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Deppisch, F. F., Desai, N., & Valle, J. W. F. (2014). Is charged lepton flavor violation a high energy phenomenon? Phys. Rev. D, 89(5), 051302–5pp.
Abstract: Searches for rare processes such as μ-> e gamma put stringent limits on lepton flavor violation expected in many beyond-the-Standard-Model physics scenarios. This usually precludes the observation of flavor violation at high energy colliders such as the LHC. We here discuss a scenario where right-handed neutrinos are produced via a Z' portal but which can only decay via small flavor violating couplings. Consequently, the process rate is unsuppressed by the small couplings and can be visible despite unobservably small μ-> e gamma rates.
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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.
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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.
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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.
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BABAR Collaboration(Lees, J. P. et al), Martinez-Vidal, F., Oyanguren, A., & Villanueva-Perez, P. (2014). Cross sections for the reactions e+e- -> K0S K0L, K0S K0L pi+ pi-, K0S K0S pi+ pi-, and K0S K0S K+ K- from events with initial- state radiation. Phys. Rev. D, 89(9), 092002–25pp.
Abstract: We study the processes e+e- -> K0S K0L gamma, K0S K0L pi+ pi- gamma, K0S K0S pi+ pi- gamma, and K0S K0S K+ K- gamma, where the photon is radiated from the initial state, providing cross section measurements for the hadronic states over a continuum of center-of-mass energies. The results are based on 469 fb-1 of data collected with the BABAR detector at SLAC. We observe the phi(1020) resonance in the K0S K0L final state and measure the product of its electronic width and branching fraction with about 3% uncertainty. We present a measurement of the e+e- -> K0S K0L cross section in the energy range from 1.06 to 2.2 GeV and observe the production of a resonance at 1.67 GeV. We present the first measurements of the e+e- -> K0S K0L pi+ pi-, K0S K0S pi+ pi-, and K0S K0S K+ K- cross sections and study the intermediate resonance structures. We obtain the first observations of J/Psi decay to the K0S K0L pi+ pi-, K0S K0S pi+ pi-, and K0S K0S K+ K- final states.
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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.
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Aguilar, A. C., Binosi, D., & Papavassiliou, J. (2014). Renormalization group analysis of the gluon mass equation. Phys. Rev. D, 89(8), 085032–19pp.
Abstract: We carry out a systematic study of the renormalization properties of the integral equation that determines the momentum evolution of the effective gluon mass in pure Yang-Mills theory, without quark effects taken into account. A detailed, all-order analysis of the complete kernel appearing in this particular equation, derived in the Landau gauge, reveals that the renormalization procedure may be accomplished through the sole use of ingredients known from the standard perturbative treatment of the theory, with no additional assumptions. However, the subtle interplay of terms operating at the level of the exact equation gets distorted by the approximations usually employed when evaluating the aforementioned kernel. This fact is reflected in the form of the obtained solutions, for which the deviations from the correct behavior are best quantified by resorting to appropriately defined renormalization-group invariant quantities. This analysis, in turn, provides a solid guiding principle for improving the form of the kernel, and furnishes a well-defined criterion for discriminating between various possibilities. Certain renormalization-group inspired Ansatze for the kernel are then proposed, and their numerical implications are explored in detail. One of the solutions obtained fulfills the theoretical expectations to a high degree of accuracy, yielding a gluon mass that is positive definite throughout the entire range of physical momenta, and displays in the ultraviolet the so-called “power-law” running, in agreement with standard arguments based on the operator product expansion. Some of the technical difficulties thwarting a more rigorous determination of the kernel are discussed, and possible future directions are briefly mentioned.
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ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fassi, F., Ferrer, A., et al. (2014). Search for Higgs boson decays to a photon and a Z boson in pp collisions at root s=7 and 8 TeV with the ATLAS detector. Phys. Lett. B, 732, 8–27.
Abstract: A search is reported for a neutral Higgs boson in the decay channel H -> Z gamma, Z -> l(+)l(-) (l = e, mu), using 4.5 fb(-1) of pp collisions at root s = 7 TeV and 20.3 fb(-1) of pp collisions at root s = 8 TeV, recorded by the ATLAS detector at the CERN Large Hadron Collider. The observed distribution of the invariant mass of the three final-state particles, m(ll gamma), is consistent with the Standard Model hypothesis in the investigated mass range of 120-150 GeV. For a Higgs boson with a mass of 125.5 GeV, the observed upper limit at the 95% confidence level is 11 times the Standard Model expectation. Upper limits are set on the cross section times branching ratio of a neutral Higgs boson with mass in the range 120-150 GeV between 0.13 and 0.5 pb for root s = 8 TeV at 95% confidence level.
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BABAR Collaboration(Lees, J. P. et al), Martinez-Vidal, F., Oyanguren, A., & Villanueva-Perez, P. (2014). Search for the decay (B)over-bar(0) -> Lambda(+)(c)(p)over-barp(p)over-bar. Phys. Rev. D, 89(7), 071102–7pp.
Abstract: We report a search for the decay (B) over bar (0) -> Lambda(+)(c)(p) over barp (p) over bar. Using a data sample of 471 x 10(6) B (B) over bar pairs collected with the BABAR detector at the PEP-II2 storage ring at SLAC, we find no events and set an upper limit on the branching fraction B((B) over bar (0) -> Lambda(+)(c)(p) over barp (p) over bar x B(Lambda(+)(c) -> pK(-)pi(+))/0.050 < 2.8 x 10(-6) at 90% C. L., where we have normalized B(Lambda(+)(c) -> pK(-)pi(+)) to the world average value.
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ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fassi, F., Ferrer, A., et al. (2014). Measurement of the production cross section of prompt j/psi mesons in association with a W (+/-) boson in pp collisions root s=7 TeV with the ATLAS detector. J. High Energy Phys., 04(4), 172–37pp.
Abstract: The process pp -> W (+/-) J/psi provides a powerful probe of the production mechanism of charmonium in hadronic collisions, and is also sensitive to multiple parton interactions in the colliding protons. Using the 2011 ATLAS dataset of 4.5 fb(-1) of root s= 7 TeV pp collisions at the LHC, the first observation is made of the production of W (+/-) + prompt J/psi events in hadronic collisions, using W (+/-) -> μnu(mu) and J/psi -> mu(+)mu(-) center dot A yield of W (+/-) + prompt J/psi events is observed, with a statistical significance of 5.1 sigma. The production rate as a ratio to the inclusive W (+/-) boson production rate is measured, and the double parton scattering contribution to the cross section is estimated.
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