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MHV rule, (Super)Symmetries and ‘Diffractive Higgs’

V.A. Khoze (IPPP, Durham & PNPI)Main aims • MHV rules and SUSY at the service of ‘diffractive Higgs’

• major QCD backgrounds to Hbb production at the LHC in the forward proton mode

(based on works with M.G. Ryskin, A.D. Martin and W.J. Stirling)

Higgs sector study- one of the central targets of FP420 physics menu

QCD and High Energy InteractionsLa Thuile (Italy) , March 8-15 2008 

ADR

(X. Rouby)

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CMS & ATLAS were designed and optimised to look beyond the SM

High -pt signatures in the central region

But…

• Main physics ‘goes Forward’•Difficult background conditions, pattern recognition, Pile Up...

• The precision measurements are limited by systematics (luminosity goal of δL ≤5% , machine ~10%)

Lack of :•Threshold scanning , resolution of nearly degenerate states (e.g. MSSM Higgs sector)•Quantum number analysing •Handle on CP-violating effects in the Higgs sector•Photon – photon reactions , …

YES Forward Proton Tagging

Rapidity Gaps Hadron Free Zones

matching Δ Mx ~ δM (Missing Mass)

RG

RGX

p

p p

p

The LHC is a very challenging machine!

Is there a way out?

The LHC is a discovery machine !

ILC/CLIC chartered territory

The LHC is not a precision machine (yet) !

(X. Rouby)

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For theoretical audience

MHV rules, Super (symmetry) and‘Diffractive Higgs’ at the LHC

Irreducible Physics Backgrounds toDiffractive Higgs Production

at the LHC

For experimental audience

Forward Proton Mode- Main Advantages for Higgs studies:

• Measurement of the Higgs mass via the missing mass technique (irrespectively of the decay channel)•Direct H bb mode opens up (Hbb Yukawa coupling); unique signature for the MSSM Higgs sector.•Quantum number/CP filter/analyzer•Cleanness of the events in the central detectors.

(K.G)

4 not so long ago: between Scylla and Charibdis:orders of magnitude differences in the theoretical predictions are now a history

(CDPE) ~ 10 (incl) -4

(Khoze-Martin-Ryskin 1997-2008)

New CDF Excl. dijet results: A killing blow to the wide range of theoretical models.

(A.Dechambre)

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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. (ADR,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

SM-like

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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 not fully complete: (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 – still in progress potentially, the largest source of theoretical uncertainties!

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

coming soon

MC

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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)

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(D. Kosower)

9(CFCA)

NNLO

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Works is progress : W.J. Stirling et al, A. Shuvaev et al

Preliminary results of calculations with the SL accuracy- very promising:a factor of 8 lower than the Born expectation (A. Shuvaev et al )

Good

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(+ n soft gluons)

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(angular brackets)

14‘Conventional’ MC algorithms cannot be used

kills soft gluon log

no collinear logs

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hard P

soft P

150 20 70 5

0.14 9d/dy|y=0

units 10-3 fbkT<5 GeVMdijet/Mbb=20%Mmissing=4GeV

signal backgd

X 1/8

SM (120 GeV) Higgs LO irreducible

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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 Higgs 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). A clear downward tendency.

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FP420, It is now or never

Such opportunities come rarely –let’s not waste this one!

UK

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

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BACKUP

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dA killing blow to the wide range of theoretical models.

Visualization of QCD Sudakovformfactor

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beam direction case

if a gluon jet is to go unobserved outside the CD or FD ( )

violation of the equality : (limited by the )

contribution is smaller than the admixture of Jz=2. KRS-06

sinmis g bbM M

b-direction case (HCA)

0.2 ( R/0.5)²

Note : soft radiation factorizes strongly suppressed is not a problem, NLLO bgd numerically small

bbgg

radiation from the screening gluon with pt~Qt :HC (Jz=2) LO ampt. ~ numerically very small

hard radiation - power suppressed

KMR-02cos

2( / )t tQ p

(R –separation cone size)

bbM

t tM p Q

MHV results for gg(Jz=0)ggg(g) amplitudes (dijet calibration, b-mistag)

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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

main uncertn. at low masses

Four major bgd sources ~ (1/4 +1/4 + (1.3)²/4 + 1/2 ) at M≈120 GeV, M= 4GeV

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mb=0