1 V.A. Khoze ( IPPP, Durham ) A. Shuvaev & KMR arXiv: [hep-ph] Physics Backgrounds Revisited

2 Not so long ago: between Scylla and. Orders of magnitude differences in the theoretical predictions are now a history  (CDPE) ~ 10  (incl) (Khoze-Martin-Ryskin )

3 A killing blow to the wide range of theoretical models. arXiv: , PRD to appear soon KMR-based 2 (+10)  Excl. Events (CDF)

4 MSSM without ‘clever hardware’: for H(SM)  bb at 60fb-1 only a handful of events due to severe exp. cuts and low efficiencies, though S/B~1. But H->WW mode at M>135 GeV. ( B.Cox et al-06 )  enhanced trigger strategy & improved timing detectors ( FP420, TDR ) The backgrounds to the diffractive H bb mode are manageable! situation in the MSSM is very different from the SM Conventionally due to overwhelming QCD backgrounds, the direct measurement of Hbb is hopeless > Studying the MSSM Higgs Sector 4 generations:  enhanced H  bb rate (~ 5 times )

5 Myths For the channel bgds are well known and incorporated in the MCs: Exclusive LO - production (mass-suppressed) + gg misident+ soft & hard PP collisions. Reality The background calculations are still in progress : (uncomfortably & unusually large high-order QCD and b-quark mass effects). About a dozen various sources ( studied by Durham group )  admixture of |Jz|=2 production.  NLO radiative contributions (hard blob and screened gluons)  NNLO one-loop box diagram ( mass- unsuppressed, cut-non-reconstructible)  ‘Central inelastic’ backgrounds ( soft and hard Pomerons )  b-quark mass effects in dijet events ……….. some regions of the MSSM parameter space are especially proton tagging friendly (at large tan  and M, S/B ) KKMR-04 HKRSTW, [hep-ph] B. Cox, F.Loebinger, A.Pilkington-07 Not fully in MCs

6 for Higgs searches in the forward proton mode QCD backgrounds are suppressed by Jz=0 selection rule and by colour, spin and mass resolution (  M/M) –factors. There must be a god Do not need many events to establish cleanly that the Higgs is a scalar and to measure the mass (KMR-2000)

7 MHV-technique: an elegant way to write down the tree-level (and loop) helicity amplitudes in a compact way, automatically accounting for the possible cancellations between different terms, caused by gauge invariance and symmetry properties (e.g. Parke & Taylor-1986). Nowadays popular among (more) formal people E. Witten et al

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9 Real gluon radiation  Mercedes-like kinematics; ( KRS-2006) should be strongly reduced by the standard selection cuts. (can be accounted by SHERPA MC ) g b b

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11 A.G. Shuvaev et al. arXiv: [hep-ph]arXiv:

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14 Approximate formula for the background  M- mass window over which we collect the signal  b-jet angular cut : ( )  both S and B should be multiplied by the overall ‘efficiency’ factor  ( combined effects of triggers, acceptances, exp. cuts, tagging efficienc., ….),  ~4.2 % (120 GeV)  g/b- misident. prob. P(g/b)=1.3% (ATLAS) Four major bgd sources ~ (1/4 +1/4 + (1.3) ²/ 4 + 1/4 ) at M≈120 GeV,  M= 4GeV c C~0.5

15 HKRSTW-07

16 FenHiggs M. Tesevsky, with new bgd PRELIMINARY

17 HKRSTW-07

18 FenHiggs M. Tesevsky, with new bgd PRELIMINARY

19  = -500 GeV PRELIMINARY

20 Andy’s talk

21 Shuvaev et al-08 arXiv: arXiv: [hep-ph]

22 Conclusion Strongly suppressed and controllable QCD backgrounds in the forward proton mode provide a potential for direct determination of the Hbb Yukawa coupling, for probing Higgs CP properties and for measuring its mass and width. In some BSM scenarios pp  p +( Hbb) + p may become a discovery channel at the LHC. Further bgd reduction may be achieved by experimental improvements, better accounting for the kinematical constraints, correlations….. The complete background calculation is still in progress (unusually & uncomfortably large high-order QCD effects, Pile-Up at high lumi)

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Thou shalt not delay, the LHC start-up is approaching.