| 1. |
- Aaij, R., et al.
(author)
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A model-independent measurement of the CKM angle γ in partially reconstructed B±→D∗h± decays with D→K0Sh+h-(h=π,K)
- 2024
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In: Journal of High Energy Physics (JHEP). - : Springer. - 1126-6708 .- 1029-8479. ; :2
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Journal article (peer-reviewed)abstract
- 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∗ → Dγ or D∗ → Dπ0 decayis not reconstructed. The D meson is reconstructed in the self-conjugate decay modes,D → K0Sπ+π− or D → K0SK+K−. The distribution of signal yields in the D decay phasespace is analysed in a model-independent way. The measurement uses a data sample collectedin proton-proton collisions at centre-of-mass energies of 7, 8, and 13 TeV, corresponding toa 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 angleγ, resulting in a measurement of γ = (92+21−17)◦. The total uncertainty includes the statisticaland systematic uncertainties, and the uncertainty due to external strong-phase inputs.
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| 2. |
- Aaij, R., et al.
(author)
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A search for rare B → Dμ+μ− decays
- 2024
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In: Journal of High Energy Physics (JHEP). - : Springer. - 1126-6708 .- 1029-8479. ; 2024:2
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Journal article (peer-reviewed)abstract
- A search for rare B → Dμ+μ− decays is performed using proton-proton collision data collected by the LHCb experiment, corresponding to an integrated luminosity of 9 fb−1. No significant signals are observed in the non-resonant μ+μ− modes, and upper limits of B(B0 → D0μ+μ−)< 5.1 × 10−8, B (B+ → D+s μ+μ−) < 3.2 × 10−8, B(B0s → D0μ+μ−)<1.6 × 10−7 and fc/fu · B (B+c → D+s μ+μ−) < 9.6 × 10−8 are set at the 95 % confidencelevel, where fc and fu are the fragmentation fractions of a B meson with a c and u quarkrespectively in proton-proton collisions. Each result is either the first such measurement oran improvement by three orders of magnitude on an existing limit. Separate upper limits arecalculated when the muon pair originates from a J/ψ → μ+μ− decay. The branching fractionof B+c → D+s J/ψ multiplied by the fragmentation-fraction ratio is measured to befc/fu · B(B+c → D+s J/ψ)= (1.63 ± 0.15 ± 0.13) × 10−5,where the first uncertainty is statistical and the second systematic.
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| 3. |
- Aaij, R., et al.
(author)
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Amplitude Analysis of the B0 → K*0 μ+μ- Decay
- 2024
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In: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 132:13
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Journal article (peer-reviewed)abstract
- An amplitude analysis of the B0 → K*0μ+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 q2-unbinned amplitude analysis, where q2 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.
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| 4. |
- Aaij, R., et al.
(author)
-
Amplitude Analysis of the B0 →k∗0μ+μ- Decay : Physical Review Letters
- 2024
-
In: Physical Review Letters. - 1079-7114. ; 132:13
-
Journal article (peer-reviewed)abstract
- An amplitude analysis of the B0→K∗0μ+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 q2-unbinned amplitude analysis, where q2 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. © 2024 CERN.
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| 5. |
- Aaij, R., et al.
(author)
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Curvature-bias corrections using a pseudomass method
- 2024
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In: Journal of Instrumentation. - 1748-0221. ; 19:3
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Journal article (peer-reviewed)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. © 2024 CERN.
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| 6. |
- Aaij, R., et al.
(author)
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Determination of short- and long-distance contributions in B0 →k∗0μ+μ- decays
- 2024
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In: Physical Review D. - 2470-0010. ; 109:5
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Journal article (peer-reviewed)abstract
- 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. © 2024 CERN.
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| 7. |
- Aaij, R., et al.
(author)
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Enhanced Production of Λb0 Baryons in High-Multiplicity pp Collisions at s =13 TeV
- 2024
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In: Physical Review Letters. - 1079-7114. ; 132:8
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Journal article (peer-reviewed)abstract
- The production rate of Λb0 baryons relative to B0 mesons in pp collisions at a center-of-mass energy s=13 TeV is measured by the LHCb experiment. The ratio of Λb0 to B0 production cross sections shows a significant dependence on both the transverse momentum and the measured charged-particle multiplicity. At low multiplicity, the ratio measured at LHCb is consistent with the value measured in e+e- collisions, and increases by a factor of ∼2 with increasing multiplicity. At relatively low transverse momentum, the ratio of Λb0 to B0 cross sections is higher than what is measured in e+e- collisions, but converges with the e+e- ratio as the momentum increases. These results imply that the evolution of heavy b quarks into final-state hadrons is influenced by the density of the hadronic environment produced in the collision. Comparisons with several models and implications for the mechanisms enforcing quark confinement are discussed. © 2024 CERN.
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| 8. |
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| 9. |
- Aaij, R., et al.
(author)
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Helium identification with LHCb
- 2024
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In: Journal of Instrumentation. - 1748-0221. ; 19:2
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Journal article (peer-reviewed)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 105 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(1012). These results demonstrate the feasibility of a rich programme of measurements of QCD and astrophysics interest involving light nuclei. © 2024 Institute of Physics. All rights reserved.
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| 10. |
- Aaij, R., et al.
(author)
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Improved Measurement of CP Violation Parameters in B0s→J/ψK+K− Decays in the Vicinity of the ϕ(1020) Resonance
- 2024
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In: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 132:5
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Journal article (peer-reviewed)abstract
- The decay-time-dependent CP asymmetry in B0s→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 B0s 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 B0s−¯B0s system, ΔΓs, and the difference of the average B0s 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=−0.0056+0.0013−0.0015±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.
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