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 the D* longitudinal polarization in B0 → D*- τ+νt decays. Phys. Rev. D, 110(9), 092007–18pp.
Abstract: The longitudinal polarization fraction of the D* meson is measured in B-0 -> D*(-) tau(+)nu(t) decays, where the tau lepton decays to three charged pions and a neutrino, using proton-proton collision data collected by the LHCb experiment at center-of-mass energies of 7, 8 and 13 TeV and corresponding to an integrated luminosity of 5 fb(-1). The D* polarization fraction F-L(D)* is measured in two q(2) regions, below and above 7 GeV2/c(4), where q(2) is defined as the squared invariant mass of the tau nu(tau) system. The F-L(D)*L values are measured to be 0.52 +/- 0.07 +/- 0.04 and 0.34 +/- 0.08 +/- 0.02 for the lower and higher q(2) regions, respectively. The first uncertainties are statistical and the second systematic. The average value over the whole q(2) range is F-L(D)* = 0.41 +/- 0.06 +/- 0.03. These results are compatible with the Standard Model predictions.
|
ATLAS Collaboration(Aad, G. et al), Aikot, A., Amos, K. R., Bouchhar, N., Cabrera Urban, S., Cantero, J., et al. (2024). Search for R-parity violating supersymmetric decays of the top squark to a b-jet and a lepton in √s=13 TeV pp collisions with the ATLAS detector. Phys. Rev. D, 110(9), 092004–32pp.
Abstract: A search is presented for direct pair production of the stop, the supersymmetric partner of the top quark, in a decay through an R-parity violating coupling to a charged lepton and a b-quark. The dataset corresponds to an integrated luminosity of 140 fb(-1) of proton-proton collisions at a center-of-mass energy of root s = 13 TeV collected between 2015 and 2018 by the ATLAS detector at the LHC. The final state has two charged leptons (electrons or muons) and two b-jets. The results of the search are interpreted in the context of a Minimal Supersymmetric Standard Model with an additional B – L gauge symmetry that is spontaneously broken. No significant excess is observed over the Standard Model background, and exclusion limits on stop pair production are set at 95% confidence level. The corresponding lower limits on the stop mass for 100% branching ratios to a b-quark and an electron, muon, or tau-lepton are 1.9 TeV, 1.8 TeV and 800 GeV, respectively, extending the reach of previous LHC searches.
|
ATLAS Collaboration(Aad, G. et al), Aikot, A., Amos, K. R., Bouchhar, N., Cabrera Urban, S., Cantero, J., et al. (2024). Search for heavy right-handed Majorana neutrinos in the decay of top quarks produced in proton-proton collisions at √s=13 TeV with the ATLAS detector. Phys. Rev. D, 110(11), 112004–33pp.
Abstract: A search for heavy right-handed Majorana neutrinos is performed with the ATLAS detector at the CERN Large Hadron Collider, using the 140 fb(-1) of proton-proton collision data at root s = 13 TeV collected during Run 2. This search targets t (t) over bar production, in which both top quarks decay into a bottom quark and a W boson, where one of the W bosons decays hadronically and the other decays into an electron or muon and a heavy neutral lepton. The heavy neutral lepton is identified through a decay into an electron or muon and another W boson, resulting in a pair of same-charge same-flavor leptons in the final state. This paper presents the first search for heavy neutral leptons in the mass range of 15-75 GeV using t (t) over bar events. No significant excess is observed over the background expectation, and upper limits are placed on the signal cross sections. Assuming a benchmark scenario of the phenomenological type-I seesaw model, these cross section limits are then translated into upper limits on the mixing parameters of the heavy Majorana neutrino with Standard Model neutrinos.
|
ATLAS Collaboration(Aad, G. et al), Aikot, A., Amos, K. R., Aparisi Pozo, J. A., Bailey, A. J., Bouchhar, N., et al. (2024). Measurements of jet cross-section ratios in 13 TeV proton-proton collisions with ATLAS. Phys. Rev. D, 110(7), 072019–41pp.
Abstract: Measurements of jet cross-section ratios between inclusive bins of jet multiplicity are performed in 140 fb(-1) of proton-proton collisions with root s = 13 TeV center-of-mass energy, recorded with the ATLAS detector at CERN's Large Hadron Collider. These ratios are constructed from double-differential cross-section measurements that are made in bins of jet multiplicity and other observables that are sensitive the energy scale and angular distribution of radiation due to the strong interaction in the final state. Additionally, the scalar sum of the two leading jets' transverse momenta is measured triple differentially, in bins of the third jet's transverse momentum and of jet multiplicity. These measurements are unfolded to account for acceptance and detector-related effects. The measured distributions are used to construct ratios of the inclusive jet-multiplicity bins, which have been shown to be sensitive to the strong coupling alpha(S) while being less sensitive than other observables to systematic uncertainties and parton distribution functions. The measured distributions are compared with state-of-the-art QCD calculations, including next-to-next-to-leading-order predictions for two- and three-jet events. These predictions are generally found to model the data well and perform best in bins with a modest requirement on the third jet's transverse momentum. Significant differences between data and Monte Carlo predictions are observed in events with large rapidity gaps and invariant masses of the leading jet pair. Studies leading to reduced jet energy scale uncertainties significantly improve the precision of this work and are documented herein.
|
LHCb Collaboration(Aaij, R. et al), Jaimes Elles, S. J., Jashal, B. K., Libralon, S., Martinez-Vidal, F., Oyanguren, A., et al. (2024). Search for the lepton-flavor violating decay Bs0 → φμ±τ∓. Phys. Rev. D, 110(7), 072014–12pp.
Abstract: A search for the lepton-flavor violating decays B-s(0) -> phi mu(+/-)tau(-/+) is presented, using a sample of proton-proton collisions at center-of-mass energies of 7, 8, and 13 TeV, collected with the LHCb detector and corresponding to a total integrated luminosity of 9 fb(-1). The tau leptons are selected using decays with three charged pions. No significant excess is observed, and an upper limit on the branching fraction is determined to be B(B-s(0) -> phi mu(+/-)tau(-/+)) < 1.0 x 10(-5) at 90% confidence level.
|
