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.

Search for pair production of first and second generation leptoquarks in proton-proton collisions at √s=8 TeV

Abstract: A search for pair production of first and second generation leptoquarks is performed in final states containing either two charged leptons and two jets, or one charged lepton, one neutrino and two jets, using proton-proton collision data at √s = 8 TeV. The data, corresponding to an integrated luminosity of 19.7 fb^(−1), were recorded with the CMS detector at the LHC. First-generation scalar leptoquarks with masses less than 1010 (850) GeV are excluded for β=1.0 (0.5), where β is the branching fraction of a leptoquark decaying to a charged lepton and a quark. Similarly, second-generation scalar leptoquarks with masses less than 1080 (760) GeV are excluded for β=1.0 (0.5). Mass limits are also set for vector leptoquark production scenarios with anomalous vector couplings, and for R-parity violating supersymmetric scenarios of top squark pair production resulting in similar final-state signatures. These are the most stringent limits placed on the masses of vector leptoquarks and RPV top squarks to date.

Measurement of prompt ψ (2S) to J /ψ yield ratios in Pb-Pb and p - p collisions at sNN =2.76 TeV

Abstract: The ratio between the prompt psi (2S) and J/psi yields, reconstructed via their decays into mu(-)mu(-) is measured in Pb-Pb and p-p collisions at root sNN = 2.76 TeV. The analysis is based on Pb-Pb and p-p data samples collected by CMS at the Large Hadron Collider, corresponding to integrated luminosities of 150 mu b(-1) and 5.4 mu b(-1), respectively. The double ratio of measured yields (N phi((2S))/NJ/(Pb-Pb)/N-psi(2S)/NJ/psi)(p-p) is computed in three Pb-Pb collision centrality bins and two kinematic ranges: one at midrapidity, vertical bar y vertical bar < 1.6, covering the transverse momentum range 6.5 < pT < 30 GeV= c, and the other at forward rapidity, 1.6 < vertical bar y vertical bar < 2.4, extending to lower pT values, 3 < pT < 30 GeV/c. The centralityintegrated double ratio changes from 0.45 +/- 0.13(stat) +/- 0.07dsyst_ in the first range to 1.67 +/- 0.34(stat) +/- 0.27dsyst_ in the second. This difference is most pronounced in the most central collisions.

Elliptic Flow of Charm and Strange Hadrons in High-Multiplicity p+Pb Collisions at √sNN=8.16 TeV

Abstract: The elliptic azimuthal anisotropy coefficient (v2) is measured for charm (D^0) and strange (K^0_S, Λ, Ξ−, and Ω−) hadrons, using a data sample of p + Pb collisions collected by the CMS experiment, at a nucleon-nucleon center-of-mass energy of √s_(NN)= 8.16 TeV. A significant positive v2 signal from long-range azimuthal correlations is observed for all particle species in high-multiplicity p + Pb collisions. The measurement represents the first observation of possible long-range collectivity for open heavy flavor hadrons in small systems. The results suggest that charm quarks have a smaller v_2 than the lighter quarks, probably reflecting a weaker collective behavior. This effect is not seen in the larger PbPb collision system at √s_(NN)= 5.02 TeV, also presented.

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.