슬라이드 1

Report
Diffraction at HERA
43rd Rencontres de Moriond : QCD and High Energy Interactions
8-15 March 2008, La Thuile, Italy
Heuijin Lim (ANL) on behalf of H1 and ZEUS collaborations
 Measurements of inclusive diffraction
 Diffractive Parton Densities
 Test of factorization in diffractive Final States
Heuijin Lim
Moriond QCD, 8-15 March 2008
1
Inclusive Diffraction in Deep Inelastic Scattering
Inclusive DIS process
 DIS : Probe structure of proton
 Diffractive DIS : Probe structure of colorless
system, Pomeron, exchange
Kinematics of ep  eXp
Q  (k  k)
2
2
W  (p  q)2  y  s
x IP 
Diffractive DIS process
N (MN)
Heuijin Lim
Q 2  M2X
Q2  W 2
t  (p  p)
2
x  Q2 (2q  p)
MX  (k  k  p  p)
Q2
x
β 2

MX  Q 2 x IP
2
xL  pZ Ep  1  x IP
In pQCD, Pomeron exchange can be
described
Moriond QCD, 8-15 March
2008 by two-gluon exchange.
2
2
Event selection
MX method
LPS method
Diffractive DIS process
Mass of X
 MX
xL=1-xIP=p⁄Z/pZ
Leading Proton Spectrometer
Outgoing proton
Large
Rapidity
Gap
LRG method
η=-ln(tan(θ/2))
Heuijin Lim
Scattered
electrons
ηmax
Inclusive DIS process
Moriond QCD, 8-15 March 2008
3
 Measurements of inclusive diffractive DIS
Diffractive cross-section : dσ(MX,W,Q2)/dMX
Comparison of diffractive and total γ*p scattering
 Q2 dependence of αIP(0) and rdiff(=σdiff/σtot)
Diffractive structure function : xIPF2D(3)(β,xIP,Q2), xIPF2D(4)(β,xIP,Q2, t)
Q2 dependence and β dependence
Comparison with MX, LRG and LPS measurements
 Diffractive Parton Densities
Extract DPDFs from QCD fit to inclusive diffractive DIS
Combined QCD fit to inclusive diffractive and Dijets
 Test of factorization in diffractive Final States
 Dijets in DIS and Photoproduction
Heuijin Lim
Moriond QCD, 8-15 March 2008
4
Diffractive Cross Section with MX method
FPCI (98-99) : 4.2 pb-1
2.2 < Q2 < 80 GeV2
Nucl. Phys. B713, 3(2005)
FPCII (99-00) : 52.4 pb-1
20 < Q2 < 450 GeV2
Submitted to Nucl. Phys. B.
(arXiv:0802.3017)
• Within systematic errors,
good agreement between
FPCI and FPCII.
Heuijin Lim
Moriond QCD, 8-15 March 2008
5
Comparison of diffractive and total γ*p scattering
tot
σ γ p

d2 σ diff
γ p
dMX
4π 2 α
2
Q (1  x)
2
tot
2 αIP (0) 1
F2 (x, Q ) ~ (W )
diff
2 2( αIP (0) 1)
~ (W )
• For Q2 < 20 GeV 2, αIPdiff(0) is consistent
with soft Pomeron.
• For Q2 > 30 GeV2, data suggest increase
with Q2.  Regge factorisation breaking.
• αIPdiff(0) is lower than αIPtot(0) :
 Different Pomeron trajectory!
 r = σdiff(0.28 < MX < 35 GeV)/σtot
• Within the errors of the measurements,
r is independent on W.
• At W=220 GeV, r ~ 15.8 % at Q2= 4 GeV2
r ~ 5.0 % at Q2= 190 GeV2
r shows a logarithmic dependence on Q2.
Heuijin Lim
Moriond QCD, 8-15 March 2008
6
Q2 dependence of xIPF2D(3)
diff
1 Q2 (Q2  M2X ) dσ γ p
D(3)
x IPF2  2
4π α
2MX
dMX
 Probability to find a quark carrying x=βxIP
in a proton undergoing a diffractive process.
x = β xIP < 0.001
• For β≥ 0.9
(dominated by events with MX<2 GeV),
Constant or slowly decreasing with Q2
Expect higher twist effect from (qq )L
• For x=β xIP < 0.001,
xIPF2D(3) increases with increasing Q2.
 Positive scaling violations.
Suggest perturbative effects such
as gluon emission
• For fixed β,
Q2 dependence of xIPF2D(3) changes
with xIP.  Inconsistent with the Regge
factorisation hypothesis
Heuijin Lim
Moriond QCD, 8-15 March 2008
7
Diffractive structure function with LPS method
F2D(4) ( , Q2 , xIP , t)  fIP (xIP , t)  F2IP ( , Q2 )  nIR  fIR (xIP , t)  F2IR ( , Q2 )
 The parameterization of xIP dependence gives the intercept of αIP.
0.01
0.040
αIP (0)  1.1  0.02(stat.) - 0.02
(syst.) 0.02(model) αIP (0)  1.114  0.018(stat.)  0.012(syst.)- 0.020
(model)
2
BIP  7.2  0.7(stat.)1.4
0.7 (syst.) GeV
2
BIP  5.5 2.0
0.7 GeV
Not Soft!
Soft
2
 0.04
2
 0.19
2



α
(0)
~
0.25
GeV
αIP (0)


0.03

0.07(stat.
)
(syst.)GeV
α
(0)

0.06
GeV
IP
 0.08
IP March 2008 0.06
Heuijin Lim
Moriond QCD, 8-15
8
Comparison of LRG with LPS measurements
ZEUS LRG 00 (prel.), ZEUS LPS 00 (prel.)
(LPS/LRG)
(LPS/LRG)
H1 LRG
with MN<1.6 GeV
ZEUS LRG with MN < 2.3 GeV
• Ratio between LRG and LPS is independent of Q2, β and xIP within errors.
 It shows 23~25 % of proton dissociation contribution in LRG data.
 For xIP > 0.01, their constant ratio tells that the LRG data also contain the
reggeon contribution.
Heuijin Lim
Moriond QCD, 8-15 March 2008
9
Factorization in Diffractive DIS
 Diffractive DIS, like inclusive DIS, is factorizable :
D
*
σ (γ p  Xp) 

D
2
2
fi p (z, Q , x IP , t)  σ γ*i (z, Q )
Diffractive parton distribution function
Universal partonic cross section
fi/pD(z,Q2,xIP,t) : Probability to find in a proton, with a probe of
resolution Q2, parton i with momentum fraction z, under the
condition that the proton remains intact and emerges with
small energy loss, xIP, and momentum transfer, t.
 Obey DGLAP
 universal for diffractive ep DIS (inclusive, Dijet, Cham)
 Assumption : Proton vertex factorization
 Shape of diffractive PDFs independent of xIP and t.
D
2
D
2
fi p (z, Q , xIP , t)  fIP p (xIP , t)  fi p (z, Q )
Regge motivated IP flux
At large xIP, a separately factorizable sub-leading exchange
(IR), with different xIP dependence and partonic composition.
Heuijin Lim
Moriond QCD, 8-15 March 2008
10
H1 2006 DPDF Fits
• Fit H1 LRG data
with Q2≥8.5 GeV2, MX>2 GeV, β≤0.8)
• Parameterize the parton density
2
B
z  (z, Q0 )  A qz q (1  z)
2
z g (z, Q 0 )  A g (1  z)
Cq
Cg
χ2 ~ 158/183 d.o.f., Q02=1.75 GeV2
• Effective Pomeron trajectory (Fit A) :
αIP  1.118  0.008(exp.) 0.029
0.010 (model)
~70 % gluons in diffractive exchange
• Due to lack of sensitivity for the
gluon density at high z.
 Fit B : using zg(z,Q02)=Ag
χ2 ~ 164/184 d.o.f. , Q02=2.5 GeV2
Heuijin Lim
Moriond QCD, 8-15 March 2008
11
Diffractive dijets in DIS
H1 2007 Jets DPDF
Fit 2006 - B
H1 2007 Jets DPDF
zIP= longitudinal momentum fraction of color singlet carried
by parton entering hard sub-process
 zIP distribution is sensitive to gluon DPDF.
Heuijin Lim
• H1 Dijet data are in better
agreement with H1 Fit B.
• ZEUS Dijet data consistent
with H1 Fit B and MRW 2006
fit.
• Combined Fit to inclusive
and Dijet data  better
constraint to quark and gluon
densities,
to H1
Moriond QCD, close
8-15 March
2008Fit B.
Fit 2006 – A
Fit 2006 -- B
12
Diffractive dijets in Photoproduction (Q2 ~ 0 GeV2)
xγ = 1
xγ < 1
Interactions destroy
gap for resolved PHP.
xγ = fraction of photon momentum in hard scattering.
• Dijets are suppressed by a factor~
0.5 for direct and resolved γ.
• Dijets are weakly suppressed by a
factor ~ 0.87 for direct and resolved γ.
(big difference: ETjet1 (ETjet2) > 5 (4) GeV)
(ETjet1 (ETjet2) > 7.5 (6.5) GeV)
Heuijin Lim
Moriond QCD, 8-15 March 2008
 ET distribution may not be well reproduced by NLO. Still work in progress. 13
Conclusion
 Inclusive diffraction was measured with high statistics for a wide
kinematic range from low to high Q2.
 Good agreement with the results measured by MX, LPS and LRG methods.
 Diffractive DIS and total γ*p process cannot be described by an unique
pomeron and r=σdiff(0.28 < MX < 35 GeV)/σtot decreases ~ ln(1+Q2).
 Indication for Regge factorisation breaking was seen in
Q2 dependence of αIPdiff(0)
Q2 dependence of xIPF2D(3) for fixed β and fixed xIP
 Evidence for pQCD evolution with Q2 as xIP0 or β  0.
 Combined QCD fit to inclusive diffractive DIS and Dijets
 It improved the gluon structure at high z.  Gluon dominated: ~ 70 %.
 Diffractive charm and Dijets DIS data are consistent with NLO predictions
based on DPDFs from inclusive data.
 Diffractive Dijets in photoproduction
ZEUS : agreement with NLO prediction and no large suppression(~0.87).
H1 : suppression(~0.5)
ETjet dependence is investigated.
Heuijin Lim
Moriond QCD, 8-15 March 2008
14

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