def get_pdf(pdfset, parton, q, xs):
"""get the PDF (xfx) for a certain set, parton, x and Q"""
lhapdf.initPDFSetByName(pdfset)
npdfs = lhapdf.numberPDF()
pdf = np.zeros((npdfs, len(xs)))
for member in range(1, npdfs + 1):
lhapdf.initPDF(member)
for (i, xi) in enumerate(xs):
if parton < 7:
pdf[member - 1][i] = lhapdf.xfx(xi, q, parton)
elif parton == 7:
#DVAL 1-(-1)
pdf[member - 1][i] = lhapdf.xfx(xi, q, 1) - \
lhapdf.xfx(xi, q, -1)
elif parton == 8:
#UVAL 2-(-2)
pdf[member - 1][i] = lhapdf.xfx(xi, q, 2) - \
lhapdf.xfx(xi, q, -2)
elif parton == 9:
#Light sea: xS=2(xubar + xdbar + xsbar)
pdf[member - 1][i] = 2*(lhapdf.xfx(xi, q, -1) + \
lhapdf.xfx(xi, q, -2) + \
lhapdf.xfx(xi, q, -3))
else:
raise ValueError('Parton id not in range 0...9')
return pdf
def _get_lhapdf_flavor(self, flavor, lhgrid_filename):
lhapdf.initPDFSetByName(lhgrid_filename)
npdfs = lhapdf.numberPDF()
pdf = numpy.zeros((npdfs + 1, self._xrange.size))
for member in range(0, npdfs + 1):
lhapdf.initPDF(member)
for (i, xi) in enumerate(self._xrange):
if flavor < 7:
pdf[member][i] = lhapdf.xfx(xi, self._q, flavor)
elif flavor == 7:
#DVAL 1-(-1)
pdf[member][i] = lhapdf.xfx(xi, self._q, 1) - \
lhapdf.xfx(xi, self._q, -1)
elif flavor == 8:
#UVAL 2-(-2)
pdf[member][i] = lhapdf.xfx(xi, self._q, 2) - \
lhapdf.xfx(xi, self._q, -2)
elif flavor == 9:
#Light sea: xS=2(xubar + xdbar + xsbar)
pdf[member][i] = 2*(lhapdf.xfx(xi, self._q, -1) + \
lhapdf.xfx(xi, self._q, -2) + \
lhapdf.xfx(xi, self._q, -3))
else:
raise Exception('Flavor not defined')
return pdf
def recalculateFactorization(x1, id1, factorizationScale1, x2, id2, factorizationScale2, multiplier):
''' Recalculate the PDF using the new factorization scale '''
lhapdfID1 = id1
if lhapdfID1 == 21:
lhapdfID1 = 0
lhapdfID2 = id1
if lhapdfID2 == 21:
lhapdfID2 = 0
# LHAPDF only returns x * f(x, Q) ... that's why I divide by x.
# Not strictly necessary, since we are interest in ratios, but anyway...
oldWeight1 = lhapdf.xfx(x1, factorizationScale1, lhapdfID1)/x1
newWeight1 = lhapdf.xfx(x1, factorizationScale1*multiplier, lhapdfID1)/x1
oldWeight2 = lhapdf.xfx(x2, factorizationScale2, lhapdfID2)/x2
newWeight2 = lhapdf.xfx(x2, factorizationScale2*multiplier, lhapdfID2)/x2
return (newWeight1*newWeight2)/(oldWeight1*oldWeight2)
q = math.sqrt(6400.0)
pdfsets = ["cteq6ll.LHpdf", "MSTW2008lo68cl.LHgrid", "MRST2001lo.LHgrid", "MRST2007lomod.LHgrid", "MRSTMCal.LHgrid"]
#pdfsets = ["cteq6ll.LHpdf", "MRST2001lo.LHgrid", "MRST2007lomod.LHgrid", "MRSTMCal.LHgrid"]
partons = { 0 : "gluon", 2 : "up" }
NPOINTS = 1000
xs = numpy.logspace(-4, -0.001, NPOINTS)
plt.figure(figsize=(13,7))
for n, parton in enumerate(sorted(partons.keys())):
plt.subplot(1, len(partons), n+1)
lhapdf.initPDFSetByName(pdfsets[0])
lhapdf.initPDF(0)
refxfxs = numpy.zeros([NPOINTS])
for i, x in enumerate(xs):
xfx = lhapdf.xfx(x, q, parton)
refxfxs[i] = xfx
lines = []
for pdfset in pdfsets:
lhapdf.initPDFSetByName(pdfset)
lhapdf.initPDF(0)
xfxs = numpy.zeros([NPOINTS])
for i, x in enumerate(xs):
xfx = lhapdf.xfx(x, q, parton)
xfxs[i] = xfx
xfxratios = xfxs/refxfxs
l = plt.plot(xs, xfxratios)
lines.append(l)
plt.xscale("log")
def weight(hats, mu, x1, x2, costh_ii):
# 1 for down-quarks, 2 for up, 3 for strange, 4 for charm and negative values for the corresponding anti-quarks. gluon is given by 21
qtype = 0 # up-type quarks
w_ii = dsigma(costh_ii, hats,
qtype) * (lhapdf.xfx(x1, mu, 2) * lhapdf.xfx(-x2, mu, 2) +
lhapdf.xfx(x1, mu, 4) * lhapdf.xfx(-x2, mu, 4))
w_ii = w_ii + dsigma(-costh_ii, hats, qtype) * (
lhapdf.xfx(-x1, mu, 2) * lhapdf.xfx(x2, mu, 2) +
lhapdf.xfx(-x1, mu, 4) * lhapdf.xfx(x2, mu, 4))
qtype = 1 # down-type quarks
w_ii = w_ii + dsigma(costh_ii, hats, qtype) * (
lhapdf.xfx(x1, mu, 1) * lhapdf.xfx(-x2, mu, 1) +
lhapdf.xfx(x1, mu, 3) * lhapdf.xfx(-x2, mu, 3))
w_ii = w_ii + dsigma(-costh_ii, hats, qtype) * (
lhapdf.xfx(-x1, mu, 1) * lhapdf.xfx(x2, mu, 1) +
lhapdf.xfx(-x1, mu, 3) * lhapdf.xfx(x2, mu, 3))
# multiply by ranges and Jacobian, divide by the x1 and x2 since xfxaQ gives x * f(x)
return w_ii
q = math.sqrt(6400.0)
pdfsets = ["cteq6ll.LHpdf", "MSTW2008lo68cl.LHgrid", "MRST2001lo.LHgrid", "MRST2007lomod.LHgrid", "MRSTMCal.LHgrid"]
#pdfsets = ["cteq6ll.LHpdf", "MRST2001lo.LHgrid", "MRST2007lomod.LHgrid", "MRSTMCal.LHgrid"]
partons = { 0 : "gluon", 2 : "up" }
NPOINTS = 1000
xs = numpy.logspace(-4, -0.001, NPOINTS)
plt.figure(figsize=(13,7))
for n, parton in enumerate(sorted(partons.keys())):
plt.subplot(1, len(partons), n+1)
lines = []
for pdfset in pdfsets:
lhapdf.initPDFSetByName(pdfset)
lhapdf.initPDF(0)
xfxs = numpy.zeros([NPOINTS])
for i, x in enumerate(xs):
xfx = lhapdf.xfx(x, q, parton)
xfxs[i] = xfx
l = plt.plot(xs, xfxs)
lines.append(l)
plt.xscale("log")
#plt.ylim(0.5, 3)
plt.legend(lines, pdfsets)
plt.title(partons[parton])
plt.xlabel("$x$")
if n == 0:
plt.ylabel("$x f(x, Q^2)$")
plt.show()
def weight(self, hats, mu, x1, x2, costh_i):
'''
1 for down-quarks, 2 for up, 3 for strange,
4 for charm and negative values for the corresponding anti-quarks. gluon is given by 21
'''
# up-type quarks
qtype = 0
w_i = self.dsig.dsigma(costh_i, hats, qtype) * (
lhapdf.xfx(x1, mu, 2) * lhapdf.xfx(-x2, mu, 2) +
lhapdf.xfx(x1, mu, 4) * lhapdf.xfx(-x2, mu, 4))
w_i = w_i + self.dsig.dsigma(-costh_i, hats, qtype) * (
lhapdf.xfx(-x1, mu, 2) * lhapdf.xfx(x2, mu, 2) +
lhapdf.xfx(-x1, mu, 4) * lhapdf.xfx(x2, mu, 4))
# down-type quarks
qtype = 1
w_i = w_i + self.dsig.dsigma(costh_i, hats, qtype) * (
lhapdf.xfx(x1, mu, 1) * lhapdf.xfx(-x2, mu, 1) +
lhapdf.xfx(x1, mu, 3) * lhapdf.xfx(-x2, mu, 3))
w_i = w_i + self.dsig.dsigma(-costh_i, hats, qtype) * (
lhapdf.xfx(-x1, mu, 1) * lhapdf.xfx(x2, mu, 1) +
lhapdf.xfx(-x1, mu, 3) * lhapdf.xfx(x2, mu, 3))
return w_i
def xpdf(self, mem, x1, x2, id1, id2, Q):
lhapdf.usePDFMember(*mem)
return lhapdf.xfx(mem[0], x1, Q, id1) * lhapdf.xfx(mem[0], x2, Q, id2)
def xpdf(self, mem, x1, x2, id1, id2, Q) :
lhapdf.usePDFMember(*mem)
return lhapdf.xfx(mem[0], x1,Q,id1) * lhapdf.xfx(mem[0], x2,Q,id2)
