Debastiani, V. R., Aceti, F., Liang, W. H., & Oset, E. (2017). Revising the f(1)(1420) resonance. Phys. Rev. D, 95(3), 034015–10pp.
Abstract: We have studied the production and decay of the f(1) (1285) into pi a(0)(980) and K* (K) over bar as a function of the mass of the resonance and find a shoulder around 1400 MeV, tied to a triangle singularity, for the pi a(0)(980) mode, and a peak around 1420 MeV with about 60 MeV width for the K* (K) over bar mode. Both of these features agree with the experimental information on which the f(1)(1420) resonance is based. In addition, we find that if the f(1)(1420) is a genuine resonance, coupling mostly to K* (K) over bar as seen experimentally, one finds unavoidably about a 20% fraction for pi a(0)(980) decay of this resonance, in drastic contradiction with all experiments. Altogether, we conclude that the f(1)(1420) is not a genuine resonance, but the manifestation of the pi a(0)(980) and K* (K) over bar decay modes of the f(1)(1285) at higher energies than the nominal one.
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BABAR Collaboration(Lees, J. P. et al), Martinez-Vidal, F., & Oyanguren, A. (2017). Measurement of the inclusive electron spectrum from B meson decays and determination of vertical bar V-ub vertical bar. Phys. Rev. D, 95(7), 072001–23pp.
Abstract: Based on the full BABAR data sample of 466.5 million B (B) over bar pairs, we present measurements of the electron spectrum from semileptonic B meson decays. We fit the inclusive electron spectrum to distinguish Cabibbo-Kobayashi-Maskawa (CKM) suppressed B -> X(u)ev decays from the CKM-favored B -> X(u)ev decays, and from various other backgrounds, and determine the total semileptonic branching fraction B(B -> X(u)ev) = (10.34 +/- 0.04(stat) +/- 0.26(syst))%, averaged over B-+/- and B-0 mesons. We determine the spectrum and branching fraction for charmless B -> X(u)ev decays and extract the CKM element vertical bar V-ub vertical bar, by relying on four different QCD calculations based on the heavy quark expansion. While experimentally, the electron momentum region above 2.1 GeV/c is favored, because the background is relatively low, the uncertainties for the theoretical predictions are largest in the region near the kinematic endpoint. Detailed studies to assess the impact of these four predictions on the measurements of the electron spectrum, the branching fraction, and the extraction of the CKM matrix element vertical bar V-ub vertical bar are presented, with the lower limit on the electron momentum varied from 0.8 GeV/c to the kinematic endpoint. We determine V-ub vertical bar using each of these different calculations and find, vertical bar V-ub vertical bar = (3.794 +/- 0.107(exp) (+0.292)(-0.219) (SF) (+0.078)(-0.068)theory) x 10(-3) (De Fazio and Neubert), (4.563 +/- 0.126(exp) (+0.230)(+0.162)(-0.208)(-0.163)theory) x 10(-3) (Bosch, Lange, Neubert, and Paz), (3.959 +/- 0.104(exp -0.154)(SF-0.079)(+0.164)(+0.042) theory )x 10(-3) (Gambino, Giordano, Ossola, and Uraltsev), (3.848 +/- 0.108(exp -0.070)(theory)(+0.084)) x 10(-3) (dressed gluon exponentiation), where the stated uncertainties refer to the experimental uncertainties of the partial branching fraction measurement, the shape function parameters, and the theoretical calculations.
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ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Barranco Navarro, L., Cabrera Urban, S., Castillo Gimenez, V., Cerda Alberich, L., et al. (2017). Search for new phenomena in events containing a same-flavour opposite-sign dilepton pair, jets, and large missing transverse momentum in root s=13 TeV pp collisions with the ATLAS detector. Eur. Phys. J. C, 77(3), 144–40pp.
Abstract: Two searches for new phenomena in final states containing a same-flavour opposite-sign lepton (electron or muon) pair, jets, and large missing transverse momentum are presented. These searches make use of proton-proton collision data, collected during 2015 and 2016 at a centre-of-mass energy root s = 13 TeV by the ATLAS detector at the large hadron collider, which correspond to an integrated luminosity of 14.7 fb(-1). Both searches target the pair production of supersymmetric particles, squarks or gluinos, which decay to final states containing a same-flavour opposite-sign lepton pair via one of two mechanisms: a leptonically decaying Z boson in the final state, leading to a peak in the dilepton invariant-mass distribution around the Z boson mass; and decays of neutralinos (e.g.. (chi) over tilde (0)(2) -> l(+)l(-1)(chi) over tilde (0)(1)), yielding a kinematic endpoint in the dilepton invariant-mass spectrum. The data are found to be consistent with the Standard Model expectation. Results are interpreted in simplified models of gluino-pair (squark-pair) production, and provide sensitivity to gluinos (squarks) with masses as large as 1.70 TeV (980 GeV).
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Arbelaez, C., Gonzalez, M., Kovalenko, S. G., & Hirsch, M. (2017). QCD-improved limits from neutrinoless double beta decay. Phys. Rev. D, 96(1), 015010–12pp.
Abstract: We analyze the impact of QCD corrections on limits derived from neutrinoless double beta decay (0 nu beta beta ). As demonstrated previously, the effect of the color mismatch arising from loops with gluons linking the quarks from different color-singlet currents participating in the effective operators has a dramatic impact on the predictions for some particular Wilson coefficients. Here, we consider all possible contributions from heavy particle exchange, i.e. the so-called short-range mechanism of 0 nu beta beta decay. All high-scale models (HSM) in this class match at some scale around a similar to few TeV with the corresponding effective theory, containing a certain set of effective dimension-9 operators. Many of these HSM receive contributions from more than one of the basic operators and we calculate limits on these models using the latest experimental data. We also show with one nontrivial example, how to derive limits on more complicated models, in which many different Feynman diagrams contribute to 0 nu beta beta decay, using our general method.
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Poley, L. et al, & Lacasta, C. (2017). Investigations into the impact of locally modified sensor architectures on the detection efficiency of silicon micro-strip sensors. J. Instrum., 12, P07006–17pp.
Abstract: The High Luminosity Upgrade of the LHC will require the replacement of the Inner Detector of ATLAS with the Inner Tracker (ITk) in order to cope with higher radiation levels and higher track densities. Prototype silicon strip detector modules are currently developed and their performance is studied in both particle test beams and X-ray beams. In previous test beam measurements of prototype modules, the response of silicon sensors has been studied in detailed scans across individual sensor strips. These scans found instances of sensor strips collecting charge across areas on the sensor deviating from the geometrical width of a sensor strip. The variations have been linked to local features of the sensor architecture. This paper presents results of detailed sensor measurements in both X-ray and particle beams investigating the impact of sensor features (metal pads and p-stops) on the sensor strip response.
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