B. D. Anderson

Improved Predictions of Neutron Detection Efficiency for Hydrocarbon Scintillators from 1 MeV to About 300 MeV

Abstract Several improvements have been made to the Monte-Carlo neutron detector efficiency code of Stanton to provide improved agreement with several different detector efficiency measurements.The impovements include a re-adjustment of the inelastic cross sections for neutron-induced reactions on carbon, adoption of new light-response functions, use of relativistic kinematics, and exact determination of light deposited by escaping charged particles. The improved calculations agree with measured efficiences for both plastic and liquid hydrocarbon scintillators for neutron energies from 1 MeV to about 300 MeV and for detector thresholds from about 0.1 MeV to 22 MeV equivalent-electron energies; in most cases the agreement is good to within a few percent.

Probing Cold Dense Nuclear Matter

The protons and neutrons in a nucleus can form strongly correlated nucleon pairs. Scattering experiments, in which a proton is knocked out of the nucleus with high-momentum transfer and high missing momentum, show that in carbon-12 the neutron-proton pairs are nearly 20 times as prevalent as proton-proton pairs and, by inference, neutron-neutron pairs. This difference between the types of pairs is due to the nature of the strong force and has implications for understanding cold dense nuclear systems such as neutron stars.

The STAR endcap electromagnetic calorimeter

The STAR endcap electromagnetic calorimeter will provide full azimuthal coverage for high-pT photons, electrons and electromagnetically decaying mesons over the pseudorapidity range 1.086⩽η⩽2.00. It includes a scintillating-strip shower-maximum detector to provide π0/γ discrimination and preshower and postshower layers to aid in distinguishing between electrons and charged hadrons. The triggering capabilities and coverage it offers are crucial for much of the spin physics program to be carried out in polarized proton–proton collisions.

Large volume neutron detectors with subnanosecond time dispersions

Abstract Design criteria and performance characteristics are described for large-volume (13.1 1 to 118 1) mean-timed plastic-scintillator detectors for neutrons from ≈2 MeV to 2 GeV. Detectors were constructed in six sizes (all 0.102 m thick) from 0.126 m × 1.016 m × 0.102 m to 0.762 m × 1.524 m × 0.102 m. Overall energy resolutions of 230 keV for 80 MeV neutrons, 320 keV for 133 MeV neutrons, and 440 keV for 157 MeV neutrons were achieved in time-of-flight experiments with flight paths of 76, 68, and 91 m, respectively. The detectors have pulse-height responses uniform to ±5% except close to the ends, position resolutions less than 5 cm, and intrinsic time dispersions less than 400 ps. Typical neutron detection efficiencies are 20% for 20 MeV neutrons at a pulse-height threshold of 2 MeV equivalent-electron energy (MeV ee) and 3.5% for 200 MeV neutrons at a pulse-height threshold of 50 MeV ee.

K(892)* resonance production in Au+Au and p+p collisions at sqrt(sNN) = 200 GeV at RHIC

Author(s): Adams, J.; Aggarwal, M.M.; Ahammed, Z.; Amonett, J.; Anderson, B.D.; Arkhipkin, D.; Averichev, G.S.; Badyal, S.K.; Bai, Y.; Balewski, J.; Barannikova, O.; Barnby, L.S.; Baudot, J.; Bekele, S.; Belaga, V.V.; Bellwied, R.; Berger, J.; Bezverkhny, B.I.; Bharadwaj, S.; Bhasin, A.; Bhati, A.K.; Bhatia, V.S.; Bichsel, H.; Billmeier, A.; Bland, L.C.; Blyth, C.O.; Bonner, B.E.; Botje, M.; Boucham, A.; Brandin, A.V.; Bravar, A.; Bystersky, M.; Cadman, R.V.; Cai, X.Z.; Caines, H.; Calderon de la Barca Sanchez, M.; Castillo, J.; Cebra, D.; Chajecki, Z.; Chaloupka, P.; Chattopadhyay, S.; Chen, H.F.; Chen, Y.; Cheng, J.; Cherney, M.; Chikanian, A.; Christie, W.; Coffin, J.P.; Cormier, T.M.; Cramer, J.G.; Crawford, H.J.; Das, D.; Das, S.; de Moura, M.M.; Derevschikov, A.A.; Didenko, L.; Dietel, T.; Dogra, S.M.; Dong, W.J.; Dong, X.; Draper, J.E.; Du, F.; Dubey, A.K.; Dunin, V.B.; Dunlop, J.C.; Dutta Mazumdar, M.R.; Eckardt, V.; Edwards, W.R.; Efimov, L.G.; Emelianov, V.; Engelage, J.; Eppley, G.; Erazmus, B.; Estienne, M.; Fachini, P.; Faivre, J.; Fatemi, R.; Fedorisin, J.; Filimonov, K.; Filip, P.; Finch, E.; Fine, V.; Fisyak, Y.; Fomenko, K.; Fu, J.The short-lived K(892)* resonance provides an efficient tool to probe properties of the hot and dense medium produced in relativistic heavy-ion collisions. We report measurements of K* in root s(NN)=200 GeV Au+Au and p+p collisions reconstructed via its hadronic decay channels K(892)*(0)-> K pi and K(892)*(+/-)-> K(S)(0)pi(+/-) using the STAR detector at the Relativistic Heavy Ion Collider at Brookhaven National Laboratory. The K*(0) mass has been studied as a function of p(T) in minimum bias p+p and central Au+Au collisions. The K(*) p(T) spectra for minimum bias p+p interactions and for Au+Au collisions in different centralities are presented. The K*/K yield ratios for all centralities in Au+Au collisions are found to be significantly lower than the ratio in minimum bias p+p collisions, indicating the importance of hadronic interactions between chemical and kinetic freeze-outs. A significant nonzero K*(0) elliptic flow (v(2)) is observed in Au+Au collisions and is compared to the K(S)(0) and Lambda v(2). The nuclear modification factor of K* at intermediate p(T) is similar to that of K(S)(0) but different from Lambda. This establishes a baryon-meson effect over a mass effect in the particle production at intermediate p(T) (2 < p(T)<= 4 GeV/c).

Gamow-Teller and spin-dipole strength in the 40,48Ca(p,n) reactions at 135 MeV

Abstract Spin-flip probabilities for 48Ca( p n )48Sc reveal that at 0° the apparent continuum under and adjacent to the Gamow-Teller giant resonance is also primarily 1+ strength. A comparison of 40Ca[ p n )40Sc and 48Ca( p n )48Sc shows no discernable signature of Gamow-Teller strength in the region −30 > Q(MeV) >−45. The spin-flip component of the dipole resonance for 40Ca is broader than the non-spin-flip component.

A high-performance polarimeter for medium-energy neutrons

Abstract 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.

Electron capture strength for Ni 60 , 62 and Ni 58 , 60 , 62 , 64 ( p , n ) Cu 58 , 60 , 62 , 64 reactions at 134.3 MeV

Background: The strength of electron capture for medium mass nuclei has a significant effect on the evolution of supernovae. There is insufficient knowledge of these strengths and very little data for important radioactive nuclei. Purpose: Determine whether it is feasible to obtain EC strength from studies of T{sub o}+1 excitations in (p, n) reactions, and whether this might yield information for radioactive nuclei. Methods: Cross sections for the {sup 58,60,62,64}Ni(p, n){sup 58,60,62,64}Cu reactions were measured over the angular range of 0.3 deg. to 11.6 deg. at 134.3 MeV using the IUCF neutron time-of-flight facility. Results: The T{sub o}+1 excitations in {sup 60,62}Ni were identified by comparison with inelastic proton scattering spectra, their B(GT) were extracted, and the corresponding electron capture rates in supernovae were calculated. Data from the TRIUMF (n, p) experiments at 198 MeV were reanalyzed; the electron capture rates for the reanalyzed data are in moderately good agreement with the higher resolution (p, n) results, but differ in detail. The possibility of future measurements with radioactive nuclei was considered. Conclusions: It may be possible to obtain low-lying electron capture strength for radioactive nuclei by studying (p, n) reactions in inverse kinematics.

12C(p,n)12N reaction at 135 MeV.

We report observations from the (p,n) reaction on

Measurement of the polarization of a pulsed electron beam with a Møller polarimeter in the coincidence mode

^{12}\mathrm{C}