797 research outputs found
A fixed angle double mirror filter for preparing a pink undulator beam at the Advanced Photon Source
Recent advances in X-ray Photon Correlation Spectroscopy (XPCS) use the full bandwidth of an undulator harmonic in order to maximize the coherent flux for small angle X-ray scattering experiments. X-ray mirrors and filters are typically used to select a given harmonic of the spectrum. At the University of Michigan/Howard University/Lucent Technologies, Bell Labs, Collaborative Access Team (MHATT-CAT) undulator beamline of the Advanced Photon Source, we have designed a fixed-angle Double Mirror Filter which will provide a “pink beam” (i.e., 2–3% bandwidth) for XPCS experiments. This device uses two small mirrors which vertically reflect a 0.1 mm×0.1 mm0.1mm×0.1mm white beam in a symmetric geometry. The doubly reflected beam propagates parallel to the incident white beam, but is offset vertically by 35 mm. Using the standard offset of the APS allows one to stop the white beam with a standard APS beam stop. In this report, we will describe our design considerations for this instrument. We also report the results of preliminary tests of the performance. The mirrors preserve the transverse coherence of the source, and filter the undulator spectrum as expected. © 2000 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87429/2/238_1.pd
Experimental data on the single spin asymmetry and their interpretations by the chromo-magnetic string model
An attempt is made to interpret the various existing experimental data on the
single spin asymmetries in inclusive pion production by the polarized proton
and antiproton beams. As the basis of analysis the chromo-magnetic string model
is used. A whole measured kinematic region is covered. The successes and fails
of such approach are outlined. The possible improvements of model are
discussed.Comment: 17 pages, 3 figure
Double Spin Asymmetries A_NN and A_SS at sqrt{s}=200 GeV in Polarized Proton-Proton Elastic Scattering at RHIC
We present the first measurements of the double spin asymmetries A_NN and
A_SS at sqrt{s}=200 GeV, obtained by the pp2pp experiment using polarized
proton beams at the Relativistic Heavy Ion Collider (RHIC). The data were
collected in the four momentum transfer t range 0.01<|t|<0.03 (GeV/c)^2. The
measured asymmetries, which are consistent with zero, allow us to estimate
upper limits on the double helicity-flip amplitudes phi_2 and phi_4 at small t
as well as on the difference Delta(sigma_T) between the total cross sections
for transversely polarized protons with antiparallel or parallel spin
orientations.Comment: 13 pages with 3 figures. Final version accepted by Phys. Lett.
Spin flipping a stored vertically polarized proton beam with an RF solenoid
A recent experiment in the IUCF cooler ring studied the spin flip of a stored vertically polarized 139 MeV proton beam. This spin flip was accomplished by using an RF solenoid to induce an artificial depolarizing resonance in the ring, and then varying the solenoid’s frequency through this resonance value to induce spin flip. We found a polarization loss after multiple spin flips of about 0.00±0.05% per flip and also losses for very long flip times. This device will be useful for reducing systematic errors in polarized beam‐internal target scattering asymmetry experiments by enabling experimenters to perform frequent beam polarization reversals in the course of the experiment. © 1995 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87478/2/118_1.pd
Identified baryon and meson distributions at large transverse momenta from Au+Au collisions at GeV
Transverse momentum spectra of , and up to 12 GeV/c
at mid-rapidity in centrality selected Au+Au collisions at GeV are presented. In central Au+Au collisions, both and
show significant suppression with respect to binary scaling at
4 GeV/c. Protons and anti-protons are less suppressed than
, in the range 1.5 6 GeV/c. The and
ratios show at most a weak dependence and no significant
centrality dependence. The ratios in central Au+Au collisions approach
the values in p+p and d+Au collisions at 5 GeV/c. The results at high
indicate that the partonic sources of , and have
similar energy loss when traversing the nuclear medium.Comment: 6 pages, 4 figure
Longitudinal double-spin asymmetry and cross section for inclusive jet production in polarized proton collisions at sqrt(s) = 200 GeV
We report a measurement of the longitudinal double-spin asymmetry A_LL and
the differential cross section for inclusive midrapidity jet production in
polarized proton collisions at sqrt(s)=200 GeV. The cross section data cover
transverse momenta 5 < pT < 50 GeV/c and agree with next-to-leading order
perturbative QCD evaluations. The A_LL data cover 5 < pT < 17 GeV/c and
disfavor at 98% C.L. maximal positive gluon polarization in the polarized
nucleon.Comment: 6 pages, 3 figures. Minor changes from review process in Phys. Rev.
Lett. Plain text tables of data in STAR publications may be found at
http://www.star.bnl.gov/central/publications
Longitudinal double-spin asymmetry for inclusive jet production in p+p collisions at sqrt(s)=200 GeV
We report a new STAR measurement of the longitudinal double-spin asymmetry
A_LL for inclusive jet production at mid-rapidity in polarized p+p collisions
at a center-of-mass energy of sqrt(s) = 200 GeV. The data, which cover jet
transverse momenta 5 < p_T < 30 GeV/c, are substantially more precise than
previous measurements. They provide significant new constraints on the gluon
spin contribution to the nucleon spin through the comparison to predictions
derived from one global fit of polarized deep-inelastic scattering
measurements.Comment: 7 pages, 4 figures + 1 tabl
Pion interferometry in Au+Au collisions at sqrt[sNN]=200GeV
We present a systematic analysis of two-pion interferometry in Au+Au collisions at sqrt[sNN]=200GeV using the STAR detector at Relativistic Heavy Ion Collider. We extract the Hanbury-Brown and Twiss radii and study their multiplicity, transverse momentum, and azimuthal angle dependence. The Gaussianness of the correlation function is studied. Estimates of the geometrical and dynamical structure of the freeze-out source are extracted by fits with blast-wave parametrizations. The expansion of the source and its relation with the initial energy density distribution is studied
Neutral Kaon Interferometry in Au+Au collisions at sqrt(s_NN) = 200 GeV
We present the first statistically meaningful results from two-K0s
interferometry in heavy-ion collisions. A model that takes the effect of the
strong interaction into account has been used to fit the measured correlation
function. The effects of single and coupled channel were explored. At the mean
transverse mass m_T = 1.07 GeV, we obtain the values R = 4.09 +/- 0.46 (stat.)
+/- 0.31 (sys) fm and lambda = 0.92 +/- 0.23 (stat) +/- 0.13 (sys), where R and
lambda are the invariant radius and chaoticity parameters respectively. The
results are qualitatively consistent with m_T systematics established with
pions in a scenario characterized by a strong collective flow.Comment: 11 pages, 10 figure
Pion interferometry in Au+Au collisions at = 200 GeV
We present a systematic analysis of two-pion interferometry in Au+Au
collisions at = 200 GeV using the STAR detector at RHIC. We
extract the HBT radii and study their multiplicity, transverse momentum, and
azimuthal angle dependence. The Gaussianess of the correlation function is
studied. Estimates of the geometrical and dynamical structure of the freeze-out
source are extracted by fits with blast wave parameterizations. The expansion
of the source and its relation with the initial energy density distribution is
studied.Comment: 21 pages, 30 figures. As published in Physics Review
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