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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 415 records · Page 23
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DOE OSTI2017

Study of J / ψ Production in Jets

The production of $J/ψ$ mesons in jets is studied in the forward region of proton-proton collisions using data collected with the LHCb detector at a center-of-mass energy of 13 TeV. The fraction of the jet transverse momentum carried by the $J/ψ$ meson, $z$($J/ψ$)≡$p$ T ($J/ψ$)/$p$ T (jet), is measured using jets with $p$ T (jet) > 20 GeV in the pseudorapidity range 2.5 < $η$(jet) < 4.0. The observed $z$($J/ψ$) distribution for $J/ψ$ mesons produced in b-hadron decays is consistent with expectations. However, the results for prompt $J/ψ$ production do not agree with predictions based on fixed-order nonrelativistic QCD. This is the first measurement of the $p$ T fraction carried by prompt $J/ψ$ mesons in jets at any experiment.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Search for the Decays B s 0 → τ + τ - and B 0 → τ + τ -

A search for the rare decays $B^0_s$→$τ$ + $τ$ - and $B$ 0 →$τ$ + $τ$ - is performed using proton-proton collision data collected with the LHCb detector. The data sample corresponds to an integrated luminosity of 3 fb -1 collected in 2011 and 2012. The $τ$ leptons are reconstructed through the decay $τ$ - →$π$ - $π$ + $π$ - $ν$ $τ$ . Assuming no contribution from B 0 →$τ$ + $τ$ - decays, an upper limit is set on the branching fraction $B$($B^0_s$→$τ$ + $τ$ - ) < 6.8×10-3 at the 95% confidence level. If instead no contribution from $B^0_s$→$τ$ + $τ$ - decays is assumed, the limit is $B$($B$ 0 →$τ$ + $τ$ - ) < 2.1×10 -3 at the 95% confidence level. These results correspond to the first direct limit on $B$($B^0_s$→$τ$+$τ$-) and the world's best limit on $B$($B$ 0 →$τ$ + $τ$ - ).

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Measurement of the C P Violation Parameter A Γ in D 0 → K + K - and D 0 → π + π - Decays

Asymmetries in the time-dependent rates of D 0 →K + K - and D 0 →$π$ + $π$ - decays are measured in a $pp$ collision data sample collected with the LHCb detector during LHC Run 1, corresponding to an integrated luminosity of 3 fb -1 . The asymmetries in effective decay widths between $D$ 0 and $\bar{D}$ 0 decays, sensitive to indirect $CP$ violation, are measured to be A $Γ$ (K + K - ) = (-0.30 ± 0.32 ± 0.10) × 10 -3 and A $Γ$ ($π$ + $π$ - ) = (0.46 ± 0.58 ± 0.12) × 10 -3 , where the first uncertainty is statistical and the second systematic. These measurements show no evidence for $CP$ violation and improve on the precision of the previous best measurements by nearly a factor of two.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

First Observation of a Baryonic B s 0 Decay

We report the first observation of a baryonic $B$$_s^0$ decay, $B$$_s^0$ → $p$$\bar{Λ}$$K$ - , using proton-proton collision data recorded by the LHCb experiment at center-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of 3.0 fb -1 . The branching fraction is measured to be $B$($B$$_s^0$ → $p$$\bar{Λ}$$K$ - ) + $B$($B$$_s^0$ → $\bar{p}$$Λ$$K$ + ) = [5.46±0.61±0.57±0.50($B$)±0.32($f$ s /$f$ d )]×10 -6 , where the first uncertainty is statistical and the second systematic, the third uncertainty accounts for the experimental uncertainty on the branching fraction of the $B$ 0 →$p$$\bar{Λ}$$π$ - decay used for normalization, and the fourth uncertainty relates to the knowledge of the ratio of $b$-quark hadronization probabilities $f$ s /$f$ d .

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Observation of the Decays Λ b 0 → χ c 1 p K - and Λ b 0 → χ c 2 p K -

The first observation of the decays Λ$^0_b$ → $χ$ c1 $pK$ - and Λ$^0_b$ → $χ$ c2 $pK$ - is reported using a data sample corresponding to an integrated luminosity of 3.0 fb -1 , collected by the LHCb experiment in $pp$ collisions at center-of-mass energies of 7 and 8 TeV. The following ratios of branching fractions are measured: $$\frac{\mathscr{B}(Λ^0_b→Χ_{c1}pK^-)}{\mathscr{B}(Λ^0_b→J/ψpK^-)}=0.242 ± 0.014 ± 0.013 ± 0.009$$ $$\frac{\mathscr{B}(Λ^0_b→Χ_{c2}pK^-)}{\mathscr{B}(Λ^0_b→J/ψpK^-)}= 0.248 ± 0.020 ± 0.014 ± 0.009$$ $$\frac{\mathscr{B}(Λ^0_b→Χ_{c2}pK^-)}{\mathscr{B}(Λ^0_b→Χ_{c1}pK^-)}= 1.02 ± 0.10 ± 0.02 ± 0.05$$ where the first uncertainty is statistical, the second systematic, and the third due to the uncertainty on the branching fractions of the $Χ_{c1}$ → $Jψγ$ and $Χ_{c2}$ → $Jψγ$ decays. Using both decay modes, the mass of the Λ$^0_b$ baryon is also measured to be $m$ Λ$^0_b$ = 5619.44 ± 0.28 ± 0.26 MeV/$c$ 2 , where the first and second uncertainties are statistical and systematic, respectively.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Observation of the Doubly Charmed Baryon Ξ c c + +

A highly significant structure is observed in the Λ$_c^+$$K$ - $π$ + $π$ + mass spectrum, where the Λ$_c^+$ baryon is reconstructed in the decay mode $pK$ - $π$ + . The structure is consistent with originating from a weakly decaying particle, identified as the doubly charmed baryon Ξ c c + + . The difference between the masses of the Ξ c c + + and Λ$_c^+$ states is measured to be 1334.94±0.72(stat.)±0.27(syst.) MeV/$c$ 2 , and the Ξ c c + + mass is then determined to be 3621.40±0.72(stat.)±0.27(syst.)±0.14(Λ$_c^+$) MeV/$c$ 2 , where the last uncertainty is due to the limited knowledge of the Λ$_c^+$ mass. The state is observed in a sample of proton-proton collision data collected by the LHCb experiment at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 1.7 fb -1 , and confirmed in an additional sample of data collected at 8 TeV.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Observation of D 0 Meson Decays to π + π – μ + μ – and K + K – μ + μ – Final States

The first observation of the D 0 → π + π - μ + μ - and D 0 → K + K - μ + μ - decays is reported using a sample of proton-proton collisions collected by LHCb at a center-of-mass energy of 8 TeV, and corresponding to 2 fb -1 of integrated luminosity. The corresponding branching fractions are measured using as normalization the decay D 0 → K - π + [μ + μ - ] ρ 0 /ω , where the two muons are consistent with coming from the decay of a ρ 0 or ω meson.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Search for Baryon-Number Violating Ξ b 0 Oscillations

A search for baryon-number violating Ξ 0 b oscillations is performed with a sample of pp collision data recorded by the LHCb experiment, corresponding to an integrated luminosity of 3 fb -1 . The baryon number at the moment of production is identified by requiring that the Ξ 0 b come from the decay of a resonance Ξ* b - → Ξ 0 b π - or Ξ' b - → Ξ 0 b π - , and the baryon number at the moment of decay is identified from the final state using the decays Ξ 0 b → Ξ + c π - , Ξ + c → pK - π + . No evidence of baryon-number violation is found, and an upper limit at the 95% confidence level is set on the oscillation rate of ω < 0.08 ps -1 , where ω is the associated angular frequency.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

First Observation of the Rare Purely Baryonic Decay B 0 → p p ¯

The first observation of the decay of a B 0 meson to a purely baryonic final state, B 0 → p p ¯ , is reported. The proton-proton collision data sample used was collected with the LHCb experiment at center-of-mass energies of 7 and 8 TeV and corresponds to an integrated luminosity of 3.0 fb - 1 . The branching fraction is determined to be B ( B 0 → p p ¯ ) = ( 1.25 ± 0.27 ± 0.18 ) × 10 - 8 , where the first uncertainty is statistical and the second systematic. The decay mode B 0 → p p ¯ is the rarest decay of the B 0 meson observed to date. The decay B s 0 → p p ¯ is also investigated. No signal is seen and the upper limit B ( B s 0 → p p ¯ ) < 1.5 × 10 - 8 at 90% confidence level is set on the branching fraction.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Search for Dark Photons Produced in 13 TeV p p Collisions

Searches are performed for both promptlike and long-lived dark photons, A ', produced in proton-proton collisions at a center-of-mass energy of 13 TeV, using A ' → μ + μ - decays and a data sample corresponding to an integrated luminosity of 1.6 fb -1 collected with the LHCb detector. The promptlike A ' search covers the mass range from near the dimuon threshold up to 70 GeV, while the long-lived A; search is restricted to the low-mass region 214 < m ( A ') < 350 MeV. No evidence for a signal is found, and 90% confidence level exclusion limits are placed on the γ– A ' kinetic-mixing strength. The constraints placed on prompt like dark photons are the most stringent to date for the mass range 10.6 < m ( A ') < 70 GeV, and are comparable to the best existing limits for m ( A ') < 0.5 GeV. The search for long-lived dark photons is the first to achieve sensitivity using a displaced-vertex signature.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Measurement of the Ratio of Branching Fractions B ( B c + → J / ψ τ + ν τ ) / B ( B c + → J / ψ μ + ν μ )

A measurement is reported of the ratio of branching fractions R( J /ψ) = B( B + c → J /ψτ + ν τ )/B( B + c → J /ψμ + ν μ ), where the τ + lepton is identified in the decay mode τ + → μ + ν μ ¯ν τ . This analysis uses a sample of proton-proton collision data corresponding to 3.0 fb –1 of integrated luminosity recorded with the LHCb experiment at center-of-mass energies of 7 and 8 TeV. A signal is found for the decay B + c → J /ψτ + ν τ at a significance of 3 standard deviations corrected for systematic uncertainty, and the ratio of the branching fractions is measured to be R( J /ψ) = 0.71 ± 0.17 (stat) ± 0.18 (syst). This result lies within 2 standard deviations above the range of central values currently predicted by the standard model.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Measurement of the Ratio of the B 0 → D * – τ + ν τ and B 0 → D * – μ + ν μ Branching Fractions Using Three-Prong τ -Lepton Decays

The ratio of branching fractions R( D * – ) ≡ B( B 0 → D * – τ + ν τ )/B( B 0 → D * – μ + ν μ ) is measured using a data sample of proton-proton collisions collected with the LHCb detector at center-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of 3 fb –1 . For the first time, R( D * – ) is determined using the τ-lepton decays with three charged pions in the final state. The B 0 → D * – τ + ν τ yield is normalized to that of the B 0 → D * – π + π – π + mode, providing a measurement of B( B 0 → D * – τ + ν τ )/B( B 0 → D * – π + π – π + ) = 1.97 ± 0.13 ± 0.18, where the first uncertainty is statistical and the second systematic. The value of B( B 0 → D * – τ + ν τ )=(1.42 ± 0.094 ± 0.129 ± 0.054)% is obtained, where the third uncertainty is due to the limited knowledge of the branching fraction of the normalization mode. Using the well-measured branching fraction of the B 0 → D * – μ + ν μ decay, a value of R( D * – ) = 0.291 ± 0.019 ± 0.026 ± 0.013 is established, where the third uncertainty is due to the limited knowledge of the branching fractions of the normalization and B 0 → D * – μ + ν μ modes. This measurement is in agreement with the standard model prediction and with previous results.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2019

First Measurement of Near-Threshold J / ψ Exclusive Photoproduction off the Proton

We report on the measurement of the $\gamma p \rightarrow J/\psi p$ cross section from $E_\gamma = 11.8$ GeV down to the threshold at $8.2$ GeV using a tagged photon beam with the GlueX experiment. We find the total cross section falls toward the threshold less steeply than expected from two-gluon exchange models. The differential cross section $d\sigma /dt$ has an exponential slope of $1.67 \pm 0.39$ GeV$^{-2}$ at $10.7$ GeV average energy. The LHCb pentaquark candidates $P_c^+$ can be produced in the $s$-channel of this reaction. We see no evidence for them and set model-dependent upper limits on their branching fractions $\mathcal{B}(P_c^+ \rightarrow J/\psi p)$ and cross sections $\sigma(\gamma p \to P_c^+)\times\mathcal{B}(P_c^+ \to J/\psi p) $.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

Model-Independent Study of Structure in B + → D + D - K + Decays

The only anticipated resonant contributions to B + → D + D - K + decays are charmonium states in the D + D - channel. A model-independent analysis, using LHCb proton-proton collision data taken at center of-mass energies of $\sqrt{s}$ = 7, 8, and 13 TeV, corresponding to a total integrated luminosity of 9 fb -1 , is carried out to test this hypothesis. The description of the data assuming that resonances only manifest in decays to the D + D - pair is shown to be incomplete. This constitutes evidence for a new contribution to the decay, potentially one or more new charm-strange resonances in the D + K - channel with masses around 2.9 GeV/c 2

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Analysis of Neutral B -Meson Decays into Two Muons

Branching fraction and effective lifetime measurements of the rare decay B s 0 → μ + μ - and searches for the decays B 0 → μ + μ - and B s 0 → μ + μ - γ are reported using proton-proton collision data collected with the LHCb detector at center-of-mass energies of 7, 8, and 13 TeV, corresponding to a luminosity of 9 fb - 1 . The branching fraction B ( B s 0 → μ + μ - ) = ( 3.0 9 - 0.43 - 0.11 + 0.46 + 0.15 ) × 10 - 9 and the effective lifetime τ ( B s 0 → μ + μ - ) = 2.07 ± 0.29 ± 0.03 ps are measured, where the first uncertainty is statistical and the second systematic. No significant signal for B 0 → μ + μ - and B s 0 → μ + μ - γ decays is found and upper limits B ( B 0 → μ + μ - ) < 2.6 × 10 - 10 and B ( B s 0 → μ + μ - γ ) < 2.0 × 10 - 9 at the 95% C.L. are determined, where the latter is limited to the range m μ μ > 4.9 GeV / c 2 . The results are in agreement with the standard model expectations.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Observation of a J / ψ Λ Resonance Consistent with a Strange Pentaquark Candidate in B - → J / ψ Λ p ¯ Decays

An amplitude analysis of Β - → J/ψ⁢Λ⁢$\overline{p}$ decays is performed using 4400 signal candidates selected on a data sample of pp collisions recorded at center-of-mass energies of 7, 8, and 13 TeV with the LHCb detector, corresponding to an integrated luminosity of 9 fb -1 . A narrow resonance in the J/ψ⁢Λ system, consistent with a pentaquark candidate with strangeness, is observed with high significance. The mass and the width of this new state are measured to be 4338.2±0.7±0.4 MeV and 7.0±1.2±1.3 MeV, where the first uncertainty is statistical and the second systematic. The spin is determined to be 1/2 and negative parity is preferred. Because of the small Q-value of the reaction, the most precise single measurement of the B- mass to date, 5279.44±0.05±0.07 MeV, is obtained.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

First Observation of a Doubly Charged Tetraquark and Its Neutral Partner

A combined amplitude analysis is performed for the decays $B^0$ → $\overline{D}$ 0 $D_s^+$$π^–$ and $B^+$ → $D^–$$D_s^+$$π^+$, which are related by isospin symmetry. The analysis is based on data collected by the LHCb detector in proton-proton collisions at center-of-mass energies of 7, 8, and 13 TeV. The full data sample corresponds to an integrated luminosity of 9 fb –1 . Two new resonant states with masses of 2.908 ± 0.011 ± 0.020 GeV and widths of 0.136 ± 0.023 ± 0.013 GeV are observed, which decay to $D_s^+$$π^+$ and $D_s^+$$π^–$ respectively. The former state indicates the first observation of a doubly charged open-charm tetraquark state with minimal quark content [c$\overline{s}$u$\overline{d}$], and the latter state is a neutral tetraquark composed of [c$\overline{s}$$\overline{u}$d] quarks. Both states are found to have spin-parity of 0 + , and their resonant parameters are consistent with each other, which suggests that they belong to an isospin triplet.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Nuclear Modification Factor of Neutral Pions in the Forward and Backward Regions in p - Pb Collisions

The nuclear modification factor of neutral pions is measured in proton-lead collisions collected at a center-of-mass energy per nucleon of 8.16 TeV with the LHCb detector. The π 0 production cross section is measured differentially in transverse momentum (p T ) for 1.5 < p Τ < 10.0 GeV and in center-of-mass pseudorapidity (η c.m. ) regions 2.5 < η c.m. < 3.5 (forward) and -4.0 < η c.m .< -3.0 (backward) defined relative to the proton beam direction. The forward measurement shows a sizable suppression of π 0 production, while the backward measurement shows the first evidence of π 0 enhancement in proton-lead collisions at the LHC. Together, these measurements provide precise constraints on models of nuclear structure and particle production in high-energy nuclear collisions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗