117860091
A review of recent E802 results
Some recent results are presented from AGS E802, a survey experiment which is studying reactions of 14.6 A {center dot} GeV beams of protons, {sup 16}O and {sup 28}Si on targets ranging from {sup 9}Be to {sup 197}Au. Spectra for the global forward and transverse energy are shown; in nucleus-nucleus collisions these two quantities are anticorrelated, consistent with a large amount of stopping. Slope parameters from inclusive particle spectra are presented, with the most interesting effect being an apparent heating'' of mid-rapidity protons which emerge from the collisions of the largest nuclei. Also given are preliminary data on the production of antiprotons. 8 refs., 4 figs., 1 tab.
16555183
Hard scattering and jets: from pp collisions in the 1970’s to Au + Au collisions at RHIC
Abstract.Hard scattering in pp collisions, discovered at the CERN ISR in 1972 by the method of leading particles, proved that the partons of Deeply Inelastic Scattering strongly interacted with each other. Further ISR measurements utilizing inclusive single or pairs of hadrons established that high $p_{\rm T}$ particles are produced from states with two roughly back-to-back jets which are the result of scattering of constituents of the nucleons as described by Quantum Chromodynamics (QCD), which was developed during the course of these measurements. These techniques, which are the only practical method to study hard-scattering and jet phenomena in Au + Au central collisions at RHIC energies, are reviewed, with application to present RHIC measurements.
116711045
Projectile energy degradation at 14. 5 GeV/u
The generation of states of high energy density hinges on the question of nuclear stopping or, in other words, on the rapidity lost by the projectile as it ploughs through the target. Recent data have shown ( 1-2 ) that, at 10 and 14.5 GeV/u, the total neutral (E/sup 0//sub TOT/) and transverse energy ( ET) distributions can be used to infer complete stopping, as measured by the inability of targets heavier than Cu to yield additional neutral energy. An alternative measurement of projectile stopping would rely on the absence of significant residual projectile energy along its direction of motion. We present experimental evidence showing that the flow of forward energy is a valuable probe of nuclear stopping and that, at 14.5 GeV/u, the projectile energy is completely degraded for central collisions in heavy targets. The forward energy observed is shown to be adequately reproduced by simple geometrical calculations. The correlation of the forward energy with E/sup 0//sub TOT/, will be shown to provide information on the number of projectile participant nucleons. 5 refs., 2 figs.
40894304
Charged hadron distributions in central and peripheral Si+A collisions at 14.6A GeV/c.
The AGS spectrometer experiment E-802 has measured transverse mass spectra for charged hadrons over a wide rapidity interval in Si+Au, Si+Cu, and Si+Al reactions at 14.6A Gev/c. These results are compared for two different trigger conditions: central collisions corresponding to 7% of the inelastic cross section selected on multiplicity of charged particles and peripheral collisions corresponding to roughly 50% of the inelastic cross section selected on high kinetic energy at zero degrees. The invariant spectra are well described by exponentials in transverse mass allowing the extraction of rapidity distributions and inverse slope parameters for each specie emitted in the different reactions.
120960510
Polarized protons at RHIC
RHIC, the heavy ion collider being built at Brookhaven, offers an exciting opportunity to collide highly polarized protons at high energy and luminosity. This new facility would combine the existing AGS polarized proton capability with the new Booster/Accumulator and spin rotators to achieve collisions between intense beams of polarized protons at a collision energy of 500 GeV. At this energy and the expected luminosity of 2 {times} 10{sup 32} cm{sup 2}/second physics probes will include high P{sub T} jets, direct photons, Drell-Yan, W{sup {plus minus}}, and heavy quarks. The accessible physics includes study of the spin content of the proton, particularly gluon and antiquark polarization, study of large PQCD-predicted asymmetries for parton-parton subprocesses, and parity violation studies and searches. The proton spin direction at a RHIC crossing can be longitudinal or transverse and can alternate bunch-to-bunch giving exquisite control of systematic errors. At RHIC double spin experiments can be done with pure beams and the energy and luminosity open a new domain for probing the physics of spin. An international collaboration is forming which proposes to exploit the unique physics available from a polarized RHIC. Important steps, leading to a polarized RHIC, have been taken. The AGS has already acceleratedmore » polarized protons. A new Booster/Accumulator has been commissioned. A beautiful series of machine experiments at Indian University have verified that spin rotators indeed remove spin resonance behavior, which is the key to achieving polarized proton acceleration to high energy. E880, an accelerator experiment which will build, install, and test a Siberian Snake in the AGS, was approved by the Brookhaven PAC in August 1991. The snake will be installed in the AGS in the summer of 1993. RHIC construction has started, with heavy ion experiments to begin in 1997.« less
126552353
Charm in PHENIX—a signal or a background?
Charm, as well as Strangeness, plays an important role in searches for the Quark Gluon Plasma.J/Φ Suppression and Strangeness Enhancement are two of the earliest proposed QGP signatures. Recent theoretical work on charm in Relativistic Heavy Ion collisions has focussed on di-lepton production. However, even before the discovery of theJ/Ψ, evidence of open charm was seen in hadron collisions via the observation of promptsingle leptons “resulting from the semi-leptonic decays of charm particles.” [1] The ‘copious’ yield of direct (i.e. not from Dalitz decays) single electrons and muons—at a levele/π∼10−4 forpT≥1.3 GeV/c—observed in the early 1970’s was explained by Hinchliffe and Llewellyn-Smith and Bourquin and Gaillard as evidence of open-charm production. It is likely thate/π at RHIC is large and is a good measure of charm production. Thus, a measurement of single electrons with moderatepT>1.5 GeV/c at RHIC should give a clean charm signal in heavy ion collisions,with no combinatoric background.
17486791
Neutral Scalar Higgs Masses and Production Cross Sections in an Extended Supersymmetric Standard Model
Abstract Upper bounds on the three neutral scalar Higgs masses are considered in the supersymmetric standard model with a gauge singlet Higgs field. When the lightest Higgs is singlet-dominated the second lightest Higgs is shown to lie near or below thetheoretical upper bound on the lightest Higgs mass. We also consider detectability of these Higgs bosons at a future e + e − linear collider with s ∼ 300 GeV and show that at least one of the neutral scalar Higgs has a production cross section larger than 0.04 pb.