## 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 CJ15 fits use less restrictive cuts on *Q* (> 1.3 GeV) and *W* (> 1.73 GeV), which greatly increases the amount of data accessible at large *x* and reduces the statistical uncertainty in large-*x* PDFs. An illustration of the quality of the fit to data is shown in **Fig. 1** for the proton *F*_{2} structure function, over a large range of *x* and *Q*.

The resulting PDFs for the *u*, *d*, anti-*u*, anti-*d*, *s* quarks and gluon *g* are illustrated in **Fig. 2** compared with PDFs from other analyses.

The new data on the *W*-boson asymmetry in particular, shown in **Fig. 3** *(left)*, significantly improve the constraints on the *d/u* quark PDF ratio. This in turns allows a more reliable determination of the deuteron to nucleon *F*_{2} ratio, **Fig. 2** *(right)*.

The effects on the *d/u* ratio are illustrated in **Fig. 4**, arising from inclusion of specific data sets, and from removing nuclear corrections and deuterium data.

**Fig. 1.** Proton *F*_{2} structure function data from various experiments *(left)* at BCDMS, SLAC, NMC, HERMES at fixed *x*, and *(right)* at Jefferson Lab for fixed angle, compared with the CJ15 fit (for a tolerance *T*=10), scaled by a factor 2* ^{i}*.

**Fig. 2.** Ratio of PDFs to the CJ15 central values for various PDF sets: CJ15 for tolerance *T*=1 and 10, MMHT14, HERAPDF1.5 and NNPDF3.0, for the *u*, *d*, anti-*u*, anti-*d*, *s* and *g* PDFs.

**Fig. 3.** *(Left)* *W*-boson charge asymmetry from as a function of the *W*-boson rapidity for CDF and D0 data, compared with the CJ15 fit with *T* = 10. *(Right)* Ratio of deuteron to free nucleon structure functions *F*_{2}^{d}/*F*_{2}^{N} for CJ15, for different deuteron wave functions.

**Fig. 4.** *(Left)* Impact of various data sets on the *d/u* ratio (for *T*=10). *(Right)* Impact on *d/u* ratio of removing nuclear corrections and omitting deuterium data.