Brian Cox and Jeff Forshaw

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POMWIG Herwig for Diffractive interactions
Brian Cox and Jeff Forshaw Comput.Phys.Commun.144
104-110,2002 (hep-ph/0010303) http//www.pomwig.c
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• Simple modification to HERWIG (doesnt affect
  functionality at Tevatron) which makes all HERWIG
  features available in diffractive collisions
• IP P, IR P, IP IP ,IR IR, e IP, e IR collisions
  with all HERWIG hard matrix elements

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WHAT IS POMWIG ?

• No doubt that Ingelman Schlein (Regge
  factorisation) works at HERA
• Pomwig uses measured structure functions and
  flux from H1 OR user defined structure functions
  / flux

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QCD Hard scattering factorisation
conditional proton parton densities for
particular xIP, t
Regge factorisation
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Modifications to Herwig

• Philosophy make as few changes as possible, do
  not change common blocks
• MODIFIED ROUTINES
• HWEGAM photon flux routine
• HWSFUN structure functions
• NEW ROUTINES
• H1QCD H1 pomeron structure
• FLUX pomeron and reggeon fluxes
• POMSTR user defined structure functions

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How to run POMWIG

• Select electron for beam particle to emit pomeorn
  / reggeon
• Q2WWMN ? TMIN, Q2WWMX ? TMAX
• YWWMIN ? XpomMIN, YWWMAX ? XpomMAX
• NSTRU6 (H1 pomeron), 7 (Reggeon), 8 (user
  defined)

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Double Diffractive Dijets and Higgs Production
POMWIG Central-inelastic process pp p
gap H X gap p

• Is this really a contender for a light Higgs
  discovery channel ?
• We wont see DD Higgs at Tevatron, BUT we do see
  DD dijets
• Question Can we see the exclusive contributions
  in the DD dijets ?
• Answer Not yet, but we should (if it exists) in
  RunII.

exclusive
Khoze, Martin Ryskin, hep-ph/0207313,
Eur.Phys.J. C23 (2002) 311-327Cox, Forshaw
Heinemann, Phys.Lett.B540263-268,2002 De Rouke,
Khoze, Martin, Orava Ryskin hep-ph/0207042 Albr
ow and Rostovtsev, hep-ph/0009336
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Double Diffractive Higgs in POMWIG
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Double Diffractive Higgs
IHEP ID IDPDG IST MO1 MO2 DA1 DA2
P-X P-Y P-Z ENERGY MASS 1
E -11 101 0 0 4 5
0.00 0.00 980.0 980.0 0.00
2 E- 11 102 0 0
6 7 0.00 0.00 -980.0 980.0
0.00 3 CMF 0 103 4
6 0 0 0.01 -1.05 -31.1
163.0 160.02 4 GAMMA 22 3
1 0 0 0 0.07 -0.81
65.9 65.9 -0.84 5 E
-11 1 1 0 0 0
-0.07 0.81 914.1 914.1 0.00 6
GAMMA 22 3 2 0 0 0
-0.06 -0.24 -97.1 97.1 -0.27
7 E- 11 1 2 0
0 0 0.06 0.24 -882.9 882.9
0.00
---HARD SUBPROCESS--- IHEP ID
IDPDG IST MO1 MO2 DA1 DA2 P-X P-Y
P-Z ENERGY MASS 8 GLUON 21
121 10 9 11 9 0.05
-0.62 50.8 50.9 0.75 9
GLUON 21 122 10 8 15 8
-0.04 -0.16 -65.0 65.0 0.75
10 HIGGS 25 120 8 9
67 67 14.85 -6.11 -14.4 117.0
115.01
---H/W/Z BOSON DECAYS--- IHEP ID
IDPDG IST MO1 MO2 DA1 DA2 P-X P-Y
P-Z ENERGY MASS 79 BQRK 5
123 67 80 81 80 25.96 -26.45
-57.1 68.2 4.95 80 BBAR
-5 124 67 79 86 79 -11.11
20.34 42.6 48.8 4.95
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Double Diffractive Dijets
Appleby Forshaw, Phys.Lett.B451108-114,2002
CDF Phys. Rev. Lett 85 4215 (2000)
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Gap Survival (factorisation breakdown)

• Its possible that the gap destruction mechanism
  is largely independent of the diffractive sub
  process
• Means that POMWIG gets the differential
  distributions correct at the Tevatron , up to a
  (process independent) normalisation factor

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KEY POINTS

• POMWIG is a simple modification to HERWIG which
  does not affect normal operation at Tevatron
  (only photoproduction routines changed).

• POMWIG makes state of the art matrix elements
  available in diffraction (if you keep HERWIG up
  to date) .

• As far as we can tell at present, all
  differential distributions in diffractive
  processes at HERA and Tevatron are correctly
  reproduced, with a universal overall
  normalisation factor of about 0.1 applied to
  account for gap survival.

• This means that it doesnt matter whether or not
  you like Regge factorisation - POMWIG is a
  useful tool for detector corrections etc.

• Double diffractive dijets are one of the most
  interesting processes to measure at RunII, if
  only because double diffractive Higgs at the LHC
  may turn out to be a competitive discovery
  channel for light Higgs.