16 research outputs found
Compton and double Compton scattering processes at colliding electron-photon beams
Radiative corrections (RC) to the Compton scattering cross section are
calculated in the leading and next-to leading logarithmic approximation to the
case of colliding high energy photon-electron beams.
RC to the double Compton scattering cross section in the same experimental
set-up are calculated in the leading logarithmic approximation.
We consider the case when no pairs are created in the final state. We show
that the differential cross section can be written in the form of the Drell-Yan
process cross-section.
Numerical values of the -factor and the leading order distribution on the
scattered electron energy fraction and scattering angle are presented
The Aladin2 experiment: sensitivity study
Aladin2 is an experiment devoted to the first measurement of variations of Casimir energy in a rigid body. The main short-term scientific motivation relies on the possibility of the first demonstration of a phase transition influenced by vacuum fluctuations while, in the long term and in the mainframe of the cosmological constant problem, it can be regarded as the first step towards a measurement of the weight of vacuum energy. In this paper, after a presentation of the guiding principle of the measurement, the experimental apparatus and sensitivity studies on final cavities will be presented
Single-spin asymmetries in semi-inclusive deep-inelastic scattering on a transversely polarized hydrogen target
Single-spin asymmetries for semi-inclusive electroproduction of charged pions
in deep-inelastic scattering of positrons are measured for the first time with
transverse target polarization. The asymmetry depends on the azimuthal angles
of both the pion () and the target spin axis () about the virtual
photon direction and relative to the lepton scattering plane. The extracted
Fourier component \cmpi is a signal of the previously unmeasured quark
transversity distribution, in conjunction with the so-called Collins
fragmentation function, also unknown. The Fourier component \smpi of the
asymmetry arises from a correlation between the transverse polarization of the
target nucleon and the intrinsic transverse momentum of quarks, as represented
by the previously unmeasured Sivers distribution function. Evidence for both
signals is observed, but the Sivers asymmetry may be affected by exclusive
vector meson productio
Measurement of unpolarized semi-inclusive pi+ electroproduction off the proton
Semi-inclusive pi+ electroproduction on protons has been measured with the
CLAS detector at Jefferson Lab. The measurement was performed on a
liquid-hydrogen target using a 5.75 GeV electron beam. The complete five-fold
differential cross sections were measured over a wide kinematic range including
the complete range of azimuthal angles between hadronic and leptonic planes,
phi, enabling us to separate the phi-dependent terms. Our measurements of
phi-independent term of the cross section at low Bjorken x were found to be in
fairly good agreement with pQCD calculations. Indeed, the conventional current
fragmentation calculation can account for almost all of the observed cross
section, even at small pi+ momentum. The measured center-of-momentum spectra
are in qualitative agreement with high energy data, which suggests a surprising
numerical similarity between the spectator diquark fragmentation in the present
reaction and the anti-quark fragmentation measured in e+e- collisions. We have
observed that the two phi-dependent terms of the cross section are small.
Within our precision the cos(2phi) term is compatible with zero, except for
low-z region, and the measured cos(phi) term is much smaller in magnitude than
the sum of the Cahn and Berger effects.Comment: 42 pages, 30 figure
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An experimental program with high duty-cycle polarized and unpolarized positron beams at Jefferson Lab
Positron beams, both polarized and unpolarized, are identified as important ingredients for the experimental programs at the next generation of lepton accelerators. In the context of the hadronic physics program at Jefferson Lab (JLab), positron beams are complementary, even essential, tools for a precise understanding of the electromagnetic structure of nucleons and nuclei, in both the elastic and deep-inelastic regimes. For instance, elastic scattering of polarized and unpolarized electrons and positrons from the nucleon enables a model independent determination of its electromagnetic form factors. Also, the deeply-virtual scattering of polarized and unpolarized electrons and positrons allows unambiguous separation of the different contributions to the cross section of the lepto-production of photons and of lepton-pairs, enabling an accurate determination of the nucleons and nuclei generalized parton distributions, and providing an access to the gravitational form factors of the energy-momentum tensor. Furthermore, positron beams offer the possibility of alternative tests of the Standard Model of particle physics through the search of a dark photon, the precise measurement of electroweak couplings, and the investigation of charged lepton flavor violation. This document discusses the perspectives of an experimental program with high duty-cycle positron beams at JLab
Cross sections for hard exclusive electroproduction of pi+ mesons on a hydrogen target
The exclusive electroproduction of pi+ mesons was studied with the Hermes
spectrometer at the DESY laboratory by scattering 27.6 GeV positron and
electron beams off an internal hydrogen gas target. The virtual-photon cross
sections were measured as a function of the Mandelstam variable t and the
squared four momentum -Q^2 of the exchanged virtual photon. A model calculation
based on Generalized Parton Distributions is in fair agreement with the data at
low values of |t| if power corrections are included. A model calculation based
on the Regge formalism gives a good description of the magnitude and the t and
Q^2 dependences of the cross section.Comment: 7 pages, 5 figures, revised tex