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About CJ

The CJ (CTEQ-Jefferson Lab) Collaboration studies the quark and gluon structure of the nucleon by performing global QCD fits of parton distribution functions (PDFs). These parametrize a vast array of data including deep-inelastic lepton-nucleon scattering, proton-proton collisions (lepton pair creation, W-boson and jet production), and other reactions, with particular focus on the large-x region.

The latest CJ12 fits use less restrictive cuts on Q2 (> 1.69 GeV2) and W 2 (> 3 GeV2), which greatly increases the amount of data accessible at large x, thereby reducing the statistical uncertainty in large-x PDFs, Fig. 1. The effects are most dramatic on the d quark PDF and the d/u ratio, illustrated in Fig. 2 and Fig. 3. The CJ12min, CJ12mid and CJ12max PDF sets correspond to nuclear models of the deuteron with mild, medium and strong nuclear corrections, respectively.

*** Stay tuned for the new set of CJ15 PDFs and strucutre functions, available in early 2015. ***

Fig. 1. (Left) Selection of DIS data points used in the CJ12 fits The long-dashed and dot-dashed curves correspond to the W 2 > 14 GeV2 and W 2 > 3 GeV2 cuts, respectively. (Right) Relative PDF errors for u and d quarks, normalized to the relative errors in the reference fit, illustrating the improved statistical precision with the weaker kinematic cuts.

Fig. 2. (Left) d quark PDF uncertainties for the CJ12min, CJ12mid and CJ12max sets, relative to the reference CJ12mid set at Q2 = 100 GeV2. (Right) PDF uncertainties compared with the nuclear correction uncertainties, and with a fit excluding all deuteron data.

Fig. 3. (Left) d/u ratio for the CJ12min, CJ12mid and CJ12max sets. (Right) d/u ratio for the CJ12mid, CT10, MSTW08 and ABKM09 PDFs, relative to their central values.