Efimov universality with Coulomb interaction

The universal properties of charged particles are modified by the presence of a long-range Coulomb interaction. We investigate the modification of Efimov universality as a function of the Coulomb strength using the Gaussian expansion method. The resonant short-range interaction is described by Gaussian potentials to which a Coulomb potential is added. We calculate binding energies and root mean square radii for the three- and four-body systems of charged particles and present our results in a generalised Efimov plot. We find that universal features can still be discerned for weak Coulomb interaction, but break down for strong Coulomb interaction. The root-mean-square radius plateaus at increasingly smaller values for strong Coulomb interaction and the probablity distributions of the states become more concentrated inside the Coulomb barrier. As an example, we apply our universal model to nuclei with an alpha-cluster substructure. Our results point to strong non-universal contributions in that sector.Comment: 18 pages, 9 figures, final version (with small orthographical corrections

Universal physics of bound states of a few charged particles

We study few-body bound states of charged particles subject to attractive zero-range/short-range plus repulsive Coulomb interparticle forces. The characteristic length scales of the system at zero energy are set by the Coulomb length scale $D$ and the Coulomb-modified effective range $r_{\mathrm{eff}}$. We study shallow bound states of charged particles with $D\gg r_{\mathrm{eff}}$ and show that these systems obey universal scaling laws different from neutral particles. An accurate description of these states requires both the Coulomb-modified scattering length and the effective range unless the Coulomb interaction is very weak ($D\to \infty$). Our findings are relevant for bound states whose spatial extent is significantly larger than the range of the attractive potential. These states enjoy universality -- their character is independent of the shape of the short-range potential.Comment: 8 pages, 6 figures, extended discussion, results unchanged, to appear in Phys. Lett.

Beam Tails in LEP

Beam tails have been measured in LEP using scraping collimators and loss monistors for separated and colliding beams. Significant non-Gaussian beam tails have been observed with colliding beams for high beam-beam tune shift parameters and bunch currents

Tune Measurements in the SPS as a Multicycling Machine

Throughout the operation cycle of the SPS different particles are accelerated : High intensity protons, leptons and heavy ions. For each particle type a measurement of the betatron tunes along the acceleration cycle is required. The paper describes the different excitation and data analysis methods used in order to minimize beam blow-up during the measurements (protons) or in order to optimize the time resolution (leptons). Measurement examples are given

Redox Entropy of Plastocyanin: Developing a Microscopic View of Mesoscopic Polar Solvation

We report applications of analytical formalisms and Molecular Dynamics (MD) simulations to the calculation of redox entropy of plastocyanin metalloprotein in aqueous solution. The goal of our analysis is to establish critical components of the theory required to describe polar solvation at the mesoscopic scale. The analytical techniques include a microscopic formalism based on structure factors of the solvent dipolar orientations and density and continuum dielectric theories. The microscopic theory employs the atomistic structure of the protein with force-field atomic charges and solvent structure factors obtained from separate MD simulations of the homogeneous solvent. The MD simulations provide linear response solvation free energies and reorganization energies of electron transfer in the temperature range 280--310 K. We found that continuum models universally underestimate solvation entropies, and a more favorable agreement is reported between the microscopic calculations and MD simulations. The analysis of simulations also suggests that difficulties of extending standard formalisms to protein solvation are related to the inhomogeneous structure of the solvation shell at the protein-water interface combining islands of highly structured water around ionized residues along with partial dewetting of hydrophobic patches. Quantitative theories of electrostatic protein hydration need to incorporate realistic density profile of water at the protein-water interface.Comment: 17 pages, 12 figure

Study of the Stabilization to the Nanometer Level of Mechanical Vibrations of the CLIC Main Beam

Original publication available at http://www.jacow.org/International audienceTo reach the design luminosity of CLIC, the movements of the quadrupoles should be limited to the nanometre level in order to limit the beam size and emittance growth. Below 1 Hz, the movements of the main beam quadrupoles will be corrected by a beambased feedback. But above 1 Hz, the quadrupoles should be mechanically stabilized. A collaboration effort is ongoing between several institutes to study the feasibility of the "nanostabilization" of the CLIC quadrupoles. The study described in this paper covers the characterization of independent measuring techniques including optical methods to detect nanometre sized displacements and analyze the vibrations. Actuators and feedback algorithms for sub-nanometre movements of magnets with a mass of more than 400 kg are being developed and tested. Input is given to the design of the quadrupole magnets, the supports and alignment system in order to limit the amplification of the vibration sources at resonant frequencies. A full scale mock-up integrating all these features is presently under design. Finally, a series of experiments in accelerator environments should demonstrate the feasibility of the nanometre stabilization

LEP1 operation, 1989-1995

In October 1995, the last run foreseen for dedicated Z production at CERN was performed in LEP, thereby bringing to a close the first phase of operation of the machine. A total luminosity of 200 pb-1 has been delivered to each of the four experiments, which together have recorded the decays of over 20 millions Zs. Machine performance has increased to the extent that a good weekend in 1995 saw as much luminosity delivered as in the whole of 1989. This improvement has been made possible by a combination of several things. Over and above general operational expertise, special care went into the treatment and stabilisation of the closed orbit in order to obtain reproducible high performances with vertical beam-beam tune shifts exceeding values of xy = 0.04. Both Pretzel and Bunch Train schemes have been introduced to double the number of bunches, and high-tune optics have been developed to produce low transverse emittances which allow operation at the beam-beam limit throughout physics runs. Included in the integrated luminosity are data taken off the peak of the Z resonance, to allow precise determination of the mass and width of this particle. Accurate measurements of the beam energy during these runs have brought to the fore some unusual effects

The SPS as accelerator of Pb82+^{82+} ions

In 1994 the CERN SPS was used for the first time to accelerate fully stripped ions of the Pb208 isotope from the equivalent proton momentum of 13 GeV/c to 400 GeV/c. In the CERN PS, which was used as injector, the lead was accelerated as Pb53+ ions and then fully stripped in the transfer line from PS to SPS. The radio frequency swing which is needed in order to keep the synchronism during acceleration is too big to have the SPS cavities deliver enough voltage for all frequencies. For that reason a new technique of fixed frequency acceleration was used. With this technique up to 70% of the injected beam could be captured and accelerated up to the extraction energy, the equivalent of 2.2 1010 charges. The beam was extracted over a 5 sec. long spill and was then delivered to different experiments at the same time

Development of a detector for bunch by bunch measurement and optimization of luminosity in the LHC

The front IR quadrupole absorbers (TAS) and the IR neutral particle absorbers (TAN) in the high luminosity insertions of the LHC each absorb approximately 1.8TeV of forward collision products on average per pp interaction ({approximately}235W at design luminosity 1034cm-2s-1). This secondary particle flux can be exploited to provide a useful storage ring operations tool for optimization of luminosity. Novel segmented, multi-gap, pressurized gas ionization chambers are proposed for sampling the energy deposited near the maxima of the hadronic/ electromagnetic showers in these absorbers. The system design choices have been strongly influenced by optimization of signal to noise ratio and by the very high radiation environment. The ionization chambers are instrumented with state of the art low noise, fast, pulse shaping electronics capable of resolving individual bunch crossings at 40 MHz. Data on each bunch are separately accumulated over multiple bunch crossings until the desired statistical accuracy is obtained. At design luminosity approximately 2x103 bunch crossings suffice for a 1% luminosity measurement