Proceedings Of Riken Bnl Research Center Workshop Volume 63 Rhic Spin Collaboration Meetings Xxiv Xxv Xxvi Nsac Review 5

The RIKEN BNL Research Center (RBRC) was established in April 1997 at Brookhaven National Laboratory. It is funded by the ''Rikagaku Kenkyusho'' (RIKEN, The Institute of Physical and Chemical Research) of Japan. The Center is dedicated to the study of strong interactions, including spin physics, lattice QCD, and RHIC physics through the nurturing of a new generation of young physicists. The RBRC has both a theory and experimental component. At present the theoretical group has 4 Fellows and 3 Research Associates as well as 11 RHIC Physics/University Fellows (academic year 2003-2004). To date there are approximately 30 graduates from the program of which 13 have attained tenure positions at major institutions worldwide. The experimental group is smaller and has 2 Fellows and 3 RHIC Physics/University Fellows and 3 Research Associates, and historically 6 individuals have attained permanent positions. Beginning in 2001 a new RIKEN Spin Program (RSP) category was implemented at RBRC. These appointments are joint positions of RBRC and RIKEN and include the following positions in theory and experiment: RSP Researchers, RSP Research Associates, and Young Researchers, who are mentored by senior RBRC Scientists. A number of RIKEN Jr. Research Associates and Visiting Scientists also contribute to the physics program at the Center. RBRC has an active workshop program on strong interaction physics with each workshop focused on a specific physics problem. Each workshop speaker is encouraged to select a few of the most important transparencies from his or her presentation, accompanied by a page of explanation. This material is collected at the end of the workshop by the organizer to form proceedings, which can therefore be available within a short time. To date there are seventy-two proceeding volumes available. The construction of a 0.6 teraflops parallel processor, dedicated to lattice QCD, begun at the Center on February 19, 1998, was completed on August 28, 1998 and is still operational. A 10 teraflops QCDOC computer in under construction and expected to be completed this year.

In the first meeting of this series (which took place at BNL on February 22, 2002), we focused on the upgrades which are expected to be completed prior to the end of this year and thus available for the next run. The two main items are the Spin Rotators in RHIC and the CNI polarimeter for the AGS. In addition, because of the progress on technical issues related to the design of partial snake in the AGS, we also had a presentation on this topic. And, finally, in keeping with a tradition of having some theoretical presentations to accompany the experimental and machine presentations, we had presentations on single spin transverse asymmetries in proton-proton reactions and Coulomb-Nuclear Interference analyzing powers in proton-carbon elastic scattering.

This RHIC Spin Workshop is the 1999 annual meeting of the RHIC Spin Collaboration, and the second to be hosted at Brookhaven and sponsored by the RIKEN BNL Research Center. The previous meetings were at Brookhaven (1998), Marseille (1996), MIT in 1995, Argonne 1994, Tucson in 1991, and the Polarized Collider Workshop at Penn State in 1990. As noted last year, the Center provides a home for combined work on spin by theorists, experimenters, and accelerator physicists. This proceedings, as last year, is a compilation of 1 page summaries and 5 selected transparencies for each speaker. It is designed to be available soon after the workshop is completed. Speakers are welcome to include web or other references for additional material. The RHIC spin program and RHIC are rapidly becoming reality. RHIC has completed its first commissioning run, as described here by Steve Peggs. The first Siberian Snake for spin has been completed and is being installed in RHIC. A new polarized source from KEK and Triumf with over 1 milliampere of polarized H− is being installed, described by Anatoli Zelenski. They have had a successful test of a new polarimeter for RHIC, described by Kazu Kurita and Haixin Huang. Spin commissioning is expected next spring (2000), and the first physics run for spin is anticipated for spring 2001. The purpose of the workshop is to get everyone together about once per year and discuss goals of the spin program, progress, problems, and new ideas. They also have many separate regular forums on spin. There are spin discussion sessions every Tuesday, now organized by Naohito Saito and Werner Vogelsang. The spin discussion schedule and copies of presentations are posted on http://riksg01.rhic.bnl.gov/rsc. Speakers and other spinners are encouraged to come to BNL and to lead a discussion on your favorite idea. They also have regular polarimeter and snake meetings on alternate Thursdays, led by Bill McGahern, the lead engineer for the accelerator spin effort (Thomas Roser is the spokesperson). Waldo Mackay, the Project Manager for spin, leads a weekly accelerator meeting on spin issues on Wednesdays. Finally, Phenix, STAR, and the pp2pp Collaboration have regular collaboration meetings including spin, and spin working groups.

The second part of the sixth RHIC Spin Collaboration (RSC) meeting was held on November 15, 2001 at Brookhaven National Laboratory. Previous meetings have elaborated on the new generation of proton spin-structure studies (e.g. gluon polarization and flavor separation of q and {bar q} polarizations via real W{sup {+-}} production) enabled by studying polarized proton collisions at energies and momentum transfers where perturbative QCD models are expected to be applicable. The focus of this meeting was on many of the experimental issues that must be resolved to achieve these physics goals. This summary is written with the benefit of hindsight following the completion of the first-ever run of a polarized proton collider. This first run can be considered as a successfully completed milestone of the RHIC Spin Collaboration. Other milestones remain important. Long term machine items were identified in Waldo Mackay's talk, the most important being the completion of the spin rotator magnets that will be installed in 2002 to allow the flexible orientation of the proton beam polarization at the PHENM and STAR experiments. At the meeting Waldo discussed a stronger partial snake magnet for the AGS as a means of producing highly polarized proton beams to inject into RHIC. Developments subsequent to this meeting suggest that a superconducting helical dipole magnet may be feasible for the AGS, and is likely to be needed to achieve the 70% beam polarization in RHIC. Longer term items were also presented, including potential increases in luminosity by the addition of electron cooling to RHIC and the possibility of increasing the collision energy by (almost equal to)20% by replacement of the DX magnets. These items could be considered for a second generation of RHIC spin experiments. The other topics covered at the meeting were related to polarimetry and to the absolute calibration of the proton beam polarization in RHIC. These topics were divided into short- and long-term solutions to polarimetry issues. George Igo led a discussion about the addition of a Coulomb-Nuclear Interference (CNI) polarimeter to the AGS prior to FY2003 RHIC operations. The experience from the first RHIC spin run reinforces the need for reducing the time needed to complete polarization measurements in the AGS, and illustrated the importance of polarization measurements at different energies in the RHIC injectors. Progress continues to be made on the completion of a CNI polarimeter for the AGS prior to the FY2003 run.

The much anticipated RHIC spin physics program will commence this fall when the first physics run with colliding beams of polarized protons is expected. More specifically, the planned year-1 RHIC-Spin measurements are (1) the double-spin asymmetry A{sub LL}{sup {pi}} in production of pions by collisions of longitudinally polarized protons (in order to obtain first information on the proton's spin-dependent gluon density,?g); (2) the transverse single-spin asymmetry A{sub N}{sup {pi}} for pion production. These two reactions provided part of the motivation for our workshop. On the first day there were informative talks on the specific plans of STAR (by Rakness) and PHENIX (by Goto) for the polarized run of Year-1. Some of the theoretical questions related to the double-spin asymmetry A{sub LL}{sup {pi}} were discussed on the first day by Vogelsang and Kretzer, which centered mostly around the questions of how well the unpolarized fragmentation functions are known, the need for next-to-leading order calculations, and on how sensitive the asymmetry is to the possible?g distributions. Vetterli presented HERMES measurements of fragmentation functions, which overlap in Q2 with the future lower-p{sub T} measurements at RHIC.

The Circum-Pan-Pacific Riken Symposium on High Energy Spin Physics was held at Oukouchi Memorial Hall in Riken from November 3 through 6, 1999. It was held as a joint meeting of the 2nd Circum-Pan-Pacific Symposium on High Energy Spin Physics and the 3rd of the series of Riken Symposia related to the RHIC-SPIN. The 1st Circum-Pan-Pacific Symposium on High Energy Spin Physics was held at Kobe in 1996 and the RHIC-SPIN Riken Symposia had been held every two years since 1995. As Prof. Ozaki mentioned in his talk at the beginning of this meeting, the RHIC was ready for the first beam, physics experiments scheduled in 2000, and the RHIC-SPIN would start in 2001. It was therefore considered to be very timely for the researchers in the field of high energy spin physics to get together, clarifying the present status of the field and discussing interesting and important topics as well as experimental subjects to be pursued. It is especially important for the success of the RHIC-SPIN project that the researchers in the neighboring countries surrounding the Pacific are actively involved in it. This is why the above two series were joined in this. symposium. The subjects discussed in the symposium include: Hard processes probing spin-structure functions, polarization mechanisms in high energy reactions, lattice studies of polarized structure functions, theoretical models for the nucleon and its spin structure, RHIC and RHIC-SPIN projects, results and future projects of existing experimental facilities. Totally 73 scientists participated in the symposium, 27 from abroad and 46 from Japan. it consisted of 13 main sessions, with 33 invited and contributed talks, and 4 discussion sessions covering recent experimental and theoretical developments and important topics in high energy spin physics and closely related fields.

The RHIC spin program is now fully underway. Several runs have been successfully completed and are producing exciting first results. Luminosity and polarization have improved remarkably and promising advances toward the higher RHIC energy of (square root)s = 500 GeV have been made. At this energy in particular, it will become possible to perform measurements of parity-violating spin asymmetries. Parity violation occurs in weak interactions, and in combination with the unique polarization capabilities at RHIC fascinating new opportunities arise. In particular, parity-violating single- and double-spin asymmetries give new insights into nucleon structure by allowing probes of up and down sea and anti-quark polarizations. Such measurements at RHIC are a DOE performance milestone for the year 2013 and are also supported by a very large effort from RIKEN. With transverse polarization, charged-current interactions may be sensitive to the Sivers effect. Parity-violating effects at RHIC have been proposed even as probes of physics beyond the Standard Model. With the era of measurements of parity-violating spin asymmetries at RHIC now rapidly approaching, we had proposed a small workshop that would bring together the main experts in both theory and experiment. We are very happy that this worked out. The whole workshop contained 17 formal talks, both experiment (10) and theory (7), and many fruitful discussions. The physics motivations for, the planned measurements were reviewed first. The RHIC machine prospects regarding polarized 500 GeV running were discussed, as well as the plans by the RHIC experiments for the vital upgrades of their detectors needed for the W physics program. We also had several talks on the topic of ''semi-inclusive deep-inelastic scattering'', which provides different access to related physics observables. On the theory side, new calculations were presented, for example in terms of QCD all-order resummations of perturbation theory. Also, new observables, such as jet and W+charrn final states and spin asymmetries in Z production, were proposed and discussed. All of the talks attracted much interest and initiated active discussions. This was a very successful workshop. It stimulated many discussions and new collaborations. We are grateful to all participants and speakers for coming to the Center, and for their excellent work. The support provided for this workshop by Dr. N. Samios and his RIKEN-BNL Research Center has been magnificent, and we are very grateful for it. We thank Brookhaven National Laboratory and the U.S. Department of Energy for providing the facilities to hold the workshop. Finally, sincere thanks go to Jane Lysik for her efficient work on organizing and running the workshop.

Understanding the structure of the nucleon is of fundamental importance in sub-atomic physics. Already the experimental studies on the electro-magnetic form factors in the 1950s showed that the nucleon has a nontrivial internal structure, and the deep inelastic scattering experiments in the 1970s revealed the partonic substructure of the nucleon. Modern research focuses in particular on the spin and the gluonic structure of the nucleon. Experiments using deep inelastic scattering or polarized p-p collisions are carried out in the US at the CEBAF and RHIC facilities, respectively, and there are other experimental facilities around the world. More than twenty years ago, the European Muon Collaboration published their first experimental results on the proton spin structure as revealed in polarized deep inelastic lepton-nucleon scattering, and concluded that quarks contribute very little to the proton's spin. With additional experimental and theoretical investigations and progress in the following years, it is now established that, contrary to naive quark model expectations, quarks and anti-quarks carry only about 30% of the total spin of the proton. Twenty years later, the discovery from the polarized hadron collider at RHIC was equally surprising. For the phase space probed by existing RHIC experiments, gluons do not seem to contribute any to the proton's spin. To find out what carries the remaining part of proton's spin is a key focus in current hadronic physics and also a major driving force for the new generation of spin experiments at RHIC and Jefferson Lab and at a future Electron Ion Collider. It is therefore very important and timely to organize a series of annual spin physics meetings to summarize the status of proton spin physics, to focus the effort, and to layout the future perspectives. This summer program on 'Nucleon Spin Physics' held at Brookhaven National Laboratory (BNL) on July 14-27, 2010 [http://www.bnl.gov/spnsp/] is the second one following the Berkeley Summer Program taken place in June of 2009. This program at BNL focused on theory and had many presentations on a wide range of theoretical aspects on nucleon spin, from perturbative-QCD calculations to models, and to the first principle lattice calculation. It also had a good number of summary talks from all major experimental collaborations on spin physics. The program facilitated many discussions between theorists as well as experimentalists. With five transparencies from each presentation at the Summer Program, this proceedings provides a valuable summary on the status and progress, as well as the future prospects of spin physics.