The OLYMPUS collaboration has recently made a precise measurement of the positron-proton to electron-proton elastic scattering cross section ratio, R2γ, over a wide range of the virtual photon ...polarization, 0.456 < ε < 0.978. This provides a direct measure of hard two-photon exchange in elastic lepton-proton scattering widely thought to explain the discrepancy observed between unpolarized and polarized measurements of the proton form factor ratio, μpGEp/GMp. The OLYMPUS results are small, within 1% on unity, over the range of momentum transfers measured and significantly lower than theoretical calculations that can explain part of the observed discrepancy in terms of two-photon exchange at higher momentum transfers. However, the results are in reasonable agreement with predictions based on phenomenological fits to the available form factor data. The motivation for measuring R2γ will be presented followed by a description of the OLYMPUS experiment. The importance of radiative corrections in the analysis will be shown also. Then we will present the OLYMPUS results and compare with results from two similar experiments and theoretical calculations.
The OLYMPUS experiment used a 0.3T toroidal magnetic spectrometer to measure the momenta of outgoing charged particles. In order to accurately determine particle trajectories, knowledge of the ...magnetic field was needed throughout the spectrometer volume. For that purpose, the magnetic field was measured at over 36,000 positions using a three-dimensional Hall probe actuated by a system of translation tables. We used these field data to fit a numerical magnetic field model, which could be employed to calculate the magnetic field at any point in the spectrometer volume. Calculations with this model were computationally intensive; for analysis applications where speed was crucial, we pre-computed the magnetic field and its derivatives on an evenly spaced grid so that the field could be interpolated between grid points. We developed a spline-based interpolation scheme suitable for SIMD implementations, with a memory layout chosen to minimize space and optimize the cache behavior to quickly calculate field values. This scheme requires only one-eighth of the memory needed to store necessary coefficients compared with a previous scheme (Lekien and Marsden, 2005 1). This method was accurate for the vast majority of the spectrometer volume, though special fits and representations were needed to improve the accuracy close to the magnet coils and along the toroidal axis.
The Bates Large Acceptance Spectrometer Toroid experiment, BLAST, at the MIT-Bates Linear Accelerator Laboratory is designed to study in a systematic manner the spindependent electromagnetic ...interaction in few-nucleon systems at momentum transfers below 1 GeV/c. Utilizing a polarized electron beam, highly polarized internal gas targets of H and D, and a symmetric detector configuration, BLAST is able to make simultaneous measurements of several reaction channels for different combinations of beam helicity and target polarization (vector for H, both vector and tensor for D). BLAST will provide new data on the nucleon and deuteron form factors as well as study few body physics and pion production. Preliminary results are presented.
The two-photon exchange experiment at DESY Alarcon, R.; Beck, R.; Bernauer, J. C. ...
The European physical journal. A, Hadrons and nuclei,
04/2024, Letnik:
60, Številka:
4
Journal Article
Recenzirano
Odprti dostop
We propose a new measurement of the ratio of positron-proton to electron-proton elastic scattering at DESY. The purpose is to determine the contributions beyond single-photon exchange, which are ...essential for the Quantum Electrodynamic (QED) description of the most fundamental process in hadronic physics. By utilizing a 20 cm long liquid hydrogen target in conjunction with the extracted beam from the DESY synchrotron, we can achieve an average luminosity of
2.12
×
10
35
cm
-
2
·
s
-
1
(
≈
200
times the luminosity achieved by OLYMPUS). The proposed two-photon exchange experiment (TPEX) entails a commissioning run at a beam energy of 2 GeV, followed by measurements at 3 GeV, thereby providing new data up to
Q
2
=
4.6
(GeV/
c
)
2
(twice the range of current measurements). We present and discuss the proposed experimental setup, run plan, and expectations.
Tests of a prototype lead tungstate calorimeter were made over two weeks at the end of September, 2019, at the DESY II Test Beam Facility in Hamburg, Germany. The purpose of these tests was to gain ...experience with the construction, operation, and performance of a simple lead tungstate calorimeter, and also to compare a traditional triggered readout scheme with a streaming readout approach. These tests are important for the proposed Two-Photon Exchange experiment at DESY and for work towards a future electromagnetic calorimeter that could be used in an Electron-Ion Collider detector. Details on the comparison of streaming and triggered readout schemes are presented here.
The separation of molecules with similar size and shape is an important technological challenge. For example, rare gases can pose either an economic opportunity or an environmental hazard and there ...is a need to separate these spherical molecules selectively at low concentrations in air. Likewise, chiral molecules are important building blocks for pharmaceuticals, but chiral enantiomers, by definition, have identical size and shape, and their separation can be challenging. Here we show that a porous organic cage molecule has unprecedented performance in the solid state for the separation of rare gases, such as krypton and xenon. The selectivity arises from a precise size match between the rare gas and the organic cage cavity, as predicted by molecular simulations. Breakthrough experiments demonstrate real practical potential for the separation of krypton, xenon and radon from air at concentrations of only a few parts per million. We also demonstrate selective binding of chiral organic molecules such as 1-phenylethanol, suggesting applications in enantioselective separation.
Status of the BLAST experiment Hasell, for the BLAST Collaboration, D.K.
The European physical journal. A, Hadrons and nuclei,
02/2004, Letnik:
19, Številka:
S1
Journal Article
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