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NA64 Collaboration(Andreev, Y. M. et al), Molina Bueno, L., & Tuzi, M. (2024). First Results in the Search for Dark Sectors at NA64 with the CERN SPS High Energy Muon Beam. Phys. Rev. Lett., 132(21), 211803–7pp.
Abstract: We report the first search for dark sectors performed at the NA64 experiment employing a high energy muon beam and a missing energy-momentum technique. Muons from the M2 beamline at the CERN Super Proton Synchrotron with a momentum of 160 GeV/c are directed to an active target. The signal signature consists of a single scattered muon with momentum < 80 GeV/c in the final state, accompanied by missing energy, i.e., no detectable activity in the downstream calorimeters. For a total dataset of (1.98 +/- 0.02) x 10(10) muons on target, no event is observed in the expected signal region. This allows us to set new limits on the remaining (m(Z)'; g(Z)') parameter space of a new Z' (L-mu – L-tau) vector boson which could explain the muon (g – 2)(mu) anomaly. Additionally, our study excludes part of the parameter space suggested by the thermal dark matter relic abundance. Our results pave the way to explore dark sectors and light dark matter with muon beams in a unique and complementary way to other experiments.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2015). First Observation of Top Quark Production in the Forward Region. Phys. Rev. Lett., 115(11), 112001–10pp.
Abstract: Top quark production in the forward region in proton-proton collisions is observed for the first time. The W + b final state with W -> μnu is reconstructed using muons with a transverse momentum, p(T), larger than 25 GeV in the pseudorapidity range 2.0 < eta < 4.5. The b jets are required to have 50 < p(T) < 100 GeV and 2.2 < eta < 4.2, while the transverse component of the sum of the muon and b-jet momenta must satisfy p(T) > 20 GeV. The results are based on data corresponding to integrated luminosities of 1.0 and 2.0 fb(-1) collected at center-of-mass energies of 7 and 8 TeV by LHCb. The inclusive top quark production cross sections in the fiducial region are sigma(top)[7 TeV] = 239 +/- 53(stat) +/- 33(syst) +/- 24(theory) fb; sigma(top)[8 TeV ] = 289 +/- 43(stat) +/- 40(syst) +/- 29(theory) fb: These results, along with the observed differential yields and charge asymmetries, are in agreement with next-to-leading order standard model predictions.
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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. (2017). First Observation of the Rare Purely Baryonic Decay B0 -> p p-bar. Phys. Rev. Lett., 119(23), 232001–10pp.
Abstract: The first observation of the decay of a B0 meson to a purely baryonic final state, B-0 -> p$(p)over-bar-$ , is reported. The proton-proton collision data sample used was collected with the LHCb experiment at center-of-mass energies of 7 and 8 TeV and corresponds to an integrated luminosity of 3.0 fb(-1). The branching fraction is determined to be B(B-0 -> p$(p)over-bar-$) = (1.25 +/- 0.27 +/- 0.18) x 10(-8), where the first uncertainty is statistical and the second systematic. The decay mode B-0 -> p$(p)over-bar-$ is the rarest decay of the B-0 meson observed to date. The decay B-s(0 )-> p$(p)over-bar-$ is also investigated. No signal is seen and the upper limit B(B-s(0) -> p$(p)over-bar-$) < 1.5 x 10(-8) at 90% confidence level is set on the branching fraction.
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LHCb Collaboration(Aaij, R. et al), Garcia Martin, L. M., Henry, L., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., et al. (2019). First Observation of the Radiative Decay Lambda(0 )(b)-> Lambda gamma. Phys. Rev. Lett., 123(3), 031801–11pp.
Abstract: The radiative decay Lambda(0 )(b)-> Lambda gamma is observed for the first time using a data sample of proton-proton collisions corresponding to an integrated luminosity of 1.7 fb(-1) collected by the LHCb experiment at a center-of-mass energy of 13 TeV. Its branching fraction is measured exploiting the B-0 -> K*(0)gamma decay as a normalization mode and is found to be B(Lambda(0 )(b)-> Lambda gamma) = (7.1 +/- 1.5 +/- 0.6 +/- 0.7) x 10(-6), where the quoted uncertainties arc statistical, systematic, and systematic from external inputs, respectively. This is the first observation of a radiative decay of a beauty baryon.
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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). First Observation of the Doubly Charmed Baryon Decay Xi(++)(cc) -> Xi(+)(c)pi(+). Phys. Rev. Lett., 121(16), 162002–10pp.
Abstract: The doubly charmed baryon decay Xi(++)(cc) -> Xi(+)(c)pi(+) is observed for the first time, with a statistical significance of 5.9 sigma, confirming a recent observation of the baryon in the Lambda K-+(c)-pi(+)pi(+) final state. The data sample used corresponds to an integrated luminosity of 1.7 fb(-1), collected by the LHCb experiment in pp collisions at a center-of-mass energy of 13 TeV. The Xi(++)(cc) mass is measured to be 3620.6 +/- 1.5(stat) +/- 0.4(syst) +/- 0.3(Xi(+)(c)) MeV/c(2) and is consistent with the previous result. The ratio of branching fractions between the decay modes is measured to be [B(Xi(++)(cc) -> Xi(+)(c)pi(+)) x B(Xi(+)(c) -> pK(-)pi(+))]/[B(Xi(++)(cc) -> Lambda K-+(c)-pi(+)pi(+)) x B(Lambda(+)(c) -> pK(-)pi(+))] = 0.035 +/- 0.009 (stat) +/- 0.003 (syst).
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LHCb Collaboration(Aaij, R. et al), Henry, L., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., et al. (2021). First Observation of the Decay B-s(0) -> K-mu(+)nu(mu) and a Measurement of vertical bar V-ub vertical bar/vertical bar V-cb vertical bar. Phys. Rev. Lett., 126(8), 081804–11pp.
Abstract: The first observation of the suppressed semileptonic B-s(0) -> K-mu(+)nu(mu) decay is reported. Using a data sample recorded in pp collisions in 2012 with the LHCb detector, corresponding to an integrated luminosity of 2 fb(-1), the branching fraction B(B-s(0) -> K-mu(+)nu(mu)) is measured to be [1.06 +/- 0.05(stat) +/- 0.08(syst)] x 10(-4), where the first uncertainty is statistical and the second one represents the combined systematic uncertainties. The decay B-s(0) -> D-s(-)mu(+)nu(mu), where D-s(-) is reconstructed in the final state K+K-pi(-), is used as a normalization channel to minimize the experimental systematic uncertainty. Theoretical calculations on the form factors of the B-s(0) -> K- and B-s(0) -> D-s(-) transitions are employed to determine the ratio of the Cabibbo-Kobayashi-Maskawa matrix elements vertical bar V-ub vertical bar/vertical bar V-cb vertical bar at low and high B-s(0) -> K- momentum transfer.
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LHCb Collaboration(Aaij, R. et al), Garcia Martin, L. M., Henry, L., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., et al. (2020). First Observation of Excited Omega(-)(b) States. Phys. Rev. Lett., 124(8), 082002–12pp.
Abstract: We report four narrow peaks in the Xi K-0(b)- mass spectrum obtained using pp collisions at center-of-mass energies of 7, 8, and 13 TeV, corresponding to a total integrated luminosity of 9 fb(-1) recorded by the LHCb experiment. Referring to these states by their mass, the mass values are m[Omega(b)(6316)(-)] = 6315.64 +/- 0.31 +/- 0.07 +/- 0.50 MeV, m[Omega(b)(6330)(-)] = 6330.30 +/- 0.28 +/- 0.07 +/- 0.50 MeV, m[Omega(b)(6340)(-)] = 6339.71 +/- 0.26 +/- 0.05 +/- 0.50 MeV, m[Omega(b)(6350)(-)] = 6349.88 +/- 0.35 +/- 0.05 +/- 0.50 MeV, where the uncertainties are statistical, systematic, and the last is due to the knowledge of the Xi(0)(b) mass. The natural widths of the three lower mass states are consistent with zero, and the 90% confidence-level upper limits are determined to be Gamma[Omega(b)(6316)(-)] < 2.8 MeV, Gamma[Omega(b)(6330)(-)] < 3.1 MeV and Gamma[Omega(b)(6340)-] < 1.5 MeV. The natural width of the Omega(b)(6350)(-) peak is 1.4(-0.8)(+1.0) +/- 0.1 MeV, which is 2.5 sigma from zero and corresponds to an upper limit of 2.8 MeV. The peaks have local significances ranging from 3.6 sigma to 7.2 sigma. After accounting for the look-elsewhere effect, the significances of the Omega(b)(6316)(-) and Omega(b)(6330)(-) peaks are reduced to 2.1 sigma and 2.6 sigma, respectively, while the two higher mass peaks exceed 5 sigma. The observed peaks are consistent with expectations for excited Omega(-)(b) resonances.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2016). First Observation of D-0 – (D)over-bar(0) Oscillations in D-0 -> K+pi(-)pi(+)pi(-) Decays and Measurement of the Associated Coherence Parameters. Phys. Rev. Lett., 116(24), 241801–10pp.
Abstract: Charm meson oscillations are observed in a time-dependent analysis of the ratio of D-0 -> K+pi(-)pi(+)pi(-) to D-0 -> K-pi(+)pi(-)pi(+) decay rates, using data corresponding to an integrated luminosity of 3.0 fb(-1) recorded by the LHCb experiment. The measurements presented are sensitive to the phase-space averaged ratio of doubly Cabibbo-suppressed to Cabibbo-favored amplitudes r(D)(K3 pi) and the product of the coherence factor R-D(K3 pi) and a charm mixing parameter y'(K3 pi). The constraints measured are r(D)(K3 pi) = (5.67 +/- 0.12) x 10(-2), which is the most precise determination to date, and R-D(K3 pi) y'(K3 pi) = (0.3 +/- 1.8) x 10(-3), which provides useful input for determinations of the CP-violating phase gamma in B-+/- -> DK +/-, D -> K--/+pi(+/-)pi(-/+)pi(+/-) decays. The analysis also gives the most precise measurement of the D-0 -> K+pi(-)pi(+)pi(-) branching fraction, and the first observation of D-0-(D) over bar (0) oscillations in this decay mode, with a significance of 8.2 standard deviations.
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LHCb Collaboration(Aaij, R. et al), Oyanguren, A., & Ruiz Valls, P. (2013). First Observation of CP Violation in the Decays of B-s(0) Mesons. Phys. Rev. Lett., 110(22), 221601–9pp.
Abstract: Using pp collision data corresponding to an integrated luminosity of 1.0 fb(-1) and collected by LHCb in 2011 at a center-of-mass energy of 7 TeV, we report the measurement of direct CP violation in B-s(0) -> K-pi(+) decays, A(CP) (B-s(0) -> K-pi(+)) = 0.27 +/- 0.04(stat) +/- 0.01(syst), with significance exceeding 5 standard deviations. This is the first observation of CP violation in the decays of B-s(0) mesons. Furthermore, we provide an improved determination of direct CP violation in B-0 -> K+pi(-) decays, A(CP)(B-0 -> K+pi(-) ) = -0.080 +/- 0.007(stat) +/- 0.003(syst), which is the most precise measurement of this quantity to date.
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BABAR and Belle Collaborations(Abdesselam, A. et al), Martinez-Vidal, F., & Oyanguren, A. (2015). First Observation of CP Violation in (B)over-bar(0) -> D(CP)((*))h(0) Decays by a Combined Time-Dependent Analysis of BABAR and Belle Data. Phys. Rev. Lett., 115(12), 121604–10pp.
Abstract: We report a measurement of the time-dependent CP asymmetry of (B) over bar (0) -> D(CP)((*))h(0) decays, where the light neutral hadron h(0) is a pi(0), eta , or omega meson, and the neutral D meson is reconstructed in the CP eigenstates K+K-, K-S(0)pi(0) or K-S(0)omega. The measurement is performed combining the final data samples collected at the Upsilon(4S) resonance by the BABAR and Belle experiments at the asymmetric-energy B factories PEP-II at SLAC and KEKB at KEK, respectively. The data samples contain (471 +/- 3) x 10(6) B (B) over bar pairs recorded by the BABAR detector and (772 +/- 11) x 10(6) B (B) over bar pairs recorded by the Belle detector. We measure the CP asymmetry parameters -eta S-f = +0.66 +/- 0.10(stat) +/- 0.06(syst) and C = -0.02 +/- 0.07(stat) +/- 0.03(syst). These results correspond to the first observation of CP violation in (B) over bar (0) -> D(CP)((*))h(0) decays. The hypothesis of no mixing-induced CP violation is excluded in these decays at the level of 5.4 standard deviations.
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