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1994

University of Massachusetts Amherst

Articles 1 - 10 of 10

Full-Text Articles in Physics

Measurements Of The (E,E’Pπ-) Reaction On Nuclei In The Nucleon Resonance Region, L Elouadrhiri, R A. Miskimen, J Button-Shafer, P Degtyarenko,, Gerald Alvin Peterson, S Shuvalov, K Wang Nov 1994

Measurements Of The (E,E’Pπ-) Reaction On Nuclei In The Nucleon Resonance Region, L Elouadrhiri, R A. Miskimen, J Button-Shafer, P Degtyarenko,, Gerald Alvin Peterson, S Shuvalov, K Wang

Gerald Alvin Peterson

Nucleon resonances beyond the Δ(1232) have been observed in complex nuclei. Measurements of the (e,e’pπ-) reaction, at an incident energy of 14.5 GeV with 1.1 GeV


Measurements Of The Electric And Magnetic Form Factors Of The Proton From Q2=1.75 To 8.83 (Gev/C)2, L Andivahis, R S. Hicks, R A. Miskimen, Gerald Alvin Peterson, S Rokni Nov 1994

Measurements Of The Electric And Magnetic Form Factors Of The Proton From Q2=1.75 To 8.83 (Gev/C)2, L Andivahis, R S. Hicks, R A. Miskimen, Gerald Alvin Peterson, S Rokni

Gerald Alvin Peterson

The proton elastic form factors GEp(Q2) and GMp(Q2) have been extracted for Q2=1.75 to 8.83 (GeV/c)2 via a Rosenbluth separation to ep elastic cross section measurements in the angular range 13°≤θ≤90°. The Q2 range covered more than doubles that of the existing data. For Q2<4 >(GeV/c)2, where the data overlap with previous measurements, the total uncertainties have been reduced to < 14% in GEp and < 1.5% in GMp. Results for GEp(Q2) are consistent with the dipole fit GD(Q2)=(1+Q2/0.71)-2, while those for GMp(Q2)/μpGD(Q2) decrease smoothly from 1.05 to 0.92. Deviations from form factor scaling are observed up to 20%. The ratio Q2F2/F1 is observed to approach a constant value for Q2>3 (GeV/c)2. Comparisons are made to vector meson dominance, dimensional scaling, QCD sum rule, diquark, and constituent quark models, none of which fully characterize all the new ...


Multiple Hadron Production By 14.5 Gev Electron And Positron Scattering From Nuclear Targets, P V. Degtyarenko, J Button-Shafer, L Elouadrhiri, R A. Miskimen, Gerald Alvin Peterson, K Wang Aug 1994

Multiple Hadron Production By 14.5 Gev Electron And Positron Scattering From Nuclear Targets, P V. Degtyarenko, J Button-Shafer, L Elouadrhiri, R A. Miskimen, Gerald Alvin Peterson, K Wang

Gerald Alvin Peterson

Multiple proton and pion electroproduction from nuclei are studied. Final states including at least two protons produced by the interaction of 14.5 GeV electrons and positrons with light nuclei (mainly 12C and 16O) have been measured, and compared with analogous data from 40Ar. Scattered electrons and positrons were detected in the energy transfer range from 0.2 to 12.5 GeV, and four-momentum transfer squared range from 0.1 to 5.0 GeV2/c2. Phenomenological characteristics of the secondary hadron production cross sections such as temperature and velocity of the effective source of hadrons were found to be dependent ...


The Reactions Gamma-Gamma-]Wl(+)Wl(-) And Gamma-Gamma-]Z(L)Z(L) In Su(N) Strongly Interacting Theories, Jf Donoghue, T Torma Jan 1994

The Reactions Gamma-Gamma-]Wl(+)Wl(-) And Gamma-Gamma-]Z(L)Z(L) In Su(N) Strongly Interacting Theories, Jf Donoghue, T Torma

Physics Department Faculty Publication Series

In theories in which the parameters of the low energy theory are not unique, perhaps having different values in different domains of the universe as is possible in some inflationary models, the fermion masses would be distributed with respect to some weight. In such a situation the specifics of the fermion masses do not have a unique explanation, yet the weight provides the visible remnant of the structure of the underlying theory. This paper introduces this concept of a weight for the distribution of masses and provides a quantitative estimate of it from the observed quarks and leptons. The weight ...


Leading Quantum Correction To The Newtonian Potential, Jf Donoghue Jan 1994

Leading Quantum Correction To The Newtonian Potential, Jf Donoghue

Physics Department Faculty Publication Series

I argue that the leading quantum corrections, in powers of the energy or inverse powers of the distance, may be computed in quantum gravity through knowledge of only the low-energy structure of the theory. As an example, I calculate the leading quantum corrections to the Newtonian gravitational potential.


Light Quark Masses And Mixing Angles, John Donoghue Jan 1994

Light Quark Masses And Mixing Angles, John Donoghue

Physics Department Faculty Publication Series

I review the present state of our knowledge about the masses and weak mixing elements of the u, d, s quarks. This is the written version of lectures given in the 1993 Theoretical Advanced Study Institute (TASI).


Testing Cosmic Censorship With Black Hole Collisions, D Brill, G Horowitz, David Kastor, Jennie Traschen Jan 1994

Testing Cosmic Censorship With Black Hole Collisions, D Brill, G Horowitz, David Kastor, Jennie Traschen

Physics Department Faculty Publication Series

There exists an upper limit on the mass of black holes when the cosmological constant Λ is positive. We study the collision of two black holes whose total mass exceeds this limit. Our investigation is based on a recently discovered exact solution describing the collision of Q=M black holes with Λ>0. The global structure of this solution is analyzed. We find that if the total mass is less than the extremal limit, then the black holes coalesce. If it is greater, then a naked singularity forms to the future of a Cauchy horizon. However, the horizon is not ...


Supersymmetric Self-Gravitating Solitons, G Gibbons, David Kastor, L London, P Townsend, Jennie Traschen Jan 1994

Supersymmetric Self-Gravitating Solitons, G Gibbons, David Kastor, L London, P Townsend, Jennie Traschen

Physics Department Faculty Publication Series

We show that the “instantonic” soliton of five-dimensional Yang-Mills theory and the closely related BPS monopole of four-dimensional Yang-Mills/Higgs theory continue to be exact static, and stable, solutions of these field theories even after the inclusion of gravitational, electromagnetic and, in the four-dimensional case, dilatonic interactions, provided that certain non-minimal interactions are included. With the inclusion of these interactions, which would be required by supersymmetry, these exact self-gravitating solitons saturate a gravitational version of the Bogomol'nyi bound on the energy of an arbitrary field configuration.


Pair Creation Of Dilaton Black Holes, F Dowker, J Gauntlett, David Kastor, Jennie Traschen Jan 1994

Pair Creation Of Dilaton Black Holes, F Dowker, J Gauntlett, David Kastor, Jennie Traschen

Physics Department Faculty Publication Series

We consider dilaton gravity theories in four spacetime dimensions parametrized by a constant a, which controls the dilaton coupling, and construct new exact solutions. We first generalize the C metric of Einstein-Maxwell theory (a=0) to solutions corresponding to oppositely charged dilaton black holes undergoing uniform acceleration for general a. We next develop a solution-generating technique which allows us to ‘‘embed’’ the dilaton C metrics in magnetic dilaton Melvin backgrounds, thus generalizing the Ernst metric of Einstein-Maxwell theory. By adjusting the parameters appropriately, it is possible to eliminate the nodal singularities of the dilaton C metrics. For a<1 (but not for a≥1), it is possible to further restrict the parameters so that the dilaton Ernst solutions have a smooth Euclidean section with topology S2×S2-{pt}, corresponding to instantons describing the pair production of dilaton black holes in a magnetic field. A different restriction on the parameters leads to smooth instantons for all values of a with topology S2×openR2.


Dispersion-Relations And The Nucleon Polarizability, Br Holstein, Am Nathan Jan 1994

Dispersion-Relations And The Nucleon Polarizability, Br Holstein, Am Nathan

Physics Department Faculty Publication Series

Recent experimental results on the proton and neutron polarizabilities are examined from the point of view of backward dispersion relations. Results are found to be in reasonable agreement with the measured values. A rigorous relationship between the nucleon and pion polarizabilities is derived and shown to be in excellent agreement with several models.