Facilities for the Energy Frontier of Nuclear Physics

The Relativistic Heavy Ion Collider at BNL has been exploring the energy frontier of nuclear physics since 2001. Its performance, flexibility and continued innovative upgrading can sustain its physics output for years to come. Now, the Large Hadron Collider at CERN is about to extend the frontier energy of laboratory nuclear collisions by more than an order of magnitude. In the coming years, its physics reach will evolve towards still higher energy, luminosity and varying collision species, within performance bounds set by accelerator technology and by nuclear physics itself. Complementary high-energy facilities will include fixed-target collisions at the CERN SPS, the FAIR complex at GSI and possible electron-ion colliders based on CEBAF at JLAB, RHIC at BNL or the LHC at CERN.Comment: Invited talk at the International Nuclear Physics Conference, Vancouver, Canada, 4-9 July 2010, to be published in Journal of Physics: Conference Series. http://inpc2010.triumf.ca

Beam losses from ultra-peripheral nuclear collisions between Pb ions in the Large Hadron Collider and their alleviation

Electromagnetic interactions between colliding heavy ions at the Large Hadron Collider (LHC) at CERN will give rise to localized beam losses that may quench superconducting magnets, apart from contributing significantly to the luminosity decay. To quantify their impact on the operation of the collider, we have used a three-step simulation approach, which consists of optical tracking, a Monte-Carlo shower simulation and a thermal network model of the heat flow inside a magnet. We present simulation results for the case of Pb ion operation in the LHC, with focus on the ALICE interaction region, and show that the expected heat load during nominal Pb operation is 40% above the quench level. This limits the maximum achievable luminosity. Furthermore, we discuss methods of monitoring the losses and possible ways to alleviate their effect.Comment: 17 pages, 20 figure

First observations of beam losses due to bound-free pair production in a heavy-ion collider

We report the first observations of beam losses due to bound-free pair production at the interaction point of a heavy-ion collider. This process is expected to be a major luminosity limit for the Large Hadron Collider (LHC) when it operates with 208Pb82+ ions because the localized energy deposition by the lost ions may quench superconducting magnet coils. Measurements were performed at the Relativistic Heavy Ion Collider (RHIC) during operation with 100 GeV/nucleon 63Cu29+ ions. At RHIC, the rate, energy and magnetic field are low enough so that magnet quenching is not an issue. The hadronic showers produced when the single-electron ions struck the RHIC beampipe were observed using an array of photodiodes. The measurement confirms the order of magnitude of the theoretical cross section previously calculated by others.Comment: 4 pages, 5 figures. Added journal ref. Corrected typos. Fixed fig 1. Minor improvements to fig. 1,3,4. Rephrased a small number of sentences (p1,3,4). Added numerical values of the aperture and the displacement for Au (p 2). Changed reference 5, added name in acknowledgments (p 4

The LHC as a Nucleus-Nucleus Collider

This paper begins with a summary of the status of the Large Hadron Collider at CERN, including the lead-ion injector chain and the plans for the first phases of commissioning and operation with colliding proton beams. In a later phase, the LHC will collide lead nuclei at centre-of-mass energies of 5.5 TeV per colliding nucleon pair. This leap to 28 times beyond what is presently accessible will open up a new regime, not only in the experimental study of nuclear matter, but also in the beam physics of hadron colliders. Ultraperipheral and hadronic interactions of highly-charged beam nuclei will cause beam losses that dominate the luminosity decay and may quench superconducting magnets, setting upper limits on luminosity and stored beam current. Lower limits are set by beam instrumentation. On the other hand, coherent radiation by the nuclear charges should provide natural cooling to overcome intra-beam scattering. As with protons, a flexible, staged approach to full performance will test the limits and make optimal use of scheduled beam time. Submitted to Journal of Physics G, Nuclear Physic

Beam Dynamics at LEP

LEP has proved to be one of the most flexible e+e- colliders built to date. It has operated at various energies, in several modes, with ever increasing demands for luminosity in clean and precisely known beam conditions. Together with some unique features, LEP therefore has much in common with future e+e- factories. Beam-dynamical phenomena have been among the crucial determinants of LEP's performance. These include single-particle dynamics (optics design, dynamic aperture, radiation effects, etc.), a variety of beam-beam effects and collective instabilities. The strategies adopted to overcome these effects and maximise performance will be described with emphasis on those relevant to the design and operation of e+e- factories

Realistic prediction of dynamic aperture and optics performance for LEP

Over the two-decade lifetime of the LEP project, techniques for evaluating the quality of optical configurations have evolved considerably to exploit the growth in computer power and improved modelling of single-particle dynamics. These developments have culminated in a highly automated Monte-Carlo evaluation process whose stages include the generation of an ensemble of imperfect machines, simulation of the operational correction procedures, correlation studies of the optical functions and parameters of (both) beams, 4-dimensional dynamic aperture scans and tracking with quantum fluctuations to determine the beam core distribution. We outline the process, with examples, and explain why each step is necessary to realistically capture essential physics affecting performance. The mechanisms determining the vertical emittance, radial beam distribution and dynamic aperture are especially important. As a storage ring in which an unusual variety of optics have been tested, LEP provides a valuable test case for the predictive power of the methodology

pax1-1 partially suppresses gain-of-function mutations in Arabidopsis AXR3/IAA17

Background: The plant hormone auxin exerts many of its effects on growth and development by controlling transcription of downstream genes. The Arabidopsis gene AXR3/IAA17 encodes a member of the Aux/IAA family of auxin responsive transcriptional repressors. Semi-dominant mutations in AXR3 result in an increased amplitude of auxin responses due to hyperstabilisation of the encoded protein. The aim of this study was to identify novel genes involved in auxin signal transduction by screening for second site mutations that modify the axr3-1 gain-of-function phenotype. Results: We present the isolation of the partial suppressor of axr3-1 (pax1-1) mutant, which partially suppresses almost every aspect of the axr3-1 phenotype, and that of the weaker axr3-3 allele. axr3-1 protein turnover does not appear to be altered by pax1-1. However, expression of an AXR3:: GUS reporter is reduced in a pax1-1 background, suggesting that PAX1 positively regulates AXR3 transcription. The pax1-1 mutation also affects the phenotypes conferred by stabilising mutations in other Aux/IAA proteins; however, the interactions are more complex than with axr3-1. Conclusion: We propose that PAX1 influences auxin response via its effects on AXR3 expression and that it regulates other Aux/IAAs secondarily