John Watson

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Papers by John Watson

Measurement of Inclusive Antiprotons fromAu+AuCollisions atsNN=130GeV

Physical Review Letters, 2001

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The spin-dipole resonance in () on 16O and 40Ca

Nuclear Physics A, 1994

The spin observable D NN′ (θ) was measured for ( ) at 135 MeV on 16 O, 40 Ca, 48 Ca, and 208 Pb. ... more

Gamow-Teller strength in the Pb208(p,n)208Bi reaction at 134.3 MeV

Physical Review C, 1989

ABSTRACT The excitation-energy distribution of transition strength to 1+ states was measured for ... more ABSTRACT The excitation-energy distribution of transition strength to 1+ states was measured for the 208Pb(p,n)208Bi reaction at 134.3 MeV for excitation energies up to 38 MeV. Structures observed in neutron time-of-flight spectra with forward-peaked (ΔL=0) angular distributions were identified as 1+ states, except for the transition to the 0+ isobaric analog state. The 1+ strength in these structures was extracted by normalizing the yield above a fitted polynomial background to the Fermi transition strength localized in the isobaric analog state. The Gamow-Teller strength observed in the 1+ peaks is 56% of the 3(N-Z) sum rule when the strength of the β+ transitions is assumed to be zero; 45% of 3(N-Z) is observed in the giant resonance and 10% is observed in structures below the giant resonance. Based on a multipole decomposition analysis, an upper limit on the 1+ strength in the apparent continuum to 38 MeV of excitation energy is estimated to be 37% of 3(N-Z). These results are compared with predictions from a shell model that includes a pairing force and a long-range Gamow-Teller force in both the parent and daughter nuclei.

Distributions of charged hadrons associated with highpTparticles

Journal of Physics: Conference Series, 2005

Recent results from STAR on angular correlations of charged hadrons associated with high transver... more Recent results from STAR on angular correlations of charged hadrons associated with high transverse momentum particles are presented. Emphasis is put on the correlations of soft associated hadrons, which provide rich information on the properties of the bulk medium created in RHIC collisions. The results are discussed in the context of three pertinent questions regarding QGP formation: sufficient energy density, parton thermalization, and deconfinement. Quantum Chromodynamics (QCD) predicts a phase transition between hadronic matter and quarkgluon plasma (QGP), a deconfined and thermalized state of quarks and gluons, at a critical energy density of approximately 1 GeV/fm 3 [1]. Such a phase transition is being actively pursued at the Relativistic Heavy Ion Collider (RHIC) at BNL via ultra-relativistic heavy-ion collisions. The RHIC experiments [2] have critically assessed the three-year wealth of experimental data and concluded that a new form of hot and dense matter has been created in RHIC collisions. Theory and theoretical models, confronting available experimental data, conclude that the matter created in RHIC collisions is a strongly coupled QGP [3]. In this proceedings article we focus on angular correlations with high transverse momentum particles and try to address three pertinent questions regarding QGP formation: (1) Is the energy density created in RHIC collisions sufficiently high for QGP formation? (2) Is the created system a thermalized state of quarks and gluons? (3) Are the quarks and gluons deconfined over a volume of nuclear size?

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A comparison of methods for determining neutron detector efficiencies at medium energies

Nuclear Instruments and Methods in Physics Research, 1983

We compare the "' Lithium Activation" (LiA) methcx.t and the "lsospin ('lebsch-Gordan Ratio" (I(.... more We compare the "' Lithium Activation" (LiA) methcx.t and the "lsospin ('lebsch-Gordan Ratio" (I(.'(;R) method for determining detection efficiencies of neutrons between 100 and 160 MeV. Each method was used to determine the efficiency bv relating a measured neutron yield to a cross section measured in another way: y-ray activation cross sections for LiA: (p. p') crc, ss sections from experiments at the Indiana University Cyclotron Facility for I('GR. Efficiencies determined by the two methods disagree substantially. Efficiencies calculated with the Monte Carlo code of Cecil et al. agree with the ICGR results. We conclude that the Lithium Activation method is inconsistent at these energies.

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A high-performance polarimeter for medium-energy neutrons

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 1988

A polarimeter for medium-energy neutrons is described. This polarimeter uses the analyzing power ... more A polarimeter for medium-energy neutrons is described. This polarimeter uses the analyzing power of n-p scattering which is typically +0 .50 for laboratory neutron scattering angles near 20°in the energy range from 50 MeV to 1 GeV. Hydrocarbon organic scintillators are employed as "active" scatterers. Calibration data for the analyzing power and the efficiency of the polarimeter are presented.

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The four-body reaction6Li(p,pα)np as a probe of the cluster structure of6Li

Journal of Physics G: Nuclear Physics, 1977

The ground state of 6Li is examined through a comparison of the reactions 6Li(p,p alpha )d and 6L... more

High-effeciency neutron detectors

ABSTRACT

GT Strength in Odd-A Nuclei^*

We measured the complete set of polarization-transfer observables (D_ij) for the ^13C(p,n)^13N an... more We measured the complete set of polarization-transfer observables (D_ij) for the ^13C(p,n)^13N and ^15N(p,n)^15O reactions at 135 MeV. From the D_ijs we constructed the spin-independent, spin-longitudinal, and spin-transverse responses [1] D_0, D_q, Dn and D_p. From these responses we extracted, in a model-independent way, the Δ J=0 and Δ J=1 (``F'' and ``GT'') fractions of the J^π=1/2^-arrow1/2^- g.s. to g.s. transitions for these reactions. The ``F'' fraction, f_F=D_0(0^circ); the ``GT'' fraction, f_GT=D_q(0^circ)+D_n(0^circ)+D_p(0^circ)= 1- D_0(0^circ). The extracted GT fractions, f_GT, are substantially larger than one would predict from β-decay matrix elements and the systematics of the (p,n) reaction on even-A nuclei. These results confirm earlier, model-dependent determinations of f_GT obtained from the (p,n) reaction on ^13C, ^15N and ^39K at other energies [2], [3], [4], indicating that considerable caution must be used when extracting B(GT) ...

α Particles from the Triton Bombardment of Li7, C12, and O16

Physical Review, 1965

... for his advice and help in performing the DWBA cal-culations and to Professor BL Cohen andPro... more

INVESTIGATION OF THE REACTION â´He(â´He,â´He) â´He* AT 64 MeV

The 4He(p, n)4Li∗ reaction at 100 and 200 MeV: Implications for the mass-four system and for astrophysics [Phys. Lett. B 368 (1996) 39]

Physics Letters B, 1996

... J. 429 (1994) 400. (1 II JM Ryan, Solar Physics with the Compton Gamma Ray Observatory, in: T... more

The 208-Pb(pol.p,pol.n)208-Bi Reaction at 135 MeV

This research was sponsored by the National Science Foundation Grant NSF PHY 87-14406

Proton and Neutron Inclusive Spectra and the Importance of the Single Nucleon-Nucleon Scattering Process

Physical Review Letters, 1981

ABSTRACT

ρ0Production and Possible Modification inAu+Auandp+pCollisions atsNN=200 GeV

Physical Review Letters, 2004

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Gamow-Teller and M 1 strength in the S 32 (p,n ) 32 Cl reaction at 135 MeV

Physical Review C, 1987

The S(p,n) Cl reaction was studied at 135 MeV by the time-of-flight technique. The overall energy... more The S(p,n) Cl reaction was studied at 135 MeV by the time-of-flight technique. The overall energy resolution obtained was about 270 kev. The forward-angle spectra are dominated by the excitation of 1+ states with characteristic AL =0 angular distributions peaked at 0. The 1+ spectrum is described well by distorted-wave Born approximation calculations with full S-D shellmodel wave functions and a normalization factor of 0.60. The strengths of the 1+ excitations are interpreted as being equivalent to Gamow-Teller strengths excited in beta decay. The (p, n) cross sections are converted to reduced transition probabilities, 8(GT), by means of a "universal" relationship obtained from other nuclei where analog beta decay measurements are available. The general distribution and total strength so obtained are represented well by full S-D shell-model calculations with Gamow-Teller matrix elements adjusted to reproduce the strengths of Garnow-Teller beta decays of S-D shell nuclei. The 1+ (p, n) cross sections are interpreted also in terms of magnetic-dipole (Ml) strength and compared with inelastic-electron scattering measurements of such strength in S. The strength observed in individual states is seen to vary considerably between the two reactions; these diff'erences are ascribed to orbital-current contributions in the electron-scattering reaction not present in the (p, n) reaction. The (p, n) measurements extend to higher excitation energies than the electron-scattering measurements.

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Identified particle elliptic flow in Au plus Au collisions at root s(NN)=130 GeV

Physical Review Letters, 2001

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ϕ meson production in Au+Au and p+p collisions at sNN=200GeV

Physics Letters B, 2005

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Measurements ofGEn/GMnfrom theH2(e→,e′n→)H1Reaction toQ2=1.45(GeV/c)2

Physical Review Letters, 2003

We report new measurements of the ratio of the electric form factor to the magnetic form factor o... more We report new measurements of the ratio of the electric form factor to the magnetic form factor of the neutron, G n E /G n M , obtained via recoil polarimetry from the quasielastic 2 H(e, e ′ n) 1 H reaction at Q 2 values of 0.45, 1.13, and 1.45 (GeV/c) 2 with relative statistical uncertainties of 7.6 and 8.4% at the two higher Q 2 points, which were not reached previously via polarization measurements. Scale and systematic uncertainties are small.

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Dynamics of the16O(e,e′p)Reaction at High Missing Energies

Physical Review Letters, 2001

The reaction dynamics of the 16 O(e, e ′ p) cross section at high missing energies

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