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LHCb Collaboration(Aaij, R. et al), Garcia Martin, L. M., Henry, L., Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., et al. (2018). Measurement of branching fractions of charmless four-body Lambda(0)(b) and Xi(0)(b) decays. J. High Energy Phys., 02(2), 098–25pp.
Abstract: A search for charmless four-body decays of Lambda(0)(b) and Xi(0)(b) baryons with a proton and three charged mesons (either kaons or pions) in the final state is performed. The data sample used was recorded in 2011 and 2012 with the LHCb experiment and corresponds to an integrated luminosity of 3 fb(-1). Six decay modes are observed, among which Lambda(0)(b) -> pK(-) pi(+)pi(-), Lambda(0)(b) -> pK(-)K(+)K(-), Xi(0)(b) pK(-) pi(+)pi(-) and Xi(0)(b) pK(-)pi K-+(-) are established for the first time. Their branching fractions (including the ratio of hadronisation fractions in the case of the Xi(0)(b) baryon) are determined relative to the Lambda(0)(b) -> Lambda(+)(c)pi(-) decay.
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ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Barranco Navarro, L., Cabrera Urban, S., Castillo Gimenez, V., Cerda Alberich, L., et al. (2017). Measurement of charged-particle distributions sensitive to the underlying event in root s=13 TeV proton-proton collisions with the ATLAS detector at the LHC. J. High Energy Phys., 03(3), 157–42pp.
Abstract: We present charged-particle distributions sensitive to the underlying event, measured by the ATLAS detector in proton-proton collisions at a centre-of-mass energy of 13 TeV, in low-luminosity Large Hadron Collider fills corresponding to an integrated luminosity of 1.6 nb-1. The distributions were constructed using charged particles with absolute pseudorapidity less than 2.5 and with transverse momentum greater than 500 MeV, in events with at least one such charged particle with transverse momentum above 1 GeV. These distributions characterise the angular distribution of energy and particle flows with respect to the charged particle with highest transverse momentum, as a function of both that momentum and of charged-particle multiplicity. The results have been corrected for detector effects and are compared to the predictions of various Monte Carlo event generators, experimentally establishing the level of underlying-event activity at LHC Run 2 energies and providing inputs for the development of event generator modelling. The current models in use for UE modelling typically describe this data to 5% accuracy, compared with data uncertainties of less than 1%.
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ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fernandez Martinez, P., Ferrer, A., et al. (2015). Measurement of charged-particle spectra in Pb plus Pb collisions at root s(NN)=2.76 TeV with the ATLAS detector at the LHC. J. High Energy Phys., 09(9), 050–51pp.
Abstract: Charged-particle spectra obtained in Pb+Pb interactions at root s(NN) = 2.76TeV and pp interactions at root s(NN) = 2.76TeV with the ATLAS detector at the LHC are presented, using data with integrated luminosities of 0.15 nb(-1) and 4.2 pb(-1), respectively, in a wide transverse momentum (0.5 < p(T) < 150 GeV) and pseudorapidity (vertical bar eta vertical bar < 2) range. For Pb+Pb collisions, the spectra are presented as a function of collision centrality, which is determined by the response of the forward calorimeters located on both sides of the interaction point. The nuclear modification factors R-AA and R-CP are presented in detail as a function of centrality, p(T) and eta. They show a distinct p(T)-dependence with a pronounced minimum at about 7 GeV. Above 60 GeV, R-AA is consistent with a plateau at a centrality-dependent value, within the uncertainties. The value is 0.55 +/- 0.01(stat.) +/- 0.04(syst.) in the most central collisions. The R-AA distribution is consistent with flat vertical bar eta vertical bar dependence over the whole transverse momentum range in all centrality classes.
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LHCb Collaboration(Aaij, R. et al), Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., & Ruiz Vidal, J. (2022). Measurement of chi(c1) (3872) production in proton-proton collisions at root s=8 and 13 TeV. J. High Energy Phys., 01(1), 131–27pp.
Abstract: The production cross-section of the chi(c1)(3872) state relative to the psi(2S) meson is measured using proton-proton collision data collected with the LHCb experiment at centre-of-mass energies of root s = 8 and 13 TeV, corresponding to integrated luminosities of 2.0 and 5.4 fb(-1), respectively. The two mesons are reconstructed in the J/psi pi(+) pi(-) final state. The ratios of the prompt and nonprompt chi(c1)(3872) to psi(2S) production cross-sections are measured as a function of transverse momentum, p(T), and rapidity, y, of the chi(c1)(3872) and psi(2S) states, in the kinematic range 4 < p(T) < 20 GeV/c and 2.0 < y < 4.5. The prompt ratio is found to increase with pT , independently of y. For the prompt component, the double ratio of the chi(c1)(3872) and psi(2S) production cross-sections between 13 and 8 TeV is observed to be consistent with unity, independent of p(T) and centre-of-mass energy.
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ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fassi, F., Ferrer, A., et al. (2014). Measurement of chi(c1) and chi(c2) production with root s=7 TeV pp collisions at ATLAS. J. High Energy Phys., 07(7), 154–52pp.
Abstract: The prompt and non-prompt production cross-sections for the chi(c1) and chi(c2) charmonium states are measured in pp collisions at root s = 7TeV with the ATLAS detector at the LHC using 4.5 fb(-1) of integrated luminosity. The chi(c) states are reconstructed through the radiative decay chi c -> J/psi gamma ( with J/psi -> mu(+)mu(-)) where photons are reconstructed from gamma -> e(+)e(-) conversions. The production rate of the chi(c2) state relative to the chi(c1) state is measured for prompt and non-prompt chi(c) as a function of J/psi transverse momentum. The prompt chi(c) cross-sections are combined with existing measurements of prompt J/psi production to derive the fraction of prompt J/psi produced in feed-down from chi(c) decays. The fractions of chi(c1) and chi(c2) produced in b-hadron decays are also measured.
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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). Measurement of CP asymmetries and branching fraction ratios of B- decays to two charm mesons. J. High Energy Phys., 09(9), 202–30pp.
Abstract: 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(*-) meson are analysed by reconstructing only the D-0 or D-s(-) decay products. This paper presents the first measurement of A(CP) (B- -> D-s(*-) D-0) and A(CP) (B- -> D-s(-) 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.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2015). Measurement of CP asymmetries and polarisation fractions in B-s(0) -> K*(0)(K)over-bar*(0) decays. J. High Energy Phys., 07(7), 166–28pp.
Abstract: An angular analysis of the decay B-s(0) -> K*(0)(K) over bar*(0) is performed using pp collisions corresponding to an integrated luminosity of 1.0 fb(-1) collected by the LHCb experiment at a centre-of-mass energy root s = 7TeV. A combined angular and mass analysis separates six helicity amplitudes and allows the measurement of the longitudinal polarisation fraction f(L) = 0.201 +/- 0.057 (stat.) +/- 0.040 (syst.) for the B-s(0) -> K*(892)(0)(K) over bar*(892)(0) decay. A large scalar contribution from the K*(0) (1430) and K*(0) (800) resonances is found, allowing the determination of additional CP asymmetries. Triple product and direct CP asymmetries are determined to be compatible with the Standard Model expectations. The branching fraction B(B-s(0) -> K*(892)(0)(K) over bar*(892)(0)) is measured to be (10.8 +/- 2.1 (stat.) +/- 1.4 (syst.) +/- 0.6 (f(d)/f(s))) x 10(-6).
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LHCb Collaboration(Aaij, R. et al), Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., & Ruiz Vidal, J. (2023). Measurement of CP asymmetries in D-(s)(+) -> eta pi(+) and D-(s)(+) -> eta 'pi(+) decays. J. High Energy Phys., 04(4), 081–23pp.
Abstract: Searches for CP violation in the decays D-(s)(+) -> eta pi(+) and D-(s)(+) -> eta'pi(+) are performed using pp collision data corresponding to 6 fb(-1) of integrated luminosity collected by the LHCb experiment. The calibration channels D-(s)(+) -> phi pi(+) are used to remove production and detection asymmetries. The resulting CP-violating asymmetries are A(CP) (D+ -> eta pi(+)) = (0.34 +/- 0.66 +/- 0.16 +/- 0.05)%, A(CP) (D-s(+) -> eta pi(+)) = (0.32 +/- 0.51 +/- 0.12)%, A(CP) (D+ -> eta'pi(+)) = (0.49 +/- 0.18 +/- 0.06 +/- 0.05)%, A(CP) (D-s(+) -> eta'pi(+)) = (0.01 +/- 0.12 +/- 0.08)%, where the first uncertainty is statistical, the second is systematic and the third, relevant for the D+ channels, is due to the uncertainty on A(CP) (D+ -> phi pi(+)). These measurements, currently the most precise for three of the four channels considered, are consistent with the absence of CP violation. A combination of these results with previous LHCb measurements is presented.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2014). Measurement of CP asymmetries in the decays B-0 -> K-*0 mu(+) mu(-) and B+ -> K+ mu(+) mu(-). J. High Energy Phys., 09(9), 177–18pp.
Abstract: The direct CP asymmetries of the decays B-0 -> K-*0 mu(+) mu(-) and B+ -> K+ mu(+) mu(-) are measured using pp collision data corresponding to an integrated luminosity of 3.0 fb(-1) collected with the LHCb detector. The respective control modes B-0 -> J/psi K+ and B+ -> J/psi K+ are used to account for detection and production asymmetries. The measurements are made in several intervals of mu(+)mu(-) invariant mass squared, with the phi(1020) and charmonium resonance regions excluded. Under the hypothesis of zero CP asymmetry in the control modes, the average values of the asymmetries are A(CP)(B-0 -> K-*0 mu(+) mu(-) and B+ -> K+ mu(+) mu(-)) = -0.035 +/- 0.024 +/- 0.003, A(CP)(B+ -> K+ mu(+) mu(-) = 0.012 +/- 0.017 +/- 0.001, where the first uncertainties are statistical and the second are due to systematic effects. Both measurements are consistent with the Standard Model prediction of small CP asymmetry in these decays.
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LHCb Collaboration(Aaij, R. et al), Garcia Martin, L. M., Henry, L., Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., et al. (2018). Measurement of CP asymmetry in B-s(0) -> (DsK +/-)-K-/+ decays. J. High Energy Phys., 03(3), 059–28pp.
Abstract: We report the measurements of the CP-violating parameters in B-s(0) -> (DsK +/-)-K--/+ decays observed in pp collisions, using a data set corresponding to an integrated luminosity of 3.0 fb(-1) recorded with the LHCb detector. We measure C-f = 0.73 +/- 0.14 +/- 0.05, A(f)(Delta Gamma) = 0.39 +/- 0.28 +/- 0.15, A(<(f)over) (Delta Gamma)(bar>) = 0.31 +/- 0.28 +/- 0.15, S-f = -0.52 +/- 0.20 +/- 0.07, S-(f) over bar = -0.49 +/- 0.20 +/- 0.07, where the uncertainties are statistical and systematic, respectively. These parameters are used together with the world-average value of the B-s(0) mixing phase, -2 beta(s), to obtain a measurement of the CKM angle gamma from B-s(0) -> (DsK +/-)-K--/+ decays, yielding gamma – (128 (+17)(-22))degrees modulo 180 degrees, where the uncertainty contains both statistical and systematic contributions. This corresponds to 3.8 sigma evidence for CP violation in the interference between decay and decay after mixing.
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