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 jet multiplicity and differential production cross sections of Z+jets events in proton-proton collisions at s =7TeV

Abstract: Measurements of differential cross sections are presented for the production of a Z boson and at least one hadronic jet in proton-proton collisions at √s=7 TeV, recorded by the CMS detector, using a data sample corresponding to an integrated luminosity of 4.9 fb^(−1). The jet multiplicity distribution is measured for up to six jets. The differential cross sections are measured as a function of jet transverse momentum and pseudorapidity for the four highest transverse momentum jets. The distribution of the scalar sum of jet transverse momenta is also measured as a function of the jet multiplicity. The measurements are compared with theoretical predictions at leading and next-to-leading order in perturbative QCD.

First Measurement of the Underlying Event Activity at the LHC with $\sqrt{s} = 0.9$ TeV

Abstract: A measurement of the underlying activity in scattering processes with transverse momentum scale in the GeV region is performed in proton-proton collisions at sqrt(s) = 0.9 TeV, using data collected by the CMS experiment at the LHC. Charged hadron production is studied with reference to the direction of a leading object, either a charged particle or a set of charged particles forming a jet. Predictions of several QCD-inspired models as implemented in PYTHIA are compared, after full detector simulation, to the data. The models generally predict too little production of charged hadrons with pseudorapidity eta 0.5 GeV/c, and azimuthal direction transverse to that of the leading object.

Constraints on the pMSSM, AMSB model and on other models from the search for long-lived charged particles in proton–proton collisions at √s = 8 TeV

Abstract: Stringent limits are set on the long-lived lepton-like sector of the phenomenological minimal supersymmetric standard model (pMSSM) and the anomaly-mediated supersymmetry breaking (AMSB) model. The limits are derived from the results presented in a recent search for long-lived charged particles in proton–proton collisions, based on data collected by the CMS detector at a centre-of-mass energy of 8 TeV at the Large Hadron Collider. In the pMSSM parameter sub-space considered, 95.9 % of the points predicting charginos with a lifetime of at least 10 ns are excluded. These constraints on the pMSSM are the first obtained at the LHC. Charginos with a lifetime greater than 100 ns and masses up to about 800 GeV in the AMSB model are also excluded. The method described can also be used to set constraints on other models.

Search for a heavy right-handed W boson and a heavy neutrino in events with two same-flavor leptons and two jets at \( \sqrt{s}=13 \) TeV

Abstract: A search for a heavy right-handed W boson (W$_{R}$) decaying to a heavy right-handed neutrino and a charged lepton in events with two same-flavor leptons (e or μ) and two jets, is presented. The analysis is based on proton-proton collision data, collected by the CMS Collaboration at the LHC in 2016 and corresponding to an integrated luminosity of 35.9 fb$^{−1}$. No significant excess above the standard model expectation is seen in the invariant mass distribution of the dilepton plus dijet system. Assuming that couplings are identical to those of the standard model, and that only one heavy neutrino flavor N$_{R}$ contributes significantly to the W$_{R}$ decay width, the region in the two-dimensional $ \left({m}_{{\mathrm{W}}_{\mathrm{R}}},{m}_{{\mathrm{N}}_{\mathrm{R}}}\right) $ mass plane excluded at 95% confidence level extends to approximately $ {m}_{{\mathrm{W}}_{\mathrm{R}}}=4.4 $ TeV and covers a large range of right-handed neutrino masses below the W$_{R}$ boson mass. This analysis provides the most stringent limits on the W$_{R}$ mass to date.

Measurement of diffractive dissociation cross sections in pp collisions at s =7TeV

Abstract: Measurements of diffractive dissociation cross sections in pp collisions at sqrt(s) = 7 TeV are presented in kinematic regions defined by the masses M[X] and M[Y] of the two final-state hadronic systems separated by the largest rapidity gap in the event. Differential cross sections are measured as a function of xi[X]= M[X]^2/s in the region -5.5 3, log[10]M[X] > 1.1, and log[10]M[Y] > 1.1, a region dominated by DD. The cross sections integrated over these regions are found to be, respectively, 2.99 +/- 0.02 (stat) +0.32 -0.29 (syst) mb, 1.18 +/- 0.02 (stat) +/- 0.13 (syst) mb, and 0.58 +/- 0.01 (stat) +0.13 -0.11 (syst) mb, and are used to extract total SD and DD cross sections. In addition, the inclusive differential cross section, d sigma /d Delta eta[F], for events with a pseudorapidity gap adjacent to the edge of the detector, is measured over Delta eta[F] = 8.4 units of pseudorapidity. The results are compared to those of other experiments and to theoretical predictions, and found compatible with slowly-rising diffractive cross sections as a function of center-of-mass energy.

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.