Transcript Hard diffraction in eA Cyrille Marquet RIKEN BNL Research Center Inclusive and diffractive structure functions.

Hard diffraction in eA
Cyrille Marquet
RIKEN BNL Research Center
Inclusive and diffractive
structure functions
Deep inelastic scattering (DIS)
k’
k
eh center-of-mass energy
S = (k+P)2
size resolution 1/Q
*h center-of-mass energy
W2 = (k-k’+P)2
photon virtuality
Q2 = - (k-k’)2 > 0
p
Q2
Q2
x
 2
2P.(k  k ' ) W  M h2  Q2
x ~ momentum fraction of the struck parton
P.(k  k ' ) Q2 / x
y

P.k
S  M h2
y ~ W²/S
Diffractive DIS
k’
when the hadron remains intact
k
momentum transfer
t = (P-P’)2 < 0
diffractive mass of the final state
MX2 = (P-P’+k-k’)2
p
p’
Q2
Q2


2( P  P' ).(k  k ' ) M X2  t  Q2
 ~ momentum fraction of the struck parton with respect to the Pomeron
xpom = x/
rapidity gap :  = ln(1/xpom)
xpom ~ momentum fraction of the Pomeron with respect to the hadron
Inclusive diffraction at HERA
Diffractive DIS with proton tagging e p  e X p
H1
ZEUS
FPS data
LPS data
Diffractive DIS without proton tagging e p  e X Y with MY cut
H1
ZEUS
LRG data MY < 1.6 GeV
FPC data MY < 2.3 GeV
Collinear factorization
vs
dipole factorization
Collinear factorization
in the limit Q²   with x fixed
• for inclusive DIS
 *p X
 tot
(x, Q2) 
1
 d 
(, Q2)ˆa(x/, Q2)  O(1/Q2)
a/ p
partons a x
a = quarks, gluons
• perturbative evolution
of  with Q2 :

ln(Q2)
 Κ
DGLAP

Dokshitzer-Gribov-Lipatov-Altarelli-Parisi
not valid if x is too small
non perturbative
• for diffractive DIS
another set of pdf’s, same Q² evolution
perturbative
Factorization with diffractive jets ?
you cannot do much with the diffractive pdfs
factorization also holds for
factorization does not hold for
diffractive jet production at high Q²
diffractive jet production at low Q²
diffractive jet production in pp collisions
for instance at the Tevatron:
predictions obtained with diffractive pdfs
overestimate CDF data by a factor of about 10
a very popular approach:
use collinear factorization anyway,
and apply a correction factor called
the rapidity gap survival probability
The QCD dipole picture in DIS
in the limit x  0 with Q² fixed
• deep inelastic scattering (DIS) at small xBj :
photon virtuality Q2 = - (k-k’)2 >> 2QCD
*p collision energy W2 = (k-k’+p)2
sensitive to values of x as small as xBj 
k’
k
Q
size resolution 1/Q
2
W2 Q
2
p
k’
• diffractive DIS :
k
diffractive mass MX2 = (k-k’+p-p’)2

Q2
M Q
2
X
2
xpom = x/
rapidity gap  = ln(1/xpom)
p
p’
Hard diffraction and small-x physics
the dipole scattering
amplitudfe
T=1
T << 1
dipole size r
Q2 DIS 
Q2 DDIS
1
1

Q2
 ln(Q2 /QS2 ) 
1

1
1

hard diffraction is directly
sensitive to the saturation region
Forshaw and Shaw
no good fit without saturation effects
contribution of the different r regions
in the hard regime Q2  Q2S
DIS dominated by relatively hard sizes
1 Q  r  1 QS
DDIS dominated by semi-hard sizes
r ~ 1 QS
Hard diffraction off nuclei
some expectations
D,A
The ratio F2
/ F2
A
following the approach of Kugeratski, Goncalves and Navarra (2006)
ratio ~ 35 %
from Kowalski-Teaney model
at HERA saturation naturally
explains the constant ratio
plots from Tuomas Lappi
The ratio F2
•
D,A
/ F2
D,p
x dependence
following Kugeratski, Goncalves and Navarra
Au / d
full : Iancu-Itakura-Munier model
linear : linearized version of IIM
shape and normalization
influenced by saturation
•
scheme dependence for
naive :
FRWS :
Freund, Rummukainen, Weigert and Schafer
ASW :
Armesto, Salgado and Wiedemann
Pb / p