[local physicists] REMINDER: Donika Plyku Thesis Defense (2/1/2013)

[Malin, Delicia M.]

Thesis Defense
Donika Plyku


"SPIN DEPENDENCE IN POLARIZED PROTON-PROTON
ELASTIC SCATTERING AT RHIC"
2:00 p.m.

Friday, February 1, 2013
Director: Dr. Stephen Bu¨eltmann
The STAR experiment at RHIC is equipped with insertion devices (Roman Pots) that allow detectors to be moved close to the beam, for the measurement of protons scattered at very small angles. This setup, together with the unique capability of RHIC to collide spin-polarized proton beams, allows STAR to study both the dynamics and the spin-dependence of proton-proton (pp) elastic scattering process. Silicon strip detectors installed inside the Roman Pots measure tracks of protons scattered diffractively at very small angles. In a dedicated run with special beam optics during the 2009 RHIC run, the collaboration collected about 20 million elastic events with transversely polarized proton beams at the center of mass energy √s = 200 GeV and four momentum transfer squared (t) range of 0.003 ≤|t|≤ 0.035 (GeV/c)2, where, due to the Coulomb Nuclear Interference (CNI), a measurable single spin asymmetry arises. While the electromagnetic interaction can be determined in QED, the description of the hadronic interaction at small-t scattering requires the use of nonperturbative techniques in QCD, and, phenomenological models, rather than pQCD, are used to describe the exchange mechanism. The high energy diffractive scattering at small-t is dominated by the exchange of the Pomeron, treated in pQCD as a color singlet combination of two gluons, carrying quantum numbers of the vacuum (JPC= 0++).

We report on a high precision measurement of the transverse single spin asymmetry AN, at √s = 200 GeV in pp elastic scattering at RHIC. The measured AN and its t-dependence are consistent with the absence of a hadronic spin-flip amplitude. The contribution from a possible hadronic spin-flip amplitude can be quantified by measuring the r5 parameter, which is proportional to the ratio of the single hadronic spin-flip to the hadronic non-flip amplitudes. The presented results provide precise measurement for non-perturbative  QCD, where experimental data are indispensable, and a significant constraint on the spin-flip component of the Pomeron.


OCNPS 304, Physics Conference Room
All interested persons are cordially invited to attend.



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