Experimental overview of diffraction

1
Experimental overview of diffraction
Aharon Levy Tel Aviv University

• Concise summary of experimental data
• Questions
• Some outlook

2
List of talks

• Review talks (by experimentalists)
• Alessia Bruni Diffraction at HERA
• Dino Goulianos Diffraction in a Nutshell
• Inclusive Diffraction (HERA)
• Marcella Capua ZEUS results on inclusive
  diffraction
• Julian Rautenberg Diffraction in CC events
  (ZEUS)
• Sebastian Schaetzel Measurement of the
  diffractive cross section and their QCD
  interpretation (H1)
• Roger Renner ZEUS results on diffractive dijets
• Svetlana Vinokurova The diffractive production
  of charm and jets

3
List of talks (2)

• Inclusive diffraction (Fermilab)
• Jean-Laurent Agram QCD and diffraction results
  from D0 run II
• Christina Mesropian Diffraction at CDF in run II
• Inclusive diffraction (RHIC)
• Greg Rakness Forward pion production at STAR
• Sebastian White Recent results on inelastic
  diffraction scattering of pp, d-Au, Au-Au beams
  at RHIC

4
List of talks (3)

• Exclusive diffraction (HERA)
• Robert Ciesielski Recent ZEUS results on vector
  mesons
• Karlheinz Hiller High t diffraction and DVCS
  from H1
• Exclusive diffraction (HERMES/COMPASS)
• Oleg Grebenyuk Exclusive electroproduction of
  pions and vector mesons at HERMES
• Bjoern Seitz Measurement of DVCS at HERMES
• Andrzej Sandacz Diffractive ?? production at
  COMPASS experiment

5
List of talks (4)

• Exclusive diffraction (RHIC)
• Wlodek Guryn Preliminary results from pp2pp
  experiment at RHIC
• Alessandro Bravar Spin dependence in polarized
  elastic pC?pC and pp?pp scattering at very low
  momentum transfer
• Ronald Longacre Ultra-peripheral Au-Au physics
  at STAR
• Exclusive diffraction (LEP/LHC)
• Valeri Pozdniakov Study of double-tagged ??
  interactions
• F. Ferro Higgs production in pp?pHp at LHC

6
Diffraction
Bj Large rapidity gap not exponentially
suppressed
7
Diffractive event selection
LPS
LRG
8
Diffractive structure function
M. Capua
S. Schätzel
9
H1-LPS-MX comparison
S. Proskuryakov
10
t-slope of LPS (FPS)
11
Diffractive structure functions
If FLD(3) 0, ?rD(3)F2D(3)
good approximation for low y

• - higher twist
• J/? - small

12
S. Schätzel
13
Energy dependence
Total inclusive and diffractive inclusive same
energy dependence
14
NLO QCD fit on LPScharm data

• xIP lt0.01
• QCDNUM
• Regge factorisation assumption
  possible for this small data set
• DL flux
• initial scale Q22 GeV2
• zf(z)(a1a2za3z2)(1-x)a4
• other PDFs parametrisation tried
• Thorne-Robert variable-flavour-
  number-scheme

(LPS)

• QCD fit describes data
• fractional gluon momentum
• is
• at initial scale

M. Capua
15
H1 2002 NLO QCD Fit
Use Regge factorization seems to be justified
by data
S. Schätzel
16
Diffractive PDFs
Are these pdfs portable? Does QCD factorization
hold?
(Note validity of pdfs Q023 GeV2, MXgt2 GeV,
xIPlt0.05)
S. Schätzel
17
Unitarity limit
Probability that a gluon from the proton will
produce a diffractive process at x10-3 and
Q24 GeV2, Pg0.4!! (unitarity limit is
0.5) (Frankfurt, Strikman)
Probability that a gluon from the proton will
produce a diffractive process at x10-3 and
Q24 GeV2, Pg0.4!! (unitarity limit is
0.5) (Frankfurt, Strikman)
Probability that a gluon from the proton will
produce a diffractive process at x10-3 and
Q24 GeV2, Pg0.4!! (unitarity limit is
0.5) (Frankfurt, Strikman)
18
Unitarity limit
Probability that a gluon from the proton will
produce a diffractive process at x10-3 and
Q24 GeV2, Pg0.4!! (unitarity limit is
0.5) (Frankfurt, Strikman)

• Kaidalov et al. ratio of diffractive to
  inclusive dijet production.
• Pumplin bound ?D/??0.5
• Unitarity effects may already be present in the
  gluon sector.
• Reason why cross section with W slower the
  expected?

(Saturation and unitarization are related. The
theory behind CGC legitimizes the GBW model)
19
dAu Correlations probing low x
G. Rakness
20
QCD factorization diffractive Dand DIS dijets
at HERA
S. Vinokurova
H1 diff dijets ?r2pT2, ?f240 GeV2 H1 fit 2002
21
QCD factorization diffractive dijets at the
Tevatron
C. Mesropian
Survival probability 0.1?
Survival probability 1 ? 0.5?
22
MRW fit
G. Watt
23
MRW fit
G. Watt
24
QCD factorization photoproduction of dijets
R. Renner, S. Vinokurova
Survival probability 0.5?
25
Questions Diffraction?

• What is diffraction? Are we measuring
  diffraction?
• Soft diffraction
• slow energy dependence (s0.08)
• amplitude (almost) imaginary (Gribov-Migdal)
• vacuum number exchange (P, P (f2))
• Gribov-Morrison rule (eg 1- ? 1-, 2, 3-, etc)
• Hard diffraction
• fast increase of cross section of processes
  initiated by parton configurations where color is
  concentrated in spatially small volume.
• amplitude can have real part, reconstructed from
  the imaginary part.

26
Diffraction?(2)
Large rapidity gap can be created by colorless
exchange. Can be Pomeron, but also Reggeon is
colorless. Where do these two components
contribute to diffraction processes? Actually a
Reggeon exchange process should not be called
diffraction. (K. Golec-Biernat, J. Kwiecinski
and A. Szczurek, Phys. Rev. D56 (1997) 3955.)
27
Reggeon and pion contributions in diffractive
processes
K. Golec-Biernat, J. Kwiecinski and A. Szczurek,
Phys. Rev. D56 (1997) 3955.
28
S. Schätzel
29
Diffraction in CC events
J. Rautenberg
30
Diffraction in CC events
S. Schätzel, J. Rautenberg
xIP, xBJ lt 0.05
31
?D/?tot
32
?D/?tot
H1 ratio at xIPlt0.03 Q2100 GeV2 ? 5
33
Questions on inclusive diffraction
Is Regge factorization broken? Also for xIP lt
0.01? Need more precise measurements. Ideally
would like to do QCD analysis for fixed
xIP. Breaking of QCD factorization explained by
survival probability? What about unitarity? Large
ratio of diffractive/total cross section.
Decreasing with Q2.
34
Exclusive diffractive processes
Situation much clearer exclusive vector meson
electroproduction deserves to be called
diffractive processes. Show soft and hard
diffraction behaviour.

• process becomes hard as scale (mass) becomes
  larger.
• real part of amplitude increases with hardness.

35
STAR gAu --gt (r0 pp- )Au
R. Longacre
36
VM - Energy dependence
R. Ciesielski
37
?VM/?tot
38
?VM/?tot
39
R ?L/?T
R. Ciesielski, O. Grebenyuk, A. Sandacz
?
?
?
J/?
40
R ?L/?T(2)
Scaling of R with Q2/MV2 ?
41
R ?L/?T(3)
R. Ciesielski
42
Large and small configurations of photon
?L small configuration ?T large and
small Large configuration ?(W) rises
slowly Small configuration ?(W) rises fast
?L/?T W independent ? large configurations of
transverse photon suppressed.
43
Large and small configurations of photon (2) -
DVCS
SCHC expected to hold ? incoming ? - transverse
K. Hiller
? Large configuration of ?T suppressed
44
Question
Why are the large configurations of ?T
suppressed in exclusive DIS VM (?) production?
45
Size of vector mesons
R. Ciesielski
46
Trajectories - ?eff (!!)
R. Ciesielski
47
Trajectories(2)
48
High-t VM
At what t does DGLAP stop to work??
K. Hiller
49
?? - BFKL
V. Pozdniakov
50
K. Hiller
51
DVCS
52
Results comparison with CNIdifferent
polarizations and CNI parameters
Is the hadronic spin-flip needed?
Curves show dependence of CNI on stot, r and B
53
AN for pp pp _at_ 100 GeV fit
AN for pC pC _at_ 100 GeV
A. Bravar
54
Back to DVCS
55
DVCS - HERMES
BSA
B. Seitz
56
Outlook
HERA Tevatron RHIC Future ep collider?