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LHCb collaboration

Publications and source records attributed to LHCb collaboration.

At least 253 records · Page 14Linked to original sources
arXiv2023

Measurement of the prompt $D^0$ nuclear modification factor in $p$Pb collisions at $\sqrt{s_\mathrm{NN}} = 8.16$ TeV

The production of prompt $D^0$ mesons in proton-lead collisions in the forward and backward configurations at a center-of-mass energy per nucleon pair of $\sqrt{s_\mathrm{NN}} = 8.16~\mathrm{TeV}$ is measured by the LHCb experiment. The nuclear modification factor of prompt $D^0$ mesons is determined as a function of the transverse momentum $p_\mathrm{T}$, and rapidity in the nucleon-nucleon center-of-mass frame $y^*$. In the forward rapidity region, significantly suppressed production with respect to $pp$ collisions is measured, which provides significant constraints of nuclear parton distributions and hadron production down to the very low Bjorken-$x$ region of $\sim 10^{-5}$. In the backward rapidity region, a suppression with a significance of 2.0 - 3.8 standard deviations compared to nPDF expectations is found in the kinematic region of $p_\mathrm{T}>6~\mathrm{GeV}/c$ and $-3.25<y^*<-2.5$, corresponding to $x\sim 0.01$.

nucl-ex↗
arXiv2023

Measurement of the time-integrated $C\!P$ asymmetry in $D^0\to K^- K^+$ decays

The time-integrated $C\!P$ asymmetry in the Cabibbo-suppressed decay $D^0\to K^-K^+$ is measured using proton-proton collision data, corresponding to an integrated luminosity of 5.7 fb$^{-1}$ collected at a center-of-mass energy of 13 TeV with the LHCb detector. The $D^0$ mesons are required to originate from promptly produced $D^{*+}\to D^0π^+$ decays and the charge of the companion pion is used to determine the flavor of the charm meson at production. The time-integrated $C\!P$ asymmetry is measured to be \begin{align*} \mathcal{A}_{C\!P}(K^-K^+) = \left[6.8 \pm 5.4 \text{ (stat)} \pm 1.6 \text{ (syst)} \right]\times 10^{-4}. \end{align*} The direct $C\!P$ asymmetries in $D^0\to K^- K^+$ and $D^0\toπ^-π^+$ decays, $a_{K^-K^+}^{d}$ and $a_{π^-π^+}^{d}$, are derived by combining $\mathcal{A}_{C\!P} (K^-K^+)$ with the time-integrated $C\!P$ asymmetry difference, $Δ\mathcal{A}_{C\!P} =\mathcal{A}_{C\!P} (K^-K^+)-\mathcal{A}_{C\!P} (π^-π^+)$, giving \begin{alignat*}{2} a_{K^-K^+}^{d} &= (\phantom{2}7.7 \pm 5.7) \times 10^{-4}, \end{alignat*} \begin{alignat*}{2} a_{π^-π^+}^{d} &= (23.2 \pm 6.1) \times 10^{-4}, \end{alignat*} with a correlation coefficient corresponding to $ρ=0.88$. The compatibility of these results with $C\!P$ symmetry is 1.4 and 3.8 standard deviations for $D^0\to K^- K^+$ and $D^0\toπ^-π^+$ decays, respectively. This is the first evidence for direct $C\!P$ violation in a specific $D^0$ decay.

hep-ex↗
arXiv2023

Search for the rare decays $W^+ \to D^+_sγ$ and $Z \to D^0γ$ at LHCb

A search for the rare decays $W^{+}\rightarrow{D^{+}_{s}γ}$ and $Z\rightarrow{D^{0}γ}$ is performed using proton-proton collision data collected by the LHCb experiment at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 2.0 fb$^{-1}$. No significant signal is observed for either decay mode and upper limits on their branching fractions are set using $W^{+}\rightarrow{μ^{+}ν}$ and $Z\rightarrow{μ^{+}μ^{-}}$ decays as normalization channels. The upper limits are $6.5\times10^{-4}$ and $2.1\times10^{-3}$ at 95% confidence level for the $W^{+}\rightarrow{D^{+}_{s}γ}$ and $Z\rightarrow{D^{0}γ}$ decay modes, respectively. This is the first reported search for the $Z\rightarrow{D^{0}γ}$ decay, while the upper limit on the $W^{+}\rightarrow{D^{+}_{s}γ}$ branching fraction improves upon the previous best limit.

hep-ex↗
arXiv2023

Study of exclusive photoproduction of charmonium in ultra-peripheral lead-lead collisions

The cross-sections of exclusive (coherent) photoproduction $J/ψ$ and $ψ(\mathrm{2S})$ mesons in ultra-peripheral PbPb collisions at a nucleon-nucleon centre-of-mass energy of $5.02\,\mathrm{TeV}$ are measured using a data sample corresponding to an integrated luminosity of $228\pm10\,\mathrm{μb}^{-1}$, collected by the LHCb experiment in 2018. The differential cross-sections are measured separately as a function of transverse momentum and rapidity in the nucleus-nucleus centre-of-mass frame for $J/ψ$ and $ψ(\mathrm{2S})$ mesons. The integrated cross-sections are measured to be \mbox{$σ^\mathrm{coh}_{J/ψ} = 5.965 \pm 0.059 \pm 0.232 \pm 0.262\,\mathrm{mb}$} and \mbox{$σ^\mathrm{coh}_{ψ(\mathrm{2S})} = 0.923 \pm 0.086 \pm 0.028 \pm 0.040\,\mathrm{mb}$}, where the first listed uncertainty is statistical, the second systematic and the third due to the luminosity determination. The cross-section ratio is measured to be \mbox{$σ^\mathrm{coh}_{ψ(\mathrm{2S})}/σ^\mathrm{coh}_{J/ψ} = 0.155 \pm 0.014 \pm 0.003$}, where the first uncertainty is statistical and the second is systematic. These results are compatible with theoretical predictions.

hep-ex↗
arXiv2023

Measurement of the $Z$ boson production cross-section in proton-lead collisions at $\sqrt{s_\mathrm{NN}}=8.16\,\mathrm{TeV}$

This article presents the first measurement of the differential $Z$-boson production cross-section in the forward region using proton-lead collisions with the LHCb detector. The dataset was collected at a nucleon-nucleon centre-of-mass energy of $\sqrt{s_\mathrm{NN}}=8.16\,\mathrm{TeV}$ in 2016, corresponding to an integrated luminosity of $30.8\,\mathrm{nb}^{-1}$. The forward-backward ratio and the nuclear modification factors are measured together with the differential cross-section as functions of the $Z$ boson rapidity in the centre-of-mass frame, the transverse momentum of the $Z$ boson and a geometric variable $ϕ^{*}$. The results are in good agreement with the predictions from nuclear parton distribution functions, providing strong constraining power at small Bjorken-$x$.

hep-ex↗
arXiv2023

Associated production of prompt $J/ψ$ and $\mathitΥ$ mesons in $pp$ collisions at $\sqrt{s}=13\,\mathrm{TeV}$

The associated production of prompt $J/ψ$ and $\mathit{\mathitΥ}$ mesons in $pp$ collisions at a centre-of-mass energy of $\sqrt{s}=13\,\mathrm{TeV}$ is studied using LHCb data, corresponding to an integrated luminosity of $4\,\mathrm{fb}^{-1}$. The measurement is performed for $J/ψ$ ($\mathitΥ$) mesons with a transverse momentum $p_{\mathrm{T}}<10\,(30)\,\mathrm{GeV}/c$ in the rapidity range $2.0<y<4.5$. In this kinematic range, the cross-section of the associated production of prompt $J/ψ$ and $\mathitΥ(1S)$ mesons is measured to be $133 \pm 22 \pm 7 \pm 3 \, \mathrm{pb}$, with a significance of $7.9\,σ$, and that of prompt $J/ψ$ and $\mathitΥ(2S)$ mesons to be $76\pm 21 \pm 4 \pm 7 \, \mathrm{pb}$, with a significance of $4.9\,σ$. The first uncertainty is statistical, the second systematic, and the third due to uncertainties on the used branching fractions. This is the first observation of the associated production of $J/ψ$ and $\mathitΥ(1S)$ in proton-proton collisions. Differential cross-sections are measured as functions of variables that are sensitive to kinematic correlations between the $J/ψ$ and $\mathitΥ(1S)$ mesons. The effective cross-sections of the associated production of prompt $J/ψ$ and $\mathitΥ$ mesons are obtained and found to be compatible with measurements using other particle productions.

hep-ex↗
arXiv2023

Study of charmonium decays to $K^0_S K π$ in the $B \to (K^0_S K π) K$ channels

A study of the $B^+\to K^0_SK^+K^-π^+$ and $B^+\to K^0_SK^+K^+π^-$ decays is performed using proton-proton collisions at center-of-mass energies of 7, 8 and 13 TeV at the LHCb experiment. The $K^0_SK π$ invariant mass spectra from both decay modes reveal a rich content of charmonium resonances. New precise measurements of the $η_c$ and $η_c(2S)$ resonance parameters are performed and branching fraction measurements are obtained for $B^+$ decays to $η_c$, $J/ψ$, $η_c(2S)$ and $χ_{c1}$ resonances. In particular, the first observation and branching fraction measurement of $B^+ \to χ_{c0} K^0 π^+$ is reported as well as first measurements of the $B^+\to K^0K^+K^-π^+$ and $B^+\to K^0K^+K^+π^-$ branching fractions. Dalitz plot analyses of $η_c \to K^0_SKπ$ and $η_c(2S) \to K^0_SKπ$ decays are performed. A new measurement of the amplitude and phase of the $K π$ $S$-wave as functions of the $K π$ mass is performed, together with measurements of the $K^*_0(1430)$, $K^*_0(1950)$ and $a_0(1700)$ parameters. Finally, the branching fractions of $χ_{c1}$ decays to $K^*$ resonances are also measured.

hep-ex↗
arXiv2023

Observation of a resonant structure near the $D_s^+ D_s^-$ threshold in the $B^+\to D_s^+ D_s^- K^+$ decay

An amplitude analysis of the $B^+\to D_s^+ D_s^- K^+$ decay is carried out to study for the first time its intermediate resonant contributions, using proton-proton collision data collected with the LHCb detector at centre-of-mass energies of 7, 8 and 13 TeV. A near-threshold peaking structure, referred to as $X(3960)$, is observed in the $D_s^+ D_s^-$ invariant-mass spectrum with significance greater than 12 standard deviations. The mass, width and the quantum numbers of the structure are measured to be $3956\pm5\pm10$ MeV, $43\pm13\pm8$ MeV and $J^{PC}=0^{++}$, respectively, where the first uncertainties are statistical and the second systematic. The properties of the new structure are consistent with recent theoretical predictions for a state composed of $c\bar{c}s\bar{s}$ quarks. Evidence for an additional structure is found around 4140 MeV in the $D_s^+ D_s^-$ invariant mass, which might be caused either by a new resonance with the $0^{++}$ assignment or by a $J/ψϕ\leftrightarrow D_s^+ D_s^-$ coupled-channel effect.

hep-ex↗
arXiv2023

Observation of the mass difference between neutral charm-meson eigenstates

A measurement of mixing and $C\!P$ violation in neutral charm mesons is performed using data reconstructed in proton-proton collisions collected by the LHCb experiment from 2016 to 2018, corresponding to an integrated luminosity of 5.4$\textrm{fb}^{-1}$. A total of $30.6$ million $D^{0}\rightarrow K^{0}_{\mathrm{S}}π^{+}π^{-}$ decays are analyzed using a method optimized for the measurement of the mass difference between neutral charm-meson eigenstates. Allowing for $C\!P$ violation in mixing and in the interference between mixing and decay, the mass and decay-width differences are measured to be $x_{C\!P} = \left[3.97\pm0.46\textrm{(stat)}\pm 0.29\textrm{(syst)}\right]\times10^{-3}$ and $y_{C\!P} = \left[4.59\pm1.20\textrm{(stat)}\pm0.85\textrm{(syst)}\right]\times10^{-3}$, respectively. The $C\!P$-violating parameters are measured as $Δx = \left[-0.27\pm0.18\textrm{(stat)}\pm0.01\textrm{(syst)}\right]\times10^{-3}$ and $Δy = \left[0.20\pm0.36\textrm{(stat)}\pm0.13\textrm{(syst)}\right]\times10^{-3}$. This is the first observation of a nonzero mass difference in the $D^0$ meson system, with a significance exceeding seven standard deviations. The data are consistent with $C\!P$ symmetry, and improve existing constraints on the associated parameters.

hep-ex↗
arXiv2023

Search for $CP$ violation using $\hat{T}$-odd correlations in $B^{0} \to p \bar p K^{+} π^{-}$ decays

A search for $CP$ and $P$ violation in charmless four-body $B^{0} \to p \bar p K^{+} π^{-}$ decays is performed using triple-product asymmetry observables. It is based on proton-proton collision data collected by the LHCb experiment at centre-of-mass energies of $7$, $8$ and $13$ TeV, corresponding to a total integrated luminosity of $8.4$ fb$^{-1}$. The $CP$- and $P$-violating asymmetries are measured both in the integrated phase space and in specific regions. No evidence is seen for $CP$ violation. $P$-parity violation is observed at a significance of 5.8 standard deviations

hep-ex↗
arXiv2023

Search for $D^{*}(2007)^0\toμ^+μ^-$ in $B^-\toπ^-μ^+μ^-$ decays

The very rare $D^{*}(2007)^0\toμ^+μ^-$ decay is searched for by analysing $B^-\toπ^-μ^+μ^-$ decays. The analysis uses a sample of beauty mesons produced in proton-proton collisions collected with the LHCb detector between 2011 and 2018, corresponding to an integrated luminosity of 9 fb$^{-1}$. The signal signature corresponds to simultaneous peaks in the $μ^+μ^-$ and $π^-μ^+μ^-$ invariant masses. No evidence for an excess of events over background is observed and an upper limit is set on the branching fraction of the decay at ${\cal B}(D^{*}(2007)^0\toμ^+μ^-) < 2.6\times 10^{-8}$ at $90\%$ confidence level. This is the first limit on the branching fraction of $D^{*}(2007)^0\toμ^+μ^-$ decays and the most stringent limit on $D^{*}(2007)^0$ decays to leptonic final states. The analysis is the first search for a rare charm-meson decay exploiting production via beauty decays.

hep-ex↗
arXiv2023

Search for the baryon- and lepton-number violating decays $B^0\to pμ^-$ and $B^0_s\to pμ^-$

A search for the baryon- and lepton-number violating decays $B^0\to pμ^-$ and $B^0_s\to pμ^-$ is performed at the LHCb experiment using data collected in proton-proton collisions at $\sqrt{s}$ = 7, 8 and 13 TeV, corresponding to integrated luminosities of 1, 2 and 6 fb$^{-1}$, respectively. No significant signal for $B^0\to pμ^-$ and $B^0_s\to pμ^-$ decays is found and the upper limits on the branching fractions are determined to be ${\cal B}(B^0\to pμ^-)<2.6\,(3.1)\times10^{-9}$ and ${\cal B}(B^0_s\to pμ^-)<12.1\,(14.0)\times10^{-9}$, respectively, at 90$\%$ (95$\%$) confidence level. These are the first limits on these decays to date.

hep-ex↗
arXiv2023

Observation of sizeable $ω$ contribution to $χ_{c1}(3872)\toπ^+π^-J/ψ$ decays

Resonant structures in the dipion mass spectrum from $χ_{c1}(3872)\toπ^+π^- J/ψ$ decays, produced via $B^+\to K^+χ_{c1}(3872)$ decays, are analyzed using proton-proton collision data collected by the LHCb experiment, corresponding to an integrated luminosity of 9 $fb^{-1}$. A sizeable contribution from the isospin conserving $χ_{c1}(3872)\toωJ/ψ$ decay is established for the first time, $(21.4\pm2.3\pm2.0)\%$, with a significance of more than $7.1σ$. The amplitude of isospin violating decay, $χ_{c1}(3872)\toρ^0 J/ψ$, relative to isospin conserving decay, $χ_{c1}(3872)\toωJ/ψ$, is properly determined, and it is a factor of six larger than expected for a pure charmonium state.

hep-ex↗
arXiv2023

Search for the lepton-flavour violating decays $B^0 \to K^{*0} μ^\pm e^\mp$ and $B_s^0 \to ϕμ^\pm e^\mp$

A search for the lepton-flavour violating decays $B^0 \to K^{*0} μ^\pm e^\mp$ and $B_s^0 \to ϕμ^\pm e^\mp$ is presented, using proton-proton collision data collected by the LHCb detector at the LHC, corresponding to an integrated luminosity of $9\,\text{fb}^{-1}$. No significant signals are observed and upper limits of \begin{align} {\cal B}( B^0 \to K^{*0} μ^+ e^- ) &< \phantom{1}5.7\times 10^{-9}~(6.9\times 10^{-9}),\newline {\cal B}( B^0 \to K^{*0} μ^- e^+ ) &< \phantom{1}6.8\times 10^{-9}~(7.9\times 10^{-9}),\newline {\cal B}( B^0 \to K^{*0} μ^\pm e^\mp ) &< 10.1\times 10^{-9}~(11.7\times 10^{-9}),\newline {\cal B}( B_s^0 \to ϕμ^\pm e^\mp ) &< 16.0\times 10^{-9}~(19.8\times 10^{-9}) \end{align} are set at $90\%~(95\%)$ confidence level. These results constitute the world's most stringent limits to date, with the limit on the decay $B_s^0 \to ϕμ^\pm e^\mp$ the first being set. In addition, limits are reported for scalar and left-handed lepton-flavour violating New Physics scenarios.

hep-ex↗
arXiv2023

Search for the doubly heavy baryon $\itΞ_{bc}^{+}$ decaying to $J/\itψ \itΞ_{c}^{+}$

A first search for the $\itΞ_{bc}^{+}\to J/\itψ\itΞ_{c}^{+}$ decay is performed by the LHCb experiment with a data sample of proton-proton collisions, corresponding to an integrated luminosity of $9\,\mathrm{fb}^{-1}$ recorded at centre-of-mass energies of 7, 8, and $13\mathrm{\,Te\kern -0.1em V}$. Two peaking structures are seen with a local (global) significance of $4.3\,(2.8)$ and $4.1\,(2.4)$ standard deviations at masses of $6571\,\mathrm{Me\kern -0.1em V\!/}c^2$ and $6694\,\mathrm{Me\kern -0.1em V\!/}c^2$, respectively. Upper limits are set on the $\itΞ_{bc}^{+}$ baryon production cross-section times the branching fraction relative to that of the $B_{c}^{+}\to J/\itψ D_{s}^{+}$ decay at centre-of-mass energies of 8 and $13\mathrm{\,Te\kern -0.1em V}$, in the $\itΞ_{bc}^{+}$ and in the $B_{c}^{+}$ rapidity and transverse-momentum ranges from 2.0 to 4.5 and 0 to $20\,\mathrm{Ge\kern -0.1em V\!/}c$, respectively. Upper limits are presented as a function of the $\itΞ_{bc}^{+}$ mass and lifetime.

hep-ex↗
arXiv2023

Amplitude analysis of $B^0 \rightarrow \overline{D}^0 D_s^+ π^-$ and $B^+ \rightarrow D^- D_s^+ π^+$ decays

Resonant contributions in $B^0 \rightarrow \overline{D}^0 D^+_sπ^-$ and $B^+\rightarrow D^- D^+_sπ^+$ decays are determined with an amplitude analysis, which is performed both separately and simultaneously, where in the latter case isospin symmetry between the decays is assumed. The analysis is based on data collected by the LHCb detector in proton-proton collisions at center-of-mass energies of 7, 8 and 13 $\rm{TeV}$. The full data sample corresponds to an integrated luminosity of 9 $\rm fb^{-1}$. A doubly charged spin-0 open-charm tetraquark candidate together with a neutral partner, both with masses near $2.9\,\rm{GeV}$, are observed in the $D_sπ$ decay channel.

hep-ex↗
arXiv2023

First observation of a doubly charged tetraquark and its neutral partner

A combined amplitude analysis is performed for the decays $B^0 \rightarrow \overline{D}^0 D^+_sπ^-$ and $B^+\rightarrow D^- D^+_sπ^+$, which are related by isospin symmetry. The analysis is based on data collected by the LHCb detector in proton-proton collisions at center-of-mass energies of 7, 8 and 13$\,\rm{TeV}$. The full data sample corresponds to an integrated luminosity of 9$\,\rm{fb^{-1}}$. Two new resonant states with masses of $2.908\pm0.011\pm0.020\,\rm{GeV}$ and widths of $0.136\pm0.023\pm0.011\,\rm{GeV}$ are observed, which decay to $D^+_sπ^+$ and $D^+_sπ^-$ respectively. The former state indicates the first observation of a doubly charged open-charm tetraquark state with minimal quark content $[c\bar{s}u\bar{d}]$, and the latter state is a neutral tetraquark composed of $[c\bar{s}\bar{u}d]$ quarks. Both states are found to have spin-parity $0^+$, and their resonant parameters are consistent with each other, which suggests that they belong to an isospin triplet.

hep-ex↗
arXiv2023

Measurement of $τ_{L}$ using the $B_{s}^{0} \to J/ψη$ decay mode

Using a proton-proton collision data sample collected by the LHCb detector and corresponding to an integrated luminosity of 5.7 $\text{fb}^{-1}$, the lifetime of the $B_{s}^{0}$ mass eigenstate, $τ_{L}$, is measured using $B_{s}^{0} \to J/ψη$ decay mode to be $τ_{L}$ = 1.445 $\pm$ 0.016(stat) $\pm$ 0.008(syst) ps. A combination of this result with a previous LHCb analysis using an independent dataset corresponding to 3 $\text{fb}^{-1}$ of integrated luminosity gives $τ_{L}$ = 1.452 $\pm$ 0.014 $\pm$ 0.007 $\pm$ 0.002 ps, where the first uncertainty is statistical, the second due to the uncorrelated part of the systematic uncertainty and the third due to the correlated part of the systematic uncertainty.

hep-ex↗