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V.A. Khoze (IPPP, Durham) (based on works with A. Kaidalov, M. Ryskin, A.D. Martin amd W.J. Stirling)

Early LHC Measurements Aiming at Reducing Uncertainties in CEP Predictions

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

aims: to list & expose the main uncertainties in the theoretical expectations for CEP rates, to propose the measurements which will allow to cross- check the predictions

By popular demand (ADR, Risto, Brian, …)

Forward Physics at the LHC December 9th - 11th 2007

with a bit of personalflavour

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reference. purposes,ExHume tuning

(Alan’s talk)

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This is what matters for the CEP rates ! KMRS-04

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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’ well justified ?

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)

clouds on the horizon ?

Theory side - •Hard rescattering corrections to CEP, (BBKM-06) (agreement with KMR at the TPF-level !) • New papers/talks by GLM-07 ( Strikman et al, 06-07 )

or

(Uri’s and Alan’s talks)

(Dino, Mike)

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(Dino, Mike)

(MC models as well)

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Saga about Soft Survival

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EXP. DATA

(Pythia, Phojet)

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PDF’s DEMOCRACY

KKMR -04 – factor of 1.5-2 difference between CTEQ6M and MRST02, ( Jeff Forshaw)

very recently, CLP-07, factor of 4 difference between CTEQ6L1 and MRST2002NLO, CTEQL1 7.38 fb for SM Higgs.

Here we are on the conservative side, but further studies and tests are needed

Higher-Order QCD effects

Uncomfortably large higher-order QCD effects in the case of exclusive processes, exemplified by the Sudakov effect. Seen now in the dijet exclusive data. (Thanks to CDF )

Further serious theoretical studies needed, NNLO Sudakov ?

Self-consistent combined treatment of higher order effects in unintegrated struct. functs and in the hard cross-section – requires detailed studies

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KMR-00(07): use 2(3)-channel eikonal+ ‘soft’ enhanced contributions (A. Martin’s talk)

Bartels,Bondarenko,Kutak,Motyka-06used pert.thy.corrn could be large and H(excl) modified ? KMR-06 arguments for small effect

enhanced absorption,discussed first KKMR-01 in the diffractive dijet context

“enhanced”correctionto H(excl)?

Semi-enhanced hard rescattering and soft-hard factorization

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Leading neutronprod. at HERA, Zeus

eikonal enhanced

gap due to exchange ~ exclusive Higgs

yi > 2 – 3

correction prop. to rap. interval prop. to energy(negative)

Prob. to observe leading neutronmust decrease with energyBut expt. flat small enhanced correction

KKMR ‘06

New ZEUS data

SD may change (flat) behaviour at the LHC if enh . contr. is large

On top of KMR theoretical arguments

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EXPERIMENTAL CHECKS(Yesterday and Today)

Up to now the diffractive production data are consistent with K(KMR)S results Still more work to be done to constrain the uncertainties

CEP of high-Et dijets (CDF: Run I, Run II) data up to (Et)min>50 GeV (Dino’s talk) , finally on the hep-ex !

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

(KKMR-01 ,a quantitative description of the results, both in normalization and the shape of the distribution)

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

• Preliminary CDF results on exclusive charmonium CEDP.

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

• CEP of γγ (….,) , PRL paper (Mike’s talk) (in line with the KMRS calculations)

Leading neutrons at HERA

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16p- scanner

p-reconstructed via W (no proton tagging)

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rich diffractive structures

-mass effects lesspronounced

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(K.G.& Montanha-98)

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y=-ln , =(1-x)

( also useful for calculations of the pile-up backgrounds)

Higher sensitivity to the parameters of models for Soft Diffraction

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Exclusive dijet Monitor & Interferometer

Dijet rate- combined effect of all basic ingredients (Surviv, Sudakov, pdfs, Enhanc. Absp) ( ET > 10 GeV)

CEP of diphotons (rate permitting) would provide an excellent combined test at M>10-20 GeV (better accuracy!)

ET-dependence -dominantly Sudakov (+anom dimens), weaker dependence on S².At low ET- higher sensitivity to the Enhanced Absorption When having the proton detectors operationalCorrelations between proton transverse momenta, azimuthal distribtsPractically insensitive to pdfs and Sudakov effects.High sensitivity to soft model parameters. Proton opacity scanner (KMR-02, also Kupco et al-05, Petrov et al -05)

Comparing dijet signals in different rapidity intervals study of Sudakov suppression

Advantages• Comparatively high rate (3 orders of magnitude higher than for the Higgs at the same ET).

• Possibility to separate different effects and to restrict different uncertainties by studying the same process

( 20 ) 1 ,0DPEjj TE GeV nb ( ) 1 10DPE b

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d(cf, Dino’s talk)

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KMR-02 Correlations

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KMR-02

High ET central jets are not required (in principle)

proton pt allows to sample different impact parameters

btOpacity Scanner

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(P. Bussey)

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By Mike’s request

ppp +Z+p at || <1, (Z) ~ 0.3 fb (in agreement with the latest evaluation by

Goncalves & Machado arXiv:0710.4287 v.3)

Could be useful for probing the predictions for deviation from the SM(for instance The LHC (White) Pomeron)

(KR-07)

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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 complete 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 (now under control: Durham-Manchester). b-quark mass effects in dijet events – still incomplete potentially, the largest source of theoretical uncertainties!

bb

bb

On top of MC studies(Andy, Marek et al. )

Uncertainties in the non-PU background calculation

hopefully coming soon

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Conclusion

We are now at the qualitatively new stage when the theoretical predictionsfor the CEP cross sections have reached the level of a factor of 3 accuracy.

So far Durham group has been able to describe/predict the diffractive data.

Essential improvement of the accuracy will require a lot of work and may not happen until the LHC experiments come FORWARD and produce the data (already) in the early runs.This will not be easy. It is not like a walk in the park.

LET THE DATA TALK !

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

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BACKUP

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Antwerpen 25/10/07, Per Grafstrom

The ALFA project in ATLASThe ALFA project in ATLAS

(special run (~100 hrs, L=1027cm-2s-1)(special run (~100 hrs, L=1027cm-2s-1)

Single diffraction triggerSingle diffraction trigger ALFA.AND.(LUCID.OR.ZDC) ALFA.AND.(LUCID.OR.ZDC) central ATLAS detector not considered for nowcentral ATLAS detector not considered for now

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In reality KMR –calculational procedure is (much) more complicated

To account for the effects of the screening corrections the calculations are performed in impact parameter bt –spaceFor illustration in a single-channel eikonal approx. hor the process

is the Fourier transform to impact parameter space

The soft rescattering effects are denoted only symbolically by a factor in theeffective PP –luminosity (even for the integrated over proton transverse momenta quantities) (KMR-hep-ph/0111078)

In practice, there is no factorized form, and should be viewed as the softsurvival factor appropriately averaged over the diffractive eigenstates (2,3 channel eikonals..)

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In the topical case of production

the introduction of the and angular correlations raise effective from 0.02 to 0.026 ( KKMR hep-ph/0307064)

There are other assumptions. for example, factorization of the unintegrated distributions

still schematically

+ correlation effects +…

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model B(2) as compared to the elastic data

secondary Regge poles can contribute

Alan Martin’s talk

370.020.04

in EPJC(2000)MRK-2007

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BBKM (first) corrn could be large and -ve,