|
|
NA48/2 Collaboration(Batley, J. R. et al), & Fiorini, L. (2015). Search for the dark photon in pi(0) decays. Phys. Lett. B, 746, 178–185.
Abstract: A sample of 1.69 x 10(7) fully reconstructed pi(0) -> gamma e(+)e(-) decay candidates collected by the NA48/2 experiment at CERN in 2003-2004 is analyzed to search for the dark photon (A') production in the pi(0) -> gamma A' decay followed by the prompt A' -> e(+)e(-) decay. No signal is observed, and an exclusion region in the plane of the dark photon mass m(A') and mixing parameter epsilon(2) is established. The obtained upper limits on epsilon(2) are more stringent than the previous limits in the mass range 9 MeV/c(2) < m(A') < 70 MeV/c(2). The NA48/2 sensitivity to the dark photon production in the K-+/- -> pi(+/-)A' decay is also evaluated.
|
|
|
|
ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Ferrer, A., Fiorini, L., et al. (2015). Measurements of the Nuclear Modification Factor for Jets in Pb plus Pb Collisions at root SNN=2.76 TeV with the ATLAS Detector. Phys. Rev. Lett., 114(7), 072302–18pp.
Abstract: Measurements of inclusive jet production are performed in pp and Pb + Pb collisions at root SNN = 2.76 TeV with the ATLAS detector at the LHC, corresponding to integrated luminosities of 4.0 and 0.14 nb(-1), respectively. The jets are identified with the anti-k(t) algorithm with R = 0.4, and the spectra are measured over the kinematic range of jet transverse momentum 32 < pT < 500 GeV and absolute rapidity |y| < 2.1 and as a function of collision centrality. The nuclear modification factor R-AA is evaluated, and jets are found to be suppressed by approximately a factor of 2 in central collisions compared to pp collisions. The RAA shows a slight increase with pT and no significant variation with rapidity.
|
|
|
|
Botella, F. J., Branco, G. C., Nebot, M., & Sanchez, A. (2015). Mixing asymmetries in B meson systems, the D0 like-sign dimuon asymmetry, and generic new physics. Phys. Rev. D, 91(3), 035013–14pp.
Abstract: The measurement of a large like-sign dimuon asymmetry A(SL)(b) by the D0 experiment at the Tevatron departs noticeably from Standard Model (SM) expectations and it may be interpreted as a hint of physics beyond the Standard Model contributing to Delta B not equal 0 transitions. In this work we analyze how the natural suppression of A(SL)(b) in the SM can be circumvented by new physics. We consider generic Standard Model extensions where the charged current mixing matrix is enlarged with respect to the usual 3 x 3 unitary Cabibbo-Kobayashi-Maskawa matrix, and show how, within this framework, a significant enhancement over Standard Model expectations for Ab SL is easily reachable through enhancements of the semileptonic asymmetries A(SL)(d) and A(SL)(s) of both B-d(0)- (B) over bar (0)(d) and B-s(0)- (B) over bar (0)(s) systems. Despite being insufficient to reproduce the D0 measurement, such deviations from SM expectations may be probed by the LHCb experiment.
|
|
|
|
BABAR Collaboration(Lees, J. P. et al), Martinez-Vidal, F., Oyanguren, A., & Villanueva-Perez, P. (2015). Observation of the baryonic decay (B)over-bar(0) -> Lambda(+)(c)(p)over-barK(-)K(+). Phys. Rev. D, 91(3), 031102–7pp.
Abstract: We report the observation of the baryonic decay (B) over bar (0) -> Lambda(+)(c)(p) over barK(-)K(+) using a data sample of 471 x 10(6) B (B) over bar pairs produced in e(+)e(-) annihilations at root s = 10.58 GeV. This data sample was recorded with the BABAR detector at the PEP- II storage ring at SLAC. We find B((B) over bar (0) -> Lambda(+)(c)(p) over barK(-)K(+)) = (2.5 +/- 0.4((stat)) +/- 0.2((syst)) +/- 0.6(B(Lambda c+)) ) x 10(-5) where the uncertainties are statistical, systematic, and due to the uncertainty of the Lambda(+)(c) -> (p) over barK(-)pi(+) branching fraction, respectively. The result has a significance corresponding to 5.0 standard deviations, including all uncertainties. For the resonant decay (B) over bar (0) -> Lambda(+)(c)(p) over bar phi, we determine the upper limit B((B) over bar (0) -> Lambda(+)(c)(p) over bar phi) < 1.2 x 10(-5) at 90% confidence level.
|
|
|
|
n_TOF Collaboration(Paradela, C. et al), Domingo-Pardo, C., Giubrone, G., & Tain, J. L. (2015). High-accuracy determination of the U-238/U-235 fission cross section ratio up to approximate to 1 GeV at n_TOF at CERN. Phys. Rev. C, 91(2), 024602–11pp.
Abstract: The U-238 to U-235 fission cross section ratio has been determined at nTOF up to approximate to 1 GeV, with two different detection systems, in different geometrical configurations. A total of four datasets has been collected and compared. They are all consistent to each other within the relative systematic uncertainty of 3-4%. The data collected at nTOF have been suitably combined to yield a unique fission cross section ratio as a function of neutron energy. The result confirms current evaluations up to 200 MeV. Good agreement is also observed with theoretical calculations based on the INCL++ /Gemini++ combination up to the highest measured energy. The n_TOF results may help solve a long-standing discrepancy between the two most important experimental datasets available so far above 20 MeV, while extending the neutron energy range for the first time up to approximate to 1 GeV.
|
|
