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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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Richard, J. M., Valcarce, A., & Vijande, J. (2024). Resonances in the Quark Model. Few-Body Syst., 65(3), 71–11pp.
Abstract: A discussion is presented of the estimates of the energy and width of resonances in constituent models, with focus on the tetraquark states containing heavy quarks.
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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). First observation of the B+ → Ds+ Ds- K+ decay. Phys. Rev. D, 108(3), 034012–14pp.
Abstract: B+ -> D-s(+) D-s(-) K+ decay is observed for the first time using proton-proton collision data collected by the LHCb detector at center-of-mass energies of 7, 8, and 13 TeV, corresponding to an integrated luminosity of 9 fb-1. Its branching fraction relative to that of the B+ -> D-s(+) D-s(-) K+ decay is measured to be B(B+ -> D-s(+) D-s(-) K+)/(KB+ -> D-s(+) D-s(-) K+) = 0.525 +/- 0.0333 +/- 0.027 +/- 0.034; where the first uncertainty is statistical, the second s D-s Kthornthorn systematic, and the third is due to the uncertainties on the branching fractions of the D-s(+/-) -> (KK +/-)-K--/+pi(+/-) and D-+/- -> K--/+pi(+/-)pi(+/-) decays. This measurement fills an experimental gap in the knowledge of the family of Cabibbo-favored (b) over bar -> (b) over barc (c) over bar transitions and opens the path for unique studies of spectroscopy in future.
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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). Search for KS(L)0 → μ+ μ- μ+ μ- decays at LHCb. Phys. Rev. D, 108(3), L031102–12pp.
Abstract: A search for K-S(L)(0) -> mu(+) mu(-) mu(+) mu(-) decays is performed using proton-proton collision data collected by the LHCb experiment at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 5.1 fb(-1). No evidence for signal is found. The 90% confidence level upper limits are the first set for both decays and are B(K-S(0)) -> mu(+) mu(-) mu(+) mu(-)) < 5.1 x 10(-12) and B(K-L(0))-> mu(+) mu(-) mu(+) mu(-)) < 2.3 x 10(-9).
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Jungclaus, A. et al, Gadea, A., & Montaner-Piza, A. (2024). Excited-State Half-Lives in 130 Cd and the Isospin Dependence of Effective Charges. Phys. Rev. Lett., 132(22), 222501–7pp.
Abstract: The known I pi = 8 & thorn; 1 , E x = 2129-keV isomer in the semimagic nucleus 130 Cd 82 was populated in the projectile fission of a 238 U beam at the Radioactive Isotope Beam Factory at RIKEN. The high counting statistics of the accumulated data allowed us to determine the excitation energy, E x = 2001.2(7) keV, and half-life, T 1 =2 = 57(3) ns, of the I pi = 6 & thorn; 1 state based on gamma gamma coincidence information. Furthermore, the halflife of the 8 & thorn; 1 state, T 1 =2 = 224(4) ns, was remeasured with high precision. The new experimental information, combined with available data for 134 Sn and large-scale shell model calculations, allowed us to extract proton and neutron effective charges for 132 Sn, a doubly magic nucleus far -off stability. A comparison to analogous information for 100 Sn provides first reliable information regarding the isospin dependence of the isoscalar and isovector effective charges in heavy nuclei.
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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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ATLAS Collaboration(Aad, G. et al), Alvarez Piqueras, D., Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fernandez Martinez, P., et al. (2016). Measurement of the charge asymmetry in top-quark pair production in the lepton-plus-jets final state in pp collision data at root s=8 TeV with the ATLAS detector. Eur. Phys. J. C, 76(2), 87–30pp.
Abstract: This paper reports inclusive and differential measurements of the t (t) over bar charge asymmetry A(C) in 20.3 fb(-1) of root s = 8 TeV pp collisions recorded by the ATLAS experiment at the Large Hadron Collider at CERN. Three differential measurements are performed as a function of the invariant mass, transverse momentum and longitudinal boost of the t (t) over bar system. The t (t) over bar pairs are selected in the single-lepton channels (e or mu) with at least four jets, and a likelihood fit is used to reconstruct the t (t) over bar event kinematics. A Bayesian unfolding procedure is performed to infer the asymmetry at parton level from the observed data distribution. The inclusive t (t) over bar charge asymmetry is measured to be A(C) = 0.009 +/- 0.005 (stat. + syst.). The inclusive and differential measurements are compatible with the values predicted by the Standard Model.
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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). Production of η and η' mesons in pp and pPb collisions. Phys. Rev. C, 109(2), 024907–20pp.
Abstract: The production of eta and eta' mesons is studied in proton -proton and proton -lead collisions collected with the LHCb detector. Proton -proton collisions are studied at center -of -mass energies of 5.02 and 13 TeV and proton -lead collisions are studied at a center -of -mass energy per nucleon of 8.16 TeV. The studies are performed in center -of -mass (c.m.) rapidity regions 2.5 < y(c.m.) < 3.5 (forward rapidity) and -4.0 < y(c.m.) < -3.0 (backward rapidity) defined relative to the proton beam direction. The eta and eta' production cross sections are measured differentially as a function of transverse momentum for 1.5 < p(T) < 10 GeV and 3 < p(T) < 10 GeV, respectively. The differential cross sections are used to calculate nuclear modification factors. The nuclear modification factors for eta and eta' mesons agree at both forward and backward rapidity, showing no significant evidence of mass dependence. The differential cross sections of eta mesons are also used to calculate eta/pi 0 cross-section ratios, which show evidence of a deviation from the world average. These studies offer new constraints on mass -dependent nuclear effects in heavy -ion collisions, as well as eta and eta' meson fragmentation.
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Guadilla, V., Algora, A., Estienne, M., Fallot, M., Gelletly, W., Porta, A., et al. (2024). First measurements with a new fl-electron detector for spectral shape studies. J. Instrum., 19(2), P02027–21pp.
Abstract: The shape of the electron spectrum emitted in /3 decay carries a wealth of information about nuclear structure and fundamental physics. In spite of that, few dedicated measurements have been made of /3 -spectrum shapes. In this work we present a newly developed detector for /3 electrons based on a telescope concept. A thick plastic scintillator is employed in coincidence with a thin silicon detector. The first measurements employing this detector have been carried out with mono -energetic electrons from the high-energy resolution electron -beam spectrometer at Bordeaux. Here we report on the good reproduction of the experimental spectra of mono -energetic electrons using Monte Carlo simulations. This is a crucial step for future experiments, where a detailed Monte Carlo characterization of the detector is needed to determine the shape of the /3 -electron spectra by deconvolution of the measured spectra with the response function of the detector. A chamber to contain two telescope assemblies has been designed for future /3 -decay experiments at the Ion Guide Isotope Separator On -Line facility in Jyvaskyla, aimed at improving our understanding of reactor antineutrino spectra.
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ATLAS Collaboration(Aad, G. et al), Amos, K. R., Aparisi Pozo, J. A., Bailey, A. J., Bouchhar, N., Cabrera Urban, S., et al. (2024). Observation of WZγ Production in pp Collisions at √s=13 TeV with the ATLAS Detector. Phys. Rev. Lett., 132(2), 021802–21pp.
Abstract: This Letter reports the observation of WZ gamma production and a measurement of its cross section using 140.1 +/- 1.2 fb(-1) of proton-proton collision data recorded at a center-of-mass energy of 13 TeV by the bosons decaying leptonically, pp -> WZ gamma -> l'(perpendicular to)nu l(+) l(-)gamma (l(')(+) = e, mu), is measured in a fiducial phasespace region defined such that the leptons and the photon have high transverse momentum and the photon is isolated. The cross section is found to be 2.01 +/- 0.30(stat) +/- 0.16(syst) fb. The corresponding standard model predicted cross section calculated at next-to-leading order in perturbative quantum chromodynamics and at leading order in the electroweak coupling constant is 1.50 +/- 0.06 fb. The observed significance of the WZ gamma signal is 6.3 sigma, compared with an expected significance of 5.0 sigma.
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