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 The Jefferson Laboratory Upgrade to 12 GeV
 (INT program September 14 - October 16 & October 26 - November 20, 2009)

  Reported by Carlos Munoz Camacho, Rolf Ent, Jerry Miller, and Tony Thomas
  Date posted February 12, 2010

The program on the The Jefferson Laboratory Upgrade to 12 GeV was held at the INT from September 14 to October 16, and from October 26 to November 20, 2009. The immediate goal was to bring experimentalists and theorists together to explore and develop important aspects of the exciting physics possibilities. This goal was well achieved, as the program brought together a wide variety of about 100 experimentalists and theorists (almost 50% experimentalists) to work together during the nine-weeks of the program.

Several presentations were adjusted, and in some cases completely new talks were drafted, as a follow-up to lively discussions on experimental possibilities. Several new experimental proposals were discussed, and some of these have already been submitted to the JLab Program Advisory Committee. Discussions on a few followup workshops or topical meetings are ongoing, and several new collaborations originated from this INT program. Overall, we believe that the rich interactions between theorists and experimentalists in a positive and productive atmosphere led to a very productive program.

        Pionic color transparency, measured in the nuclear e,e'π reaction.

The program was organized into three categories, following the unique opportunities allowed by this Upgrade through its combination of luminosity, duty factor and kinematic reach, which are foreseen to make profound contributions to the study of hadronic matter.

  • Determining the spin and flavor generalized parton distributions and transverse momentum distributions, of the valence quarks that reside in the nucleon. This would culminate in nucleon tomography measurements to discover the true three-dimensional structure of nucleons. Major progress was made to bring the, often distinct, communities interested in both distributions together, discuss commonalities and pitfalls in the frameworks, and raise questions about the validity of various factorization schemes. Elucidating possibilities to make headway in extracting and interpreting these distributions was a major theme. This activity occured during the period of 9/14 to 10/16, including a dedicated one-week workshop during the first week.

  • Nuclear effects. Measurements using nuclear targets with the Upgrade will allow unprecedented access to the role of valence quarks in nuclei, and the dynamical process by which such quarks propagate through the nuclear medium and form hadrons. Many talks discussed novel ways to investigate the nuclear EMC effect, discovered some 25 years ago. The effect is that the momentum distribution of valence quarks inside the nuclei differs, notably in the valence region, from that of quarks in a free nucleon. To date, there are hundreds of papers on this subject, but no universally accepted explanation. Using the high luminosity at 12 GeV, would allow experimentalists and theorists multiple ways to disentangle the different suggested causes of the EMC effect and their consequences for other processes. The effects of color transparency and short-range nucleon-nucleon correlations are closely related to these topics and also formed focus points of the program. An example, of the potential impact of the Upgrade on measurements of color transparency is shown in the accompanying figure. This activity spanned the period of 10/26-11/06.

  • The search for exotic mesons using high energy photon-proton collisions. Fluctuations of the gluonic vacuum are an unavoidable part of the structure of mesons. A new generation of hadron spectroscopy experiments and theoretical investigations was discussed to allow the search for exotic hadrons and investigate various puzzles involving mesonic and baryonic spectra. Finding such exotic hadrons and determining their spectrum will unambiguosly underline the role of gluon self-interactions in hadrons, and provide the basis for understanding the confinement mechanism that eternally locks quarks and gluons in hadrons. To make substantial progress, it is vital that theorists concerned with the physics of reaction mechanisms work with experimentalists to understand the relevant energy-dependent physics backgrounds that could mimic potential signals of a resonant state. This was exactly the topic of a dedicated workshop held Nov. 9-13 that was followed by another week of intense discussions amongst theorists and experimentalists on the ins and outs of Partial Wave Analysis methods. Plans were developed to produce a White Paper.