ATLAS Collaboration(Aad, G. et al), Alvarez Piqueras, D., Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fernandez Martinez, P., et al. (2015). Search for vectorlike B quarks in events with one isolated lepton, missing transverse momentum, and jets at root s=8 TeV with the ATLAS detector. Phys. Rev. D, 91(11), 112011–30pp.
Abstract: A search has been performed for pair production of heavy vectorlike down-type (B) quarks. The analysis explores the lepton-plus-jets final state, characterized by events with one isolated charged lepton (electron or muon), significant missing transverse momentum, and multiple jets. One or more jets are required to be tagged as arising from b quarks, and at least one pair of jets must be tagged as arising from the hadronic decay of an electroweak boson. The analysis uses the full data sample of pp collisions recorded in 2012 by the ATLAS detector at the LHC, operating at a center-of-mass energy of 8 TeV, corresponding to an integrated luminosity of 20.3 fb(-1). No significant excess of events is observed above the expected background. Limits are set on vectorlike B production, as a function of the B branching ratios, assuming the allowable decay modes are B -> Wt/Zb/Hb. In the chiral limit with a branching ratio of 100% for the decay B -> Wt, the observed (expected) 95% C.L. lower limit on the vectorlike B mass is 810 GeV (760 GeV). In the case where the vectorlike B quark has branching ratio values corresponding to those of an SU(2) singlet state, the observed (expected) 95% C.L. lower limit on the vectorlike B mass is 640 GeV (505 GeV). The same analysis, when used to investigate pair production of a colored, charge 5/3 exotic fermion T-5/3, with subsequent decay T-5/3 -> Wt, sets an observed (expected) 95% C.L. lower limit on the T-5/3 mass of 840 GeV (780 GeV).
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T2K Collaboration(Abe, K. et al), Cervera-Villanueva, A., Escudero, L., Izmaylov, A., Sorel, M., & Stamoulis, P. (2015). Measurement of the electron neutrino charged-current interaction rate on water with the T2K ND280 pi(0) detector. Phys. Rev. D, 91(11), 112010–11pp.
Abstract: This paper presents a measurement of the charged current interaction rate of the electron neutrino beam component of the beam above 1.5 GeV using the large fiducial mass of the T2K pi(0) detector. The predominant portion of the v(e) flux (similar to 85%) at these energies comes from kaon decays. The measured ratio of the observed beam interaction rate to the predicted rate in the detector with water targets filled is 0.89 +/- 0.08(stat) +/- 0.11(sys), and with the water targets emptied is 0.90 +/- 0.09(stat) +/- 0.13 (sys). The ratio obtained for the interactions on water only from an event subtraction method is 0.87 +/- 0.33(stat) +/- 0.21(sys). This is the first measurement of the interaction rate of electron neutrinos on water, which is particularly of interest to experiments with water Cherenkov detectors.
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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). Search for massive supersymmetric particles decaying to many jets using the ATLAS detector in pp collisions at root s=8 TeV. Phys. Rev. D, 91(11), 112016–37pp.
Abstract: Results of a search for decays of massive particles to fully hadronic final states are presented. This search uses 20.3 fb(-1) of data collected by the ATLAS detector in root s = 8 TeV proton-proton collisions at the LHC. Signatures based on high jet multiplicities without requirements on the missing transverse momentum are used to search for R-parity-violating supersymmetric gluino pair production with subsequent decays to quarks. The analysis is performed using a requirement on the number of jets, in combination with separate requirements on the number of b-tagged jets, as well as a topological observable formed from the scalar sum of the mass values of large-radius jets in the event. Results are interpreted in the context of all possible branching ratios of direct gluino decays to various quark flavors. No significant deviation is observed from the expected Standard Model backgrounds estimated using jet counting as well as data-driven templates of the total-jet-mass spectra. Gluino pair decays to ten or more quarks via intermediate neutralinos are excluded for a gluino with mass m((g) over tilde) < 1 TeV for a neutralino mass m(<(chi)over tilde>10) = 500 GeV. Direct gluino decays to six quarks are excluded for m((g) over tilde) < 917 GeV for light-flavor final states, and results for various flavor hypotheses are presented.
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Fujita, Y. et al, Algora, A., Estevez-Aguado, E., Molina, F., & Rubio, B. (2015). High-resolution study of Gamow-Teller excitations in the Ca-42(He-3,t)Sc-42 reaction and the observation of a “low-energy super-Gamow-Teller state”. Phys. Rev. C, 91(6), 064316–15pp.
Abstract: To study the Gamow-Teller (GT) transitions from the T-z = +1 nucleus Ca-42 to the T-z = 0 nucleus Sc-42, where T-z is the z component of isospin T, we performed a (p, n)-type (He-3, t) charge-exchange reaction at 140 MeV/nucleon and scattering angles around 0 degrees. With an energy resolution of 29 keV, states excited by GT transitions (GT states) could be studied accurately. The reduced GT transition strengths B(GT) were derived up to the excitation energy of 13 MeV, assuming the proportionality between the cross sections at 0 degrees and B(GT) values. The main part of the observed GT transition strength is concentrated in the lowest 0.611-MeV, J(pi) = 1(+) GT state. All the other states at higher energies are weakly excited. Shell-model calculations could reproduce the gross feature of the experimental B(GT) distribution, and random-phase-approximation calculations including an attractive isoscalar interaction showed that the 0.611-MeV state has a collective nature. It was found that this state has all of the properties of a “low-energy super-Gamow-Teller state.” It is expected that low-lying J(pi) = 1(+) GT states have T = 0 in the T-z = 0 nucleus Sc-42. However, T = 1 states are situated in a higher energy region. Assuming an isospin-analogous structure in A = 42 isobars, analogous T = 1, 1(+) states are also expected in Ca-42. Comparing the Ca-42(He-3, t)Sc-42 and Ca-42(p, p') spectra measured at 0 degrees, candidates for T = 1 GT states could be found in the 10-12-MeV region of Sc-42. They were all weakly excited. The mass dependence of the GT strength distributions in Sc isotopes is also discussed.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2015). Study of CP violation in B-/+ -> Dh(-/+) (h = K,pi) with the modes D -> K-/+pi(+/-)pi(0), D -> pi(+)pi(-)pi(0) and D -> K+K-pi(0). Phys. Rev. D, 91(11), 112014–15pp.
Abstract: An analysis of the decays of B--/+ -> DK -/+ and B--/+ -> D pi(-/+) is presented in which the D meson is reconstructed in the three-body final states K--/+pi(+/-)pi(0), pi(+)pi(-)pi(0) and K+K-pi(0). Using data from LHCb corresponding to an integrated luminosity of 3.0 fb(-1) of pp collisions, measurements of several CP observables are performed. First observations are obtained of the suppressed Atwood-Dunietz-Soni decay B--/+ -> [pi K-+(+/-)pi(0)](D)pi(-/+) and the quasi-Gronau-London-Wyler decay B--/+ -> [K+K-pi(0)](D)pi(-/+). The results are interpreted in the context of the unitarity triangle angle gamma and related parameters.
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