9 research outputs found
Two-photon exchange in elastic electron-proton scattering : QCD factorization approach
We estimate the two-photon exchange contribution to elastic electron-proton
scattering at large momentum transfer . It is shown that the leading
two-photon exchange amplitude behaves as relative to the one-photon
amplitude, and can be expressed in a model independent way in terms of the
leading twist nucleon distribution amplitudes. Using several models for the
nucleon distribution amplitudes, we provide estimates for existing data and for
ongoing experiments.Comment: 4 pages, 4 figure
Soft spectator scattering in the nucleon form factors at large within the SCET approach
The proton form factors at large momentum transfer are dominated by two
contributions which are associated with the hard and soft rescattering
respectively. Motivated by a very active experimental form factor program at
intermediate values of momentum transfers, ,
where an understanding in terms of only a hard rescattering mechanism cannot
yet be expected, we investigate in this work the soft rescattering contribution
using soft collinear effective theory (SCET). Within such description, the form
factor is characterized, besides the hard scale , by a semi-hard scale , which arises due to presence of soft spectators, with virtuality
( GeV), such that . We show that in this case a two-step factorization can be
successfully carried out using the SCET approach. In a first step (SCET),
we perform the leading order matching of the QCD electromagnetic current onto
the relevant SCET operators and perform a resummation of large logarithms
using renormalization group equations. We then discuss the further matching
onto a SCET framework, and propose the complete factorization formula
for the Dirac form factor, accounting for both hard and soft contributions. We
also present a qualitative discussion of the phenomenological consequences of
this new framework.Comment: 33 pages, 19 figures; typos corrected, text improved. Version to
appear in Phys.Rev.
Study of Two-Photon Corrections in the Process: Hard Rescattering Mechanism
We investigate the two-photon corrections to the process at large momentum transfer, aimed to access the time-like nucleon form
factors. We estimate the two-photon corrections using a hard rescattering
mechanism, which has already been used to calculate the corresponding
corrections to elastic electron-proton scattering. Using different nucleon
distribution amplitudes, we find that the two-photon corrections to the
cross sections in the momentum transfer range 5 - 30
GeV is below the 1 % level
Radiative corrections to hard spectator scattering in decays
We present the calculation of the next-to-leading corrections to the tree
amplitudes which appear in the description of non-leptonic B-decays in the
factorization approach. These corrections, together with radiative corrections
to the jet functions, represent the full next-to-leading contributions to the
dominant hard spectator scattering term generated by operators in the
decay amplitudes. Using obtained analytical results we estimate
branchings fractions in the physical (or BBNS) factorization scheme. We have
also found that the imaginary part generated in the hard spectator scattering
term is rather large compared to the imaginary part of the vertex contribution.Comment: text is improved and typos are corrected, accepted for publication in
JHE
238U(n, Îł) reaction cross section measurement with C6D6 detectors at the n_TOF CERN facility
The radiative capture cross section of 238U is very important for the developing of new reactor technologies and the safety of existing ones. Here the preliminary results of the 238U(n,Îł) cross section measurement performed at n_TOF with C6D6 scintillation detectors are presented, paying particular attention to data reduction and background subtraction
Recent Results In Nuclear Astrophysics At The n_TOF Facility At CERN
International audienceThe neutron time of flight (n_TOF) facility at CERN is a spallation source characterized by a white neutron spectrum. The innovative features of the facility, in the two experimental areas, (20 m and 185 m), allow for an accurate determination of the neutron cross section for radioactive samples or for isotopes with small neutron capture cross section, of interest for Nuclear Astrophysics. The recent results obtained at n_TOF facility are presented
Destruction of the cosmic Îł-ray emitter 26Al in massive stars: study of the key 26Al(n,p) reaction
The 26Al(n,p)26Mg reaction is the key reaction impacting on the abundances of the cosmic Îł-ray emitter 26Al produced in massive stars and impacts on the potential pollution of the early solar system with 26Al by asymptotic giant branch stars. We performed a measurement of the 26Al(n,p)26Mg cross section at the high-flux beam line EAR-2 at the n_TOF facility (CERN). We report resonance strengths for eleven resonances, nine being measured for the first time, while there is only one previous measurement for the other two. Our resonance strengths are significantly lower than the only previous values available. Our cross-section data range to 150 keV neutron energy, which is sufficient for a reliable determination of astrophysical reactivities up to 0.5 GK stellar temperature