Irene Bachiller

The first simultaneous test of muon-electron universality using $B^{+}\rightarrow K^{+}\ell^{+}\ell^{-}$ and $B^{0}\rightarrow K^{*0}\ell^{+}\ell^{-}$ decays is performed, in two ranges of the dilepton invariant-mass squared, $q^{2}$. The analysis uses beauty mesons produced in proton-proton collisions collected with the LHCb detector between 2011 and 2018, corresponding to an integrated luminosity of 9 $\mathrm{fb}^{-1}$. Each of the four lepton universality measurements reported is either the first in the given $q^{2}$ interval or supersedes previous LHCb measurements. The results are compatible with the predictions of the Standard Model.

A simultaneous analysis of the B+→K+ℓ+ℓ− and B0→K*0ℓ+ℓ− decays is performed to test muon-electron universality in two ranges of the square of the dilepton invariant mass, q2. The measurement uses a sample of beauty meson decays produced in proton-proton collisions collected with the LHCb detector between 2011 and 2018, corresponding to an integrated luminosity of 9 fb−1. A sequence of multivariate selections and strict particle identification requirements produce a higher signal purity and a better statistical sensitivity per unit luminosity than previous LHCb lepton universality tests using the same decay modes. Residual backgrounds due to misidentified hadronic decays are studied using data and included in the fit model. Each of the four lepton universality measurements reported is either the first in the given q2 interval or supersedes previous LHCb measurements. The results are compatible with the predictions of the Standard Model.22 MoreReceived 20 December 2022Accepted 6 June 2023DOI:https://doi.org/10.1103/PhysRevD.108.032002Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.© 2023 CERN, for the LHCb CollaborationPhysics Subject Headings (PhySH)Research AreasFlavor changing neutral currentsRare decaysPhysical SystemsBottom mesonsElectronsMuonsTechniquesHadron collidersParticles & Fields

The branching fraction B(B0→D*−τ+ντ) is measured relative to that of the normalization mode B0→D*−π+π−π+ using hadronic τ+→π+π−π+(π0)¯ντ decays in proton-proton collision data at a center-of-mass energy of 13 TeV collected by the LHCb experiment, corresponding to an integrated luminosity of 2 fb−1. The measured ratio is B(B0→D*−τ+ντ)/B(B0→D*−π+π−π+)=1.70±0.10+0.11−0.10, where the first uncertainty is statistical and the second is related to systematic effects. Using established branching fractions for the B0→D*−π+π−π+ and B0→D*−μ+νμ modes, the lepton universality test R(D*−)≡B(B0→D*−τ+ντ)/B(B0→D*−μ+νμ) is calculated, R(D*−)=0.247±0.015±0.015±0.012, where the third uncertainty is due to the uncertainties on the external branching fractions. This result is consistent with the Standard Model prediction and with previous measurements.Received 3 May 2023Accepted 6 June 2023DOI:https://doi.org/10.1103/PhysRevD.108.012018Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Funded by SCOAP3.© 2023 CERN, for the LHCb CollaborationPhysics Subject Headings (PhySH)Research AreasParticle decaysParticle interactionsPhysical SystemsLeptonsQuarksPropertiesFlavor symmetriesTechniquesHadron collidersParticles & Fields

The ratios of branching fractions R(D * ) ≡ B(B → D * τ -ν τ )/B(B → D * µ -ν µ ) and R(D 0 ) ≡ B(B -→ D 0 τ -ν τ )/B(B -→ D 0 µ -ν µ ) are measured, assuming isospin symmetry, using a sample of proton-proton collision data corresponding to 3.0 fb -1 of integrated luminosity recorded by the LHCb experiment during 2011 and 2012.The tau lepton is identified in the decay mode τ -→ µ -ν τ ν µ .The measured values are R(D * ) = 0.281 ± 0.018 ± 0.024 and R(D 0 ) = 0.441 ± 0.060 ± 0.066, where the first uncertainty is statistical and the second is systematic.The correlation between these measurements is ρ = -0.43.Results are consistent with the current average of these quantities and are at a combined 1.9 standard deviations from the predictions based on lepton flavor universality in the Standard Model.

An amplitude analysis of B^{0}→J/ψϕK_{S}^{0} decays is performed using proton-proton collision data, corresponding to an integrated luminosity of 9 fb^{-1}, collected with the LHCb detector at center-of-mass energies of 7, 8, and 13 TeV. Evidence with a significance of 4.0 standard deviations of a structure in the J/ψK_{S}^{0} system, named T_{ψs1}^{θ}(4000)^{0}, is seen, with its mass and width measured to be 3991_{-10}^{+12} _{-17}^{+9} MeV/c^{2} and 105_{-25}^{+29} _{-23}^{+17} MeV, respectively, where the first uncertainty is statistical and the second systematic. The T_{ψs1}^{θ}(4000)^{0} state is likely to be the isospin partner of the T_{ψs1}^{θ}(4000)^{+} state, previously observed in the J/ψK^{+} system of the B^{+}→J/ψϕK^{+} decay. When isospin symmetry for the charged and neutral T_{ψs1}^{θ}(4000) states is assumed, the signal significance increases to 5.4 standard deviations.

The branching fraction of the rare decay ${\mathrm{\ensuremath{\Lambda}}}_{b}^{0}\ensuremath{\rightarrow}\mathrm{\ensuremath{\Lambda}}(1520){\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$ is measured for the first time, in the squared dimuon mass intervals ${q}^{2}$, excluding the $J/\ensuremath{\psi}$ and $\ensuremath{\psi}(2S)$ regions. The data sample analyzed was collected by the LHCb experiment at center-of-mass energies of 7, 8, and 13 TeV, corresponding to a total integrated luminosity of $9\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$. The result in the highest ${q}^{2}$ interval, ${q}^{2}>15.0\text{ }\text{ }{\mathrm{GeV}}^{2}/{c}^{4}$, where theoretical predictions have the smallest model dependence, agrees with the predictions.

The Compact Muon Solenoid (CMS) experiment prepares its Phase-2 upgrade for the high-luminosity era of the LHC operation (HL-LHC). Due to the increase of occupancy, trigger latency and rates, the full electronics of the CMS Drift Tube (DT) chambers will need to be replaced. In the new design, the time bin for the digitization of the chamber signals will be of around 1 ns, and the totality of the signals will be forwarded asynchronously to the service cavern at full resolution. The new backend system will be in charge of building the trigger primitives of each chamber. These trigger primitives contain the information at chamber level about the muon candidates position, direction, and collision time, and are used as input in the L1 CMS trigger. The added functionalities will improve the robustness of the system against ageing. An algorithm based on analytical solutions for reconstructing the DT trigger primitives, called Analytical Method, has been implemented both as a software C++ emulator and in firmware. Its performance has been estimated using the software emulator with simulated and real data samples, and through hardware implementation tests. Measured efficiencies are 96 to 98% for all qualities and time and spatial resolutions are close to the ultimate performance of the DT chambers. A prototype chain of the HL-LHC electronics using the Analytical Method for trigger primitive generation has been installed during Long Shutdown 2 of the LHC and operated in CMS cosmic data taking campaigns in 2020 and 2021. Results from this validation step, the so-called Slice Test, are presented.

A study of the B+→K0SK+K−π+ and B+→K0SK+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 K0SKπ invariant mass spectra from both decay modes reveal a rich content of charmonium resonances. New precise measurements of the ηc and ηc(2S) resonance parameters are performed and branching fraction measurements are obtained for B+ decays to ηc, J/ψ, ηc(2S) and χc1 resonances. In particular, the first observation and branching fraction measurement of B+→χc0K0π+ is reported as well as first measurements of the B+→K0K+K−π+ and B+→K0K+K+π− branching fractions. Dalitz plot analyses of ηc→K0SKπ and ηc(2S)→K0SKπ decays are performed. A new measurement of the amplitude and phase of the Kπ S-wave as functions of the Kπ mass is performed, together with measurements of the K∗0(1430), K∗0(1950) and a0(1700) parameters. Finally, the branching fractions of χc1 decays to K∗ resonances are also measured.22 MoreReceived 5 May 2023Accepted 27 June 2023DOI:https://doi.org/10.1103/PhysRevD.108.032010Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.© 2023 CERN, for the LHCb CollaborationPhysics Subject Headings (PhySH)Research AreasParticle decaysQuark modelParticles & Fields

A bstract A search for CP violation in D 0 → π − π + π 0 decays is reported, using pp collision data collected by the LHCb experiment from 2015 to 2018 corresponding to an integrated luminosity of 6 fb − 1 . An unbinned model-independent approach provides sensitivity to local CP violation within the two-dimensional phase space of the decay. The method is validated using the Cabibbo-favoured channel D 0 → K − π + π 0 and background regions of the signal mode. The results are consistent with CP symmetry in this decay.

A flavor-tagged time-dependent angular analysis of the decay B0s→ϕϕ is performed using pp collision data collected by the LHCb experiment at the center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 6 fb−1. The CP-violating phase and direct CP-violation parameter are measured to be ϕs¯sss=−0.042±0.075±0.009 rad and |λ|=1.004±0.030±0.009, respectively, assuming the same values for all polarization states of the ϕϕ system. In these results, the first uncertainties are statistical and the second systematic. These parameters are also determined separately for each polarization state, showing no evidence for polarization dependence. The results are combined with previous LHCb measurements using pp collisions at center-of-mass energies of 7 and 8 TeV, yielding ϕs¯sss=−0.074±0.069 rad and |λ|=1.009±0.030. This is the most precise study of time-dependent CP violation in a penguin-dominated B meson decay. The results are consistent with CP symmetry and with the standard model predictions.Received 20 April 2023Revised 28 June 2023Accepted 1 August 2023DOI:https://doi.org/10.1103/PhysRevLett.131.171802Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Funded by SCOAP3.© 2023 CERN, for the LHCb CollaborationPhysics Subject Headings (PhySH)Research AreasCabibbo–Kobayashi–Maskawa matrixHadronic decaysParticle mixing & oscillationsPhysical SystemsBottom mesonsPropertiesCP violationTechniquesHadron collidersParticles & Fields

The decay-time-dependent CP asymmetry in Bs0→J/ψ(→μ+μ−)K+K− decays is measured using proton-proton collision data, corresponding to an integrated luminosity of 6 fb−1, collected with the LHCb detector at a center-of-mass energy of 13 TeV. Using a sample of approximately 349 000 Bs0 signal decays with an invariant K+K− mass in the vicinity of the ϕ(1020) resonance, the CP-violating phase ϕs is measured, along with the difference in decay widths of the light and heavy mass eigenstates of the Bs0−B¯s0 system, ΔΓs, and the difference of the average Bs0 and B0 meson decay widths, Γs−Γd. The values obtained are ϕs=−0.039±0.022±0.006 rad, ΔΓs=0.0845±0.0044±0.0024 ps−1, and Γs−Γd=−0.056−0.0015+0.0013±0.0014 ps−1, where the first uncertainty is statistical and the second systematic. These are the most precise single measurements to date and are consistent with expectations based on the Standard Model and with the previous LHCb analyses of this decay. These results are combined with previous independent LHCb measurements. The phase ϕs is also measured independently for each polarization state of the K+K− system and shows no evidence for polarization dependence.Received 4 August 2023Accepted 4 December 2023DOI:https://doi.org/10.1103/PhysRevLett.132.051802Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.© 2024 CERN, for the LHCb CollaborationPhysics Subject Headings (PhySH)Research AreasCabibbo–Kobayashi–Maskawa matrixElectroweak interactionParticle mixing & oscillationsQuark mixingPropertiesCP symmetryFlavor symmetriesParticles & Fields

Abstract The identification of helium nuclei at LHCb is achieved using a method based on measurements of ionisation losses in the silicon sensors and timing measurements in the Outer Tracker drift tubes. The background from photon conversions is reduced using the RICH detectors and an isolation requirement. The method is developed using pp collision data at √( s ) = 13 TeV recorded by the LHCb experiment in the years 2016 to 2018, corresponding to an integrated luminosity of 5.5 fb -1 . A total of around 10 5 helium and antihelium candidates are identified with negligible background contamination. The helium identification efficiency is estimated to be approximately 50% with a corresponding background rejection rate of up to 𝒪(10 12 ). These results demonstrate the feasibility of a rich programme of measurements of QCD and astrophysics interest involving light nuclei.

A bstract A measurement of CP -violating observables in B ± → D * K ± and B ± → D * π ± decays is made where the photon or neutral pion from the D * → D γ or D * → D π 0 decay is not reconstructed. The D meson is reconstructed in the self-conjugate decay modes, D → $$ {K}_S^0 $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>K</mml:mi> <mml:mi>S</mml:mi> <mml:mn>0</mml:mn> </mml:msubsup> </mml:math> π + π − or D → $$ {K}_S^0 $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>K</mml:mi> <mml:mi>S</mml:mi> <mml:mn>0</mml:mn> </mml:msubsup> </mml:math> K + K − . The distribution of signal yields in the D decay phase space is analysed in a model-independent way. The measurement uses a data sample collected in proton-proton collisions at centre-of-mass energies of 7, 8, and 13 TeV, corresponding to a total integrated luminosity of approximately 9 fb − 1 . The B ± → D * K ± and B ± → D * π ± CP -violating observables are interpreted in terms of hadronic parameters and the CKM angle γ, resulting in a measurement of γ = ( $$ {92}_{-17}^{+21} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mn>92</mml:mn> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>17</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>21</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> ) ° . The total uncertainty includes the statistical and systematic uncertainties, and the uncertainty due to external strong-phase inputs.

The first observation of the singly Cabibbo-suppressed Ω_{c}^{0}→Ω^{-}K^{+} and Ω_{c}^{0}→Ξ^{-}π^{+} decays is reported, using proton-proton collision data at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 5.4 fb^{-1}, collected with the LHCb detector between 2016 and 2018. The branching fraction ratios are measured to be B(Ω_{c}^{0}→Ω^{-}K^{+})/B(Ω_{c}^{0}→Ω^{-}π^{+})=[6.08±0.51(stat)±0.40(syst)]%,B(Ω_{c}^{0}→Ξ^{-}π^{+})/B(Ω_{c}^{0}→Ω^{-}π^{+})=[15.81±0.87(stat)±0.44(syst)±0.16(ext)]%. In addition, using the Ω_{c}^{0}→Ω^{-}π^{+} decay channel, the Ω_{c}^{0} baryon mass is measured to be M(Ω_{c}^{0})=2695.28±0.07(stat)±0.27(syst)±0.30(ext) MeV, improving the precision of the previous world average by a factor of 4.

A bstract A study of $$ {B}_c^{+}\to {\chi}_c{\pi}^{+} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>B</mml:mi> <mml:mi>c</mml:mi> <mml:mo>+</mml:mo> </mml:msubsup> <mml:mo>→</mml:mo> <mml:msub> <mml:mi>χ</mml:mi> <mml:mi>c</mml:mi> </mml:msub> <mml:msup> <mml:mi>π</mml:mi> <mml:mo>+</mml:mo> </mml:msup> </mml:math> decays is reported using proton-proton collision data, collected with the LHCb detector at centre-of-mass energies of 7, 8, and 13 TeV, corresponding to an integrated luminosity of 9 fb − 1 . The decay $$ {B}_c^{+}\to {\chi}_{c2}{\pi}^{+} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>B</mml:mi> <mml:mi>c</mml:mi> <mml:mo>+</mml:mo> </mml:msubsup> <mml:mo>→</mml:mo> <mml:msub> <mml:mi>χ</mml:mi> <mml:mrow> <mml:mi>c</mml:mi> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> <mml:msup> <mml:mi>π</mml:mi> <mml:mo>+</mml:mo> </mml:msup> </mml:math> is observed for the first time, with a significance exceeding seven standard deviations. The relative branching fraction with respect to the $$ {B}_c^{+}\to J/\psi {\pi}^{+} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>B</mml:mi> <mml:mi>c</mml:mi> <mml:mo>+</mml:mo> </mml:msubsup> <mml:mo>→</mml:mo> <mml:mi>J</mml:mi> <mml:mo>/</mml:mo> <mml:mi>ψ</mml:mi> <mml:msup> <mml:mi>π</mml:mi> <mml:mo>+</mml:mo> </mml:msup> </mml:math> decay is measured to be $$ \frac{{\mathcal{B}}_{B_c^{+}\to {\chi}_{c2}{\pi}^{+}}}{{\mathcal{B}}_{B_c^{+}\to J/\psi {\pi}^{+}}}=0.37\pm 0.06\pm 0.02\pm 0.01, $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mfrac> <mml:msub> <mml:mi>B</mml:mi> <mml:mrow> <mml:msubsup> <mml:mi>B</mml:mi> <mml:mi>c</mml:mi> <mml:mo>+</mml:mo> </mml:msubsup> <mml:mo>→</mml:mo> <mml:msub> <mml:mi>χ</mml:mi> <mml:mrow> <mml:mi>c</mml:mi> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> <mml:msup> <mml:mi>π</mml:mi> <mml:mo>+</mml:mo> </mml:msup> </mml:mrow> </mml:msub> <mml:msub> <mml:mi>B</mml:mi> <mml:mrow> <mml:msubsup> <mml:mi>B</mml:mi> <mml:mi>c</mml:mi> <mml:mo>+</mml:mo> </mml:msubsup> <mml:mo>→</mml:mo> <mml:mi>J</mml:mi> <mml:mo>/</mml:mo> <mml:mi>ψ</mml:mi> <mml:msup> <mml:mi>π</mml:mi> <mml:mo>+</mml:mo> </mml:msup> </mml:mrow> </mml:msub> </mml:mfrac> <mml:mo>=</mml:mo> <mml:mn>0.37</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.06</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.02</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.01</mml:mn> <mml:mo>,</mml:mo> </mml:math> where the first uncertainty is statistical, the second is systematic, and the third is due to the knowledge of the χ c 2 → J/ψγ branching fraction. No significant $$ {B}_c^{+}\to {\chi}_{c1}{\pi}^{+} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>B</mml:mi> <mml:mi>c</mml:mi> <mml:mo>+</mml:mo> </mml:msubsup> <mml:mo>→</mml:mo> <mml:msub> <mml:mi>χ</mml:mi> <mml:mrow> <mml:mi>c</mml:mi> <mml:mn>1</mml:mn> </mml:mrow> </mml:msub> <mml:msup> <mml:mi>π</mml:mi> <mml:mo>+</mml:mo> </mml:msup> </mml:math> signal is observed and an upper limit for the relative branching fraction for the $$ {B}_c^{+}\to {\chi}_{c1}{\pi}^{+} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>B</mml:mi> <mml:mi>c</mml:mi> <mml:mo>+</mml:mo> </mml:msubsup> <mml:mo>→</mml:mo> <mml:msub> <mml:mi>χ</mml:mi> <mml:mrow> <mml:mi>c</mml:mi> <mml:mn>1</mml:mn> </mml:mrow> </mml:msub> <mml:msup> <mml:mi>π</mml:mi> <mml:mo>+</mml:mo> </mml:msup> </mml:math> and $$ {B}_c^{+}\to {\chi}_{c2}{\pi}^{+} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>B</mml:mi> <mml:mi>c</mml:mi> <mml:mo>+</mml:mo> </mml:msubsup> <mml:mo>→</mml:mo> <mml:msub> <mml:mi>χ</mml:mi> <mml:mrow> <mml:mi>c</mml:mi> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> <mml:msup> <mml:mi>π</mml:mi> <mml:mo>+</mml:mo> </mml:msup> </mml:math> decays of $$ \frac{{\mathcal{B}}_{B_c^{+}\to {\chi}_{c1}{\pi}^{+}}}{{\mathcal{B}}_{B_c^{+}\to {\chi}_{c2}{\pi}^{+}}}=&lt;0.49 $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mfrac> <mml:msub> <mml:mi>B</mml:mi> <mml:mrow> <mml:msubsup> <mml:mi>B</mml:mi> <mml:mi>c</mml:mi> <mml:mo>+</mml:mo> </mml:msubsup> <mml:mo>→</mml:mo> <mml:msub> <mml:mi>χ</mml:mi> <mml:mrow> <mml:mi>c</mml:mi> <mml:mn>1</mml:mn> </mml:mrow> </mml:msub> <mml:msup> <mml:mi>π</mml:mi> <mml:mo>+</mml:mo> </mml:msup> </mml:mrow> </mml:msub> <mml:msub> <mml:mi>B</mml:mi> <mml:mrow> <mml:msubsup> <mml:mi>B</mml:mi> <mml:mi>c</mml:mi> <mml:mo>+</mml:mo> </mml:msubsup> <mml:mo>→</mml:mo> <mml:msub> <mml:mi>χ</mml:mi> <mml:mrow> <mml:mi>c</mml:mi> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> <mml:msup> <mml:mi>π</mml:mi> <mml:mo>+</mml:mo> </mml:msup> </mml:mrow> </mml:msub> </mml:mfrac> <mml:mo>=</mml:mo> <mml:mo>&lt;</mml:mo> <mml:mn>0.49</mml:mn> </mml:math> is set at the 90% confidence level.

Abstract A model-independent study of $$C\!P$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>C</mml:mi> <mml:mspace /> <mml:mi>P</mml:mi> </mml:mrow> </mml:math> violation in $${{B} ^0} \rightarrow {D} {{K} ^{*0}} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msup> <mml:mrow> <mml:mi>B</mml:mi> </mml:mrow> <mml:mn>0</mml:mn> </mml:msup> <mml:mo>→</mml:mo> <mml:mi>D</mml:mi> <mml:msup> <mml:mrow> <mml:mi>K</mml:mi> </mml:mrow> <mml:mrow> <mml:mrow /> <mml:mo>∗</mml:mo> <mml:mn>0</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> decays is presented using data corresponding to an integrated luminosity of 9 $$\text {\,fb} ^{-1}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mtext>\,fb</mml:mtext> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:math> collected by the LHCb experiment at centre-of-mass energies of $$\sqrt{s}=7, \, 8$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msqrt> <mml:mi>s</mml:mi> </mml:msqrt> <mml:mo>=</mml:mo> <mml:mn>7</mml:mn> <mml:mo>,</mml:mo> <mml:mspace /> <mml:mn>8</mml:mn> </mml:mrow> </mml:math> and 13 $$\text {\,Te\hspace{-1.00006pt}V}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mtext>\,Te</mml:mtext> <mml:mspace /> <mml:mtext>V</mml:mtext> </mml:mrow> </mml:math> . The CKM angle $$\gamma $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>γ</mml:mi> </mml:math> is determined by examining the distributions of signal decays in phase-space bins of the self-conjugate $${D} \rightarrow {{K} ^0_{\textrm{S}}} h^+ h^-$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>D</mml:mi> <mml:mo>→</mml:mo> <mml:msubsup> <mml:mrow> <mml:mi>K</mml:mi> </mml:mrow> <mml:mtext>S</mml:mtext> <mml:mn>0</mml:mn> </mml:msubsup> <mml:msup> <mml:mi>h</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:msup> <mml:mi>h</mml:mi> <mml:mo>-</mml:mo> </mml:msup> </mml:mrow> </mml:math> decays, where $$h = \pi , K$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>h</mml:mi> <mml:mo>=</mml:mo> <mml:mi>π</mml:mi> <mml:mo>,</mml:mo> <mml:mi>K</mml:mi> </mml:mrow> </mml:math> . Observables related to $$C\!P$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>C</mml:mi> <mml:mspace /> <mml:mi>P</mml:mi> </mml:mrow> </mml:math> violation are measured and the angle $$\gamma $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>γ</mml:mi> </mml:math> is determined to be $$\gamma =(49^{+ 22}_{-19})^\circ $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>γ</mml:mi> <mml:mo>=</mml:mo> <mml:msup> <mml:mrow> <mml:mo>(</mml:mo> <mml:msubsup> <mml:mn>49</mml:mn> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>19</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>22</mml:mn> </mml:mrow> </mml:msubsup> <mml:mo>)</mml:mo> </mml:mrow> <mml:mo>∘</mml:mo> </mml:msup> </mml:mrow> </mml:math> . Measurements of the amplitude ratio and strong-phase difference between the favoured and suppressed $${B} ^0$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow> <mml:mi>B</mml:mi> </mml:mrow> <mml:mn>0</mml:mn> </mml:msup> </mml:math> decays are also presented.

The fraction of χc1 and χc2 decays in the prompt J/ψ yield, Fχc→J/ψ=σχc→J/ψ/σJ/ψ, is measured by the LHCb detector in pPb collisions at sNN=8.16 TeV. The study covers the forward (1.5<y*<4.0) and backward (−5.0<y*<−2.5) rapidity regions, where y* is the J/ψ rapidity in the nucleon-nucleon center-of-mass system. Forward and backward rapidity samples correspond to integrated luminosities of 13.6±0.3 and 20.8±0.5 nb−1, respectively. The result is presented as a function of the J/ψ transverse momentum pT,J/ψ in the range 1<pT,J/ψ<20 GeV/c. The Fχc→J/ψ fraction at forward rapidity is compatible with the LHCb measurement performed in pp collisions at s=7 TeV, whereas the result at backward rapidity is 2.4σ larger than in the forward region for 1<pT,J/ψ<3 GeV/c. The increase of Fχc→J/ψ at low pT,J/ψ at backward rapidity is compatible with the suppression of the ψ(2S) contribution to the prompt J/ψ yield. The lack of in-medium dissociation of χc states observed in this study sets an upper limit of 180 MeV on the free energy available in these pPb collisions to dissociate or inhibit charmonium state formation.Received 2 November 2023Revised 5 January 2024Accepted 6 February 2024DOI:https://doi.org/10.1103/PhysRevLett.132.102302Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Funded by SCOAP3.© 2024 CERN, for the LHCb CollaborationPhysics Subject Headings (PhySH)Research AreasJets & heavy flavor physicsRelativistic heavy-ion collisionsNuclear Physics

Abstract Momentum measurements for very high momentum charged particles, such as muons from electroweak vector boson decays, are particularly susceptible to charge-dependent curvature biases that arise from misalignments of tracking detectors. Low momentum charged particles used in alignment procedures have limited sensitivity to coherent displacements of such detectors, and therefore are unable to fully constrain these misalignments to the precision necessary for studies of electroweak physics. Additional approaches are therefore required to understand and correct for these effects. In this paper the curvature biases present at the LHCb detector are studied using the pseudomass method in proton-proton collision data recorded at centre of mass energy √( s )=13 TeV during 2016, 2017 and 2018. The biases are determined using Z → μ + μ - decays in intervals defined by the data-taking period, magnet polarity and muon direction. Correcting for these biases, which are typically at the 10 -4 GeV -1 level, improves the Z → μ + μ - mass resolution by roughly 18% and eliminates several pathological trends in the kinematic-dependence of the mean dimuon invariant mass.

A bstract The production cross-section of J/ψ pairs in proton-proton collisions at a centre-of-mass energy of $$ \sqrt{s} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msqrt> <mml:mi>s</mml:mi> </mml:msqrt> </mml:math> = 13 TeV is measured using a data sample corresponding to an integrated luminosity of 4 . 2 fb − 1 collected by the LHCb experiment. The measurement is performed with both J/ψ mesons in the transverse momentum range 0 &lt; p T &lt; 14 GeV/ c and rapidity range 2 . 0 &lt; y &lt; 4 . 5. The cross-section of this process is measured to be 16 . 36 ± 0 . 28 (stat) ± 0 . 88 (syst) nb. The contributions from single-parton scattering and double-parton scattering are separated based on the dependence of the cross-section on the absolute rapidity difference ∆ y between the two J/ψ mesons. The effective cross-section of double-parton scattering is measured to be σ eff = 13 . 1 ± 1 . 8 (stat) ± 2 . 3 (syst) mb. The distribution of the azimuthal angle ϕ CS of one of the J/ψ mesons in the Collins-Soper frame and the p T -spectrum of the J/ψ pairs are also measured for the study of the gluon transverse-momentum dependent distributions inside protons. The extracted values of ⟨cos 2 ϕ CS ⟩ and ⟨cos 4 ϕ CS ⟩ are consistent with zero, but the presence of azimuthal asymmetry at a few percent level is allowed.

A bstract A search for CP violation in $$ {D}^0\to {K}_S^0{K}^{+}{\pi}^{-} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mi>D</mml:mi> <mml:mn>0</mml:mn> </mml:msup> <mml:mo>→</mml:mo> <mml:msubsup> <mml:mi>K</mml:mi> <mml:mi>S</mml:mi> <mml:mn>0</mml:mn> </mml:msubsup> <mml:msup> <mml:mi>K</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:msup> <mml:mi>π</mml:mi> <mml:mo>−</mml:mo> </mml:msup> </mml:math> and $$ {D}^0\to {K}_S^0{K}^{-}{\pi}^{+} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mi>D</mml:mi> <mml:mn>0</mml:mn> </mml:msup> <mml:mo>→</mml:mo> <mml:msubsup> <mml:mi>K</mml:mi> <mml:mi>S</mml:mi> <mml:mn>0</mml:mn> </mml:msubsup> <mml:msup> <mml:mi>K</mml:mi> <mml:mo>−</mml:mo> </mml:msup> <mml:msup> <mml:mi>π</mml:mi> <mml:mo>+</mml:mo> </mml:msup> </mml:math> decays is reported. The search is performed using an unbinned model-independent method known as the energy test that probes local CP violation in the phase space of the decays. The data analysed correspond to an integrated luminosity of 5 . 4 fb − 1 collected in proton-proton collisions by the LHCb experiment at a centre-of-mass energy of $$ \sqrt{s} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msqrt> <mml:mi>s</mml:mi> </mml:msqrt> </mml:math> = 13 TeV, amounting to approximately 950 thousand and 620 thousand signal candidates for the $$ {D}^0\to {K}_S^0{K}^{-}{\pi}^{+} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mi>D</mml:mi> <mml:mn>0</mml:mn> </mml:msup> <mml:mo>→</mml:mo> <mml:msubsup> <mml:mi>K</mml:mi> <mml:mi>S</mml:mi> <mml:mn>0</mml:mn> </mml:msubsup> <mml:msup> <mml:mi>K</mml:mi> <mml:mo>−</mml:mo> </mml:msup> <mml:msup> <mml:mi>π</mml:mi> <mml:mo>+</mml:mo> </mml:msup> </mml:math> and $$ {D}^0\to {K}_S^0{K}^{+}{\pi}^{-} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mi>D</mml:mi> <mml:mn>0</mml:mn> </mml:msup> <mml:mo>→</mml:mo> <mml:msubsup> <mml:mi>K</mml:mi> <mml:mi>S</mml:mi> <mml:mn>0</mml:mn> </mml:msubsup> <mml:msup> <mml:mi>K</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:msup> <mml:mi>π</mml:mi> <mml:mo>−</mml:mo> </mml:msup> </mml:math> modes, respectively. The method is validated using D 0 → K − π + π − π + and $$ {D}^0\to {K}_S^0{\pi}^{+}{\pi}^{-} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mi>D</mml:mi> <mml:mn>0</mml:mn> </mml:msup> <mml:mo>→</mml:mo> <mml:msubsup> <mml:mi>K</mml:mi> <mml:mi>S</mml:mi> <mml:mn>0</mml:mn> </mml:msubsup> <mml:msup> <mml:mi>π</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:msup> <mml:mi>π</mml:mi> <mml:mo>−</mml:mo> </mml:msup> </mml:math> decays, where CP -violating effects are expected to be negligible, and using background-enhanced regions of the signal decays. The results are consistent with CP symmetry in both the $$ {D}^0\to {K}_S^0{K}^{-}{\pi}^{+} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mi>D</mml:mi> <mml:mn>0</mml:mn> </mml:msup> <mml:mo>→</mml:mo> <mml:msubsup> <mml:mi>K</mml:mi> <mml:mi>S</mml:mi> <mml:mn>0</mml:mn> </mml:msubsup> <mml:msup> <mml:mi>K</mml:mi> <mml:mo>−</mml:mo> </mml:msup> <mml:msup> <mml:mi>π</mml:mi> <mml:mo>+</mml:mo> </mml:msup> </mml:math> and the $$ {D}^0\to {K}_S^0{K}^{+}{\pi}^{-} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mi>D</mml:mi> <mml:mn>0</mml:mn> </mml:msup> <mml:mo>→</mml:mo> <mml:msubsup> <mml:mi>K</mml:mi> <mml:mi>S</mml:mi> <mml:mn>0</mml:mn> </mml:msubsup> <mml:msup> <mml:mi>K</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:msup> <mml:mi>π</mml:mi> <mml:mo>−</mml:mo> </mml:msup> </mml:math> decays, with p -values for the hypothesis of no CP violation of 70% and 66%, respectively.

An amplitude analysis of the B0→K*0μ+μ− decay is presented. The analysis is based on data collected by the LHCb experiment from proton-proton collisions at s=7, 8 and 13 TeV, corresponding to an integrated luminosity of 4.7 fb−1. For the first time, Wilson coefficients and nonlocal hadronic contributions are accessed directly from the unbinned data, where the latter are parametrized as a function of q2 with a polynomial expansion. Wilson coefficients and nonlocal hadronic parameters are determined under two alternative hypotheses: the first relies on experimental information alone, while the second one includes information from theoretical predictions for the nonlocal contributions. Both models obtain similar results for the parameters of interest. The overall level of compatibility with the Standard Model is evaluated to be between 1.8 and 1.9 standard deviations when looking at the C9 Wilson coefficient alone, and between 1.3 and 1.4 standard deviations when considering the full set of C9,C10,C9′ and C10′ Wilson coefficients. The ranges reflect the theoretical assumptions made in the analysis.4 MoreReceived 15 December 2023Accepted 25 January 2024DOI:https://doi.org/10.1103/PhysRevD.109.052009Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Funded by SCOAP3.© 2024 CERN, for the LHCb CollaborationPhysics Subject Headings (PhySH)Research AreasFlavor changing neutral currentsParticles & Fields

An amplitude analysis of the B^{0}→K^{*0}μ^{+}μ^{-} decay is presented using a dataset corresponding to an integrated luminosity of 4.7 fb^{-1} of pp collision data collected with the LHCb experiment. For the first time, the coefficients associated to short-distance physics effects, sensitive to processes beyond the standard model, are extracted directly from the data through a q^{2}-unbinned amplitude analysis, where q^{2} is the μ^{+}μ^{-} invariant mass squared. Long-distance contributions, which originate from nonfactorizable QCD processes, are systematically investigated, and the most accurate assessment to date of their impact on the physical observables is obtained. The pattern of measured corrections to the short-distance couplings is found to be consistent with previous analyses of b- to s-quark transitions, with the largest discrepancy from the standard model predictions found to be at the level of 1.8 standard deviations. The global significance of the observed differences in the decay is 1.4 standard deviations.

A study of prompt Ξ+c production in proton-lead collisions is performed with the LHCb experiment at a center-of-mass energy per nucleon pair of 8.16 TeV in 2016 in pPb and Pbp collisions with an estimated integrated luminosity of approximately 12.5 and 17.4 nb−1, respectively. The Ξ+c production cross section, as well as the Ξ+c to Λ+c production cross-section ratio, are measured as a function of the transverse momentum and rapidity and compared to the latest theory predictions. The forward-backward asymmetry is also measured as a function of the Ξ+c transverse momentum. The results provide strong constraints on theoretical calculation and are a unique input for hadronization studies in different collision systems.3 MoreReceived 17 May 2023Revised 6 November 2023Accepted 11 January 2024DOI:https://doi.org/10.1103/PhysRevC.109.044901Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Funded by SCOAP3.©2024 CERN, for the LHCb CollaborationPhysics Subject Headings (PhySH)Hadron collidersTechniquesExperimental TechniquesParticle acceleratorsHadron collidersResearch AreasFragmentation into hadronsRelativistic heavy-ion collisionsPhysical SystemsHadronsTechniquesHadron collidersParticle productionNuclear PhysicsParticles & Fields

The four decays, $\Lambda_{b}^{0} \rightarrow \Sigma_c^{(*)++} D^{(*)-} K^{-}$, are observed for the first time using proton-proton collision data collected with the LHCb detector at a centre-of-mass energy of $13\,\rm{TeV}$, corresponding to an integrated luminosity of $6\,\rm{fb}^{-1}$. By considering the $\Lambda_b^0 \rightarrow \Lambda_c^{+} \overline{D}^0 K^{-}$ decay as reference channel, the following branching fraction ratios are measured to be, $$\frac{\cal{B} (\Lambda_{b}^{0} \rightarrow \Sigma_{c}^{++} \rm{D}^{-} {K}^{-})}{\cal{B}(\Lambda_{b}^{0} \rightarrow \Lambda_c^{+} \rm \overline{D}^0 {K}^{-})} = {0.282}\pm{0.016}\pm{0.016}\pm{0.005}, \frac{\cal{B}(\Lambda_{b}^{0} \rightarrow \Sigma_{c}^{*++} \rm {D}^{-} {K}^{-})}{\cal{B}(\Lambda_{b}^{0} \rightarrow \Sigma_c^{++} \rm {D}^{-} {K}^{-})} = {0.460}\pm{0.052}\pm{0.028}, \frac{\cal{B}(\Lambda_{b}^{0} \rightarrow \Sigma_{c}^{++} \rm {D}^{*-} {K}^{-})}{\cal{B}(\Lambda_{b}^{0} \rightarrow \Sigma_c^{++} \rm {D}^{-} {K}^{-})} = {2.261}\pm{0.202}\pm{0.129}\pm{0.046}, \frac{\cal{B}(\Lambda_{b}^{0} \rightarrow \Sigma_{c}^{*++} \rm D^{*-} K^{-})}{\cal{B}(\Lambda_{b}^{0} \rightarrow \Sigma_c^{++} \rm D^{-} K^{-})} = {0.896}\pm{0.137}\pm{0.066}\pm{0.018},$$ where the first uncertainties are statistical, the second are systematic, and the third are due to uncertainties in the branching fractions of intermediate particle decays. These initial observations mark the beginning of pentaquark searches in these modes, with more data set to become available following the LHCb upgrade.

Abstract The first search for nonresonant $${{B} _{c} ^+} \!\rightarrow {{\pi } ^+} {\mu ^+\mu ^-} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msubsup> <mml:mi>B</mml:mi> <mml:mrow> <mml:mi>c</mml:mi> </mml:mrow> <mml:mo>+</mml:mo> </mml:msubsup> <mml:mspace/> <mml:mo>→</mml:mo> <mml:msup> <mml:mrow> <mml:mi>π</mml:mi> </mml:mrow> <mml:mo>+</mml:mo> </mml:msup> <mml:mrow> <mml:msup> <mml:mi>μ</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:msup> <mml:mi>μ</mml:mi> <mml:mo>-</mml:mo> </mml:msup> </mml:mrow> </mml:mrow> </mml:math> decays is reported. The analysis uses proton–proton collision data collected with the LHCb detector between 2011 and 2018, corresponding to an integrated luminosity of 9 $$\,\text {fb} ^{-1}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mspace/> <mml:msup> <mml:mtext>fb</mml:mtext> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> . No evidence for an excess of signal events over background is observed and an upper limit is set on the branching fraction ratio $${\mathcal {B}} ({{B} _{c} ^+} \!\rightarrow {{\pi } ^+} {\mu ^+\mu ^-} )/{\mathcal {B}} ({{B} _{c} ^+} \!\rightarrow {{J \hspace{-1.66656pt}/\hspace{-1.111pt}\psi }} {{\pi } ^+} ) &lt; 2.1\times 10^{-4}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>B</mml:mi> <mml:mrow> <mml:mo>(</mml:mo> <mml:msubsup> <mml:mi>B</mml:mi> <mml:mrow> <mml:mi>c</mml:mi> </mml:mrow> <mml:mo>+</mml:mo> </mml:msubsup> <mml:mspace/> <mml:mo>→</mml:mo> <mml:msup> <mml:mrow> <mml:mi>π</mml:mi> </mml:mrow> <mml:mo>+</mml:mo> </mml:msup> <mml:mrow> <mml:msup> <mml:mi>μ</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:msup> <mml:mi>μ</mml:mi> <mml:mo>-</mml:mo> </mml:msup> </mml:mrow> <mml:mo>)</mml:mo> </mml:mrow> <mml:mo>/</mml:mo> <mml:mi>B</mml:mi> <mml:mrow> <mml:mo>(</mml:mo> <mml:msubsup> <mml:mi>B</mml:mi> <mml:mrow> <mml:mi>c</mml:mi> </mml:mrow> <mml:mo>+</mml:mo> </mml:msubsup> <mml:mspace/> <mml:mo>→</mml:mo> <mml:mrow> <mml:mi>J</mml:mi> <mml:mspace/> <mml:mo>/</mml:mo> <mml:mspace/> <mml:mi>ψ</mml:mi> </mml:mrow> <mml:msup> <mml:mrow> <mml:mi>π</mml:mi> </mml:mrow> <mml:mo>+</mml:mo> </mml:msup> <mml:mo>)</mml:mo> </mml:mrow> <mml:mo>&lt;</mml:mo> <mml:mn>2.1</mml:mn> <mml:mo>×</mml:mo> <mml:msup> <mml:mn>10</mml:mn> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>4</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> at $$90\%$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>90</mml:mn> <mml:mo>%</mml:mo> </mml:mrow> </mml:math> confidence level. Additionally, an updated measurement of the ratio of the $${{B} _{c} ^+} \!\rightarrow {\psi {(2S)}} {{\pi } ^+} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msubsup> <mml:mi>B</mml:mi> <mml:mrow> <mml:mi>c</mml:mi> </mml:mrow> <mml:mo>+</mml:mo> </mml:msubsup> <mml:mspace/> <mml:mo>→</mml:mo> <mml:mrow> <mml:mi>ψ</mml:mi> <mml:mrow> <mml:mo>(</mml:mo> <mml:mn>2</mml:mn> <mml:mi>S</mml:mi> <mml:mo>)</mml:mo> </mml:mrow> </mml:mrow> <mml:msup> <mml:mrow> <mml:mi>π</mml:mi> </mml:mrow> <mml:mo>+</mml:mo> </mml:msup> </mml:mrow> </mml:math> and $${{B} _{c} ^+} \!\rightarrow {{J \hspace{-1.66656pt}/\hspace{-1.111pt}\psi }} {{\pi } ^+} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msubsup> <mml:mi>B</mml:mi> <mml:mrow> <mml:mi>c</mml:mi> </mml:mrow> <mml:mo>+</mml:mo> </mml:msubsup> <mml:mspace/> <mml:mo>→</mml:mo> <mml:mrow> <mml:mi>J</mml:mi> <mml:mspace/> <mml:mo>/</mml:mo> <mml:mspace/> <mml:mi>ψ</mml:mi> </mml:mrow> <mml:msup> <mml:mrow> <mml:mi>π</mml:mi> </mml:mrow> <mml:mo>+</mml:mo> </mml:msup> </mml:mrow> </mml:math> branching fractions is reported. The ratio $${\mathcal {B}} ({{B} _{c} ^+} \!\rightarrow {\psi {(2S)}} {{\pi } ^+} )/{\mathcal {B}} ({{B} _{c} ^+} \!\rightarrow {{J \hspace{-1.66656pt}/\hspace{-1.111pt}\psi }} {{\pi } ^+} )$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>B</mml:mi> <mml:mrow> <mml:mo>(</mml:mo> <mml:msubsup> <mml:mi>B</mml:mi> <mml:mrow> <mml:mi>c</mml:mi> </mml:mrow> <mml:mo>+</mml:mo> </mml:msubsup> <mml:mspace/> <mml:mo>→</mml:mo> <mml:mrow> <mml:mi>ψ</mml:mi> <mml:mrow> <mml:mo>(</mml:mo> <mml:mn>2</mml:mn> <mml:mi>S</mml:mi> <mml:mo>)</mml:mo> </mml:mrow> </mml:mrow> <mml:msup> <mml:mrow> <mml:mi>π</mml:mi> </mml:mrow> <mml:mo>+</mml:mo> </mml:msup> <mml:mo>)</mml:mo> </mml:mrow> <mml:mo>/</mml:mo> <mml:mi>B</mml:mi> <mml:mrow> <mml:mo>(</mml:mo> <mml:msubsup> <mml:mi>B</mml:mi> <mml:mrow> <mml:mi>c</mml:mi> </mml:mrow> <mml:mo>+</mml:mo> </mml:msubsup> <mml:mspace/> <mml:mo>→</mml:mo> <mml:mrow> <mml:mi>J</mml:mi> <mml:mspace/> <mml:mo>/</mml:mo> <mml:mspace/> <mml:mi>ψ</mml:mi> </mml:mrow> <mml:msup> <mml:mrow> <mml:mi>π</mml:mi> </mml:mrow> <mml:mo>+</mml:mo> </mml:msup> <mml:mo>)</mml:mo> </mml:mrow> </mml:mrow> </mml:math> is measured to be $$0.254\pm 0.018 \pm 0.003 \pm 0.005$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>0.254</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.018</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.003</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.005</mml:mn> </mml:mrow> </mml:math> , where the first uncertainty is statistical, the second systematic, and the third is due to the uncertainties on the branching fractions of the leptonic $${J \hspace{-1.66656pt}/\hspace{-1.111pt}\psi }$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>J</mml:mi> <mml:mspace/> <mml:mo>/</mml:mo> <mml:mspace/> <mml:mi>ψ</mml:mi> </mml:mrow> </mml:math> and $$\psi {(2S)}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>ψ</mml:mi> <mml:mrow> <mml:mo>(</mml:mo> <mml:mn>2</mml:mn> <mml:mi>S</mml:mi> <mml:mo>)</mml:mo> </mml:mrow> </mml:mrow> </mml:math> decays. This measurement is the most precise to date and is consistent with previous LHCb results.

A bstract A measurement of CP -violating observables associated with the interference of B 0 → D 0 K ⋆ (892) 0 and $$ {B}^0\to {\overline{D}}^0{K}^{\star }{(892)}^0 $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mi>B</mml:mi> <mml:mn>0</mml:mn> </mml:msup> <mml:mo>→</mml:mo> <mml:msup> <mml:mover> <mml:mi>D</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> <mml:mn>0</mml:mn> </mml:msup> <mml:msup> <mml:mi>K</mml:mi> <mml:mo>⋆</mml:mo> </mml:msup> <mml:msup> <mml:mfenced> <mml:mn>892</mml:mn> </mml:mfenced> <mml:mn>0</mml:mn> </mml:msup> </mml:math> decay amplitudes is performed in the D 0 → K ∓ π ± ( π + π − ), D 0 → π + π − ( π + π − ), and D 0 → K + K − final states using data collected by the LHCb experiment corresponding to an integrated luminosity of 9 fb − 1 . CP -violating observables related to the interference of $$ {B}_s^0\to {D}^0{\overline{K}}^{\star }{(892)}^0 $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>B</mml:mi> <mml:mi>s</mml:mi> <mml:mn>0</mml:mn> </mml:msubsup> <mml:mo>→</mml:mo> <mml:msup> <mml:mi>D</mml:mi> <mml:mn>0</mml:mn> </mml:msup> <mml:msup> <mml:mover> <mml:mi>K</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> <mml:mo>⋆</mml:mo> </mml:msup> <mml:msup> <mml:mfenced> <mml:mn>892</mml:mn> </mml:mfenced> <mml:mn>0</mml:mn> </mml:msup> </mml:math> and $$ {B}_s^0\to {\overline{D}}^0{\overline{K}}^{\star }{(892)}^0 $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>B</mml:mi> <mml:mi>s</mml:mi> <mml:mn>0</mml:mn> </mml:msubsup> <mml:mo>→</mml:mo> <mml:msup> <mml:mover> <mml:mi>D</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> <mml:mn>0</mml:mn> </mml:msup> <mml:msup> <mml:mover> <mml:mi>K</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> <mml:mo>⋆</mml:mo> </mml:msup> <mml:msup> <mml:mfenced> <mml:mn>892</mml:mn> </mml:mfenced> <mml:mn>0</mml:mn> </mml:msup> </mml:math> are also measured, but no evidence for interference is found. The B 0 observables are used to constrain the parameter space of the CKM angle γ and the hadronic parameters $$ {r}_{B^0}^{DK\star } $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>r</mml:mi> <mml:msup> <mml:mi>B</mml:mi> <mml:mn>0</mml:mn> </mml:msup> <mml:mrow> <mml:mi>DK</mml:mi> <mml:mo>⋆</mml:mo> </mml:mrow> </mml:msubsup> </mml:math> and $$ {\delta}_{B^0}^{DK\star } $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>δ</mml:mi> <mml:msup> <mml:mi>B</mml:mi> <mml:mn>0</mml:mn> </mml:msup> <mml:mrow> <mml:mi>DK</mml:mi> <mml:mo>⋆</mml:mo> </mml:mrow> </mml:msubsup> </mml:math> with inputs from other measurements. In a combined analysis, these measurements allow for four solutions in the parameter space, only one of which is consistent with the world average.

A search for ${K}_{\mathrm{S}(\mathrm{L})}^{0}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$ decays is performed using proton-proton collision data collected by the LHCb experiment at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of $5.1\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$. No evidence for signal is found. The 90% confidence level upper limits are the first set for both decays and are $\mathcal{B}({K}_{\mathrm{S}}^{0}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}})&lt;5.1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}12}$ and $\mathcal{B}({K}_{\mathrm{L}}^{0}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}})&lt;2.3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}$.

The mass difference between the Ω−b and Ξ−b baryons is measured using proton-proton collision data collected by the LHCb experiment, corresponding to an integrated luminosity of 9 fb−1, and is found to be m(Ω−b)−m(Ξ−b)=248.54±0.51(stat)±0.38(syst) MeV/c2. The mass of the Ω−b baryon is measured to be m(Ω−b)=6045.9±0.5(stat)±0.6(syst) MeV/c2. This is the most precise determination of the Ω−b mass to date. In addition, the production rate of Ω−b baryons relative to that of Ξ−b baryons is measured for the first time in pp collisions, using an LHCb dataset collected at a center-of-mass energy of 13 TeV and corresponding to an integrated luminosity of 6 fb−1. Reconstructing beauty baryons in the kinematic region 2<η<6 and pT<20 GeV/c with their decays to a J/ψ meson and a hyperon, the ratio fΩ−bfΞ−b×B(Ω−b→J/ψΩ−)B(Ξ−b→J/ψΞ−)=0.120±0.008(stat)±0.008(syst), is obtained, where fΩ−b and fΞ−b are the fragmentation fractions of b quarks into Ω−b and Ξ−b baryons, respectively, and B represents the branching fractions of their respective decays.Received 31 May 2023Accepted 9 August 2023DOI:https://doi.org/10.1103/PhysRevD.108.052008Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.© 2023 CERN, for the LHCb CollaborationPhysics Subject Headings (PhySH)Bottom baryonsPhysical SystemsHadronsBaryonsHeavy baryonsBottom baryonsResearch AreasFragmentation into hadronsHadron productionPhysical SystemsBottom baryonsHeavy baryonsHyperonsPropertiesMassParticles & Fields

The first observation and study of two new baryonic structures in the final state Ξ0bπ+π− and the confirmation of the Ξb(6100)− state in the Ξ−bπ+π− decay mode are reported using proton-proton collision data collected by the LHCb experiment, corresponding to an integrated luminosity of 9 fb−1. In addition, the properties of the known Ξ*0b, Ξ'−b and Ξ*−b resonances are measured with improved precision. The new decay mode of the Ξ0b baryon to the Ξ+c π− π+ π− final state is observed and exploited for the first time in these measurements.Received 30 July 2023Accepted 14 September 2023DOI:https://doi.org/10.1103/PhysRevLett.131.171901Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Funded by SCOAP3.© 2023 CERN, for the LHCb CollaborationPhysics Subject Headings (PhySH)Research AreasBottom quark productionParticle decaysPhysical SystemsBottom baryonsParticles & Fields

The CMS drift tubes (DT) muon detector, built for withstanding the LHC expected integrated and instantaneous luminosities, will be used also in the High Luminosity LHC (HL-LHC) at a 5 times larger instantaneous luminosity and, consequently, much higher levels of radiation, reaching about 10 times the LHC integrated luminosity. Initial irradiation tests of a spare DT chamber at the CERN gamma irradiation facility (GIF++), at large (∼ O(100)) acceleration factor, showed ageing effects resulting in a degradation of the DT cell performance. However, full CMS simulations have shown almost no impact in the muon reconstruction efficiency over the full barrel acceptance and for the full integrated luminosity. A second spare DT chamber was moved inside the GIF++ bunker in October 2017. The chamber was being irradiated at lower acceleration factors, and only 2 out of the 12 layers of the chamber were switched at working voltage when the radioactive source was active, being the other layers in standby. In this way the other non-aged layers are used as reference and as a precise and unbiased telescope of muon tracks for the efficiency computation of the aged layers of the chamber, when set at working voltage for measurements. An integrated dose equivalent to two times the expected integrated luminosity of the HL-LHC run has been absorbed by this second spare DT chamber and the final impact on the muon reconstruction efficiency is under study. Direct inspection of some extracted aged anode wires presented a melted resistive deposition of materials. Investigation on the outgassing of cell materials and of the gas components used at the GIF++ are underway. Strategies to mitigate the ageing effects are also being developed. From the long irradiation measurements of the second spare DT chamber, the effects of radiation in the performance of the DTs expected during the HL-LHC run will be presented.

The first study of $C\!P$ violation in the decay mode $B^\pm\to[K^+K^-\pi^+\pi^-]_D h^\pm$, with $h=K,\pi$, 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 $\gamma$ 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 $B^\pm\to[K^+K^-\pi^+\pi^-]_D h^\pm$ and $B^\pm\to[\pi^+\pi^-\pi^+\pi^-]_D h^\pm$ decays.

A bstract The CP asymmetries of seven B − decays to two charm mesons are measured using data corresponding to an integrated luminosity of 9 fb − 1 of proton-proton collisions collected by the LHCb experiment. Decays involving a D *0 or $$ {D}_s^{\ast -} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>D</mml:mi> <mml:mi>s</mml:mi> <mml:mrow> <mml:mo>∗</mml:mo> <mml:mo>−</mml:mo> </mml:mrow> </mml:msubsup> </mml:math> meson are analysed by reconstructing only the D 0 or $$ {D}_s^{-} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>D</mml:mi> <mml:mi>s</mml:mi> <mml:mo>−</mml:mo> </mml:msubsup> </mml:math> decay products. This paper presents the first measurement of $$ \mathcal{A} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>A</mml:mi> </mml:math> CP ( B − → $$ {D}_s^{\ast -} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>D</mml:mi> <mml:mi>s</mml:mi> <mml:mrow> <mml:mo>∗</mml:mo> <mml:mo>−</mml:mo> </mml:mrow> </mml:msubsup> </mml:math> D 0 ) and $$ \mathcal{A} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>A</mml:mi> </mml:math> CP ( B − → $$ {D}_s^{-} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>D</mml:mi> <mml:mi>s</mml:mi> <mml:mo>−</mml:mo> </mml:msubsup> </mml:math> D ∗ 0 ), and the most precise measurement of the other five CP asymmetries. There is no evidence of CP violation in any of the analysed decays. Additionally, two ratios between branching fractions of selected decays are measured.

A bstract A measurement of the CP-violating observables from B ± → D * K ± and B ± → D * π ± decays is presented, where D * ( D ) is an admixture of D *0 and $$ {\overline{D}}^{\ast 0} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mover> <mml:mi>D</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> <mml:mrow> <mml:mo>∗</mml:mo> <mml:mn>0</mml:mn> </mml:mrow> </mml:msup> </mml:math> ( D 0 and $$ {\overline{D}}^0 $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mover> <mml:mi>D</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> <mml:mn>0</mml:mn> </mml:msup> </mml:math> ) states and is reconstructed through the decay chains D * → Dπ 0 /γ and $$ D\to {K}_S^0{\pi}^{+}{\pi}^{-}/{K}_S^0{K}^{+}{K}^{-} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>D</mml:mi> <mml:mo>→</mml:mo> <mml:msubsup> <mml:mi>K</mml:mi> <mml:mi>S</mml:mi> <mml:mn>0</mml:mn> </mml:msubsup> <mml:msup> <mml:mi>π</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:msup> <mml:mi>π</mml:mi> <mml:mo>−</mml:mo> </mml:msup> <mml:mo>/</mml:mo> <mml:msubsup> <mml:mi>K</mml:mi> <mml:mi>S</mml:mi> <mml:mn>0</mml:mn> </mml:msubsup> <mml:msup> <mml:mi>K</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:msup> <mml:mi>K</mml:mi> <mml:mo>−</mml:mo> </mml:msup> </mml:math> . The measurement is performed by analysing the signal yield variation across the D decay phase space and is independent of any amplitude model. The data sample used was collected by the LHCb experiment in proton-proton collisions and corresponds to a total integrated luminosity of 9 fb − 1 at centre-of-mass energies of 7, 8 and 13 TeV. The CKM angle γ is determined to be $$ {\left({69}_{-14}^{+13}\right)}^{\circ } $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mfenced> <mml:msubsup> <mml:mn>69</mml:mn> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>14</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>13</mml:mn> </mml:mrow> </mml:msubsup> </mml:mfenced> <mml:mo>∘</mml:mo> </mml:msup> </mml:math> using the measured CP-violating observables. The hadronic parameters $$ {r}_B^{D^{\ast }{K}^{\pm }},{r}_B^{D^{\ast }{\pi}^{\pm }},{\delta}_B^{D^{\ast }{K}^{\pm }},{\delta}_B^{D^{\ast }{\pi}^{\pm }} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>r</mml:mi> <mml:mi>B</mml:mi> <mml:mrow> <mml:msup> <mml:mi>D</mml:mi> <mml:mo>∗</mml:mo> </mml:msup> <mml:msup> <mml:mi>K</mml:mi> <mml:mo>±</mml:mo> </mml:msup> </mml:mrow> </mml:msubsup> <mml:mo>,</mml:mo> <mml:msubsup> <mml:mi>r</mml:mi> <mml:mi>B</mml:mi> <mml:mrow> <mml:msup> <mml:mi>D</mml:mi> <mml:mo>∗</mml:mo> </mml:msup> <mml:msup> <mml:mi>π</mml:mi> <mml:mo>±</mml:mo> </mml:msup> </mml:mrow> </mml:msubsup> <mml:mo>,</mml:mo> <mml:msubsup> <mml:mi>δ</mml:mi> <mml:mi>B</mml:mi> <mml:mrow> <mml:msup> <mml:mi>D</mml:mi> <mml:mo>∗</mml:mo> </mml:msup> <mml:msup> <mml:mi>K</mml:mi> <mml:mo>±</mml:mo> </mml:msup> </mml:mrow> </mml:msubsup> <mml:mo>,</mml:mo> <mml:msubsup> <mml:mi>δ</mml:mi> <mml:mi>B</mml:mi> <mml:mrow> <mml:msup> <mml:mi>D</mml:mi> <mml:mo>∗</mml:mo> </mml:msup> <mml:msup> <mml:mi>π</mml:mi> <mml:mo>±</mml:mo> </mml:msup> </mml:mrow> </mml:msubsup> </mml:math> , which are the ratios and strong phase differences between favoured and suppressed B ± decays, are also reported.

The decay Ξb−→Λb0π− is observed using a proton-proton collision data sample collected at center-of-mass energy s=13 TeV with the LHCb detector, corresponding to an integrated luminosity of 5.5 fb−1. This process is mediated by the s→uu¯d quark-level transition, where the b quark in the Ξb− baryon is a spectator in the decay. Averaging the results obtained using the two Λb0 decay modes, Λb0→Λc+π− and Λb0→Λc+π−π+π−, the relative production ratio is measured to be (fΞb−/fΛb0)B(Ξb−→Λb0π−)=(7.3±0.8±0.6)×10−4. Here the uncertainties are statistical and systematic, respectively, and fΞb−(fΛb0) is the fragmentation fraction for a b quark into a Ξb− (Λb0) baryon. Using an independent measurement of fΞb−/fΛb0, the branching fraction B(Ξb−→Λb0π−)=(0.89±0.10±0.07±0.29)% is obtained, where the last uncertainty is due to the assumed SU(3) flavor symmetry in the determination of fΞb−/fΛb0.Received 18 July 2023Accepted 23 August 2023DOI:https://doi.org/10.1103/PhysRevD.108.072002Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Funded by SCOAP3.© 2023 CERN, for the LHCb CollaborationPhysics Subject Headings (PhySH)Physical SystemsBottom baryonsParticles & Fields

During the High Luminosity LHC, the Drift Tube chambers installed in the CMS detector need to operate with an integrated dose ten times higher than expected at the LHC due to the increase in integrated luminosity from 300 fb-1 to 3000 fb-1. Irradiations have been performed to assess the performance of the detector under such conditions and to characterize the radiation aging of the detector. The presented analysis focuses on the behaviour of the high voltage currents and the dose measurements needed to extrapolate the results to High Luminosity conditions, using data from the photon irradiation campaign at GIF++ in 2016 as well as the efficiency analysis from the irradiation campaign started in 2017. Although the single-wire loss of high voltage gain observed of 70% is very high, the muon reconstruction efficiency is expected to decrease less than 20% during the full duration of High Luminosity LHC in the areas under highest irradiation.

To sustain and extend its discovery potential, the Large Hadron Collider (LHC) will undergo a major upgrade in the coming years, referred to as High Luminosity LHC (HLLHC), aimed to increase its instantaneous luminosity, 5 times larger than the designed limit, and, consequently leading to high levels of radiation, with the goal to collect 10 times larger the original designed integrated luminosity. The drift tube chambers (DT) of CMS muon detector system is built to proficiently measure and trigger on muons in the harsh radiation environment expected during the HL-LHC era. Ageing studies are performed at the CERNs gamma ray irradiation facility (GIF++) by measuring the muon hit efficiency of these detectors at various LHC operation conditions. One such irradiation campaign was started in October 2017, when a spare MB2 chamber moved inside the bunker and irradiated at lower acceleration factors. Two out of twelve layers of the DT chamber were operated while being irradiated with the radioactive source and then their muon hit efficiency was calculated in coincidence with other ten layers which were kept on the standby. The chamber absorbed an integrated dose equivalent to two times the expected integrated luminosity of the HL-LHC. Investigation on the outgassing of cell materials and of the gas components used at the GIF++ are underway and strategies to mitigate the aging effects are also being developed. The effect of radiation on the performance of DT chamber and its impact on the overall muon reconstruction efficiency expected during the HL-LHC are presented.