Nuclear PDFs Page: 4 of 6
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D. DE FLORIAN, R. SASSOT, M. STRATMANN AND P. ZURITA
with it, we treat the heavy quark flavours (charm and bottom) using a general mass
variable flavour number scheme. We also estimate the uncertainties of the nPDFs using
the Hessian method  and examine their range of applicability.
2. - Framework
We assume that the theoretical expressions for observables involving a nucleus factor-
ize into calculable partonic hard scattering cross sections, and appropriate combinations
of non-perturbative collinear parton densities and fragmentation functions. The relation
between the nPDFs and the proton PDFs is given by
(1) ffA(x, Go) = RA(x, Golff (x, GO) ,
with Qo the initial scale (1 GeV in the present case) and x the usual DIS scaling vari-
able. We assigned the same nuclear modification factor to both valence distributions,
(2) Rj(x, Qo) Eix" (1 - ) (1 + 62(1 - x) )(1 + az(1 - )N) .
To achieve an excellent description of the data it is enough for the sea and gluon densities
to relate the factors R8 and R9 to Rv, but giving a more flexible low x behaviour:
R(x, Qo) = Rjj(x, Qo) -1+ ax s
3) i a 8+ 1
A A Eg 1 + Gg x9
Rg(x, Qo) = R$(x, 6 Qo) 1 + .a
ci a9 +1
Charge and momentum conservation fix three parameters and due to the limited kine-
matical coverage of the data, we can further impose E5 =E. The remaining parameters
are given an A dependence through = a + )v A6e. Furthermore, the mild A depen-
dence observed for some of the 's accommodates setting 3ia9 =a, and 3n, = &s . This
leaves us with 25 free parameters to be determined through a standard X2 minimization,
in which no artificial weights for certain data sets were used, i.e. w = 1, and with
statistical and systematic errors added in quadrature in Az:
(4) (du7? - doih)2
(4) X = 2 2, 2 -
3. - Results
For 1579 data points we found a total X2/d.o.f. 0.994, with all sets reproduced
within the nominal statistical range X2 n g 2n, with n the number of data points.
Fig. 1 exemplifies the goodness of the agreement between the fit and charged lepton
DIS (left) and hadroproduction (right) data; see  for details. For the DIS data the
agreement is remarkable, but the dAu collisions data are harder to understand in terms
of nPDFs. The cross sections might be in principle sensitive to medium induced effects
in the hadronization process. Assuming factorizability, such final-state effects can be
absorbed into effective nuclear fragmentation functions (nFFs). The solid line in the
right panel of Fig. 1 represents the result of our best fit using the nFFs of . While a
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D., De Florian; M., Stratmann; Zurita, P. & Sassot, R. Nuclear PDFs, article, October 22, 2012; United States. (digital.library.unt.edu/ark:/67531/metadc844710/m1/4/: accessed November 16, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.