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Popov, A.

Publications and source records attributed to Popov, A..

101 records · Page 6
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Beam test performance of prototype silicon detectors for the Outer Tracker for the Phase-2 Upgrade of CMS

A new CMS tracker detector will be installed for operation at the High Luminosity LHC (HL-LHC). This detector comprises modules with two closely spaced parallel sensor plates and front-end ASICs capable of transmitting tracking information to the CMS Level-1 (L1) trigger at the 40 MHz beam crossing rate. The inclusion of tracking information in the L1 trigger decision will be essential for selecting events of interest efficiently at the HL-LHC. The CMS Binary Chip (CBC)has been designed to read out and correlate hits from pairs of tracker sensors, forming so called track stubs. For the first time, a prototype irradiated module and a full-sized module, both equipped with the version 2 of the CBC, have been operated in test beam facilities. The efficiency of the stub finding logic of the modules for various angles of incidence has been studied. The ability of the modules to reject tracks with transverse momentum less than 2 GeV has been demonstrated. For modules built with irradiated sensors, no significant drop in the stub finding performance has been observed. Results from the beam tests are described in this paper.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2020

Search for dark matter particles produced in association with a Higgs boson in proton-proton collisions at $\sqrt{\mathrm{s}}$ = 13 TeV

A search for dark matter (DM) particles is performed using events with a Higgs boson candidate and large missing transverse momentum. The analysis is based on proton-proton collision data at a center-of-mass energy of 13 TeV collected by the CMS experiment at the LHC in 2016, corresponding to an integrated luminosity of 35.9 fb$^{-1}$. The search is performed in five Higgs boson decay channels: h$ \to \mathrm{b\bar{b}}$, $\gamma\gamma$, $\tau^{+}\tau^{-}$, W$^{+}$W$^{-}$, and ZZ and the results from the individual channels are combined to maximize the sensitivity of the analysis. No significant excess over the expected standard model background is observed in any of the five channels or in their combination. Limits are set on DM production in the context of two simplified models. The results are also interpreted in terms of a spin-independent DM-nucleon scattering cross section and compared to those from direct-detection DM experiments. This is the first search for DM particles produced in association with a Higgs boson decaying to a pair of W or Z bosons, and the first statistical combination based on five Higgs boson decay channels.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

Search for a heavy Higgs boson decaying to a pair of W bosons in proton-proton collisions at s$$ \sqrt{s} $$ = 13 TeV

A search for a heavy Higgs boson in the mass range from 0.2 to 3.0 TeV, decaying to a pair of W bosons, is presented. The analysis is based on proton-proton collisions at $\sqrt{s} =$ 13 TeV recorded by the CMS experiment at the LHC in 2016, corresponding to an integrated luminosity of 35.9 fb$^{-1}$. The W boson pair decays are reconstructed in the 2$\ell$2$\nu$ and $\ell\nu$2q final states (with $\ell =$ e or $\mu$). Both gluon fusion and vector boson fusion production of the signal are considered. Interference effects between the signal and background are also taken into account. The observed data are consistent with the standard model (SM) expectation. Combined upper limits at 95% confidence level on the product of the cross section and branching fraction exclude a heavy Higgs boson with SM-like couplings and decays up to 1870 GeV. Exclusion limits are also set in the context of a number of two-Higgs-doublet model formulations, further reducing the allowed parameter space for SM extensions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

Measurement of top quark pair production in association with a Z boson in proton-proton collisions at s$$ \sqrt{\mathrm{s}} $$ = 13 TeV

A measurement of the inclusive cross section of top quark pair production in association with a Z boson using proton-proton collisions at a center-of-mass energy of 13 TeV at the LHC is performed. The data sample corresponds to an integrated luminosity of 77.5 fb$^{-1}$, collected by the CMS experiment during 2016 and 2017. The measurement is performed using final states containing three or four charged leptons (electrons or muons), and the Z boson is detected through its decay to an oppositely charged lepton pair. The production cross section is measured to be σ($ \mathrm{t}\overline{\mathrm{t}}\mathrm{Z} $) = 0.95 ± 0.05 (stat) ± 0.06 (syst) pb. For the first time, differential cross sections are measured as functions of the transverse momentum of the Z boson and the angular distribution of the negatively charged lepton from the Z boson decay. The most stringent direct limits to date on the anomalous couplings of the top quark to the Z boson are presented, including constraints on the Wilson coefficients in the framework of the standard model effective field theory.[graphic not available: see fulltext]

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

Search for direct pair production of supersymmetric partners to the $\tau$ lepton in proton–proton collisions at $\sqrt{s}=13\,\text {TeV} $

A search is presented for $\tau$ slepton pairs produced in proton-proton collisions at a center-of-mass energy of 13 TeV. The search is carried out in events containing two $\tau$ leptons in the final state, on the assumption that each $\tau$ slepton decays primarily to a $\tau$ lepton and a neutralino. Events are considered in which each $\tau$ lepton decays to one or more hadrons and a neutrino, or in which one of the $\tau$ leptons decays instead to an electron or a muon and two neutrinos. The data, collected with the CMS detector in 2016 and 2017, correspond to an integrated luminosity of 77.2 fb$^{-1}$. The observed data are consistent with the standard model background expectation. The results are used to set 95% confidence level upper limits on the cross section for $\tau$ slepton pair production in various models for $\tau$ slepton masses between 90 and 200 GeV and neutralino masses of 1, 10, and 20 GeV. In the case of purely left-handed $\tau$ slepton production and decay to a $\tau$ lepton and a neutralino with a mass of 1 GeV, the strongest limit is obtained for a $\tau$ slepton mass of 125 GeV at a factor of 1.14 larger than the theoretical cross section.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

A multi-dimensional search for new heavy resonances decaying to boosted $\text{W}$ $\text{W}$, $\text{W}$ $\text{Z}$, or $\text{Z}$ $\text{Z}$ boson pairs in the dijet final state at 13 $\text {Te}\text{V}$

A search in an all-jet final state for new massive resonances decaying to $\text{ W }{}{}\text{ W }{}{}$, $\text{ W }{}{}\text{ Z }{}{}$, or $\text{ Z }{}{}\text{ Z }{}{}$ boson pairs using a novel analysis method is presented. The analysis is performed on data corresponding to an integrated luminosity of 77.3 $\,\text {fb}^{-1}$ recorded with the CMS experiment at the LHC at a centre-of-mass energy of 13 $\text {Te}\text {V}$. The search is focussed on potential narrow-width resonances with masses above 1.2 $\text {Te}\text {V}$, where the decay products of each $\text{ W }{}{}$ or $\text{ Z }{}{}$ boson are expected to be collimated into a single, large-radius jet. The signal is extracted using a three-dimensional maximum likelihood fit of the two jet masses and the dijet invariant mass, yielding an improvement in sensitivity of up to 30% relative to previous search methods. No excess is observed above the estimated standard model background. In a heavy vector triplet model, spin-1 ${\text {Z}}^{\prime }$ and ${\text {W}}^{\prime }$ resonances with masses below 3.5 and 3.8 $\text {Te}\text {V}$, respectively, are excluded at 95% confidence level. In a bulk graviton model, upper limits on cross sections are set between 27 and 0.2 $\,\text {fb}$ for resonance masses between 1.2 and 5.2 $\text {Te}\text {V}$, respectively. The limits presented in this paper are the best to date in the dijet final state.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

Production of Λ c + baryons in proton-proton and lead-lead collisions at s NN = 5.02 TeV

The transverse momentum ( p T ) spectra of inclusively produced Λ c + baryons are measured via the exclusive decay channel Λ c + → p K – π + using the CMS detector at the LHC. Spectra are measured as a function of transverse momentum in proton-proton ( p p ) and lead-lead (PbPb) collisions at a nucleon-nucleon center-of-mass energy of 5.02 TeV. The measurement is performed within the Λ c + rapidity interval | y | < 1 in the p T range of 5–20 GeV/ c in p p and 10–20 GeV/ c in PbPb collisions. The observed yields of Λ c + for p T of 10–20 GeV/ c suggest a suppression in central PbPb collisions compared to p p collisions scaled by the number of nucleon-nucleon (NN) interactions. The Λ c + / D 0 production ratio in p p collisions is compared to theoretical models. In PbPb collisions, this ratio is consistent with the result from p p collisions in their common p T range.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

Search for production of four top quarks in final states with same-sign or multiple leptons in proton–proton collisions at $\sqrt{s}=13$ ${TeV}$

The standard model (SM) production of four top quarks ($\text {t} {}{\overline{\text {t}}} \text {t} {}{\overline{\text {t}}} $) in proton–proton collisions is studied by the CMS Collaboration. The data sample, collected during the 2016–2018 data taking of the LHC, corresponds to an integrated luminosity of 137$\,\text {fb}^{-1}$ at a center-of-mass energy of 13$\,\text {TeV}$. The events are required to contain two same-sign charged leptons (electrons or muons) or at least three leptons, and jets. The observed and expected significances for the $\text {t} {}{\overline{\text {t}}} \text {t} {}{\overline{\text {t}}} $ signal are respectively 2.6 and 2.7 standard deviations, and the $\text {t} {}{\overline{\text {t}}} \text {t} {}{\overline{\text {t}}} $ cross section is measured to be $12.6^{+5.8}_{-5.2}\,\text {fb} $. The results are used to constrain the Yukawa coupling of the top quark to the Higgs boson, $y_{\text {t}}$, yielding a limit of $|y_{\text {t}}/y_{\text {t}}^{\mathrm {SM}} | < 1.7$ at $95\%$ confidence level, where $y_{\text {t}}^{\mathrm {SM}}$ is the SM value of $y_{\text {t}}$. They are also used to constrain the oblique parameter of the Higgs boson in an effective field theory framework, $\hat{H}<0.12$. Limits are set on the production of a heavy scalar or pseudoscalar boson in Type-II two-Higgs-doublet and simplified dark matter models, with exclusion limits reaching 350–470$\,\text {GeV}$ and 350–550$\,\text {GeV}$ for scalar and pseudoscalar bosons, respectively. Upper bounds are also set on couplings of the top quark to new light particles.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS2006

The ALTCRISS Project On Board the International Space Station

The Altcriss project aims to perform a long term survey of the radiation environment on board the International Space Station. Measurements are being performed with active and passive devices in different locations and orientations of the Russian segment of the station. The goal is perform a detailed evaluation of the differences in particle fluence and nuclear composition due to different shielding material and attitude of the station. The Sileye-3/Alteino detector is used to identify nuclei up to Iron in the energy range above approximately equal to 60 MeV/n; a number of passive dosimeters (TLDs, CR39) are also placed in the same location of Sileye-3 detector. Polyethylene shielding is periodically interposed in front of the detectors to evaluate the effectiveness of shielding on the nuclear component of the cosmic radiation. The project was submitted to ESA in reply to the AO the Life and Physical Science of 2004 and was begun in December 2005. Dosimeters and data cards are rotated every six months: up to now three launches of dosimeters and data cards have been performed and have been returned with the end expedition 12 and 13.

Cucinotta, Francis A.↗