R. Fatemi

-Measurement of the proton's electric to magnetic form factor ratio from 1H(over -->)(e(over -->),e'p).

We report the first precision measurement of the proton electric to magnetic form factor ratio from spin-dependent elastic scattering of longitudinally polarized electrons from a polarized hydrogen internal gas target. The measurement was performed at the MIT-Bates South Hall Ring over a range of four-momentum transfer squared Q2 from 0.15 to 0.65 (GeV/c)(2). Significantly improved results on the proton electric and magnetic form factors are obtained in combination with existing cross-section data on elastic electron-proton scattering in the same Q2 region.

Measurement of the proton's electric to magnetic form factor ratio from H→1(e→,e′p)

We report the first precision measurement of the proton electric to magnetic form factor ratio from spin-dependent elastic scattering of longitudinally polarized electrons from a polarized hydrogen internal gas target. The measurement was performed at the MIT-Bates South Hall Ring over a range of four-momentum transfer squared Q2 from 0.15 to 0.65 (GeV/c)(2). Significantly improved results on the proton electric and magnetic form factors are obtained in combination with existing cross-section data on elastic electron-proton scattering in the same Q2 region.

The Charge Form Factor of the Neutron at Low Momentum Transfer from the H-2-polarized (e-polarized, e-prime n) p Reaction

We report new measurements of the neutron charge form factor at low momentum transfer using quasielastic electrodisintegration of the deuteron. Longitudinally polarized electrons at an energy of 850 MeV were scattered from an isotopically pure, highly polarized deuterium gas target. The scattered electrons and coincident neutrons were measured by the Bates Large Acceptance Spectrometer Toroid (BLAST) detector. The neutron form factor ratio GEn/GMn was extracted from the beam-target vector asymmetry AedV at four-momentum transfers Q2=0.14, 0.20, 0.29, and 0.42 (GeV/c)2.

The Charge Form Factor of the Neutron at Low Momentum Transfer from the

We report new measurements of the neutron charge form factor at low momentum transfer using quasielastic electrodisintegration of the deuteron. Longitudinally polarized electrons at an energy of 850 MeV were scattered from an isotopically pure, highly polarized deuterium gas target. The scattered electrons and coincident neutrons were measured by the Bates Large Acceptance Spectrometer Toroid (BLAST) detector. The neutron form factor ratio GEn/GMn was extracted from the beam-target vector asymmetry AedV at four-momentum transfers Q2=0.14, 0.20, 0.29, and 0.42 (GeV/c)2.

^{2}\vec{\rm H}(\vec{\rm e},{\rm e}'{\rm n}){\rm p}

The roles played by mesons in the electromagnetic form factors of the nucleon are explored using as a basis a model containing vector mesons with coupling to the continuum together with the asymptotic Q 2 behavior of perturbative QCD. Specifically, the vector dominance model (GKex) developed by E. L. Lomon is employed, as it is known to be very successful in representing the existing high-quality data published to date. An analysis is made of the experimental uncertainties present when the differences between the GKex model and the data are expanded in orthonormal basis functions. A main motivation for the present study is to provide insight into how the various ingredients in this model yield the measured behavior, including discussions of when dipole form factors are to be expected or not, of which mesons are the major contributors, for instance, at low Q 2 or large distances, and of what effects are predicted from coupling to the continuum. Such insights are first discussed in momentum space, followed by an analysis of how different and potentially useful information emerges when both the experimental and theoretical electric form factors are Fourier transformed to coordinate space. While these Fourier transforms should not be interpreted as “charge distributions,” nevertheless the roles played by the various mesons, especially those which are dominant at large or small distance scales, can be explored via such experiment‐theory comparisons.

Reaction

We report measurements of Υ meson production in p + p, d + Au, and Au + Au collisions using the STAR ndetector at RHIC. We compare the Υ yield to the measured cross section in p + p collisions in order to nquantify any modifications of the yield in cold nuclear matter using d+Au data and in hot nuclear matter nusing Au+Au data separated into three centrality classes. Our p+ p measurement is based on three times nthe statistics of our previous result. We obtain a nuclear modification factor for Υ (1S + 2S + 3S) in the nrapidity range |y| < 1 in d + Au collisions of RdAu = 0.79 ± 0.24(stat.) ± 0.03(syst.) ± 0.10(p + p syst.). nA comparison with models including shadowing and initial state parton energy loss indicates the npresence of additional cold-nuclear matter suppression. Similarly, in the top 10% most-central Au + Au ncollisions, we measure a nuclear modification factor of R A A = 0.49 ± 0.1(stat.) ± 0.02(syst.) ± 0.06(p + p syst.), which is a larger suppression factor than that seen in cold nuclear matter. Our results are nconsistent with complete suppression of excited-state Υ mesons in Au + Au collisions. The additional nsuppression in Au + Au is consistent with the level expected in model calculations that include the npresence of a hot, deconfined Quark–Gluon Plasma. However, understanding the suppression seen in nd + Au is still needed before any definitive statements about the nature of the suppression in Au + Au ncan be made

Role of mesons in the electromagnetic form factors of the nucleon

This contribution presents the most recent mid-rapidity inclusive jet results from 3 pb 1 of data collected from longitudinally polarized proton collisions at p s = 200 GeV during the 2005 RHIC run. The inclusive jet asymmetry, ALL, with it’s increased transverse momentum range and precision, provides strong constraints on the gluon helicity distribution when compared with existing next-to-leading order perturbative QCD evaluations. Measurements of the partonic helicity distribution functions in the proton are essential for a complete understanding of the long range, non-perturbative properties of Quantum Chromodynamics (QCD). Three decades of polarized lepton-nucleon deep-inelastic-scattering (DIS) experiments [2] have shown that the probability for a quark spin to be aligned with the spin of the parent proton is 25%. Conservation of angular momentum requires the quark ( Q) and gluon ( G) total spin and orbital angular momentum (LQ + LG) within the proton to sum to ~ , motivating investigations into the size of the remaining components of the sum rule. Traditional fixed-target DIS experiments couple to the gluon distributions only at next-to-leading order (NLO), providing limited constraints on G[3][4]. As a result, several programs designed to directly access G have been established and have produced initial results [5][6][7][8][9]. Measurements of higher statistical precision and broader Q 2 reach continue to be recorded and released [10]. During the 2005 RHIC run STAR sampled 3 pb 1 of proton collisions with an average longitudinal beam polarization of 50% and p s = 200 GeV. As a result, the inclusive jet asymmetry measurement, spanning a transverse momentum (pT ) range of 5 32 GeV, represents the most precise measurement over the largestpT range to date. The Solenoidal Tracker at RHIC (STAR) Collaboration utilizes the polarized proton beam provided by the Relativistic Heavy Ion Collider (RHIC) to study final state interactions resulting from quark-quark (qq), quark-gluon (qg) and gluon-gluon (gg) scattering. STAR’s large acceptance facilitates jet reconstruction, allowing for a nearly fragmentation independent reconstruction of the partonic characteristics inside the proton. The inclusive jet double spin asymmetry ALL, ALL = 1

Suppression of Υ production in d + Au and Au + Au collisions at √ s NN = 200 GeV

An electron‐proton/ion collider facility (eRHIC) is under consideration at Brookhaven National Laboratory. This high energy, high intensity polarized electron/positron beam facility is designed to provide collisions with the existing RHIC heavy ion and polarized proton beams. This upgraded facility will require the design and construction of detectors, optimized for the reconstruction of the underlying e‐p/ion event kinematics and tailored to the constraints of the interaction region. Two independent and complimentary detector designs have been discussed by the MIT and MPI‐Munich groups respectively. Design details, simulation results and primary physics goals will be discussed for each proposal.