arXiv subjects

M. Calvi

Publications and source records attributed to M. Calvi.

At least 199 records · Page 11Linked to original sources

arXiv2014

Updated measurements of exclusive $J/ψ$ and $ψ(2S)$ production cross-sections in $pp$ collisions at $\sqrt{s}=7$ TeV

The differential cross-section as a function of rapidity has been measured for the exclusive production of $J/ψ$ and $ψ(2S)$ mesons in proton-proton collisions at $\sqrt{s}=7$ TeV, using data collected by the LHCb experiment, corresponding to an integrated luminosity of 930 pb$^{-1}$. The cross-sections times branching fractions to two muons having pseudorapidities between 2.0 and 4.5 are measured to be $$\begin{array}{rl} σ_{pp\rightarrow J/ψ\rightarrow{μ^+}{μ^-}}(2.0<η_{μ^\pm }<4.5)=&291\pm 7\pm19 {\rm \ pb},\\ σ_{pp\rightarrowψ(2S)\rightarrow{μ^+}{μ^-}}(2.0<η_{μ^\pm}<4.5)=&6.5\pm 0.9\pm 0.4 {\rm \ pb},\end{array}$$ where the first uncertainty is statistical and the second is systematic. The measurements agree with next-to-leading order QCD predictions as well as with models that include saturation effects.

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arXiv2014

Observation of B^0_(s) -> J/ψf_1(1285) decays and measurement of the f_1(1285) mixing angle

Decays of Bs and B0 mesons into J/ψπ+π-π+π- final states, produced in pp collisions at the LHC, are investigated using data corresponding to an integrated luminosity of 3/fb collected with the LHCb detector. B^0_(s) -> Jψf_1(1285) decays are seen for the first time, and the branching fractions are measured. Using these rates, the f_1(1285) mixing angle between strange and non-strange components of its wave function in the q-qbar structure model is determined to be \pm (24.0^{+3.1+0.6}_{-2.6-0.8}) degrees. Implications on the possible tetraquark nature of the f_1(1285) are discussed.

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arXiv2014

Observation of associated production of a $Z$ boson with a $D$ meson in the~forward region

A search for associated production of a $Z$ boson with an open charm meson is presented using a data sample, corresponding to an integrated luminosity of $1.0\,\mathrm{fb}^{-`}$ of proton--proton collisions at a centre-of-mass energy of 7\,TeV, collected by the LHCb experiment. %% Seven candidate events for associated production of a $Z$ boson with a $D^0$ meson and four candidate events for a $Z$ boson with a $D^+$ meson are observed with a combined significance of 5.1standard deviations. The production cross-sections in the forward region are measured to be $$σ_{Z\rightarrowμ^+μ^-\!,D^0} = 2.50\pm1.12\pm0.22pb$$ $$σ_{Z\rightarrowμ^+μ^-\!,D^+} = 0.44\pm0.23\pm0.03pb,$$ where the first uncertainty is statistical and the second systematic.

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arXiv2014

Measurement of the flavour-specific CP-violating asymmetry $a_{\rm sl}^s$ in $B_s^0$ decays

The CP-violating asymmetry a_{sl}^s is studied using semileptonic decays of Bs and anti-Bs mesons produced in pp collisions at a centre-of-mass energy of 7 TeV at the LHC, exploiting a data sample corresponding to an integrated luminosity of 1.0/fb. The reconstructed final states are Ds^(+/-)μ^(-/+), with the Ds^(+/-) particle decaying in the ϕπ^(+/-) mode. The Ds^(+/-)μ^{-/+) yields are summed over Bs and anti-Bs initial states, and integrated with respect to decay time. Data-driven methods are used to measure efficiency ratios. We obtain $a_{sl}^s$ = (-0.06 +/- 0.50 +/- 0.36)%, where the first uncertainty is statistical and the second systematic.

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arXiv2014

Search for CP violation in the decay $D^+ \to π^-π^+π^+$

A search for CP violation in the phase space of the decay $D^+\toπ^-π^+π^+$ is reported using $pp$ collision 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. The Dalitz plot distributions for $3.1\times 10^6$ $D^+$ and $D^-$ candidates are compared with binned and unbinned model-independent techniques. No evidence for CP violation is found.

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arXiv2014

Search for the doubly charmed baryon Xi_cc^+

A search for the doubly charmed baryon Xi_cc^+ in the decay mode Xi_cc^+ -> Lambda_c^+ K^- pi^+ is performed with a data sample, corresponding to an integrated luminosity of 0.65/fb, of pp collisions recorded at a centre-of-mass energy of 7 TeV. No significant signal is found in the mass range 3300-3800 MeV/c^2. Upper limits at the 95% confidence level on the ratio of the Xi_cc^+ production cross-section times branching fraction to that of the Lambda_c^+, R, are given as a function of the Xi_cc^+ mass and lifetime. The largest upper limits range from R < 1.5 x 10^-2 for a lifetime of 100 fs to R < 3.9 x 10^-4 for a lifetime of 400 fs.

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arXiv2013

Observation of the decay $B_s^0\to\bar{D}^0ϕ$

First observation of the decay Bs -> D0bar phi is reported using pp collision 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. The significance of the signal is 6.2 standard deviations. The branching fraction is measured relative to that of the decay Bs -> D0bar K*0bar to be 0.069 +/- 0.013 (stat) +/- 0.007 (syst). The first measurement of the ratio of branching fractions for the decays Bs -> D0bar K*0bar and Bd->D0bar K*0 is found to be 7.8 +/- 0.7 (stat) +/- 0.3 (syst) +/- 0.6 (f_s/f_d), where the last uncertainty is due to the ratio of the Bs and Bd fragmentation fractions.

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arXiv2013

Search for the decay D0 to π+ π- μ+ μ-

A search for the D0 to π+ π- μ+ μ- decay, where the muon pair does not originate from a resonance, is performed using proton-proton collision data corresponding to an integrated luminosity of 1.0 fb-1 recorded by the LHCb experiment at a centre-of-mass energy of 7 TeV. No signal is observed and an upper limit on the relative branching fraction with respect to the resonant decay mode D0 to π+ π- ϕ(to μ+ μ-), under the assumption of a phase-space model, is found to be B(D0 to π+ π- mu+ mu-)/B(D0 to π+ π- ϕ(to μ+ μ-)) < 0.96 at the 90% confidence level. The upper limit on the absolute branching fraction is evaluated to be B(D0 to π+ π- μ+ μ-) < 5.5 x 10-7 at 90% confidence level. This is the most stringent to date.

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arXiv2013

Measurement of the charge asymmetry in $B^{\pm}\rightarrow ϕK^{\pm}$ and search for $B^{\pm}\rightarrow ϕπ^{\pm}$ decays

The \CP-violating charge asymmetry in $B^{\pm}\rightarrow ϕK^{\pm}$ decays is measured in a sample of $pp$ collisions at 7 TeV centre-of-mass energy, corresponding to an integrated luminosity of 1.0 fb$^{-1}$ collected by the LHCb experiment. The result is $\mathcal{A}_{CP}(B^{\pm}\rightarrow ϕK^{\pm}) = \rm 0.022\pm 0.021 \pm 0.009$, where the first uncertainty is statistical and the second systematic. In addition, a search for the $B^{\pm}\rightarrow ϕπ^{\pm}$ decay mode is performed, using the $B^{\pm}\rightarrow ϕK^{\pm}$ decay rate for normalization. An upper limit on the branching fraction $\mathcal{B}(B^{\pm}\rightarrow ϕπ^{\pm})< 1.5\times 10^{-7}$ is set at 90% confidence level.

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arXiv2013

Study of forward Z+jet production in pp collisions at $\sqrt{s} = 7$ TeV

A measurement of the $Z(\rightarrowμ^+μ^-)$+jet production cross-section in $pp$ collisions at a centre-of-mass energy $\sqrt{s} = 7$ TeV is presented. The analysis is based on an integrated luminosity of $1.0\,\text{fb}^{-1}$ recorded by the LHCb experiment. Results are shown with two jet transverse momentum thresholds, 10 and 20 GeV, for both the overall cross-section within the fiducial volume, and for six differential cross-section measurements. The fiducial volume requires that both the jet and the muons from the Z boson decay are produced in the forward direction ($2.0<η<4.5$). The results show good agreement with theoretical predictions at the second-order expansion in the coupling of the strong interaction.

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arXiv2013

Measurement of the $\bar{B}_s^0\to D_s^-D_s^+$ and $\bar{B}_s^0\to D^-D_s^+$ effective lifetimes

The first measurement of the effective lifetime of the $\bar{B}_s^0$ meson in the decay $\bar{B}_s^0\to D_s^-D_s^+$ is reported using a proton-proton collision dataset, corresponding to an integrated luminosity of 3 fb$^{-1}$, collected by the LHCb experiment. The measured value of the $\bar{B}_s^0\to D_s^-D_s^+$ effective lifetime is $1.379\pm0.026\pm0.017$ ps, where the uncertainties are statistical and systematic, respectively. This lifetime translates into a measurement of the decay width of the light $\bar{B}_s^0$ mass eigenstate of Γ_L$=0.725\pm0.014\pm0.009$ ps$^{-1}$. The $\bar{B}_s^0$ lifetime is also measured using the flavor-specific $\bar{B}_s^0\to D^-D_s^+$ decay to be $1.52\pm0.15\pm0.01 {\rm ps}$.

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arXiv2013

Studies of beauty baryon decays to $D^0 p h^-$ and $Λ_c^+ h^-$ final states

Decays of beauty baryons to the $D^0 p h^-$ and $Λ_c^+ h^-$ final states (where $h$ indicates a pion or a kaon) are studied using a data sample of $pp$ collisions, corresponding to an integrated luminosity of 1.0 fb$^{-1}$, collected by the LHCb detector. The Cabibbo-suppressed decays $Λ_b^0\to D^0 p K^-$ and $Λ_b^0\to Λ_c^+ K^-$ are observed and their branching fractions are measured with respect to the decays $Λ_b^0\to D^0 p π^-$ and $Λ_b^0\to Λ_c^+ π^-$. In addition, the first observation is reported of the decay of the neutral beauty-strange baryon $Ξ_b^0$ to the $D^0 p K^-$ final state, and a measurement of the $Ξ_b^0$ mass is performed. Evidence of the $Ξ_b^0\to Λ_c^+ K^-$ decay is also reported.

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arXiv2013

First measurement of time-dependent CP violation in Bs -> K+K- decays

Direct and mixing-induced CP-violating asymmetries in Bs -> K+K- decays are measured for the first time using a data sample of pp collisions, corresponding to an integrated luminosity of 1.0 fb^{-1}, collected with the LHCb detector at a centre-of-mass energy of 7 TeV. The results are C_{KK} = 0.14 \pm 0.11 \pm 0.03 and S_{KK} = 0.30 \pm 0.12 \pm 0.04, where the first uncertainties are statistical and the second systematic. The corresponding quantities are also determined for B0 -> pi+pi- decays to be C_{pipi} = -0.38 \pm 0.15 \pm 0.02 and S_{pipi} = -0.71 \pm 0.13 \pm 0.02, in good agreement with existing measurements.

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arXiv2013

Measurement of $J/ψ$ polarization in $pp$ collisions at $\sqrt{s}=7$ TeV

An angular analysis of the decay $J/ψ\rightarrow μ^{+} μ^{-}$ is performed to measure the polarization of prompt $J/ψ$ mesons produced in $pp$ collisions at $\sqrt{s}=7\; \mathrm{TeV}$. The dataset corresponds to an integrated luminosity of 0.37 fb$^{-1}$ collected with the LHCb detector. The measurement is presented as a function of transverse momentum, $p_\mathrm{T}$, and rapidity, $y$, of the $J/ψ$ meson, in the kinematic region $2 < p_\mathrm{T} < 15\; \mathrm{GeV}/c$ and $2.0<y<4.5$.

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arXiv2013

Observation of the decay Bc+ -> Bs0 pi+

The result of a search for the decay Bc+ -> Bs0 pi+ is presented, using the Bs0 -> Ds- pi+ and Bs0 -> J/psi Phi channels. The analysis is based on a data sample of pp collisions collected with the LHCb detector, corresponding to an integrated luminosity of 1 fb-1 taken at a center-of-mass energy of 7 TeV, and 2 fb-1 taken at 8 TeV. The decay Bc+ -> Bs0 pi+ is observed with significance in excess of five standard deviations independently in both decay channels. The measured product of the ratio of cross-sections and branching fraction is sigma(Bc+)/sigma(Bs0) x BR(Bc+ -> Bs0 pi+) = (2.37 \pm 0.31 (stat) \pm 0.11 (syst)^{+0.17}_{-0.13} (tau_Bc)) x 10^-3 in the pseudorapidity range 2 < eta(B) < 5, where the first uncertainty is statistical, the second is systematic and the third is due to the uncertainty on the Bc lifetime. This is the first observation of a B meson decaying to another B meson via the weak interaction.

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arXiv2013

Measurement of the CKM angle gamma from a combination of B->Dh analyses

A combination of three LHCb measurements of the CKM angle gamma is presented. The decays B->DK and B->Dpi are used, where D denotes an admixture of D0 and D0-bar mesons, decaying into K+K-, pi+pi-, K+-pi-+, K+-pi-+pi+-pi-+, KSpi+pi-, or KSK+K- final states. All measurements use a dataset corresponding to 1.0 fb-1 of integrated luminosity. Combining results from B->DK decays alone a best-fit value of gamma = 72.0 deg is found, and confidence intervals are set gamma in [56.4,86.7] deg at 68% CL, gamma in [42.6,99.6] deg at 95% CL. The best-fit value of gamma found from a combination of results from B->Dpi decays alone, is gamma = 18.9 deg, and the confidence intervals gamma in [7.4,99.2] deg or [167.9,176.4] deg at 68% CL, are set, without constraint at 95% CL. The combination of results from B->DK and B->Dpi decays gives a best-fit value of gamma = 72.6 deg and the confidence intervals gamma in [55.4,82.3] deg at 68% CL, gamma in [40.2,92.7] deg at 95% CL are set. All values are expressed modulo 180 deg, and are obtained taking into account the effect of D0-D0bar mixing.

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arXiv2013

Study of $B_{(s)}^0 \to K_{\rm S}^0 h^{+} h^{\prime -}$ decays with first observation of $B_{s}^0 \to K_{\rm S}^0 K^{\pm} π^{\mp}$ and $B_{s}^0 \to K_{\rm S}^0 π^{+} π^{-}$

A search for charmless three-body decays of $B^0$ and $B_{s}^0$ mesons with a $K_{\rm S}^0$ meson in the final state is performed using the $pp$ collision data, corresponding to an integrated luminosity of $1.0\,\mbox{fb}^{-1}$, collected at a centre-of-mass energy of $7\mathrm{\,Te\kern -0.1em V}$ recorded by the LHCb experiment. Branching fractions of the $B_{(s)}^0 \to K_{\rm S}^0 h^{+} h^{\prime -}$ decay modes ($h^{(\prime)} = π, K$), relative to the well measured $B^0 \to K_{\rm S}^0 π^{+} π^{-}$ decay, are obtained. First observation of the decay modes $B_s^0 \to K_{\rm S}^0 K^{\pm} π^{\mp}$ and $B_s^0 \to K_{\rm S}^0 π^{+} π^{-}$ and confirmation of the decay $B^0 \to K_{\rm S}^0 K^{\pm} π^{\mp}$ are reported. The following relative branching fraction measurements or limits are obtained \begin{eqnarray*} \nonumber \frac{{\cal B}(B^0 \to K_{\rm S}^0 K^{\pm} π^{\mp})}{{\cal B}(B^0 \to K_{\rm S}^0 π^{+} π^{-})} &=& 0.128 \pm 0.017 \, ({\rm stat.}) \pm 0.009 \, ({\rm syst.}) \,, \\ \nonumber \frac{{\cal B}(B^0 \to K_{\rm S}^0 K^{+} K^{-} )}{{\cal B}(B^0 \to K_{\rm S}^0 π^{+} π^{-})} &=& 0.385 \pm 0.031 \, ({\rm stat.}) \pm 0.023 \, ({\rm syst.}) \,, \\ \nonumber \frac{{\cal B}(B_s^0 \to K_{\rm S}^0 π^{+} π^{-} )}{{\cal B}(B^0 \to K_{\rm S}^0 π^{+} π^{-})} &=& 0.29\phantom{0} \pm 0.06\phantom{0} \, ({\rm stat.}) \pm 0.03\phantom{0} \, ({\rm syst.}) \pm 0.02 \, (f_s/f_d) \,, \\ \nonumber \frac{{\cal B}(B_s^0 \to K_{\rm S}^0 K^{\pm} π^{\mp})}{{\cal B}(B^0 \to K_{\rm S}^0 π^{+} π^{-})} &=& 1.48\phantom{0} \pm 0.12\phantom{0} \, ({\rm stat.}) \pm 0.08\phantom{0} \, ({\rm syst.}) \pm 0.12 \, (f_s/f_d) \,, \\ \nonumber \frac{{\cal B}(B_s^0 \to K_{\rm S}^0 K^{+} K^{-} )}{{\cal B}(B^0 \to K_{\rm S}^0 π^{+} π^{-})} &\in& [0.004;0.068] \; {\rm at \;\; 90\% \; CL} \,. \end{eqnarray*}

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arXiv2013

Branching fraction and CP asymmetry of the decays $B^+ \to K_{\rm \scriptscriptstyle S}^0 π^+$ and $B^+ \to K_{\rm \scriptscriptstyle S}^0 K^+$

An analysis of $B^+ \to K_{\rm \scriptscriptstyle S}^0 π^+$ and $B^+ \to K_{\rm \scriptscriptstyle S}^0 K^+$ decays is performed with the LHCb experiment. The $pp$ collision data used correspond to integrated luminosities of $1{\,fb}^{-1}$ and $2{\,fb}^{-1}$ collected at centre-of-mass energies of $\sqrt{s}=7\mathrm{\,Te\kern -0.1em V}$ and $\sqrt{s}=8\mathrm{\,Te\kern -0.1em V}$, respectively. The ratio of branching fractions and the direct {\it CP} asymmetries are measured to be $\mathcal{B}(B^+ \to K_{\rm \scriptscriptstyle S}^0 K^+)/\mathcal{B}(B^+ \to K_{\rm \scriptscriptstyle S}^0 π^+) = 0.064 \pm 0.009\textrm{(stat.)} \pm 0.004\textrm{(syst.)}$, $\mathcal{A}^{\it CP}(B^+ \to K_{\rm \scriptscriptstyle S}^0 π^+) = -0.022 \pm 0.025\textrm{(stat.)} \pm 0.010\textrm{(syst.)}$ and $\mathcal{A}^{\it CP}(B^+ \to K_{\rm \scriptscriptstyle S}^0 K^+) = -0.21 \pm 0.14\textrm{(stat.)} \pm 0.01\textrm{(syst.)}$. The data sample taken at $\sqrt{s}=7\mathrm{\,Te\kern -0.1em V}$ is used to search for $B_c^+ \to K_{\rm \scriptscriptstyle S}^0 K^+$ decays and results in the upper limit $(f_c\cdot\mathcal{B}(B_c^+ \to K_{\rm \scriptscriptstyle S}^0 K^+))/(f_u\cdot\mathcal{B}(B^+ \to K_{\rm \scriptscriptstyle S}^0 π^+)) < 5.8\times10^{-2}\textrm{at 90% confidence level}$, where $f_c$ and $f_u$ denote the hadronisation fractions of a $\bar{b}$ quark into a $B_c^+$ or a $B^+$ meson, respectively.

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