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

1. Small x and Diffraction, FNAL Sept 2003 It isn’t … unless this diagram exists, and has a large enough cross section: degrades the beam energy for minimal or no gain at all. This : Brian Cox Why is double proton tagging potentially useful for detecting new physics?

2. Advantages of exclusive central production For s >> M2,t For colour singlet bbar production, the born level contributions of a) and b) cancel in the limit mb -> 0 V. A. Khoze, A. D. Martin and M. G. Ryskin Eur.Phys.J. C23 (2002) 311-327 • 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

3. Exclusive central production 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) gluon screens the colour Hard subprocess cross section • The cross section ~ factorises … … so can be checked by measuring higher rate processes in Run II (-> Angela Wyatt’s talk) Effective luminosity for production of mass M at rapidity y V. A. Khoze, A. D. Martin and M. G. Ryskin Eur.Phys.J. C23 (2002) 311-327

4. An example in which double tagging may be the only way In the CPX scenario, the three neutral MSSM Higgs bosons, (CP even) h0 and H0, and (CP odd) a mix to produce 3 physical mass eigenstates H 1 , H 2 and H 3 with mixed CP Then, (very schematically), the lightest Higgs could be predominantly CP odd, and not couple strongly to the Z. Imagine a light scalar which couples predominantly to glue, and decays to b jets … would we see it at LEP, Tevatron or LHC? A. Pilaftsis, Phys. Rev. D58 (1998) 096010; Phys. Lett. B435 (1998) 88.

5. Light neutral Higgs bosons in the CPX scenario Medium grey Dark grey “there are small regions of parameter space in which none of the neutral Higgs bosons can be detected at the Tevatron and the LHC” CPX scenario: M. Carena, J. Ellis, A. Pilaftsis and C. E. M. Wagner , Nucl. Phys. B586 (2000) 92. Plot from M. Carena, J. Ellis, S. Mrenna, A. Pilaftsis and C. E. M. Wagner, hep-ph/0211467

6. Central exclusive CPX Higgs cross sections LHC Tevatron At LHC, 120 GeV Higgs s ~ 3 fb (KMR Eur. Phys. J. C23 (2002) 311.) B.C., J. R. Forshaw, J. S. Lee, J. W. Monk and A. Pilaftsis hep-ph/0303206

7. Another example: very preliminary results for Radion production Radion field doesn’t couple to Z, BUT mixing can occur D.Dominici et. al. hep-ph/0206192

8. Signal to Background • misidentification of large glue – glue subprocess Assuming 1% b misidentification probability B/S ~ 0.06 • non-forward ( i.e. non-zero t) JZ = 2 admixture B/S ~ 0.08 • order contribution from massive b quarks B/S ~ 0.06 • bbar glue in which gluon goes undetected down beam pipe Removed by requiring • bbar glue in which gluon co-linear with b jet B/S ~ 0.06 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 A. De Roeck, V. A. Khoze, A. D. Martin, R. Orava and M. G. Ryskin Eur.Phys.J. C23 (2002) 311-327

9. Soft pomeron – pomeron background “Inclusive” (Central-inelastic) process p+p p + gap + H + X + gap + p Removed by requiring

10. 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

11. Signal to Background for light CPX Higgs Mass resolution of pots (1 GeV) • JZ = 0 selection rule less effective at small masses Cross section for exclusive bb production ~ > 2  for MH > 20 GeV at LHC Probably no chance at Tevatron, even though cross section is potentially large • Cross sections ~ order of magnitude larger, so more chance of seeing it, right?

12. The Experimental Strategy p P1U P2O Q4 Q3 Q2 Q2 S D Q3 Q4 S A1 D1 A2 D2 P1D P2I Veto p 57 59 23 0 33 23 33 CDF and D0 ~ 0.035 < x < 0.095 D0 ~ all x, |t| > 0.6 GeV • Tag both protons at low t, in the appropriate x range (Missing mass) Tevatron: 10 GeV < MH < 50 GeV, 0.005 < x < 0.025 LHC: 10 GeV < MH < 50 GeV, 0.0007 < x < 0.0035 • 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

13. Conclusions Physics with forward proton taggers at the Tevatron and LHC Manchester 14, 15, 16 December 2003 glodwick.hep.man.ac.uk/conference • 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),