This is the first circular announcing the workshop on 
"Spin Physics at RHIC in Year-1 and Beyond" to be held at 
the Brookhaven National Laboratory from May 14 to 18, 2001. 

The much anticipated RHIC spin physics program will commence 
this fall when the first physics run with colliding beams of 
polarized protons is expected. This will open the door to a 
new laboratory for studying the structure of the proton, for 
advancing our understanding of the strong interactions, but 
also for tests of the Standard Model. 

The intention of the workshop is to have experts report on and 
discuss pressing issues related to the following topics:

o the double-spin asymmetry A_LL^pi
o the transverse single-spin asymmetry A_N^pi
o issues in measurements of polarization asymmetries 
o strategies for global analyses of future spin data for 
  various reactions
o measurement of the polarized strange quark density Delta s
o sensitivity to physics beyond the Standard Model at RHIC

Below we have included more detailed physics information about the 
workshop's scope. 

We plan to have seminar-type presentations in the mornings and leave 
the afternoons free for further discussions and informal presentations. 

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Physics motivation:

The planned year-1 RHIC-Spin measurements are

o the double-spin asymmetry A_LL^pi in production of pions at large 
  transverse momentum, p_T, by collisions of longitudinally polarized 
  protons. This reaction is expected to provide a first determination of the 
  proton's spin-dependent gluon density, Delta g. 

o the transverse single-spin asymmetry A_LL^pi for pion production
  at p_T = 1-3 GeV and large x_F. Despite its `higher-twist' (that is, 
  power-suppressed in p_T) nature, previous experiments at lower energies 
  have found sizable values for the asymmetry. If A_N^pi remains 
  substantial at RHIC energies, its measurement will be an ideal testing 
  ground for verifying that all beam polarization issues are fully under 
  control at RHIC. Also, its fall-off with p_T, as anticipated from its 
  higher-twist nature, will be a crucial test for our understanding of 
  high-energy spin physics in QCD.

The intention is to review the experimental situation in both cases as well as
the theoretical predictions that are available, and their uncertainties. 
There are still issues to be clarified here. In case of A_LL^pi, one 
objective is to initiate the calculation of higher-order QCD corrections to 
the partonic hard scattering reactions. These are required for arriving at
a sufficiently precise theoretical prediction of A_LL^pi and
thus for reliably extracting Delta g from the future data. Another
ingredient for predictions for A_LL^pi are the ``parton-to-pion''
fragmentation functions. These have been measured in e+e- annihilation,
and several groups have presented analyses of these data. Our plan
for the workshop is to assess the uncertainties in the fragmentation
functions and to see in how far they will have an impact on determinations
of Delta g from A_LL^pi. We also plan to review the theoretical 
situation for pi^0 production in unpolarized hadron collisions. 

Concerning A_N^pi, the available predictions for RHIC need to be reviewed
and where possible improvements need to be made.

In addition to these theoretical issues, there are experimental issues
about making polarization asymmetry measurements in a collider. The
workshop is intended to review these issues. For example, what can be learned
from recent SLAC measurements of polarization observables in e+e- 
collisions at root(s)=M_Z.
 
Another objective of the workshop is to focus on the broader context of 
RHIC-Spin:

o ``global analyses'': measurements of, say, A_LL^pi and related 
reactions do not give Delta g directly, but involve convolutions of 
Delta g with partonic hard-scattering cross sections. In addition, 
they usually rely on knowledge of the spin-dependent quark and antiquark 
densities of the proton. The way to extract information on Delta g is 
known from the unpolarized case: one performs a simultaneous (``global'') 
analysis of all data sets that are described by partonic reactions, that is, 
of deep-inelastic (g_1) data and of A_LL^pi. In this way one also 
tests the viability of the employed theoretical framework. The workshop is
intended to set the stage for global analyses in the polarized case.

o measurement of the polarized strange quark density, Delta s:
so far, there have been no detailed studies on possible measurements of
Delta s at RHIC, which plays a central role in proton spin structure.
For example, one could use the reaction s+g -> c+W and the plan is to 
initiate studies of this reaction in the course of the workshop.

o sensitivity to physics beyond the Standard Model: it is conceivable that 
measurements of certain asymmetries at RHIC will probe, or at least further 
constrain, physics beyond the Standard Model. There are, however, several 
open questions in this context, concerning for example the uncertainty in the
actual Standard Model predictions for the reactions of interest. Also, the 
influence of existing limits on beyond-Standard Model physics on the 
sensitivities to be expected at RHIC needs further investigation. 

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