73519332
RHIC Performance for FY10 200 GeV Au+Au Heavy Ion Run
Since the last successful RHIC Au+Au run in 2007 (Run-7), the RHIC experiments have made numerous detector improvements and upgrades. In order to benefit from the enhanced detector capabilities and to increase the yield of rare events in the acquired heavy ion data a significant increase in luminosity is essential. In Run-7 RHIC achieved an average store luminosity of = 12 × 10 cm−2 s−1 by operating with 103 bunches (out of 111 possible), and by squeezing to β∗ = 0.85 m. This year, Run-10, we achieved = 20 × 10 cm−2 s−1, which put us an order of magnitude above the RHIC design luminosity. To reach these luminosity levels we decreased β∗ to 0.75 m, operated with 111 bunches per ring, and reduced longitudinal and transverse emittances by means of bunched-beam stochastic cooling. In addition we introduced a lattice to suppress intra-beam scattering (IBS) in both RHIC rings, upgraded the RF control system, and separated transition crossing times in the two rings. We present an overview of the changes and the results of Run-10 performance.
56408435
Optimization of the AGS superconducting helical partial snake strength.
Two helical partial snakes, one super-conducting (a.k.a cold snake) and one normal conducting (a.k.a warm snake), have preserved the polarization of proton beam up to 65% in the Brookhaven Alternating Gradient Synchrotron (AGS) at the extraction energy from 85% at injection. In order to overcome spin resonances, stronger partial snakes would be required. However, the stronger the partial snake, the more the stable spin direction tilted producing a stronger horizontal intrinsic resonance. The balance between increasing the spin tune gap generated by the snakes and reducing the tilted stable spin direction has to be considered to maintain the polarization. Because the magnetic field of the warm snake has to be a constant, only the cold snake with a maximum 3T magnetic field can be varied to find out the optimum snake strength. This paper presents simulation results by spin tracking with different cold snake magnetic fields. Some experimental data are also analyzed.
118056950
The RHIC p‐Carbon CNI Polarimeter Upgrade For The Beam Polarization And Intensity Measurements
Proton polarization measurements in the AGS and RHIC (Relativistic Heavy Ion Collider at the beam energies 24–250 GeV) are based on proton‐carbon and proton‐proton elastic scattering in the Coulomb Nuclear Interference (CNI) region. Polarimeter operation in the scanning mode also gives polarization profile and beam intensity profile (beam emittance) measurements. Bunch by bunch emittance measurement is a very powerful tool for machine setup. Presently, the polarization and beam intensity profile measurements (in both vertical and horizontal planes) are restricted by the long target switching time and possible target destruction during this complicated motion. The RHIC polarimeters were operated near the limit of the counting rate for present silicon strip detectors. The ongoing polarimeter upgrade for the 2009 run will address all these problems. The upgrade should allow significant reduction of the polarization measurement errors by making feasible the complete polarization measurements, which includes p...
117489591
EXPERIMENTAL EFFECTS OF ORBIT ON POLARIZATION LOSS IN RHIC
We are performing several experiments during the RHIC ramp to better understand the impact of orbit errors on the polarization at our current working point. These will be conducted by exciting specified orbit harmonics during the final two large intrinsic resonance crossing in RHIC during the 250 GeV polarized proton ramp. The resultant polarization response will then be measured.
120986648
Rhic Polarized Proton New Working Point Commissioning
The RHIC 2003 polarized proton run showed a limitation on the luminosity due to the beam-beam effect at a betatron tune working point of (0.225,0.235). The integer parts of the horizontal and vertical betatron tunes are 28 and 29, respectively. The polarization transmission efficiency was also compromised because of the tight tune space due to the snake resonances. It was decided to explore the RHIC pp luminosity capability as well as the polarization capability with new working points during the RHIC pp 2004 Run. The working point (0.690.0.685) at a RHIC stored energy of 100GeVk was found to ameliorate the beam-beam effect, and also improve the polarization transmission efficiency as well as polarization lifetime during store. This paper reports the commissioning efforts and results of the new working point commissioning during the latest RHIC polarized proton run.
17951392
Measurements of Single and Double Spin Asymmetry in pp Elastic Scattering in the CNI Region with Polarized Hydrogen Gas Jet Target
Precise measurements of the single spin asymmetry, AN and the double spin asymmetry, ANN, in proton‐proton (pp) elastic scattering in the region of four‐momentum transfer squared 0.001 < −t < 0.032 (GeV/c)2 have been performed using a polarized atomic hydrogen gas jet target and the RHIC polarized proton beam at 24 GeV/c and 100 GeV/c. The polarized gaseous proton target allowed us to achieve the measurement of ANN in the CNI region for the first time. Our results of AN and ANN provide significant constraints to determine the magnitude of poorly known hadronic single and double spin‐flip amplitudes at this energy.
8777025
Quantum chromodynamics in background fields.
We try to build a framework for quantum chromodynamics in background fields. The nonvanishing vacuum condensates are described by the classical fields, while the corresponding quantum fields are quantized in the Furry representation and the physical states are defined in the physical QCD vacuum. The complete quark and gluon propagators are discussed in this framework and running condensate parameters are introduced by the renormalization requirement. A modified Callan-Symanzik equation is derived by taking account of the nonperturbative corrections.
7473966
Renormalization of the quantum stress-energy tensor in inhomogeneous spacetimes: Adiabatic regularization method.
The adiabatic regularization method, known to be a particularly efficient method for numerical study of quantum field dynamics in curved spacetimes, is applicable to evaluate the renormalized stress-energy tensor for matter in any background metric which has sufficient symmetry to allow a decomposition of the quantized field into modes. In this paper we extend this method to more general spacetimes with a small inhomogeneity which is invariant under spatial reflection. We overcome the difficulty of the mode-mixing behavior arising from the inhomogeneity of spacetime and show a possible way of obtaining the WKB solution of the time-dependent mode function under the early-time approximation. As an illustration, we investigate the renormalization of the quantum stress-energy tensor for a massive scalar field with an arbitrary curvature coupling to the inhomogeneous conformally flat spacetime. Our expressions are useful in formulating the semiclassical theory of gravity and in the numerical study of the back reaction of quantized fields in the early Universe with a small inhomogeneity.
5758218
Adiabatic regularization of the quantum stress-energy tensor in curved spacetimes: Stochastic quantization method.
It is found that the adiabatic regularized quantum stress-energy tensor for matter in any background spacetime can be obtained in the framework of stochastic quantization. As an illustration, we investigate the modes of a massive scalar field with arbitrary curvature coupling to the inhomogeneous conformally flat spacetime. The difficulty of the mode-mixing behavior arising from the spacetime inhomogeneity is overcome and a simple algorithm is presented to evaluate the adiabatic regularized quantum stress-energy tensor. The expressions so obtained are useful in formulating the semiclassical theory of gravity and in the numerical study of the back-reaction effects of quantized fields in inhomogeneous spacetimes, such as the problems of homogenization in the early universe and the evaporation of a quantum black hole. It can be seen that our prescriptions may be extended to investigate more realistic models with fermions and gauge fields. This will be studied in future papers.
16523443
Heavy to light baryon transition form factors.
Recently, Stech found form factor relations for heavy to light transitions based on two simple dynamical assumptions for a spectator particle. In this paper we generalize his approach to the case of baryons and find that for ${\mathrm{\ensuremath{\Lambda}}}_{\mathit{Q}}$\ensuremath{\rightarrow}\ensuremath{\Lambda} (Q=b or c) only one independent form factor remains in the limit ${\mathit{m}}_{\mathit{Q}}$\ensuremath{\rightarrow}\ensuremath{\infty}. Furthermore, combining with the model of Guo and Kroll we determine both of the two form factors for ${\mathrm{\ensuremath{\Lambda}}}_{\mathit{Q}}$\ensuremath{\rightarrow}\ensuremath{\Lambda} in the heavy quark limit. The results are applied to ${\mathrm{\ensuremath{\Lambda}}}_{\mathit{b}}$\ensuremath{\rightarrow}\ensuremath{\Lambda}+J/\ensuremath{\psi} which is not clarified both theoretically and experimentally. It is found that the branching ratio of ${\mathrm{\ensuremath{\Lambda}}}_{\mathit{b}}$\ensuremath{\rightarrow}\ensuremath{\Lambda}+J/\ensuremath{\psi} is of order ${10}^{\mathrm{\ensuremath{-}}5}$. \textcopyright{} 1996 The American Physical Society.
39608513
Bethe-Salpeter wave functions for mesons of arbitrary spin and the covariant instantaneous approximation.
The most general form of the Bethe-Salpeter (BS) wave functions for mesons of arbitrary spin and definite parity is given. Using the BS equation, the constraints on the BS wave function due to assuming the covariant instantaneous approximation are found. The application of the general formalism to heavy mesons is given and, in particular, the results from the spin SU(2) symmetry of the heavy quark are naturally obtained in the infinite quark mass limit.