Unburied Higgs boson: Jet substructure techniques for searching for Higgs’ decay into gluons
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Falkowski, Adam↗
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Study of the pure annihilation B{sub c}{yields}A{sub 2}A{sub 3} decays
In this work, we calculate the CP-averaged branching ratios and the polarization fractions of the charmless hadronic B{sub c}{yields}A{sub 2}A{sub 3} decays within the framework of perturbative QCD (pQCD) approach, where A is either a light {sup 3}P{sub 1} or {sup 1}P{sub 1} axial-vector meson. These 32 decay modes can occur through the annihilation topology only. Based on the perturbative calculations and phenomenological analysis, we find the following results: (a) the branching ratios of the considered 32 B{sub c}{yields}A{sub 2}A{sub 3} decays are in the range of 10{sup -5} to 10{sup -8}; (b) B{sub c}{yields}a{sub 1}b{sub 1}, K{sub 1}{sup 0}K{sub 1}{sup +} and some other decays have sizable branching ratios and can be measured at the LHC experiments; (c) the branching ratios of B{sub c}{yields}A{sub 2}({sup 1}P{sub 1})A{sub 3}({sup 1}P{sub 1}) decays are generally much larger than those of B{sub c}{yields}A{sub 2}({sup 3}P{sub 1})A{sub 3}({sup 3}P{sub 1}) decays with a factor around (10{approx}100); (d) the branching ratios of B{sub c}{yields}K{sub 1}{sup 0}K{sub 1}{sup +} decays are sensitive to the value of {theta}{sub K}, which will be tested by the running LHC and forthcoming SuperB experiments; (e) the large longitudinal polarization contributions govern most considered decays and play the dominant role.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Sneutrino-antisneutrino oscillation at the Tevatron
Sneutrino-antisneutrino oscillation can be a very useful probe to look for signatures of lepton number violation ({Delta}L=2) at the Tevatron. Here, we discuss a scenario where the total decay width of the sneutrino is very small, producing interesting signals at the Tevatron for a mass splitting {Delta}m as small as 10{sup -14} GeV between the sneutrino mass eigenstates.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Next-to-leading order QCD predictions for the signal of dark matter and photon associated production at the LHC
We study the potential of the LHC to discover the signal of dark matter associated production with a photon induced by a dimension six effective operator, including next-to-leading order QCD corrections. We investigate the main backgrounds from the standard model, i.e. Z boson and a photon associated production with invisible decay of Z boson, and Z boson and a jet production with the jet misidentified as a photon. We find that the p{sub T}{sup {gamma}} distributions of the backgrounds decrease faster than that of the signal with increasing of the transverse momentum of the photon. The {eta}{sup {gamma}} distributions of the backgrounds are almost flat in the full range of {eta}{sup {gamma}}. In contrast, the signal lies mainly in the central region of {eta}{sup {gamma}}. These characteristics may help to select the events in experiments. We show that in the parameter space allowed by the relic abundance constraint, which we have calculated at the next-to-leading-order QCD level, the LHC with {radical}(S)=7 TeV may discover this signal at the 5{sigma} level after collecting an integrated luminosity of 1 fb{sup -1}. On the other hand, if this signal is not observed at the LHC, we can set a lower limit on the new physics scale at the 3{sigma} level.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Standard model CP violation and cold electroweak baryogenesis
Using large-scale real-time lattice simulations, we calculate the baryon asymmetry generated at a fast, cold electroweak symmetry breaking transition. CP-violation is provided by the leading effective bosonic term resulting from integrating out the fermions in the Minimal Standard Model at zero-temperature, and performing a covariant gradient expansion [A. Hernandez, T. Konstandin, and M. G. Schmidt, Nucl. Phys. B812, 290 (2009).]. This is an extension of the work presented in [A. Tranberg, A. Hernandez, T. Konstandin, and M. G. Schmidt, Phys. Lett. B 690, 207 (2010).]. The numerical implementation is described in detail, and we address issues specifically related to using this CP-violating term in the context of Cold Electroweak Baryogenesis.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Ultrahigh energy predictions of proton-air cross sections from accelerator data: An update
At {radical}(s)=57{+-}7 TeV, the Pierre Auger Observatory (PAO) measured the p-air inelastic production cross section, {sigma}{sub p-air}{sup prod}=475{+-}22(stat){+-}{sub 15}{sup 20}(syst) mb, assuming a proton cosmic ray beam with a 25% helium contamination. From a Glauber calculation, they found the inelastic pp cross section, {sigma}{sub inel}=90{+-}7(stat){+-}{sub 11}{sup 9}(syst){+-}1.5(Glaub) mb. Our parameterization of pp and pp total cross sections, {sigma}{sub tot}, using analyticity constraints and unitarity gives accurate extrapolations to ultrahigh energies, and after using a Glauber calculation, accurate predictions for {sigma}{sub p-air}{sup prod}. We find (i) a pp total cross section, {sigma}{sub tot}=133.4{+-}1.6 mb and (ii) {sigma}{sub p-air}{sup prod}=483{+-}3 mb, independently determining a 19% helium contamination. Using our 57 TeV value for pp {sigma}{sub tot}[M. M. Block and F. Halzen, arXiv:1109-2041], we find a pp inelastic cross section, {sigma}{sub inel}=92.9{+-}1.6 mb, agreeing with POA.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
The cos2{phi} azimuthal asymmetry of unpolarized dilepton production at the Z pole
We calculate the Boer-Mulders effect contribution to the cos2{phi} azimuthal asymmetry of unpolarized dilepton production near the Z-pole. Based on the tree-level expression in the transverse momentum dependent factorization framework, we show that the corresponding asymmetry near the Z-pole is negative, which is opposite to the asymmetry in the low Q{sup 2} region, dominated by the production via a virtual photon. We calculate the asymmetry generated by the Boer-Mulders effect near the Z-pole at the Relativistic Heavy Ion Collider (RHIC), with {radical}(s)=500 GeV. We find that the magnitude of the asymmetry is several percent, and therefore it is measurable. The experimental confirmation of this sign change of the asymmetry from the low Q{sup 2} region to the Z-pole provides direct evidence of the chiral-odd structure of quarks inside an unpolarized nucleon.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Dijet invariant mass distribution in top quark hadronic decay with QCD corrections
The dijet invariant mass distributions from the hadronic decay of unpolarized top quark (t{yields}bW{sup +} followed by W{sup +}{yields}ud) are calculated, including the next-to-leading order QCD radiative corrections. We treat the top decay in the complex mass scheme due to the existence of the intermediate state W boson. Our analytical expressions are also available in different dimensional regularization schemes and {gamma}{sub 5} strategies. Finally, in order to construct the jets, we use different jet algorithms to compare their influences on our results. The obtained dijet mass distributions from the top quark decay are useful to distinguish these dijets from those produced via other sources and to clarify the issue about the recent CDF Collaboration's Wjj anomaly.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Chirally symmetric and confining dense matter with a diffused quark Fermi surface
It is possible that at low temperatures and large density there exists a confining matter with restored chiral symmetry, just after the dense nuclear matter with broken chiral symmetry. Such a phase has, so far, been studied within a confining and chirally symmetric model, assuming a rigid quark Fermi surface. In the confining quarkyonic matter, however, near the Fermi surface, quarks group into color-singlet baryons. Interaction between quarks leads to a diffusion of the quark Fermi surface. Here, we study effects of such diffusion and verify that it does not destroy a possible existence of a confining but chirally symmetric matter at low temperatures.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Bottomonium in a Bethe-Salpeter-equation study
Using a well-established effective interaction in a rainbow-ladder truncation model of QCD, we fix the remaining model parameter to the bottomonium ground-state spectrum in a covariant Bethe-Salpeter equation approach and find surprisingly good agreement with the available experimental data including the 2{sup --} {Upsilon}(1D) state. Furthermore, we investigate the consequences of such a fit for charmonium and light-quark ground states.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Resonance region structure functions and parity-violating deep inelastic scattering
The primary motive of parity-violating deep inelastic scattering experiments has been to test the standard model, particularly the axial couplings to the quarks, in the scaling region. The measurements can also test for the validity of models for the off-diagonal structure functions ${F}_{1,2,3}^{γZ}$($x,Q^2$) in the resonance region. The off-diagonal structure functions are important for the accurate calculation of the $γZ$-box correction to the weak charge of the proton. Currently, with no data to determine ${F}_{1,2,3}^{γZ}$($x,Q^2$) directly, models are constructed by modifying existing fits to electromagnetic data. Here, we present the asymmetry value for deuteron and proton targets predicted by several different ${F}_{1,2,3}^{γZ}$($x,Q^2$) models and demonstrate that there are notable disagreements.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
First Glances at the Transversity Parton Distribution through Dihadron Fragmentation Functions
We present first observations of the transversity parton distribution based on an analysis of pion-pair production in deep-inelastic scattering off transversely polarized targets. The extraction of transversity relies on the knowledge of dihadron fragmentation functions, which we take from electron-positron annihilation measurements. This is the first attempt to determine the transversity distribution in the framework of collinear factorization.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
No Collective Neutrino Flavor Conversions during the Supernova Accretion Phase
We perform a dedicated study of the supernova (SN) neutrino flavor evolution during the accretion phase, using results from recent neutrino radiation hydrodynamics simulations. In contrast to what was expected in the presence of only neutrino-neutrino interactions, we find that the multiangle effects associated with the dense ordinary matter suppress collective oscillations. The matter suppression implies that neutrino oscillations will start outside the neutrino decoupling region and therefore will have a negligible impact on the neutrino heating and the explosion dynamics. Furthermore, the possible detection of the next galactic SN neutrino signal from the accretion phase, based on the usual Mikheyev-Smirnov-Wolfenstein effect in the SN mantle and Earth matter effects, can reveal the neutrino mass hierarchy in the case that the mixing angle {theta}{sub 13} is not very small.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
First Use of High Charge States for Mass Measurements of Short-Lived Nuclides in a Penning Trap
Penning trap mass measurements of short-lived nuclides have been performed for the first time with highly charged ions, using the TITAN facility at TRIUMF. Compared to singly charged ions, this provides an improvement in experimental precision that scales with the charge state q. Neutron-deficient Rb isotopes have been charge bred in an electron beam ion trap to q=8-12+ prior to injection into the Penning trap. In combination with the Ramsey excitation scheme, this unique setup creating low energy, highly charged ions at a radioactive beam facility opens the door to unrivaled precision with gains of 1-2 orders of magnitude. The method is particularly suited for short-lived nuclides such as the superallowed {beta} emitter {sup 74}Rb (T{sub 1/2}=65 ms). The determination of its atomic mass and an improved Q{sub EC} value are presented.
74 ATOMIC AND MOLECULAR PHYSICS↗
Observation of Electroweak Production of a Same-Sign W Boson Pair in Association with Two Jets in pp Collisions root s=13 TeV with the ATLAS Detector
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72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Measurement of Electron-Neutrino Charged-Current Cross Sections on 127 I with the COHERENT NaI$ν$E Detector
Using an 185-kg NaI[Tl] array, COHERENT has measured the inclusive electron-neutrino chargedcurrent cross section on 127 I with pion decay-at-rest neutrinos produced by the Spallation Neutron Source at Oak Ridge National Laboratory. Iodine is one the heaviest targets for which low-energy (≤ 50 MeV) inelastic neutrino-nucleus processes have been measured, and this is the first measurement of its inclusive cross section. After a five-year detector exposure, COHERENT reports a flux-averaged cross section for electron neutrinos of ${9.2}_{–1.8}^{+2.1}$ × 10 –40 cm 2 . This corresponds to a value that is ~41% lower than predicted using the MARLEY event generator with a measured Gamow-Teller strength distribution. In addition, the observed visible spectrum from charged-current scattering on 127 I has been measured between 10 and 55 MeV, and the exclusive zero-neutron and one-or-more-neutron emission cross sections are measured to be ${5.2}_{–3.1}^{+3.4}$ × 10 –40 and ${2.2}_{—2.2}^{+3.5}$ × 10 –40 cm 2 , respectively.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Production of a pair by a polarized photon in a uniform constant electromagnetic field
The total probability of production of an electron-positron pair by a polarized photon in a constant uniform electromagnetic field of an arbitrary configuration is determined using the imaginary part of the diagonalized polarization operator. Approximate expressions are derived for this probability in four ranges of photon energy. In the high-energy range, the corrections to the standard semiclassical approximation are calculated. In the range of intermediate energies, in which this approximation is inapplicable, the probability of the process is calculated using the steepest descent method. It is shown that in the range of photon energies higher than the pair production threshold in a magnetic field, a weak electric field removes root divergences in the probability of production of the particles at the Landau levels. For relatively low photon energies, a low-energy approximation is developed. At such energies, the effect of the electric field on the process is decisive, while the effect of the magnetic field is associated with its interaction with the magnetic moment of the particles being produced. Such an interaction is manifested, in particular, in the difference in the probabilities of production of a pair by an external field for scalar and spinor particles.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗