arXiv subjects

M. Baszczyk

Publications and source records attributed to M. Baszczyk.

At least 55 records · Page 3Linked to original sources

arXiv2017

Measurement of matter-antimatter differences in beauty baryon decays

Differences in the behaviour of matter and antimatter have been observed in $K$ and $B$ meson decays, but not yet in any baryon decay. Such differences are associated with the non-invariance of fundamental interactions under the combined charge-conjugation and parity transformations, known as $C\!P$ violation. Using data from the LHCb experiment at the Large Hadron Collider, a search is made for $C\!P$-violating asymmetries in the decay angle distributions of $Λ^0_b$ baryons decaying to $pπ^-π^+π^-$ and $pπ^-K^+K^-$ final states. These four-body hadronic decays are a promising place to search for sources of $C\!P$ violation both within and beyond the Standard Model of particle physics. We find evidence for $C\!P$ violation in $Λ^0_b$ to $pπ^-π^+π^-$ decays with a statistical significance corresponding to 3.3 standard deviations including systematic uncertainties. This represents the first evidence for $C\!P$ violation in the baryon sector.

hep-ex↗

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.

hep-ex↗

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.

hep-ex↗

arXiv2017

Measurement of the $J/ψ$ pair production cross-section in $pp$ collisions at $\sqrt{s} = 13 \,{\mathrm{TeV}}$

The production cross-section of $J/ψ$ pairs is measured using a data sample of $pp$ collisions collected by the LHCb experiment at a centre-of-mass energy of $\sqrt{s} = 13 \,{\mathrm{TeV}}$, corresponding to an integrated luminosity of $279 \pm 11 \,{\mathrm{pb^{-1}}}$. The measurement is performed for $J/ψ$ mesons with a transverse momentum of less than $10 \,{\mathrm{GeV}}/c$ in the rapidity range $2.0<y<4.5$. The production cross-section is measured to be $15.2 \pm 1.0 \pm 0.9 \,{\mathrm{nb}}$. The first uncertainty is statistical, and the second is systematic. The differential cross-sections as functions of several kinematic variables of the $J/ψ$ pair are measured and compared to theoretical predictions.

hep-ex↗

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.

hep-ex↗

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 $B(η_c(1S)\toϕϕ)/B(η_c(1S)\to p\bar{p})=1.79\pm0.14\pm0.32$.

hep-ex↗

arXiv2017

Measurements of $π^\pm$, K$^\pm$, p and $\bar{\textrm{p}}$ spectra in proton-proton interactions at 20, 31, 40, 80 and 158 GeV/c with the NA61/SHINE spectrometer at the CERN SPS

Measurements of inclusive spectra and mean multiplicities of $π^\pm$, K$^\pm$, p and $\bar{\textrm{p}}$ produced in inelastic p+p interactions at incident projectile momenta of 20, 31, 40, 80 and 158 GeV/c ($\sqrt{s} = $ 6.3, 7.7, 8.8, 12.3 and 17.3 GeV, respectively) were performed at the CERN Super Proton Synchrotron using the large acceptance NA61/SHINE hadron spectrometer. Spectra are presented as function of rapidity and transverse momentum and are compared to predictions of current models. The measurements serve as the baseline in the NA61/SHINE study of the properties of the onset of deconfinement and search for the critical point of strongly interacting matter.

nucl-ex↗

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.

hep-ex↗

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 $f_s/f_d$.

hep-ex↗

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.

hep-ex↗

arXiv2017

Observation of the suppressed decay $Λ^{0}_{b}\rightarrow pπ^{-}μ^{+}μ^{-}$

The suppressed decay $Λ^{0}_{b}\rightarrow pπ^{-}μ^{+}μ^{-}$, excluding the $J/ψ$ and $ψ(2S)\rightarrow μ^{+}μ^{-}$ resonances, is observed for the first time with a significance of 5.5 standard deviations. The analysis is performed with proton-proton collision data corresponding to an integrated luminosity of $3\mathrm{fb}^{-1}$ collected with the LHCb experiment. The $Λ^{0}_{b}\rightarrow pπ^{-}μ^{+}μ^{-}$ branching fraction is measured relative to the $Λ^{0}_{b}\rightarrow J/ψ(\rightarrow μ^{+}μ^{-})pπ^{-}$ branching fraction giving \begin{align} \nonumber \frac{\mathcal{B}(Λ^{0}_{b}\rightarrow pπ^{-}μ^{+}μ^{-})}{\mathcal{B}({Λ^{0}_{b}\rightarrow J/ψ(\rightarrow μ^{+}μ^{-})pπ^{-}})} &= 0.044\pm0.012\pm0.007, \end{align} where the first uncertainty is statistical and the second is systematic. This is the first observation of a $b\rightarrow d$ transition in a baryonic decay.

hep-ex↗

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.

hep-ex↗

arXiv2017

Search for long-lived scalar particles in $B^+ \to K^+ χ(μ^+μ^-)$ decays

A search for a long-lived scalar particle $χ$ is performed, looking for the decay ${B^+ \to K^+ χ}$ with ${χ\to μ^+μ^-}$ in $pp$ collision data corresponding to an integrated luminosity of $3\, {\rm fb}^{-1}$, collected by the LHCb experiment at centre-of-mass energies of $\sqrt{s}=7$ and 8$\,$TeV. This new scalar particle, predicted by Hidden Sector models, is assumed to have a narrow width. The signal would manifest itself as an excess in the dimuon invariant mass distribution over the Standard Model background. No significant excess is observed in the accessible ranges of mass ${250 < m(χ) < 4700\,\rm MeV/c^2}$ and lifetime ${0.1 < τ(χ) < 1000\,\rm ps}$. Upper limits on the branching fraction $\mathcal{B}(B^+ \to K^+ χ(μ^+μ^-))$ at 95% confidence level are set as a function of $m(χ)$ and $τ(χ)$, varying between $2\times10^{-10}$ and $10^{-7}$. These are the most stringent limits to date. The limits are interpreted in the context of a model with a light inflaton particle.

hep-ex↗

arXiv2017

Observation of the decays $Λ_b^0 \to χ_{c1} p K^-$ and $Λ_b^0 \to χ_{c2} p K^-$

The first observation of the decays $Λ_b^0 \to χ_{c1} p K^-$ and $Λ_b^0 \to χ_{c2} p K^-$ is reported using a data sample corresponding to an integrated luminosity of $3.0$ fb$^{-1}$, collected by the LHCb experiment in $pp$ collisions at centre-of-mass energies of 7 and 8 TeV. The following ratios of branching fractions are measured \begin{eqnarray*} \frac{{\cal B}(Λ_b^0 \to χ_{c1} p K^-)}{{\cal B}(Λ_b^0 \to J/ψp K^-)} = 0.242 \pm 0.014 \pm 0.013 \pm 0.009, \frac{{\cal B}(Λ_b^0 \to χ_{c2} p K^-)}{{\cal B}(Λ_b^0 \to J/ψp K^-)} = 0.248 \pm 0.020 \pm 0.014 \pm 0.009, \frac{{\cal B}(Λ_b^0 \to χ_{c2} p K^-)}{{\cal B}(Λ_b^0 \to χ_{c1} p K^-)} = 1.02 \pm 0.10 \pm 0.02 \pm 0.05, \end{eqnarray*} where the first uncertainty is statistical, the second systematic and the third due to the uncertainty on the branching fractions of the $χ_{c1}\to J/ψγ$ and $χ_{c2} \to J/ψγ$ decays. Using both decay modes, the mass of the $Λ_b^0$ baryon is also measured to be $m_{Λ_b^0} = 5619.44 \pm 0.28 \pm 0.26$ MeV/$c^2$, where the first and second uncertainties are statistical and systematic, respectively.

hep-ex↗

arXiv2017

Measurement of the $C\!P$ violation parameter $A_Γ$ in $D^0 \to K^+K^-$ and $D^0 \to π^+π^-$ decays

Asymmetries in the time-dependent rates of $D^0 \to K^+K^-$ and $D^0 \to π^+π^-$ decays are measured in a $pp$ collision data sample collected with the LHCb detector during LHC Run 1, corresponding to an integrated luminosity of $3\,\mathrm{fb}^{-1}$. The asymmetries in effective decay widths between $D^0$ and $\overline{D}^0$ decays, sensitive to indirect $CP$ violation, are measured to be $A_Γ(K^+ K^-) = (-0.30 \pm 0.32 \pm 0.10)\times 10^{-3}$ and $A_Γ(π^+π^-) = (0.46 \pm 0.58 \pm 0.12)\times 10^{-3}$, where the first uncertainty is statistical and the second systematic. These measurements show no evidence for $C\!P$ violation and improve on the precision of the previous best measurements by nearly a factor of two.

hep-ex↗

arXiv2017

Evidence for the two-body charmless baryonic decay $B^+ \to p \barΛ$

A search for the rare two-body charmless baryonic decay $B^+ \to p \barΛ$ is performed with $pp$ collision data, corresponding to an integrated luminosity of $3\,\mbox{fb}^{-1}$, collected by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. An excess of $B^+ \to p \barΛ$ candidates with respect to background expectations is seen with a statistical significance of 4.1 standard deviations, and constitutes the first evidence for this decay. The branching fraction, measured using the $B^+ \to K^0_{\mathrm S} π^+$ decay for normalisation, is \begin{eqnarray} \mathcal{B}(B^+ \to p \barΛ) & = & ( 2.4 \,^{+1.0}_{-0.8} \pm 0.3 ) \times 10^{-7} \,, \nonumber \end{eqnarray} where the first uncertainty is statistical and the second systematic.

hep-ex↗

arXiv2017

Search for the $B^{0}_{s} \to η^{\prime}ϕ$ decay

A search for the charmless $B^{0}_{s} \to η^{\prime}ϕ$ decay is performed using $pp$ collision data collected by the LHCb experiment at centre-of-mass energies of $7$ and $8$ TeV, corresponding to an integrated luminosity of 3 fb$^{-1}$. No signal is observed and upper limits on the $B^{0}_{s} \to η^{\prime}ϕ$ branching fraction are set to $0.82\times 10^{-6}$ at $90\%$ and $1.01\times 10^{-6}$ at $95\%$ confidence level.

hep-ex↗

arXiv2017

Search for $CP$ violation in the phase space of $D^0\rightarrowπ^+π^-π^+π^-$ decays

A search for time-integrated $CP$ violation in the Cabibbo-suppressed decay $\mbox{$D^0\rightarrowπ^+π^-π^+π^-$}$ is performed using an unbinned, model-independent technique known as the energy test. This is the first application of the energy test in four-body decays. The search is performed for $P$-even $CP$ asymmetries and, for the first time, is extended to probe the $P$-odd case. Using proton-proton collision data corresponding to an integrated luminosity of 3.0 fb$^{-1}$ collected by the LHCb detector at centre-of-mass energies of $\sqrt{s}=$7 TeV and 8 TeV, the world's best sensitivity to $CP$ violation in this decay is obtained. The data are found to be consistent with the hypothesis of $CP$ symmetry with a $p$-value of $(4.6\pm0.5)\%$ in the $P$-even case, and marginally consistent with a $p$-value of $(0.6\pm0.2)\%$ in the $P$-odd case, corresponding to a significance for $CP$ non-conservation of 2.7 standard deviations.

hep-ex↗