arXiv subjects

S. Beranek

Publications and source records attributed to S. Beranek.

At least 145 records · Page 8Linked to original sources

arXiv2017

$χ_{c1}$ and $χ_{c2}$ resonance parameters with the decays $χ_{c1,c2}\to J/ψμ^+μ^-$

The decays $χ_{c1} \rightarrow J/ψμ^+ μ^-$ and $χ_{c2} \rightarrow J/ψμ^+ μ^-$ are observed and used to study the resonance parameters of the $χ_{c1}$ and $χ_{c2}$ mesons. The masses of these states are measured to be m(χ_{c1}) = 3510.71 \pm 0.04(stat) \pm 0.09(syst)MeV\,, m(χ_{c2}) = 3556.10 \pm 0.06(stat) \pm 0.11(syst)MeV\,, where the knowledge of the momentum scale for charged particles dominates the systematic uncertainty. The momentum-scale uncertainties largely cancel in the mass difference m(χ_{c2}) - m(χ_{c1}) = 45.39 \pm 0.07(stat) \pm 0.03(syst)MeV\,. The natural width of the $χ_{c2}$ meson is measured to be $$Γ(χ_{c2}) = 2.10 \pm 0.20(stat) \pm 0.02(syst)MeV\,.$$ These results are in good agreement with and have comparable precision to the current world averages.

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arXiv2017

Measurement of $CP$ observables in $B^\pm \to D^{()} K^\pm$ and $B^\pm \to D^{()} π^\pm$ decays

Measurements of $CP$ observables in $B^\pm \rightarrow D^{(*)} K^\pm$ and $B^\pm \rightarrow D^{(*)} π^\pm$ decays are presented, where $D^{(*)}$ indicates a neutral $D$ or $D^*$ meson that is an admixture of $D^{(*)0}$ and $\bar{D}^{(*)0}$ states. Decays of the $D^*$ meson to the $Dπ^0$ and $Dγ$ final states are partially reconstructed without inclusion of the neutral pion or photon, resulting in distinctive shapes in the $B$ candidate invariant mass distribution. Decays of the $D$ meson are fully reconstructed in the $K^\pm π^\mp$, $K^+ K^-$ and $π^+ π^-$ final states. The analysis uses a sample of charged $B$ mesons produced in $pp$ collisions collected by the LHCb experiment, corresponding to an integrated luminosity of 2.0, 1.0 and 2.0 fb$^{-1}$ taken at centre-of-mass energies of $\sqrt{s}$ = 7, 8 and 13 TeV, respectively. The study of $B^{\pm} \to D^{*} K^{\pm}$ and $B^{\pm} \to D^{*} π^{\pm}$ decays using a partial reconstruction method is the first of its kind, while the measurement of $B^{\pm} \to D K^{\pm}$ and $B^{\pm} \to D π^{\pm}$ decays is an update of previous LHCb measurements. The $B^{\pm} \to D K^{\pm}$ results are the most precise to date.

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arXiv2017

Measurement of the $B^{\pm}$ production cross-section in pp collisions at $\sqrt{s} =$ 7 and 13 TeV

The production of $B^{\pm}$ mesons is studied in $pp$ collisions at centre-of-mass energies of 7 and 13 TeV, using $B^{\pm}\rightarrow J/ψK^{\pm}$ decays and data samples corresponding to 1.0 fb$^{-1}$ and 0.3 fb$^{-1}$, respectively. The production cross-sections summed over both charges and integrated over the transverse momentum range $0<p_{\text{T}}< 40$ GeV/$c$ and the rapidity range $2.0<y<4.5$ are measured to be $σ(pp \rightarrow B^{\pm} X, \sqrt{s} = \text{7 TeV}) = 43.0 \pm 0.2 \pm 2.5 \pm 1.7μb,$ $σ(pp \rightarrow B^{\pm} X, \sqrt{s} = \text{13 TeV}) = 86.6 \pm 0.5 \pm 5.4 \pm 3.4μb,$ where the first uncertainties are statistical, the second are systematic, and the third are due to the limited knowledge of the $B^{\pm}\rightarrow J/ψK^{\pm}$ branching fraction. The ratio of the cross-section at 13 TeV to that at 7 TeV is determined to be $2.02\pm0.02\text{(stat)}\pm0.12\text{(syst)}$. Differential cross-sections are also reported as functions of $p_{\text{T}}$ and $y$. All results are in agreement with theoretical calculations based on the state-of-art fixed next-to-leading order quantum chromodynamics.

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arXiv2017

First observation of the rare purely baryonic decay $B^0 \to p \bar{p}$

The first observation of the decay of a $B^0$ meson to a purely baryonic final state, $B^0 \to p \bar{p}$, is reported. The proton-proton collision data sample used was collected with the LHCb experiment at center-of-mass energies of 7 and 8 TeV and corresponds to an integrated luminosity of 3.0 fb$^{-1}$. The branching fraction is determined to be $${\cal B}(B^0 \to p \bar{p}) = ( 1.25 \pm 0.27 \pm 0.18 ) \times 10^{-8} ,$$ where the first uncertainty is statistical and the second systematic. The decay mode $B^0 \to p \bar{p}$ is the rarest decay of the $B^0$ meson observed to date. The decay $B_s^0 \to p \bar{p}$ is also investigated. No signal is seen and the upper limit ${\cal B}(B_s^0 \to p \bar{p}) < 1.5 \times 10^{-8}$ at 90% confidence level is set on the branching fraction.

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arXiv2017

Updated search for long-lived particles decaying to jet pairs

A search is presented for long-lived particles with a mass between 25 and 50 GeV/$c^2$ and a lifetime between 2 and 500 ps, using proton-proton collision data corresponding to an integrated luminosity of 2.0 fb$^{-1}$, collected by the LHCb detector at centre-of-mass energies of 7 and 8 TeV. The particles are assumed to be pair-produced in the decay of a 125 GeV/$c^2$ Standard-Model-like Higgs boson. The experimental signature is a single long-lived particle, identified by a displaced vertex with two associated jets. No excess above background is observed and limits are set on the production cross-section as a function of the mass and lifetime of the long-lived particle.

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arXiv2017

Prompt and nonprompt J/$ψ$ production and nuclear modification in $p$Pb collisions at $\sqrt{s_{\text{NN}}}= 8.16$ TeV

The production of J/$ψ$ mesons is studied in proton-lead collisions at the centre-of-mass energy per nucleon pair $\sqrt{s_{\text{NN}}}=8.16$ TeV with the LHCb detector at the LHC. The double differential cross-sections of prompt and nonprompt J/$ψ$ production are measured as functions of the J/$ψ$ transverse momentum and rapidity in the nucleon-nucleon centre-of-mass frame. Forward-to-backward ratios and nuclear modification factors are determined. The results are compared with theoretical calculations based on collinear factorisation using nuclear parton distribution functions, on the colour glass condensate or on coherent energy loss models.

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arXiv2017

Updated branching fraction measurements of $B^0_{(s)} \to K_{\mathrm{\scriptscriptstyle S}}^0 h^+ h^{\prime -}$ decays

The charmless three-body decays $B^0_{(s)} \to K_{\mathrm{\scriptscriptstyle S}}^0 h^+ h^{\prime -}$ (where $h^{(\prime)} = π, K$) are analysed using a sample of $pp$ collision data recorded by the LHCb experiment, corresponding to an integrated luminosity of $3\mbox{fb}^{-1}$. The branching fractions are measured relative to that of the $B^0 \to K_{\mathrm{\scriptscriptstyle S}}^0 π^{+} π^{-}$ decay, and are determined to be: \begin{eqnarray*} \frac{{\cal B}(B^0\rightarrow K^0_{\rm S}K^{\pm}π^{\mp})}{{\cal B}(B^0\rightarrow K^0_{\rm S}π^{+}π^{-})} = {} & 0.123 \pm 0.009 \; \mathrm{\,(stat)}\; \pm 0.015 \; \mathrm{\,(syst)}\,, \frac{{\cal B}(B^0\rightarrow K^0_{\rm S}K^{+}K^{-})} {{\cal B}(B^0\rightarrow K^0_{\rm S}π^{+}π^{-})} = {} & 0.549 \pm 0.018 \; \mathrm{\,(stat)}\; \pm 0.033 \; \mathrm{\,(syst)}\,, \frac{{\cal B}(B_{s}^0\rightarrow K^0_{\rm S}π^{+}π^{-})}{{\cal B}(B^0\rightarrow K^0_{\rm S}π^{+}π^{-})} = {} & 0.191 \pm 0.027 \; \mathrm{\,(stat)}\; \pm 0.031 \; \mathrm{\,(syst)}\; \pm 0.011 \; (f_s/f_d) \,, \frac{{\cal B}(B_{s}^0\rightarrow K^0_{\rm S}K^{\pm}π^{\mp})} {{\cal B}(B^0\rightarrow K^0_{\rm S}π^{+}π^{-})} = {} & 1.70\phantom{0} \pm 0.07\phantom{0} \; \mathrm{\,(stat)} \; \pm 0.11\phantom{0} \; \mathrm{\,(syst)}\; \pm 0.10\phantom{0} \; (f_s/f_d) \,, \frac{{\cal B}(B_{s}^0\rightarrow K^0_{\rm S}K^{+}K^{-})}{{\cal B}(B^0\rightarrow K^0_{\rm S}π^{+}π^{-})} \in {} & [0.008 - 0.051] \rm ~at~90\%~confidence~level, \end{eqnarray*} where $f_s/f_d$ represents the ratio of hadronisation fractions of the $B^0_s$ and $B^0$ mesons.

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arXiv2017

Observation of $D^0$ meson decays to $π^+π^-μ^+μ^-$ and $K^+K^-μ^+μ^-$ final states

The first observation of the $D^0 \to π^+π^-μ^+μ^-$ and $D^0 \to K^+K^-μ^+μ^-$ decays is reported using a sample of proton-proton collisions collected by LHCb at a center-of-mass energy of 8$\,$TeV, and corresponding to 2$\,$fb$^{-1}$ of integrated luminosity. The corresponding branching fractions are measured using as normalization the decay $D^0 \to K^- π^+[μ^+μ^-]_{ρ^0/ω}$, where the two muons are consistent with coming from the decay of a $ρ^0$ or $ω$ meson. The results are $\mathcal{B}(D^0 \to π^+π^-μ^+μ^-)=(9.64\pm0.48\pm0.51\pm0.97)\times10^{-7}$ and $\mathcal{B}(D^0 \to K^+K^-μ^+μ^-)=( 1.54\pm0.27\pm0.09\pm0.16)\times10^{-7}$, where the uncertainties are statistical, systematic, and due to the limited knowledge of the normalization branching fraction. The dependence of the branching fraction on the dimuon mass is also investigated.

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arXiv2017

Search for baryon-number-violating $Ξ_b^0$ oscillations

A search for baryon-number-violating $Ξ_b^0$ oscillations is performed with a sample of $pp$ collision data recorded by the LHCb experiment, corresponding to an integrated luminosity of 3 fb$^{-1}$. The baryon number at the moment of production is identified by requiring that the $Ξ_b^0$ come from the decay of a resonance $Ξ_b^{*-} \to Ξ_b^0 π^-$ or $Ξ_b^{\prime-} \to Ξ_b^0 π^-$, and the baryon number at the moment of decay is identified from the final state using the decays $Ξ_b^0 \to Ξ_c^+ π^-, ~ Ξ_c^+ \to p K^- π^+$. No evidence of baryon number violation is found, and an upper limit at the 95% confidence level is set on the oscillation rate of $ω< 0.08$ ps$^{-1}$, where $ω$ is the associated angular frequency.

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arXiv2017

Improved limit on the branching fraction of the rare decay $K^0_{\scriptscriptstyle S}\toμ^+μ^-$

A search for the decay $K^0_{\scriptscriptstyle S}\toμ^+μ^-$ is performed, based on a data sample of proton-proton collisions corresponding to an integrated luminosity of 3 fb$^{-1}$, collected by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. The observed yield is consistent with the background-only hypothesis, yielding a limit on the branching fraction of ${\cal B}(K^0_{\scriptscriptstyle S}\toμ^+μ^-) < 0.8~(1.0) \times 10^{-9}$ at $90\%~(95\%)$ confidence level. This result improves the previous upper limit on the branching fraction by an order of magnitude.

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arXiv2017

Observation of the $B^+ \to D^{*-}K^+π^+$ decay

The $B^+ \to D^{*-}K^+π^+$ decay potentially provides an excellent way to investigate charm meson spectroscopy. The decay is searched for in a sample of proton-proton collision data collected with the LHCb detector at centre-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of $3~{\rm fb}^{-1}$. A clear signal is observed, and the ratio of its branching fraction to that of the $B^+ \to D^{*-}π^+π^+$ normalisation channel is measured to be \begin{equation*} \frac{\mathcal{B}(B^+ \to D^{*-}K^+π^+)}{\mathcal{B}(B^+ \to D^{*-}π^+π^+)} = \left( 6.39 \pm 0.27 \pm 0.48 \right) \times 10^{-2} \, , \end{equation*} where the first uncertainty is statistical and the second is systematic. This is the first observation of the $B^+ \to D^{*-}K^+π^+$ decay.

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arXiv2017

Observation of charmless baryonic decays $B^0_{(s)} \to p \overline{p} h^+ h^{\prime-}$

Decays of $B^0$ and $B_{s}^0$ mesons to the charmless baryonic final states $p \overline{p} h^+ h^{\prime-}$, where $h$ and $h^\prime$ each denote a kaon or a pion, are searched for using the LHCb detector. The analysis is based on a sample of proton-proton collision data collected at center-of-mass energies of $7$ and $8\,$TeV, corresponding to an integrated luminosity of $3\,$fb$^{-1}$. Four-body charmless baryonic $B_{s}^0$ decays are observed for the first time. The decays $B^0_{s}\to p \overline{p} K^+ K^-$, $B^0_{s}\to p \overline{p} K^\pm π^\mp$, $B^0\to p \overline{p} K^\pm π^\mp$ and $B^0\to p \overline{p} π^+π^-$ are observed with a significance greater than $5$ standard deviations; evidence at $4.1$ standard deviations is found for the $B^0\to p \overline{p} K^+ K^-$ decay and an upper limit is set on the branching fraction for $B^0_{s}\to p \overline{p} π^+ π^-$. Branching fractions in the kinematic region $m(p \overline{p})<2850\,$MeV$/c^2$ are measured relative to the $B^0 \to J/ψ(\to p \overline{p}) K^*(892)^0$ channel.

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arXiv2017

Study of charmonium production in $b$-hadron decays and first evidence for the decay $B_s^0 \rightarrow ϕϕϕ$

Using decays to $ϕ$-meson pairs, the inclusive production of charmonium states in $b$-hadron decays is studied with $pp$ collision data corresponding to an integrated luminosity of $3.0fb^{-1}$, collected by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. Denoting by $B_C\equiv B(b\to CX)\times B(C\toϕϕ)$ the inclusive branching fraction of a $b$ hadron to a charmonium state $C$ that decays into a pair of $ϕ$ mesons, ratios $R^{C1}_{C2}\equiv B_{C1}/B_{C2}$ are determined as $R^{χ_{c0}}_{η_c(1S)}=0.147\pm0.023\pm0.011$, $R^{χ_{c1}}_{η_c (1S)}=0.073\pm0.016\pm0.006$, $R^{χ_{c2}}_{η_c (1S)}=0.081\pm0.013\pm0.005$, $R^{χ_{c1}}_{χ_{c0}}=0.50\pm0.11\pm0.01$, $R^{χ_{c2}}_{χ_{c0}}=0.56\pm0.10\pm0.01$ and $R^{η_c (2S)}_{η_c(1S)}=0.040\pm0.011\pm0.004$. Here and below the first uncertainties are statistical and the second systematic. Upper limits at $90\%$ confidence level for the inclusive production of $X(3872)$, $X(3915)$ and $χ_{c2}(2P)$ states are obtained as $R^{X(3872)}_{χ_{c1}}<0.34$, $R^{X(3915)}_{χ_{c0}}<0.12$ and $R^{χ_{c2}(2P)}_{χ_{c2}}<0.16$. Differential cross-sections as a function of transverse momentum are measured for the $η_c(1S)$ and $χ_c$ states. The branching fraction of the decay $B_s^0\rightarrowϕϕϕ$ is measured for the first time, $B(B_s^0\toϕϕϕ)=(2.15\pm0.54\pm0.28\pm0.21_{B})\times 10^{-6}$. Here the third uncertainty is due to the branching fraction of the decay $B_s^0\toϕϕ$, which is used for normalization. No evidence for intermediate resonances is seen. A preferentially transverse $ϕ$ polarization is observed. The measurements allow the determination of the ratio of the branching fractions for the $η_c(1S)$ decays to $ϕϕ$ and $p\bar{p}$ as $B(η_c(1S)\toϕϕ)/B(η_c(1S)\to p\bar{p})=1.79\pm0.14\pm0.32$.

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arXiv2017

Measurement of $B^{0}_{s}$ and $D^{-}_{s}$ meson lifetimes

We report on a measurement of the flavor-specific $B^{0}_{s}$ lifetime and of the $D^{-}_{s}$ lifetime using proton-proton collisions at center-of-mass energies of 7 and 8 TeV, collected by the LHCb experiment and corresponding to 3.0 fb$^{-1}$ of integrated luminosity. Approximately 407 000 $B^{0}_{s} \rightarrow D^{(*)-}_{s} μ^{+}ν_μ$ decays are partially reconstructed in the $K^{+}K^{-}π^{-}μ^{+}$ final state. The $B^{0}_{s}$ and $D^{-}_{s}$ natural widths are determined using, as a reference, kinematically similar $B^{0} \rightarrow D^{(*)-}μ^{+}ν_μ$ decays reconstructed in the same final state. The resulting differences between widths of $B^{0}_{s}$ and $B^{0}$ mesons and of $D^{-}_{s}$ and $D^{-}$ mesons are $Δ_Γ(B) =-0.0115 \pm 0.0053 (stat) \pm 0.0041 (syst)$ ps$^{-1}$ and $Δ_Γ(D) = 1.0131 \pm 0.0117 (stat) \pm 0.0065 (syst)$ ps$^{-1}$, respectively. Combined with the known $B^{0}$ and $D^{-}$ lifetimes, these yield the flavor-specific $B^{0}_{s}$ lifetime, $τ^{\rm fs}_{B^{0}_{s}} = 1.547 \pm 0.013 (stat) \pm 0.010 (syst) \pm 0.004 (τ_{B})$ ps and the $D^{-}_{s}$ lifetime, $τ_{D^{-}_{s}} = 0.5064 \pm 0.0030 (stat) \pm 0.0017 (syst) \pm 0.0017 (τ_{D})$ ps The last uncertainties originate from the limited knowledge of the $B^0$ and $D^{-}$ lifetimes. The results improve upon current determinations.

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arXiv2017

Observation of the doubly charmed baryon $Ξ_{cc}^{++}$

A highly significant structure is observed in the $Λ_c^+K^-π^+π^+$ mass spectrum, where the $Λ_c^+$ baryon is reconstructed in the decay mode $pK^-π^+$. The structure is consistent with originating from a weakly decaying particle, identified as the doubly charmed baryon $Ξ_{cc}^{++}$. The difference between the masses of the $Ξ_{cc}^{++}$ and $Λ_c^+$ states is measured to be $1334.94 \pm 0.72 (\mathrm{stat}) \pm 0.27 (\mathrm{syst}~\mathrm{MeV}/c^2$, and the $Ξ_{cc}^{++}$ mass is then determined to be $3621.40 \pm 0.72 (\mathrm{stat}) \pm 0.27 (\mathrm{syst} \pm 0.14 \, (Λ_c^+)~\mathrm{MeV}/c^2$, where the last uncertainty is due to the limited knowledge of the $Λ_c^+$ mass. The state is observed in a sample of proton-proton collision data collected by the LHCb experiment at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 1.7 $\mathrm{fb}^{-1}$, and confirmed in an additional sample of data collected at 8 TeV.

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arXiv2017

First observation of a baryonic $B_s^0$ decay

We report the first observation of a baryonic $B_s^0$ decay, $B_s^0 \to p \kern 0.1em\overline{\kern -0.1emΛ} K^-$, using proton-proton collision data recorded by the LHCb experiment at center-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of $3.0\,\mathrm{fb}^{-1}$. The branching fraction is measured to be $ \mathcal{B}(B_s^0 \to p \kern 0.1em\overline{\kern -0.1emΛ} K^-) + \mathcal{B}(B_s^0 \to \bar{p} ΛK^+) = \left[5.46 \pm 0.61 \pm 0.57 \pm 0.50 (\mathcal{B}) \pm 0.32 (f_s/f_d)\right]\times 10^{-6}, $ where the first uncertainty is statistical and the second systematic, the third uncertainty accounts for the experimental uncertainty on the branching fraction of the $B^0 \to p \kern 0.1em\overline{\kern -0.1emΛ} π^-$ decay used for normalization, and the fourth uncertainty relates to the knowledge of the ratio of $b$-quark hadronization probabilities $f_s/f_d$.

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arXiv2017

Resonances and $CP$ violation in $B_s^0$ and $\overline{B}_s^0 \to J/ψK^+K^-$ decays in the mass region above the $ϕ(1020)$

The decays of $B_s^0$ and $\overline{B}_s^0$ mesons into the $J/ψK^+K^-$ final state are studied in the $K^+K^-$ mass region above the $ϕ(1020)$ meson in order to determine the resonant substructure and measure the $CP$-violating phase, $ϕ_s$, the decay width, $Γ_s$, and the width difference between light and heavy mass eigenstates, $ΔΓ_s$. A decay-time dependent amplitude analysis is employed. The data sample corresponds to an integrated luminosity of $3{\rm fb}^{-1}$ produced in 7 and 8 Tev $pp$ collisions at the LHC, collected by the LHCb experiment. The measurement determines $ϕ_s = 119\pm107\pm34 {\rm \, mrad}$. A combination with previous LHCb measurements using similar decays into the $J/ψπ^+π^-$ and $J/ψϕ(1020)$ final states gives $ϕ_s=1\pm37 {\rm \,mrad}$, consistent with the Standard Model prediction.

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arXiv2017

Test of lepton universality with $B^{0} \rightarrow K^{*0}\ell^{+}\ell^{-}$ decays

A test of lepton universality, performed by measuring the ratio of the branching fractions of the $B^{0} \rightarrow K^{*0}μ^{+}μ^{-}$ and $B^{0} \rightarrow K^{*0}e^{+}e^{-}$ decays, $R_{K^{*0}}$, is presented. The $K^{*0}$ meson is reconstructed in the final state $K^{+}π^{-}$, which is required to have an invariant mass within 100$\mathrm{\,MeV}c^2$ of the known $K^{*}(892)^{0}$ mass. The analysis is performed using proton-proton collision data, corresponding to an integrated luminosity of about 3$\mathrm{\,fb}^{-1}$, collected by the LHCb experiment at centre-of-mass energies of 7 and 8$\mathrm{\,TeV}$. The ratio is measured in two regions of the dilepton invariant mass squared, $q^{2}$, to be \begin{eqnarray*} R_{K^{*0}} = \begin{cases} 0.66~^{+~0.11}_{-~0.07}\mathrm{\,(stat)} \pm 0.03\mathrm{\,(syst)} & \textrm{for } 0.045 < q^{2} < 1.1~\mathrm{\,GeV^2}c^4 \, , \\ 0.69~^{+~0.11}_{-~0.07}\mathrm{\,(stat)} \pm 0.05\mathrm{\,(syst)} & \textrm{for } 1.1\phantom{00} < q^{2} < 6.0~\mathrm{\,GeV^2}c^4 \, . \end{cases} \end{eqnarray*} The corresponding 95.4\% confidence level intervals are $[0.52, 0.89]$ and $[0.53, 0.94]$. The results, which represent the most precise measurements of $R_{K^{*0}}$ to date, are compatible with the Standard Model expectations at the level of 2.1--2.3 and 2.4--2.5 standard deviations in the two $q^{2}$ regions, respectively.

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