|
|
Gomez Dumm, D., Noguera, S., Scoccola, N. N., & Scopetta, S. (2014). Pion distribution amplitude and the pion-photon transition form factor in a nonlocal chiral quark model. Phys. Rev. D, 89(5), 054031–14pp.
Abstract: We study the pion distribution amplitude (pi DA) in the context of a nonlocal chiral quark model. The corresponding Lagrangian reproduces the phenomenological values of the pion mass and decay constant, as well as the momentum dependence of the quark propagator obtained in lattice calculations. It is found that the obtained pi DA has two symmetric maxima, which arise from the new contributions generated by the nonlocal character of the interactions. This pi DA is applied to leading order and next-to-leading order calculations of the pion-photon transition form factor. Implications of the results are discussed.
|
|
|
|
LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., & Ruiz Valls, P. (2014). Measurement of Upsilon production in collisions at root s=2.76 TeV. Eur. Phys. J. C, 74(4), 2835–11pp.
Abstract: The production of , and mesons decaying into the dimuon final state is studied with the LHCb detector using a data sample corresponding to an integrated luminosity of collected in proton-proton collisions at a centre-of-mass energy of TeV. The differential production cross-sections times dimuon branching fractions are measured as functions of the transverse momentum and rapidity, over the ranges GeV/ and . The total cross-sections in this kinematic region, assuming unpolarised production, are measured to be sigma (pp -> Upsilon(1S)X) x B(Upsilon(1S) -> mu(+)mu(-)) = 1.111 +/- 0.043 +/- 0.044 nb, sigma (pp -> Upsilon(2S)X) x B(Upsilon(2S) -> mu(+)mu(-)) = 0.264 +/- 0.023 +/- 0.011 nb, sigma (pp -> Upsilon(3S)X) x B(Upsilon(3S) -> mu(+)mu(-))s = 0.159 +/- 0.020 +/- 0.007 nb, where the first uncertainty is statistical and the second systematic.
|
|
|
|
Barenboim, G., & Rasero, J. (2014). Structure formation during an early period of matter domination. J. High Energy Phys., 04(4), 138–17pp.
Abstract: In this work we show that modifying the thermal history of the Universe by including an early period of matter domination can lead to the formation of astronomical objects. However, the survival of these objects can only be possible if the dominating matter decays to a daughter particle which is not only almost degenerate with the parent particle but also has an open annihilation channel. This requirement translates in an upper bound for the coupling of such a channel and makes the early structure formation viable.
|
|
|
|
n_TOF Collaboration(Fraval, K. et al), Domingo-Pardo, C., Giubrone, G., & Tain, J. L. (2014). Measurement and analysis of the Am-241(n,gamma) cross section with liquid scintillator detectors using time-of-flight spectroscopy at the n_TOF facility at CERN. Phys. Rev. C, 89(4), 044609–14pp.
Abstract: The Am-241(n,gamma) cross section has been measured at the n_TOF facility at CERN using deuterated benzene liquid scintillators, commonly known as C6D6 detectors, and time-of-flight spectrometry. The results in the resolved resonance range bring new constraints to evaluations below 150 eV, and the energy upper limit was extended from 150 to 320 eV with a total of 172 new resonances not present in current evaluations. The thermal capture cross section was found to be sigma(th) = 678 +/- 68 b, which is in good agreement with evaluations and most previous measurements. The capture cross section in the unresolved resonance region was extracted in the remaining energy range up to 150 keV, and found to be larger than current evaluations and previous measurements.
|
|
|
|
ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fassi, F., Ferrer, A., et al. (2014). Study of heavy-flavor quarks produced in association with top-quark pairs at root s=7 TeV using the ATLAS detector. Phys. Rev. D, 89(7), 072012–23pp.
Abstract: Using a sample of dilepton top-quark pair ((tt) over bar) candidate events, a study is performed of the production of top-quark pairs together with heavy-flavor (HF) quarks, the sum of (tt) over bar + b + X and (tt) over bar + c + X, collectively referred to as (tt) over bar + HF. The data set used corresponds to an integrated luminosity of 4.7 fb(-1) of proton-proton collisions at a center-of-mass energy of 7 TeV recorded by the ATLAS detector at the CERN Large Hadron Collider. The presence of additional HF (b or c) quarks in the (tt) over bar sample is inferred by looking for events with at least three b-tagged jets, where two are attributed to the b quarks from the (tt) over bar decays and the third to additional HF production. The dominant background to (tt) over bar + HF in this sample is (tt) over bar + jet events in which a light-flavor jet is misidentified as a heavy-flavor jet. To determine the heavy-and light-flavor content of the additional b-tagged jets, a fit to the vertex mass distribution of b-tagged jets in the sample is performed. The result of the fit shows that 79 +/- 14 (stat) +/- 22 (syst) of the 105 selected extra b-tagged jets originate from HF quarks, 3 standard deviations away from the hypothesis of zero (tt) over bar + HF production. The result for extra HF production is quoted as a ratio (R-HF) of the cross section for (tt) over bar + HF production to the cross section for (tt) over bar production with at least one additional jet. Both cross sections are measured in a fiducial kinematic region within the ATLAS acceptance. R-HF is measured to be [6.2 +/- 1.1(stat) +/- 1.8 (syst)]% for jets with p(T) > 25 GeV and vertical bar eta vertical bar < 2.5, in agreement with the expectations from Monte Carlo generators.
|
|
