********************************************************************** GAUSTEQ Germany and U.S. Nuclear Theory Exchange Program for QCD Studies of Hadrons and Nuclei *************************** VISITOR REPORT *************************** Please use the following template to prepare your report in plain text format. Short, itemized answers are preferred. Send your report by E-mail to (as an attachment to preserve formating). ---------------------------------------------------------------------- 1) NAME AND HOME INSTITUTION OF TRAVELER (INCL. E-MAIL ADDRESS) Andreas Metz Temple University metza@temple.edu ---------------------------------------------------------------------- 2) POSITION OF TRAVELER (FACULTY/STAFF/POSTDOC/STUDENT) Faculty ---------------------------------------------------------------------- 3) DATES OF TRAVEL June 15 - June 21 (Regensburg) June 29 - July 4 (Tuebingen) July 17 - July 18 (Darmstadt) (The trips to Regensburg, Tuebingen and Darmstadt took place during a long-term stay in Europe.) ---------------------------------------------------------------------- 4) INSTITUTIONS VISITED (LIST PLACES AND TIME SPENT THERE) University of Regensburg (June 16 - June 20) University of Tuebingen (June 30 - July 4) University of Darmstadt (July 17 - July 18) ---------------------------------------------------------------------- 5) SCIENTIFIC CONTACTS AND COLLABORATORS (INDICATE NATURE OF CONTACTS, LIKE "NEW COLLABORATION," "CONTINUING COLLABORATION," "USEFUL DISCUSSION," ETC.) Andreas Schaefer: continuing collaboration Jian Zhou: continuing collaboration Vladimir Braun: useful discussion Werner Vogelsang: continuing collaboration Marc Schlegel: continuing collaboration Patriz Hinderer: new collaboration Hans-Werner Hammer: useful discussion ---------------------------------------------------------------------- 6) TOPICS DISCUSSED DURING VISIT - Longitudinal-transverse double-spin asymmetry in pp -> gammaX - Model estimates for 3-parton correlators - NLO corrections for the process ep -> hX - Transverse spin physics at FAIR ---------------------------------------------------------------------- 7) IMPACT ON TRAVELER'S OR HOST'S RESEARCH (INCL. EXPECTED PUBLICATIONS) - Longitudinal-transverse double-spin asymmetry in pp -> gammaX: This observable can give valuable insight into both the transverse spin structure of the nucleon and the gluon helicity distribution at small x. Together with Andreas Schaefer and Jian Zhou I looked at the analytical calculation for this observable, in particular at a class of diagrams which have been overlooked previously. In the meantime we finished the analytical calculation and we aim at a numerical estimate for RHIC kinematics. We plan to publish our results. - Model estimates for 3-parton correlators: 3-parton correlators at twist-3 enter the description of the afore-mentioned double-spin asymmetry as well as other spin-related observables in high-energy collisions. Vladimir Braun and coworkers made a very appealing model for those entities. I discussed with him about this model and the possibility to use it for numerical estimates. - NLO corrections for the process ep -> hX: The process ep -> hX recently has attracted a lot of attention. In particular we now have new, very precise data from HERMES and JLab on the transverse single spin asymmetry A_N for that process. Those data may also shed new light on the underlying mechanism of A_N observed in hadron-hadron collisions. However, NLO corrections for this process are generally expected to be very large. I discussed this with Werner Vogelsang, Marc Schlegel and a PhD student (Patriz Hinderer). In fact we came up with a new idea of how to compute such NLO corrections in an approximate yet reliable manner. Especially for the twist-3 observable A_N we are aiming at a common publication. - Transverse spin physics at FAIR: I discussed with Hans-Werner Hammer several topics of hadronic/nuclear physics. In particular, I spoke with him also about the opportunities to study transverse spin physics at FAIR. - Talks: At the University of Regensburg and the University of Tuebingen I gave a seminar on transverse spin observables with an emphasis on own recent contributions. In Darmstadt I gave a somewhat more general seminar on transverse spin physics. ---------------------------------------------------------------------- 8) RELEVANCE TO JEFFERSON LAB OR GSI-FAIR (LIST RELEVANT PROGRAMS) In general, the topics discussed/worked on during the three visits aim at a deeper understanding of (transverse) spin asymmetries in hard semi-inclusive reactions. Studies of such spin asymmetries already played a key role at JLab-6, and they will be an important part of the physics program at JLab-12. They will also be studied in the future at GSI-FAIR. ---------------------------------------------------------------------- 9) SUGGESTIONS/RECOMMENDATIONS FOR PROGRAM ADMINISTRATORS (IF ANY) ---------------------------------------------------------------------- 10) SUPPORT PROVIDED BY HOSTS (INDICATE TYPE AND EXTENT OF SUPPORT, NOT EXACT AMOUNTS) Office space was provided by hosts, but no financial support. ---------------------------------------------------------------------- 11) ACKNOWLEDGMENTS Please acknowledge support from the GAUSTEQ program in any publication benefiting from the results of your visit, by including the following text in your acknowledgments: "This work was supported partially through GAUSTEQ (Germany and U.S. Nuclear Theory Exchange Program for QCD Studies of Hadrons and Nuclei) under contract number DE-SC0006758." ---------------------------------------------------------------------- updated: Nov. 2011 **********************************************************************