arXiv subjects

S. R. Klein

Publications and source records attributed to S. R. Klein.

53 records · Page 3Linked to original sources

arXiv2007

The Physics of Ultraperipheral Collisions at the LHC

We discuss the physics of large impact parameter interactions at the LHC: ultraperipheral collisions (UPCs). The dominant processes in UPCs are photon-nucleon (nucleus) interactions. The current LHC detector configurations can explore small $x$ hard phenomena with nuclei and nucleons at photon-nucleon center-of-mass energies above 1 TeV, extending the $x$ range of HERA by a factor of ten. In particular, it will be possible to probe diffractive and inclusive parton densities in nuclei using several processes. The interaction of small dipoles with protons and nuclei can be investigated in elastic and quasi-elastic $J/ψ$ and $Υ$ production as well as in high $t$ $ρ^0$ production accompanied by a rapidity gap. Several of these phenomena provide clean signatures of the onset of the new high gluon density QCD regime. The LHC is in the kinematic range where nonlinear effects are several times larger than at HERA. Two-photon processes in UPCs are also studied. In addition, while UPCs play a role in limiting the maximum beam luminosity, they can also be used a luminosity monitor by measuring mutual electromagnetic dissociation of the beam nuclei. We also review similar studies at HERA and RHIC as well as describe the potential use of the LHC detectors for UPC measurements.

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arXiv2007

Photoproduction at collider energies: from RHIC and HERA to the LHC

We present the mini-proceedings of the workshop on ``Photoproduction at collider energies: from RHIC and HERA to the LHC'' held at the European Centre for Theoretical Studies in Nuclear Physics and Related Areas (ECT*, Trento) from January 15 to 19, 2007. The workshop gathered both theorists and experimentalists to discuss the current status of investigations of high-energy photon-induced processes at different colliders (HERA, RHIC, and Tevatron) as well as preparations for extension of these studies at the LHC. The main physics topics covered were: (i) small-$x$ QCD in photoproduction studies with protons and in electromagnetic (aka. ultraperipheral) nucleus-nucleus collisions, (ii) hard diffraction physics at hadron colliders, and (iii) photon-photon collisions at very high energies: electroweak and beyond the Standard Model processes. These mini-proceedings consist of an introduction and short summaries of the talks presented at the meeting.

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arXiv2005

Heavy Quarkonium Physics

This report is the result of the collaboration and research effort of the Quarkonium Working Group over the last three years. It provides a comprehensive overview of the state of the art in heavy-quarkonium theory and experiment, covering quarkonium spectroscopy, decay, and production, the determination of QCD parameters from quarkonium observables, quarkonia in media, and the effects on quarkonia of physics beyond the Standard Model. An introduction to common theoretical and experimental tools is included. Future opportunities for research in quarkonium physics are also discussed.

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arXiv2003

Inhomogeneous Shadowing Effects on J/ψProduction in dA Collisions

We study the effect of spatially homogeneous and inhomogeneous shadowing on $J/ψ$ production in deuterium-nucleus collisions. We discuss how the shadowing and its spatial dependence may be measured by comparing central and peripheral $dA$ collisions. These event classes may be selected by using gray protons from heavy ion breakup and events where the proton or neutron in the deuterium does not interact. We find that inhomogenous shadowing has a significant effect on central $dA$ collisions, larger than is observed in central $AA$ collisions. The inhomogeneity may be measured by comparing the rapidity dependence of $J/ψ$ production in central and peripheral collisions. Results are presented for $d$Au collisions at $\sqrt{s_{NN}} = 200$ GeV and $d$Pb collisions at $\sqrt{s_{NN}} = 6.2$ TeV.

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arXiv2003

The STAR Time Projection Chamber: A Unique Tool for Studying High Multiplicity Events at RHIC

The STAR Time Projection Chamber (TPC) is used to record collisions at the Relativistic Heavy Ion Collider (RHIC). The TPC is the central element in a suite of detectors that surrounds the interaction vertex. The TPC provides complete coverage around the beam-line, and provides complete tracking for charged particles within +- 1.8 units of pseudo-rapidity of the center-of-mass frame. Charged particles with momenta greater than 100 MeV/c are recorded. Multiplicities in excess of 3,000 tracks per event are routinely reconstructed in the software. The TPC measures 4 m in diameter by 4.2 m long, making it the largest TPC in the world.

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arXiv2002

Nuclear Shadowing and High-$p_T$ Hadron Spectra in Relativistic Heavy Ion Collisions

We explore how nuclear modifications to the nucleon parton distributions affect production of high-$p_T$ hadrons in heavy ion collisions. We perform a leading order calculation of the high-$p_T$ charged pion, kaon and proton spectra using standard fragmentation functions and shadowing parameterizations. We also consider alternate models of shadowing. Near midrapidity, shadowing is a small effect and cannot explain the large observed suppression of high-$p_T$ hadrons. We also consider the isospin difference between protons and nuclei and find that it is also a small effect on high-$p_T$ hadron production.

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arXiv2002

The Forward Time Projection Chamber (FTPC) in STAR

Two cylindrical forward TPC detectors are described which were constructed to extend the phase space coverage of the STAR experiment to the region 2.5 < |η| < 4.0. For optimal use of the available space and in order to cope with the high track density of central Au+Au collisions at RHIC, a novel design was developed using radial drift in a low diffusion gas. From prototype measurements a 2-track resolution of 1-2 mm is expected.

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arXiv2002

Diffraction at RHIC

The relativistic heavy ion collider (RHIC) offers many opportunities to study diffraction in pp, pA and AA collisions. Because both proton beams can be polarized, RHIC offers the unique possibility of studying polarization effects in diffraction. We will introduce diffraction at RHIC and present three compelling physics topics: hard diffraction with polarized beams, identification of exotic mesons (non-q q-bar states) in double-Pomeron collisions, and using diffraction to measure the low-x gluon density in $pA$ collisions, testing models of gluon saturation and the colored glass condensate. This note developed from discussion at a workshop on ``Diffraction and Glueball Production at RHIC'' at Brookhaven National Laboratory, May 17-18, 2002.

hep-ex↗

arXiv2002

A Readout System for the STAR Time Projection Chamber

We describe the readout electronics for the STAR Time Projection Chamber. The system is made up of 136,608 channels of waveform digitizer, each sampling 512 time samples at 6-12 Mega-samples per second. The noise level is about 1000 electrons, and the dynamic range is 800:1, allowing for good energy loss ($dE/dx$) measurement for particles with energy losses up to 40 times minimum ionizing. The system is functioning well, with more than 99% of the channels working within specifications.

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arXiv2002

Hot Topics in Ultra-Peripheral Collisions

Ultra-peripheral collisions of relativistic heavy ions involve long-ranged electromagnetic interactions at impact parameters too large for hadronic interactions to occur. The nuclear charges are large; with the coherent enhancement, the cross sections are also large. Many types of photonuclear and purely electromagnetic interactions are possible. We present here an introduction to ultra-peripheral collisions, and present four of the most compelling physics topics. This note developed from a discussion at a workshop on ``Electromagnetic Probes of Fundamental Physics,'' in Erice, Italy, Oct. 16-21, 2001.

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arXiv1999

The Effect of Shadowing on Initial Conditions, Transverse Energy and Hard Probes in Ultrarelativistic Heavy Ion Collisions

The effect of shadowing on the early state of ultrarelativistic heavy ion collisions is investigated along with transverse energy and hard process production, specifically Drell-Yan, $J/ψ$, and $Υ$ production. We choose several parton distributions and parameterizations of nuclear shadowing, as well as the spatial dependence of shadowing, to study the influence of shadowing on relevant observables. Results are presented for Au+Au collisions at $\sqrt{s_{NN}} = 200$ GeV and Pb+Pb collisions at $\sqrt{s_{NN}} = 5.5$ TeV.

hep-ph↗

arXiv1999

Shadowing Effects on Particle and Transverse Energy Production

The effect of shadowing on the early state of ultrarelativistic heavy ion collisions and transverse energy production is discussed. Results are presented for RHIC Au+Au collisions at $\sqrt{s_{NN}} = 200$ GeV and LHC Pb+Pb collisions at $\sqrt{s_{NN}} = 5.5$ TeV.

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arXiv1998

Impact Parameter Dependence of $J/ψ$ and Drell-Yan Production in Heavy Ion Collisions at $\sqrt{s_{NN}} = 17.3$ GeV

In heavy-ion collisions, $J/ψ$ and Drell-Yan production are expected to be affected by nuclear modifications to the free nucleon structure functions. If these modifications, known as shadowing, are proportional to the local nuclear density, the per nucleon cross sections will depend on centrality. Differences in quark and gluon shadowing will lead to a new source of impact parameter dependence of the $J/ψ$ to Drell-Yan production ratio. We calculate this ratio in the CERN NA50 acceptance with several shadowing parameterizations to explore its centrality dependence.

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arXiv1998

Spatial Variation of Nuclear Structure Functions and Heavy Quark Production

We explore how nuclear modifications to the free nucleon structure functions (also known as shadowing) affect heavy quark production in collisions at different impact parameters. We assume that the nuclear modifications arise from a density dependent effect such as gluon recombination and are thus proportional to the local density. We calculate the dependence of charm and bottom quark production on impact parameter and show that density dependent modifications can lead to significant reductions in the heavy quark production cross sections in central relative to peripheral interactions.

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arXiv1997

Charm Quark Production in Non-central Heavy Ion Collisions

The effect of gluon shadowing on charm quark production in large impact parameter ultrarelativistic heavy ion collisions is investigated. Charm production cross sections are calculated for a range of non-central impact parameters which can be accurately inferred from the global transverse energy distribution. We show that charm production is a good probe of the local parton density which determines the effectiveness of shadowing. The spatial dependence of shadowing can only be studied in heavy ion collisions.

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arXiv1997

Bremsstrahlung Suppression due to the LPM and Dielectric Effects in a Variety of Materials

The cross section for bremsstrahlung from highly relativistic particles is suppressed due to interference caused by multiple scattering in dense media, and due to photon interactions with the electrons in all materials. We present here a detailed study of bremsstrahlung production of 200 keV to 500 MeV photons from 8 and 25 GeV electrons traversing a variety of target materials. For most targets, we observe the expected suppressions to a good accuracy. We observe that finite thickness effects are important for thin targets.

hep-ex↗

arXiv1995

Measurement of Dielectric Suppression of Bremsstrahlung

In 1953, Ter-Mikaelian predicted that the bremsstrahlung of low energy photons in a medium is suppressed because of interactions between the produced photon and the electrons in the medium. This suppression occurs because the emission takes place over on a long distance scale, allowing for destructive interference between different instantaneous photon emission amplitudes. We present here measurements of bremsstrahlung cross sections of 200 keV to 20 MeV photons produced by 8 and 25 GeV electrons in carbon and gold targets. Our data shows that dielectric suppression occurs at the predicted level, reducing the cross section up to 75 percent in our data.

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