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.

Measurements of the differential jet cross section as a function of the jet mass in dijet events from proton-proton collisions at √s=13 TeV

Abstract: Measurements of the differential jet cross section are presented as a function of the jet mass in dijet events, in bins of jet transverse momentum, with and without a jet grooming algorithm. The data have been recorded by the CMS Collaboration in proton-proton collisions at the LHC at a center-of-mass energy of 13 TeV and correspond to an integrated luminosity of 2.3 fb(-1). The absolute cross sections show slightly different jet transverse momentum spectra in data and Monte Carlo event generators for the settings used. Removing this transverse momentum dependence, the normalized cross section for ungroomed jets is consistent with the prediction from Monte Carlo event generators for masses below 30% of the transverse momentum. The normalized cross section for groomed jets is measured with higher precision than the ungroomed cross section. Semi-analytical calculations of the jet mass beyond leading logarithmic accuracy are compared to data, as well as predictions at leading order and next-to-leading order, which include parton showering and hadronization. Overall, in the normalized cross section, the theoretical predictions agree with the measured cross sections within the uncertainties for masses from 10 to 30% of the jet transverse momentum.

Measurement of top quark–antiquark pair production in association with a W or Z boson in pp collisions at √s = 8 TeV

Abstract: A measurement of the cross section for the production of top quark-antiquark pairs (ttbar) in association with a vector boson V (W or Z) in proton-proton collisions at sqrt(s) = 8 TeV is presented. The results are based on a dataset corresponding to an integrated luminosity of 19.5 inverse femtobarns recorded with the CMS detector at the LHC. The measurement is performed in three leptonic (e and mu) channels: a same-sign dilepton analysis targeting ttbar W events, and trilepton and four-lepton analyses designed for ttbar Z events. In the same-sign dilepton channel, the ttbar W cross section is measured as sigma[ttbar W] = 170 +90/-80 (stat) +/- 70 (syst) fb, corresponding to a significance of 1.6 standard deviations over the background-only hypothesis. Combining the trilepton and four-lepton channels, a direct measurement of the ttbar Z cross section, sigma[ttbar Z] = 200 +80/-70 (stat) +40/-30 (syst) fb, is obtained with a significance of 3.2 standard deviations. The measured cross sections are compatible with standard model predictions within their experimental uncertainties. The inclusive ttbar V process is observed with a significance of 3.7 standard deviations from the combination of all three leptonic channels.

Relative modification of prompt ψ (2S) and J /ψ yields from pp to PbPb collisions at sNN =5.02 TeV

Abstract: The relative modification of the prompt ψ(2S) and J/ψ yields from pp to PbPb collisions, at the center-of-mass energy of 5.02 TeV per nucleon pair, is presented. The analysis is based on pp and PbPb data samples collected by the CMS experiment at the LHC in 2015, corresponding to integrated luminosities of 28.0 pb^(−1) and 464 μb^(−1), respectively. The double ratio of measured yields of prompt charmonia reconstructed through their decays into muon pairs, (N_ψ(2S)/N_J/ψ)_PbPb/(N_ψ(2S)/N_J/ψ)_pp, is determined as a function of PbPb collision centrality and charmonium transverse momentum p_T, in two kinematic intervals: |y| < 1.6 covering 6.5 < p_T < 30 GeV/c and 1.6 < |y| < 2.4 covering 3 < p_T < 30 GeV/c. The centrality-integrated double ratios are 0.36 ± 0.08 (stat) ± 0.05 (syst) in the first interval and 0.24 ± 0.22 (stat) ± 0.09 (syst) in the second. The double ratio is lower than unity in all the measured bins, suggesting that the ψ(2S) yield is more suppressed than the J/ψ yield in the explored phase space.

Measurement of the W+W− cross section in pp collisions at $\sqrt{s} = 7\mbox{ TeV}$ and limits on anomalous WWγ and WWZ couplings

Abstract: A measurement of W+W− production in pp collisions at $\sqrt{s} = 7~\mathrm{TeV}$ is presented. The data were collected with the CMS detector at the LHC, and correspond to an integrated luminosity of 4.92±0.11 fb−1. The W+W− candidates consist of two oppositely charged leptons, electrons or muons, accompanied by large missing transverse energy. The W+W− production cross section is measured to be 52.4±2.0 (stat.)±4.5 (syst.)±1.2 (lum.) pb. This measurement is consistent with the standard model prediction of 47.0±2.0 pb at next-to-leading order. Stringent limits on the WWγ and WWZ anomalous triple gauge-boson couplings are set.

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.