119101875
Prompt photons in photoproduction at HERA
AbstractThe production of prompt photons is measured in the photoproduction regime of electron–proton scattering at HERA. The analysis is based on a data sample corresponding to a total integrated luminosity of 340 pb−1 collected by the H1 experiment. Cross sections are measured for photons with transverse momentum and pseudorapidity in the range 
$6<\ensuremath{E_{T}^{\gamma}}<15$
 GeV and −1.0<ηγ<2.4, respectively. Cross sections for events with an additional jet are measured as a function of the transverse energy and pseudorapidity of the jet, and as a function of the fractional momenta xγ and xp carried by the partons entering the hard scattering process. The correlation between the photon and the jet is also studied. The results are compared with QCD predictions based on the collinear and on the kT factorization approaches.
2659846
Determination of the integrated luminosity at HERA using elastic QED Compton events
A measurement of the integrated luminosity at the ep collider HERA is presented, exploiting the elastic QED Compton process ep→eγp. The electron and the photon are detected in the backward calorimeter of the H1 experiment. The integrated luminosity of the data recorded in 2003 to 2007 is determined with a precision of 2.3 %. The measurement is found to be compatible with the corresponding result obtained using the Bethe–Heitler process.
118644038
Search for new physics in events with photons, jets, and missing transverse energy in pp collisions at $ \sqrt{s}=7 $ TeV
A bstractA search for physics beyond the standard model involving events with one or more photons, jets, and missing transverse energy has been performed by the CMS experiment. The data sample corresponds to an integrated luminosity of 4.93 fb−1 of proton-proton collisions at $ \sqrt{s}=7 $ TeV, produced at the Large Hadron Collider. No excess of events with large missing transverse energy is observed beyond expectations from standard model processes, and upper limits on the signal production cross sections for new physics processes are set at the 95% confidence level. The results of this search are interpreted in the context of three models of new physics: a general model of gauge-mediated supersymmetry breaking, Simplified Models, and a theory involving universal extra dimensions. In the absence of evidence for new physics, exclusion regions are derived in the parameter spaces of the respective models.
54180669
DARK MATTER AND MASSIVE NEUTRINOS
118340898
Measurement of the charm and beauty structure functions using the H1 vertex detector at HERA
Inclusive charm and beauty cross sections are measured in e−p and e+p neutral current collisions at HERA in the kinematic region of photon virtuality 5≤Q2≤2000 GeV2 and Bjorken scaling variable 0.0002≤x≤0.05. The data were collected with the H1 detector in the years 2006 and 2007 corresponding to an integrated luminosity of 189 pb−1. The numbers of charm and beauty events are determined using variables reconstructed by the H1 vertex detector including the impact parameter of tracks to the primary vertex and the position of the secondary vertex. The measurements are combined with previous data and compared to QCD predictions.
122330531
Search for dark matter and large extra dimensions in monojet events in pp collisions at $ \sqrt {s} = {7} $ TeV
A bstractA search has been made for events containing an energetic jet and an imbalance in transverse momentum using a data sample of pp collisions at a center-of-mass energy of 7 TeV. This signature is common to both dark matter and extra dimensions models. The data were collected by the CMS detector at the LHC and correspond to an integrated luminosity of 5.0 fb−1. The number of observed events is consistent with the standard model expectation. Constraints on the dark matter-nucleon scattering cross sections are determined for both spin-independent and spin-dependent interaction models. For the spin-independent model, these are the most constraining limits for a dark matter particle with mass below 3.5 GeV/c2, a region unexplored by direct detection experiments. For the spin-dependent model, these are the most stringent constraints over the 0.1–200 GeV/c2 mass range. The constraints on the Arkani-Hamed, Dimopoulos, and Dvali model parameter MD determined as a function of the number of extra dimensions are also an improvement over the previous results.
118744951
COSMIC EMULATION: THE CONCENTRATION-MASS RELATION FOR wCDM UNIVERSES
The concentration-mass relation for dark matter-dominated halos is one of the essential results expected from a theory of structure formation. We present a simple prediction scheme, a cosmic emulator, for the concentration-mass (c-M) relation as a function of cosmological parameters for wCDM models. The emulator is constructed from 37 individual models, with three nested N-body gravity-only simulations carried out for each model. The mass range covered by the emulator is 2 × 1012 M ☉ < M < 1015 M ☉ with a corresponding redshift range of z = 0-1. Over this range of mass and redshift, as well as the variation of cosmological parameters studied, the mean halo concentration varies from c ~ 2 to c ~ 8. The distribution of the concentration at fixed mass is Gaussian with a standard deviation of one-third of the mean value, almost independent of cosmology, mass, and redshift over the ranges probed by the simulations. We compare results from the emulator with previously derived heuristic analytic fits for the c-M relation, finding that they underestimate the halo concentration at high masses. Using the emulator to investigate the cosmology dependence of the c-M relation over the currently allowable range of values, we find—not surprisingly—that σ8 and ω m influence it considerably, but also that the dark energy equation-of-state parameter w has a substantial effect. In general, the concentration of lower-mass halos is more sensitive to changes in cosmological parameters as compared to cluster mass halos. The c-M emulator is publicly available from http://www.hep.anl.gov/cosmology/CosmicEmu.
118387873
Origin of the Cosmic Network: Nature vs Nurture
The large-scale structure of the Universe, as traced by the distribution of galaxies, is now being revealed by large-volume cosmological surveys. The structure is characterized by galaxies distributed along filaments, the filaments connecting in turn to form a percolating network. Our objective here is to quantitatively specify the underlying mechanisms that drive the formation of the cosmic network: By combining percolation-based analyses with N-body simulations of gravitational structure formation, we elucidate how the network has its origin in the properties of the initial density field (nature) and how its contrast is then amplified by the nonlinear mapping induced by the gravitational instability (nurture).
20819433
Beam halo studies using a 3-dimensional particle-core model
In this paper we present a study of beam halo based on a three-dimensional particle-core model of an ellipsoidal bunched beam in a constant focusing channel. For an initially mismatched beam, three linear envelope modes-a high frequency mode, a low frequency mode and a quadrupole mode-are identified. Stroboscopic plots are obtained for particle motion in the three modes. With higher focusing strength ratio, a 1:2 transverse parametric resonance between the test particle and core oscillation is observed for all three modes. The particle-high mode resonance has the largest amplitude and presents potentially the most dangerous beam halo in machine design and operation. For the longitudinal dynamics of a test particle, a 1:2 resonance is observed only between the particle and high mode oscillation, which suggests that the particle-high mode resonance will also be responsible for longitudinal beam halo formation.
119516986
Nonequilibrium dynamics of symmetry breaking in lambda Phi**4 field theory
The time evolution of O(N) symmetric lambda Phi^4 scalar field theory is studied in the large N limit. In this limit the mean field and two-point correlation function evolve together as a self-consistent closed Hamiltonian system, characterized by a Gaussian density matrix. The static part of the effective Hamiltonian defines the True Effective Potential U_eff for configurations far from thermal equilibrium. Numerically solving the time evolution equations for energy densities corresponding to a quench in the unstable spinodal region, we find results quite different from what might be inferred from the equilibrium free energy ``effective'' potential F. Typical time evolutions show effectively irreversible energy flow from the coherent mean fields to the quantum fluctuating modes, due to the creation of massless Goldstone bosons near threshold. The plasma frequency and collisionless damping rate of the mean fields are calculated in terms of the particle number density by a linear response analysis and compared with the numerical results. Dephasing of the fluctuations leads also to the growth of an effective entropy and the transition from quantum to classical behavior of the ensemble. In addition to casting some light on fundamental issues of nonequilibrium quantum statistical mechanics, the general framework presented in this work may be applied to a study of the dynamics of second order phase transitions in a wide variety of Landau-Ginsburg systems described by a scalar order parameter.
9366117
Multiplicative Noise: Applications in Cosmology and Field Theorya
Physical situations involving multiplicative noise arise generically in cosmology and field theory. In this paper, the focus is first on exact nonlinear Langevin equations, appropriate in a cosmological setting, for a system with one degree of freedom. The Langevin equations are derived using an appropriate time-dependent generalization of a model due to Zwanzig. These models axe then extended to field theories and the generation of multiplicative noise in such a context is discussed. Important issues in both the cosmological and field theoretic cases are the fluctuation-dissipation relations and the relaxation time scale. Of some importance in cosmology is the fact that multiplicative noise can substantially reduce the relaxation time. In the field theoretic context such a noise can lead to a significant enhancement in the nucleation rate of topological defects.