119217305
Overview of Deeply Virtual Compton Scattering at HERMES
Deeply Virtual Compton Scattering represents the best experimental channel through which to understand Generalised Parton Distributions. The HERMES experiment measured the most diverse set of DVCS results of any experiment; this talk discusses the most recent sets of DVCS results released by HERMES and the unique experimental conditions found at HERMES that facilitated the measurements. We also examine the various ways in which the HERMES experimental measurements are being used to constrain GPDs and how future experiments can learn from the HERMES program.
122525362
DVCS at HERMES: The Recoil Detector & Transverse Target Spin Asymmetries
The HERMES experiment is a large forward angle spectrometer located at the HERA accelerator ring at DESY, Hamburg. One of the most exciting topics studied at HERMES is Deeply Virtual Compton Scattering (DVCS) which is the simplest interaction that provides a gateway for access to Generalised Parton Distributions (GPDs). GPDs are a theoretical framework which can be used to calculate the total angular momentum of the quarks in the nucleon. As such, they provide one piece of the puzzle of nucleonic spin structure. In 2005, HERMES was upgraded in the target region with a Recoil Detector that allows it to make truly exclusive measurements of the DVCS interaction for the first time. The design and construction of the Recoil Detector is discussed herein, in addition to a complete analysis of the Transverse Target Spin Asymmetry (TTSA) in DVCS. Experimental facilities that enable measurement of this asymmetry are rare. The importance of the information on the TTSA from HERMES is made yet greater as the transversely polarised target that allows the asymmetry to be measured has been replaced by an unpolarised target. This was to allow the Recoil Detector to be installed. The final stage of this thesis shows a model-dependent method for constraining the angular momentum of the quarks in the nucleon and speculates as to the other pieces of the spin puzzle.
120484753
The front-end readout electronics for the P̄ANDA Focussing-Lightguide Disc DIRC
One of the key detectors of the upcoming ANDA experiment for particle identification will be the Focussing-Lightguide Disc DIRC, based on a novel detector technique. It will use a fused silica disc as a solid radiator to generate Cherenkov light by the passing of charged particles. These photons will be transported by total-internal-reflection to the rim, where LiF crystals will be used to perform dispersion corrections. Focussing lightguides will map propagation angles to spatial positions on the surface of photon detectors. Fast single photon detection devices will be used to measure azimuthal angles and spatial positions, which can be used to reconstruct kinematic properties of the passing particles. The expected average interaction rate of 20 MHz yields a photon detection rate of 1.3 MHz, as it is foreseen to use 128 MCP-PMT, each with 32 channels, for continuous readout. Moderate timing resolution of 300 ps improves signal from noise separation. The readout design requirements for the Focussing-Lightguide Disc DIRC will be introduced. The current candidate for implementation of the front-end readout electronic system will be described and several alternative readout scenarios will be discussed. Finally, a summary and an outlook for further developments and tests will be given.
113252484
Reconstruction methods — PANDA Focussing-Lightguide Disc DIRC
The Focussing-Lightguide Disc DIRC will provide crucial Particle Identification (PID) information for the PANDA experiment at FAIR, GSI. This detector presents a challenging environment for reconstruction due to the complexity of the expected hit patterns and the operating conditions of the PANDA experiment. A discussion of possible methods to reconstruct PID from this detector is given here. Reconstruction software is currently under development.
123332232
Hard exclusive measurements with a polarised target at HERMES
Hard exclusive measurements at HERMES provide access to the information framework of Generalised Parton Distributions. This framework has the potential to provide a thorough, phenomenological description of the nucleon and aspects of it can be constrained by recent measurements made at the HERMES experiment at DESY. Consideration of meson production allows access to some GPDs, whilst observables from the deeply virtual Compton scattering process can allow a constraint on model parameters which are directly connected to the total angular momentum contribution of up and down quarks to the nucleon's spin.
119536751
The Focusing Disc DIRC for the PANDA experiment at FAIR
The Focusing Disc DIRC is a novel detector concept for particle identification based on the detection of internally-reflected Cherenkov light. A thin synthetic silica disc of 1 m radius will be used as radiator and for light transportation. At the rim LiF bars are foreseen to passively correct for dispersion. Focusing elements map the angles of the propagating photons to spatial positions on the focal plane covered with position sensitive photon detection devices. This novel 2D(+1t) detector concept will contribute to the outstanding particle identification performance of the general purpose PANDA detector. The aims of the PANDA experiment are to address fundamental questions of the strong force, to explore the structure of the nucleon and to search for new matter. The technical design, the current status of the development and recent results from prototype test experiments for the Focusing Disc DIRC are presented.
118773890
Limiting fragmentation of chemical potentials in heavy ion collisions
Thermal models have been used to successfully describe the hadron yields from heavy ion collisions at a variety of energies. For root(S)<17 GeV this has usually been done using yields integrated over 4pi but at the higher energies available at RHIC, yields measured at central rapidity have been used. Recent BRAHMS data allows us to test whether thermal models can be generalized to describe the rapidity dependence of particle ratios. We have used the THERMUS package to fit BRAHMS data for the 5% most central Au+Au collisions for several rapidities at root(S) = 62 and 200 GeV. We have found a relationship between the strange and light quark chemical potentials, muS = 0.21 +-0.01muB. Using this relation we are able to describe the energy dependence of Lambda, Xsi and Omega ratios from other experiments. We also find that the chemical potentials are consistent with limiting fragmentation.
118432204
Particle spectra and HBT results from NA44
Recent results on baryon spectra and interferometry from NA44 are compared to RQMD and a hydrodynamical model. The importance of flow and rescattering on the rapidity and transverse mass distributions is discussed. The yields of protons and antiprotons are compared as a function of system, rapidity and multiplicity.
118874275
Tracing the evolution of temperature in near Fermi energy heavy ion collisions
The kinetic-energy variation of emitted light clusters has been employed as a clock to explore the time evolution of the temperature for thermalizing composite systems produced in the reactions of 26A, 35A, and 47A MeV {sup 64}Zn with {sup 58}Ni, {sup 92}Mo, and {sup 197}Au. For each system investigated, the double-isotope ratio temperature curve exhibits a high maximum apparent temperature, in the range of 10-25 MeV, at high ejectile velocity. These maximum values increase with increasing projectile energy and decrease with increasing target mass. The time at which the maximum in the temperature curve is reached ranges from 80 to 130 fm/c after contact. For each different target, the subsequent cooling curves for all three projectile energies are quite similar. Temperatures comparable with those of limiting temperature systematics are reached 30 to 40 fm/c after the times corresponding to the maxima, at a time when antisymmetrized molecular dynamics transport model calculations predict entry into the final evaporative or fragmentation stage of deexcitation of the hot composite systems. Evidence for the establishment of thermal and chemical equilibrium is discussed.
56435207
Ghoshal-like test of equilibration in near-Fermi-energy heavy-ion collisions
Calorimetric and coalescence techniques have been employed to probe equilibration for hot nuclei produced in heavy-ion collisions of 35 to 55 MeV/nucleon projectiles with medium mass targets. Entrance channel mass asymmetries and energies were selected so that very hot composite nuclei of similar mass and excitation would remain after early stage preequilibrium particle emission. Intercomparison of the properties and deexcitation patterns for these different systems provides evidence for the production of hot nuclei with decay patterns relatively independent of the specific entrance channel.
117724729
Particle spectra and interferometry results from NA44