Soft Double Pomeron Exchange in CDF Run I

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Soft Double Pomeron Exchange in CDF Run I
Small-x and Diffraction 2003 Fermilab, Illinois,
USA

• Kenichi Hatakeyama
• The Rockefeller University
• for the CDF Collaboration

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Introduction
Shaded Area Region of Particle Production
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Main Issue in Hadronic Diffraction results from
single diffractive (SD) dijet production
CDF Collaboration, Phys. Rev. Lett. 84, 5043-5048
(2000).

• The diffractive structure function measured using
  SD dijet events at the Tevatron is smaller than
  that at HERA by approximately an order of
  magnitude.
• The discrepancy is generally attributed to
  additional color exchanges which spoil the
  diffractive rapidity gap.

Factorization Breakdown
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Dijet Production in DPE
CDF Collaboration, Phys. Rev. Lett. 85, 4215-4220
(2000).

• Dijet production by double pomeron exchange was
  studied by CDF.
• RDPE/SD is larger than RSD/ND by a factor of
  about 5.

The formation of the 2nd gap is not as
suppressed as the 1st gap.
Extract diffractive structure function
from RDPE/SD and compare it with expectations
from HERA results.
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Diffractive Structure Functionmeasured using DPE
dijet events
Factorization holds?
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Soft Diffraction Inclusive (Soft) SD Results
Unitarity problem

• The measured SD cross section is smaller than the
  Regge theory prediction by approximately an order
  of magnitude at the Tevatron energy.
• Normalizing the integral of the pomeron flux
  (fIP/p) to unity yields the correct vs-dependence
  of sSD.

Tevatron data
Renormalization
Similar results were obtained for double
diffraction as well.
Study DPE
Is the formation of the second gap suppressed?
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Inclusive (Soft) DPE Cross Section

• Regge theory prediction factorization
• Flux renorm. model
• (both gaps are suppressed.) K. Goulianos, Phys.
  Lett. B 353, 379 (1995).
• Gap probability (Pgap) renorm. model Pgap is
  renormalized.
• (only one gap is suppressed.) K. Goulianos, e.g.
  hep-ph/0110240 (2001).

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Analysis Strategy

• Use events triggered on a leading antiproton.
• ?pbar is measured by Roman Pots ?pbarRPS.
• Measure ?p (?pbar) from BBC and calorimeters
  ?pX (?pbarX).
• Calibrate ?X by comparing ?pbarRPS and ?pbarX.
• Plot ?pX distribution and look for a DPE signal
  expected in the small ?pX region.

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Reconstruction of ?pX
Calorimeters
Use calorimeter towers and BBC hits to
reconstruct ?p

• Calorimeters use ET and ? of towers above noise
  level.
• BBC use hits in BBC scintillation arrays.
• pT is chosen to follow the known pT spectrum

BBC
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Calibration of ?X
?X distribution in every ?RPS bin is fitted to
P1 Peak P2 Width
?X ?RPS, (?X is calibrated so that ?X ?RPS.)
P2/P1 0.57 (?X resolution is 60.)
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?pX Distribution

• The input ?p distribution in DPE MC is 1/?p1e (e
  0.104 is obtained from pp/pp/Kp total cross
  sections).
• The DPE and SD MC distributions are independently
  normalized to the data distribution.
• The measured ?pX distribution is in agreement
  with the DPESD MC distribution.

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DPE Fraction in SD Events
RDPE/SD(incl) RDPE/SD(incl)
Source _at_ 1800 GeV _at_ 630 GeV
Data 0.1950.0010.011 0.1680.0010.012
Regge factorization 0.36 0.25
Flux Renormalization 0.041 0.041
Pgap Renormalization 0.21 0.17
In agreement with the renormalized gap
predictions!
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Soft Diffraction Summary
SD
DD
s (mb)
DPE
SDD
Gap Fraction
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Conclusions

• The measured ?pX distribution exhibits 1/?1e
  behavior (e 0.104).
• The measured DPE fraction in SD is
• for 0.035 lt?pbarlt 0.095 and ?plt 0.02 at vs
  1800 GeV.
• in agreement with the renormalized gap prediction.