Measurements of Inclusive Diffraction at HERA

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Measurements of Inclusive

Diffraction at HERA

• M.Kapishin, JINR, Dubna
• Diffractive DIS at HERA
• Factorization in diffractive DIS
• Diffractive cross section measurements
• Charged current measurements
• Summary

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H1 and ZEUS experiments
HERA collider p (920 GeV) x e (27.6 GeV), vs
320 GeV
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Diffractive DIS at HERA
HERA 10 of low-x DIS events are diffractive
? study QCD structure of high energy diffraction
with virtual photon
Standard DIS
Diffractive DIS

e
e
?
x

• Probe structure of color singlet exchange ? F2D

• Probe structure of proton ? F2

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Diffractive DIS at HERA
Large rapidity gap between leading proton p and X
?max

W

• Momentum fraction of proton carried by color
  singlet exchange
• Momentum fraction of color singlet carried by
  struck quark

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Diffractive Reduced Cross Section
Relation to F2D and FLD
t

• Integrate over t while proton is not measured ?

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Factorization in Diffractive DIS
QCD hard scattering factorization

• universal hard scattering cross section (same as
  in inclusive DIS)
• diffractive parton distribution function ? obey
  DGLAP,
• universal for diffractive ep DIS (inclusive,
  di-jets, charm)
• Additional assumption ? Regge factorization

- pomeron flux factor - pomeron parton
distribution function
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Selection of diffraction Mx method

• Properties of Mx distribution
• exponential rise with Mx
• for non-diffractive events
• flat vs ln Mx2 for diffractive events

Forward Plug Calorimeter (FPC) ?acceptance
extended to higher Mx and lower W range
?p-dissociation MY lt 2.3 GeV

• non-diffractive events subtracted
• from fit
• contamination from reaction
• ep?eXY

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W dependence of dsdiff/dMx
(Mx method)

• 2.2 lt Q2 lt 80 GeV2
• p-dissociation contribution MYlt2.3 GeV
  
• Mx lt 2 GeV weak W dependence
• Mx gt 2 GeV ds/dMx rises with W
• power-like fit ? extract aIPdiff

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Effective aIP(0) vs Q2
Diffractive cross section
Inclusive cross section according to optical
theorem

• Effective aIP(0)
• lower than for inclusive cross section
• consistent with soft IP at low Q2
• data suggest increase with Q2
• Regge factorization breaking
• similar W dependence of diffractive and
  inclusive cross section
• 2(aIPdiff -1) aIPtot - 1

n

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LPS proton vs Rapidity Gap

• Large rapidity gap selection
• MYlt1.6 GeV and tlt1 GeV2
• LPS proton selection MY mp
• extrapolated to tlt1 GeV2
• ?Good agreement between two methods and two
  experiments
• ?Data well described by
• H1 QCD fit to LRG data
• ZEUS Mx data should be scaled by 0.69
  to account for p-diss
• ?see also Heuijin Lim talk for ZEUS LPS results

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srD measurements

• Data at Low Q2, L 3.4 pb-1
• Good agreement between measurements
• Data well described by H1 NLO QCD Fit to medium
  Q2 data ? diffractive PDFs
• IR contribution needed at high xIP
• Data at Medium Q2, L 10.6 pb-1
• Data at High Q2, L 65 pb-1

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NLO DGLAP Fit ? PDF
Zq
PDF

• ? Diffractive PDFs
• PDF extend to large fractional momentum z
• Precise measurement of quark singlet distribution
• Gluon distribution dominated
• ? 75 15
• Large gluon uncertainty at high z
• Can be applied to test QCD factorization in ep
  final states (charm, di-jets) ? see next talk

?see also Heuijin Lim talk for ZEUS QCD Fit
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Measurement at High Q2 vs Prediction of
QCD Fit

• Improved statistics and kinematical range of new
  measurement compared to previous measurement
• ? good agreement
• Prediction of NLO Fit based on Medium Q2
  data
• ? good agreement
• Sub-leading trajectory needed at high xIP
  and low ß

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Q2 dependence

• Evolution of NLO Fit over an order of magnitude
  in Q2
• good agreement with High Q2 data
• scaling violations in a wide ß range
• High Q2 data will provide additional constraints
  on singlet and gluon distributions

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High Q2 charged current events
Probe LRG processes via weak interactions ep ?
?Wp ? ?XY
PDF

• H1 L 63 pb-1
• Large rapidity gap selection
• xIPlt0.05, MY lt 1.6 GeV
• Q2 gt 200 GeV2, y lt 0.9
• ? 14 CC events

• ZEUS L 60.9 pb-1
• Large rapidity gap selection xIPlt0.05
• Q2 gt 200 GeV2, y lt 0.9 ? 9 CC events

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High Q2 charged current events
Incl
LRG

• Probe diffractive PDFs from H1 94 QCD Fit
  assuming flavor symmetry ? RAPGAP
• RAPGAP ARIADNE give reasonable description of
  LRG and inclusive CC data

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Differential CC cross sections

• First measurement of differential LRG CC cross
  sections
• RAPGAP with diffractive PDFs from H1 2002 LO QCD
  Fit describes LRG CC cross sections
• ?contribution of sub-leading trajectory at
  high xIP

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High Q2 CC cross section

• LRG CC cross section (Q2gt200GeV2,xIPlt0.05,ylt0.9)
  
• ZEUS sCC LRG 0.49 0.20(stat)0.13(syst) pb
• H1 sCC LRG 0.42 0.13(stat)0.09(syst) pb
• Ratio of LRG to inclusive CC cross section
  (xBjlt0.05)
• ZEUS sCC LRG / sCC Incl 2.9 1.2(stat)0.8(syst)
  
• H1 sCC LRG / sCC Incl 2.5
  0.8(stat)0.6(syst)
• ? Results are in good agreement

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Summary

• ZEUS recent measurement of diffractive data with
  improved precision and extended kinematic range
• indication that aIP increases with Q2
• similar W dependence of diffractive and inclusive
  DIS
• H1 measurement of diffractive cross section at
  high Q2
• data are consistent with NLO DGLAP Fit to medium
  Q2 data including additional contribution from
  sub-leading trajectory
• ZEUS and H1 first measurement of LRG CC cross
  section at high Q2
• probe LRG processes via weak interactions
• data are consistent with model based on
  diffractive PDFs
• results of two experiments are in good agreement

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