References - Bogoliubov Laboratory of Theoretical Physics - JINR

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Figure 1: (a) H-Jet layout of silicon detectors with strips oriented perpendicular to the beam line;
atomic hydrogen jet goes from the top to the bottom; forward strips are used to measure recoil carbon
from the interaction of jet with one beam, and backward strips - with the other beam. (b) Analyzing
power (AN ) for elastic pp scattering defined as ɛtarget/Ptarget; 24 GeV and 100 GeV data are from
RHIC Run 2004 ( [5] and [6]), 31 GeV and 250 GeV preliminary data are from Run 2006 and 2009,
correspondingly.
The accumulated statistics in H-Jet in the first long polarized proton RHIC run in
2006 provided 2.4% uncertainty for the pC polarimeter absolute normalization for each
of 100 GeV beams. Other uncertainties came from the molecular hydrogen background,
∼ 2%, and from background in the identification of eleastically scattered recoil protons,
∼ 1.5%. The latter background didn’t show any beam or target polarization dependence,
so that it diluted both ɛbeam and ɛtarget in the same way, and according to Eq. (2) didn’t
affect beam polarization measurements.
3 Proton-Carbon Polarimeter
Both RHIC rings are equipped with pC polarimeters, which provide fast relative measurements
of beam polarizations, which subsequently is normalized to the absolute polarization
measurements performed by H-Jet polarimeter. Repeated measurements during
a store also provide a handle on the beam polarization vs time as well as measurements
of beam polarization profile in the transverse plane. The latter directly enters the average
beam polarization observed in collisions at the interaction regions of the RHIC
experiments.
The pC polarimeters consist of a carbon target and six silicon strip detectors mounted
in a vacuum chamber at 45, 90 and 135 degrees relative to vertical axis in both left
and right sides with respect to the beam direction, Fig. 2a. It allows to monitor not only
vertical component of beam polarization through left-right asymmetry, but also horizontal
component through up-down asymmetry using 45 and 135 degree detectors. The details
of pC polarimeter setup are described elsewhere [7].
pC polarimeters utilize the analyzing power for the elastic polarized proton-carbon
scattering in the CNI region (Fig. 2b). For the the recoil carbon kinetic energy range
TR =400–900 keV used for the asymmetry measurements the average analyzing power
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