1

V.A. Khoze (IPPP, Durham)

A. Shuvaev & KMR arXiv:0806.1447 [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) -4

(Khoze-Martin-Ryskin 1997-2008)

3

A killing blow to the wide range of theoretical models.

arXiv:0712.0604 ,PRD to appear soon

KMR-based

2 (+10) Excl. Events (CDF)

4

MSSMwithout ‘clever hardware’: for H(SM)bb at 60fb-1 onlya handful of events due tosevere 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 Hbb 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 ………..

bb

bb

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

250 20

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

8

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

10

11

A.G. Shuvaev et al. arXiv:0806.1447 [hep-ph]

12

13

14

Approximate formula for the background

bb

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)

1 2|60 12 .0 1| 1

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

16FenHiggs 2.6.2 M. Tesevsky, with new bgd

PRELIMINARY

17

HKRSTW-07

18FenHiggs 2.6.2 M. Tesevsky, with new bgd

PRELIMINARY

19

= -500 GeVPRELIMINARY

20

Andy’s talk

21

Shuvaev et al-08arXiv:0806.1447 [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 +(Hbb) +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)

23

24

11. 11. Thou shalt notThou shalt not delay, thedelay, the LHC start-upLHC start-up isis approaching.approaching.