Diffractive Structure Functions and Exclusive Production from CDF to LHC

1
Diffractive Structure Functionsand Exclusive
Production from CDF to LHC
Konstantin Goulianos The Rockefeller
University and the CDF Collaboration
2
Contents

• Introduction
• Elastic and total cross sections
• Soft diffraction
• Hard diffraction
• Exclusive Production

3
p-p Interactions

• Diffractive
• Colorless exchange with vacuum quantum numbers

Non-diffractive Color-exchange
rapidity gap
Incident hadrons retain their quantum
numbers remaining colorless
pseudo- DECONFINEMENT
Goal understand the QCD nature of the
diffractive exchange
4
Diffractive pp Processes
sTIm fel (t0)
Elastic scattering
Total cross section
f
f
OPTICAL THEOREM
GAP
h
h
DD
DPE
SDDSDDD
SD
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CDF Run 1-0 (1988-89)
Elastic, diffractive, and total cross section
_at_ 546 and 1800 GeV
Roman Pot Spectrometers
CDF-I

• Roman Pot Detectors
• Scintillation trigger counters
• Wire chamber
• Double-sided silicon strip detector

Roman Pots with Trackers up to h 7
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CDF-I
Run-IA,B
beam
Forward Detectors BBC 3.2lthlt5.9 FCAL
2.4lthlt4.2
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CDF-II
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The MiniPlugs _at_ CDF
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ELASTIC AND TOTAL CROSS SECTIONS
_at_ Tevatron CDF and E710/811 ? use luminosity
independent method ?
Optical theorem
optical theorem

• Alert
• background Ninel yields small sT
• undetected Ninel yields large sT

10
Total Cross Sections Regge fit
CMG fit Covolan, Montagna, Goulianos PLB 389
(1995) 176
Born level

• Simultaneous Regge fit to
• pp, pp, and Kp x-sections
• using the eikonal approach
• to ensure unitarity
• s ? Se
• e 1.104 /- 0.002
• ? sLHC 115 mb
• _at_14 TeV

DL
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sT other approaches
eg, M. Block, arXivhep-ph/0601210 (2006) ? fit
data using analyticity constraints M. Block and
F. Halzen, Phys. Rev. D 72, 036006
sT (LHC) 107.3 1.2 mb
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sT and r-values from PDG
r ratio of real/imaginary parts of elastic
scattering amplitude at t0
CDF
CDF and E710/811 disagree
E710
E811
sT optical theorem Im fel(t0)
dispersion relations Re fel(t0)
CDF UA4
E811
N. Khuri and A. Martin measuring r at the LHC
tests discreteness of space-time
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SOFT DIFFRACTION
Key words renormalization scaling QCD multi-gap
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Renormalization
Factorization ?
Pomeron flux

• Regge theory
• sSD exceeds sT at
• Renormalization
• Pomeron flux integral
• (re)normalized to unity

KG, PLB 358 (1995) 379
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A Scaling Law in Diffraction
KGJM, PRD 59 (1999) 114017
? Independent of S over 6 orders of magnitude in
M2 !
Factorization breaks down so as to ensure
M2-scaling!
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The QCD Connection
Total cross section power law increase versus s
f
y
1/as
The exponential rise of sT(Dy) is due to the
increase of wee partons with Dy (E. Levin, An
Introduction to Pomerons,Preprint DESY 98-120)
Elastic cross section forward scattering
amplitude
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Single Diffraction in QCD
(KG, hep-ph/0205141)
t
2 independent variables
color factor
Gap probability
Renormalization removes the s-dependence
SCALING
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Multi-gap Renormalization
(KG, hep-ph/0205141)
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Central and Double Gaps _at_ CDF

• Double Diffraction Dissociation
• One central gap

• Double Pomeron Exchange
  
• Two forward gaps

• SDD SingleDouble Diffraction
• One forward one central gap

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Central Double-Gap CDF Results
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Gap Survival Probability
Results similar to predictions by Gotsman-Levin-M
aor Kaidalov-Khoze-Martin-Ryskin Soft color
interactions
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HARD DIFFRACTION

• Diffractive fractions
• Diffractive structure function
• ? factorization breakdown
• Restoring factorization
• Q2 dependence
• t dependence
• Hard diffraction in QCD

JJ, W, b, J/y
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Diffractive Fractions _at_ CDF
Fraction()
Fraction SD/ND ratio at 1800 GeV
All ratios 1 ? uniform suppression
FACTORIZATION !
1.15 (0.55)
W
0.75 (0.10)
JJ
0.62 (0.25)
b
1.45 (0.25)
J/y
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Diffractive Structure FunctionBreakdown of QCD
Factorization
b momentum fraction of parton in Pomeron

• The diffractive structure function at the
  Tevatron is suppressed by a factor of 10
  relative to expectation from pdfs measured by H1
  at HERA
• Similar suppression factor
• as in soft diffraction
• relative to Regge expectations!

H1
CDF
Using preliminary pdfs from
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Restoring QCD Factorization
The diffractive structure function measured on
the proton side in events with a leading
antiproton is NOT suppressed relative to
predictions based on DDIS
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Diffractive Structure FunctionQ2 dependence
ETjet 100 GeV !

• Small Q2 dependence in region 100 lt Q2 lt 10,000
  GeV2
• Pomeron evolves as the proton!

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Diffractive Structure Functiont- dependence
Fit ds/dt to a double exponential

• No diffraction dips
• No Q2 dependence in slope
• from inclusive to Q2104 GeV2

• Same slope over entire region of
• 0 lt Q2 lt 4,500 GeV2
• across soft and hard diffraction!

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Hard Diffraction in QCD
deep sea
valence quarks
Derive diffractive from inclusive PDFs and color
factors
xx
proton
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EXCLUSIVE PRODUCTION
Measure exclusive jj gg ? ?
? Calibrate predictions for

H production rates _at_ LHC
Bialas, Landshoff, Phys.Lett. B 256,540
(1991) Khoze, Martin, Ryskin, Eur. Phys. J. C23,
311 (2002) C25,391 (2002)C26,229 (2002) C.
Royon, hep-ph/0308283 B. Cox, A. Pilkington, PRD
72, 094024 (2005) OTHER
KMR sH(LHC) 3 fb S/B 1 if DM 1 GeV
Clean discovery channel

• Search for exclusive gg
• 3 candidate events found
• 1 (2/-1) predicted
• from ExHuME MC
• background under study
• See talk by V. Khoze

Search for exclusive dijets Measure dijet mass
fraction Look for signal as Mjj? 1
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Exclusive Dijet Signal
b-tagged dijet fraction
Dijet fraction all jets
DIJETS
Exclusive b-jets are suppressed by JZ 0
selection rule
Excess over MC predictions at large dijet mass
fraction
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RJJ(excl) Data vs MC
Exclusive DPE (DPEMC) ? non-pQCD based on Regge
theory
ExHuME (KMR) gg?gg process ? uses LO pQCD
Shape of excess of events at high Rjj is well
described by both models
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jjexcl Exclusive Dijet Signal
COMPARISON Inclusive data vs MC _at_ b/c-jet data vs
inclusive
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JJexcl x-section vs ET(min)
Comparison with hadron level predictions
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JJexcl cross section predictions

• ExHuME Hadron-Level Differential Exclusive Dijet
  Cross Section vs Dijet Mass
• (dotted/red) Default ExHuME prediction
• (points) Derived from CDF Run II Preliminary
  excl. dijet cross sections

Statistical and systematic errors are
propagated from measured cross section
uncertainties using ExHuME Mjj
distribution shapes.
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Summary

• TEVATRON what we have learnt
• M2 scaling
• Non-suppressed double-gap to single-gap ratios
• Pomeron composite object made up from
  underlying
• pdfs subject to color constraints
• LHC - what to do
• Elastic and total cross sections r-value
• High mass (?4 TeV) and multi-gap diffraction
• Exclusive production (FP420 project)
• ? Reduced bgnd for std Higgs to study
  properties
• ? Discovery channel for certain Higgs
  scenarios