 and 3.6 TeV can be excluded additionally. Similarly, excited quark resonances, q∗, decaying to qW and qZ with masses less than 5.0 and 4.7 TeV, respectively, are excluded. In a narrow-width bulk graviton model, upper limits are set on cross sections ranging from 0.6 fb for high resonance masses above 3.6 TeV, to 36.0 fb for low resonance masses of 1.3 TeV.

Differential Cross Section Measurements For The Production Of A W Boson In Association With Jets In Proton-proton Collisions At S = 7 Tev

Abstract: 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 inverse femtobarns. 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.

Measurement of the underlying event in the Drell-Yan process in proton-proton collisions at √{s} = 7 {TeV}

Abstract: A measurement of the underlying event (UE) activity in proton-proton collisions at a centre-of-mass energy of 7 TeV is performed using Drell--Yan events in a data sample corresponding to an integrated luminosity of 2.2 inverse femtobarns, collected by the CMS experiment at the LHC. The activity measured in the muonic final state (q q-bar to opposite sign muons) is corrected to the particle level and compared with the predictions of various Monte Carlo generators and hadronization models. The dependence of the UE activity on the dimuon invariant mass is well described by PYTHIA and HERWIG++ tunes derived from the leading jet/track approach, illustrating the universality of the UE activity. The UE activity is observed to be independent of the dimuon invariant mass in the region above 40 GeV, while a slow increase is observed with increasing transverse momentum of the dimuon system. The dependence of the UE activity on the transverse momentum of the dimuon system is accurately described by MADGRAPH, which simulates multiple hard emissions.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

The automated computation of tree-level and next-to-leading order differential cross sections, and their matching to parton shower simulations

Abstract: We discuss the theoretical bases that underpin the automation of the computations of tree-level and next-to-leading order cross sections, of their matching to parton shower simulations, and of the merging of matched samples that differ by light-parton multiplicities. We present a computer program, MadGraph5 aMC@NLO, capable of handling all these computations — parton-level fixed order, shower-matched, merged — in a unified framework whose defining features are flexibility, high level of parallelisation, and human intervention limited to input physics quantities. We demonstrate the potential of the program by presenting selected phenomenological applications relevant to the LHC and to a 1-TeV e + e − collider. While next-to-leading order results are restricted to QCD corrections to SM processes in the first public version, we show that from the user viewpoint no changes have to be expected in the case of corrections due to any given renormalisable Lagrangian, and that the implementation of these are well under way.