C. A. Gagliardi

New limit for the family number nonconserving decay mu+ ---> e+ gamma

The transport properties of a quasi-three-dimensional, 200 layer quantum well structure are investigated at integer filling in the quantum Hall state. We find that the transverse magnetoresistance R xx , the Hall resistance R xy , and the vertical resistance R zz all follow a similar behavior with both temperature and in-plane magnetic field. A general feature of the influence of increasing in-plane field B in is that the Hall conductance quantization first improves, but above a characteristic value B C in , the quantization is systematically removed. We consider the interplay of the chid edge state transport and the bulk (quantum Hall) transport properties. This mechanism may arise from the competition of the cyclotron energy with the superlattice band structure energies. A comparison of the resuIts with existing theories of the chiral edge state transport with in-plane field is also discussed.An experiment has been performed to search for the muon- and electron-number non-conserving decay mu+ to e+_gamma. The upper limit for the branching ratio to be GAMMA(mu+ to e+_gamma)/GAMMA(mu+ to e+_nu_nubar) < 1.2e-11 with 90% confidence.

Global Λ hyperon polarization in nuclear collisions

The extreme energy densities generated by ultra-relativistic collisions between heavy atomic nuclei produce a state of matter that behaves surprisingly like a fluid, with exceptionally high temperature and low viscosity. Non-central collisions have angular momenta of the order of 1,000ћ, and the resulting fluid may have a strong vortical structure that must be understood to describe the fluid properly. The vortical structure is also of particular interest because the restoration of fundamental symmetries of quantum chromodynamics is expected to produce novel physical effects in the presence of strong vorticity. However, no experimental indications of fluid vorticity in heavy ion collisions have yet been found. Since vorticity represents a local rotational structure of the fluid, spin–orbit coupling can lead to preferential orientation of particle spins along the direction of rotation. Here we present measurements of an alignment between the global angular momentum of a non-central collision and the spin of emitted particles (in this case the collision occurs between gold nuclei and produces Λ baryons), revealing that the fluid produced in heavy ion collisions is the most vortical system so far observed. (At high energies, this fluid is a quark–gluon plasma.) We find that Λ and hyperons show a positive polarization of the order of a few per cent, consistent with some hydrodynamic predictions. (A hyperon is a particle composed of three quarks, at least one of which is a strange quark; the remainder are up and down quarks, found in protons and neutrons.) A previous measurement that reported a null result, that is, zero polarization, at higher collision energies is seen to be consistent with the trend of our observations, though with larger statistical uncertainties. These data provide experimental access to the vortical structure of the nearly ideal liquid created in a heavy ion collision and should prove valuable in the development of hydrodynamic models that quantitatively connect observations to the theory of the strong force.The extreme temperatures and energy densities generated by ultra-relativistic collisions between heavy nuclei produce a state of matter with surprising fluid properties1. Non-central collisions have angular momentum on the order of 1000~, and the resulting fluid may have a strong vortical structure2–4 that must be understood to properly describe the fluid. It is also of particular interest because the restoration of fundamental symmetries of quantum chromodynamics is expected to produce novel physical effects in the presence of strong vorticity15. However, no experimental indications of fluid vorticity in heavy ion collisions have so far been found. Here we present the first measurement of an alignment between the angular momentum of a non-central collision and the spin of emitted particles, revealing that the fluid produced in heavy ion collisions is by far the most vortical system ever observed. We find that Λ and Λ hyperons show a positive polarization of the order of a few percent, consistent with some hydrodynamic predictions5. A previous measurement6 that reported a null result at higher collision energies is seen to be consistent with the trend of our new observations, though with larger statistical uncertainties. These data provide the first experimental access to the vortical structure of the “perfect fluid”7 created in a heavy ion collision. They should prove valuable in the development of hydrodynamic models that quantitatively connect observations to the theory of the Strong Force. Our results extend the recent discovery8 of

Parton Energy Loss Limits and Shadowing in Drell-Yan Dimuon Production

A precise measurement of the ratios of the Drell-Yan cross section per nucleon for an 800 GeV/{ital c} proton beam incident on Be, Fe, and W targets is reported. The behavior of the Drell-Yan ratios at small target-parton momentum fraction is well described by an existing fit to the shadowing observed in deep-inelastic scattering. The cross-section ratios as a function of the incident-parton momentum fraction set tight limits on the energy loss of quarks passing through a cold nucleus. {copyright} {ital 1999} {ital The American Physical Society}

Measurement of Angular Distributions of Drell-Yan Dimuons in p + d Interaction at 800 GeV/c

We report a measurement of the angular distributions of Drell-Yan dimuons produced using an 800 GeV/c proton beam on a deuterium target. The muon angular distributions in the dilepton rest frame have been measured over the kinematic range 4.5<m{mu mu}<15 GeV/c{2}, 0<p{T}<4 GeV/c, and 0<x{F}<0.8. No significant cos2phi dependence is found in these proton-induced Drell-Yan data, in contrast with the situation for pion-induced Drell-Yan data. The data are compared with expectations from models which attribute the cos2phi distribution to a QCD vacuum effect or to the presence of the transverse-momentum-dependent Boer-Mulders structure function h{1}{perpendicular}. Constraints on the magnitude of the sea-quark h{1}{perpendicular} structure functions are obtained.

MARS: A momentum achromat recoil spectrometer

Abstract We are building a Momentum Achromat Recoil Spectrometer (MARS) for use with the new K500 superconducting cyclotron at Texas A&M University. MARS uses a unique optical design utilizing two dispersive planes to combine a momentum achromat with a recoil mass spectrometer. This configuration makes MARS applicable to a broad range of nuclear reaction studies utilizing inverse kinematics. It also leads to a system that is well matched to the range of secondary particle energies that will be produced in reactions with K500 beams. MARS will have a typical mass resolution of δM M ≅ 1 300 , with an energy acceptance of ± 9% ΔE E and a geometric solid angle of up to 9 msr. A beam swinger system will allow reaction products in the angular range 0° to 30° to be studied. MARS will be used to study both the excited states and decay properties of very proton- and neutron-rich nuclei. MARS will also be used to provide a reaction mechanism filter to assist investigations of the dynamics of heavy ion collisions and to produce secondary radioactive beams for reaction and spectroscopic studies of particular interest for nuclear astrophysics. We describe the design of MARS, together with a brief discussion of the scientific program planned for it.

Bulk Properties of the Medium Produced in Relativistic Heavy-Ion Collisions from the Beam Energy Scan Program

© 2017 American Physical Society. We present measurements of bulk properties of the matter produced in Au+Au collisions at sNN=7.7,11.5,19.6,27, and 39 GeV using identified hadrons (π±, K±, p, and p) from the STAR experiment in the Beam Energy Scan (BES) Program at the Relativistic Heavy Ion Collider (RHIC). Midrapidity (|y| < 0.1) results for multiplicity densities dN/dy, average transverse momenta (pT), and particle ratios are presented. The chemical and kinetic freeze-out dynamics at these energies are discussed and presented as a function of collision centrality and energy. These results constitute the systematic measurements of bulk properties of matter formed in heavy-ion collisions over a broad range of energy (or baryon chemical potential) at RHIC.

Tests of transfer reaction determinations of astrophysical {bold {ital S}} factors

The {sup 16}O({sup 3}He,d){sup 17}F reaction has been used to determine asymptotic normalization coefficients for transitions to the ground and first excited states of {sup 17}F. The coefficients provide the normalization for the tails of the overlap functions for {sup 17}F{r_arrow}{sup 16}O+p and allow us to calculate the {ital S} factors for {sup 16}O(p,{gamma}){sup 17}F at astrophysical energies. The calculated {ital S} factors are compared to measurements and found to be in very good agreement. This provides a test of this indirect method to determine astrophysical direct capture rates using transfer reactions. In addition, our results yield S(0) for capture to the ground and first excited states in {sup 17}F, without the uncertainty associated with extrapolation from higher energies. {copyright} {ital 1999} {ital The American Physical Society}

Asymptotic normalization coefficient of 8B from breakup reactions and the S17 astrophysical factor.

We show that asymptotic normalization coefficients (ANC) can be extracted from one-nucleon breakup reactions of loosely bound nuclei at 30-300 MeV/nucleon. In particular, the breakup of 8B is described in terms of an extended Glauber model. The 8B ANC extracted from breakup data at several energies and on different targets, C(2)(tot) = 0.450+/-0.039 fm(-1), leads to the astrophysical factor S17(0) = 17.4+/-1.5 eV b for the key reaction for solar neutrino production 7Be(p, gamma)8B. The procedure described provides an indirect method to determine reaction rates of astrophysical interest with beams of loosely bound radioactive nuclei.

Improved measurement of the anti-d / anti-u asymmetry in the nucleon sea

Measurements of the ratio of Drell-Yan yields from an 800 \rm{GeV/c} proton beam incident on liquid hydrogen and deuterium targets are reported. Approximately 360,000 Drell-Yan muon pairs remained after all cuts on the data. From these data, the ratio of anti-down (

High precision measurement of the superallowed 0+ --> 0+ beta decay of 22Mg.

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