The LHCb Data Acquisition during LHC Run 1 Alessio, F; Brarda, L; Bonaccorsi, E ...
Journal of physics. Conference series,
01/2014, Letnik:
513, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The LHCb Data Acquisition system reads data from over 300 read-out boards and distributes them to more than 1500 event-filter servers. It uses a simple push-protocol over Gigabit Ethernet. After ...filtering, the data is consolidated into files for permanent storage using a SAN-based storage system. Since the beginning of data-taking many lessons have been learned and the reliability and robustness of the system has been greatly improved. We report on these changes and improvements, their motivation and how we intend to develop the system for Run 2. We also will report on how we try to optimise the usage of CPU resources during the running of the LHC ("deferred triggering") and the implications on the data acquisition.
Results are reported from an amplitude analysis of the B+ → D+D− K+ decay. The analysis is carried out using LHCb proton-proton collision data taken at √s = 7, 8, and 13 TeV, corresponding to a total ...integrated luminosity of 9 fb−1. In order to obtain a good description of the data, it is found to be necessary to include new spin-0 and spin-1 resonances in the D−K+ channel with masses around 2.9 GeV/c2, and a new spin-0 charmonium resonance in proximity to the spin-2 χc2(3930) state.
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 sqrts=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}.
An improved measurement of the decay $B^0_S$ → $μ^+μ^-$ and searches for the decays $B^0$ → $μ^+μ^+$ and $B^0_S$ → $μ^+μ^-γ$ are performed at the LHCb experiment using data collected in proton-proton ...collisions at $\sqrt{s}$ = 7, 8 and 13 TeV. corresponding to integrated luminosities of 1, 2 and 6 fb-1, respectively. The $B^0_S$ → $μ^+μ^-$ branching fraction and effective lifetime are measured to be $\mathscr{B}$($B^0_S$ → $μ^+μ^-$) = (3.09$^{(+0.46+0.15)}_{(-0.43-0.11)}$) x 10-9 and $τ(B^0_s →μ^+μ^-)$ = (2.07 ± 0.29 ± 0.03) ps, respectively, where the uncertainties include both statistical and systematic contributions. No significant signal for $B^0$ → $μ^+μ^-$ and $B^0_S$ → $μ^+μ^-γ$ decays is found and the upper limits $\mathscr{B}$($B^0$ → $μ^+μ^-$) < 2.6 x 10-10 and $B^0_S$ → $μ^+μ^-γ$ < 2.0 x 10-9 at 95% confidence level are determined, where the latter is limited to the range $m_{μμ}$ > 4.9 GeV/c2. Additionally, the ratio between the $B^0$ → $μ^+μ^-$ and $B^0_S$ → $μ^+μ^-$ branching fractions is measured to be $\mathscr{R}_{μ+μ-}$ < 0.095 at 95% confidence level. The results are in agreement with the Standard Model predictions.
A study of the lineshape of the χc1 ( 3872 ) state is made using a data sample corresponding to an integrated luminosity of 3 fb−1 collected in p p collisions at center-of-mass energies of 7 and ...8 TeV with the LHCb detector. Candidate χc1 ( 3872 ) and ψ ( 2S ) mesons from b -hadron decays are selected in the J / ψ π+ π− decay mode. Describing the lineshape with a Breit-Wigner function, the mass splitting between the χc1 ( 3872 ) and ψ ( 2S ) states, Δm, and the width of the χc1 ( 3872 ) state, ΓBW, are determined to be ..., where the first uncertainty is statistical and the second systematic. Using a Flatté-inspired model, the mode and full width at half maximum of the lineshape are determined to be ... . An investigation of the analytic structure of the Flatté amplitude reveals a pole structure, which is compatible with a quasibound D0 D*0 state but a quasivirtual state is still allowed at the level of 2 standard deviations. (ProQuest: ... denotes formulae omited.).
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^{-})=(3.09_{-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_{μμ}>4.9 GeV/c^{2}. The results are in agreement with the standard model expectations.
Observation of a new Ξb0 state Ackernley, T.; Alessio, F.; Amato, S. ...
Physical review. D,
01/2021, Letnik:
103, Številka:
1
Journal Article
Recenzirano
Using a proton-proton collision data sample collected by the LHCb experiment, corresponding to an integrated luminosity of 8.5 fb-1, the observation of a new excited $Ξ^{0}_{b}$ resonance decaying to ...the $Ξ^{-}_{b}$$π$+ final state is presented. The state, referred to as $Ξ_b$(6227)0, has a measured mass and natural width of $m$$(Ξ_b$(6227)0) = $6227.1^{+1.4}_{-1.5}$ ± 0.5 MeV and Γ($Ξ_b$(6227)0) = $18.6^{+5.0}_{-4.1}$ ± 1.4 MeV, where the uncertainties are statistical and systematic. The production rate of the $Ξ_b$(6227)0 state relative to that of the $Ξ^{-}_{b}$ baryon in the kinematic region 2 < $η$ < 5 and pT < 30 GeV is measured to be $\frac{f_{Ξ_b}(6227)^0}{f_{Ξ_b^-}}$ $\mathscr{B}$($Ξ_b$(6227)0 → $Ξ^-_b$$π^+$) = 0.045 ± 0.008 ± 0.004; where $\mathscr{B}$($Ξ_b$(6227)0 → $Ξ^-_b$$π^+$) is the branching fraction of the decay, and $f$$Ξ$$_{b}$$_{(6227)^0}$ and $f$$Ξ$$_{b}^-$ represent fragmentation fractions. Improved measurements of the mass and natural width of the previously observed $Ξ_b$$(6227)^-$ state, along with the mass of the $Ξ^{-}_{b}$ baryon, are also reported. Both measurements are significantly more precise than, and consistent with, previously reported values.
The fraction of $χ$c1 and $χ$c2 decays in the prompt $J/ψ$ yield, $F$χc→J/ψ = σχc→J/ψ/σJ/ψ, is measured by the LHCb detector in $p$ Pb collisions at $\sqrt{^sNN}$ = 8.16 $TeV$. The study covers the ...forward (1.5 < y* < 4.0) and backward (-5.0 < y* < - 2.5) rapidity regions, where y* is the $J/ψ$ rapidity in the nucleon-nucleon center-of-mass system. Forward and backward rapidity samples correspond to integrated luminosities of 13.6 ± 0.3 and 20.8 ± 0.5 nb-1, respectively. The result is presented as a function of the $J/ψ$ transverse momentum $p$T,J/ψ in the range 1 < $p$T,J/ψ < 20 $GeV$ /c. The $F$χc→J/ψ fraction at forward rapidity is compatible with the LHCb measurement performed in $pp$ collisions at $\sqrt{s}$ = 7 $TeV$, whereas the result at backward rapidity is $2.4σ$ larger than in the forward region for 1 < $p$T,J/ψ < 3 $GeV$ /c. The increase of $F$χc→J/ψ at low pT,J/ψ at backward rapidity is compatible with the suppression of the $ψ$ ($2S$) contribution to the prompt $J/ψ$ yield. The lack of in-medium dissociation of $χ$c states observed in this study sets an upper limit of 180 MeV on the free energy available in these $pPb$ collisions to dissociate or inhibit charmonium state formation.
The production rate of $Λ^{0}_{b}$ baryons relative to $B$0 mesons in $pp$ collisions at a center-of-mass energy $\sqrt{s}$ = $13$ $TeV$ is measured by the LHCb experiment. The ratio of $Λ^{0}_{b}$ ...to $B$0 production cross sections shows a significant dependence on both the transverse momentum and the measured charged-particle multiplicity. At low multiplicity, the ratio measured at LHCb is consistent with the value measured in e+e- collisions, and increases by a factor of ~ 2 with increasing multiplicity. At relatively low transverse momentum, the ratio of $Λ^{0}_{b}$ to $B$0 cross sections is higher than what is measured in e+e- collisions, but converges with the e+e- ratio as the momentum increases. These results imply that the evolution of heavy $b$ quarks into final-state hadrons is influenced by the density of the hadronic environment produced in the collision. Comparisons with several models and implications for the mechanisms enforcing quark confinement are discussed.
The production rate of $B^{0}_{s}$ mesons relative to $B^0$ mesons is measured by the LHCb experiment in $pp$ collisions at a center-of-mass energy $\sqrt{s}$ = 13 TeV over the forward rapidity ...interval 2 < $y$ < 4.5 as a function of the charged particle multiplicity measured in the event. Evidence at the 3.4$σ$ level is found for an increase of the ratio of $B^{0}_{s}$ to $B^0$ cross sections with multiplicity at transverse momenta below 6 GeV /$c$, with no significant multiplicity dependence at higher transverse momentum. Comparison with data from $e^+$ $e^–$ collisions implies that the density of the hadronic medium may affect the production rates of $B$ mesons. This is qualitatively consistent with the emergence of quark coalescence as an additional hadronization mechanism in high-multiplicity collisions.
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