The upgraded CERN LHCb detector, due to start data taking in 2021, will have to reconstruct 4 TB/s of raw detector data in real time using commodity processors. This is one of the biggest real-time ...data processing challenges in any scientific domain. We present an intrinsically parallel reconstruction algorithm for the vertex detector of the LHCb experiment designed to optimally exploit multi-core general purpose architectures. We evaluate the algorithm on two high-end architectures from two different vendors and discuss in detail the impact of different SIMD Instruction Set Architecture extensions on the performance. We further compare the algorithm to current state-of-the-art scalar pattern recognition algorithms. We show a factor 2 speedup while achieving similar or better levels of physics performance.
We describe a fully GPU-based implementation of the first level trigger for the upgrade of the LHCb detector, due to start data taking in 2021. We demonstrate that our implementation, named Allen, ...can process the 40 Tbit/s data rate of the upgraded LHCb detector and perform a wide variety of pattern recognition tasks. These include finding the trajectories of charged particles, finding proton–proton collision points, identifying particles as hadrons or muons, and finding the displaced decay vertices of long-lived particles. We further demonstrate that Allen can be implemented in around 500 scientific or consumer GPU cards, that it is not I/O bound, and can be operated at the full LHC collision rate of 30 MHz. Allen is the first complete high-throughput GPU trigger proposed for a HEP experiment.
A narrow pentaquark state, Pc(4312)+, decaying to J/ψp, is discovered with a statistical significance of 7.3σ in a data sample of Λb0→J/ψpK− decays, which is an order of magnitude larger than that ...previously analyzed by the LHCb Collaboration. The Pc(4450)+ pentaquark structure formerly reported by LHCb is confirmed and observed to consist of two narrow overlapping peaks, Pc(4440)+ and Pc(4457)+, where the statistical significance of this two-peak interpretation is 5.4σ. The proximity of the Σc+D¯0 and Σc+D¯*0 thresholds to the observed narrow peaks suggests that they play an important role in the dynamics of these states.
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.
Observation of the Doubly Charmed Baryon Ξ++cc Alfonso Albero, Alejandro; Badalov, Alexey; Calvo Gómez, Míriam ...
Physical review letters,
09/2017, Letnik:
119, Številka:
11
Journal Article
Recenzirano
Odprti dostop
A highly significant structure is observed in the Λc+K-π+π+ mass spectrum, where the Λc+ baryon is reconstructed in the decay mode p K-π+. The structure is consistent with originating from a weakly ...decaying particle, identified as the doubly charmed baryon Ξcc ++. The difference between the masses of the Ξcc ++ and Λc+ states is measured to be 1334.94 ±0.72 (stat.) ±0.27 (syst. ) MeV /c2 , and the Ξcc ++ mass is then determined to be 3621.40 ±0.72 (stat.) ±0.27 (syst. ) ±0.14 (Λc+) MeV /c2 , where the last uncertainty is due to the limited knowledge of the Λc+ 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.
A test of lepton universality, performed by measuring the ratio of the branching fractions of the $B^0 → K^{*0}μ^+μ^-$ and $B^0$ → $K^{*0}e^+e^-$ decays, $R_{K^{*0}}$, is presented. The $K^{*0}$ ...meson is reconstructed in the final state $K^+π^-$, which is required to have an invariant mass within 100 MeV/c2 of the known $K^*$ (892)0 mass. The analysis is performed using proton-proton collision data, corresponding to an integrated luminosity of about 3 fb-1, collected by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. The ratio is measured in two regions of the dilepton invariant mass squared, q2, to be R K ∗ 0 = { 0.66 − + 0.07 0.11 ( s t a t ) ± 0.03 ( s y s t ) f o r 0.045 < q 2 < 1.1 G e V 2 / c 4 , 0.69 − + 0.07 0.11 ( s t a t ) ± 0.05 ( s y s t ) f o r 1.1 < q 2 < 6.0 G e V 2 / c 4 . The corresponding 95.4% confidence level intervals are 0.52, 0.89 and 0.53, 0.94. The results, which represent the most precise measurements of $R_{K^{*0}}$ to date, are compatible with the Standard Model expectations at the level of 2.1–2.3 and 2.4–2.5 standard deviations in the two q2 regions, respectively.
The ratio of branching fractions R(D*−)≡B(B0→D*−τ+ντ)/B(B0→D*−μ+νμ) 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. The τ lepton is reconstructed with three charged pions in the final state. A novel method is used that exploits the different vertex topologies of signal and backgrounds to isolate samples of semitauonic decays of b hadrons with high purity. Using the B0→D*−π+π−π+ decay as the normalization channel, the ratio B(B0→D*−τ+ντ)/B(B0→D*−π+π−π+) is measured to be 1.97±0.13±0.18, where the first uncertainty is statistical and the second systematic. An average of branching fraction measurements for the normalization channel is used to derive B(B0→D*−τ+ντ)=(1.42±0.094±0.129±0.054)%, where the third uncertainty is due to the limited knowledge of B(B0→D*−π+π−π+). A test of lepton flavor universality is performed using the well-measured branching fraction B(B0→D*−μ+νμ) to compute R(D*−)=0.291±0.019±0.026±0.013, where the third uncertainty originates from the uncertainties on B(B0→D*−π+π−π+) and B(B0→D*−μ+νμ). This measurement is in agreement with the Standard Model prediction and with previous measurements.
A search for the rare decays $B^0_s$→$μ$+$μ$- and B0→$μ$+$μ$- is performed at the LHCb experiment using data collected in pp collisions corresponding to a total integrated luminosity of 4.4 fb-1. An ...excess of $B^0_s$→$μ$+$μ$- decays is observed with a significance of 7.8 standard deviations, representing the first observation of this decay in a single experiment. The branching fraction is measured to be $B$($μ$+$μ$-)=(3.0 ± $0.6^{+0.3}_{-0.2}$) × 10-9, where the first uncertainty is statistical and the second systematic. The first measurement of the $B^0_s$→$μ$+$μ$- effective lifetime, τ($B^0_s$→($μ$+$μ$-) = 2.04 ± 0.44 ± 0.05 ps, is reported. No significant excess of B0→($μ$+$μ$- decays is found, and a 95% confidence level upper limit, $B$(B0→($μ$+$μ$-) < 3.4 × 10-10, is determined. All results are in agreement with the standard model expectations.
The $\Xi{^+_c}$$K^-$ mass spectrum is studied with a sample of $pp$ collision data corresponding to an integrated luminosity of 3.3 fb-1, collected by the LHCb experiment. The $\Xi{^+_c}$ is ...reconstructed in the decay mode $pK^-$$π^+$. Five new, narrow excited $Ω_c^0$ states are observed: the $Ω_c$(3000)$^0$, $Ω_c$(3050)$^0$, $Ω_c$(3066)$^0$, $Ω_c$(3090)$^0$, and $Ω_c$(3119)$^0$. Measurements of their masses and widths are reported.
The doubly charmed baryon decay Ξ + + c c → Ξ + c π + is observed for the first time, with a statistical significance of 5.9 σ , confirming a recent observation of the baryon in the Λ + c K − π + π + ...final state. The data sample used corresponds to an integrated luminosity of 1.7 fb − 1 , collected by the LHCb experiment in p p collisions at a center-of-mass energy of 13 TeV. The Ξ + + c c mass is measured to be 3620.6 ± 1.5 ( stat ) ± 0.4 ( syst ) ± 0.3 ( Ξ + c ) MeV / c 2 and is consistent with the previous result. The ratio of branching fractions between the decay modes is measured to be B ( Ξ + + c c → Ξ + c π + ) × B ( Ξ + c → p K − π + ) / B ( Ξ + + c c → Λ + c K − π + π + ) × B ( Λ + c → p K − π + ) = 0.035 ± 0.009 ( stat ) ± 0.003 ( syst )
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