28803633
Measurement of the Cross Section for High-$p_T$ Hadron Production in Scattering of 160 GeV/c Muons off Nucleons
The cross section for production of charged hadrons with high transversemomenta in scattering of 160 GeV/c muons off nucleons at low photonvirtualities has been measured at the COMPASS experiment at CERN. The results,which cover transverse momenta from 1.1 to 3.6 GeV/c, are compared to anext-to-leading order perturbative Quantum Chromodynamics (NLO pQCD)calculation in order to evaluate the applicability of pQCD to this process inthe kinematic domain of the experiment. The shape of the calculateddifferential cross section as a function of transverse momentum is found to bein good agreement with the experimental data, but the normalization isunderestimated by NLO pQCD. This discrepancy may point towards the relevance ofterms beyond NLO in the pQCD framework. The dependence of the cross section onthe pseudo-rapidity and on the charge of the hadrons is also discussed.
125583262
Scintillating fiber detectors using position sensitive photomultipliers
119282146
First Results of the Full-Scale OSQAR Photon Regeneration Experiment
Recent intensive theoretical and experimental studies shed light on possible new physics beyond the standard model of particle physics, which can be probed with sub-eV energy experiments. In the second run of the OSQAR photon regeneration experiment, which looks for the conversion of photon to axion (or Axion-Like Particle), two spare superconducting dipole magnets of the Large Hadron Collider (LHC) have been used. In this paper we report on first results obtained from a light beam propagating in vacuum within the 9 T field of two LHC dipole magnets. No excess of events above the background was detected and the two-photon couplings of possible new scalar and pseudo-scalar particles could be constrained.
122905204
Detection of single photons with ThickGEM-based counters
The photon detectors based on MPGD (MicroPattern Gaseous Detector) represent the new generation of gaseous photon detectors. We report about an R&D programme dedicated to study both the principles and the engineering aspects of photon detectors based on Thick GEMs (THGEM) electron multipliers coupled to a CsI photoconverting coating. The goal is the development of a gaseous detector of single UV photons, able to stably operate at high gain and high rate, to provide good time resolution and insensitive to magnetic field to be used in the Cherenkov imaging counter RICH-1 of the COMPASS experiment at CERN SPS.
76657892
Hadron transverse momentum distributions in muon deep inelastic scattering at 160 GeV/c
Multiplicities of charged hadrons produced in deep inelastic muon scattering off a 6LiD target have been measured as a function of the DIS variables xBj, Q2, W2 and the final state hadron variables pT and z. The $p_{T}^{2}$ distributions are fitted with a single exponential function at low values of $p_{T}^{2}$ to determine the dependence of $\langle p_{T}^{2} \rangle$ on xBj, Q2, W2 and z. The z-dependence of $\langle p_{T}^{2} \rangle$ is shown to be a potential tool to extract the average intrinsic transverse momentum squared of partons, $\langle k_{\perp}^{2} \rangle$, as a function of xBj and Q2 in a leading order QCD parton model.
121781142
Development of a scintillating-fibre detector for fast topological triggers in high-luminosity particle physics experiments
Abstract In the framework of the RD-17 project at CERN an extensive work is in progress on the development of scintillating-fibre detectors using position-sensitive photomultipliers. With 0.5 mm diameter fibres a spatial resolution of about 125 μm was obtained with a detection efficiency higher than 95%. The time resolution of the detector is about 600 ps, and the track position is properly digitised in real time in less than 10 ns by a peak sensing circuit. A simulation, based on experimental data, has also been performed to compare different types of front-end electronics.
120128989
Measurement of the inclusive production cross sections for forward jets and for dijet events with one forward and one central jet in pp collisions at $ \sqrt {s} = 7 $ TeV
A bstractThe inclusive production cross sections for forward jets, as well for jets in dijet events with at least one jet emitted at central and the other at forward pseudorapidities, are measured in the range of transverse momenta pT = 35-150 GeV/c in proton-proton collisions at $ \sqrt {s} = 7 $ TeV by the CMS experiment at the LHC. Forward jets are measured within pseudorapidities 3.2 < |η| < 4.7, and central jets within the |η| < 2.8 range. The differential cross sections d2σ/dpT dη are compared to predictions from three approaches in perturbative quantum chromodynamics: (i) next-to-leading-order calculations obtained with and without matching to parton-shower Monte Carlo simulations, (ii) pythia and herwig parton-shower event generators with different tunes of parameters, and (iii) cascade and hej models, including different non-collinear corrections to standard single-parton radiation. The single-jet inclusive forward jet spectrum is well described by all models, but not all predictions are consistent with the spectra observed for the forward-central dijet events.
19155671
When A Standard Candle Flickers
The Crab Nebula is the only hard X-ray source in the sky that is both bright enough and steady enough to be easily used as a standard candle. As a result, it has been used as a normalization standard by most X-ray/gamma-ray telescopes. Although small-scale variations in the nebula are well known, since the start of science operations of the Fermi Gamma-ray Burst Monitor (GBM) in 2008 August, a ~7% (70 mCrab) decline has been observed in the overall Crab Nebula flux in the 15-50 keV band, measured with the Earth occultation technique. This decline is independently confirmed in the ~15-50 keV band with three other instruments: the Swift Burst Alert Telescope (Swift/BAT), the Rossi X-ray Timing Explorer Proportional Counter Array (RXTE/PCA), and the Imager on-Board the INTEGRAL Satellite (IBIS). A similar decline is also observed in the ~3-15 keV data from the RXTE/PCA and in the 50-100 keV band with GBM, Swift/BAT, and INTEGRAL/IBIS. The pulsed flux measured with RXTE/PCA since 1999 is consistent with the pulsar spin-down, indicating that the observed changes are nebular. Correlated variations in the Crab Nebula flux on a ~3 year timescale are also seen independently with the PCA, BAT, and IBIS from 2005 to 2008, with a flux minimum in 2007 April. As of 2010 August, the current flux has declined below the 2007 minimum.
18403432
Physical Mechanisms for the Variable Spin-down of Sgr 1900 + 14
We consider the physical implications of the rapid spindown of Soft Gamma Repeater 1900+14 reported by Woods et al. During an 80 day interval between June 1998 and the large outburst on August 27 1998, the mean spin-down rate increased by a factor 2.3, resulting in a positive period offset of ∆P/P = 1 × 10−4. A radiation-hydrodynamical outflow associated with the August 27th event could impart the required torque, but only if the dipole magnetic field is stronger than ∼ 1014 G and the outflow lasts longer and/or is more energetic than the observed X-ray flare. A positive period increment is also a natural consequence of a gradual, plastic deformation of the neutron star crust by an intense magnetic field, which forces the neutron superfluid to rotate more slowly than the crust. Sudden unpinning of the neutron vortex lines during the August 27th event would then induce a glitch opposite in sign to those observed in young pulsars, but of a much larger magnitude as a result of the slower rotation. The change in the persistent X-ray lightcurve following the August 27 event is ascribed to continued particle heating in the active region of that outburst. The enhanced X-ray output can be powered by a steady current flowing through the magnetosphere, induced by the twisting motion of the crust. The long term rate of spindown appears to be accelerated with respect to a simple magnetic dipole torque. Accelerated spindown of a seismically-active magnetar will occur when its persistent output of Alfvén waves and particles exceeds its spindown luminosity. We suggest that SGRs experience some episodes of relative inactivity, with diminished Ṗ , and that such inactive magnetars are observed as Anomalous X-ray Pulsars (AXPs). The reappearence of persistent X-ray emission from SGR 1900+14 within one day of the August 27 event provides strong evidence that the persistent emission is not powered by accretion. Department of Physics and Astronomy, University of North Carolina, Philips Hall, Chapel Hill, NC 27599-3255 Department of Astronomy, University of Texas, RLM 15.308, Austin, TX 78712-1083 Department of Physics, University of Alabama in Huntsville, Huntsville, AL 35899 Universities Space Research Association NASA Marshall Space Flight Center, SD50, Huntsville, AL 35812 Astronomical Institute “Anton Pannekoek”, University of Amsterdam, 403 Kruislaan, 1098 SJ Amsterdam, NL
17283290
Outbursts Large and Small from EXO 2030+375
During the summer of 2006, the accreting X-ray pulsar EXO 2030+375 underwent its first giant outburst since its discovery in 1985. Our observations include the first ever of the rise of a giant outburst of EXO 2030+375. EXO 2030+375 was monitored daily with the Rossi X-Ray Timing Explorer (RXTE) from 2006 June to 2007 May. During the giant outburst we discovered evidence for a cyclotron feature at ~11 keV. This feature was confidently detected for about 90 days, during the brighter portion of the outburst. Daily observations of the next five EXO 2030+375 orbits detected pulsations at all orbital phases and normal outbursts shifted to a later orbital phase than before the giant outburst. An accretion disk appears to be present in both the normal and giant outbursts, suggesting that the long-term behavior is a product of the state of the Be star disk and the accretion disk. Here we will present flux and frequency histories from our detailed RXTE observations of the giant outburst and the normal outbursts that surrounded it. A new orbital analysis is presented that includes observations from 1991 to 2007 August.
88509175
Measurement of the Drell-Yan cross section in pp collisions at $ \sqrt {s} = 7 $ TeV
The Drell-Yan differential cross section is measured in pp collisions at $ \sqrt {s} = 7 $ TeV, from a data sample collected with the CMS detector at the LHC, corresponding to an integrated luminosity of 36 pb−1. The cross section measurement, normalized to the measured cross section in the Z region, is reported for both the dimuon and dielectron channels in the dilepton invariant mass range 15–600 GeV. The normalized cross section values are quoted both in the full phase space and within the detector acceptance. The effect of final state radiation is also identified. The results are found to agree with theoretical predictions.