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ATLAS Collaboration(Aad, G. et al), Amos, K. R., Aparisi Pozo, J. A., Bailey, A. J., Cabrera Urban, S., Cantero, J., et al. (2023). Test of CP Invariance in Higgs Boson Vector-Boson-Fusion Production Using the H → γγ Channel with the ATLAS Detector. Phys. Rev. Lett., 131(6), 061802–23pp.
Abstract: A test of CP invariance in Higgs boson production via vector-boson fusion has been performed in the H -> gamma gamma channel using 139 fb(-1) of proton-proton collision data at root s = 13 TeV collected by the ATLAS detector at the LHC. The optimal observable method is used to probe the CP structure of interactions between the Higgs boson and electroweak gauge bosons, as described by an effective field theory. No sign of CP violation is observed in the data. Constraints are set on the parameters describing the strength of the CP-odd component in the coupling between the Higgs boson and the electroweak gauge bosons in two effective field theory bases: (d) over tilde in the HISZ basis and c(H (W) over tilde) in the Warsaw basis. The results presented are the most stringent constraints on CP violation in the coupling between Higgs and weak bosons. The 95% C.L. constraint on (d) over tilde is derived for the first time and the 95% C.L. constraint on c(H (W) over tilde) has been improved by a factor of 5 compared to the previous measurement.
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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 Modification of b Quark Hadronization in High-Multiplicity pp Collisions at √s=13 TeV. Phys. Rev. Lett., 131(6), 061901–11pp.
Abstract: The production rate of B-s(0) mesons relative to B-0 mesons is measured by the LHCb experiment in pp collisions at a center-of-mass energy root s = 13 TeV over the forward rapidity interval 2 < y < 4.5 as a function of the charged particle multiplicity measured in the event. Evidence at the 3.4 sigma level is found for an increase of the ratio of B-s(0) to B-0 cross sections with multiplicity at transverse momenta below 6 GeV=c, with no significant multiplicity dependence at higher transverse momentum. Comparison with data from e(+)e(-) collisions implies that the density of the hadronic medium may affect the production rates of B mesons. This is qualitatively consistent with the emergence of quark coalescence as an additional hadronization mechanism in high-multiplicity collisions.
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Batra, A., Camara, H. B., Joaquim, F. R., Srivastava, R., & Valle, J. W. F. (2024). Axion Paradigm with Color-Mediated Neutrino Masses. Phys. Rev. Lett., 132(5), 051801–7pp.
Abstract: We propose a generalized Kim-Shifman-Vainshtein-Zakharov-type axion framework in which colored fermions and scalars act as two -loop Majorana neutrino -mass mediators. The global Peccei-Quinn symmetry under which exotic fermions are charged solves the strong CP problem. Within our general proposal, various setups can be distinguished by probing the axion-to-photon coupling at helioscopes and haloscopes. We also comment on axion dark -matter production in the early Universe.
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ATLAS and CMS Collaborations(Aad, G. et al), Aikot, A., Amos, K. R., Aparisi Pozo, J. A., Bailey, A. J., Bouchhar, N., et al. (2024). Evidence for the Higgs Boson Decay to a Z Boson and a Photon at the LHC. Phys. Rev. Lett., 132(2), 021803–32pp.
Abstract: The first evidence for the Higgs boson decay to a Z boson and a photon is presented, with a statistical significance of 3.4 standard deviations. The result is derived from a combined analysis of the searches performed by the ATLAS and CMS Collaborations with proton -proton collision datasets collected at the CERN Large Hadron Collider (LHC) from 2015 to 2018. These correspond to integrated luminosities of around 140 fb-1 for each experiment, at a center -of -mass energy of 13 TeV. The measured signal yield is 2.2 +/- 0.7 times the standard model prediction, and agrees with the theoretical expectation within 1.9 standard deviations.
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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). Observation of Cabibbo-Suppressed Two-Body Hadronic Decays and Precision Mass Measurement of the Ω0c Baryon. Phys. Rev. Lett., 132(8), 081802–11pp.
Abstract: The first observation of the singly Cabibbo-suppressed 0c -> -K thorn and 0c -> -z thorn decays is reported, using proton -proton collision data at a center -of -mass energy of 13 TeV, corresponding to an integrated luminosity of 5.4 fb-1, collected with the LHCb detector between 2016 and 2018. The branching fraction ratios are measured to be Bo0c ->-K thorn thorn Bo0c ->-z thorn thorn 1/4 1/26.08 ⠂ 0.51ostat thorn ⠂ 0.40osyst thorn ⠃%; Bo0c ->-z thorn thorn Bo0c ->-z thorn thorn 1/4 1/215.81 ⠂ 0.87ostat thorn ⠂ 0.44osyst thorn ⠂ 0.16oext thorn ⠃%. In addition, using the 0c -> -z thorn decay channel, the 0c baryon mass is measured to be Mo0c thorn 1/4 2695.28 ⠂ 0.07ostat thorn ⠂ 0.27osyst thorn ⠂ 0.30oext thorn MeV; improving the precision of the previous world average by a factor of 4.
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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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ATLAS Collaboration(Aad, G. et al), Aikot, A., Amos, K. R., Aparisi Pozo, J. A., Bailey, A. J., Bouchhar, N., et al. (2024). Search for New Phenomena in Two-Body Invariant Mass Distributions Using Unsupervised Machine Learning for Anomaly Detection at root s=13 TeV with the ATLAS Detector. Phys. Rev. Lett., 132(8), 081801–23pp.
Abstract: Searches for new resonances are performed using an unsupervised anomaly-detection technique. Events with at least one electron or muon are selected from 140 fb-1 of pp collisions at p ffi s ffi= 13 TeV recorded by ATLAS at the Large Hadron Collider. The approach involves training an autoencoder on data, and subsequently defining anomalous regions based on the reconstruction loss of the decoder. Studies focus on nine invariant mass spectra that contain pairs of objects consisting of one light jet or b jet and either one lepton (e; mu), photon, or second light jet or b jet in the anomalous regions. No significant deviations from the background hypotheses are observed. Limits on contributions from generic Gaussian signals with various widths of the resonance mass are obtained for nine invariant masses in the anomalous regions.
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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). Improved Measurement of CP Violation Parameters in B0s → J/ψ K+ K- Decays in the Vicinity of the φ(1020) Resonance. Phys. Rev. Lett., 132(5), 051802–12pp.
Abstract: The decay-time-dependent CP asymmetry in B0s -> J=psi(-> mu+mu-)K+K- decays is measured using proton-proton collision data, corresponding to an integrated luminosity of 6 fb-1, collected with the LHCb detector at a center-of-mass energy of 13 TeV. Using a sample of approximately 349 000 B0s signal decays with an invariant K+K- mass in the vicinity of the phi(1020) resonance, the CP-violating phase phi s is measured, along with the difference in decay widths of the light and heavy mass eigenstates of the B0s-B over bar 0s system, Delta Gamma s, and the difference of the average B0s and B0 meson decay widths, Gamma s – Gamma d. The values obtained are phi s = -0.039 +/- 0.022 +/- 0.006 rad, Delta Gamma s = 0.0845 +/- 0.0044 +/- 0.0024 ps-1, and -0.0015 +/- 0.0014 ps-1, where the first uncertainty is statistical and the second systematic. These are the most precise single measurements to date and are consistent with expectations based on the Standard Model and with the previous LHCb analyses of this decay. These results are combined with previous independent LHCb measurements. The phase phi s is also measured independently for each polarization state of the K+K- system and shows no evidence for polarization dependence.
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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). Amplitude Analysis of the B0 -> K*0 μ+μ- Decay. Phys. Rev. Lett., 132(13), 131801–13pp.
Abstract: An amplitude analysis of the B-0 -> K*(0) mu(+)mu(-) decay is presented using a dataset corresponding to an integrated luminosity of 4.7 fb(-1) of pp collision data collected with the LHCb experiment. For the first time, the coefficients associated to short-distance physics effects, sensitive to processes beyond the standard model, are extracted directly from the data through a q(2)-unbinned amplitude analysis, where q(2) is the mu(+)mu(-) invariant mass squared. Long-distance contributions, which originate from nonfactorizable QCD processes, are systematically investigated, and the most accurate assessment to date of their impact on the physical observables is obtained. The pattern of measured corrections to the short-distance couplings is found to be consistent with previous analyses of b- to s-quark transitions, with the largest discrepancy from the standard model predictions found to be at the level of 1.8 standard deviations. The global significance of the observed differences in the decay is 1.4 standard deviations.
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ATLAS Collaboration(Aad, G. et al), Aikot, A., Amos, K. R., Aparisi Pozo, J. A., Bailey, A. J., Bouchhar, N., et al. (2024). Measurement of the Centrality Dependence of the Dijet Yield in p plus Pb Collisions at √sNN=8.16 TeV with the ATLAS Detector. Phys. Rev. Lett., 132(10), 102301–22pp.
Abstract: ATLAS measured the centrality dependence of the dijet yield using 165 nb-1 of p + Pb data collected at root sNN = 8.16 TeV in 2016. The event centrality, which reflects the p + Pb impact parameter, is characterized by the total transverse energy registered in the Pb-going side of the forward calorimeter. The central-to-peripheral ratio of the scaled dijet yields, RCP, is evaluated, and the results are presented as a function of variables that reflect the kinematics of the initial hard parton scattering process. The RCP shows a scaling with the Bjorken x of the parton originating from the proton, xp, while no such trend is observed as a function of xPb. This analysis provides unique input to understanding the role of small proton spatial configurations in p + Pb collisions by covering parton momentum fractions from the valence region down to xp similar to 10-3 and xPb similar to 4 x 10-4.
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