# Presentation: 785145

## POMWIG – Herwig for Diffractive interactions

**Comput.Phys.Commun.144:104-110,2002 **
**(hep-ph/0010303)**
**http://www.pomwig.com**

**POMWIG – Herwig for Diffractive interactions**

-  Simple modification to HERWIG (doesn’t 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

## 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

##  conditional proton parton densities for particular xIP, t

-  **QCD Hard scattering factorisation :**

-  conditional proton parton densities for particular xIP, t

**Regge factorisation :**

## 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

## Slide 5

## How to run POMWIG

- Select electron for beam particle to emit pomeorn / reggeon
- Q2WWMN  TMIN, Q2WWMX  TMAX
- YWWMIN  XpomMIN, YWWMAX  XpomMAX
- NSTRU=6 (H1 pomeron), 7 (Reggeon), 8 (user defined)

## Double Diffractive Dijets and Higgs Production

-  POMWIG : “Central-inelastic” process
- p+p       p + gap + H + X + gap + p

- Khoze, Martin & Ryskin, hep-ph/0207313, Eur.Phys.J. C23 (2002) 311-327Cox, Forshaw & Heinemann, Phys.Lett.B540:263-268,2002
- De Rouke, Khoze, Martin, Orava & Ryskin  hep-ph/0207042
- Albrow and Rostovtsev, hep-ph/0009336 ...

-  “exclusive”

-  Is this really a contender for a light Higgs discovery channel ?
-  We won’t 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.

## Double Diffractive Higgs in POMWIG

## 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

## Double Diffractive Dijets

- CDF Phys. Rev. Lett 85 4215 (2000)

- Appleby & Forshaw, Phys.Lett.B451:108-114,2002

## 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

## 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 doesn’t 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.