V A Khoze IPPP Durham Physics Backgrounds Revisited

V. A. Khoze (IPPP, Durham) Physics Backgrounds Revisited A. Shuvaev & KMR ar. Xiv: 0806. 1447 [hep-ph] 1

(Khoze-Martin-Ryskin 1997 -2008) -4 (CDPE) ~ 10 (incl) Not so long ago: between Scylla and. Orders of magnitude differences in theoretical predictions are now a history 2

KMR-based ar. Xiv: 0712. 0604 , PRD to appear soon A killing blow to the wide range of theoretical models. 3 2 (+10) Excl. Events (CDF)

Studying the MSSM Higgs Sector MSSM without ‘clever hardware’: for H(SM) bb at 60 fb-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 Ge. V. (B. Cox et al-06) enhanced trigger strategy & improved timing detectors (FP 420, TDR) situation in the MSSM is very different from the SM > 4 generations: enhanced H bb rate (~ 5 times ) Conventionally due to overwhelming QCD backgrounds, the direct measurement of Hbb is hopeless The backgrounds to the diffractive H bb mode are manageable! 4

some regions of the MSSM parameter space are especially proton tagging friendly (at large tan and M , S/B ) KKMR-04 HKRSTW, 0. 7083052[hep-ph] B. Cox, F. Loebinger, A. Pilkington-07 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 ………. . Not fully in MCs 5

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. (KMR-2000) There must be a god Do not need many events to establish cleanly that the Higgs is a scalar and to measure the mass 6

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 7

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

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A. G. Shuvaev et al. ar. Xiv: 0806. 1447 [hep-ph] 11

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Approximate formula for the background c M- mass window over which we collect the signal C~0. 5 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 Ge. V) g/b- misident. prob. P(g/b)=1. 3% (ATLAS) Four major bgd sources ~ (1/4 + (1. 3)²/4 + 1/4 ) at M≈120 Ge. V, M= 4 Ge. V 14

HKRSTW-07 15

PRELIMINARY Fen. Higgs 2. 6. 2 M. Tesevsky, with new bgd 16

HKRSTW-07 17

PRELIMINARY Fen. Higgs 2. 6. 2 M. Tesevsky, with new bgd 18

= -500 Ge. V PRELIMINARY 19

Andy’s talk 20

Shuvaev et al-08 ar. Xiv: 0806. 1447 [hep-ph] 21

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) 22

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11. Thou shalt not delay, the LHC start-up is approaching. 24