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 dark matter particles in proton-proton collisions at √s = 8 TeV using the razor variables

Abstract: A search for dark matter particles directly produced in proton-proton collisions recorded by the CMS experiment at the LHC is presented. The data correspond to an integrated luminosity of 18.8 fb−1, at a center-of-mass energy of 8 TeV. The event selection requires at least two jets and no isolated leptons. The razor variables are used to quantify the transverse momentum balance in the jet momenta. The study is performed separately for events with and without jets originating from b quarks. The observed yields are consistent with the expected backgrounds and, depending on the nature of the production mechanism, dark matter production at the LHC is excluded at 90% confidence level for a mediator mass scale Λ below 1 TeV. The use of razor variables yields results that complement those previously published.

Search for an excited lepton that decays via a contact interaction to a lepton and two jets in proton-proton collisions at √ s = 13 TeV

Abstract: Results are presented from a search for events containing an excited lepton (electron or muon) produced in association with an ordinary lepton of the same flavor and decaying to a lepton and two hadronic jets. Both the production and the decay of the excited leptons are assumed to occur via a contact interaction with a characteristic energy scale Λ. The branching fraction for the decay mode under study increases with the mass of the excited lepton and is the most sensitive channel for very heavy excited leptons. The analysis uses a sample of proton-proton collisions collected by the CMS experiment at the LHC at $$ \sqrt{s} $$ = 13 TeV, corresponding to an integrated luminosity of 77.4 fb−1. The four-body invariant mass of the two lepton plus two jet system is used as the primary discriminating variable. No significant excess of events beyond the expectation for standard model processes is observed. Assuming that Λ is equal to the mass of the excited leptons, excited electrons and muons with masses below 5.6 and 5.7 TeV, respectively, are excluded at 95% confidence level. These are the best limits to date.

Measurement of quark- and gluon-like jet fractions using jet charge in PbPb and pp collisions at 5.02 TeV

Abstract: BMBWF (Austria); FWF (Austria)Austrian Science Fund (FWF); FNRS (Belgium)Fonds de la Recherche Scientifique - FNRS; FWO (Belgium)FWO; CNPq (Brazil)National Council for Scientific and Technological Development (CNPq); CAPES (Brazil)CAPES; FAPERJ (Brazil)Carlos Chagas Filho Foundation for Research Support of the State of Rio de Janeiro (FAPERJ); FAPERGS (Brazil)Foundation for Research Support of the State of Rio Grande do Sul (FAPERGS); FAPESP (Brazil)Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP); MES (Bulgaria); CERN; CAS (China)Chinese Academy of Sciences; MoST (China)Ministry of Science and Technology, China; NSFC (China)National Natural Science Foundation of China (NSFC); COLCIENCIAS (Colombia)Departamento Administrativo de Ciencia, Tecnologia e Innovacion Colciencias; MSES (Croatia); CSF (Croatia); RPF (Cyprus); SENESCYT (Ecuador); MoER (Estonia); ERC IUT (Estonia)Estonian Research Council; PUT (Estonia); ERDF (Estonia)European Union (EU); Academy of Finland (Finland)Academy of Finland; MEC (Finland); HIP (Finland); CEA (France)French Atomic Energy Commission; CNRS/IN2P3 (France)Centre National de la Recherche Scientifique (CNRS); BMBF (Germany)Federal Ministry of Education & Research (BMBF); DFG (Germany)German Research Foundation (DFG); HGF (Germany); GSRT (Greece)Greek Ministry of Development-GSRT; NKFIA (Hungary); DAE (India)Department of Atomic Energy (DAE); DST (India)Department of Science & Technology (India); IPM (Iran); SFI (Ireland)Science Foundation Ireland; INFN (Italy)Istituto Nazionale di Fisica Nucleare (INFN); MSIP (Republic of Korea); NRF (Republic of Korea); MES (Latvia); LAS (Lithuania); MOE (Malaysia); UM (Malaysia); UASLP-FAI (Mexico); BUAP (Mexico); CINVESTAV (Mexico); CONACYT (Mexico)Consejo Nacional de Ciencia y Tecnologia (CONACyT); LNS (Mexico); SEP (Mexico); MOS (Montenegro); MBIE (New Zealand); PAEC (Pakistan); NSC (Poland); MSHE (Poland); FCT (Portugal)Portuguese Foundation for Science and Technology; JINR (Dubna); NRC KI (Russia); MON (Russia); RosAtom (Russia); RAS (Russia)Russian Academy of Sciences; RFBR (Russia)Russian Foundation for Basic Research (RFBR); MESTD (Serbia); SEIDI (Spain); CPAN (Spain); PCTI (Spain); FEDER (Spain)European Union (EU); MOSTR (Sri Lanka); MST (Taipei); NSTDA (Thailand); ThEPCenter (Thailand); IPST (Thailand); STAR (Thailand); TUBITAK (Turkey)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK); TAEK (Turkey)Ministry of Energy & Natural Resources - Turkey; NASU (Ukraine); STFC (United Kingdom)Science & Technology Facilities Council (STFC); DOE (U.S.A.)United States Department of Energy (DOE); NSF (U.S.A.)National Science Foundation (NSF)

Search for the pair production of light top squarks in the e ± μ ∓ final state in proton-proton collisions at √s=13 TeV

Abstract: A search for the production of a pair of top squarks at the LHC is presented. This search targets a region of parameter space where the kinematics of top squark pair production and top quark pair production are very similar, because of the mass difference between the top squark and the neutralino being close to the top quark mass. The search is performed with 35.9 fb(-1) of proton-proton collisions at a centre-of-mass energy of root s = 13 TeV, collected by the CMS detector in 2016, using events containing one electron-muon pair with opposite charge. The search is based on a precise estimate of the top quark pair background, and the use of the M-T2 variable, which combines the transverse mass of each lepton and the missing transverse momentum. No excess of events is found over the standard model predictions. Exclusion limits are placed at 95% confidence level on the production of top squarks up to masses of 208 GeV for models with a mass difference between the top squark and the lightest neutralino close to that of the top quark.

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.