119246325
Measurement of photon production in the very forward direction in deep-inelastic scattering at HERA
The production of photons at very small angles with respect to the proton beam direction is studied in deep-inelastic positron–proton scattering at HERA. The data are taken with the H1 detector in the years 2006 and 2007 and correspond to an integrated luminosity of 126 pb−1. The analysis covers the range of negative four momentum transfer squared at the positron vertex 6<Q2<100 GeV2 and inelasticity 0.05<y<0.6. Cross sections are measured for the most energetic photon with pseudorapidity η>7.9as a function of its transverse momentum $p_{T}^{\mathrm{lead}}$ and longitudinal momentum fraction of the incoming proton $x_{L}^{\mathrm{lead}}$. In addition, the cross sections are studied as a function of the sum of the longitudinal momentum fraction $x_{L}^{\mathrm{sum}}$ of all photons in the pseudorapidity range η>7.9. The cross sections are normalised to the inclusive deep-inelastic scattering cross section and compared to the predictions of models of deep-inelastic scattering and models of the hadronic interactions of high energy cosmic rays.
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.
119204233
Search for new physics in events with same-sign dileptons and b-tagged jets in pp collisions at $ \sqrt {s} = 7 $ TeV
A bstractA search for new physics is performed using isolated same-sign dileptons with at least two b-quark jets in the final state. Results are based on a 4.98 fb−1 sample of proton-proton collisions at a centre-of-mass energy of 7 TeV collected by the CMS detector. No excess above the standard model background is observed. Upper limits at 95% confidence level are set on the number of events from non-standard-model sources. These limits are used to set constraints on a number of new physics models. Information on acceptance and efficiencies are also provided so that the results can be used to confront additional models in an approximate way.
117033883
Measurement of the single-top-quark t-channel cross section in pp collisions at $ \sqrt{s}=7 $ TeV
A bstractA measurement of the single-top-quark t-channel production cross section in pp collisions at $ \sqrt{s}=7 $ TeV with the CMS detector at the LHC is presented. Two different and complementary approaches have been followed. The first approach exploits the distributions of the pseudorapidity of the recoil jet and reconstructed top-quark mass using background estimates determined from control samples in data. The second approach is based on multivariate analysis techniques that probe the compatibility of the candidate events with the signal. Data have been collected for the muon and electron final states, corresponding to integrated luminosities of 1.17 and 1.56 fb−1, respectively. The single-top-quark production cross section in the t-channel is measured to be 67.2±6.1 pb, in agreement with the approximate next-to-next-to-leading-order standard model prediction. Using the standard model electroweak couplings, the CKM matrix element |Vtb| is measured to be 1.020 ± 0.046 (meas.) ± 0.017 (theor.).
18536190
Search for Excited Electrons in ep Collisions at HERA
A search for excited electrons is performed using the full e±p data sample collected by the H1 experiment at HERA, corresponding to a total luminosity of 475 pb−1. The electroweak decays of excited electrons e*→eγ, e*→eZ and e*→νW with subsequent hadronic or leptonic decays of the W and Z bosons are considered. No evidence for excited electron production is found. Mass dependent exclusion limits on e* production cross sections and on the ratio f/Λ of the coupling to the compositeness scale are derived within gauge mediated models. These limits extend the excluded region compared to previous excited electron searches. The e* production via contact interactions is also addressed for the first time in ep collisions.
36326465
Search for third-generation leptoquarks and scalar bottom quarks in pp collisions at $ \sqrt{s}=7\;TeV $
A bstractResults are presented from a search for third-generation leptoquarks and scalar bottom quarks in a sample of proton-proton collisions at $ \sqrt{s}=7\;TeV $ collected by the CMS experiment at the LHC, corresponding to an integrated luminosity of 4.7 fb−1. A scenario where the new particles are pair produced and each decays to a b quark plus a tau neutrino or neutralino is considered. The number of observed events is found to be in agreement with the standard model prediction. Upper limits are set at 95% confidence level on the production cross sections. Leptoquarks with masses below ~450 GeV are excluded. Upper limits in the mass plane of the scalar quark and neutralino are set such that scalar bottom quark masses up to 410 GeV are excluded for neutralino masses of 50 GeV.
16061870
Virial scaling of massive dark matter halos: why clusters prefer a high normalization cosmology
We present a precise estimate of the bulk virial scaling relation of halos formed via hierarchical clustering in an ensemble of simulated cold dark matter cosmologies. The result is insensitive to cosmological parameters; the presence of a trace, dissipationless gas component; and numerical resolution down to a limit of ~1000 particles. The dark matter velocity dispersion scales with total mass as log [?DM(M,z)] = = log(1082.9 ? 4.0 km s?1) + (0.3361 ? 0.0026)log[h(z)M200/1015 M?], with h(z) being the dimensionless Hubble parameter. At fixed mass, the velocity dispersion likelihood is nearly lognormal, with scatter ?ln ? = 0.0426 ? 0.015, except for a tail with higher dispersions containing 10% of the population that are merger transients. We combine this relation with the halo mass function in ?CDM models and show that a low normalization condition, S8 = ?8(?m/0.3)0.35 = 0.69, favored by recent WMAP and SDSS analysis requires that galaxy and gas-specific energies in rich clusters be 50% larger than that of the underlying dark matter. Such large energetic biases are in conflict with the current generation of direct simulations of cluster formation. A higher normalization, S8 = 0.80, alleviates this tension and implies that the hot gas fraction within r500 is , a value consistent with recent Sunyaev-Zel'dovich observations.
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.
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.
122697839
A Combined Three-Phase Signal Extraction of the Sudbury Neutrino Observatory Data Using Markov Chain Monte Carlo Technique
Neutrino physics has entered an era of precision, after proving that the Standard Solar Model is a viable theory and going beyond the current Standard Model of particle physics by proving that neutrinos possess nonzero masses. The Sudbury Neutrino Observatory (SNO) experiment, along with other experiments, has restricted neutrino mixing angle (θ12) and the mass square difference (∆m21) to lie within the large mixing solution area. SNO, located 2 km underground in Sudbury, Canada, was an ultraclean heavy-water (D2O) imaging detector for observing neutrinos produced by fusion reactions in the Sun. Neutrino interactions with heavy water resulted in flashes of light called C̆erenkov radiation which was detected by an array of photomultiplier tubes. SNO took data from November 1999 to November 2006, totalling 1082 days of data taking. This work describes an improved measurement of the mixing parameters from a combined fit of all the data. For the signal extraction fit on the data consisting of 4 observable of an event – radial position, recoil electron energy, direction relative to the Sun and event isotropy – Markov Chain Monte Carlo (MCMC) method based on Metropolis algorithm was employed. The nuisance parameters (systematics), weighted by external constraints, were allowed to vary in the fit. The goal of the thesis was to extract the survival probabilities of electron neutrinos and determine the total flux of active-flavour neutrinos from B decay in the Sun measured through the neutral current interactions of neutrinos on deuterium. The B flux from the fit is (5.24 ± 0.02) × 10 cm−2 s−1; uncertainty from statistics and systematics is 3.56%. Along with B flux, the fit extracted energy spectra of charged current interactions of neutrinos on deuterium and elastic scattering interactions of neutrinos on electrons. The fit described the energy-dependent day survival probability of solar neutrinos as a quadratic equation and asymmetry on the day survival probability as a linear equation. Four polynomial coefficients of the survival probability were extracted from the fit: constant coefficient as 0.3206± 0.0197, linear coefficient as 0.005± 0.008 and quadratic coefficient as −0.0014± 0.0033. There are two coefficients on the day-night asymmetry: constant coefficient as 0.0496 ± 0.0347 and the linear coefficient as −0.018 ± 0.028. The day-night asymmetry (0.0496) observed is 1.4σ away from zero. Using these findings, the oscillation space in terms of ∆m21 and θ12 will be further constrained. Compared to the previous published SNO results, the uncertainty on B went down from 3.83% to 3.56% and average B νe survival probability (p0) went down from 6.57% to 6.14%. If the data were analysed with the same assumptions, the decrease in uncertainties would have been approximately twice as big; however, more conservative systematic uncertainties were assigned in some cases.
18849577
Parallel beam dynamics calculations on high performance computers
Faced with a backlog of nuclear waste and weapons plutonium, as well as an ever-increasing public concern about safety and environmental issues associated with conventional nuclear reactors, many countries are studying new, accelerator-driven technologies that hold the promise of providing safe and effective solutions to these problems. Proposed projects include accelerator transmutation of waste (ATW), accelerator-based conversion of plutonium (ABC), accelerator-driven energy production (ADEP), and accelerator production of tritium (APT). Also, next-generation spallation neutron sources based on similar technology will play a major role in materials science and biological science research. The design of accelerators for these projects will require a major advance in numerical modeling capability. For example, beam dynamics simulations with approximately 100 million particles will be needed to ensure that extremely stringent beam loss requirements (less than a nanoampere per meter) can be met. Compared wi...