John Hill

Measurement of the stopping power of nuclei for 100 GeV/c protons and antiprotons

Abstract We have studied the reactions p+A→ (p, n)+X and p +A→ p +X at beam momenta of 100 GeV/c for Mg, Ag and Au targets. The rapidity loss of the leading final state protons, antiprotons, and neutrons has been obtained as a measurement of the nuclear stopping power and correlated with the number of slow protons and the multiplicity and momentum of the associated charged particles.

Secondary particle identification using the relativistic rise in ionization

Abstract We report on the data analysis and techniques used to determine particle identification from the relativistic rise in ionization as detected by CRISIS, a 1 × 1 × 3 m 3 , 192 cell, ionization-sampling drift chamber containing an 80% argon/20% carbon dioxide gas mixture. For 100 GeV/ c protons/antiprotons (pions) we obtain an ionization FWHM of 7.6% (7.9%), which compares well with the design value of 7.8%. The separation between the mean ionization values for the protons and pions was determined to be 7.9%. We also present the analysis of particle identification for secondary particles produced by interactions in the bubble chamber. A statistical method for correcting for the overlapping ionization curves from secondary protons/antiprotons and pions is discussed.

Measurement and prediction of the drift-distance/drift-time relationship of a small jet chamber operated with carbon dioxide/isobutane

Abstract As part of the preliminary studies for the vertex jet chamber of OPAL a small prototype chamber has been operated using carbon dioxide/isobutane and argon/ethane. A nitrogen laser has been used to produce an ionizing track in the chamber at a distance to the sense-wire plane that could be varied by means of a quartz pentaprism attached to a micrometer. This has enabled the drift-distance/drift-time relationship to be measured with an accuracy of 5–10 μm. The drift-distance/drift-time relationship has also been predicted from calculations of the electric field configuration inside the chamber and of the electron drift-velocity as a function of electric field. Measurement and predictions agree to the level of ∼ 10 μ m, thus demonstrating the feasibility of drift-distance/drift-time predictions for the final vertex jet chamber of OPAL, for which detailed laser measurements will not be possible. Corrections to the drift-distance/drift-time relationship for small variations in pressure, temperature and gas composition have also been predicted and shown to be in agreement with experimental measurements. An an alternative to the separate measurement of pressure, temperature and gas composition, it has been demonstrated that a direct measurement of the drift-velocity at one point in the chamber enabled the corrections to the drift-distance/drift-time relationship over the entire chamber volume to be calculated to the ∼10 μ m level.

Gen Shirane's Legacy in Polarized Beam Scattering: From Neutrons to X-rays

We pay tribute to Gen Shiranes legacy by summarizing the results of x-ray magnetic scattering studies of a series of interesting materials, including chromium, NiO, MnF 2 , rare earth boro-carbide...

Decay of mass-separated /sup 138/I

>The levels of /sup 93/Zr populated in the BETA decay of sup 93/Y have been deduced from Ge(Li) -Ge(Li) coincidence and Ge(Li) singles gamma -ray spectra. 22 of the 23 observed gamma -ray transitions have been placed in a level scheme for /sup 91/Zr with 11 excited states. These results are compared with those of previous investigations. A number of corrections, clarifications, and expansions of decay schemes previously reported resulted from the use of high- resolution detectors and a mass-separated source strong enough to permit coincidence studies of the weak as well as the intense transitions. Spin-parity assignments of the /sup 91/Zr levels have been deduced using relative gamma -ray transition rates, BETA -decay log(ft) values, and results of nuclear-reaction studies. Possible interpretations of some of the levels are presented, based on shell-model descriptions. (auth)

Nuclear modification of electron spectra and implications for heavy quark energy loss in Au + Au collisions at root s(NN)=200 GeV

The PHENIX experiment has measured midrapidity ([FORMULA: SEE TEXT]) transverse momentum spectra ([FORMULA: SEE TEXT]) of electrons as a function of centrality in Au+Au collisions at [FORMULA: SEE TEXT]. Contributions from photon conversions and from light hadron decays, mainly Dalitz decays of pi0 and eta mesons, were removed. The resulting nonphotonic electron spectra are primarily due to the semileptonic decays of hadrons carrying heavy quarks. Nuclear modification factors were determined by comparison to nonphotonic electrons in p+p collisions. A significant suppression of electrons at high pT is observed in central Au+Au collisions, indicating substantial energy loss of heavy quarks.

Measurement of Lambda and Anti-Lambda particles in Au plus Au collisions at root s(NN)=130 GeV

We present results on the measurement of Lambda and Lambda(macro) production in Au+Au collisions at square root of (S (NN) = 130 GeV with the PHENIX detector at the Relativistic Heavy Ion Collider. The transverse momentum spectra were measured for minimum bias and for the 5% most central events. The Lambda;/Lambda ratios are constant as a function of p(T) and the number of participants. The measured net Lambda density is significantly larger than predicted by models based on hadronic strings (e.g., HIJING) but in approximate agreement with models which include the gluon-junction mechanism.We present results on the measurement of Λ and Λ - production in Au+Au collisions at √s NN =130 GeV with the PHENIX detector at the Relativistic Heavy Ion Collider. The transverse momentum spectra were measured for minimum bias and for the 5% most central events. The Λ - /Λ ratios are constant as a function of p T and the number of participants. The measured net Λ density is significantly larger than predicted by models based on hadronic strings (e.g., HIJING) but in approximate agreement with models which include the gluon-junction mechanism.

Centrality dependence of pi(+/-), K-+/-, p, and (p)over-bar production from root(NN)-N-S = 130 GeV Au+Au collisions at RHIC

Identified pi(+/-), K(+/-), p, and (-)p transverse momentum spectra at midrapidity in sqrt[s(NN)] = 130 GeV Au+Au collisions were measured by the PHENIX experiment at RHIC as a function of collision centrality. Average transverse momenta increase with the number of participating nucleons in a similar way for all particle species. Within errors, all midrapidity particle yields per participant are found to be increasing with the number of participating nucleons. There is an indication that K(+/-), p, and (-)p yields per participant increase faster than the pi(+/-) yields. In central collisions at high transverse momenta (p(T) > or =2 GeV/c), (-)p and p yields are comparable to the pi(+/-) yields.

X-ray resonant scattering studies of charge and ortibal ordering in Pr{sub 1-X}Ca{sub X}MnO{sub 3}

We present the results of a systematic x-ray scattering study of the charge and orbital ordering in the manganite series

Magnetic moments of the21+states in146,148Ce

{\mathrm{Pr}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}{\mathrm{MnO}}_{3}