Computing for ongoing experiments on high-energy physics at Laboratory of Particle Physics at JINR

A computer infrastructure constructed at JINR’s Laboratory of Particle Physics, purposed for the effective participation of JINR’s experts in ongoing experiments in particle and nuclear physics is presented. The principles of the design and construction of the PC farm are outlined, and the computer and information services used for effective application of distributed computer and information resources are described.     

Laser micro-machining of small objects for high-energy laser experiments

Targets for high-energy laser experiments are polymer or metal objects of small dimensions. These objects need high-precision processes (typical sizes of a few hundred micrometers with micrometer accuracy). In this paper, some targets for high-energy laser experiments obtained by picosecond Q-switched Nd:YAG laser and KrF excimer laser micro-machining are presented. All of the targets use an original process. Activities include cutting, drilling, and marking elements. A summary of targets made using laser processes will be presented.     

A proposal for fs-electron microscopy experiments on high-energy excitations in solids

Recent advances in ultrafast technology enable both the study and the control of materials properties thanks to the ability to record high temporal resolution movies of their transformations, or the ability to generate new states of matter by selecting ad hoc an excitation to drive the system out of equilibrium. The holy grail of this type of experiments is to combine a high tuneability of the excitation with a wide observation window. For example, this is achieved in multidimensional optical spectroscopy where the response to several excitation energies is monitored in a broad energy range by a large bandwidth optical pulse. In this article, the possibility to combine the chemical sensitivity of intense tuneable X-rays pulses from a free electron laser, with the wide range of observables available in an ultrafast transmission electron microscope is discussed. The requirements for such experiments are quantified via estimates based on state of the art experiments and simulations, and it is proposed that ultrafast electron imaging, diffraction and spectroscopy experiments can be performed in combination with a chemically selective X-ray excitation of materials.     

A multilayer scintillation detector of high-energy particles for satellite experiments

We describe the detecting system of a high-energy charged particle telescope spectrometer for a space experiment to be performed on the outer surface of the Russian section of the International Space Station and other spacecraft, including small satellites. The spectrometer’s detecting system is a multilayer scintillation detector (MSD) of polystyrene plates scanned by photomultipliers. It allows high-intensity fluxes of electrons (up to ～10⁵ cm^?2 s^?1) several milliseconds long with energies of 3 to 30 MeV to be measured with an accuracy of ～1 μs, along with time profiles and the evolution of particle energy spectra. The MSD is characterized by an energy resolution no worse than 10%, an angular resolution of ～10 degrees, a geometric factor of ～40 cm² sr, and a trigger system time resolution of ～20 ns.     

Pentaquarks in high-energy colliding experiments: perspectives from HERA

Several issues related to pentaquark searches relevant for current and future high-energy colliding experiments are discussed. We make an attempt to explain why pentaquark candidates are not seen by some experiments, and what makes the HERA experiments so special in such searches. Received: 7 March 2005, Published online: 27 September 2005     

Evidence for radial flow of thermal dileptons in high-energy nuclear collisions

The NA60 experiment at the CERN SPS has studied low-mass dimuon production in 158A GeV In-In collisions. An excess of pairs above the known meson decays has been reported before. We now present precision results on the associated transverse momentum spectra. The slope parameter Teff extracted from the spectra rises with dimuon mass up to the rho, followed by a sudden decline above. While the initial rise is consistent with the expectations for radial flow of a hadronic decay source, the decline signals a transition to an emission source with much smaller flow. This may well represent the first direct evidence for thermal radiation of partonic origin in nuclear collisions.     

Pulse compression at 1.06 microm in dispersion-decreasing holey fibers

We report compression of low-power femtosecond pulses at 1.06 microm in a dispersion-decreasing holey fiber. Near-adiabatic compression of 130 fs pulses down to 60 fs has been observed. Measured spectra and pulse shapes agree well with numerical simulations. Compression factors of ten are possible in optimized fibers.     

Evidence for collisional narrowing in the infrared laser Stark spectrum of CH3CN

The infrared laser Stark lineshape of the Jkm = 211 ← 111 transition in the ν₄ band of CH₃CN was recorded under computer control at several pressures. Analysis of the lineshapes by means of the usual Voigt profile gives a plot of collision broadening vs pressure that shows marked curvature in the low-pressure region. In addition, extrapolation to zero pressure of the best straight line through the high-pressure points gives a negative intercept. By choosing an appropriate narrowing parameter in either of the limiting soft-collision or hard-collision models of collisional narrowing, it is possible to obtain plots of collision broadening vs pressure that are linear and have acceptable intercepts. The pressure broadening and collisional narrowing parameters derived are 69.4 ± 0.7 and 17.2 ± 1.7 MHz/Torr, respectively, for the soft-collision model and 68.6 ± 0.7 and 11.5 ± 1.2 MHz/Torr, respectively, for the hard-collision model.     

Splitting the plasmon peak in high-energy reflection electron energy loss experiments

Elastic scattering of energetic electrons over large angles (in this study 40 keV and 120°$120°$) implies momentum and hence energy transfer from an electron to a nucleus. Due to the large mass of the nucleus (relative to the mass of an electron) this energy transfer is small, but it has recently been shown that it can be resolved in a modern spectrometer. Hence the elastic peak of an overlayer/substrate system splits into different components corresponding to atoms with different mass. Here we extend this type of experiment to the plasmon part of a reflection energy loss spectroscopy (REELS) spectrum. It is shown that, for suitable systems, the plasmon peak of an overlayer/substrate system is split by the same amount as the elastic peak. This is a consequence of the fact that detection of an electron in REELS always requires a large-angle elastic scattering event. Moreover, we show that the relative intensity of the plasmon components contains information on the depth distribution of the scatterers.     

Evidence for skyrmion crystallization from NMR relaxation experiments

A resistively detected NMR technique was used to probe the two-dimensional electron gas in a GaAs/AlGaAs quantum well. The spin-lattice relaxation rate (1/T(1)) was extracted at near complete filling of the first Landau level by electrons. The nuclear spin of (75)As is found to relax much more efficiently with T --> 0 and when a well developed quantum Hall state with R(xx) approximately 0 occurs. The data show a remarkable correlation between the nuclear spin relaxation and localization. This suggests that the magnetic ground state near complete filling of the first Landau level may contain a lattice of topological spin texture, i.e., a Skyrmion crystal.     

On the effect of incident angular resolution in high-energy fixed-target collision experiments

A general calculation of the correction to the measured cross section in fixed-target experiments, due to the angular resolution of the incident beam, is carried out. A first-order expression in the incident solid angle ΔΩ is explicity given, and shows that, in the TeV region, angular resolutions as accurate as 10^?1 mrad are required for measurements within the cross-section forward peak.     

LAA: a project using dedicated funding to develop technology for high-energy physics experiments

The European Physical Journal H - In the mid-1980s, the cost of investment in infrastructure for particle accelerators and colliders at the highest energy had risen to such level that the host...