Poljak, N. (2012) STAR results and perspectives on transverse-spin asymmetries. Il nuovo cimento C, 35 (2). pp. 193-198. ISSN 1826-9885
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Abstract
The STAR Collaboration reported precision measurements on the transverse-single-spin asymmetries for the production of forward π0 mesons from polarized proton collisions at √s = 200 GeV. To disentangle contributions to measured forward asymmetries one has to look beyond inclusive π0 production to the production of forward jets or direct photons. In 2006, STAR with the Forward Pion Detector++ (FPD++) in place, collected 6.8 pb−1 of forward data with an average polarization of 60%. FPD++ had sufficient acceptance for “jet-like” objects, which are clustered responses of an electromagnetic calorimeter primarily sensitive to incident photons, electrons and positrons. For these objects, the angle of the outgoing leading π0 with respect to the fragmenting parton was reconstructed, thus enabling us to disentangle the contributions to the forward π0 asymmetries. The simulated data set shows that on average there are approximately 2.5 fragmenting mesons per one “jet-like” object, making them reasonably “jetty”. Preliminary results provide no evidence of measured contributions to the asymmetry from jet fragmentation, implying the Sivers distribution functions play a substantial role in producing the large inclusive forward π0 asymmetries. A similar effort was made in the mid-rapidity (|η| < 1) region of the STAR detector, where 2.2 pb−1 of data was collected. We present progress made by making measurements of the azimuthal asymmetry of leading charged pions in jets produced by transversely polarized proton collisions.
| Item Type: | Article |
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| Uncontrolled Keywords: | Polarization in interactions and scattering ; Inclusive production with identified hadrons ; Protons and neutrons |
| Subjects: | 500 Scienze naturali e Matematica > 530 Fisica |
| Depositing User: | Marina Spanti |
| Date Deposited: | 16 Apr 2020 17:04 |
| Last Modified: | 16 Apr 2020 17:04 |
| URI: | http://eprints.bice.rm.cnr.it/id/eprint/17772 |
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