Edward Brash - Academia.edu (original) (raw)
Papers by Edward Brash
Nuclear Physics A, 1994
Studies of the production of the Delta resonance in hadronic charge exchange reactions show a shi... more Studies of the production of the Delta resonance in hadronic charge exchange reactions show a shift in the Delta peak position. Measurements looking also at the Delta decay products give some evidence for coherent pion production. We have recently completed a new measurement of the 12C(p,n) reaction leading to the Delta resonance, including a higher resolution coincidence measurement of decay
Nuclear Physics A, 2001
ABSTRACT
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 1998
We have developed an apparatus that can polarize muonic 3He and detect the triton from the reacti... more We have developed an apparatus that can polarize muonic 3He and detect the triton from the reaction μ− + 3He → ν + 3H. With this apparatus, we have measured the vector analyzing power of the reaction. This technique promises to provide a good test of QCD.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 1994
An adiabatic spin rotator has been constructed for use with the TRIUMF optically pumped polarized... more An adiabatic spin rotator has been constructed for use with the TRIUMF optically pumped polarized 3 He target. It consists of two orthogonal pairs of Helmholtz coils allowing adiabatic rotation of the 3 He spin into any arbitrary direction. Thus, the target may be polarized alternately in the sideways, longitudinal, and normal directions allowing measurements of complete sets of spin observables in nuclear scattering experiments during a single experimental run. Recently the system was used to measure all parity-allowed spin correlation observables A 00 , i in 3 He(p, p) elastic scattering at 200 and 500 MeV. The system permits reasonably rapid spin reversals (30 s) with minimal polarization losses (< 1 X 10-5 per spin reversal). This allows the target spin to be reversed frequently during an experimental run thus reducing systematic uncertainties from variations in the response of other components in the experimental setup
AIP Conference Proceedings, 1993
AIP Conference Proceedings, 1995
Asymmetries, Ay, for π+ elastic scattering from polarized 3He were measured in the P33 resonance ... more Asymmetries, Ay, for π+ elastic scattering from polarized 3He were measured in the P33 resonance region, where the π-nucleon force is strongly energy and isospin dependent. Preliminary results at energies of 142 and 180 MeV show large positive Ay near 90°, shifted to larger angles than predicted. At angles near 50° there is evidence for negative asymmetries of about −0.2
AIP Conference Proceedings, 1992
Polarized 3He targets suitable for experiments with a variety of primary and secondary beams have... more Polarized 3He targets suitable for experiments with a variety of primary and secondary beams have been developed using the method of optical pumping of Rb and polarization transfer by spin exchange collisions. Results obtained with these targets include: i) spin-momentum correlations of nucleons probed by 3He(p,2p) and (p,pn) knockout reactions at Ep=220 and 290 MeV; ii) spin-dependent amplitudes for elastic
Physical Review C, 1994
We have measured cross sections and analyzing powers for pi+ and pi- elastic scattering from a po... more We have measured cross sections and analyzing powers for pi+ and pi- elastic scattering from a polarized 3He target at Tpi=100 MeV. Measurements have been made over an angular range of 60° to 110° which extends over the region of the cross section minimum where spin effects in pi-nucleus scattering are predicted to be largest. This is evident from the
Physical Review Letters, Mar 4, 2002
The ratio of the electric and magnetic form factors of the proton, G{sub E{sub p}}/G{sub M{sub p}... more The ratio of the electric and magnetic form factors of the proton, G{sub E{sub p}}/G{sub M{sub p}}, was measured at the Thomas Jefferson National Accelerator Facility (JLab) using the recoil polarization technique. The ratio of the form factors is directly proportional to the ratio of the transverse to longitudinal components of the polarization of the recoil proton in the elastic {rvec e}p {yields} e{sup {rvec p}} reaction. The new data presented in this article span the range 3.5 < Q{sup 2} < 5.6 GeV{sup 2} and are well described by a linear Q{sup 2} fit. Also, the ratio {radical}Q{sup 2} F{sub 2{sub p}}/F{sub 1{sub p}} reaches a constant value above Q{sup 2} = 2 GeV{sup 2}.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 1997
We describe a device used in experiment 1231 at LAMPF and in e683 at TRIUMF to study the spin dep... more We describe a device used in experiment 1231 at LAMPF and in e683 at TRIUMF to study the spin dependence of the reaction μ− + 3He → 3H + vμ. In order to study the spin dependence, we needed to form and polarize muonic 3He and in the same volume detect the 1.9 MeV tritons created in the reaction. Furthermore,
This paper describes the fist measurement of spin observables in nuclear muon capture by 3He. The... more This paper describes the fist measurement of spin observables in nuclear muon capture by 3He. The sensitivity of spin observables to the pseudoscalar coupling is described.
The first (e,e'p) polarization transfer measurements on a nucleus heavier than deuterium have... more The first (e,e'p) polarization transfer measurements on a nucleus heavier than deuterium have been carried out at Jefferson Laboratory. Transverse and longitudinal components of the polarization of protons ejected in the reaction 16O(e,e'p) were measured in quasielastic perpendicular kinematics at a Q^2 of 0.8 (GeV/c)^2. The data are in good agreement with state of the art calculations, but do not exclude possible changes in the ratio of the electric to magnetic form factors of the nucleon in the nuclear medium at the level of recent theoretical predictions.
Physical Review C, 2015
Background: Measurements of forward exclusive meson production at different squared four-momenta ... more Background: Measurements of forward exclusive meson production at different squared four-momenta of the exchanged virtual photon, Q 2 , and at different four-momentum transfer, t, can be used to probe QCD's transition from meson-nucleon degrees of freedom at long distances to quark-gluon degrees of freedom at short scales. Ratios of separated response functions in π − and π + electroproduction are particularly informative. The ratio for transverse photons may allow this transition to be more easily observed, while the ratio for longitudinal photons provides a crucial verification of the assumed pole dominance, needed for reliable extraction of the pion form factor from electroproduction data.
The sixth conference on the intersections of particle and nuclear physcis, 1997
The focal plane polarimeter FPP for Hall A at the Thomas Jefferson National Accelerator Facility ... more The focal plane polarimeter FPP for Hall A at the Thomas Jefferson National Accelerator Facility TJNAF is ready for experiments. The ability to calibrate the FPP on-site using elastic scattering of polarized electrons from an unpolarized hydrogen target is demonstrated. The ratio of the proton electric form factor to its magnetic form factor has been measured at Q 2 = 0:810 GeV=c 2 .
FEW-BODY PROBLEMS IN PHYSICS - Proceedings of the 3rd Asia-Pacific Conference, 2007
Physical Review Letters, 2007
Physical Review C, 2005
The ratio of the proton elastic electromagnetic form factors, GEp/GMp, was obtained by measuring ... more The ratio of the proton elastic electromagnetic form factors, GEp/GMp, was obtained by measuring Pt and P ℓ , the transverse and longitudinal recoil proton polarization components, respectively, for the elastic ep → e p reaction in the four-momentum transfer squared range of 0.5 to 3.5 GeV 2. In the single-photon exchange approximation, the ratio GEp/GMp is directly proportional to the ratio Pt/P ℓ. The simultaneous measurement of Pt and P ℓ in a polarimeter reduces systematic uncertainties. The results for the ratio GEp/GMp show a systematic decrease with increasing Q 2 , indicating for the first time a definite difference in the distribution of charge and magnetization in the proton. The data have been re-analyzed and systematic uncertainties have become significantly smaller than previously published results.
Physical Review C, 2007
The data analysis for the reaction 1 H(e, e ′ π +)n, which was used to determine values for the c... more The data analysis for the reaction 1 H(e, e ′ π +)n, which was used to determine values for the charged pion form factor Fπ for values of Q 2 =0.6-1.6 GeV 2 , has been repeated with careful inspection of all steps and special attention to systematic uncertainties. Also the method used to extract Fπ from the measured longitudinal cross section was critically reconsidered. Final values for the separated longitudinal and transverse cross sections and the extracted values of Fπ are presented.
Physical Review C, 1999
A large reduction of the ρ 0 mass in the nuclear medium is reported, inferred from dipion photopr... more A large reduction of the ρ 0 mass in the nuclear medium is reported, inferred from dipion photoproduction spectra in the 1 GeV region, for the reaction 3 He(γ,π + π −)X with a 10% duty factor tagged-photon beam and the TAGX multi-particle spectrometer. The energy range covered (800≤Eγ ≤1120 MeV) lies mostly below the free ρ 0 production threshold, a region which is believed sensitive to modifications of light vector-meson properties at nuclear-matter densities. The ρ 0 masses extracted from the MC fitting of the data, m * ρ 0 = 642±40, 669±32, and 682±56 MeV/c 2 for Eγ in the 800-880, 880-960, and 960-1040 MeV regions respectively, are independently corroborated by a measured, assumption-free, kinematical observable. This mass shift, far exceeding current mean
Physical Review C, 1999
ABSTRACT
Nuclear Physics A, 1994
Studies of the production of the Delta resonance in hadronic charge exchange reactions show a shi... more Studies of the production of the Delta resonance in hadronic charge exchange reactions show a shift in the Delta peak position. Measurements looking also at the Delta decay products give some evidence for coherent pion production. We have recently completed a new measurement of the 12C(p,n) reaction leading to the Delta resonance, including a higher resolution coincidence measurement of decay
Nuclear Physics A, 2001
ABSTRACT
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 1998
We have developed an apparatus that can polarize muonic 3He and detect the triton from the reacti... more We have developed an apparatus that can polarize muonic 3He and detect the triton from the reaction μ− + 3He → ν + 3H. With this apparatus, we have measured the vector analyzing power of the reaction. This technique promises to provide a good test of QCD.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 1994
An adiabatic spin rotator has been constructed for use with the TRIUMF optically pumped polarized... more An adiabatic spin rotator has been constructed for use with the TRIUMF optically pumped polarized 3 He target. It consists of two orthogonal pairs of Helmholtz coils allowing adiabatic rotation of the 3 He spin into any arbitrary direction. Thus, the target may be polarized alternately in the sideways, longitudinal, and normal directions allowing measurements of complete sets of spin observables in nuclear scattering experiments during a single experimental run. Recently the system was used to measure all parity-allowed spin correlation observables A 00 , i in 3 He(p, p) elastic scattering at 200 and 500 MeV. The system permits reasonably rapid spin reversals (30 s) with minimal polarization losses (< 1 X 10-5 per spin reversal). This allows the target spin to be reversed frequently during an experimental run thus reducing systematic uncertainties from variations in the response of other components in the experimental setup
AIP Conference Proceedings, 1993
AIP Conference Proceedings, 1995
Asymmetries, Ay, for π+ elastic scattering from polarized 3He were measured in the P33 resonance ... more Asymmetries, Ay, for π+ elastic scattering from polarized 3He were measured in the P33 resonance region, where the π-nucleon force is strongly energy and isospin dependent. Preliminary results at energies of 142 and 180 MeV show large positive Ay near 90°, shifted to larger angles than predicted. At angles near 50° there is evidence for negative asymmetries of about −0.2
AIP Conference Proceedings, 1992
Polarized 3He targets suitable for experiments with a variety of primary and secondary beams have... more Polarized 3He targets suitable for experiments with a variety of primary and secondary beams have been developed using the method of optical pumping of Rb and polarization transfer by spin exchange collisions. Results obtained with these targets include: i) spin-momentum correlations of nucleons probed by 3He(p,2p) and (p,pn) knockout reactions at Ep=220 and 290 MeV; ii) spin-dependent amplitudes for elastic
Physical Review C, 1994
We have measured cross sections and analyzing powers for pi+ and pi- elastic scattering from a po... more We have measured cross sections and analyzing powers for pi+ and pi- elastic scattering from a polarized 3He target at Tpi=100 MeV. Measurements have been made over an angular range of 60° to 110° which extends over the region of the cross section minimum where spin effects in pi-nucleus scattering are predicted to be largest. This is evident from the
Physical Review Letters, Mar 4, 2002
The ratio of the electric and magnetic form factors of the proton, G{sub E{sub p}}/G{sub M{sub p}... more The ratio of the electric and magnetic form factors of the proton, G{sub E{sub p}}/G{sub M{sub p}}, was measured at the Thomas Jefferson National Accelerator Facility (JLab) using the recoil polarization technique. The ratio of the form factors is directly proportional to the ratio of the transverse to longitudinal components of the polarization of the recoil proton in the elastic {rvec e}p {yields} e{sup {rvec p}} reaction. The new data presented in this article span the range 3.5 < Q{sup 2} < 5.6 GeV{sup 2} and are well described by a linear Q{sup 2} fit. Also, the ratio {radical}Q{sup 2} F{sub 2{sub p}}/F{sub 1{sub p}} reaches a constant value above Q{sup 2} = 2 GeV{sup 2}.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 1997
We describe a device used in experiment 1231 at LAMPF and in e683 at TRIUMF to study the spin dep... more We describe a device used in experiment 1231 at LAMPF and in e683 at TRIUMF to study the spin dependence of the reaction μ− + 3He → 3H + vμ. In order to study the spin dependence, we needed to form and polarize muonic 3He and in the same volume detect the 1.9 MeV tritons created in the reaction. Furthermore,
This paper describes the fist measurement of spin observables in nuclear muon capture by 3He. The... more This paper describes the fist measurement of spin observables in nuclear muon capture by 3He. The sensitivity of spin observables to the pseudoscalar coupling is described.
The first (e,e'p) polarization transfer measurements on a nucleus heavier than deuterium have... more The first (e,e'p) polarization transfer measurements on a nucleus heavier than deuterium have been carried out at Jefferson Laboratory. Transverse and longitudinal components of the polarization of protons ejected in the reaction 16O(e,e'p) were measured in quasielastic perpendicular kinematics at a Q^2 of 0.8 (GeV/c)^2. The data are in good agreement with state of the art calculations, but do not exclude possible changes in the ratio of the electric to magnetic form factors of the nucleon in the nuclear medium at the level of recent theoretical predictions.
Physical Review C, 2015
Background: Measurements of forward exclusive meson production at different squared four-momenta ... more Background: Measurements of forward exclusive meson production at different squared four-momenta of the exchanged virtual photon, Q 2 , and at different four-momentum transfer, t, can be used to probe QCD's transition from meson-nucleon degrees of freedom at long distances to quark-gluon degrees of freedom at short scales. Ratios of separated response functions in π − and π + electroproduction are particularly informative. The ratio for transverse photons may allow this transition to be more easily observed, while the ratio for longitudinal photons provides a crucial verification of the assumed pole dominance, needed for reliable extraction of the pion form factor from electroproduction data.
The sixth conference on the intersections of particle and nuclear physcis, 1997
The focal plane polarimeter FPP for Hall A at the Thomas Jefferson National Accelerator Facility ... more The focal plane polarimeter FPP for Hall A at the Thomas Jefferson National Accelerator Facility TJNAF is ready for experiments. The ability to calibrate the FPP on-site using elastic scattering of polarized electrons from an unpolarized hydrogen target is demonstrated. The ratio of the proton electric form factor to its magnetic form factor has been measured at Q 2 = 0:810 GeV=c 2 .
FEW-BODY PROBLEMS IN PHYSICS - Proceedings of the 3rd Asia-Pacific Conference, 2007
Physical Review Letters, 2007
Physical Review C, 2005
The ratio of the proton elastic electromagnetic form factors, GEp/GMp, was obtained by measuring ... more The ratio of the proton elastic electromagnetic form factors, GEp/GMp, was obtained by measuring Pt and P ℓ , the transverse and longitudinal recoil proton polarization components, respectively, for the elastic ep → e p reaction in the four-momentum transfer squared range of 0.5 to 3.5 GeV 2. In the single-photon exchange approximation, the ratio GEp/GMp is directly proportional to the ratio Pt/P ℓ. The simultaneous measurement of Pt and P ℓ in a polarimeter reduces systematic uncertainties. The results for the ratio GEp/GMp show a systematic decrease with increasing Q 2 , indicating for the first time a definite difference in the distribution of charge and magnetization in the proton. The data have been re-analyzed and systematic uncertainties have become significantly smaller than previously published results.
Physical Review C, 2007
The data analysis for the reaction 1 H(e, e ′ π +)n, which was used to determine values for the c... more The data analysis for the reaction 1 H(e, e ′ π +)n, which was used to determine values for the charged pion form factor Fπ for values of Q 2 =0.6-1.6 GeV 2 , has been repeated with careful inspection of all steps and special attention to systematic uncertainties. Also the method used to extract Fπ from the measured longitudinal cross section was critically reconsidered. Final values for the separated longitudinal and transverse cross sections and the extracted values of Fπ are presented.
Physical Review C, 1999
A large reduction of the ρ 0 mass in the nuclear medium is reported, inferred from dipion photopr... more A large reduction of the ρ 0 mass in the nuclear medium is reported, inferred from dipion photoproduction spectra in the 1 GeV region, for the reaction 3 He(γ,π + π −)X with a 10% duty factor tagged-photon beam and the TAGX multi-particle spectrometer. The energy range covered (800≤Eγ ≤1120 MeV) lies mostly below the free ρ 0 production threshold, a region which is believed sensitive to modifications of light vector-meson properties at nuclear-matter densities. The ρ 0 masses extracted from the MC fitting of the data, m * ρ 0 = 642±40, 669±32, and 682±56 MeV/c 2 for Eγ in the 800-880, 880-960, and 960-1040 MeV regions respectively, are independently corroborated by a measured, assumption-free, kinematical observable. This mass shift, far exceeding current mean
Physical Review C, 1999
ABSTRACT