arXiv subjects

X. Cid Vidal

Publications and source records attributed to X. Cid Vidal.

30 records · Page 2Linked to original sources

arXiv2012

Observation of $J/ψ$ pair production in pp collisions at $\sqrt{s}=7 TeV$

The production of $J/ψ$ pairs in proton-proton collisions at a centre-of-mass energy of 7 TeV has been observed using an integrated luminosity of $37.5 pb^{-1}$ collected with the LHCb detector. The production cross-section for pairs with both \jpsi in the rapidity range $2<y^{J/ψ}<4.5$ and transverse momentum $p_{T}^{J/ψ}<10 GeV/c$ is $$ σ^{J/ψJ/ψ} = 5.1\pm1.0\pm1.1 nb,$$ where the first uncertainty is statistical and the second systematic.

hep-ex↗

arXiv2011

Determination of f_s/f_d for 7 TeV pp collisions and a measurement of the branching fraction of the decay Bd->D-K+

The relative abundance of the three decay modes $B_d \to D^- K^+$, $B_d \to D^- π^+$ and $B_s \to D_s^- π^+$ produced in 7 TeV $pp$ collisions at the LHC is determined from data corresponding to an integrated luminosity of 35 pb$^{-1}$. The branching fraction of $B_d \to D^- K^+$ is found to be $\cal B (B_d \to D^- K^+) = (2.01 \pm 0.18^{\textrm{stat}} \pm 0.14^{\textrm{syst}})\times 10^{-4}$. The ratio of fragmentation fractions \fsfdt is determined through the relative abundance of $B_s \to D_s^- π^+$ to $B_d \to D^- K^+$ and $B_d \to D^-π^+$, leading to $f_s/f_d = 0.253 \pm 0.017 \pm 0.017 \pm 0.020$, where the uncertainties are statistical, systematic, and theoretical respectively.

hep-ex↗

arXiv2011

First observation of the decay $\bar{B}^0_s \to D^0 K^{0}$ and a measurement of the ratio of branching fractions $\frac{{\cal B}(\bar{B}^0_s \to D^0 K^{0})}{{\cal B}(\bar{B}^0 \to D^0 ρ^0)}$

The first observation of the decay $\bar{B}^0_s \to D^0 K^{*0}$ using $pp$ data collected by the LHCb detector at a centre-of-mass energy of 7 TeV, corresponding to an integrated luminosity of 36 pb$^{-1}$, is reported. A signal of $34.4 \pm 6.8$ events is obtained and the absence of signal is rejected with a statistical significance of more than nine standard deviations. The $\bar{B}^0_s \to D^0 K^{*0}$ branching fraction is measured relative to that of $\bar{B}^0 \to D^0 ρ^0$: $\frac{{\cal B}(\bar{B}^0_s \to D^0 K^{*0})}{{\cal B}(\bar{B}^0 \to D^0 ρ^0)} = 1.48 \pm 0.34 \pm 0.15 \pm 0.12$, where the first uncertainty is statistical, the second systematic and the third is due to the uncertainty on the ratio of the $B^0$ and $B^0_s$ hadronisation fractions.

hep-ex↗

arXiv2011

Search for CP violation in $D^{+} \to K^{-}K^{+}π^{+}$ decays

A model-independent search for direct CP violation in the Cabibbo suppressed decay $D^+ \to K^- K^+π^+$ in a sample of approximately 370,000 decays is carried out. The data were collected by the LHCb experiment in 2010 and correspond to an integrated luminosity of 35 pb$^{-1}$. The normalized Dalitz plot distributions for $D^+$ and $D^-$ are compared using four different binning schemes that are sensitive to different manifestations of CP violation. No evidence for CP asymmetry is found.

hep-ex↗

arXiv2011

Measurements of the Branching fractions for $B_(s) -> D_(s)πππ$ and $Λ_b^0 -> Λ_c^+πππ$

Branching fractions of the decays $H_b\to H_cπ^-π^+π^-$ relative to $H_b\to H_cπ^-$ are presented, where $H_b$ ($H_c$) represents B^0-bar($D^+$), $B^-$ ($D^0$), B_s^0-bar ($D_s^+$) and $Λ_b^0$ ($Λ_c^+$). The measurements are performed with the LHCb detector using 35${\rm pb^{-1}}$ of data collected at $\sqrt{s}=7$ TeV. The ratios of branching fractions are measured to be B(B^0-bar -> D^+π^-π^+π^-)/ B(B^0-bar -> D^+π^-) = 2.38\pm0.11\pm0.21 B(B^- -> D^0π^-π^+π^-) / B(B^- -> D^0π^-) = 1.27\pm0.06\pm0.11 B(B_s^0-bar -> D_s^+π^-π^+π^-) / B(B_s^0-bar -> D_s^+π^-) = 2.01\pm0.37\pm0.20 B(Λ_b^0->Λ_c^+π^-π^+π^-) / B(Λ_b^0 -> Λ_c^+π^-) = 1.43\pm0.16\pm0.13. We also report measurements of partial decay rates of these decays to excited charm hadrons. These results are of comparable or higher precision than existing measurements.

hep-ex↗

arXiv2011

Measurement of the inclusive phi cross-section in pp collisions at sqrt(s) = 7 TeV

The cross-section for inclusive phi meson production in pp collisions at a centre-of-mass energy of sqrt(s) = 7 TeV has been measured with the LHCb detector at the Large Hadron Collider. The differential cross-section is measured as a function of the phi transverse momentum p_T and rapidity y in the region 0.6 < p_T < 5.0 GeV/c and 2.44 < y < 4.06. The cross-section for inclusive phi production in this kinematic range is sigma(pp -> phi X) = 1758 pm 19(stat) ^{+43}_{-14}(syst) pm 182(scale) microbarn, where the first systematic uncertainty depends on the p_T and y region and the second is related to the overall scale. Predictions based on the Pythia 6.4 generator underestimate the cross-section.

hep-ex↗

arXiv2011

Measurement of $V^0$ production ratios in $pp$ collisions at $\sqrt{s} = 0.9$ and 7\,TeV

The $\barΛ / Λ$ and $\barΛ / K^0_\mathrm{S}$ production ratios are measured by the LHCb detector from $0.3\,\mathrm{nb}^{-1}$ of $pp$ collisions delivered by the LHC at $\sqrt{s} = 0.9$\,TeV and $1.8\,\mathrm{nb}^{-1}$ at $\sqrt{s} = 7$\,TeV. Both ratios are presented as a function of transverse momentum, $p_\mathrm{T}$, and rapidity, $y$, in the ranges {$0.15 < p_\mathrm{T} < 2.50\,\mathrm{GeV}/c$} and {$2.0<y<4.5$}. Results at the two energies are in good agreement as a function of rapidity loss, $Δy = y_\mathrm{beam} - y$, and are consistent with previous measurements. The ratio $\barΛ / Λ$, measuring the transport of baryon number from the collision into the detector, is smaller in data than predicted in simulation, particularly at high rapidity. The ratio $\barΛ / K^0_\mathrm{S}$, measuring the baryon-to-meson suppression in strange quark hadronisation, is significantly larger than expected.

hep-ex↗

arXiv2011

Measurement of J/psi production in pp collisions at sqrt(s)=7 TeV

The production of J/psi mesons in proton-proton collisions at sqrt(s)=7 TeV is studied with the LHCb detector at the LHC. The differential cross-section for prompt J/psi production is measured as a function of the J/psi transverse momentum pT and rapidity y in the fiducial region 0<pT<14 GeV/c and 2.0<y<4.5. The differential cross-section and fraction of J/psi from b-hadron decays are also measured in the same pT and y ranges. The analysis is based on a data sample corresponding to an integrated luminosity of 5.2pb-1. The measured cross-sections integrated over the fiducial region are 10.52 +/- 0.04 +/- 1.40 +1.64/-2.20 mub for prompt J/psi production and 1.14 +/- 0.01 +/- 0.16 mub for J/psi from b-hadron decays, where the first uncertainty is statistical and the second systematic. The prompt J/psi production cross-section is obtained assuming no J/psi polarisation and the third error indicates the acceptance uncertainty due to this assumption.

hep-ex↗

arXiv2011

First observation of Bs -> D_{s2}^{*+} X mu nu decays

Using data collected with the LHCb detector in proton-proton collisions at a centre-of-mass energy of 7 TeV, the semileptonic decays Bs -> Ds+ X mu nu and Bs -> D0 K+ X mu nu are detected. Two structures are observed in the D0 K+ mass spectrum at masses consistent with the known D^+_{s1}(2536) and $D^{*+}_{s2}(2573) mesons. The measured branching fractions relative to the total Bs semileptonic rate are B(Bs -> D_{s2}^{*+} X mu nu)/B(Bs -> X mu nu)= (3.3\pm 1.0\pm 0.4)%, and B(Bs -> D_{s1}^+ X munu)/B(Bs -> X mu nu)= (5.4\pm 1.2\pm 0.5)%, where the first uncertainty is statistical and the second is systematic. This is the first observation of the D_{s2}^{*+} state in Bs decays; we also measure its mass and width.

hep-ex↗

arXiv2011

First observation of Bs -> J/psi f0(980) decays

Using data collected with the LHCb detector in proton-proton collisions at a centre-of-mass energy of 7 TeV, the hadronic decay Bs -> J/psi f0(980) is observed. This CP eigenstate mode could be used to measure mixing-induced CP violation in the B_s system. Using a fit to the pi+ pi- mass spectrum with interfering resonances gives R_{f0/phi} = [Gamma(Bs -> J/psi f0, f0 -> pi+ pi-)]/[Gamma(Bs -> J/psi phi, phi -> K+K-)] = 0.252^{+0.046+0.027}_{-0.032-0.033}, where the uncertainties are statistical and systematic, respectively.

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arXiv2010

Roadmap for selected key measurements of LHCb

Six of the key physics measurements that will be made by the LHCb experiment, concerning CP asymmetries and rare B decays, are discussed in detail. The "road map" towards the precision measurements is presented, including the use of control channels and other techniques to understand the performance of the detector with the first data from the LHC.

hep-ex↗

arXiv2010

Muon Identification in the LHCb experiment

A short summary of the LHCb muon identification procedure is given in this article. First, the muon system of LHCb is presented, together with some examples of physics measurements of the experiment where the muon identification is crucial. Then, the muon identification algorithm is introduced in three single steps. With this, the efficiency vs. misidentification rate is shown for MC simulated data. The way this method will be calibrated with real data is also seen. Finally, some preliminary muon identification results with proton-proton collisions at sqrt(s) = 900 GeV are presented.

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