Diffraction at the Tevatron: CDF Results

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Diffraction at the Tevatron CDF Results
K. Goulianos The Rockefeller University
? presented on behalf of the CDF Collaboration ?
Diffraction 2006Milos island, Greece, 5-10
September 2006
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Contents

• Run-I diffraction _at_ CDF
• Run II results
• Diffractive structure function
• ? xBj, Q2, and t dependence
• Exclusive production
• ? dijet diphoton

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Run-I Diffraction _at_ CDF
sTIm fel (t0)
Elastic scattering
Total cross section
f
f
OPTICAL THEOREM
GAP
h
h
DD
DPE
SDDSDDD
SD
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Run I-0 (1988-89)
Elastic, single diffractive, and total cross
sections
_at_ 546 and 1800 GeV
Roman Pot Spectrometers

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

Additional Detectors Trackers up to h 7

• Results
• Total cross section stot se
• Elastic cross section ds/dt exp2a
  lns ? shrinking forward peak
• Single diffraction Breakdown of Regge
  factorization

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Breakdown of Regge factorization
Factorization ?
Pomeron flux
KG, PLB 358 (1995) 379
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Run-IA,B,C
Run-IA,B
Forward Detectors BBC 3.22.4 7
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

Results DD, like SD, is suppressed The
formation of the second gap in two-gap events is
not suppressed!
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Hard Diffractive Fractions _at_ CDF
Fraction SD/ND ratio at 1800 GeV
All ratios 1 ? uniform suppression
FACTORIZATION !
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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 factorizationmultigap diffraction
w/preliminary pdfs from
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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Run II Results

• Diffractive structure function
• NEW
• Q2 - dependence
• t - dependence
• Exclusive production
• dijet
• diphoton

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CDF in Run-II
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The MiniPlugs _at_ CDF
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DIFFRACTIVE STRUCTURE FUNCTION
Systematic uncertainties due to energy scale and
resolution cancel out in the ratio
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Diffractive Dijet Signal

• - Bulk of data taken with RPS trigger but no RPS
  tracking
• Extract x from calorimetric information
• Calibrate calorimetric x using limited sample of
  RPS tracking data
• Subtract overlap background using a rescaled
  dijet event sample
• Verify diffractive x range by comparing xRPS
  with xCAL

Overlap events mainly ND dijets plus SD low x
RPS trigger
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Alignment of RPS using Data
maximize the t-slope ? determine X and Y offsets
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xCAL Calibration
overlap events
signal region
xcal distribution for slice of xRPS
? / mean 30
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Dijet Properties
SD boosted opposite to pbar
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ET distributions
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Diffractive Structure FunctionQ2 dependence
ETjet 100 GeV !

• Small Q2 dependence in region 100 GeV2
• Pomeron evolves as the proton!

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

• Same slope over entire region of
• 0
• across soft and hard diffraction!

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

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Diffractive dijets Dffpbar-fdijet
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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 Search for events with
two high ET gammas and no other activity in the
calorimeters or BSCs
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 ExHuME
(red) Exclusive DPE in DPEMC (blue)
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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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JJexcl R(excl/incl) vs ETmin
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Exclusive gg/ee Search
QED process cross-check to exclusive gg

• (anti)proton not detected
• require 2 EM showers (ET5 GeV, h
• veto on all BSCs and cal towers except for those
  of the 2 EM showers
• L530 pb-1 delivered ? Leffective46 pb-1
• ? 19 events with 2 EM showers nothing above
  threshold

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Exclusive ee Search
control sample for gg search
ET16.1 GeV ET26.0 GeV
?16 candidate events found background
good agreement with LPAIR
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Exclusive gg Search
ET16.8 GeV/c ET25.9 GeV/c
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Summary

• Run I
• Suppression of single gap diffraction
• M2 scaling ds/dM2 independent of s
• Non-suppressed double-gap to single-gap ratios
  
• Run II
• Diffractive structure function vs xBj, Q2, and
  t
• ? Composite Pomeron
• made up from proton pdfs ?
• Exclusive production dijet and diphoton
• ? Diffractive Higgs _at_ LHC under control

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BACKUP
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p-p Interactions

• Diffractive
• Colorless exchange w/vacuum quantum numbers

Non-diffractive Color-exchange
rapidity gap
Incident hadrons acquire color and break apart
Incident hadrons retain their quantum
numbers remaining colorless
Goal understand the QCD nature of the
diffractive exchange
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M2 - scaling
KGJM, PRD 59 (1999) 114017
? Independent of S over a range of six
orders of magnitude in M2 !
Factorization breaks down so as to ensure
M2-scaling!
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x-dependence Inclusive vs Dijet
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The MiniPlug Calorimeters
About 1500 wavelength shifting fibers of 1 mm
dia. are strung through holes drilled in 36x¼
lead plates sandwiched between reflective Al
sheets and guided into bunches to be viewed
individually by multi-channel photomultipliers.