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LHCb collaboration

Publications and source records attributed to LHCb collaboration.

At least 271 records · Page 15Linked to original sources

arXiv2023

Amplitude analysis of the $Λ^+_c\to pK^-π^+$ decay and $Λ^+_c$ baryon polarization measurement in semileptonic beauty hadron decays

An amplitude analysis of $Λ^+_c \to pK^-π^+$ decays together with a measurement of the $Λ^+_c$ polarization vector in semileptonic beauty hadron decays is presented. A sample of $400\,000$ candidates is selected from proton-proton collisions recorded by the LHCb detector at a center-of-mass energy of 13 TeV. An amplitude model is developed and the resonance fractions as well as two- and three-body decay parameters are reported. The mass and width of the $Λ(2000)$ state are also determined. A significant $Λ^+_c$ polarization is found. A large sensitivity of the $Λ^+_c \to pK^-π^+$ decay to the polarization is seen, making the amplitude model suitable for $Λ^+_c$ polarization measurements in other systems.

hep-ex↗

arXiv2023

A study of $C\!P$ violation in the decays $B^\pm\to[K^+K^-π^+π^-]_D h^{\pm}$ ($h = K, π$) and $B^\pm\to[π^+π^-π^+π^-]_D h^{\pm}$

The first study of $C\!P$ violation in the decay mode $B^\pm\to[K^+K^-π^+π^-]_D h^\pm$, with $h=K,π$, is presented, exploiting a data sample of proton-proton collisions collected by the LHCb experiment that corresponds to an integrated luminosity of $9$ fb$^{-1}$. The analysis is performed in bins of phase space, which are optimised for sensitivity to local $C\!P$ asymmetries. $C\!P$-violating observables that are sensitive to the angle $γ$ of the Unitarity Triangle are determined. The analysis requires external information on charm-decay parameters, which are currently taken from an amplitude analysis of LHCb data, but can be updated in the future when direct measurements become available. Measurements are also performed of phase-space integrated observables for $B^\pm\to[K^+K^-π^+π^-]_D h^\pm$ and $B^\pm\to[π^+π^-π^+π^-]_D h^\pm$ decays.

hep-ex↗

arXiv2023

Nuclear modification factor of neutral pions in the forward and backward regions in $p$-Pb collisions

The nuclear modification factor of neutral pions is measured in proton-lead collisions collected at a center-of-mass energy per nucleon of $8.16~{\rm TeV}$ with the LHCb detector. The $π^0$ production cross section is measured differentially in transverse momentum ($p_{\rm T}$) for $1.5<p_{\rm T}<10.0~{\rm GeV}$ and in center-of-mass pseudorapidity ($η_{\rm c.m.}$) regions $2.5<η_{\rm c.m.}<3.5$ (forward) and $-4.0<η_{\rm c.m.}<-3.0$ (backward) defined relative to the proton beam direction. The forward measurement shows a sizable suppression of $π^0$ production, while the backward measurement shows the first evidence of $π^0$ enhancement in proton-lead collisions at the LHC. Together, these measurements provide precise constraints on models of nuclear structure and particle production in high-energy nuclear collisions.

nucl-ex↗

arXiv2023

Measurement of $Υ$ production in $pp$ collisions at $\sqrt{s}=5 \ \rm{TeV}$

The production cross-sections of $Υ$ mesons, namely $Υ(1S)$, $Υ(2S)$ and $Υ(3S)$, in $pp$ collisions at $\sqrt{s}=5 \ \rm{TeV}$ are measured with a data sample corresponding to an integrated luminosity of $9.13\pm{0.18} \ \rm{pb}^{-1}$ collected by the LHCb detector. The $Υ$ mesons are reconstructed in the decay mode $Υ\to μ^+ μ^-$. Double differential cross-sections times branching fractions, as functions of the transverse momentum $p_{\rm{T}}$ and the rapidity $y$ of the $Υ$ mesons, are measured in the range $p_{\rm{T}} < 20 \ \rm{GeV}/c$ and $2.0<y<4.5$. The results integrated over these $p_{\rm{T}}$ and $y$ ranges are $σ(Υ(1S)) \times\mathcal{B}(Υ(1S)\to μ^+ μ^-) = 2101\pm33\pm83 \ \rm{pb},$ $σ(Υ(2S)) \times\mathcal{B}(Υ(2S)\to μ^+ μ^-) = 526\pm20\pm21 \ \rm{pb},$ $σ(Υ(3S)) \times\mathcal{B}(Υ(3S)\to μ^+ μ^-) = 242\pm16\pm10 \ \rm{pb},$ where the first uncertainties are statistical and the second are systematic. The ratios of cross-sections between measurements of two different $Υ$ states and between measurements at different center-of-mass energies are determined. The nuclear modification factor of $Υ(1S)$ at $\sqrt{s}=5 \ \rm{TeV}$ is updated as well using the directly measured cross-section results from this analysis.

hep-ex↗

arXiv2023

Search for the rare hadronic decay $B_s^0\to p \bar{p}$

A search for the rare hadronic decay $B_s^0\to p \bar{p}$ is performed using proton-proton collision data recorded by the LHCb experiment at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 6 fb$^{-1}$. No evidence of the decay is found and an upper limit on its branching fraction is set at ${\cal B}(B_s^0\to p \bar{p}) < 4.4~(5.1) \times 10^{-9}$ at 90% (95%) confidence level; this is currently the world's best upper limit. The decay mode $B^0\to p \bar{p}$ is measured with very large significance, confirming the first observation by the LHCb experiment in 2017. The branching fraction is determined to be ${\cal B}(B^0\to p \bar{p}) = \rm (1.27 \pm 0.15 \pm 0.05 \pm 0.04) \times 10^{-8}$, where the first uncertainty is statistical, the second is systematic and the third is due to the external branching fraction of the normalization channel $B^0\to K^+π^-$. The combination of the two LHCb measurements of the $B^0\to p \bar{p}$ branching fraction yields ${\cal B}(B^0\to p \bar{p}) = \rm (1.27 \pm 0.13 \pm 0.05 \pm 0.03) \times 10^{-8}$.

hep-ex↗

arXiv2023

Measurement of the ratio of branching fractions $\mathcal{B}(B_c^+ \to B_s^0 π^+)/\mathcal{B}(B_c^+ \to J/ψπ^+)$

The ratio of branching fractions of $B_c^+ \to B_s^0 π^+$ and $B_c^+ \to J/ψπ^+$ decays is measured with proton-proton collision data of a centre-of-mass energy of $13\text{TeV}$. The data were collected with the LHCb experiment during 2016--2018, corresponding to an integrated luminosity of $5.4 \text{fb}^{-1}$. The $B_s^0$ mesons are reconstructed via the decays $B_s^0 \to J/ψϕ$ and $B_s^0 \to D_s^- π^+$. The ratio of branching fractions is measured to be $\mathcal{B}(B_c^+ \to B_s^0 π^+)/\mathcal{B}(B_c^+ \to J/ψπ^+) = 91 \pm 10 \pm 8 \pm 3$ where the first uncertainty is statistical, the second is systematic and the third is due to the knowledge of the branching fractions of the intermediate state decays.

hep-ex↗

arXiv2023

Search for $\it{CP}$ violation in $D_{(s)}^{+}\rightarrow K^{-}K^{+}K^{+}$ decays

A search for direct $\it{CP}$ violation in the Cabibbo-suppressed decay $D_{s}^{+}\rightarrow K^{-}K^{+}K^{+}$ and in the doubly Cabibbo-suppressed decay $D^{+}\rightarrow K^{-}K^{+}K^{+}$ is reported. The analysis is performed with data collected by the LHCb experiment in proton-proton collisions at a centre-of-mass energy of 13 TeV corresponding to an integrated luminosity of 5.6 $\textrm{fb}^{-1}$. The search is conducted by comparing the $D^+_{(s)}$ and $D^-_{(s)}$ Dalitz-plot distributions through a model-independent binned technique, based on fits to the $K^{-}K^{+}K^{+}$ invariant-mass distributions, with a total of 0.97 (1.27) million $D_{s}^{+}$ ($D^{+}$) signal candidates. The results are given as $p$-values for the hypothesis of $\it{CP}$ conservation and are found to be 13.3% for the $D_{s}^{+}\rightarrow K^{-}K^{+}K^{+}$ decay and 31.6% for the $D^{+}\rightarrow K^{-}K^{+}K^{+}$ decay. No evidence for $\it{CP}$ violation is observed in these decays.

hep-ex↗

arXiv2023

First observation and branching fraction measurement of the $Λ_b^0\to D_s^- p$ decay

The first observation of the $Λ_b^0\to D_s^- p$ decay is presented using proton-proton collision data collected by the LHCb experiment at a centre-of-mass energy of ${\sqrt{s}=13 \,\textrm{TeV}}$, corresponding to a total integrated luminosity of $6\,\textrm{fb}^{-1}$. Using the $Λ_b^0\toΛ_c^+π^-$ decay as the normalisation mode, the branching fraction of the $Λ_b^0\to D_s^- p$ decay is measured to be ${\mathcal{B}(Λ_b^0\to D_s^- p)=(12.6 \pm 0.5 \pm 0.3 \pm 1.2 )\times 10^{-6}}$, where the first uncertainty is statistical, the second systematic and the third due to uncertainties in the branching fractions of the $Λ_b^0\toΛ_c^+π^-$, $D_s^- \to K^-K^+π^-$ and $Λ_c^+\to p K^- π^+$ decays.

hep-ex↗

arXiv2023

Observation of the $B^0_s\!\to D^{+}D^{-}$ decay

The first observation of the $B^0_s\!\to D^{*+}D^{*-}$ decay and the measurement of its branching ratio relative to the $B^0\!\to D^{*+}D^{*-}$ decay are presented. The data sample used corresponds to an integrated luminosity of $9\,\text{fb}^{-1}$ of proton-proton collisions recorded by the LHCb experiment at centre-of-mass energies of 7, 8 and $13\,\text{TeV}$ between 2011 and 2018. The decay is observed with more than $10$ standard deviations and the time-integrated ratio of branching fractions is determined to be \begin{align*} \frac{\mathcal{B}(B^0_s\!\to D^{*+}D^{*-})}{\mathcal{B}(B^0\!\to D^{*+}D^{*-})} = 0.269 \pm 0.032 \pm 0.011 \pm 0.008\, , \end{align*} where the first uncertainty is statistical, the second systematic and the third due to the uncertainty of the fragmentation fraction ratio $f_s/f_d$. The $B^0_s\!\to D^{*+}D^{*-}$ branching fraction is calculated to be \begin{align*} \mathcal{B}(B^0_s\!\to D^{*+}D^{*-}) = (2.15 \pm 0.26 \pm 0.09 \pm 0.06 \pm 0.16)\times 10^{-4} \,, \end{align*} where the fourth uncertainty is due to the $B^0\!\to D^{*+}D^{*-}$branching fraction. These results are calculated using the average $B^0_s$ meson lifetime in simulation. Correction factors are reported for scenarios where either a purely heavy or a purely light $B^0_s$ eigenstate is considered.

hep-ex↗

arXiv2023

Exotic hadron naming convention

Many new exotic hadrons, that do not fit into the existing naming scheme for hadrons, have been discovered over the past few years. A new scheme is set out, extending the existing protocol, in order to provide a consistent naming convention for these newly discovered states, and other new hadrons that may be discovered in future.

hep-ex↗

arXiv2023

Observation of the decay $ Λ_b^0\rightarrow Λ_c^+τ^-\overlineν_τ$

The first observation of the semileptonic $b$-baryon decay $ Λ_b^0 \rightarrow Λ_c^+ τ^-\overlineν_τ$, with a significance of $6.1\,σ$, is reported using a data sample corresponding to 3 fb$^{-1}$ of integrated luminosity, collected by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV at the LHC. The $τ^-$ lepton is reconstructed in the hadronic decay to three charged pions. The branching fraction ${\mathcal{B}}(Λ_b^0 \rightarrow Λ_c^+τ^-\overlineν_τ) = (1.50 \pm 0.16\pm 0.25\pm 0.23)\%$ is obtained, where uncertainties are statistical, systematic and from the external branching fraction of the normalisation channel $Λ_b^0\rightarrow Λ_c^+π^-π^+π^-$. The ratio of semileptonic branching fractions ${\mathcal{R}}( Λ_c^+)\equiv {\mathcal{B}}( Λ_b^0 \rightarrow Λ_c^+ τ^-\overlineν_τ)/{\mathcal{B}}( Λ_b^0 \rightarrow Λ_c^+ μ^-\overlineν_μ)$ is derived to be $0.242 \pm 0.026 \pm 0.040\pm 0.059$, where the external branching fraction uncertainty from the channel $Λ_b^0\rightarrow Λ_c^+μ^-\overlineν_μ$ contributes to the last term. This result is in agreement with the Standard Model prediction.

hep-ex↗

arXiv2022

Searches for the rare hadronic decays $B^0 \rightarrow p\bar{p}p\bar{p}$ and $B^0_{s} \rightarrow p\bar{p}p\bar{p}$

Searches for the rare hadronic decays $B^0 \rightarrow p\bar{p}p\bar{p}$ and $B^0_{s} \rightarrow p\bar{p}p\bar{p}$ are performed using proton-proton collision data recorded by the LHCb experiment and corresponding to an integrated luminosity of 9$\rm{fb}^{-1}$. Significances of $9.3\,σ$ and $4.0\,σ$, including statistical and systematic uncertainties, are obtained for the $B^0 \rightarrow p\bar{p}p\bar{p}$ and $B^0_{s} \rightarrow p\bar{p}p\bar{p}$ signals, respectively. The branching fractions are measured relative to the topologically similar normalisation decays $B^0 \rightarrow J/ψ(\rightarrow p\bar{p}) K^{*0}(\rightarrow K^+ π^-)$ and $B^0_{s} \rightarrow J/ψ(\rightarrow p\bar{p}) ϕ(\rightarrow K^+ K^-)$. The branching fractions are measured to be $ \mathcal{B}(B^0 \rightarrow p\bar{p}p\bar{p}) = ( 2.2 \pm 0.4 \pm 0.1 \pm 0.1 ) \times 10^{-8} $ and $ \mathcal{B}(B^0_{s} \rightarrow p\bar{p}p\bar{p}) = ( 2.3 \pm 1.0 \pm 0.2 \pm 0.1 ) \times 10^{-8}$. In these measurements, the first uncertainty is statistical, the second is systematic and the third one is due to the external branching fraction of the normalisation channel.

hep-ex↗

arXiv2022

LHCb measurements of Quarkonia Production in Ultraperipheral PbPb collisions and Z production in $p$Pb collisions

Measurements of quarkonia production in ultra-peripheral heavy-ion collisions are of important value to study photon-photon and photon-nucleus interactions, the partonic structure of nuclei, and mechanisms of vector-meson production. LHCb has studied both coherent $J/ψ$ and $ψ(2S)$ mesons in ultra-peripheral collisions using PbPb data at forward rapidity with the highest precision currently accessible. In addition, measurements of $Z$ production in $p$Pb collisions provide new constraints on the partonic structure of nucleons bound inside nuclei. Here will present these measurements of quarkonia and $Z$ production, along with comparisons with the latest theoretical models. Measurements of quarkonia production in ultra-peripheral heavy-ion collisions are of important value to study photon-photon and photon-nucleus interactions, the partonic structure of nuclei, and mechanisms of vector-meson production. LHCb has studied both coherent $J/ψ$ and $ψ(2S)$ mesons in ultra-peripheral collisions using PbPb data at forward rapidity with the highest precision currently accessible. In addition, measurements of $Z$ production in $p$Pb collisions provide new constraints on the partonic structure of nucleons bound inside nuclei. Here will present these measurements of quarkonia and $Z$ production, along with comparisons with the latest theoretical models.

hep-ex↗

arXiv2022

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

A first search for the lepton-flavour violating decays $B^0 \to K^{*0} τ^\pm μ^\mp$ is presented. The analysis is performed using a sample of proton-proton collision data, collected with the LHCb detector at centre-of-mass energies of 7, 8 and 13 TeV between 2011 and 2018, corresponding to an integrated luminosity of 9 fb$^{-1}$. No significant signal is observed, and upper limits on the branching fractions are determined to be ${\cal{B}}(B^0 \to K^{*0} τ^+ μ^-)< 1.0$ $(1.2)\times 10^{-5} $ and ${\cal{B}}(B^0 \to K^{*0} τ^- μ^+)< 8.2$ $(9.8) \times 10^{-6}$ at the 90% (95%) confidence level.

hep-ex↗

arXiv2022

Probing the valence quark region of nucleons with Z bosons at LHCb

In this high-$x$ region, both the flavour content and structure of the nucleon parton distribution functions remains relatively poorly known. New LHCb measurements of Z and charm jet associated production could indicate a valence-like intrinsic-charm component in the proton wave function, and measurements of Z production in pPb collisions provide new constraints on the partonic structure of nucleons bound inside nuclei. Here we will discuss these new LHCb measurements and comparisons with state-of-the-art parton distribution function calculations.

hep-ex↗

arXiv2022

Test of lepton universality in beauty-quark decays

The Standard Model of particle physics currently provides our best description of fundamental particles and their interactions. The theory predicts that the different charged leptons, the electron, muon and tau, have identical electroweak interaction strengths. Previous measurements have shown a wide range of particle decays are consistent with this principle of lepton universality. This article presents evidence for the breaking of lepton universality in beauty-quark decays, with a significance of 3.1 standard deviations, based on proton-proton collision data collected with the LHCb detector at CERN's Large Hadron Collider. The measurements are of processes in which a beauty meson transforms into a strange meson with the emission of either an electron and a positron, or a muon and an antimuon. If confirmed by future measurements, this violation of lepton universality would imply physics beyond the Standard Model, such as a new fundamental interaction between quarks and leptons.

hep-ex↗

arXiv2022

Search for massive long-lived particles decaying semileptonically at sqrt(s)=13 TeV

A search is performed for massive long-lived particles (LLP) decaying semileptonically into a muon and two quarks. Two kinds of LLP production processes were considered. In the first, a Higgs-like boson with mass from 30 to 200 GeV is produced by gluon fusion and decays into two LLPs. The analysis covers LLP mass values from 10 GeV up to about one half the Higgs-like boson mass. The second LLP production mode is directly from quark interactions, with LLP masses from 10 to 90 GeV. The LLP lifetimes considered range from 5 to 200 ps. This study uses LHCb data collected from proton-proton collisions at sqrt(s)=13 TeV, corresponding to an integrated luminosity of 5.4 1/fb. No evidence of these long-lived states has been observed, and upper limits on the production cross-section times branching ratio have been set for each model considered.

hep-ex↗

arXiv2022

First measurement of the $Z\rightarrow μ^+ μ^-$ angular coefficients in the forward region of $pp$ collisions at $\sqrt{s}=13$ TeV

The first study of the angular distribution of $μ^+ μ^-$ pairs produced in the forward rapidity region via the Drell-Yan reaction $pp \rightarrow γ^{*}/Z +X \rightarrow l^+ l^- + X$ is presented, using data collected with the LHCb detector at a centre-of-mass energy of 13TeV, corresponding to an integrated luminosity of 5.1 $\rm{fb}^{-1}$. The coefficients of the five leading terms in the angular distribution are determined as a function of the dimuon transverse momentum and rapidity. The results are compared to various theoretical predictions of the $Z$-boson production mechanism and can also be used to probe transverse-momentum-dependent parton distributions within the proton.

hep-ex↗