1. RIKEN/BNL Lunch Time Talk

    "The transverse single-spin asymmetry "spin crisis" in proton-proton collisions"

    Presented by Daniel Pitonyak, RBRC

    Thursday, February 27, 2014, 12:30 pm
    Physics, Bldg. 510, Room 2-160

    Hosted by: Kouji Kashiwa

    The measurement of transverse single-spin asymmetries (TSSAs) in proton-proton collisions has been one of the main focuses of the RHIC spin program. Large effects have been seen, yet issues still remain on the theoretical side. Namely, the assumption that the so-called Qiu-Sterman distribution function dominates the observable has led to a "sign mismatch" with the so-called Sivers function that arises in TSSAs in semi-inclusive deep-inelastic scattering. This disagreement is really an indication that we still do not fully understand what causes TSSAs in proton-proton collisions, which is truly a "spin crisis". Speculation in recent years is that significant contributions arise from the fragmentation side of the process. In this talk I will review the current theoretical formalism for this observable and explore the role that fragmentation can play in the reaction.