arXiv subjects

A. Birnkraut

Publications and source records attributed to A. Birnkraut.

At least 163 records · Page 9Linked to original sources

arXiv2017

Search for the decays $B_s^0\toτ^+τ^-$ and $B^0\toτ^+τ^-$

A search for the rare decays $B_s^0\toτ^+τ^-$ and $B^0\toτ^+τ^-$ is performed using proton--proton collision data collected with the LHCb detector. The data sample corresponds to an integrated luminosity of 3fb$^{-1}$ collected in 2011 and 2012. The $τ$ leptons are reconstructed through the decay $τ^-\toπ^-π^+π^-ν_τ$. Assuming no contribution from $B^0\toτ^+τ^-$ decays, an upper limit is set on the branching fraction $\mathcal{B}(B_s^0\toτ^+τ^-) < 6.8\times 10^{-3}$ at 95% confidence level. If instead no contribution from $B_s^0\toτ^+τ^-$ decays is assumed, the limit is $\mathcal{B}(B^0\toτ^+τ^-)< 2.1 \times 10^{-3}$ at 95% confidence level. These results correspond to the first direct limit on $\mathcal{B}(B_s^0\toτ^+τ^-)$ and the world's best limit on $\mathcal{B}(B^0\toτ^+τ^-)$.

hep-ex↗

arXiv2017

Observation of the $\varXi^{-}_{b}\to J/ψ\varLambda K^{-}$ decay

The observation of the decay $\varXi^{-}_{b}\to J/ψ\varLambda K^{-}$ is reported, using a data sample corresponding to an integrated luminosity of $3~\mathrm{fb}^{-1}$, collected by the LHCb detector in $pp$ collisions at centre-of-mass energies of $7$ and $8~\mathrm{TeV}$. The production rate of $\varXi_{b}^{-}$ baryons detected in the decay $\varXi_{b}^{-}\to J/ψ\varLambda K^{-}$ is measured relative to that of $\varLambda_{b}^{0}$ baryons using the decay $\varLambda_{b}^{0}\to J/ψ\varLambda$. Integrated over the $b$-baryon transverse momentum $p_{\rm T}<25~\mathrm{GeV/}c $ and rapidity $2.0<y<4.5$, the measured ratio is \begin{equation*} \frac{f_{\varXi_{b}^{-}}}{f_{\varLambda_{b}^{0}}}\frac{\mathcal{B}(\varXi_{b}^{-}\to J/ψ\varLambda K^{-})}{\mathcal{B}(\varLambda_{b}^{0}\to J/ψ\varLambda)}=(4.19\pm 0.29~(\mathrm{stat})\pm0.15~(\mathrm{syst}))\times 10^{-2}, \end{equation*}where $f_{\varXi_{b}^{-}}$ and $f_{\varLambda_{b}^{0}}$ are the fragmentation fractions of $b\to\varXi_{b}^{-}$ and $b\to\varLambda_{b}^{0}$ transitions, and $\mathcal{B}$ represents the branching fraction of the corresponding $b$-baryon decay. The mass difference between $\varXi_{b}^{-}$ and $\varLambda_{b}^{0}$ baryons is measured to be \begin{equation*} M(\varXi_{b}^{-})-M(\varLambda_{b}^{0})=177.08\pm0.47~(\mathrm{stat})\pm0.16~(\mathrm{syst} )~\mathrm{MeV/}c^{2}. \end{equation*}

hep-ex↗

arXiv2017

Study of prompt D$^0$ meson production in pPb collisions at $\sqrt{s}$=5 TeV

Production of prompt D$^0$ mesons is studied in proton-lead and lead-proton collisions recorded at the LHCb detector at the LHC. The data sample corresponds to an integrated luminosity of $1.58\pm0.02$ nb$^{-1}$ recorded at a nucleon-nucleon centre-of-mass energy of $\sqrt{s}=5$ TeV. Measurements of the differential cross-section, the forward-backward production ratio and the nuclear modification factor are reported using D$^0$ candidates with transverse momenta less than 10 GeV/c and rapidities in the ranges $1.5<y^*<4.0$ and $-5.0<y^*<-2.5$ in the nucleon-nucleon centre-of-mass system.

hep-ex↗

arXiv2017

Measurement of the $B^0_s\toμ^+μ^-$ branching fraction and effective lifetime and search for $B^0\toμ^+μ^-$ decays

A search for the rare decays $B^0_s\toμ^+μ^-$ and $B^0\toμ^+μ^-$ is performed at the LHCb experiment using data collected in $pp$ collisions corresponding to a total integrated luminosity of 4.4 fb$^{-1}$. An excess of $B^0_s\toμ^+μ^-$ decays is observed with a significance of 7.8 standard deviations, representing the first observation of this decay in a single experiment. The branching fraction is measured to be ${\cal B}(B^0_s\toμ^+μ^-)=\left(3.0\pm 0.6^{+0.3}_{-0.2}\right)\times 10^{-9}$, where the first uncertainty is statistical and the second systematic. The first measurement of the $B^0_s\toμ^+μ^-$ effective lifetime, $τ(B^0_s\toμ^+μ^-)=2.04\pm 0.44\pm 0.05$ ps, is reported. No significant excess of $B^0\toμ^+μ^-$ decays is found and a 95 % confidence level upper limit, ${\cal B}(B^0\toμ^+μ^-)<3.4\times 10^{-10}$, is determined. All results are in agreement with the Standard Model expectations.

hep-ex↗

arXiv2017

Measurement of $CP$ asymmetries in $D^{\pm}\rightarrow η^{\prime} π^{\pm}$ and $D_s^{\pm}\rightarrow η^{\prime} π^{\pm}$ decays

A search for $CP$ violation in $D^{\pm}\rightarrow η^{\prime} π^{\pm}$ and $D^{\pm}_{s}\rightarrow η^{\prime} π^{\pm}$ decays is performed using proton-proton collision data, corresponding to an integrated luminosity of $3$ fb$^{-1}$, recorded by the LHCb experiment at centre-of-mass energies of $7$ and $8$ TeV. The measured $CP$-violating charge asymmetries are $A_{CP}(D^{\pm} \rightarrow η^{\prime} π^{\pm})=(-0.61\pm 0.72 \pm 0.53 \pm 0.12)\%$ and $A_{CP}(D^{\pm}_{s}\rightarrow η^{\prime} π^{\pm})=(-0.82\pm 0.36 \pm 0.22 \pm 0.27)\%$, where the first uncertainties are statistical, the second systematic, and the third are the uncertainties on the $A_{CP}(D^{\pm} \rightarrow K^0_S π^{\pm})$ and $A_{CP}(D^{\pm}_{s}\rightarrow ϕπ^{\pm})$ measurements used for calibration. The results represent the most precise measurements of these asymmetries to date.

hep-ex↗

arXiv2017

Measurements of prompt charm production cross-sections in $pp$ collisions at $\sqrt{s} = 13\,\mathrm{TeV}$

Production cross-sections of prompt charm mesons are measured with the first data from $pp$ collisions at the LHC at a centre-of-mass energy of $13\,\mathrm{TeV}$. The data sample corresponds to an integrated luminosity of $4.98 \pm 0.19\,\mathrm{pb}^{-1}$ collected by the LHCb experiment. The production cross-sections of $D^{0}$, $D^{+}$, $D_{s}^{+}$, and $D^{*+}$ mesons are measured in bins of charm meson transverse momentum, $p_{\mathrm{T}}$, and rapidity, $y$, and cover the range $0 < p_{\mathrm{T}} < 15\,\mathrm{GeV}/c$ and $2.0 < y < 4.5$. The inclusive cross-sections for the four mesons, including charge conjugation, within the range of $1 < p_{\mathrm{T}} < 8\,\mathrm{GeV}/c$ are found to be \begin{equation} σ(pp \to D^{0} X) = 2072 \pm 2 \pm 124\,μ\mathrm{b}\\ σ(pp \to D^{+} X) = 834 \pm 2 \pm \phantom{1}78\,μ\mathrm{b}\\ σ(pp \to D_{s}^{+} X) = 353 \pm 9 \pm \phantom{1}76\,μ\mathrm{b}\\ σ(pp \to D^{*+} X) = 784 \pm 4 \pm \phantom{1}87\,μ\mathrm{b} \end{equation} where the uncertainties are due to statistical and systematic uncertainties, respectively.

hep-ex↗

arXiv2017

Measurement of the ratio of branching fractions $\mathcal{B}(B_{c}^{+} \to J/ψK^{+})/\mathcal{B}(B_{c}^{+} \to J/ψπ^{+})$

The ratio of branching fractions $R_{K/π} \equiv \mathcal{B}(B_{c}^{+} \to J/ψK^{+})/\mathcal{B}(B_{c}^{+} \to J/ψπ^{+})$ is measured with $pp$ collision data collected by the LHCb experiment at centre-of-mass energies of 7 TeV and 8 TeV, corresponding to an integrated luminosity of 3${\mbox{fb}^{-1}}$. It is found to be $ R_{K/π} = 0.079\pm0.007\pm0.003$, where the first uncertainty is statistical and the second is systematic. This measurement is consistent with the previous LHCb result, while the uncertainties are significantly reduced.

hep-ex↗

arXiv2017

Study of the $D^0 p$ amplitude in $Λ_b^0\to D^0 p π^-$ decays

An amplitude analysis of the decay $Λ_b^0\to D^0 p π^-$ is performed in the part of the phase space containing resonances in the $D^0 p$ channel. The study is based on a data sample corresponding to an integrated luminosity of 3.0 fb$^{-1}$ of $pp$ collisions recorded by the LHCb experiment. The spectrum of excited $Λ_c^+$ states that decay into $D^0 p$ is studied. The masses, widths and quantum numbers of the $Λ_c(2880)^+$ and $Λ_c(2940)^+$ resonances are measured. The constraints on the spin and parity for the $Λ_c(2940)^+$ state are obtained for the first time. A near-threshold enhancement in the $D^0 p$ amplitude is investigated and found to be consistent with a new resonance, denoted the $Λ_c(2860)^+$, of spin $3/2$ and positive parity.

hep-ex↗

arXiv2017

Measurements of prompt charm production cross-sections in $pp$ collisions at $\sqrt{s} = 5\,$TeV

Production cross-sections of prompt charm mesons are measured using data from $pp$ collisions at the LHC at a centre-of-mass energy of $5\,$TeV. The data sample corresponds to an integrated luminosity of $8.60\pm0.33\,$pb$^{-1}$ collected by the LHCb experiment. The production cross-sections of $D^0$, $D^+$, $D_s^+$, and $D^{*+}$ mesons are measured in bins of charm meson transverse momentum, $p_{\text{T}}$, and rapidity, $y$. They cover the rapidity range $2.0<y<4.5$ and transverse momentum ranges $0 < p_{\text{T}} < 10\, \text{GeV}/c$ for $D^0$ and $D^+$ and $1 < p_{\text{T}} < 10\, \text{GeV}/c$ for $D_s^+$ and $D^{*+}$ mesons. The inclusive cross-sections for the four mesons, including charge-conjugate states, within the range of $1 < p_{\text{T}} < 8\, \text{GeV}/c$ are determined to be σ(pp\rightarrow D^0 X) = 1004 \pm 3 \pm 54\,μ\text{b} σ(pp\rightarrow D^+ X) = 402 \pm 2 \pm 30\,μ\text{b} σ(pp\rightarrow D_s^+ X) = 170 \pm 4 \pm 16\,μ\text{b} σ(pp\rightarrow D^{*+} X)= 421 \pm 5 \pm 36\,μ\text{b} where the uncertainties are statistical and systematic, respectively.

hep-ex↗

arXiv2017

Measurement of forward $J/ψ$ production cross-sections in $pp$ collisions at $\sqrt{s}=13$ TeV

The production of $J/ψ$ mesons in proton-proton collisions at a centre-of-mass energy of $\sqrt{s}=13$ TeV is studied with the \lhcb detector. Cross-section measurements are performed as a function of the transverse momentum $p_\mathrm{T}$ and the rapidity $y$ of the $J/ψ$ meson in the region $p_\mathrm{T}<14\mathrm{GeV}/c$ and $2.0<y<4.5$, for both prompt $J/ψ$ mesons and $J/ψ$ mesons from $b$-hadron decays. The production cross-sections integrated over the kinematic coverage are $15.03\pm 0.03\pm 0.94$ $μ$b for prompt $J/ψ$ and $2.25\pm 0.01\pm 0.14$ $μ$b for $J/ψ$ from $b$-hadron decays, assuming zero polarization of the $J/ψ$ meson. The first uncertainties are statistical and the second systematic. The cross-section reported for $J/ψ$ mesons from $b$-hadron decays is used to extrapolate to a total $b\bar{b}$ cross-section. The ratios of the cross-sections with respect to $\sqrt{s}=8$ TeV are also determined.

hep-ex↗

arXiv2017

Observation of five new narrow $Ω_c^0$ states decaying to $Ξ_c^+ K^-$

The $Ξ_c^+ K^-$ mass spectrum is studied with a sample of $pp$ collision data corresponding to an integrated luminosity of 3.3 fb$^{-1}$, collected by the LHCb experiment. The $Ξ_c^+$ is reconstructed in the decay mode $p K^- π^+$. Five new, narrow excited $Ω_c^0$ states are observed: the $Ω_c(3000)^0$, $Ω_c(3050)^0$, $Ω_c(3066)^0$, $Ω_c(3090)^0$, and $Ω_c(3119)^0$. Measurements of their masses and widths are reported.

hep-ex↗

arXiv2017

New algorithms for identifying the flavour of $B^0$ mesons using pions and protons

Two new algorithms for use in the analysis of $pp$ collision are developed to identify the flavour of $B^0$ mesons at production using pions and protons from the hadronization process. The algorithms are optimized and calibrated on data, using $B^0 \rightarrow D^- π^+$ decays from $pp$ collision data collected by LHCb at centre-of-mass energies of 7 and 8 TeV. The tagging power of the new pion algorithm is 60 % greater than the previously available one; the algorithm using protons to identify the flavour of a $B^0$ meson is the first of its kind.

hep-ex↗

arXiv2017

Measurements of the S-wave fraction in $B^{0}\rightarrow K^{+}π^{-}μ^{+}μ^{-}$ decays and the $B^{0}\rightarrow K^{\ast}(892)^{0}μ^{+}μ^{-}$ differential branching fraction

A measurement of the differential branching fraction of the decay ${B^{0}\rightarrow K^{\ast}(892)^{0}μ^{+}μ^{-}}$ is presented together with a determination of the S-wave fraction of the $K^+π^-$ system in the decay $B^{0}\rightarrow K^{+}π^{-}μ^{+}μ^{-}$. The analysis is based on $pp$-collision data corresponding to an integrated luminosity of 3\,fb$^{-1}$ collected with the LHCb experiment. The measurements are made in bins of the invariant mass squared of the dimuon system, $q^2$. Precise theoretical predictions for the differential branching fraction of $B^{0}\rightarrow K^{\ast}(892)^{0}μ^{+}μ^{-}$ decays are available for the $q^2$ region $1.1<q^2<6.0\,{\rm GeV}^2/c^4$. In this $q^2$ region, for the $K^+π^-$ invariant mass range $796 < m_{Kπ} < 996\,{\rm MeV}/c^2$, the S-wave fraction of the $K^+π^-$ system in $B^{0}\rightarrow K^{+}π^{-}μ^{+}μ^{-}$ decays is found to be \begin{equation*} F_{\rm S} = 0.101\pm0.017({\rm stat})\pm0.009 ({\rm syst}), \end{equation*} and the differential branching fraction of $B^{0}\rightarrow K^{\ast}(892)^{0}μ^{+}μ^{-}$ decays is determined to be \begin{equation*} {\rm d}\mathcal{B}/{\rm d} q^2 = (0.342_{\,-0.017}^{\,+0.017}({\rm stat})\pm{0.009}({\rm syst})\pm0.023({\rm norm}))\times 10^{-7}c^{4}/{\rm GeV}^{2}. \end{equation*} The differential branching fraction measurements presented are the most precise to date and are found to be in agreement with Standard Model predictions.

hep-ex↗

arXiv2017

Measurement of the phase difference between short- and long-distance amplitudes in the $B^{+}\to K^{+}μ^{+}μ^{-}$ decay

A measurement of the phase difference between the short- and long-distance contributions to the $B^{+}\to K^{+}μ^{+}μ^{-}$ decay is performed by analysing the dimuon mass distribution. The analysis is based on $pp$ collision data corresponding to an integrated luminosity of 3 $\rm fb^{-1}$ collected by the LHCb experiment in 2011 and 2012. The long-distance contribution to the $B^{+}\to K^{+}μ^{+}μ^{-}$ decay is modelled as a sum of relativistic Breit--Wigner amplitudes representing different vector meson resonances decaying to muon pairs, each with their own magnitude and phase. The measured phases of the $J/ψ$ and $ψ(2S)$ resonances are such that the interference with the short-distance component in dimuon mass regions far from their pole masses is small. In addition, constraints are placed on the Wilson coefficients, $\mathcal{C}_{9}$ and $\mathcal{C}_{10}$, and the branching fraction of the short-distance component is measured.

hep-ex↗

arXiv2017

Study of $J/ψ$ production in jets

The production of $J/ψ$ mesons in jets is studied in the forward region of proton-proton collisions using data collected with the LHCb detector at a center-of-mass energy of 13 TeV. The fraction of the jet transverse momentum carried by the $J/ψ$ meson, $z \equiv p_{\rm T}(J/ψ)/p_{\rm T}({\rm jet})$, is measured using jets with $p_{\rm T}({\rm jet}) > 20$ GeV in the pseudorapidity range $2.5 < η({\rm jet}) < 4.0$. The observed $z$ distribution for $J/ψ$ mesons produced in $b$-hadron decays is consistent with expectations. However, the results for prompt $J/ψ$ production do not agree with predictions based on fixed-order non-relativistic QCD. This is the first measurement of the $p_{\rm T}$ fraction carried by prompt $J/ψ$ mesons in jets at any experiment.

hep-ex↗

arXiv2017

Observation of $B_{c}^{+} \to J/ψD^{()} K^{()}$ decays

A search for the decays $B_c^+ \to J/ψD^{(*)0} K^+$ and $B_c^+ \to J/ψD^{(*)+} K^{*0}$ is performed with data collected at the LHCb experiment corresponding to an integrated luminosity of 3 fb$^{-1}$. The decays $B_c^+ \to J/ψD^0 K^+$ and $B_c^+ \to J/ψD^{*0} K^+$ are observed for the first time, while first evidence is reported for the $B_c^+ \to J/ψD^{*+} K^{*0}$ and $B_c^+ \to J/ψD^+ K^{*0}$ decays. The branching fractions of these decays are determined relative to the $B_c^+ \to J/ψπ^+$ decay. The $B_c^+$ mass is measured, using the $J/ψD^0 K^+$ final state, to be $6274.28 \pm 1.40 (stat) \pm 0.32 (syst)$ MeV/$c^2$. This is the most precise single measurement of the $B_c^+$ mass to date.

hep-ex↗

arXiv2017

Observation of $B_{c}^{+} \rightarrow D^{0} K^{+}$ decays

Using proton-proton collision data corresponding to an integrated luminosity of 3.0 fb$^{-1}$, recorded by the LHCb detector at centre-of-mass energies of 7 and 8 TeV, the $B_{c}^{+} \rightarrow D^{0} K^{+}$ decay is observed with a statistical significance of 5.1 standard deviations. By normalising to $B^{+} \rightarrow \bar{D}^{0} π^{+}$ decays, a measurement of the branching fraction multiplied by the production rates for $B_{c}^{+}$ relative to $B^{+}$ mesons in the LHCb acceptance is obtained, $$ R_{D^{0} K} = \frac{f_{c}}{f_{u}}\times\mathcal{B}(B_{c}^{+} \rightarrow D^{0} K^{+}) = (9.3\,^{+2.8}_{-2.5} \pm 0.6) \times 10^{-7}\,, $$ where the first uncertainty is statistical and the second is systematic. This decay is expected to proceed predominantly through weak annihilation and penguin amplitudes, and is the first $B_{c}^{+}$ decay of this nature to be observed.

hep-ex↗

arXiv2017

Search for decays of neutral beauty mesons into four muons

A search for the non-resonant decays $B^0_s \rightarrow μ^{+}μ^{-}μ^{+}μ^{-}$ and $B^0 \rightarrow μ^{+}μ^{-}μ^{+}μ^{-}$ is presented. The measurement is performed using the full Run 1 data set collected in proton-proton collisions by the LHCb experiment at the LHC. The data correspond to integrated luminosities of $1$ and $2~\mathrm{fb}^{-1}$ collected at centre-of-mass energies of $7$ and $8~\mathrm{TeV}$, respectively. No signal is observed and upper limits on the branching fractions of the non-resonant decays at $95\%$ confidence level are determined to be \mathcal{B}(B^0_s \rightarrow μ^{+}μ^{-}μ^{+}μ^{-}) & < 2.5 \times 10^{-9} \mathcal{B}(B^0 \rightarrow μ^{+}μ^{-}μ^{+}μ^{-}) & < 6.9 \times 10^{-10}.

hep-ex↗