1

V.A. Khoze (IPPP, Durham & Manchester)

main aim: to highlight recent development in the theory and phenomenology of the CED Higgs production

(Based on works with S.Heinemeyer, A.Martin, M.Ryskin, W.J.Stirling, M.Tasevsky and G.Weiglein)

Studying the BSM Higgs sector by forward proton tagging at the LHC (Introduction)

2

1. Central Exclusive Diffractive Production (only a taste).

2. Models and current understanding of uncertainties (Dino, Alan, Misha, Jean-Rene)

3. Prospects for CED Higgs-boson production in BSM scenarios. (VAK, Marek, Andy) .

4. Physics backgrounds revisited.

5. Conclusion.

PLAN

3

New CDF results

orders of magnitude differences in the theoretical predictions for the CEP of the Higgs are now a history

(CDPE) ~ 10 (incl) -4

(Khoze-Martin-Ryskin 1997-2008)

4

d

A killing blow to the wide range of theoretical models.

Visualization of QCD Sudakovformfactor

arXiv:0712.0604 ,PRD-2008CDF

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How reliable are the calculations ? Are they well tested experimentally ?

● How well we understand/model soft physics ?● How well we understand hard diffraction ?● Is ‘hard-soft factorization’ justified ? (Misha)

What else could/should be done in order to improve the accuracy of the calculations ?

So far the Tevatron diffractive data have been Durham-friendly ( Dino, Jim,

Mike),

clouds on the horizon ?or

(Jean-Rene, Misha)

(Alan,Misha)

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‘Well, it is a possible supposition.’‘You think so, too ?’‘I did not say a probable one’

Much more theoretical papers than the expected number of the CED produced SM Higgs events

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Survival of the Survival Factor

Importance for the Forward Physics Studies at the LHC

Serve as a litmus paper indicator of the level of our knowledge (theory & experiment) on diffractive physics at high energies

Account for the absorption effects -necessitated by unitarity

S² -a crucial ingredient of the calculations of the rate of the Central Excl. Diffractive processes +….. Prospects of New Physics studies in the Forward Proton mode

qualitatively new stage

• orders of magnitude differences in theoretical expectations – are a history

(not so long ago- between Scylla and Charybdis)

• new (encouraging) CED Tevatron results available, more results to come

• we are discussing now the differences on the level of a factor of (3-4)

(Alan, Misha)

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We have to be open-eyed when the soft physics is involved.Theoretical models contain various assumptions and parameters.

Available data on soft diffraction at high energies are still fragmentary,especially concerning the (low mass) diffractive dissociation.

Selection Criteria for the Models of Soft Diffraction

A viable model should:

incorporate the inelastic diffraction :SD, DD (for instance 2-3 channel eikonal of KMR or GLM(M))

describe all the existing experimental data on elastic pp- scattering and SD ,DD and CED at the Tevatron energies and below (KMR; GLM(M), 0805.2799 )

be able to explain the existing CDF data on the HERA-Tevatron factorization breaking and on the CED production of the di-jets, di-photons, , J/, .., lead. neutr. at HERA

provide testable pre-dictions or at least post-dictions for the Tevatron and HERA So far KMR model has passed these tests.

Only a large enough data set would impose the restriction order on the theoretical models and to create a full confidence in the determination of S².

Program of Early LHC measurements (KMR, M.Albrow et al.- FSC )

LET THE DATA TALK !

with a bit of personal

flavour

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(Alan, Misha)

-2000

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(tot) , (el) , (SD)

Bread and butter of TOTEM and ALFA measurements

Importance for various LHC studies ( e.g. notorious Pile-Up)

Low mass SD (DD)- one of the major current limitations on the models( still not sufficient exp. Information) KMR-07: relatively low (about 20% below the ‘standard’ central value) value of (tot) at the LHC

( S.Sapeta and K. Golec-Biernat-05)

, (tot) 90 mb …cosmic rays, (early) LHC tests – coming soon

inescapable consequence of the absorptive corrections caused by the higher-mass excitations GLM (arXiv; 0805.0418): (tot ) =110.5 mb, (el) =25.3 mb

(GLM)M (arXiv; 0805.2799): (tot ) = 92,1 mb, (el) =20.9 mb KMR (2007) (tot ) =90.5 mb, (el) =20.8 mb

GLM(M)- essential improvement of their description of the Tevatron elastic and SD data

(Alan, Misha)

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th

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Are the early LHC runs,without proton taggers,able to check estimatesfor pp p+A+p ?

Possible checks of:

(i) survival factor S2: W+gaps, Z+gaps

(ii) generalised gluon fg : p p

(iii) Sudakov factor T : 3 central jets

(iv) soft-hard factorisation #(A+gap) evts (enhanced absorptive corrn) #(inclusive A) evts with A = W, dijet, …

gap

gapKMR: 0802.0177

Divid

e et

Impe

ra

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The main advantages of CED Higgs production

• Prospects for high accuracy (~1%) mass measurements (irrespectively of the decay mode).

• Quantum number filter/analyser. ( 0++ dominance ;C,P-even)

• H ->bb opens up (Hbb- coupl.)

(gg)CED bb in LO ; NLO,NNLO, b- mass effects - controllable.

• For some areas of the MSSM param. space CEDP may become a discovery

channel !• H →WW*/WW - an added value ( less challenging experimentally + small bgds., better PU cond. )

• New leverage –proton momentum correlations (probes of QCD dynamics , CP- violation effects…)

LHC : ‘after discovery stage’, Higgs ID……

H

How do we know what we’ve found?

mass, spin, couplings to fermions and Gauge Bosons, invisible modes… for all these purposes the CEDP will be particularly handy !

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MSSM

without ‘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

>

SM-like

4 generations:enhanced Hbb rate (~ 5 times )

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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 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-07; B. Cox, F.Loebinger, A.Pilkington-07

250 20(Marek,Andy)

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A.G. Shuvaev & KMR. arXiv:0806.1447 [hep-ph]

Further improvement of the g-b misidentification probability 1.3%0.5% or even better.

In the CEP environment gbb could/should be menagable

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The MSSM and more ‘exotic ‘scenarios

If the coupling of the Higgs-like object to gluons is large, double proton tagging becomes very attractive

• The intense coupling regime of the MSSM

(E.Boos et al, 02-03)

CP-violating MSSM Higgs physics (B.Cox et al . 03, KMR-03, J. Ellis et al. -05)

Potentially of great importance for electroweak baryogenesis

• an ‘Invisible’ Higgs (BKMR-04)

• NMSSM (J. Gunion, J.Forshaw et al.) searches for the Higgs triplets

(Andy)

(Andy,Marek)

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New Tevatron data still pouring

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Mhmax benchmark scenario Improved theory & background

3 countours

“600X 2” scenario covers nearly the whole allowed region for the light Higgs.

For large tan heavy Higgs reach goesbeyond 235 GeV.

For the H-boson the area reachable in the “60”-scenario is to large extent ruled out by the Tevatron data.

(Marek)

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CDM benchmarks

Compliant with the Cold Dark Matter and EW bounds (EHHOW-07)

Tevatron limits New bb-backgrounds

3 contours P3- NUHM scenario

LEP limit

TEVATRON

(M. Tasevsky + HKRW)

(Marek)

22

CDM P3 scenario 3 contours

Abundance of the lightest neutralinioin the early universe compatiblewith the CDM constraints as measured by WMAP.

The MA – tan planes are in agreement with the EW and B-physics constraints

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at 220 GeV:CED (HWW/ZZ) rate – factor of ~9; at 120 GeV CED (Hbb) rate – factor of ~5.

HZZ – especially beneficial Simplest example of the BSM Higgs physics

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Experts claim that :

Hints from B- factories

Baryon asymmetry of the Universe

Baryogenesis at the EW scale

4G is allowed by precision measurements

4G allows for the heavy Higgs

4G

26for the light Higgs below 200 GeV

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CDF & D0

At 60 fb-1 : for M=120 GeV , ~25 bb ev; for M=220 GeV, ~ 50 WW ev; favourable bgs, S/B>5

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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

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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Backup

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☻ Up to now the diffractive production data are consistent with K(KMR)S

results Still more work to be done to constrain the uncertainties.

Exclusive high-Et dijets CDF: data up to (Et)min>35 GeV

• ‘Factorization breaking’ between the effective diffractive structure functions measured at the Tevatron and HERA.

•The ratio of high Et dijets in production with one and two rapidity gaps

•CDF results on exclusive charmonium CEDP, (CDF to be submitted to PRL)

•Energy dependence of the RG survival (D0, CDF).

Central Diffractive Production of γγ (…., ) (CDF, PRL-07)( in line with the KMRS calculations) ( 3 candidates & >10 more candidates in the new data)

Leading neutrons at HERA

LET THE DATA TALK !

CURRENT EXPERIMENTAL CHECKS

Only a large data set would allow to impose a restriction order on the theoretical models

(PRD-2008)

Dino, Mike

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Mike Albrow (Fermilab) for the CDF

75+- 14

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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) ,

P(g/b)0.5 % (new software)

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