Vardan Khachatryan

A.I.Alikhanyan National Science Laboratory · Experimental

A new electron scattering experiment (E12-21-003) to verify and understand the nature of hidden sector particles, with particular emphasis on the so-called X17 particle, has been approved at Jefferson Lab. The search for these particles is motivated by new hidden sector models introduced to account for a variety of experimental and observational pu...

When protons and neutrons (nucleons) are bound into atomic nuclei, they are close enough together to feel significant attraction, or repulsion, from the strong, short-distance part of the nucleon-nucleon interaction. These strong interactions lead to hard collisions between nucleons, generating pairs of highly-energetic nucleons referred to as shor...

When protons and neutrons (nucleons) are bound into atomic nuclei, they are close enough to feel significant attraction, or repulsion, from the strong, short-distance part of the nucleon–nucleon interaction. These strong interactions lead to hard collisions between nucleons, generating pairs of highly energetic nucleons referred to as short-range c...

We report high-precision measurements of the deeply virtual Compton scattering (DVCS) cross section at high values of the Bjorken variable x_{B}. DVCS is sensitive to the generalized parton distributions of the nucleon, which provide a three-dimensional description of its internal constituents. Using the exact analytic expression of the DVCS cross...

The ratio of the nucleon F_{2} structure functions, F_{2}^{n}/F_{2}^{p}, is determined by the MARATHON experiment from measurements of deep inelastic scattering of electrons from ^{3}H and ^{3}He nuclei. The experiment was performed in the Hall A Facility of Jefferson Lab using two high-resolution spectrometers for electron detection, and a cryogen...

We present a search for axionlike particles, a, produced in photon-proton collisions at a center-of-mass energy of approximately 4 GeV, focusing on the scenario where the a-gluon coupling is dominant. The search uses a → γγ and a → π þ π − π 0 decays, and a data sample corresponding to an integrated luminosity of 168 pb −1 collected with the GlueX...

We report new precision measurements of the elastic electron-proton scattering cross section for momentum transfer squared (Q^2) up to 15.75~GeV. These data allow for improved extraction of the proton magnetic form factor at high Q^2 and nearly double the Q^2range of direct longitudinal/transverse separated cross sections. A comparison of our resul...

We report on the measurement of spin density matrix elements of the Λ(1520) in the photoproduction reaction γp→Λ(1520)K+, via its subsequent decay to K−p. The measurement was performed as part of the GlueX experimental program in Hall D at Jefferson Laboratory using a linearly polarized photon beam with Eγ=8.2GeV–8.8GeV. These are the first such me...

We report high-precision measurements of the Deeply Virtual Compton Scattering (DVCS) cross section at high values of the Bjorken variable $x_B$. DVCS is sensitive to the Generalized Parton Distributions of the nucleon, which provide a three-dimensional description of its internal constituents. Using the exact analytic expression of the DVCS cross...

We report measurements of the exclusive neutral pion electroproduction cross section off protons at large values of xB (0.36, 0.48, and 0.60) and Q2 (3.1 to 8.4 GeV2) obtained from Jefferson Lab Hall A experiment E12-06-014. The corresponding structure functions dσT/dt+εdσL/dt, dσTT/dt, dσLT/dt, and dσLT′/dt are extracted as a function of the proto...

We present a search for axion-like particles, $a$, produced in photon-proton collisions at a center-of-mass energy of approximately 4 GeV, focusing on the scenario where the $a$-gluon coupling is dominant. The search uses $a\to\gamma\gamma$ and $a\to\pi^+\pi^-\pi^0$ decays, and a data sample corresponding to an integrated luminosity of 168 pb$^{-1}...

In our quest for investigating the nature of dark matter from the way its constituents interact with ordinary matter, we propose an experiment using a \pbo ~calorimeter to search for or set new limits on the production rate of i) hidden sector dark matter mediator in the $3 - 60$ MeV mass range via their $e^+e^-$ decay (or $\gamma\gamma$ decay with...

Positron beams, both polarized and unpolarized, are identified as important ingredients for the experimental programs at the next generation of lepton accelerators. In the context of the hadronic physics program at Jefferson Lab (JLab), positron beams are complementary, even essential, tools for a precise understanding of the electromagnetic struct...

The ratio of the nucleon $F_2$ structure functions, $F_2^n/F_2^p$, is determined by the MARATHON experiment from measurements of deep inelastic scattering of electrons from $^3$H and $^3$He nuclei. The experiment was performed in the Hall A Facility of Jefferson Lab and used two high resolution spectrometers for electron detection, and a cryogenic...

We report new precision measurements of the elastic electron-proton scattering cross section for momentum transfer squared (Q$^2$) up to 15.75~\gevsq. These data allow for improved extraction of the proton magnetic form factor at high Q$^2$ and nearly double the Q$^2$ range of direct longitudinal/transverse separated cross sections. A comparison of...

The physics motivation, detector design, triggers, calibration, alignment, simulation, and overall performance of the very forward CASTOR calorimeter of the CMS experiment are reviewed. The CASTOR Cherenkov sampling calorimeter is located very close to the LHC beam line, at a radial distance of about 1 cm from the beam pipe, and at 14.4 m from the...

We report the first measurement of the (e,e′p) three-body breakup reaction cross sections in helium-3 (He3) and tritium (H3) at large momentum transfer [⟨Q2⟩≈1.9 (GeV/c)2] and xB>1 kinematics, where the cross section should be sensitive to quasielastic (QE) scattering from single nucleons. The data cover missing momenta 40≤pmiss≤500 MeV/c that, in...

We report the first measurement of the (e,e'p) three-body breakup reaction cross sections in Helium-3 ($^3$He) and Tritium ($^3$H) at large momentum transfer ($<Q^2> ~ 1.9$ (GeV/c)$^2$) and $x_B > 1$ kinematics, covering a missing momentum range of $40 \leq p_{miss} \leq 500$ MeV/c. The measured cross sections are compared with different plane-wave...

We report the first measurement of the (e,e′p) reaction cross-section ratios for Helium-3 (He3), Tritium (H3), and Deuterium (d). The measurement covered a missing momentum range of 40≤pmiss≤550MeV/c, at large momentum transfer (〈Q2〉≈1.9 (GeV/c)2) and xB>1, which minimized contributions from non quasi-elastic (QE) reaction mechanisms. The data is c...

We report the first measurement of the $(e,e'p)$ reaction cross-section ratio for Helium-3 ($^3$He) relative to Tritium ($^3$H). The measurement covered a missing momentum range of $40 \le p_{miss} \le 550$ MeV/$c$, at large momentum transfer ($\langle Q^2 \rangle \approx 1.9$ (GeV/$c$)$^2$) and $x_B>1$, which minimized contributions from non quasi...

During 2015, the Relativistic Heavy Ion Collider (RHIC) provided collisions of transversely polarized protons with Au and Al nuclei for the first time, enabling the exploration of transverse-single-spin asymmetries with heavy nuclei. Large single-spin asymmetries in very forward neutron production have been previously observed in transversely polar...

Measurements of the associated production of a \(\mathrm{Z}\) boson with at least one jet originating from a b quark in proton–proton collisions at \(\sqrt{s} = 8\,\text {TeV} \) are presented. Differential cross sections are measured with data collected by the CMS experiment corresponding to an integrated luminosity of 19.8\(\,\text {fb}^{-1}\). \...

A search is presented for decays beyond the standard model of the 125 GeV Higgs bosons to a pair of light bosons, based on models with extended scalar sectors. Light boson masses between 5 and 62.5 GeV are probed in final states containing four τ leptons, two muons and two b quarks, or two muons and two τ leptons. The results are from data in proto...

Provided here are the results of calculations of tagging jet identification in the process of Higgs boson production via the mechanism of coalescence of vector bosons with subsequent decay into τ-leptons (VBF H→τ⁻τ⁺) for different transverse segmentations against the parts of modernized hadronic calorimeter of Compact Muonic Solenoid in the Large H...

Results are reported from a search for physics beyond the standard model in final states with at least three charged leptons, in any combination of electrons or muons. The data sample corresponds to an integrated luminosity of 2.3 fb−1 of proton–proton collisions at √s = 13 TeV, recorded by the CMS experiment at the LHC in 2015. Two jets are requir...

A search for heavy narrow resonances decaying into four-lepton final states has been performed using proton–proton collision data at s=8TeV collected by the CMS experiment, corresponding to an integrated luminosity of 19.7fb−1. No excess of events over the standard model background expectation is observed. Upper limits for a benchmark model on the...

Results are reported from a search for physics beyond the standard model in final states with at least three charged leptons, in any combination of electrons or muons. The data sample corresponds to an integrated luminosity of 2.3\(\,\text {fb}^{-1}\) of proton–proton collisions at \(\sqrt{s} =13\)\(\,\text {TeV}\), recorded by the CMS experiment a...

We present measurements of the elliptic flow, $v_2$, as a function of transverse momentum ($p_T$), pseudorapidity ($\eta$), and centrality in $d$$+$Au collisions at $\sqrt{s_{_{NN}}}=$200, 62.4, 39, and 19.6 GeV. The beam-energy scan of $d$$+$Au collisions provides a testing ground for the onset of flow signatures in small collision systems. We mea...

The differential cross sections for inclusive production of B+ hadrons are measured as a function of the B+ transverse momentum pTB and rapidity yB in pp collisions at a centre-of-mass energy of 13 TeV, using data collected by the CMS experiment that correspond to an integrated luminosity of 48.1 pb−1. The measurement uses the exclusive decay chann...

A search for single production of vector-like top quark partners (T) decaying into a Higgs boson and a top quark is performed using data from pp collisions at a centre-of-mass energy of 13 TeV collected by the CMS experiment at the CERN LHC, corresponding to an integrated luminosity of 2.3 fb−1. The top quark decay includes an electron or a muon wh...

A search for single production of vector-like top quark partners (T) decaying into a Higgs boson and a top quark is performed using data from pp collisions at a centre-of-mass energy of 13 TeV collected by the CMS experiment at the CERN LHC, corresponding to an integrated luminosity of 2.3 fb⁻¹. The top quark decay includes an electron or a muon wh...

Two-particle correlations in pPb collisions at a nucleon-nucleon center-of-mass energy of 5.02TeV are studied as a function of the pseudorapidity separation (Δη) of the particle pair at small relative azimuthal angle (|Δϕ|<π/3). The correlations are decomposed into a jet component that dominates the short-range correlations (|Δη|<1), and a componen...

A search is presented for supersymmetry in all-hadronic events with missing transverse momentum and tagged top quarks. The data sample was collected with the CMS detector at the LHC and corresponds to an integrated luminosity of 2.3 fb−1 of proton-proton collisions at a center-of-mass energy of 13 TeV. Search regions are defined using the propertie...

Inclusive jet spectra from pp and PbPb collisions at a nucleon-nucleon center-of-mass energy of 2.76TeV, collected with the CMS detector at the CERN Large Hadron Collider, are presented. Jets are reconstructed with three different distance parameters (R=0.2, 0.3, and 0.4) for transverse momentum (pT) greater than 70GeV/c and pseudorapidity |η|<2. N...

A measurement is presented of the cross section for the electroweak production of a Z boson and a photon in association with two jets in proton–proton collisions at √ s = 8 TeV. The Z bosons are identified through their decays to electron or muon pairs. The measurement is based on data collected with the CMS detector corresponding to an integrated...

A search is presented for W′ bosons in events with an electron or muon and large missing transverse momentum, using proton–proton collision data at s=13 TeV collected with the CMS detector in 2015 and corresponding to an integrated luminosity of 2.3 fb⁻¹. No evidence of an excess of events relative to the standard model expectations is observed. Fo...

The cross section for coherent photoproduction accompanied by at least one neutron on one side of the interaction point and no neutron activity on the other side, , is measured with the CMS experiment in ultra-peripheral PbPb collisions at . The analysis is based on a data sample corresponding to an integrated luminosity of 159 , collected during t...

A method for experimental investigation of the effect of X-ray focusing inside a single crystal subject to temperature gradient is proposed. The definition of diffracted X-ray focusing inside the crystal is shown to increase depending on the value of temperature gradient.

A measurement of electroweak-induced production of Wγ and two jets is performed, where the W boson decays leptonically. The data used in the analysis correspond to an integrated luminosity of 19.7 fb−1 collected by the CMS experiment in √ s = 8 TeV proton-proton collisions produced at the LHC. Candidate events are selected with exactly one muon or...

The results of a search for new physics in final states with photons and missing transverse energy are reported. The study is based on a sample of proton–proton collisions collected at a center-ofmass energy of 13 TeV with the CMS detector in 2015, corresponding to an integrated luminosity of 2.3 fb−1. Final states with two photons and significant...

A search for narrow resonances in dielectron and dimuon invariant mass spectra has been performed using data obtained from proton–proton collisions at s=13TeV collected with the CMS detector. The integrated luminosity for the dielectron sample is 2.7 fb−1 and for the dimuon sample 2.9 fb−1. The sensitivity of the search is increased by combining th...

A search for heavy resonances decaying to a Higgs boson and a vector boson is presented. The analysis is performed using data samples collected in 2015 by the CMS experiment at the LHC in proton–proton collisions at a center-of-mass energy of 13 TeV, corresponding to integrated luminosities of 2.2–2.5 fb−1. The search is performed in channels in wh...

A search for new phenomena is performed in final states containing one or more jets and an imbalance in transverse momentum in pp collisions at a centre-of-mass energy of 13 TeVTeV . The analysed data sample, recorded with the CMS detector at the CERN LHC, corresponds to an integrated luminosity of 2.3 fb−1fb−1 . Several kinematic variables are emp...

Pair production of Y(1S) mesons is observed at the LHC in proton-proton collisions at s√=8s=8 TeV by the CMS experiment in a data sample corresponding to an integrated luminosity of 20.7 fb−1. Both Y(1S) candidates are fully reconstructed via their decays to μ+μ−. The fiducial acceptance region is defined by an absolute Y(1S) rapidity smaller than...

Differential and double-differential cross sections for the production of top quark pairs in proton-proton collisions at 13 TeV are measured as a function of jet multiplicity and of kinematic variables of the top quarks and the top quark-antiquark system. This analysis is based on data collected by the CMS experiment at the LHC corresponding to an...

A measurement is presented of the cross section for the electroweak production of a Z boson and a photon in association with two jets in proton-proton collisions at s=8TeV. The Z bosons are identified through their decays to electron or muon pairs. The measurement is based on data collected with the CMS detector corresponding to an integrated lumin...

Pair production of Y(1S) mesons is observed at the LHC in proton-proton collisions at \( \sqrt{s}=8 \) TeV by the CMS experiment in a data sample corresponding to an integrated luminosity of 20.7 fb−1. Both Y(1S) candidates are fully reconstructed via their decays to μ+μ−. The fiducial acceptance region is defined by an absolute Y(1S) rapidity smal...

The differential cross sections for inclusive production of B+ hadrons are measured as a function of the B+ transverse momentum pTB and rapidity yB in pp collisions at a centre-of-mass energy of 13 TeV, using data collected by the CMS experiment that correspond to an integrated luminosity of 48.1 pb⁻¹. The measurement uses the exclusive decay chann...

An inclusive search is performed for supersymmetry in final states containing jets and an apparent imbalance in transverse momentum, p^→miss_T, due to the production of unobserved weakly interacting particles in pp collisions at a centre-of-mass energy of 8TeV. The data, recorded with the CMS detector at the CERN LHC, correspond to an integrated lu...

An inclusive search is performed for supersymmetry in final states containing jets and an apparent imbalance in transverse momentum, p→Tmiss, due to the production of unobserved weakly interacting particles in pp collisions at a centre-of-mass energy of 8 TeV. The data, recorded with the CMS detector at the CERN LHC, correspond to an integrated lum...

A search for the resonant production of high-mass photon pairs is presented. The search focuses on spin-0 and spin-2 resonances with masses between 0.5 and 4.5 TeV, and with widths, relative to the mass, between 1.4 × 10−4 and 5.6 × 10−2. The data sample corresponds to an integrated luminosity of 12.9 fb−1 of proton–proton collisions collected with...

The spectra of charged particles produced within the pseudorapidity window |η| < 1 at √ sNN = 5.02 TeV are measured using 404 µb −1 of PbPb and 27.4 pb−1 of pp data collected by the CMS detector at the LHC in 2015. The spectra are presented over the transverse momentum ranges spanning 0.5 < pT < 400 GeV in pp and 0.7 < pT < 400 GeV in PbPb collisio...

The spectra of charged particles produced within the pseudorapidity window |η| < 1 at \( \sqrt{s_{\mathrm{N}\;\mathrm{N}}}=5.02 \) TeV are measured using 404 μb−1 of PbPb and 27.4 pb−1 of pp data collected by the CMS detector at the LHC in 2015. The spectra are presented over the transverse momentum ranges spanning 0.5 < pT< 400 GeV in pp and 0.7 <...

Cross sections for the production of a Z boson in association with jets in proton-proton collisions at a centre-of-mass energy of \( \sqrt{s}=8 \) TeV are measured using a data sample collected by the CMS experiment at the LHC corresponding to 19.6 fb−1. Differential cross sections are presented as functions of up to three observables that describe...

Results are presented from a search for the electroweak production of supersymmetric particles in pp collisions in final states with two τ leptons. The data sample corresponds to an integrated luminosity between 18.1 fb−1 and 19.6 fb−1 depending on the final state of τ lepton decays, at \( \sqrt{s}=8 \) TeV, collected by the CMS experiment at the L...

The WZ production cross section is measured by the CMS experiment at the CERN LHC in proton–proton collision data samples corresponding to integrated luminosities of 4.9\(\,\text{fb}^{-1}\) collected at \(\sqrt{s} = 7\,\text{TeV} \), and 19.6\(\,\text{fb}^{-1}\) at \(\sqrt{s} = 8\,\text{TeV} \). The measurements are performed using the fully-lepton...

The production yields of ϒ(1S), ϒ(2S), and ϒ(3S) quarkonium states are measured through their decays into muon pairs in the CMS detector, in PbPb and pp collisions at the centre-of-mass energy per nucleon pair of 2.76TeV. The data correspond to integrated luminosities of 166μb−1and 5.4pb−1for PbPb and pp collisions, respectively. Differential produ...

The invariance of the standard model (SM) under the CPT transformation predicts equality of particle and antiparticle masses. This prediction is tested by measuring the mass difference between the top quark and antiquark (Δmt=mt−mt‾) that are produced in pp collisions at a center-of-mass energy of 8 TeV, using events with a muon or an electron and...

The nuclear modification factor RAA and the azimuthal anisotropy coefficient v2 of prompt and nonprompt (i.e. those from decays of b hadrons) J/ψ mesons, measured from PbPb and pp collisions at √sNN = 2.76 TeV at the LHC, are reported. The results are presented in several event centrality intervals and several kinematic regions, for transverse mome...

A measurement of the double-differential inclusive jet cross section as a function of the jet transverse momentum pT and the absolute jet rapidity |y| is presented. Data from LHC proton-proton collisions at √ s = 8 TeV, corresponding to an integrated luminosity of 19.7 fb−1 , have been collected with the CMS detector. Jets are reconstructed using t...

Charge-dependent azimuthal particle correlations with respect to the second-order event plane in p−Pb and PbPb collisions at a nucleon-nucleon center-of-mass energy of 5.02 TeV have been studied with the CMS experiment at the LHC. The measurement is performed with a three-particle correlation technique, using two particles with the same or opposite...

The cross section of top quark-antiquark pair production in proton–proton collisions at √s = 13 TeV is measured by the CMS experiment at the LHC, using data corresponding to an integrated luminosity of 2.2 fb^(−1) . The measurement is performed by analyzing events in which the final state includes one electron, one muon, and two or more jets, at le...

A search for new particles has been conducted using events with two high transverse momentum (pT) τ leptons that decay hadronically, at least two high-pT jets, and missing transverse energy from the τ lepton decays. The analysis is performed using data from proton-proton collisions, collected by the CMS experiment in 2015 at √ s = 13 TeV, correspon...

Differential cross sections for a W boson produced in association with jets are measured in a data sample of proton-proton collisions at a center-of-mass energy of 8 TeV recorded with the CMS detector and corresponding to an integrated luminosity of 19.6 fb^(−1). The W bosons are identified through their decay mode W → μν. The cross sections are re...

Differential cross sections for a W boson produced in association with jets are measured in a data sample of proton-proton collisions at a center-of-mass energy of 8 TeV recorded with the CMS detector and corresponding to an integrated luminosity of 19.6 fb−1. The W bosons are identified through their decay mode W → μν. The cross sections are repor...