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Bashir, S.

Publications and source records attributed to Bashir, S..

30 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Search for the radiative $Ξ_b^{-}$ → $Ξ^-γ$ decay

The first search for the rare radiative decay $Ξ_b^{-}$ → $Ξ^-γ$ is performed using data collected by the LHCb experiment in proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 5.4 fb -1 . $Ξ_b^{-}$ → $Ξ^-J/ψ$ channel is used as normalization. No $Ξ_b^{-}$ → $Ξ^-γ$ signal is found and an upper limit of $\mathcal{B}$( $Ξ_b^{-}$ → $Ξ^-γ$) < 1.3 x 10 -4 at 95% confidence level is obtained.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Study of $\mathrm{B}_{c}^{+}$ decays to charmonia and three light hadrons

Using proton-proton collision data, corresponding to an integrated luminosity of 9 fb -1 collected with the LHCb detector, seven decay modes of the $B^+_c$ meson into a $J/ψ$ or $ψ(2S)$ meson and three charged hadrons, kaons or pions, are studied. The decays $B^+_c$ → $(ψ(2S)$ →J/$ψπ^+π^-$)$π^+$, $B^+_c$→$ψ(2S)π^+π^-π^+, B^+_c$→ J/$ψK^+π^-π^+$ and $B^+_c$ → J/$ψK^+K^-K^+$ are observed for the first time, and evidence for the $B^+_c$ →$ψ(2S)K^+K^-π^+$, decay is found, where J/ψ and $(ψ(2S)$ mesons are reconstructed in their dimuon decay modes. The ratios of branching fractions between the different $B^+_c$ decays are reported as well as the fractions of the decays proceeding via intermediate resonances. The results largely support the factorisation approach used for a theoretical description of the studied decays.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Measurement of the W boson mass

The W boson mass is measured using proton-proton collision data at $\sqrt{s}$ = 13 TeV corresponding to an integrated luminosity of 1.7 fb -1 recorded during 2016 by the LHCb experiment. With a simultaneous fit of the muon $q/ρ_T$ distribution of a sample of W →$μv$ decays and the $\phi^*$ distribution of a sample of Z → $μμ$ decays the W boson mass is determined to be $m_w$ =80354±23 stat ±10 exp ±17 theory ±9 PDF MeV, where uncertainties correspond to contributions from statistical, experimental systematic, theoretical and parton distribution function sources. This is an average of results based on three recent global parton distribution function sets. The measurement agrees well with the prediction of the global electroweak fit and with previous measurements.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Updated search for $ {B}_c^{+} $ decays to two charm mesons

A data set corresponding to an integrated luminosity of 9 fb -1 of proton-proton collisions collected by the LHCb experiment has been analysed to search for B c + → D s &lowast; + — D &lowast; 0 decays. The decays are fully or partially reconstructed, where one or two missing neutral pions or photons from the decay of an excited charm meson are allowed. Upper limits for the branching fractions, normalised to B + decays to final states with similar topologies, are obtained for sixteen $ {B}_c^{+} $ decay modes. For the decay $ {B}_c^{+}\to {D}_s^{+}{\overline{D}}^0 $, an excess with a significance of 3.4 standard deviations is found.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Search for the doubly charmed baryon $ {\varXi}_{cc}^{+} $ in the $ {\varXi}_c^{+}{\pi}^{-}{\pi}^{+} $ final state

A search for the doubly charmed baryon $ {\varXi}_{cc}^{+} $ is performed in the $ {\varXi}_c^{+}{\pi}^{-}{\pi}^{+} $ invariant-mass spectrum, where the $ {\varXi}_c^{+} $ baryon is reconstructed in the pK - π + final state. The study uses proton-proton collision data collected with the LHCb detector at a centre- of-mass energy of 13 TeV, corresponding to a total integrated luminosity of 5.4 fb -1 . No significant signal is observed in the invariant-mass range of 3.4–3.8 GeV/ c 2 . Upper limits are set on the ratio of branching fractions multiplied by the production cross-section with respect to the $ {\varXi}_{cc}^{++} $ →( $ {\varXi}_c^{+} $ → pK - π + ) π + decay for different $ {\varXi}_{cc}^{+} $ mass and lifetime hypotheses in the rapidity range from 2.0 to 4.5 and the transverse momentum range from 2.5 to 25 GeV/ c . The results from this search are combined with a previously published search for the $ {\varXi}_{cc}^{+} $ → $ {\varLambda}_c^{+} $ K - π + decay mode, yielding a maximum local significance of 4.0 standard deviations around the mass of 3620 MeV/ c 2 , including systematic uncertainties. Taking into account the look-elsewhere effect in the 3.5–3.7 GeV/ c 2 mass window, the combined global significance is 2.9 standard deviations including systematic uncertainties.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Simultaneous determination of CKM angle γ and charm mixing parameters

A combination of measurements sensitive to the CP violation angle γ of the Cabibbo-Kobayashi-Maskawa unitarity triangle and to the charm mixing parameters that describe oscillations between D 0 and $ \overline{D} $ 0 mesons is performed. Results from the charm and beauty sectors, based on data collected with the LHCb detector at CERN’s Large Hadron Collider, are combined for the first time. This method provides an improvement on the precision of the charm mixing parameter y by a factor of two with respect to the current world average. The charm mixing parameters are determined to be $ x=\left({0.400}_{-0.053}^{+0.052}\right)\% $ and y = $ \left({0.630}_{-0.030}^{+0.033}\right)\% $. The angle γ is found to be γ = ($ 65.4_{-4.2}^{+3.8} $)° and is the most precise determination from a single experiment.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Measurement of $J/ψ$ production cross-sections in $pp$ collisions at $\sqrt{s}$ = 5 TeV

The production cross-sections of J/ψ mesons in proton-proton collisions at a centre-of-mass energy of $\sqrt{s} = 5 TeV are measured using a data sample corresponding to an integrated luminosity of 9.13 ± 0.18 pb -1 , collected by the LHCb experiment. The cross-sections are measured differentially as a function of transverse momentum, p T , and rapidity, y, and separately for J/ψ mesons produced promptly and from beauty hadron decays (nonprompt). With the assumption of unpolarised J/ψ mesons, the production cross-sections integrated over the kinematic range 0 < p T < 20 GeV/c and 2.0 < y < 4.5 are σ prompt J/Ψ = 8.154 ± 0.010 ± 0.283 μb, σnonprompt J/Ψ = 0.820 ± 0.003 ± 0.034 μb, where the first uncertainties are statistical and the second systematic. These cross-sections are compared with those at $\sqrt{s}$ = 8 TeV and 13 TeV, and are used to update the measurement of the nuclear modification factor in proton-lead collisions for J/ψ mesons at a centre-of-mass energy per nucleon pair of $\sqrt{s_{NN}}$ = 5 TeV. The results are compared with theoretical predictions.

quarkonium↗
DOE OSTI2021

Angular analysis of the rare decay $B_s^0$ → $\phi μ^+μ^-$

An angular analysis of the rare decay B$^0_s$ → $\phi μ^+μ^-$ is presented, using proton-proton collision data collected by the LHCb experiment at centre-of-mass energies of 7, 8 and 13 TeV, corresponding to an integrated luminosity of 8.4 fb -1 . The observables describing the angular distributions of the decay B$^0_s$ → $\phi μ^+μ^-$ are determined in regions of q 2 , the square of the dimuon invariant mass. The results are consistent with Standard Model predictions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Observation of a $ {\varLambda}_b^0 $ - $ {\overline{\varLambda}}_b^0 $ production asymmetry in proton-proton collisions at $ \sqrt{s} $ = 7 and 8 TeV

This article presents differential measurements of the asymmetry between $ {\varLambda}_b^0 $ - $ {\overline{\varLambda}}_b^0 $ baryon production rates in proton-proton collisions at centre-of-mass energies of $\sqrt{s}$ = 7 and 8 TeV collected with the LHCb experiment, corresponding to an integrated luminosity of 3 fb -1 . The ${\varLambda}_b^0 $ baryons are reconstructed through the inclusive semileptonic decay ${\varLambda}_b^0 $ → Λ+c μ - $\overline{ν}$ μX. The production asymmetry is measured both in intervals of rapidity in the range 2.15 < y < 4.10 and transverse momentum in 2 < p T < 27 GeV/c. The results are found to be incompatible with symmetric production with a significance of 5.8 standard deviations for both $\sqrt{s}$ = 7 and 8 TeV data, assuming no CP violation in the decay. There is evidence for a trend as a function of rapidity with a significance of 4 standard deviations. Comparisons to predictions from hadronisation models in PYTHIA and heavy-quark recombination are provided. This result constitutes the first observation of a particle-antiparticle asymmetry in b-hadron production at LHC energies.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS1984

The effect of microstructure, temperature, and hold-time on low-cycle fatigue of As HIP P/M Rene 95

The effects of microstructure, temperature, plastic strain range, and hold time on the low-cycle fatigue (LCF) life were studied for Rene 95, an important Ni base superalloy used in jet engine disks. It was shown that the life could be varied by approximately an order of magnitude at elevated temperatures by simple heat treatments. The life was largest for the microstructure that promoted the most homogeneous deformation mode. The results are explained using the concept of a synergistic interaction between the deformation mode and boundary oxidation.

Bashir, S.↗
NASA NTRS1983

Unique material requirements in the Space Shuttle Main Engines

Components operating in staged-combustion cycle liquid fuel rocket engines such as the Space Shuttle Main Engines (SSMEs) are subjected to severe temperature changes during start/stop transients, together with extremely high pressures, corrosive gases, high fluid velocities, demanding weight-control criteria, etc. Attention is given to the selection and application of metallic and nonmetallic materials for high temperature resistance, cryogenic properties, and hydrogen and oxygen compatibility. The materials in question include polyimides, Kel-F, Armalon, and Teflon among plastics, and gold and copper platings, weld-overlays and heat treatment modifications among metals and metallic processing techniques. The polymeric materials are oxygen-resistant, and the metallic ones hydrogen-resistant.

Fulton, D. L.↗