LHCb Collaboration(Aaij, R. et al), Jaimes Elles, S. J., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., Rebollo De Miguel, M., et al. (2024). Curvature-bias corrections using a pseudomass method. J. Instrum., 19(3), P03010–22pp.
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 root s = 13 TeV during 2016, 2017 and 2018. The biases are determined using Z -> mu(+)mu(-) 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 -> mu(+)mu(-) mass resolution by roughly 18% and eliminates several pathological trends in the kinematic-dependence of the mean dimuon invariant mass.
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LHCb Collaboration(Aaij, R. et al), Jaimes Elles, S. J., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., Rebollo De Miguel, M., et al. (2024). Helium identification with LHCb. J. Instrum., 19(2), P02010–23pp.
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 root 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.
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LHCb Collaboration(Aaij, R. et al), Jaimes Elles, S. J., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., Rebollo De Miguel, M., et al. (2024). A model-independent measurement of the CKM angle γ in partially reconstructed B±→D∗h± decays with D→K0Sh+h-(h=π,K). J. High Energy Phys., 02(2), 118–30pp.
Abstract: A measurement of CP-violating observables in B-+/-->(DK +/-)-K-& lowast; and B-+/--> D-& lowast;pi(+/-) decays is made where the photon or neutral pion from the D-& lowast;-> D gamma or D-& lowast;-> D pi(0) decay is not reconstructed. The D meson is reconstructed in the self-conjugate decay modes, D -> K-S(0)pi(+)pi(-) or D ->(KSK+K-)-K-0. 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-+/-->(DK +/-)-K-& lowast; and B-+/--> D-& lowast;pi(+/-) CP-violating observables are interpreted in terms of hadronic parameters and the CKM angle gamma, resulting in a measurement of gamma=(92(-17)(+21))degrees. The total uncertainty includes the statistical and systematic uncertainties, and the uncertainty due to external strong-phase inputs.
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LHCb Collaboration(Aaij, R. et al), Jaimes Elles, S. J., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., Rebollo De Miguel, M., et al. (2024). Search for CP violation in the phase space of D0 → KS0 K± π∓ decays with the energy test. J. High Energy Phys., 03(3), 107–20pp.
Abstract: A search for CP violation in D-0 -> (KSK+)-K-0 pi(-) and D-0 -> (KSK-)-K-0 pi(+) 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 root s = 13TeV, amounting to approximately 950 thousand and 620 thousand signal candidates for the D-0 -> (KSK-)-K-0 pi(+) and D-0 -> (KSK+)-K-0 pi(-) modes, respectively. The method is validated using D-0 -> K-pi(+)pi(-)pi(+) and D-0 -> K-S(0)pi(+)pi(-) 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 -> (KSK-)-K-0 pi(+) and the D-0 -> (KSK+)-K-0 pi(-) decays, with p-values for the hypothesis of no CP violation of 70% and 66%, respectively.
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LHCb Collaboration(Aaij, R. et al), Jaimes Elles, S. J., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., Rebollo De Miguel, M., et al. (2023). Evidence for the decays B0 → (D)over-bar(*)0 φ and updated measurements of the branching fractions of the Bs0 → (D)over-bar(*)0 φ decays. J. High Energy Phys., 10(10), 123–26pp.
Abstract: Evidence for the decays B-0 -> (D) over bar (0)phi and B-0 -> (D) over bar (*0) phi is reported with a significance of 3.6 sigma and 4.3 sigma, respectively. The analysis employs pp collision data at centre-of-mass energies root s = 7, 8 and 13TeV collected by the LHCb detector and corresponding to an integrated luminosity of 9 fb(-1). The branching fractions are measured to be B(B-0 -> (D) over bar (0)phi) = (7.7 +/- 2.1 +/- 0.7 +/- 0.7) x 10(-7), B(B-0 -> (D) over bar (*0)phi) = (2.2 +/- 05 +/- 0.2 +/- 0.2) x 10(-6). In these results, the first uncertainty is statistical, the second systematic, and the third is related to the branching fraction of the B-0 -> (D) over bar K-0(+) K- decay, used for normalisation. By combining the branching fractions of the decays B-0 -> (D) over bar ((*)0)phi and B-0 -> (D) over bar ((*)0)omega, the omega-phi mixing angle delta is constrained to be tan(2)delta = (3.6 +/- 0.7 +/- 0.4) x 10(-3), where the first uncertainty is statistical and the second systematic. An updated measurement of the branching fractions of the B-s(0) -> (D) over bar ((*)0).phi decays, which can be used to determine the CKM angle gamma, leads to B(B-s(0) -> (D) over bar (0)phi) = (2.30 +/- 0.10 +/- 0.11 +/- 0.20) x 10(-5), B(B-s(0) -> (D) over bar (*0)phi) = (3.17 +/- 0.16 +/- 0.17 +/- 0.27) x 10(-5).
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