Diffractive partons from perturbative QCD

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Diffractive partons from perturbative QCD
Alan Martin, Misha Ryskin and Graeme Watt
Conventionally DDIS analyses use two levels of
factorisation - collinear
factorization and Regge factorization
We replace Regge factorization by pQCD
Collinear factorization, which holds
asymptotically, needs modification in
the HERA regime -- inhomogeneous term
in DGLAP evolution -- direct charm
contribution -- twist-4 FLD component
We present universal diffractive partons
XVIIth Rencontre de Blois, May 2005 Alan Martin
(IPPP,Durham)
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factorization proved for DDIS (Collins),
but important modifications in the HERA regime
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• H1 Large rapidity gap selection
• MYlt1.6 GeV and tlt1 GeV2
• H1 LPS proton selection MY mp
• extrapolated to tlt1 GeV2
• ?Good agreement between two
• methods and two experiments
• ?Data well described by
• H1 QCD fit to LRG data

M.Kapishin, ICHEP04, Beijing
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x0.18
b0.67
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lots of gluons at high b, theoretically puzzling
from a perturbative viewpoint
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• H1 NLO fits to
• H1 LRG data
• ZEUS MX data

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• H1 NLO fits to
• H1 LRG data
• ZEUS MX data

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Hint of problem with Regge factorisation
assumption
assumes Pomeron hadron of size R Regge factn
occurs in non-pert region mltm0, where m1/R but
aP(0)1.2 from DDIS gt aP(0)1.08 from soft
data ? small-size component from pQCD domain
with larger aP(0)
MRW study impact of applying pQCD to DDIS
find DDIS factorization OK asymptotically,
but important modifications in HERA
(subasymptotic) regime
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rapidity gap
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given by pQCD
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m2 fP ? flux does not behave as
1/m2
convergence decreases as xP decreases
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inclusion of the inhomogeneous term makes gP
smaller
gP
inhomog. term
xP0.003 Q215 GeV2
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In practice, more convenient to solve standard
DGLAP for each m starting from its own scale m
(provided mgtQ0). Then to integrate over m.
m2
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dm2 m2
input forms
first try assume xg x -l
following Wusthoff, BEKW loosely
based parametrizations on such forms
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Fit to ZEUS and H1 diffractive DIS (prelim.) data
xg x -l
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xg x -l
gD
SD
ZEUS l0.22 H1 l0.13 combn l0.17
H1 2002 fit use as0.1085 cf. 0.1187(PDG) H1
have steeper Q2 dep. of S, hence larger g. Also
no twist-4 FL
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but one of the HERA surprises.
global partons at
g valence-like S Pomeron-like whereas
expect lg lS 0.1 (xg x lg xS x lS
)
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need to introduce Pomeron made of col. singlet qq
pair
Pomeron made of two gluons
as well as
Now Pomeron flux factors depend on Sp as well
as gp
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dm2 m2
input forms
use MRST/CTEQ partons
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gD
SD
Fit with qq as well as gg Pomeron
Uses MRST gp and Sp to calculate Pomeron flux
factors
v.good fit
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diffractive charm production
constrains gluon
direct contribution
from gPom
add separately. No evolution and no DDIS
factorization
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the description of ZEUS diffractive charm
production
from gPom
direct
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The corresponding MRW fit to the ZEUS LPS data
? and H1 (prelim.) data
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MRW 2005 ZEUS LPS, charm, MX
MRW 2005 ZEUS LPS, charm, H1
H1 fit 2002
MRW 2004 ZEUS LPS,MX, H1
MRW 2004?2005 parametrize bgP in DIS scheme
then transform to MSbar
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H1
MRW
CDF dijet data
g
rapidity gap survival prob.
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Conclusions
Analysis of DDIS, which goes beyond collinear
Regge factn Regge factorization replaced by
pQCD --need quark-antiquark Pomeron, in addition
to two-gluon Pomeron --the input forms of the
Pomeron PDFs given by QCD diagrams
Collinear DDIS factorization modified in HERA
regime --inhomogeneous DGLAP evolution ?
smaller gPom
Good description of H1, ZEUS DDIS data
We obtain universal diffractive partons
--diffractive gluon considerably smaller than
that of H1 fit
--for hadron-hadron diffraction, must include
rap. gap survival probability
Moreover---the diffractive fit allows an
estimate of the absorptive corrections in global
DIS fit
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Contribution of diffractive F2 to inclusive F2
Apply the AGK cutting rules to
contrib.
AGK in QCD Bartels Ryskin
Im Tel stot
DF2abs - F2D
negative (Glauber shadowing)