arXiv subjects

A. Cardini

Publications and source records attributed to A. Cardini.

At least 199 records · Page 11Linked to original sources

arXiv2013

Precision measurement of the Lambda_b baryon lifetime

The ratio of the Λb baryon lifetime to that of the B0 meson is measured using 1.0/fb of integrated luminosity in 7 TeV center-of-mass energy pp collisions at the LHC. The Λb baryon is observed for the first time in the decay mode Λb -> J/ψpK-, while the B0 meson decay used is the well known B0 -> J/ψpi+K- mode, where the pi+ K- mass is consistent with that of the K*0(892) meson. The ratio of lifetimes is measured to be 0.976 +/- 0.012 +/- 0.006, in agreement with theoretical expectations based on the heavy quark expansion. Using previous determinations of the B0 meson lifetime, the Λb lifetime is found to be 1.482 +/- 0.018 +/- 0.012 ps. In both cases the first uncertainty is statistical and the second systematic.

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arXiv2013

Dual-readout Calorimetry

The RD52 Project at CERN is a pure instrumentation experiment whose goal is to understand the fundamental limitations to hadronic energy resolution, and other aspects of energy measurement, in high energy calorimeters. We have found that dual-readout calorimetry provides heretofore unprecedented information event-by-event for energy resolution, linearity of response, ease and robustness of calibration, fidelity of data, and particle identification, including energy lost to binding energy in nuclear break-up. We believe that hadronic energy resolutions of σ/E $\approx$ 1 - 2% are within reach for dual-readout calorimeters, enabling for the first time comparable measurement preci- sions on electrons, photons, muons, and quarks (jets). We briefly describe our current progress and near-term future plans. Complete information on all aspects of our work is available at the RD52 website http://highenergy.phys.ttu.edu/dream/.

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arXiv2013

Studies of the decays $B^+ \to p \bar p h^+$ and observation of $B^+ \to \kern 0.1em\bar{\kern -0.1emΛ}(1520)p$

Dynamics and direct $C¶$ violation in three-body charmless decays of charged $B$ mesons to a proton, an antiproton and a light meson (pion or kaon) are studied using data, corresponding to an integrated luminosity of 1.0$ {\,fb}^{-1}$, collected by the ${LHCb}$ experiment in $pp$ collisions at a center-of-mass energy of 7 TeV. Production spectra are determined as a function of Dalitz-plot and helicity variables. The forward-backward asymmetry of the light meson in the $p\bar p$ rest frame is measured. No significant $C¶$ asymmetry in $B^+ \to p \bar p K^+$ decay is found in any region of the Dalitz plane. We present the first observation of the decay $B^+ \to \kern 0.1em\bar{\kern -0.1emΛ}(1520)(\to K^+\bar p)p$ near the $K^+\bar p$ threshold and measure $\mathcal{B}(B^+ \to \kern 0.1em\bar{\kern -0.1emΛ}(1520)p)=(3.9^{+1.0}_{-0.9} (\mathrm{stat})\pm0.1 (\mathrm{syst})\pm0.3 (\mathrm{BF}))\times 10^{-7}$, where BF denotes the uncertainty on secondary branching fractions.

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arXiv2013

Measurements of the branching fractions of $B^{+} \to p \bar p K^{+}$ decays

The branching fractions of the decay $B^{+} \to p \bar p K^{+}$ for different intermediate states are measured using data, corresponding to an integrated luminosity of $1.0 fb^{-1}$, collected by the LHCb experiment. The total branching fraction, its charmless component $(M_{p\bar p} <2.85 {GeV/}c^{2})$ and the branching fractions via the resonant $c\bar c$ states $η_{c}(1S)$ and $ψ(2S)$ relative to the decay via a $J/ψ$ intermediate state are {align*} \frac{{\mathcal B}(B^{+} \to p \bar p K^{+})_{total}}{{\mathcal B}(B^{+} \to J/ψK^{+} \to p \bar p K^{+})}=& \, 4.91 \pm 0.19 \, {(\rm stat)} \pm 0.14 \, {(\rm syst)}, \frac{{\mathcal B}(B^{+} \to p \bar p K^{+})_{M_{p\bar p} <2.85 {GeV/}c^{2}}}{{\mathcal B}(B^{+} \to J/ψK^{+} \to p \bar p K^{+})}=& \, 2.02 \pm 0.10 \, {(\rm stat)}\pm 0.08 \, {(\rm syst)}, \frac{{\mathcal B} (B^{+} \to η_{c}(1S) K^{+} \to p \bar p K^{+})}{{\mathcal B}(B^{+} \to J/ψK^{+} \to p \bar p K^{+})} = & \, 0.578 \pm 0.035 \, {(\rm stat)} \pm 0.027 \, {(\rm syst)}, \frac{{\mathcal B} (B^{+} \to ψ(2S) K^{+} \to p \bar p K^{+})}{{\mathcal B}(B^{+} \to J/ψK^{+} \to p \bar p K^{+})}=& \, 0.080 \pm 0.012 \, {(\rm stat)} \pm 0.009 \, {(\rm syst)}. {align*} Upper limits on the $B^{+}$ branching fractions into the $η_{c}(2S)$ meson and into the charmonium-like states X(3872) and X(3915) are also obtained.

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arXiv2013

Observation of $B^+_c \rightarrow J/ψD_s^+$ and $B^+_c \rightarrow J/ψD_s^{*+}$ decays

The decays $B^+_c \rightarrow J/ψD_s^+$ and $B^+_c \rightarrow J/ψD_s^{*+}$ are observed for the first time using a dataset, corresponding to an integrated luminosity of 3$fb^{-1}$, collected by the LHCb experiment in proton-proton collisions at centre-of-mass energies of $\sqrt{s}$=7 and 8 TeV. The statistical significance for both signals is in excess of 9 standard deviations. The following ratios of branching fractions are measured to be $BR(B^+_c \rightarrow J/ψD_s^+)/BR(B^+_c \rightarrow J/ψπ+) = 2.90 \pm 0.57 \pm 0.24$, $BR(B^+_c \rightarrow J/ψD_s^{*+}) / BR (B^+_c \rightarrow J/ψD_s^+) = 2.37 \pm 0.56 \pm 0.10$, where the first uncertainties are statistical and the second systematic. The mass of the \Bc meson is measured to be $m_{B^+_c} = 6276.28 \pm 1.44 (stat) \pm 0.36(syst) MeV/c^2$, using the $B^+_c \rightarrow J/ψD_s^+$ decay mode.

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arXiv2013

Production of J/psi and Upsilon mesons in pp collisions at sqrt(s) = 8 TeV

The production of J/psi and Upsilon mesons in pp collisions at sqrt(s) = 8 TeV is studied with the LHCb detector. The J/psi and Upsilon mesons are reconstructed in the mu+mu- decay mode and the signal yields are determined with a fit to the mu+mu- invariant mass distributions. The analysis is performed in the rapidity range 2.0<y<4.5 and transverse momentum range 0<p_T<14(15) GeV/c of the J/psi(Upsilon) mesons. The J/psi and Upsilon production cross-sections and the fraction of J/psi mesons from b-hadron decays are measured as a function of the meson p_T and y.

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arXiv2013

Search for CP violation in D+ -> phi pi+ and Ds+ -> Ks pi+ decays

A search for CP violation in D+ -> phi pi+ decays is performed using data collected in 2011 by the LHCb experiment corresponding to an integrated luminosity of 1.0 fb^{-1} at a centre of mass energy of 7 TeV. The CP-violating asymmetry is measured to be (-0.04+/-0.14+/-0.14)% for candidates with K-K+ mass within 20 MeV/c^{2} of the phi meson mass. A search for a CP-violating asymmetry that varies across the phi mass region of the D+ -> K-K+pi+ Dalitz plot is also performed, and no evidence for CP violation is found. In addition, the CP asymmetry in the Ds+ -> Ks pi+ decay is measured to be (0.61+/-0.83+/-0.14)%.

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arXiv2013

First observation of the decay $B_{c}^{+}\to J/ψK^+$

The decay $B_c^+\to J/ψK^+$ is observed for the first time using a data sample, corresponding to an integrated luminosity of 1.0 ${\,fb}^{-1}$, collected by the LHCb experiment in $pp$ collisions at a centre-of-mass energy of $7\mathrm{\,Te\kern -0.1em V}$. A yield of $46\pm12$ events is reported, with a significance of 5.0 standard deviations. The ratio of the branching fraction of $B_c^+\to J/ψK^+$ to that of $B_c^+\to J/ψπ^+$ is measured to be $0.069\pm0.019\pm0.005$, where the first uncertainty is statistical and the second is systematic.

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arXiv2013

SuperB Technical Design Report

In this Technical Design Report (TDR) we describe the SuperB detector that was to be installed on the SuperB e+e- high luminosity collider. The SuperB asymmetric collider, which was to be constructed on the Tor Vergata campus near the INFN Frascati National Laboratory, was designed to operate both at the Upsilon(4S) center-of-mass energy with a luminosity of 10^{36} cm^{-2}s^{-1} and at the tau/charm production threshold with a luminosity of 10^{35} cm^{-2}s^{-1}. This high luminosity, producing a data sample about a factor 100 larger than present B Factories, would allow investigation of new physics effects in rare decays, CP Violation and Lepton Flavour Violation. This document details the detector design presented in the Conceptual Design Report (CDR) in 2007. The R&D and engineering studies performed to arrive at the full detector design are described, and an updated cost estimate is presented. A combination of a more realistic cost estimates and the unavailability of funds due of the global economic climate led to a formal cancelation of the project on Nov 27, 2012.

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arXiv2013

Precision measurement of D meson mass differences

Using three- and four-body decays of $D$ mesons produced in semileptonic $b$-hadron decays, precision measurements of $D$ meson mass differences are made together with a measurement of the $D^{0}$ mass. The measurements are based on a dataset corresponding to an integrated luminosity of $1.0 fb^{-1}$ collected in $pp$ collisions at 7\,TeV. Using the decay $D^0 \rightarrow K^{+} K^{-} K^{-} π^{+}$, the $D^0$ mass is measured to be $M(D^0) &=& 1864.75 \pm 0.15 \,({\rm stat}) \pm 0.11 \,({\rm syst}) \, \textrm{MeV/c^2}$. The mass differences $M(D^{+}) - M(D^{0}) = 4.76 \pm 0.12 \,({\rm stat}) \pm 0.07 \,({\rm syst}) \, \textrm{MeV/c^2}$ and $M(D^{+}_s) - M(D^{+}) = 98.68 \pm 0.03 \,({\rm stat}) \pm 0.04 \,({\rm syst}) \, \textrm{MeV/c^2}$ are measured using the $D^0 \rightarrow K^{+} K^{-} π^{+} π^{-}$ and $D^{+}_{(s)} \rightarrow K^{+}K^{-} π^{+}$ modes.

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arXiv2013

Measurement of CP violation and the B_s^0 meson decay width difference with B_s^0\to J/ψK^+ K^- and B_s^0\to J/ψπ^+π^- decays

The time-dependent CP asymmetry in B_s^0\to J/ψK^+K^- decays is measured using $pp$ collision data at \sqrt{s}=7TeV, corresponding to an integrated luminosity of 1.0fb^-1, collected with the LHCb detector. The decay time distribution is characterised by the decay widths Γ_L and Γ_H of the light and heavy mass eigenstates of the B_s^0--\bar{B}_s^0 system and by a CP-violating phase ϕ_s. In a sample of 27\,617 B_s^0\to J/ψK^+K^- decays, where the dominant contribution comes from B_s^0\to J/ψϕ decays, these parameters are measured to be ϕ_s = 0.07 \pm 0.09 (stat) \pm 0.01 (syst) rad, Γ_s \equiv (Γ_L+Γ_H)/2 = 0.663 \pm 0.005 (stat) \pm 0.006 (syst) ps^-1, ΔΓ_s \equiv Γ_L -Γ_H = 0.100 \pm 0.016 (stat) \pm 0.003 (syst) & ps^-1, corresponding to the single most precise determination of ϕ_s, ΔΓ_s and Γ_s. The result of performing a combined analysis with B_s^{0} \to J/ψπ^+π^- decays gives ϕ_s = 0.01 \pm 0.07 (stat) \pm 0.01 (syst) rad, Γ_s = 0.661 \pm 0.004 (stat) \pm 0.006 (syst) ps^-1, ΔΓ_s = 0.106 \pm 0.011 (stat) \pm 0.007 (syst) & ps^-1. All measurements are in agreement with the Standard Model predictions.

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arXiv2013

Searches for violation of lepton flavour and baryon number in tau lepton decays at LHCb

Searches for the lepton flavour violating decay $τ^-\rightarrow μ^-μ^+μ^-$ and the lepton flavour and baryon number violating decays $τ^-\rightarrow \bar{p}μ^+μ^-$ and $τ^-\rightarrow pμ^-μ^-$ have been carried out using proton-proton collision data, corresponding to an integrated luminosity of 1.0 fb$^{-1}$, taken by the LHCb experiment at $\sqrt{s} = 7$ TeV. No evidence has been found for any signal, and limits have been set at 90% confidence level on the branching fractions: $\cal B(τ^-\rightarrow μ^-μ^+μ^-) < 8.0 \times 10^{-8}$, $\cal B(τ^-\rightarrow \bar{p}μ^+μ^-) < 3.3 \times 10^{-7}$ and $\cal B(τ^-\rightarrow pμ^-μ^-) < 4.4 \times 10^{-7}$. The results for the $τ^-\rightarrow \bar{p}μ^+μ^-$ and $τ^-\rightarrow pμ^-μ^-$ decay modes represent the first direct experimental limits on these channels.

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arXiv2013

First measurement of the CP-violating phase in $B_s^0 \to ϕϕ$ decays

A first flavour-tagged measurement of the time-dependent CP-violating asymmetry in $B_s^0 \to ϕϕ$ decays is presented. In this decay channel, the CP-violating weak phase arises due to CP violation in the interference between $B_s^0$-$\bar{B}_s^0$ mixing and the $b \to s \bar{s} s $ gluonic penguin decay amplitude. Using a sample of $pp$ collision data corresponding to an integrated luminosity of $1.0\; fb^{-1}$ and collected at a centre-of-mass energy of $7 \rm TeV$ with the LHCb detector, $880\ \B_s^0 \to ϕϕ$ signal decays are obtained. The CP-violating phase is measured to be in the interval [-2.46, -0.76] \rm rad$ at 68% confidence level. The p-value of the Standard Model prediction is 16%.

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arXiv2013

Measurements of the Lambda_b0 -> J/psi Lambda decay amplitudes and the Lambda_b0 polarisation in pp collisions at sqrt(s) = 7 TeV

An angular analysis of Lambda_b0 -> J/psi Lambda decays is performed using a data sample corresponding to 1.0 fb^{-1} collected in pp collisions at sqrt(s) = 7 TeV with the LHCb detector at the LHC. A parity violating asymmetry parameter characterising the Lambda_b0 -> J/psi Lambda decay of 0.05 +/- 0.17 +/- 0.07 and a Lambda_b0 transverse production polarisation of 0.06 +/- 0.07 +/- 0.02 are measured, where the first uncertainty is statistical and the second systematic.

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arXiv2013

Measurement of the differential branching fraction of the decay $Λ_b^0\rightarrowΛμ^+μ^-$

The differential branching fraction of the decay $Λ_b^0\rightarrowΛμ^+μ^-$ is measured as a function of the square of the dimuon invariant mass, $q^2$. A yield of $78\pm12$ $Λ_b^0\rightarrowΛμ^+μ^-$ decays is observed using data, corresponding to an integrated luminosity of 1.0\,fb$^{-1}$, collected by the LHCb experiment at a centre-of-mass energy of 7\,TeV. A significant signal is found in the $q^2$ region above the square of the $J/ψ$ mass, while at lower-$q^2$ values upper limits are set on the differential branching fraction. Integrating the differential branching fraction over $q^2$, while excluding the $J/ψ$ and $ψ(2S)$ regions, gives a branching fraction of $\BF($Λ_b^0\rightarrowΛμ^+μ^-$)=(0.96\pm 0.16\stat\pm 0.13\syst\pm 0.21 (\mathrm{norm}))\times 10^{-6}$, where the uncertainties are statistical, systematic and due to the normalisation mode, $$Λ_b^0\rightarrow J/psiΛ$, respectively.

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arXiv2013

First observation of CP violation in the decays of Bs mesons

Using pp collision data, corresponding to an integrated luminosity of $1.0 \mathrm{fb}^{-1}$, collected by LHCb in 2011 at a center-of-mass energy of 7 TeV, we report the measurement of direct CP violation in $B^0_s \to K^-π^+$ decays, $A_{C/!P}(B^0_s \rightarrow K^- π^+)=0.27 \pm 0.04\,\mathrm{(stat)} \pm 0.01\,\mathrm{(syst)}$, with significance exceeding five standard deviations. This is the first observation of CP violation in the decays of $B^0_s$ mesons. Furthermore, we provide an improved determination of direct CP violation in $B^0 \to K^+π^-$ decays, $A_{C/!P}(B^0\rightarrow K^+ π^-)=-0.080 \pm 0.007\,\mathrm{(stat)} \pm 0.003\,\mathrm{(syst)}$, which is the most precise measurement of this quantity to date.

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arXiv2013

Measurement of CP violation in the phase space of $B^{\pm} \to K^{\pm} π^{+} π^{-}$ and $B^{\pm} \to K^{\pm} K^{+} K^{-}$ decays

The charmless decays $B^{\pm}\to K^{\pm}π^+π^-$ and $B^{\pm}\to K^{\pm}K^+K^-$ are reconstructed using data, corresponding to an integrated luminosity of 1.0 fb$^{-1}$, collected by LHCb in 2011. The inclusive charge asymmetries of these modes are measured as $A_{C\!P}(B^{\pm}\to K^{\pm}π^+π^-) = 0.032 \pm 0.008 \stat \pm 0.004 \syst \pm 0.007 (JψK^{\pm})$ and $A_{C\!P}(B^{\pm}\to K^{\pm}K^+K^-) = -0.043 \pm 0.009 \stat \pm 0.003 \syst \pm 0.007 (JψK^{\pm})$, where the third uncertainty is due to the $C\!P$ asymmetry of the $B^{\pm}\to JψK^{\pm}$ reference mode. The significance of $A_{C\!P}(B^{\pm}\to K^{\pm}K^+K^-)$ exceeds three standard deviations and is the first evidence of an inclusive $C\!P$ asymmetry in charmless three-body $B$ decays. In addition to the inclusive $C\!P$ asymmetries, larger asymmetries are observed in localised regions of phase space.

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arXiv2013

Measurement of the branching fractions of the decays Bs -> D0bar K- π+ and B0 -> D0bar K+ π-

The first observation of the decay Bs -> D0bar K- π+ is reported. The analysis is based on a data sample, corresponding to an integrated luminosity of 1.0 fb-1 of pp collisions, collected with the LHCb detector. The branching fraction relative to that of the topologically similar decay B0 -> D0bar π+ π- is measured to be BR(Bs -> D0bar K- π+)/BR(B0 -> D0bar π+ π-) = 1.18 +- 0.05 (stat.) +- 0.12 (syst.). In addition, the relative branching fraction of the decay B0 -> D0bar K+ π- is measured to be BR(B0 -> D0bar K+ π-)/BR(B0 -> D0bar π+ π-) = 0.106 +- 0.007 (stat.) +- 0.008 (syst.).

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