Diffractive Physics

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Diffractive Physics
Andrew Brandt, U. Texas at Arlington

• Focus on mature analyses
• Diffractive Z
• Elastic Scattering

DØ Physics Workshop July 30, 2004 Fermilab
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Search for diffractive Z?µµ

• Inclusive Z?µµ sample well understood

• 2 muons, pT gt 15GeV, opposite charge

• at least one muon isolated in tracker and
  calorimeter

• cosmic rejection

Mµµ (GeV)
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Gap Definition Luminosity Monitor

• LM is Scintillating detector
• 2.7 lt ? lt 4.4
• Charge from wedges on one side are summed
  Detector is on/off on each side, North and South

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Gap Definition Calorimeter

• Use energy sum to distinguish proton break-up
  from empty calorimeter

Log(energy sum) on North side
Areas are normalised to 1
empty events
physics samples
10 GeV

• Esum cut of 10GeV was chosen for current study
• Final value will be optimised using full data
  sample

• Compare 'empty event' sample with physics
  samples
• Empty event sample random trigger. Veto LM
  signals and primary vertex, i.e. mostly empty
  bunch crossings
• Physics samples minimum bias (coincidence in
  LM), jet and Z?µµ events

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Z Mass Comparison
No GAP

• Add Esumlt10 GeV requirement
• to LM gap samples

One GAP

• Invariant mass for gap
• events looks like standard
• Z sample
• Will be able to compare Z boson kinematics
  (pT, pz, rapidity)

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Problem Run Dependent Esum
Two different run ranges show different noise
distributions forward noise study in progress
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Z?µµ gaps Summary

• Preliminary definition of rapidity gap at DØ Run
  II
• Study of Z?µµ- events with a rapidity gap
  signature (little or no energy detected in the
  forward direction)
• Current status
• Evidence of Z events with a rapidity gap
  signature
• Quantitative studies of gap definition,
  backgrounds, efficiency in progress
• No interpretation in terms of diffractive
  physics possible yet
• Plans
• Understand run dependent effects
• Measurement of the fraction of diffractively
  produced Z events
• properties of gap candidate events
• Diffractive W?µ?, W/Z?electrons, jets and other
  channels
• Use tracks from Forward Proton Detector

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Elastic Scattering

• Elastic scattering ? 0 (no momentum lost by
  beam particle)

• Quadrupole acceptance
• t gt 0.8 GeV2 (requires sufficient scattering
  angle to leave beam envelope)
• all ? (no longitudinal momentum loss necessary)

• Measure dN/dt for elastic scattering using early
  stand-alone FPD data

• antiproton side
• quadrupole up spectrometer
• trigger only

• proton side
• quadrupole down spectrometer
• full detector read-out

veto on LM and VETO counters, early time hits
(halo tracks)
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Preliminary Elastic Results

• The ds/dt data collected by different
  experiments at different energies
• A factor of 10-2 must be applied to each
  curve
• New DØ dN/dt distribution has been normalized
  by E710 data
• Compare slope with model Block et al, Phys.
  Rev. D41, pp 978, 1990.

This analysis based on Jorge Molinas
thesisfirst FPD Ph D
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Separator plates
Fall 2003 shutdown survey data (points AB) made
available by accelerator in March shows offsets
of up to 0.7 cm! Required rewriting of MC to
separate separators, reanalysis of acceptance.
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The acceptance for the PD spectrometer
Before sep correction
After sep correction
Much better high-t acceptance (previously high-t
data thought to be halo)
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When the correlations are introduced, the
acceptance is reduced, beginning at higher values
of t due to the positions reached by the AU pots
Which acceptance to use?
Note that trigger is based only on scintillator
hits and dominated by halo spray (only 2 real
tracks), so low-t data is presumably single arm
elastics, high-t double arm elastics
No acc. for low t !
Separator corrected
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Elastic Summary

• Re-evaluating acceptance and backgrounds
• Will decide soon if sufficient confidence in
  results to publish
• Silver lining nearly 100 of effort directly
  transferable to new analyses

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DØ Run II Diffractive Topics
Soft Diffraction and Elastic Scattering
Inclusive Single Diffraction Elastic
scattering (t dependence) Total Cross
Section Centauro Search
Inclusive double pomeron
Search for glueballs/exotics Hard
Diffraction Diffractive jet
Diffractive b,c ,t , Higgs
Diffractive W/Z
Diffractive photon Other
hard diffractive topics Double
Pomeron jets Other Hard Double Pomeron
topics
Rapidity Gaps Central gapsjets Double
pomeron with gaps Gap tags vs. proton tags
Topics in RED were studied with gaps only in Run
I
lt100 W boson events in Run I, gt1000 tagged events
expected in Run II
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Diffractive Topics and Students!
New student, Vlatislav Hynek (Czech), working on
forward diffractive jets
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Diffractive Data Samples

• Start with a list of all global physics runs for
  which the FPD pots are inserted that have not
  been declared bad by another sub-detector group
• Filter out interesting triggers (from diffractive
  POV) on a run by run basis

Extract raw fpd fiber information from raw
(pre-Nov 03), DST (post-Nov 03) put in a root tree
Use QCD_analyze to extract all other information
from TMBs and put in a root tree (using fixtmb2
version)
Sort tree by event number
Sort tree by event number
Clone QCD tree, add matching FPD branch, compare
each entry in trees for matching event numbers
and output to a merged tree for analysis

• With p17, FPD information is in TMB so everything
  will be done with QCD_analyze
• Current Status
• Final merging of pre-Nov 03 data underway
• post-Nov 03 stripping started

New UTA post-doc Duncan Brown leading
diffractive analysis group