## 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.