208867227
Investigation of power corrections to event shape variables measured in deep-inelastic scattering
As the high abstention rate during the last european election shows, it seems that a large part of the european population is rather sceptical towards the european integration process. One ascribe this "euroscepticism" to the European Union communication. Our paper aims to evaluate this hypothesis which is not as obvious as it seems first. To do so we have evaluated the communication policy which as been set up by the European Commission (before the Romano Prodi Presidence) to conclude that the lack of a real european public sphere is probably a better explanation of this phenomenon.
14063112
Measurement and QCD Analysis of Neutral and Charged Current Cross Sections at HERA
The inclusive e(+)p single and double differential cross sections for neutral and charged current processes axe measured with the H1 detector at HERA. The data were taken in 1999 and 2000 at a centre-of-mass energy of roots = 319 GeV and correspond to an integrated luminosity of 65.2 pb(-1). The cross sections are measured in the range of four-momentum transfer squared Q(2) between 100 and 30 000 GeV2 and Bjorken x between 0.0013 and 0.65. The neutral current analysis for the new e(+)p data and the earlier e-p data taken in 1998 and 1999 is extended to small energies of the scattered electron and therefore to higher values of inelasticity y, allowing a determination of the longitudinal structure function F-L at high Q(2) (110 - 700 GeV2). A new measurement of the structure function x (F) over tilde (3) is obtained using the new e(+)p and previously published e p neutral current cross section data at high Q(2). These data together with H1 low Q(2) precision data are further used to perform new next-to-leading order QCD analyses in the framework of the Standard Model to extract flavour separated parton distributions in the proton.
8656457
Three-jet production in deep-inelastic scattering at HERA
Abstract Three-jet production is studied for the first time in deep-inelastic positron–proton scattering. The measurement carried out with the H1 detector at HERA covers a large range of four-momentum transfer squared 5 2 000 GeV 2 and invariant three-jet masses 25 3 jet ≲140 GeV . Jets are defined by the inclusive k ⊥ algorithm in the Breit frame. The size of the three-jet cross section and the ratio of the three-jet to the dijet cross section R 3/2 are described over the whole phase space by the predictions of perturbative QCD in next-to-leading order. The shapes of angular jet distributions deviate significantly from a uniform population of the available phase space but are well described by the QCD calculation.
122848941
Deep inelastic inclusive e p scattering at low x and a determination of alpha(s)
A precise measurement of the inclusive deep-inelastic \(e^+ p\) scattering cross section is reported in the kinematic range \(1.5 \le Q^2 \le 150\) GeV\(^2\) and \( 3 \cdot 10^{-5} \le x \le 0.2\). The data were recorded with the H1 detector at HERA in 1996 and 1997, and correspond to an integrated luminosity of 20 pb\(^{-1}\). The double differential cross section, from which the proton structure function \(\) and the longitudinal structure function \(F_L(x,Q^2)\) are extracted, is measured with typically 1% statistical and 3% systematic uncertainties. The measured derivative \((\partial F_2(x,Q^2) / \partial \ln Q^2)_x \) is observed to rise continuously towards small x for fixed \(Q^2\). The cross section data are combined with published H1 measurements at high \(Q^2\) for a next-to-leading order DGLAP QCD analysis. The H1 data determine the gluon momentum distribution in the range \(3 \cdot 10^{-4} \le x \le 0.1\) to within an experimental accuracy of about 3% for \(Q^2 =20\) GeV\(^2\). A fit of the H1 measurements and the \(\mu p \) data of the BCDMS collaboration allows the strong coupling constant \(\alpha_s\) and the gluon distribution to be simultaneously determined. A value of \(\alpha_s (M_Z^2) =0.1150 \pm 0.0017 (exp)^{+0.0009}_{-0.0005} (model)\) is obtained in NLO, with an additional theoretical uncertainty of about \(\pm 0.005\), mainly due to the uncertainty of the renormalisation scale.
122702137
Elastic Electroproduction of $\rho$ Mesons at HERA
The elastic electroproduction of rho mesons is studied at HERA with the H1 detector for a photon virtuality in the range 1 Q^2 60 GeV^2 and for a hadronic centre of mass energy in the range 30 W 140 GeV. The shape of the pipi mass distribution in the rho resonance region is measured as a function of Q^2. The full set of rho spin density matrix elements is determined, and evidence is found for a helicity flip amplitude at the level of 8 +- 3 % of the non-flip amplitudes. Measurements are presented of the dependence of the cross section on Q^2, W and t (the four-momentum transfer squared to the proton). They suggest that, especially at large Q^2, the gamma^*p cross section develops a stronger W dependence than that expected from the behaviour of elastic and total hadron-hadron cross sections.
13227053
Search for leptoquark bosons in ep collisions at HERA
A search for scalar and vector leptoquarks coupling to first generation fermions is performed using the e(+) p and e(-) p scattering data collected by the H1 experiment between 1994 and 2000. The data correspond to a total integrated luminosity of 117 pb(-1). No evidence for the direct or indirect production of such particles is found in data samples with a large transverse momentum final state electron or with large missing transverse momentum. Constraints on leptoquark models are established. For leptoquark couplings of electromagnetic strength, leptoquarks with masses up to 275-325 GeV are ruled out at 95% confidence level. These limits improve and supercede earlier H1 limits based on subsamples of the data used here.
14381196
Evidence against an association between gamma-ray bursts and Type I supernovae
We use a rigorous method, based on Bayesian inference, for calculating the odds favoring the hypothesis that any particular class of astronomical transients pro- duce gamma-ray bursts over the hypothesis that they do not. We then apply this method to a sample of 83 Type Ia supernovae and a sample of 20 Type Ib-Ic supernovae. We nd overwhelming odds against the hypothesis that all Type Ia supernovae produce gamma-ray bursts, whether at low redshift (10 9 :1) or high-redshift (10 12 :1), and very large odds (6000:1) against the hypothesis that all Type Ib, Ib/c, and Ic supernovae produce observable gamma-ray bursts. We nd large odds (34:1) against the hypothesis that a fraction of Type Ia supernovae produce observable gamma-ray bursts, and moderate odds (6:1) against the hypothesis that a fraction of Type Ib-Ic supernovae pro- duce observable bursts.
204935009
Early-Time Chromatic Variations in the Wind-Swept Medium of GRB 021211 and the Faintness of its Afterglow
We present Follow-Up Network for Gamma-Ray Bursts (FUN GRB) Collaboration observations of the optical afterglow of GRB 021211 made between 143 s and 102 days after the burst. Our unique data set includes the earliest filtered detections and color information for an afterglow in the pre-Swift era. We find that the afterglow is best described by (1) a propagation through a wind-swept medium, (2) a cooling break that is blueward of the observed optical frequencies, and (3) a hard electron energy distribution. However, superimposed on this "standard model" behavior we find, one and possibly two, significant chromatic variations during the first few hours after the burst. We consider possible reasons for these variations, including the possibility that they are due to a dust echo. Finally, we constrain physical parameters that describe the afterglow and the surrounding medium for a variety of scenarios and find that GRB 021211's afterglow is faint for a combination of reasons: (1) a low fraction of energy in relativistic electrons, (2) a low density for the wind-swept medium, implying either a low mass-loss rate and/or a high wind velocity for the progenitor, (3) a wide opening/viewing angle for the jet, and possibly (4) moderate source-frame extinction. The jet appears to be significantly far from equipartition and magnetically dominated. More extreme versions of this might explain the darkness of many afterglows in the Swift era.
28688372
Effects of the Geometry of the Line-forming Region on the Properties of Cyclotron Resonant Scattering Lines
We use a Monte Carlo radiative transfer code to examine the dependence of the properties of cyclotron resonant scattering lines on the spatial geometry and the optical depth of the line-forming region. We focus most of our attention on a line-forming region that is a plane-parallel slab threaded by a uniform magnetic field oriented at an angle Ψ to the slab normal. We also consider a cylindrical line-forming region with the magnetic field oriented along the cylinder axis. In both cases, the line-forming region contains an electron-proton plasma at the equilibrium Compton temperature, TC, and the field strength is ~1012 gauss. We consider geometries in which the photon source illuminates the line-forming region from below and in which the photon source is embedded in the line-forming region. The former may correspond to a line-forming region in the magnetosphere of a neutron star, illuminated from below, the latter to a line-forming region on or near the surface of a neutron star as in an accretion column. We calculate the cyclotron line spectra produced by line-forming regions having a range of Thomson optical depths from τTo = 8 × 10-4 to τTo = 10. Our findings have implications for accretion-powered pulsars and gamma-ray bursters. In particular, the absence of pronounced shoulders on both sides of the cyclotron first harmonic line in the spectra of accretion-powered pulsars suggests that the line-forming region is either illuminated from below or has a large optical depth (Thomson optical depth τTo 10). However, we (like earlier workers) find that models in which the line-forming region is either a static slab or a static cylinder and has a large optical depth are unable to explain the modest equivalent widths WE of the cyclotron lines in the observed spectra of accretion-powered pulsars. In addition, we find that approximating the injected photon spectrum as a Wien spectrum, an approximation made by almost all workers to date, is not valid because of the frequency dependence of the cyclotron scattering cross section below the cyclotron fundamental. Consequently, future work in this area should explore physical effects that have not been included so far, such as the plasma flow velocity in the accretion column and the injected photon spectrum resulting from energy deposition in the surface layers of the neutron star; more complicated geometries, such as accretion mounds and multiple component magnetic fields; and alternative models, such as cyclotron scattering in the magnetosphere. We find that slab line-forming regions in which the magnetic field is parallel to the slab are able to produce narrow lines with large equivalent widths WE, suggesting that the lines observed in the X-ray spectra of some gamma-ray bursts might be able to be formed not only in plasma near the magnetic poles of a neutron star but also in plasma trapped at the magnetic equator of the star.
15041671
Two Additions to the New Class of Low Accretion Rate Magnetic Binaries
Two new magnetic white dwarf accretion binaries with extremely low mass transfer rates have been discovered in the course of the Sloan Digital Sky Survey. Measured magnetic fields are 42 and 57 MG, and one system orbits with a period of just 82 minutes. The new systems therefore significantly expand the range in properties exhibited by the small class. The measured accretion rates are very low, 0.6-5 × 10-13 M☉ yr-1, and multiple visits spanning more than a year confirm that this is not a short-lived characteristic. It is becoming increasingly clear that the low- magnetic white dwarf binaries accrete by nearly complete magnetic capture of the stellar wind from the secondary star rather than by Roche lobe overflow. The accretion rates therefore provide some of the first realistic estimates of the total wind loss rates from M dwarfs. Although one or more of the eight systems known to date may be interrupted or possibly even extinct Polars, several lines of evidence suggest that most are pre-Polars whose evolution has not yet brought the secondaries into contact with their Roche surfaces. Considering the difficulties of identifying binaries over a wide range in field strength and accretion rate, it is quite possible that the space density of wind-accreting magnetic binaries exceeds that of the classical X-ray-emitting, Roche lobe overflow Polars.
119080503
A Low-Latitude Halo Stream around the Milky Way
We present evidence for a ring of stars in the plane of the Milky Way, extending at least from l = 180° to 227° with turnoff magnitude g ~ 19.5; the ring could encircle the Galaxy. We infer that the low Galactic latitude structure is at a fairly constant distance of R = 18 ± 2 kpc from the Galactic center above the Galactic plane and has R = 20 ± 2 kpc in the region sampled below the Galactic plane. The evidence includes 500 Sloan Digital Sky Survey spectroscopic radial velocities of stars within 30° of the plane. The velocity dispersion of the stars associated with this structure is found to be 27 km s-1 at (l, b) = (198°, - 27°), 22 km s-1 at (l, b) = (225°, 28°), 30 km s-1 at (l, b) = (188°, 24°), and 30 km s-1 at (l, b) = (182°, 27°). The structure rotates in the same prograde direction as the Galactic disk stars but with a circular velocity of 110 ± 25 km s-1. The narrow measured velocity dispersion is inconsistent with power-law spheroid or thick-disk populations. We compare the velocity dispersion in this structure with the velocity dispersion of stars in the Sagittarius dwarf galaxy tidal stream, for which we measure a velocity dispersion of 20 km s-1 at (l, b) = (165°, - 55°). We estimate a preliminary metallicity from the Ca II (K) line and color of the turnoff stars of [Fe/H] = -1.6 with a dispersion of 0.3 dex and note that the turnoff color is consistent with that of the spheroid population. We interpret our measurements as evidence for a tidally disrupted satellite of 2 × 107 to 5 × 108 M☉ that rings the Galaxy.