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.

Searches for physics beyond the standard model with the MT2variable in hadronic final states with and without disappearingtracks in proton–proton collisions at √s = 13 TeV

Abstract: Two related searches for phenomena beyond the standard model (BSM) are performed using events with hadronic jets and significant transverse momentum imbalance. The results are based on a sample of proton–proton collisions at a center-of-mass energy of 13 TeV, collected by the CMS experiment at the LHC in 2016–2018 and corresponding to an integrated luminosity of 137 fb−1. The first search is inclusive, based on signal regions defined by the hadronic energy in the event, the jet multiplicity, the number of jets identified as originating from bottom quarks, and the value of the kinematic variable MT2 for events with at least two jets. For events with exactly one jet, the transverse momentum of the jet is used instead. The second search looks in addition for disappearing tracks produced by BSM longlived charged particles that decay within the volume of the tracking detector. No excess event yield is observed above the predicted standard model background. This is used to constrain a range of BSM models that predict the following: the pair production of gluinos and squarks in the context of supersymmetry models conserving R-parity, with or without intermediate long-lived charginos produced in the decay chain; the resonant production of a colored scalar state decaying to a massive Dirac fermion and a quark; or the pair production of scalar and vector leptoquarks each decaying to a neutrino and a top, bottom, or light-flavor quark. In most of the cases, the results obtained are the most stringent constraints to date.

Erratum: Search for the associated production of the Higgs boson with a top-quark pair

Abstract: The x-axis of figure 2, lower left panel (“Lepton + ≥ 6 jets + 2 b-tags”) should be replaced with “3rd highest CSV output”.

Combinations of single-top-quark production cross-section measurements and |fLVVtb| determinations at √s = 7 and 8 TeV with the ATLAS and CMS experiments

Abstract: This paper presents the combinations of single-top-quark production cross-section measurements by the ATLAS and CMS Collaborations, using data from LHC proton-proton collisions at $ \sqrt{s} $ = 7 and 8 TeV corresponding to integrated luminosities of 117 to 51 fb$^{−1}$ at $ \sqrt{s} $ = 7 TeV and 122 to 203 fb$^{−1}$ at $ \sqrt{s} $ = 8 TeV These combinations are performed per centre-of-mass energy and for each production mode: t-channel, tW, and s-channel The combined t-channel cross-sections are 675 ± 57 pb and 877 ± 58 pb at $ \sqrt{s} $ = 7 and 8 TeV respectively The combined tW cross-sections are 163 ± 41 pb and 231 ± 36 pb at $ \sqrt{s} $ = 7 and 8 TeV respectively For the s-channel cross-section, the combination yields 49 ± 14 pb at $ \sqrt{s} $ = 8 TeV The square of the magnitude of the CKM matrix element V$_{tb}$ multiplied by a form factor f$_{LV}$ is determined for each production mode and centre-of-mass energy, using the ratio of the measured cross-section to its theoretical prediction It is assumed that the top-quark-related CKM matrix elements obey the relation |V$_{td}$|, |V$_{ts}$| ≪ |V$_{tb}$| All the |f$_{LV}$V$_{tb}$|$^{2}$ determinations, extracted from individual ratios at $ \sqrt{s} $ = 7 and 8 TeV, are combined, resulting in |f$_{LV}$V$_{tb}$| = 102 ± 004 (meas) ± 002 (theo) All combined measurements are consistent with their corresponding Standard Model predictions

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.