[local physicists] FW: REMINDER: Colloquium Announcement (Matthias Grosse-Perdekamp) 2/26/2013

[Malin, Delicia M.]

Old Dominion University
Department of Physics

Spring Colloquium Series

Tuesday February 26, 2013


"Studying the Quark Structure of the Proton with High Energy Pion Beams at CERN"


Dr. Matthias Grosse-Perdekamp
UIUC

The exploration of the quark and gluon structure of the proton has been subject of a 40 year long worldwide experimental effort involving experiments at all major accelerator laboratories in North America, Europe and Asia. Significant progress has been made in obtaining quantitative information with regards to the quark- and gluon-momentum and spin distributions. However, important questions still remain without answer:

A longstanding challenge in further advancing our theoretical understanding of proton structure exists in the explanation of the large transverse single spin asymmetries (SSAs) observed in reactions between high energy probe particles and transversely polarized proton targets. For many years the observed large SSAs appeared inconsistent with the more than 1000 times smaller asymmetries expected from theory predictions for the underlying higher energy reactions with quarks and gluons.

The COMPASS measurement of Drell-Yan production of muon pairs with negative pion beams on transversely polarized proton targets constitutes a critical test of a new theoretical approach within quantum chromodynamics (QCD) to describe transverse spin and momentum dependent (TMD) processes in high-energy reactions of hadrons. This so-called TMD framework makes it possible for the first time to consistently describe transverse-spin dependent observables in many processes: semi-inclusive deep inelastic scattering (SIDIS at Jefferson Laboratory, COMPASS, and HERMES), proton-proton scattering (FNAL, AGS and RHIC) and electron-positron annihilation (BELLE and BaBar).

The observed transverse-spin phenomena are related to the unknown orbital angular momentum of quarks inside the proton. They have garnered so much interest that they now constitute a major focus of future hadronic structure research, both experimental and theoretical. A broad experimental program to explore TMD phenomena is e.g. planned at Jefferson Laboratory with the upgraded 12 GeV electron beam. The success of this future program critically depends on the validity
and accurate theoretical interpretation of the TMD framework. A key issue is the unexpected modification of the concepts of universality and factorization and these urgently require confirmation. It has been predicted that the Sivers effect changes sign between two processes: SIDIS and DY. The verification of this sign change has been designated by NSAC as a performance milestone for the US hadron physics program. The COMPASS measurement presently is the only approved experiment that can carry out this test. In this colloquium I will review past results for SSAs in high energy scattering, discuss their theoretical interpretation and introduce the planned Drell-Yan measurement at COMPASS. The colloquium will conclude with a brief summary of the COMPASS physics program with muon beams including the planned precision measurements of the strangeness quark distribution and measurements in exclusive processes.



Presentation: OCNPS 200 @ 3:00 pm
Refreshments: Atrium @ 2:30 pm
More details at http://sci.odu.edu/physics/
All are Welcome!



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