arXiv subjects

M. Calvi

Publications and source records attributed to M. Calvi.

At least 145 records · Page 8Linked to original sources

arXiv2014

Study of $η-η^{\prime}$ mixing from measurement of $B^0_{(s)} \rightarrow J/ψη^{(\prime)}$~decay rates

A study of $B^0$~and $B^0_s$ meson decays into $J/ψη$~and $J/ψη^{\prime}$ final states is performed using a data set of proton-proton collisions at centre-of-mass energies of 7 and 8TeV, collected by the LHCb experiment and corresponding to 3.0fb$^{-1}$ of integrated luminosity. The decay $B^0 \rightarrow J/ψη^{\prime}$ is observed for thefirst time. The following ratios of branching fractions are measured: $$ \frac{\mathcal{B}(B^0 \rightarrow J/ψη^{\prime})}{\mathcal{B}(B^0_s \rightarrow J/ψη^{\prime})} = (2.28\pm0.65\,(stat)\,\pm0.10\,(syst)\,\pm0.13\,(f_{s}/f_{d}))\times10^{-2},$$ $$ \frac{\mathcal{B}(B^0 \rightarrow J/ψη)}{\mathcal{B}(B^0_s \rightarrow J/ψη)} = (1.85\pm0.61\,(stat)\,\pm0.09\,(syst)\,\pm0.11\,(f_{s}/f_{d}))\times10^{-2},$$ where the third uncertainty is related to the present knowledge of $f_{s}/f_{d}$, the ratio between the probabilities for a $b$ quark to form a $B^0_s$ or $B^0$ meson. The branching fraction ratios are used to determine the parameters of $η-η^{\prime}$ meson mixing. In addition, the first evidence for the decay $B^0_s \rightarrow ψ(2S) η^{\prime}$ is reported, and the relative branching fraction is measured, $$\frac{\mathcal{B}(B^0_s \rightarrow ψ(2S) η^{\prime})}{\mathcal{B}(B^0_s \rightarrow J/ψη^{\prime})} = (38.7\pm9.0\,(stat)\,\pm1.3\,(syst)\,\pm0.9(\mathcal{B}))\times10^{-2},$$ where the third uncertainty is due to the limited knowledge of the branching fractions of $J/ψ$ and $ψ(2S)$~mesons.

hep-ex↗

arXiv2014

Measurement of the $χ_b(3P)$ mass and of the relative rate of $χ_{b1}(1P)$ and $χ_{b2}(1P)$ production

The production of $χ_b$ mesons in proton-proton collisions is studied using a data sample collected by the LHCb detector, at centre-of-mass energies of $\sqrt{s}=7$ and $8$ TeV and corresponding to an integrated luminosity of 3.0 fb$^{-1}$. The $χ_b$ mesons are identified through their decays to $Υ(1S)γ$ and $Υ(2S)γ$ using photons that converted to $e^+e^-$ pairs in the detector. The relative prompt production rate of $χ_{b1}(1P)$ and $χ_{b2}(1P)$ mesons is measured as a function of the $Υ(1S)$ transverse momentum in the $χ_b$ rapidity range $2.0<y<4.5$. A precise measurement of the $χ_b(3P)$ mass is also performed. Assuming a mass splitting between the $χ_{b1}(3P)$ and the $χ_{b2}(3P)$ states of 10.5 MeV/$c^2$, the measured mass of the $χ_{b1}(3P)$ meson is $ m(χ_{b1}(3P))= 10515.7^{+2.2}_{-3.9}(stat) ^{+1.5}_{-2.1}(syst) MeV/c^2.$

hep-ex↗

arXiv2014

Measurement of the CKM angle γusing B^\pm --> D K^\pm with D-->K_Sπ^+π^-, K_SK^+K^- decays

A binned Dalitz plot analysis of $B^\pm \to D K^\pm$ decays, with $D \to K_S π^+π^-$ and $D \to K_S K^+ K^-$, is performed to measure the \CP-violating observables $x_{\pm}$ and $y_{\pm}$, which are sensitive to the Cabibbo-Kobayashi-Maskawa angle $γ$. The analysis exploits a sample of proton-proton collision data corresponding to 3.0\invfb collected by the LHCb experiment. Measurements from CLEO-c of the variation of the strong-interaction phase of the $D$ decay over the Dalitz plot are used as inputs. The values of the parameters are found to be $x_+ = (-7.7 \pm 2.4 \pm 1.0 \pm 0.4)\times 10^{-2}$, $x_- = (2.5 \pm 2.5 \pm 1.0 \pm 0.5) \times 10^{-2}$, $y_+ = (-2.2 \pm 2.5 \pm 0.4 \pm 1.0)\times 10^{-2}$, and $y_- = (7.5 \pm 2.9 \pm 0.5 \pm 1.4) \times 10^{-2}$. The first, second, and third uncertainties are the statistical, the experimental systematic, and that associated with the precision of the strong-phase parameters. These are the most precise measurements of these observables and correspond to $γ= (62^{\,+15}_{\,-14})^\circ$, with a second solution at $γ\to γ+ 180^\circ$, and $r_B = 0.080^{+ 0.019}_{-0.021}$, where $r_B$ is the ratio between the suppressed and favoured $B$ decay amplitudes.

hep-ex↗

arXiv2014

Dalitz plot analysis of $B_s^0 \rightarrow \bar{D}^0 K^- π^+$ decays

The resonant substructure of $B_s^0 \rightarrow \bar{D}^0 K^- π^+$ decays is studied with the Dalitz plot analysis technique. The study is based on a data sample corresponding to an integrated luminosity of $3.0\,{\rm fb}^{-1}$ of $pp$ collision data recorded by LHCb. A structure at $m(\bar{D}^0 K^-) \approx 2.86 {\rm GeV}/c^2$ is found to be an admixture of spin-1 and spin-3 resonances. The masses and widths of these states and of the $D^*_{s2}(2573)^-$ meson are measured, as are the complex amplitudes and fit fractions for all the $\bar{D}^0 K^-$ and $K^-π^+$ components included in the amplitude model. In addition, the $D^*_{s2}(2573)^-$ resonance is confirmed to be spin-2.

hep-ex↗

arXiv2014

Observation of overlapping spin-1 and spin-3 $\bar{D}^0 K^-$ resonances at mass $2.86 {\rm GeV}/c^2$

The resonant substructure of $B_s^0 \rightarrow \bar{D}^0 K^- π^+$ decays is studied using a data sample corresponding to an integrated luminosity of $3.0\,{\rm fb}^{-1}$ of $pp$ collision data recorded by the LHCb detector. An excess at $m(\bar{D}^0 K^-) \approx 2.86 {\rm GeV}/c^2$ is found to be an admixture of spin-1 and spin-3 resonances. Therefore the $D^*_{sJ}(2860)^-$ state previously observed in inclusive $e^+e^- \rightarrow \bar{D}^0 K^- X$ and $pp \rightarrow \bar{D}^0 K^- X$ processes consists of at least two particles. This is the first observation of a heavy flavoured spin-3 resonance, and the first time that any spin-3 particle has been seen to be produced in $B$ decays. The masses and widths of the new states and of the $D^*_{s2}(2573)^-$ meson are measured, giving the most precise determinations to date.

hep-ex↗

arXiv2014

Search for $CP$ violation using $T$-odd correlations in $D^0 \to K^+K^-π^+π^-$ decays

A search for $CP$ violation using $T$-odd correlations is performed using the four-body $D^0 \to K^+K^-π^+π^-$ decay, selected from semileptonic $B$ decays. The data sample corresponds to integrated luminosities of $1.0\,\text{fb}^{-1}$ and $2.0\,\text{fb}^{-1}$ recorded at the centre-of-mass energies of 7 TeV and 8 TeV, respectively. The $CP$-violating asymmetry $a_{CP}^{T\text{-odd}}$ is measured to be $(0.18\pm 0.29\text{(stat)}\pm 0.04\text{(syst)})\%$. Searches for $CP$ violation in different regions of phase space of the four-body decay, and as a function of the $D^0$ decay time, are also presented. No significant deviation from the $CP$ conservation hypothesis is found.

hep-ex↗

arXiv2014

Study of $Υ$ production and cold nuclear matter effects in pPb collisions at $\sqrt{s_{NN}}=5~\mathrm{TeV}$

Production of $Υ$ mesons in proton-lead collisions at a nucleon-nucleon centre-of-mass energy $\sqrt{s_{NN}}=5 \mathrm{TeV}$ is studied with the LHCb detector. The analysis is based on a data sample corresponding to an integrated luminosity of $1.6 \mathrm{nb}^{-1}$. The $Υ$ mesons of transverse momenta up to $15 \mathrm{GeV}/c$ are reconstructed in the dimuon decay mode. The rapidity coverage in the centre-of-mass system is $1.5<y<4.0$ (forward region) and $-5.0<y<-2.5$ (backward region). The forward-backward production ratio and the nuclear modification factor for $Υ(1S)$ mesons are determined. The data are compatible with the predictions for a suppression of $Υ(1S)$ production with respect to proton-proton collisions in the forward region, and an enhancement in the backward region. The suppression is found to be smaller than in the case of prompt $J/ψ$ mesons.

nucl-ex↗

arXiv2014

First observations of the rare decays $B^+-> K^+π^+π^-μ^+μ^-$ and $B^+->ϕK^+μ^+μ^-$

First observations of the rare decays $B^+\rightarrow K^+π^+π^-μ^+μ^-$ and $B^+\rightarrow ϕK^+μ^+μ^-$ are presented using data corresponding to an integrated luminosity of $3.0\,{fb}^{-1}$, collected by the LHCb experiment at centre-of-mass energies of $7$ and $8\mathrm{\,TeV}$. The branching fractions of the decays are \begin{eqnarray*} \mathcal{B}(B^+\rightarrow K^+π^+π^-μ^+μ^-) &=& (4.36\,^{+0.29}_{-0.27}\,\mathrm{(stat)}\pm 0.21\,\mathrm{(syst)}\pm0.18\,\mathrm{(norm)})\times10^{-7},\\ \mathcal{B}(B^+\rightarrowϕK^+μ^+μ^-) &=& (0.82 \,^{+0.19}_{-0.17}\,\mathrm{(stat)}\,^{+0.10}_{-0.04}\,\mathrm{(syst)}\pm0.27\,\mathrm{(norm)}) \times10^{-7},\end{eqnarray*} where the uncertainties are statistical, systematic, and due to the uncertainty on the branching fractions of the normalisation modes. A measurement of the differential branching fraction in bins of the invariant mass squared of the dimuon system is also presented for the decay $B^+\rightarrow K^+π^+π^-μ^{+}μ^{-}$.

hep-ex↗

arXiv2014

Observation of $Z$ production in proton-lead collisions at LHCb

The first observation of $Z$ boson production in proton-lead collisions at a centre-of-mass energy per proton-nucleon pair of $\sqrt{s_{NN}}=5~\text{TeV}$ is presented. The data sample corresponds to an integrated luminosity of $1.6~\text{nb}^{-1}$ collected with the LHCb detector. The $Z$ candidates are reconstructed from pairs of oppositely charged muons with pseudorapidities between 2.0 and 4.5 and transverse momenta above $20~\text{GeV}/c$. The invariant dimuon mass is restricted to the range $60-120~\text{GeV}/c^2$. The $Z$ production cross-section is measured to be \begin{eqnarray*} σ_{Z\toμ^+μ^-}(\text{fwd})&=&13.5^{+5.4}_{-4.0}\text{(stat.)}\pm1.2\text{(syst.)}~\text{nb} \end{eqnarray*} in the direction of the proton beam and \begin{eqnarray*} σ_{Z\toμ^+μ^-}(\text{bwd}) & =&10.7^{+8.4}_{-5.1}\text{(stat.)}\pm1.0\text{(syst.)}~\text{nb} \end{eqnarray*} in the direction of the lead beam, where the first uncertainty is statistical and the second systematic.

hep-ex↗

arXiv2014

Measurement of $CP$ violation and constraints on the CKM angle $γ$ in $B^{\pm}\rightarrow D K^{\pm}$ with $D \rightarrow K_S^0 π^+ π^-$ decays

A model-dependent amplitude analysis of $B^{\pm} \rightarrow D K^{\pm}$ with $D \rightarrow K_S^0 π^+ π^-$ decays is performed using proton-proton collision data, corresponding to an integrated luminosity of $1$ fb$^{-1}$, recorded by LHCb at a centre-of-mass energy of $7$ TeV in $2011$. Values of the $CP$ violation observables $x_{\pm}$ and $y_{\pm}$, which are sensitive to the CKM angle $γ$, are measured to be \begin{align*} x_- &= +0.027 \pm 0.044 ^{+0.010}_{-0.008} \pm 0.001, \\ y_- &= +0.013 \pm 0.048 ^{+0.009}_{-0.007} \pm 0.003, \\ x_+ &= -0.084 \pm 0.045 \pm 0.009 \pm 0.005, \\ y_+ &= -0.032 \pm 0.048 ^{+0.010}_{-0.009} \pm 0.008, \end{align*} where the first uncertainty is statistical, the second systematic and the third arises from the uncertainty of the $D \rightarrow K_S^0 π^+ π^-$ amplitude model. The value of $γ$ is determined to be $(84^{+49}_{-42})^\circ$, including all sources of uncertainty. Neutral $D$ meson mixing is found to have negligible effect.

hep-ex↗

arXiv2014

Measurement of $C\!P$ asymmetries in the decays $B^0 \rightarrow K^{*0} μ^+ μ^-$ and $B^+ \rightarrow K^{+} μ^+ μ^-$

The direct $C\!P$ asymmetries of the decays $B^0 \rightarrow K^{*0} μ^+ μ^-$ and $B^+ \rightarrow K^{+} μ^+ μ^-$ are measured using $pp$ collision data corresponding to an integrated luminosity of 3.0$\mbox{fb}^{-1}$ collected with the LHCb detector. The respective control modes $B^0 \rightarrow J/ψK^{*0}$ and $B^+ \rightarrow J/ψK^{+}$ are used to account for detection and production asymmetries. The measurements are made in several intervals of $μ^+ μ^-$ invariant mass squared, with the $ϕ(1020)$ and charmonium resonance regions excluded. Under the hypothesis of zero $C\!P$ asymmetry in the control modes, the average values of the asymmetries are \begin{align} {\cal A}_{C\!P}(B^0 \rightarrow K^{*0} μ^+ μ^-) &= -0.035 \pm 0.024 \pm 0.003, \cr {\cal A}_{C\!P}(B^+ \rightarrow K^{+} μ^+ μ^-) &= \phantom{-}0.012 \pm 0.017 \pm 0.001, \end{align} where the first uncertainties are statistical and the second are due to systematic effects. Both measurements are consistent with the Standard Model prediction of small $C\!P$ asymmetry in these decays.

hep-ex↗

arXiv2014

Measurement of CP violation in $B_s^0 \to ϕϕ$ decays

A measurement of the decay time dependent CP-violating asymmetry in $B_s^0 \to ϕϕ$ decays is presented, along with measurements of the $T$-odd triple-product asymmetries. In this decay channel, the CP-violating weak phase arises from the interference between $B_s^0$-$\bar{B}_s^0$ mixing and the loop-induced decay amplitude. Using a sample of proton-proton collision data corresponding to an integrated luminosity of $3.0\, fb^{-1}$ collected with the LHCb detector, a signal yield of approximately 4000 $B_s^0 \to ϕϕ$ decays is obtained. The CP-violating phase is measured to be ${ϕ_s =-0.17\pm0.15\mathrm{\,(stat)}\pm0.03\mathrm{\,(syst)}}$ rad. The triple-product asymmetries are measured to be ${A_U=-0.003\pm0.017\mathrm{\,(stat)}\pm0.006\mathrm{\,(syst)}}$ and ${A_V=-0.017\pm0.017\mathrm{\,(stat)}\pm0.006\mathrm{\,(syst)}}$. Results are consistent with the hypothesis of CP conservation.

hep-ex↗

arXiv2014

Observation of charmonium pairs produced exclusively in $pp$ collisions

A search is performed for the central exclusive production of pairs of charmonia produced in proton-proton collisions. Using data corresponding to an integrated luminosity of $3{\rm\ fb}^{-1}$ collected at centre-of-mass energies of 7 and 8 TeV, $J/ψJ/ψ$ and $J/ψψ(2S)$ pairs are observed, which have been produced in the absence of any other activity inside the LHCb acceptance that is sensitive to charged particles in the pseudorapidity ranges $(-3.5,-1.5)$ and $(1.5,5.0)$. Searches are also performed for pairs of P-wave charmonia and limits are set on their production. The cross-sections for these processes, where the dimeson system has a rapidity between 2.0 and 4.5, are measured to be $$ \begin{array}{rl} σ^{J/ψJ/ψ} &= 58\pm10{(\rm stat)} \pm 6{(\rm syst)} {\rm\ pb} , \\ σ^{J/ψψ(2S)} &= 63 ^{+27}_{-18}{(\rm stat)}\pm 10{(\rm syst)} {\rm\ pb} , \\ σ^{ψ(2S)ψ(2S)} &< 237 {\rm\ pb}, \\ σ^{χ_{c0}χ_{c0}} &< 69 {\rm\ nb}, \\ σ^{χ_{c1}χ_{c1}} &< 45 {\rm\ pb}, \\ σ^{χ_{c2}χ_{c2}} &< 141 {\rm\ pb}, \\ \end{array} $$ where the upper limits are set at the 90% confidence level. The measured $J/ψJ/ψ$ and $J/ψψ(2S)$ cross-sections are consistent with theoretical expectations.

hep-ex↗

arXiv2014

Study of the kinematic dependences of $Λ_b^0$ production in $pp$ collisions and a measurement of the $Λ_b^0 \rightarrow Λ_c^+ π^-$ branching fraction

The kinematic dependences of the relative production rates, $f_{Λ_b^0}/f_d$, of $Λ_b^0$ baryons and $\bar{B}^0$ mesons are measured using $Λ_b^0 \rightarrow Λ_c^+ π^-$ and $\bar{B}^0 \rightarrow D^+ π^-$ decays. The measurements use proton-proton collision data, corresponding to an integrated luminosity of 1 fb$^{-1}$ at a centre-of-mass energy of 7 TeV, recorded in the forward region with the LHCb experiment. The relative production rates are observed to depend on the transverse momentum, $p_T$, and pseudorapidity, $η$, of the beauty hadron, in the studied kinematic region $1.5 < p_T < 40$ GeV/$c$ and $2 < η< 5$. Using a previous LHCb measurement of $f_{Λ_b^0}/f_d$ in semileptonic decays, the branching fraction $\mathcal{B}(Λ_b^0 \rightarrow Λ_c^+ π^-) = \Big( 4.30 \pm 0.03 \,\, ^{+0.12}_{-0.11} \pm 0.26 \pm 0.21 \Big) \times 10^{-3}$ is obtained, where the first uncertainty is statistical, the second is systematic, the third is from the previous LHCb measurement of $f_{Λ_b^0}/f_d$ and the fourth is due to the $\bar{B}^0 \rightarrow D^+ π^-$ branching fraction. This is the most precise measurement of a $Λ_b^0$ branching fraction to date.

hep-ex↗

arXiv2014

First measurement of the charge asymmetry in beauty-quark pair production at a hadron collider

The difference in the angular distributions between beauty quarks and antiquarks, referred to as the charge asymmetry, is measured for the first time in $b\bar{b}$ pair production at a hadron collider. The data used correspond to an integrated luminosity of 1.0fb$^{-1}$ collected at 7TeV center-of-mass energy in proton-proton collisions with the LHCb detector. The measurement is performed in three regions of the invariant mass of the $b\bar{b}$ system. The results obtained are: \begin{eqnarray} A_{C}^{b\bar{b}}(40 < M_{b\bar{b}} < 75\,\rm{GeV/c^2}) &=& 0.4 \pm 0.4(\rm{stat}) \pm 0.3(\rm{syst})\%\newline A_{C}^{b\bar{b}}(75 < M_{b\bar{b}} < 105\,\rm{GeV/c^2}) &=& 2.0 \pm 0.9(\rm{stat}) \pm 0.6(\rm{syst})\%\newline A_{C}^{b\bar{b}}(M_{b\bar{b}} > 105\,\rm{GeV/c^2}) &=&1.6 \pm 1.7(\rm{stat}) \pm 0.6(\rm{syst})\% \end{eqnarray} where $A_{C}^{b\bar{b}}$ is defined as the asymmetry in the difference in rapidity between jets formed from the beauty quark and antiquark. The beauty jets are required to satisfy $2<η<4$, $E_{\rm T} > 20$GeV, and have an opening angle in the transverse plane $Δϕ>2.6$rad. These measurements are consistent with the predictions of the Standard Model.

hep-ex↗

arXiv2014

Effective lifetime measurements in the $B_{s}^{0} \rightarrow K^{+}K^{-}$, $B^{0} \rightarrow K^{+}π^{-}$ and $B_{s}^{0} \rightarrow π^{+}K^{-}$ decays

Measurements of the effective lifetimes in the $B_{s}^{0} \rightarrow K^{+}K^{-}$, $B^{0} \rightarrow K^{+}π^{-}$ and $B_{s}^{0} \rightarrow π^{+}K^{-}$ decays are presented using $1.0~\mathrm{fb^{-1}}$ of $pp$ collision data collected at a centre-of-mass energy of 7 TeV by the LHCb experiment. The analysis uses a data-driven approach to correct for the decay time acceptance. The measured effective lifetimes are $τ_{B_{s}^{0} \rightarrow K^{+}K^{-}}$ = $1.407~\pm~0.016~\pm~0.007~\mathrm{ps}$, $τ_{B^{0} \rightarrow K^{+}π^{-}}$ = $1.524~\pm~0.011~\pm~0.004~\mathrm{ps}$, $τ_{B_{s}^{0} \rightarrow π^{+}K^{-}}$ = $1.60~\pm~0.06~\pm~0.01~\mathrm{ps}$. This is the most precise determination to date of the effective lifetime in the $B_{s}^{0} \rightarrow K^{+}K^{-}$ decay and provides constraints on contributions from physics beyond the Standard Model to the $B_{s}^{0}$ mixing phase and the width difference $ΔΓ_{s}$.

hep-ex↗

arXiv2014

Observation of the $B^{0}_{s}\rightarrow J/ψK_{\rm S}^{0} K^{\pm} π^{\mp}$ decay

Decays of the form $B^{0}_{(s)}\rightarrow J/ψK_{\rm S}^{0} h^+ h^{\left(\prime\right) -}$ ($h^{(\prime)} = K, π$) are searched for in proton-proton collision data corresponding to an integrated luminosity of $1.0 \, {\rm fb}^{-1}$ recorded with the LHCb detector. The first observation of the $B^{0}_{s}\rightarrow J/ψK_{\rm S}^{0} K^{\pm} π^{\mp}$ decay is reported, with significance in excess of 10 standard deviations. The $B^{0}\rightarrow J/ψK_{\rm S}^{0} K^{+} K^{-}$ decay is also observed for the first time. The branching fraction of $B^{0}\rightarrow J/ψK_{\rm S}^{0} π^{+} π^{-}$ is determined, to significantly better precision than previous measurements, using $B^0 \rightarrow J/ψK_{\rm S}^{0}$ as a normalisation channel. Branching fractions and upper limits of the other $B^{0}_{(s)}\rightarrow J/ψK_{\rm S}^{0} h^+ h^{\left(\prime\right) -}$ modes are determined relative to that of the $B^{0}\rightarrow J/ψK_{\rm S}^{0} π^{+} π^{-}$ decay.

hep-ex↗

arXiv2014

Measurement of the $Ξ_b^-$ and $Ω_b^-$ baryon lifetimes

Using a data sample of pp collisions corresponding to an integrated luminosity of $3~ \rm fb^{-1}$, the $Ξ_b^-$ and $Ω_b^-$ baryons are reconstructed in the $Ξ_b^- \rightarrow J/ψΞ^-$ and $Ω_b^- \rightarrow J/ψΩ^-$ decay modes and their lifetimes measured to be $τ(Ξ_b^-) = 1.55\, ^{+0.10}_{-0.09}~{\rm(stat)} \pm 0.03\,{\rm(syst)}$ ps, $τ(Ω_b^-) = 1.54\, ^{+0.26}_{-0.21}~{\rm(stat)} \pm 0.05\,{\rm(syst)}$ ps. These are the most precise determinations to date. Both measurements are in good agreement with previous experimental results and with theoretical predictions.

hep-ex↗