ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Ferrer, A., Fiorini, L., et al. (2014). Search for the Standard Model Higgs boson decay to mu(+)mu(-) with the ATLAS detector. Phys. Lett. B, 738, 68–86.
Abstract: A search is reported for Higgs boson decay to mu(+)mu(-) using data with an integrated luminosity of 24.8 fb(-1) collected with the ATLAS detector in pp collisions at root s = 7 and 8 TeV at the CERN Large Hadron Collider. The observed dimuon invariant mass distribution is consistent with the Standard Model background-only hypothesis in the 120-150 GeV search range. For a Higgs boson with a mass of 125.5 GeV, the observed (expected) upper limit at the 95% confidence level is 7.0 (7.2) times the Standard Model expectation. This corresponds to an upper limit on the branching ratio BR(H -> mu(+)mu(-)) of 1.5 x10(-3).
|
Albertus, C., Hernandez, E., Hidalgo-Duque, C., & Nieves, J. (2014). (B)over-bar(s) -> K semileptonic decay from an Omnes improved constituent quark model. Phys. Lett. B, 738, 144–149.
Abstract: We study the f(+) form factor for the semileptonic (B) over bar (s) -> K+ l(-) (V) over bar (l) decay in a constituent quark model. The valence quark estimate is supplemented with the contribution from the (B) over bar* pole that dominates the high q(2) region. We use a multiply-subtracted Omnes dispersion relation to extend the quark model predictions from its region of applicability near q(max)(2) = (M-Bs – M-K)(2) similar to 23.75 GeV2 to all q(2) values accessible in the physical decay. To better constrain the dependence of f(+) on q(2), we fit the subtraction constants to a combined input from previous light cone sum rule by Duplancic and Melic (2008) [11] and the present quark model results. From this analysis, we obtain Gamma ( (B) over bar (s) -> K+ l(-) (V) over bar (l)) = (5.47(-0.46)(+0.54)) vertical bar Vub vertical bar(2) x 10(-9) MeV, which is about 10% and 20% higher than the predictions based on Lattice QCD and QCD light cone sum rules respectively. The former predictions, for both the form factor f(+) (q(2)) and the differential decay width, lie within the 1 sigma band of our estimated uncertainties for all q(2) values accessible in the physical decay, except for a quite small region very close to q(max)(2). Differences with the light cone sum results for the form factor f(+) are larger than 20% in the region above q(2) = 15 GeV2.
|
Taprogge, J. et al, Gadea, A., & Montaner-Piza, A. (2014). Identification of a millisecond isomeric state in Cd-129(81) via the detection of internal conversion and Compton electrons. Phys. Lett. B, 738, 223–227.
Abstract: The decay of an isomeric state in the neutron-rich nucleus Cd-129 has been observed via the detection of internal conversion and Compton electrons providing first experimental information on excited states in this nucleus. The isomer was populated in the projectile fission of a U-238 beam at the Radioactive Isotope Beam Factory at RIKEN. From the measured yields of gamma-rays and internal conversion electrons, a multipolarity of E3 was tentatively assigned to the isomeric transition. A half-life of T-1/2 = 3.6(2) ms was determined for the new state which was assigned a spin of (21/2(+)), based on a comparison to shell model calculations performed using state-of-the-art realistic effective interactions.
|
ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Ferrer, A., Fiorini, L., et al. (2014). Fiducial and differential cross sections of Higgs boson production measured in the four-lepton decay channel in pp collisions at root s=8 TeV with the ATLAS detector. Phys. Lett. B, 738, 234–253.
Abstract: Measurements of fiducial and differential cross sections of Higgs boson production in the H -> ZZ* -> 4l decay channel are presented. The cross sections are determined within a fiducial phase space and corrected for detection efficiency and resolution effects. They are based on 20.3 fb(-1) of pp collision data, produced at root s= 8 TeV centre-of-mass energy at the LHC and recorded by the ATLAS detector. The differential measurements are performed in bins of transverse momentum and rapidity of the four-lepton system, the invariant mass of the subleading lepton pair and the decay angle of the leading lepton pair with respect to the beam line in the four-lepton rest frame, as well as the number of jets and the transverse momentum of the leading jet. The measured cross sections are compared to selected theoretical calculations of the Standard Model expectations. No significant deviation from any of the tested predictions is found.
|
ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Ferrer, A., Fiorini, L., et al. (2014). Search for new resonances in W gamma and Z gamma final states in pp collisions at root s=8 TeV with the ATLAS detector. Phys. Lett. B, 738, 428–447.
Abstract: This Letter presents a search for new resonances decaying to final states with a vector boson produced in association with a high transverse momentum photon, V gamma, with V = W(-> l nu) or Z(-> l(+)l(-)), where l = μor mu. The measurements use 20.3fb(-1) of proton-proton collision data at a center-of-mass energy of root s = 8 TeV recorded with the ATLAS detector. No deviations from the Standard Model expectations are found, and production cross section limits are set at 95% confidence level. Masses of the hypothetical a(T) and omega(T) states of a benchmark Low Scale Technicolor model are excluded in the ranges [275, 960] GeV and [200, 700]boolean OR[750, 890] GeV, respectively. Limits at 95% confidence level on the production cross section of a singlet scalar resonance decaying to Z gamma final states have also been obtained for masses below 1180 GeV.
|
AGATA Collaboration(Pellegri, L. et al), & Gadea, A. (2014). Pygmy dipole resonance in Sn-124 populated by inelastic scattering of O-17. Phys. Lett. B, 738, 519–523.
Abstract: The gamma decay from the high-lying states of Sn-124 was measured using the inelastic scattering of O-17 at 340 MeV. The emitted gamma rays were detected with high resolution with the AGATA demonstrator array and the scattered ions were detected in two segmented Delta E-E silicon telescopes. The angular distribution was measured both for the gamma rays and the scattered O-17 ions. An accumulation of E1 strength below the particle threshold was found and compared with previous data obtained with (gamma,gamma') and (alpha,alpha'gamma) reactions. The present results of elastic scattering, and excitation of E2 and E1 states were analysed using the DWBA approach. From this comprehensive description the isoscalar component of the 1-excited states was extracted. The obtained values are based on the comparison of the data with DWBA calculations including a form factor deduced using a microscopic transition density.
|
BABAR Collaboration(Lees, J. P. et al), Martinez-Vidal, F., Oyanguren, A., & Villanueva-Perez, P. (2014). Measurements of direct CP asymmetries in B -> X-s gamma decays using sum of exclusive decays. Phys. Rev. D, 90(9), 092001–12pp.
Abstract: We measure the direct CP violation asymmetry, A(CP), in B -> X-s gamma and the isospin difference of the asymmetry, Delta A(CP), using 429 fb(-1) of data collected at Upsilon(4S) resonance with the BABAR detector at the PEP- II asymmetric- energy e(+)e(-) storage rings operating at the SLAC National Accelerator Laboratory. B mesons are reconstructed from ten charged B final states and six neutral B final states. We find A(CP) = +(1.7 +/- 1.9 +/- 1.0)%, which is in agreement with the Standard Model prediction and provides an improvement on the world average. Moreover, we report the first measurement of the difference between A(CP) for charged and neutral decay modes, Delta A(CP) = +(5.0 +/- 3.9 +/- 1.5)%. Using the value of Delta A(CP), we also provide 68% and 90% confidence intervals on the imaginary part of the ratio of theWilson coefficients corresponding to the chromomagnetic dipole and the electromagnetic dipole transitions.
|
Maiezza, A., & Nemevsek, M. (2014). Strong P invariance, neutron electric dipole moment, and minimal left-right parity at LHC. Phys. Rev. D, 90(9), 095002–10pp.
Abstract: In the minimal left-right model the choice of left-right symmetry is twofold: either generalized parity P or charge conjugation C. In the minimal model with spontaneously broken strict P, a large tree-level contribution to strong CP violation can be computed in terms of the spontaneous phase alpha. Searches for the neutron electric dipole moments then constrain the size of alpha. Following the latest update on indirect CP violation in the kaon sector, a bound on W-R mass at 20 TeV is set. Possible ways out of this bound require a further hypothesis, either a relaxation mechanism or explicit breaking of P. To this end, the chiral loop of the neutron electric dipole moment at next-to-leading order is recomputed and provides an estimate of the weak contribution. Combining this constraint with other CP-violating observables in the kaon sector allows for M-WR greater than or similar to 3 TeV. On the other hand, C symmetry is free from such constraints, leaving the right-handed scale within the experimental reach.
|
ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Ferrer, A., Fiorini, L., et al. (2014). Measurement of differential production cross-sections for a Z boson in association with b-jets in 7 TeV proton-proton collisions with the ATLAS detector. J. High Energy Phys., 10(10), 141–49pp.
Abstract: Measurements of differential production cross-sections of a Z boson in association with b-jets in pp collisions at root s = 7 TeV are reported. The data analysed correspond to an integrated luminosity of 4.6 fb(-1) recorded with the ATLAS detector at the Large Hadron Collider. Particle-level cross-sections are determined for events with a Z boson decaying into an electron or muon pair, and containing b-jets. For events with at least one b-jet, the cross-section is presented as a function of the Z boson transverse momentum and rapidity, together with the inclusive b-jet cross-section as a function of b-jet transverse momentum, rapidity and angular separations between the b-jet and the Z boson. For events with at least two b-jets, the cross-section is determined as a function of the invariant mass and angular separation of the two highest transverse momentum b-jets, and as a function of the Z boson transverse momentum and rapidity. Results are compared to leading-order and next-to-leading-order perturbative QCD calculations.
|
Rinaldi, M., Scopetta, S., Traini, M., & Vento, V. (2014). Double parton correlations and constituent quark models: a light front approach to the valence sector. J. High Energy Phys., 12(12), 028–23pp.
Abstract: An explicit evaluation of the double parton distribution functions (dPDFs), within a relativistic Light-Front approach to constituent quark models, is presented. dPDFs encode information on the correlations between two partons inside a target and represent the non-perturbative QCD ingredient for the description of double parton scattering in proton-proton collisions, a crucial issue in the search of new Physics at the LHC. Valence dPDFs are evaluated at the low scale of the model and the perturbative scale of the experiments is reached by means of QCD evolution. The present results show that the strong correlation effects present at the scale of the model are still sizable, in the valence region, at the experimental scale. At the low values of x presently studied at the LHC the correlations become less relevant, although they are still important for the spin-dependent contributions to unpolarized proton scattering.
|
