192 research outputs found
Low-x scaling in gamma*p total cross sections
No full textSchildknecht D, Surrow B, Tentyukov M. Low-x scaling in gamma*p total cross sections. PHYSICS LETTERS B. 2001;499(1-2):116-124.We show that the experimental data for the total virtual-photon proton cross section, sigma gamma *p(W-2,Q(2)) for x(bj) less than or similar to 0.1 lie on a universal curve, when plotted against eta = (Q(2) + m(0)(2))/Lambda (2)(W-2), where Lambda (2)(W-2) = C-l(W-2 + W-0(2))(C2) is determined by the parameters C-1, C-2 and W-0(2) . The observed scaling law follows from the generalized-vector-dominance/colour-dipole picture (GVD/CDP) of low-x deep inelastic scattering. (C) 2001 Elsevier Science B.V. All rights reserved
Vector-meson electroproduction from generalized vector dominance
No full textSchildknecht D, Schuler GA, Surrow B. Vector-meson electroproduction from generalized vector dominance. PHYSICS LETTERS B. 1999;449(3-4):328-338.Including destructively interfering off-diagonal transitions of diffraction-dissociation type, we arl ive at a formulation of GVD for exclusive vector-meson production in terms of a continuous spectral representation of dipole form. The transverse cross-section, sigma(T.gamma*p) (-->) (Vp), behaves asymptotically as 1/Q(4), while R-v equivalent to sigma(L.gamma*p --> Vp)/sigma(T.gamma*p --> Vp) becomes asymptotically constant. Contributions violating s-channel helicity conservation stay at the level established in low-energy photoproduction and diffractive hadron-hadron interactions. The data on rho(0)-meson production from the Fermilab E665 Collaboration and on phi- and rho(0)-meson production from HERA are found to be in agreement with these predictions. (C) 1999 Elsevier Science B.V. All rights reserved
Low-x physics at a future electron-ion collider (EIC) facility
No full textThe proposed polarized electron-ion collider (EIC) facility will allow for precision exploration of various novel aspects of QCD including low-x phenomena and the spin structure of the proton. As this project gains momentum, it is increasingly important for the QCD community to understand quantitatively the kinematic reach and expected sensitivities for various measurements. We briefly summarize key accelerator design parameters and then focus on expected measurement sensitivities, thus exposing how the EIC will allow an extension of the successful HERA program into exciting new regimes
Automated silicon module assembly for the CMS silicon tracker
No full textThe CMS silicon tracker requires the assembly of about 20000 individual silicon detector modules. To ensure the assembly of such an amount with high, reproducible quality, an automated procedure has been developed for module assembly based on a high-precision robotic positioning machine. This procedure allows a much higher throughput and will result in much reduced manpower requirements than for traditional manual techniques. (1 refs)
Phenomenological studies of inclusive ep scattering at low momentum transfer Q^2
No full textPhenomenological studies on the proton structure function F^2 have been carried out to investigate the behavior of F^2, i.e. its x and Q^2 dependence, in the transition from the deep-inelastic scattering region (Q^2 >> 1 GeV^2) to the photoproduction region (Q^2 approx. 0 GeV^2). An overview of various results of F^2 at low Q^2 is given. To quantify the behavior of F2 at low Q^2, the derivatives dln(F^2)/dln(x) for fixed Q^2 and dF^2/dlog(Q^2) for fixed x haven been determined and compared to expectations within the framework of perturbative and non-perturbative QCD. Furthermore, the derivatives were compared to results of the total inclusive diffractive cross-section and vector-meson production. An interpretation of inclusive ep results is given in the framework of the GVD/CDP picture with special emphasis on the limit of Q^2 --> 0 for fixed W^2 and x --> for fixed Q^2
The Gamma Intensity Monitor at the Crystal-Barrel-Experiment
No full textThesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2008.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Includes bibliographical references (p. 69).This thesis details the motivation, design, construction, and testing of the Gamma Intensity Monitor (GIM) for the Crystal-Barrel-Experiment at the Universität Bonn. The CB-ELSA collaboration studies the baryon excitation spectrum; resonances are produced by exciting nucleons in a polarized target with a linearly or circularly polarized, GeV-order photon beam. The photoproduced decay states are measured by a variety of detectors covering almost 4[pi] of the solid angle about the target. To measure the total cross section of these reactions, the total flux of photons through the target must be known to high accuracy. As the total cross section for nuclear photoproduction is low, counting the photons unscattered in the target is sufficiently accurate measurement of this quantity{this is the purpose of the Gamma Intensity Monitor. It is the final detector along the beam path and counts all photons that do not react with the target. The major design parameter is that the detector must consistently count GeV order photons at 10 MHz. This is accomplished by allowing the gammas to electronpositron pair produce within Ĉerenkov radiating PbF2 crystals. The Cerenkov light from these highly relativistic lepton pairs is measured with industrial photomultiplier tubes to provide an effective efficiency close to unity. Special bases were built for photomultiplier to ensure stable signal amplication even high count rates. Detailed descriptions of the GIM are provided to ensure that its inner working are completely transparent and to enable efficient operation and maintenance of the detector.by William R. McGehee.S.B
Measurement of the proton structure function F 2 at low Q 2 and very low kappa with the ZEUS beam pipe calorimeter at HERA
No full textThe structure of the photon and its interactions
No full textThe OPAL experiment at LEP has performed a variety of measurements of photon-photon and electron-photon scattering at the electron-positron collider LEP to gain a deeper insight into the structure of the photon and its interactions. This review presents a summary of these results.The OPAL experiment at LEP has performed a variety of measurements of photon-photon and electron-photon scattering at the electron-positron collider LEP to gain a deeper insight into the structure of the photon and its interactions. This review presents a summary of these results
RECENT RESULTS ON HIGH-ENERGY SPIN PHENOMENA OF GLUONS AND SEA-QUARKS IN POLARIZED PROTON-PROTON COLLISIONS AT RHIC AT BNL
No full text The STAR experiment at the Relativistic Heavy-Ion Collider at Brookhaven National Laboratory is carrying out a spin physics program in high-energy polarized proton collisions at [Formula: see text] GeV and [Formula: see text] GeV to gain a deeper insight into the spin structure and dynamics of the proton. One of the main objectives of the spin physics program at RHIC is the precise determination of the polarized gluon distribution function. The STAR detector is well suited for the reconstruction of various final states involving jets, π0, π±, e± and γ, which allows to measure several different processes. Recent results suggest a gluon spin contribution to the proton spin at the same level as the quark spin contribution itself. The production of W bosons in polarized p+p collisions at [Formula: see text] GeV opens a new era in the study of the spin-flavor structure of the proton. W-(+) bosons are produced in [Formula: see text] collisions and can be detected through their leptonic decays, [Formula: see text], where only the respective charged lepton is measured. Results of W-(+) production suggest a large asymmetry between the polarization of anti-u and anti-d quarks. </jats:p
Recent STAR results and future prospects of W^-(+) boson production in polarized p+p collisions at RHIC
No full text- …
