# Presentation: 537897

## Why is double proton tagging potentially useful for detecting new physics?

**Why is double proton tagging potentially useful for detecting new physics?**

- Brian Cox

- Small x and Diffraction,  FNAL Sept 2003

## Advantages of exclusive central production 

-  tagging the protons means the mass of the central system is known, irrespective of decay channel, up to the resolution of the taggers ...

- ... if there is no other particle production in the central region

-  only 0++ central systems can be produced, if the protons remain intact and scatter through small angles ...

- ... QCD bbar background is greatly surpressed

- ... if you see a resonance, you know it’s a CP-even, spin 0 particle

- Very schematically it’s a glue – glue collider where you know the beam energy of the gluons

**Notes:**
Make point about tagging protons – ONLY if all these things are true does one gain enough to pay off the reductiuon in C of M energy

## Exclusive central production  

- gluon screens the colour

-  The cross section ~ factorises ...

- Hard subprocess cross section

- V. A. Khoze, A. D. Martin and M. G. Ryskin Eur.Phys.J. C23 (2002) 311-327

- Effective luminosity for production of mass M at rapidity y

- ... so can be checked by measuring higher rate processes in Run II (-> Angela Wyatt’s talk)

- Sudakov factors ‘cut off’ Qt integral
-  (as Qt-> 0 probability for NO emission -> 0, and hence there is no contribution to the exclusive cross section)

## An example in which double tagging may be the only way

- A. Pilaftsis, Phys. Rev. D58 (1998) 096010; Phys. Lett. B435 (1998) 88.

*Imagine a light scalar which couples predominantly to glue, and decays to b jets ... would we see it at LEP, Tevatron or LHC?*

## Light neutral Higgs bosons in the CPX scenario 

**Light neutral Higgs bosons in the CPX scenario**

- “there are small regions of parameter space in which none of the neutral Higgs bosons can be detected at the Tevatron and the LHC”

- Plot from M. Carena, J. Ellis, S. Mrenna, A. Pilaftsis and C. E. M. Wagner, hep-ph/0211467

**CPX scenario: ** M. Carena, J. Ellis, A. Pilaftsis and C. E. M. Wagner , Nucl. Phys. B586 (2000) 92.

## Central exclusive CPX Higgs cross sections  

**Central exclusive CPX Higgs cross sections  **

- LHC

- B.C., J. R. Forshaw, J. S. Lee, J. W. Monk and A. Pilaftsis hep-ph/0303206

- At LHC, 120 GeV Higgs ~ 3 fb
- (KMR Eur. Phys. J. C23 (2002) 311.)

- Tevatron

## Another example: very preliminary results for Radion production

- D. Dominici et. al. hep-ph/0206192

- Radion field doesn’t couple to Z, BUT mixing can occur

## Signal to Background  

- A. De Roeck, V. A. Khoze, A. D. Martin, R. Orava and M. G. Ryskin Eur.Phys.J. C23 (2002) 311-327

- A detailed study for 120 GeV Standard model Higgs at LHC (De Roeck et. al.)

-  Leading order ‘bbbar’ backgrounds

-  NLO backgrounds

-  NNLO shown to be negligibly small

## Soft pomeron – pomeron background  

-  “Inclusive” (Central-inelastic) process
- p+p       p + gap + H + X + gap + p

**Soft pomeron – pomeron background  **

- Removed by requiring

## L = 30 fb-1

- A. De Roeck, V. A. Khoze, A. D. Martin, R. Orava and M. G. Ryskin Eur.Phys.J. C23 (2002) 311-327

- L = 30 fb-1

## Signal to Background for light CPX Higgs  

-  Cross sections ~ order of magnitude larger, so more chance of seeing it, right?

## The Experimental Strategy 

-  Tag both protons at low t, in the appropriate range (Missing mass)

- Tevatron: 10 GeV < MH < 50 GeV, 0.005 <  < 0.025

-  Tag b jets

-  Impose approximate mass equality Mmissing = Mbbar

- M. G. Albrow and A. Rostovtsev hep-ph/0009336

- A. De Roeck, V. A. Khoze, A. D. Martin, R. Orava and M. G. Ryskin Eur.Phys.J. C23 (2002) 311-327

- LHC: 10 GeV < MH < 50 GeV, 0.0007 < x < 0.0035

## Conclusions 

-  There may be light scalars in nature, and we should be prepared to look for them

-  Proton tagging can in principle deliver the required mass resolution and background suppression

-  Proton tagging gives us a high energy ‘pure’, ‘colourless’ glue – glue collider with variable beam energy (for a very small cost)

-  BUT !! The cross section predictions must be verified experimentally at the Tevatron - see new CDF results (Angela Wyatt),