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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). Measurement of prompt D+ and Ds+ production in pPb collisions at √s_NN=5.02 TeV. J. High Energy Phys., 01(1), 070–43pp.
Abstract: The production of prompt D+ and D-s(+) mesons is studied in proton-lead collisions at a centre-of-mass energy of root s(NN) = 5.02TeV. The data sample corresponding to an integrated luminosity of (1.58 +/- 0.02)nb(-1) is collected by the LHCb experiment at the LHC. The differential production cross-sections are measured using D+ and D-s(+) candidates with transverse momentum in the range of 0 < p(T) < 14 GeV/c and rapidities in the ranges of 1.5 < y* < 4.0 and -5.0 < y* < -2.5 in the nucleon-nucleon centre-of-mass system. For both particles, the nuclear modification factor and the forward-backward production ratio are determined. These results are compared with theoretical models that include initial-state nuclear effects. In addition, measurements of the cross-section ratios between D+, D-s(+) and D-0 mesons are presented, providing a baseline for studying the charm hadronization in lead-lead collisions at LHC energies.
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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). Observation of the B+ → Jψη'K+ decay. J. High Energy Phys., 08(8), 174–27pp.
Abstract: The B+ -> J psi eta'K+ decay is observed for the first time using proton-proton collision data collected by the LHCb experiment at centre-of-mass energies of 7, 8, and 13TeV, corresponding to a total integrated luminosity of 9 fb(-1). The branching fraction of this decay is measured relative to the known branching fraction of the B+ -> psi(2S)K+ decay and found to be B(B+ -> J psi eta'K+)/B(B+ -> psi(2S)K+) = (4.91 +/- 0.47 +/- 0.29 +/- 0.07) x 10(-2), where the first uncertainty is statistical, the second is systematic and the third is related to external branching fractions. A first look at the J/psi eta' mass distribution is performed and no signal of intermediate resonances is observed.
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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). Study of Bc+ → χc π+ decays. J. High Energy Phys., 02(2), 173–30pp.
Abstract: A study of B-c(+) -> chi(c) pi(+) decays is reported using proton-proton collision data, collected with the LHCb detector at centre-of-mass energies of 7, 8, and 13TeV, corresponding to an integrated luminosity of 9 fb(-1). The decay B-c(+) -> chi(c2)pi(+) is observed for the first time, with a significance exceeding seven standard deviations. The relative branching fraction with respect to the B-c(+) -> J/psi pi(+) decay is measured to be BBc+ ->chi c2 pi+/BBc+ -> (J/psi pi+) = 0.37 +/- 0.06 +/- 0.02 +/- 0.01, where the first uncertainty is statistical, the second is systematic, and the third is due to the knowledge of the chi(c2) -> J/psi gamma branching fraction. No significant B-c(+) -> chi(+)(c1 pi) signal is observed and an upper limit for the relative branching fraction for the B-c(+) -> chi(c1)pi(+) and B-c(+) -> chi(c2)pi(+) decays of BBc+ ->chi c1 pi+/BBc+ -> chi(c2)pi(+) < 0.49 is set at the 90% confidence level.
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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). Measurement of J/ψ-pair production in pp collisions at √s=13 TeV and study of gluon transverse-momentum dependent PDFs. J. High Energy Phys., 03(3), 088–40pp.
Abstract: The production cross-section of J/psi pairs in proton-proton collisions at a centre-of-mass energy of root s = 13TeV 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/psi mesons in the transverse momentum range 0 < p(T) < 14 GeV/c and rapidity range 2.0 < y < 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 Delta y between the two J/psi mesons. The effective cross-section of double-parton scattering is measured to be sigma(eff) = 13.1 +/- 1.8 (stat) +/- 2.3 (syst) mb. The distribution of the azimuthal angle phi(CS) of one of the J/psi mesons in the Collins-Soper frame and the p(T)-spectrum of the J/psi pairs are also measured for the study of the gluon transverse-momentum dependent distributions inside protons. The extracted values of < cos4 phi(CS)> and < cos2 phi(CS)> are consistent with zero, but the presence of azimuthal asymmetry at a few percent level is allowed.
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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). Prompt and nonprompt ψ(2S) production in pPb collisions at √sNN = 8.16 TeV. J. High Energy Phys., 04(4), 111–52pp.
Abstract: The production of psi(2S) mesons in proton-lead collisions at a centre-of-mass energy per nucleon pair of root s(NN) = 8.16TeV is studied with the LHCb detector using data corresponding to an integrated luminosity of 34 nb(-1). The prompt and nonprompt psi(2S) production cross-sections and the ratio of the psi(2S) to J/psi cross-section are measured as a function of the meson transverse momentum and rapidity in the nucleon-nucleon centre-of-mass frame, together with forward-to-backward ratios and nuclear modification factors. The production of prompt psi(2S) is observed to be more suppressed compared to pp collisions than the prompt J/psi production, while the nonprompt productions have similar suppression factors.
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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), Oyanguren, A., & Ruiz Valls, P. (2013). Precision measurement of the B-s(0)-(B)over-bar(s)(0) oscillation frequency with the decay B-s(0) -> D-s(-)pi(+). New J. Phys., 15, 053021–15pp.
Abstract: A key ingredient to searches for physics beyond the Standard Model in B-s(0) mixing phenomena is the measurement of the B-s(0)-(B) over bar (0)(s) oscillation frequency, which is equivalent to the mass difference Delta m(s) of the B-s(0) mass eigenstates. Using the world's largest B-s(0) meson sample accumulated in a dataset, corresponding to an integrated luminosity of 1.0 fb(-1), collected by the LHCb experiment at the CERN LHC in 2011, a measurement of Delta m(s) is presented. A total of about 34 000 B-s(0) -> D-s(-)pi(+) signal decays are reconstructed, with an average decay time resolution of 44 fs. The oscillation frequency is measured to be Delta m(s) = 17.768 +/- 0.023 (stat) +/- 0.006 (syst) ps(-1), which is the most precise measurement to date.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2014). Observation of B-s(0) -> K* (+/-) K -/+ and evidence for B-s(0) -> K*(-) pi(+) decays. New J. Phys., 16, 123001–18pp.
Abstract: Measurements of the branching fractions of B-s(0) -> K*K-+/-(-/+) and B-s(0) -> K*(+/-) pi(-/+) decays are performed using a data sample corresponding to 1.0 fb(-1) of protonproton collision data collected with the LHCb detector at a centre-of- mass energy of 7 TeV, where the K*(+/-) mesons are reconstructed in the K-s(0) pi(+/-) final state. The first observation of the B-s(0) -> K*(+/-) K--/+ decay and the first evidence for the B-s(0) -> K*(-) pi(+) decay are reported with branching fractions B(B-s(0) -> K*K-+/-(-/+)) = (12.7 +/- 1.9 +/- 1.9) x 10(-6) , B(B-s(0) -> K*(-) pi(+)) = (3.3 +/- 1.1 +/- 0.5) x 10(-6) , where the first uncertainties are statistical and the second are systematic. In addition, an upper limit of B(B-0 -> K*K-+/-(-/+)) < 0.4 (0.5) x 10(-6) is set at 90% (95%) confidence level.
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DELPHI Collaboration(Abdallah, J. et al), Costa, M. J., Ferrer, A., Fuster, J., Garcia, C., Oyanguren, A., et al. (2010). Study of the dependence of direct soft photon production on the jet characteristics in hadronic Z (0) decays. Eur. Phys. J. C, 67(3-4), 343–366.
Abstract: An analysis of the direct soft photon production rate as a function of the parent jet characteristics is presented, based on hadronic events collected by the DELPHI experiment at LEP1. The dependences of the photon rates on the jet kinematic characteristics (momentum, mass, etc.) and on the jet charged, neutral and total hadron multiplicities are reported. Up to a scale factor of about four, which characterizes the overall value of the soft photon excess, a similarity of the observed soft photon behavior to that of the inner hadronic bremsstrahlung predictions is found for the momentum, mass, and jet charged multiplicity dependences. However for the dependence of the soft photon rate on the jet neutral and total hadron multiplicities a prominent difference is found for the observed soft photon signal as compared to the expected bremsstrahlung from final state hadrons. The observed linear increase of the soft photon production rate with the jet total hadron multiplicity and its strong dependence on the jet neutral multiplicity suggest that the rate is proportional to the number of quark pairs produced in the fragmentation process, with the neutral pairs being more effectively radiating than the charged ones.
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