700 research outputs found
Anti-Lambda polarization in high energy pp collisions with polarized beam
We study the polarization of the anti-Lambda particle in polarized high
energy pp collisions at large transverse momenta. The anti-Lambda polarization
is found to be sensitive to the polarization of the anti-strange sea of the
nucleon. We make predictions using different parameterizations of the polarized
quark distribution functions. The results show that the measurement of
longitudinal anti-Lambda polarization can distinguish different
parameterizations, and that similar measurements in the transversely polarized
case can give some insights into the transversity distribution of the
anti-strange sea of nucleon.Comment: 11 pages, 4 figure
Search for Lorentz and CPT Violation Effects in Muon Spin Precession
The spin precession frequency of muons stored in the storage ring has
been analyzed for evidence of Lorentz and CPT violation. Two Lorentz and CPT
violation signatures were searched for: a nonzero
(=); and a sidereal variation of
. No significant effect is found, and the following
limits on the standard-model extension parameters are obtained: GeV; GeV; and the 95% confidence level limits
GeV and
GeV.Comment: 5 pages, 3 figures, submitted to Physical Review Letters, Modified to
answer the referees suggestion
The Muon Anomalous Magnetic Moment and the Standard Model
The muon anomalous magnetic moment measurement, when compared with theory,
can be used to test many extensions to the standard model. The most recent
measurement made by the Brookhaven E821 Collaboration reduces the uncertainty
on the world average of a_mu to 0.7 ppm, comparable in precision to theory.
This paper describes the experiment and the current theoretical efforts to
establish a correct standard model reference value for the muon anomaly.Comment: Plenary Talk; PANIC'02 XVI Particles and Nuclear International
Conference, Osaka, Japan; Sept. 30 - Oct. 4, 2002; Report describes the
published 0.7 ppm result and updates the theory statu
An Improved Limit on the Muon Electric Dipole Moment
Three independent searches for an electric dipole moment (EDM) of the
positive and negative muons have been performed, using spin precession data
from the muon g-2 storage ring at Brookhaven National Laboratory. Details on
the experimental apparatus and the three analyses are presented. Since the
individual results on the positive and negative muon, as well as the combined
result, d=-0.1(0.9)E-19 e-cm, are all consistent with zero, we set a new muon
EDM limit, |d| < 1.9E-19 e-cm (95% C.L.). This represents a factor of 5
improvement over the previous best limit on the muon EDM.Comment: 19 pages, 15 figures, 7 table
Search for Lorentz and CPT Violation Effects in Muon Spin Precession
The spin precession frequency of muons stored in the storage ring has
been analyzed for evidence of Lorentz and CPT violation. Two Lorentz and CPT
violation signatures were searched for: a nonzero
(=); and a sidereal variation of
. No significant effect is found, and the following
limits on the standard-model extension parameters are obtained: GeV; GeV; and the 95% confidence level limits
GeV and
GeV.Comment: 5 pages, 3 figures, submitted to Physical Review Letters, Modified to
answer the referees suggestion
Final Report of the Muon E821 Anomalous Magnetic Moment Measurement at BNL
We present the final report from a series of precision measurements of the
muon anomalous magnetic moment, a_mu = (g-2)/2. The details of the experimental
method, apparatus, data taking, and analysis are summarized. Data obtained at
Brookhaven National Laboratory, using nearly equal samples of positive and
negative muons, were used to deduce a_mu(Expt) = 11 659 208.0(5.4)(3.3) x
10^-10, where the statistical and systematic uncertainties are given,
respectively. The combined uncertainty of 0.54 ppm represents a 14-fold
improvement compared to previous measurements at CERN. The standard model value
for a_mu includes contributions from virtual QED, weak, and hadronic processes.
While the QED processes account for most of the anomaly, the largest
theoretical uncertainty, ~0.55 ppm, is associated with first-order hadronic
vacuum polarization. Present standard model evaluations, based on e+e- hadronic
cross sections, lie 2.2 - 2.7 standard deviations below the experimental
result.Comment: Summary paper of E821 Collaboration measurements of the muon
anomalous magnetic moment, each reported earlier in Letters or Brief Reports;
96 pages, 41 figures, 16 tables. Revised version submitted to PR
News from the Muon (g-2) Experiment at BNL
The magnetic moment anomaly a_mu = (g_mu - 2) / 2 of the positive muon has
been measured at the Brookhaven Alternating Gradient Synchrotron with an
uncertainty of 0.7 ppm. The new result, based on data taken in 2000, agrees
well with previous measurements. Standard Model evaluations currently differ
from the experimental result by 1.6 to 3.0 standard deviations.Comment: Talk presented at RADCOR - Loops and Legs 2002, Kloster Banz,
Germany, September 8-13 2002, to be published in Nuclear Physics B (Proc.
Suppl.); 5 pages, 3 figure
Measurement of the Negative Muon Anomalous Magnetic Moment to 0.7 ppm
The anomalous magnetic moment of the negative muon has been measured to a
precision of 0.7 parts per million (ppm) at the Brookhaven Alternating Gradient
Synchrotron. This result is based on data collected in 2001, and is over an
order of magnitude more precise than the previous measurement of the negative
muon. The result a_mu= 11 659 214(8)(3) \times 10^{-10} (0.7 ppm), where the
first uncertainty is statistical and the second is sytematic, is consistend
with previous measurements of the anomaly for the positive and negative muon.
The average for the muon anomaly a_{mu}(exp) = 11 659 208(6) \times 10^{-10}
(0.5ppm).Comment: 4 pages, 4 figures, submitted to Physical Review Letters, revised to
reflect referee comments. Text further revised to reflect additional referee
comments and a corrected Fig. 3 replaces the older versio
System-Size Independence of Directed Flow Measured at the BNL Relativistic Heavy-Ion Collider
We measure directed flow (ν_1) for charged particles in Au+Au and Cu+Cu collisions at √S_(NN)=200 and 62.4 GeV, as a function of pseudorapidity (η), transverse momentum (p_t), and collision centrality, based on data from the STAR experiment. We find that the directed flow depends on the incident energy but, contrary to all available model implementations, not on the size of the colliding system at a given centrality. We extend the validity of the limiting fragmentation concept to ν_1 in different collision systems, and investigate possible explanations for the observed sign change in ν_1(p_t)
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