arXiv subjects

D. Brett

Publications and source records attributed to D. Brett.

At least 91 records · Page 5Linked to original sources

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.

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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.

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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.

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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.

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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.

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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 $ΔΓ_{s}$.

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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.

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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.

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arXiv2014

First observation of a baryonic $B_c^+$ decay

A baryonic decay of the $B_c^+$ meson, $B_c^+\to J/ψp\overline{p}π^+$, is observed for the first time, with a significance of $7.3$ standard deviations, in $pp$ collision data collected with the LHCb detector and corresponding to an integrated luminosity of $3.0$ fb$^{-1}$ taken at center-of-mass energies of $7$ and $8$ $\mathrm{TeV}$. With the $B_c^+\to J/ψπ^+$ decay as normalization channel, the ratio of branching fractions is measured to be \begin{equation*} \frac{\mathcal{B}(B_c^+\to J/ψp\overline{p}π^+)}{\mathcal{B}(B_c^+\to J/ψπ^+)} = 0.143^{\,+\,0.039}_{\,-\,0.034}\,(\mathrm{stat})\pm0.013\,(\mathrm{syst}). \end{equation*} The mass of the $B_c^+$ meson is determined as $M(B_c^+)=6274.0\pm1.8\,(\mathrm{stat})\pm0.4\,(\mathrm{syst})\,\mathrm{MeV}/c^2$, using the $B_c^+\to J/ψp\overline{p}π^+$ channel.

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arXiv2014

Observation of the $Λ_b^0\rightarrow J/ψp π^-$ decay

The first observation of the Cabibbo-suppressed decay $Λ_b^0\rightarrow J/ψp π^-$ is reported using a data sample of proton-proton collisions at 7 and 8 TeV, corresponding to an integrated luminosity of 3 $\rm fb^{-1}$. A prominent signal is observed and the branching fraction relative to the decay mode $Λ_b^0\rightarrow J/ψp K^-$ is determined to be $$ \frac{{\cal B}(Λ_b^0\rightarrow J/ψp π^-)}{{\cal B}(Λ_b^0\rightarrow J/ψp K^-)}=0.0824\pm0.0025\:(\text{stat})\pm0.0042\:(\text{syst}). $$ A search for direct CP violation is performed. The difference in the CP asymmetries between these two decays is found to be $$ {\cal A}_{CP}(Λ_b^0\rightarrow J/ψp π^-)-{\cal A}_{CP}(Λ_b^0\rightarrow J/ψp K^-)=(+5.7\pm 2.4\:(\text{stat})\pm1.2\:(\text{syst}))\%, $$ which is compatible with CP symmetry at the $2.2σ$ level.

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arXiv2014

Study of $χ_{b}$ meson production in pp collisions at $\sqrt{s}=7$ and 8TeV and observation of the decay $χ_{b}\rightarrow Υ(3S) γ$

A study of $χ_{b}$ meson production at LHCb is performed on proton-proton collision data, corresponding to 3.0fb$^{-1}$ of integrated luminosity collected at centre-of-mass energies $\sqrt{s}=7$ and 8TeV. The fraction of $Υ(nS)$ mesons originating from $χ_{b}$ decays is measured as a function of the $Υ$ transverse momentum in the rapidity range $2.0 < y^Υ < 4.5$. The radiative transition of the $χ_{b}(3P)$ meson to $Υ(3S)$ is observed for the first time. The $χ_{b1}(3P)$ mass is determined to be $$m(χ_{b1}(3P)) = 10\,511.3 \pm 1.7 \pm 2.5 MeV/c^2,$$ where the first uncertainty is statistical and the second is systematic.

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arXiv2014

Measurement of the $B_s^0$ meson lifetime in $D_s^+π^-$ decays

We present a measurement of the ratio of the Bs meson lifetime, in the flavor-specific decay to $D_s^+π^-$, to that of the B0 meson. The pp collision data used correspond to an integrated luminosity of 1/fb, collected with the LHCb detector, at a center-of-mass energy of 7 TeV. Combining our measured value of 1.010 +/- 0.010 +/- 0.008 for this ratio with the known lifetime, we determine the flavor-specific Bs lifetime to be tau(Bs) = 1.535 +/- 0.015 +/- 0.014 ps, where the uncertainties are statistical and systematic, respectively. This is the most precise measurement to date, and is consistent with previous measurements and theoretical predictions.

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arXiv2014

Precision measurement of the mass and lifetime of the $Ξ_b^0$ baryon

Using a proton-proton collision data sample corresponding to an integrated luminosity of 3 fb$^{-1}$ collected by LHCb at center-of-mass energies of 7 and 8 TeV, about 3800 $Ξ_b^0\toΞ_c^+π^-$, $Ξ_c^+\to pK^-π^+$ signal decays are reconstructed. From this sample, the first measurement of the $Ξ_b^0$ baryon lifetime is made, relative to that of the $Λ_b^0$ baryon. The mass differences $M(Ξ_b^0)-M(Λ_b^0)$ and $M(Ξ_c^+)-M(Λ_c^+)$ are also measured with precision more than four times better than the current world averages. The resulting values are $\frac{τ_{Ξ_b^0}}{τ_{Λ_b^0}} = 1.006\pm0.018\pm0.010$, $M(Ξ_b^0) - M(Λ_b^0) = 172.44\pm0.39\pm0.17 MeV/c^2$, $M(Ξ_c^+) - M(Λ_c^+) = 181.51\pm0.14\pm0.10 MeV/c^2$, where the first uncertainty is statistical and the second is systematic. The relative rate of $Ξ_b^0$ to $Λ_b^0$ baryon production is measured to be $\frac{f_{Ξ_b^0}}{f_{Λ_b^0}}\frac{\cal{B}(Ξ_b^0\toΞ_c^+π^-)}{\cal{B}(Λ_b^0\toΛ_c^+π^-)}\frac{\cal{B}(Ξ_c^+\to pK^-π^+)}{\cal{B}(Λ_c^+\to pK^-π^+)} = (1.88\pm0.04\pm0.03)\times10^{-2}$, where the first factor is the ratio of fragmentation fractions, $b\toΞ_b^0$ relative to $b\toΛ_b^0$. Relative production rates as functions of transverse momentum and pseudorapidity are also presented.

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arXiv2014

Measurement of $CP$ asymmetry in $D^0 \rightarrow K^- K^+$ and $D^0 \rightarrow π^- π^+$ decays

Time-integrated $CP$ asymmetries in $D^0$ decays to the final states $K^- K^+$ and $π^- π^+$ are measured using proton-proton collisions corresponding to $3\mathrm{\,fb}^{-1}$ of integrated luminosity collected at centre-of-mass energies of $7\mathrm{\,Te\kern -0.1em V}$ and $8\mathrm{\,Te\kern -0.1em V}$. The $D^0$ mesons are produced in semileptonic $b$-hadron decays, where the charge of the accompanying muon is used to determine the initial flavour of the charm meson. The difference in $CP$ asymmetries between the two final states is measured to be \begin{align} ΔA_{CP} = A_{CP}(K^-K^+)-A_{CP}(π^-π^+) = (+0.14 \pm 0.16\mathrm{\,(stat)} \pm 0.08\mathrm{\,(syst)})\% \ . \nonumber \end{align} A measurement of $A_{CP}(K^-K^+)$ is obtained assuming negligible $CP$ violation in charm mixing and in Cabibbo-favoured $D$ decays. It is found to be \begin{align} A_{CP}(K^-K^+) = (-0.06 \pm 0.15\mathrm{\,(stat)} \pm 0.10\mathrm{\,(syst)}) \% \ ,\nonumber \end{align} where the correlation coefficient between $ΔA_{CP}$ and $A_{CP}(K^-K^+)$ is $ρ=0.28$. By combining these results, the $CP$ asymmetry in the $D^0\rightarrowπ^-π^+$ channel is $A_{CP}(π^-π^+)=(-0.20\pm0.19\mathrm{\,(stat)}\pm0.10\mathrm{\,(syst)})\%$.

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arXiv2014

Measurement of the ratio of $B_c^+$ branching fractions to $J/ψπ^+$ and $J/ψμ^+ν_μ$

The first measurement that relates semileptonic and hadronic decay rates of the $B_c^+$ meson is performed using proton-proton collision data corresponding to 1.0 fb$^{-1}$ of integrated luminosity collected with the LHCb detector. The measured value of the ratio of branching fractions, ${\cal B}(B_c^+ \to J/ψπ^+)/{\cal B}(B_c^+\to J/ψμ^+ν_μ)=0.0469 \pm 0.0028 (stat.) \pm 0.0046 (syst.)$, is at the lower end of available theoretical predictions.

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arXiv2014

Measurement of the resonant and CP components in $\overline{B}^0\rightarrow J/ψπ^+π^-$ decays

The resonant structure of the reaction $\overline{B}^0\rightarrow J/ψπ^+π^-$ is studied using data from 3 fb$^{-1}$ of integrated luminosity collected by the LHCb experiment, one-third at 7 Tev center-of-mass energy and the remainder at 8 Tev. The invariant mass of the $π^+π^-$ pair and three decay angular distributions are used to determine the fractions of the resonant and non-resonant components. Six interfering $π^+π^-$ states: $ρ(770)$, $f_0(500)$, $f_2(1270)$, $ρ(1450)$, $ω(782)$ and $ρ(1700)$ are required to give a good description of invariant mass spectra and decay angular distributions. The positive and negative CP fractions of each of the resonant final states are determined. The $f_0(980)$ meson is not seen and the upper limit on its presence, compared with the observed $f_0(500)$ rate, is inconsistent with a model of tetraquark substructure for these scalar mesons at the eight standard deviation level. In the $q\overline{q}$ model, the absolute value of the mixing angle between the $f_0(980)$ and the $f_0(500)$ scalar mesons is limited to be less than $17^{\circ}$ at 90% confidence level.

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arXiv2014

Test of lepton universality using $B^{+}\rightarrow K^{+}\ell^{+}\ell^{-}$ decays

A measurement of the ratio of the branching fractions of the $B^{+}\rightarrow K^{+}μ^{+}μ^{-}$ and $B^{+}\rightarrow K^{+}e^{+}e^{-}$ decays is presented using proton-proton collision data, corresponding to an integrated luminosity of 3.0 fb$^{-1}$, recorded with the LHCb experiment at center-of-mass energies of 7 and 8 $\mathrm{\,Te\kern -0.1em V}$. The value of the ratio of branching fractions for the dilepton invariant mass squared range $1<q^{2}<6\mathrm{\,Ge\kern -0.1em V^2\!/}c^4$ is measured to be $0.745^{+0.090}_{-0.074}\mathrm{\,(stat)}\,\pm0.036\mathrm{\,(syst)}$. This value is the most precise measurement of the ratio of branching fractions to date and is compatible with the SM prediction within $2.6$ standard deviations.

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arXiv2014

Differential branching fractions and isospin asymmetries of $B \to K^{(*)}μ^{+}μ^{-}$ decays

The isospin asymmetries of $B \to Kμ^+μ^-$ and $B \to K^{*}μ^+μ^-$ decays and the partial branching fractions of the $B^0 \to K^0μ^+μ^-$, $B^+ \to K^+μ^+μ^-$ and $B^+ \to K^{*+}μ^+μ^-$ decays are measured as functions of the dimuon mass squared, $q^2$. The data used correspond to an integrated luminosity of 3$~$fb$^{-1}$ from proton-proton collisions collected with the LHCb detector at centre-of-mass energies of 7$\,$TeV and 8$\,$TeV in 2011 and 2012, respectively. The isospin asymmetries are both consistent with the Standard Model expectations. The three measured branching fractions, while individually consistent, all favour lower values than their respective Standard Model predictions.

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