The completely general radiative corrections to lowest order, including the final- and initial-state radiations, are studied in proton-antiproton annihilation into an electron-positron pair. ...Numerical estimates have been made in a realistic configuraton of the PANDA detector at FAIR for the proton time-like form factors measurements.
The importance of the knowledge of the background in parity violating (PV) experiments is shown. Some improvements in Monte Carlo simulations are presented and discussed.
Baryon-to-meson Transition Distribution Amplitudes (TDAs) encoding valuable new information on hadron structure appear as building blocks in the collinear factorized description for several types of ...hard exclusive reactions. In this paper, we address the possibility of accessing nucleon-to-pion (
πN
) TDAs from
reaction with the future P̄ANDA detector at the FAIR facility. At high center-of-mass energy and high invariant mass squared of the lepton pair
q
2
, the amplitude of the signal channel
admits a QCD factorized description in terms of
πN
TDAs and nucleon Distribution Amplitudes (DAs) in the forward and backward kinematic regimes. Assuming the validity of this factorized description, we perform feasibility studies for measuring
with the P̄ANDA detector. Detailed simulations on signal reconstruction efficiency as well as on rejection of the most severe background channel,
i.e.
were performed for the center-of-mass energy squared
s
= 5 GeV
2
and
s
= 10 GeV
2
, in the kinematic regions 3.0 <
q
2
< 4.3 GeV
2
and 5 <
q
2
GeV
2
, respectively, with a neutral pion scattered in the forward or backward cone
in the proton-antiproton center-of-mass frame. Results of the simulation show that the particle identification capabilities of the P̄ANDA detector will allow to achieve a background rejection factor of 5 · 10
7
(1 · 10
7
) at low (high)
q
2
for
s
= 5 GeV
2
, and of 1 · 10
8
(6 · 10
6
) at low (high)
q
2
for
s
= 10 GeV
2
, while keeping the signal reconstruction efficiency at around 40%. At both energies, a clean lepton signal can be reconstructed with the expected statistics corresponding to 2 fb
−1
of integrated luminosity. The cross sections obtained from the simulations are used to show that a test of QCD collinear factorization can be done at the lowest order by measuring scaling laws and angular distributions. The future measurement of the signal channel cross section with P̄ANDA will provide a new test of the perturbative QCD description of a novel class of hard exclusive reactions and will open the possibility of experimentally accessing
π
TDAs.
This book contains the proceedings of the third international workshop on "From Parity Violation to Hadronic Structure and more ..." which was held from May 16 to May 20, 2006, at the George ...Eliopoulos conference center on the Greek island of Milos. It is part of a series that started in Mainz in 2002 and was followed by a second workshop in Grenoble in 2004. While originally initiated by the extraction of the strangeness contribution to the electromagnetic form factors of the nucleon, the workshop series has continuously broadened the focus to the application of Parity Violation using hadronic probes and to Parity Violation experiments in atomic physics. Meanwhile there have been many exciting new proposals for using Parity Violation in other areas like in the search for new physics beyond the standard model or in exploring hadron structure. There are also close connections to the open question on the size of the two photon exchange amplitude. Fifty years after the 1956 proposal of Lee and Yang to test the hypothesis of violation of parity symmetry in the weak interaction, the many applications of parity violation in very different experiments are way beyond the scope of what Lee and Yang could have imagined. For the physics topics discussed during this workshop, the application of parity violation has become a standard work horse that allows to extract many physics topics in different experiments.
This document describes the technical layout and the expected performance of the Straw Tube Tracker (STT), the main tracking detector of the PANDA target spectrometer. The STT encloses a ...Micro-Vertex-Detector (MVD) for the inner tracking and is followed in beam direction by a set of GEM stations. The tasks of the STT are the measurement of the particle momentum from the reconstructed trajectory and the measurement of the specific energy loss for a particle identification. Dedicated simulations with full analysis studies of certain proton-antiproton reactions, identified as being benchmark tests for the whole PANDA scientific program, have been performed to test the STT layout and performance. The results are presented, and the time lines to construct the STT are described.
QED radiative corrections have been calculated for leptonic and hadronic variables in parity-violating elastic ep scattering. For the first time, the calculation of the asymmetry in the elastic ...radiative tail is performed without the peaking-approximation assumption in hadronic variables configuration. A comparison with the PV-A4 data validates our approach. This method has been also used to evaluate the radiative corrections to the parity-violating asymmetry measured in the G0 experiment. The results obtained are here presented.
CD27 and CD28 have emerged as indicators demarcating the transition of thymocytes through β-selection. We found that CD28 exhibits a greater dynamic range of expression during this phase, thus it was ...employed to further parse the DN/CD44− compartment in order to assess IL-7 signaling during the β-selection process. Plotting CD28 versus CD25 expression revealed six DN/CD44− populations. OP9-DL1 stromal cell co-culture was used to demonstrate a developmental linkage from DN3a (CD25+CD28−/lo) to DN3b (CD25+CD28+) to DN3c (CD25intCD28+) to DN4a (CD25−CD28+) to double positive (DP) and showed the DN4b (CD25−CD28hi) and DN4c (CD25−CD28−/lo) populations to be inefficient in producing DP cells. Using CD69 as an additional marker to further parse the DN4a population, we found the pre-DP cells to be the CD44−CD25−CD28intCD69−CD4−/loCD8−/lo subset. Using this refined developmental scheme, IL-7Rα expression was found to be transiently up-regulated post-β-selection in the DN3b and DN3c subsets; however, this increase did not confer enhanced responsiveness over that observed in the DN3a population. CD28 messenger RNA expression was up-regulated in post-β-selected cells, whereas transcripts for CD27, IL-7Rα and Bcl-2 were lower than that observed in the DN3a population. This study refines the current thymocyte differentiation scheme to allow for more detailed evaluation of events controlling early T-cell development, specifically surrounding the β-selection checkpoint.
In the G0 experiment, performed at Jefferson Lab, the parity-violating elastic scattering of electrons from protons and quasi-elastic scattering from deuterons is measured in order to determine the ...neutral weak currents of the nucleon. Asymmetries as small as 1 part-per-million in the scattering of a polarized electron beam are determined using a dedicated apparatus. It consists of specialized beam monitoring and control systems, a cryogenic hydrogen (or deuterium) target, and a superconducting, toroidal magnetic spectrometer equipped with plastic scintillation and aerogel Cherenkov detectors, as well as fast readout electronics for the measurement of individual events. The overall design and performance of this experimental system is discussed.
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