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Diffraction at the LHC: a theoretical review

Diffraction at the LHC: a theoretical review. Soft diffraction. ,…. Predictions for. Hard diffraction. especially pp  p + A + p with A = H(bb bar ). survival of rapidity gaps depends on soft rescattering. Alan Martin (Durham), Physics at the LHC, Split, Sept-October 2008.

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Diffraction at the LHC: a theoretical review

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  1. Diffraction at the LHC: a theoretical review Soft diffraction ,… Predictions for Hard diffraction especially pp  p + A + p with A = H(bbbar) survival of rapidity gaps depends on soft rescattering Alan Martin (Durham), Physics at the LHC, Split, Sept-October 2008

  2. at high energy use Regge Optical theorems but screening important so stotal suppressed gN2 High mass diffractive dissociation M2 triple-Pomeron diag but screening important g3P so (g3P)bare increased

  3. diagonal in b elastic unitarity  S2el = e-W is the probability of no inelastic interaction

  4. directly related to elastic data LHC Tevatron from model fits to elastic data

  5. Elastic amp. Tel(s,b) bare amp. (20%) multichannel eikonal Low-mass diffractive dissociation introduce diffve estates fi, fk (combns of p,p*,..) which only undergo “elastic” scattering (Good-Walker) (40%) (SD 80%) include high-mass diffractive dissociation

  6. triple-Regge analysis of ds/dtdx, including screening (includes compilation of SD data by Goulianos and Montanha) fit: c2 = 171 / 206 d.o.f. CERN-ISR Tevatron PPP PPR PPP PPR RRR RRP RRP ppP ppP x x Luna+KMR; Poghosyan, Kaidalov g3P large, need to include multi-Pomeron effects g3P=l gNl~0.2

  7. KMR New analysis of soft data model: 3-channel eikonal, fi with i=1,3 include multi-Pomeron diagrams attempt to mimic BFKL diffusion in log qt by including three components to approximate qt distribution – possibility of seeing “soft  hard” Pomeron transition

  8. Use four exchanges in the t channel 3 to mimic BFKL diffusion in ln qt sec. Reggeon a = Plarge, Pintermediate, Psmall, R soft pQCD average qt1~0.5, qt2~1.5, qt3~5 GeV VRP1 ~ gPPR,gRRP VPiPj ~ BFKL evolve up from y=0 bare pole absorptive effects evolve down from y’=Y-y=0 solve for Waik(y,b) by iteration

  9. Parameters multi-Pomeron coupling l from xdsSD/dxdt data ( x~0.01) diffractive eigenstates from sSD(low M)=2mb at sqrt(s)=31 GeV, -- equi-spread in R2, and t dep. from dsel/dt Results All soft data well described g3P=lgN with l=0.25 (compared to l=0.2 in Luna et al.) DPi = 0.3 (close to the BFKL NLL resummed value) a’P1 = 0.05 GeV-2 These values of the bare Pomeron trajectory yield, after screening, the expected soft Pomeron behaviour --- “soft-hard” matching (since P1 heavily screened,….P3~bare) DR = -0.4 (as expected for secondary Reggeon) D = a(0) - 1

  10. KMR 3-ch eikonal, multi-Regge analysis of available “soft” data predict at LHC: stotal = 90.5 mb Other fits with absorptive effects predict stotal~90 mb Sapeta, Golec-Biernat; Gotsman, Levin, Maor sqrt(s)

  11. Predictions for LHC stotal (mb) stotal = 90.5 mb sel = 20.8 mb sSD = 14.8 mb All Pom. compts have Dbare=0.3 parton multiplicity pppX “soft”, screened, little growth, partons saturated “hard” ~ no screening much growth, s0.3

  12. f1*f1 LHC (x0.1) ~ g, sea f3*f3 f1: “large” f3: “small” more valence

  13. DIS: epeX (g*pX) HERA finds that about 10% of these events are diffractive DIS: epeX+p (g*pX+p) electron outgoing proton gap X

  14. DIS same Diffractive DIS gap If then assume, Regge factorization:

  15. direct+resolved Pomeron (cf. photon) Diffve partons from HERA data diffractive partons gD, qD can be used to predict diffractive processes with hard scale? Yes, but…

  16. soft rescatt. HERA prediction CDF diffr. dijet data gap gap CDF HERA S2(b) ~ 0.1

  17. Photoproduction of leading n ZEUS data S2 ~ 0.48 D’Alesio, Pirner; Nikolaev,Speth,Zakharov; Kaidalov,Khoze,M,Ryskin; Kopeliovich,Potashnikova, Schmidt,Soffer.

  18. Advantages of pp  p + (Hbb) + p -- accurate determination of MH using tagged protons, MH=Mmissing -- MH=Mdecay must match MH=Mmissing -- bbbar QCD background suppressed by Jz=0 selection rule -- can determine JPC. Selection rule favours 0++ production -- S/B ~ O(1) for SM 120 GeV Higgs (…but s ~ few fb) -- s x 10 for some SUSY Higgs scenarios Kaidalov+KMR Heinemeyer,Khoze et al Cox,Loebinger,Pilkington e.g. MA > 140 GeV: then h  hSM H, A decouple from gauge bosons H, A  bbbar, tt enhanced by tan b

  19. Survival Probability of gaps for pp  p + H +p prob. of proton to be in diffractive estate i survival factor w.r.t. soft i-k interaction hard m.e. i k  H over b average over diff. estates i,k S2 ~ 0.02 for 120 GeV Higgs at the LHC

  20. bbbar background to pp  p + (Hbbbar) + p signal -- irreducible QCD ggPPbbbar events -- gluons mimicing b jets -- Jz=2 contribution New results: NLO calculation of ggPPbbbar reduces irreducible background by factor of 2 or more Shuvaev et al Also, experimentally, there has been a reduction in the chance that gluons mimic b jets.

  21. Experimental checks of calculation of s(pp  p + A + p) KMR cross section predictions are consistent with the recent observed rates of three exclusive processes at the Tevatron: CDF ppbar p + gg+ pbar ppbar p + dijet + pbar ppbar p + cc+ pbar (68 cc0  J/y + g events) Early LHC runs can give detailed checks of all of the ingredients of the calculation of s(pp  p + A + p), even without proton taggers

  22. CDF 3 events observed (one due to p0gg) s(excl gg)measured ~ 0.09pb s(excl gg)predicted ~ 0.04pb s(gg) = 10 fb for ETg>14 GeVat LHC

  23. CDF exclusive dijet exclusive region ET exclusive cross section v ET bbbar prod. suppressed in exclusive region -- as expected ET

  24. Early LHC checks of pp  p + A + p ? gap KMR Sen gap Possible checks of: (i) survival factor S2: W+gaps, Z+gaps (ii) generalised gluon fg : gp Up (iii) Sudakov factor T : 3 central jets (iv) soft-hard factorisation #(A+gap) evts (broken by enhanced #(inclusive A) evts absorptive effects) with A = W, dijet, U…

  25. S2en = gap survival to rescattering on intermediate partons There is controversy about its size. Seik Sen Evidence is that S2en ~ 1 for pp  p + H + p -- explicit calc. using soft model -- kinematic suppression, need Dy > 2.3 to establish Pomeron exchange -- HERA leading neutron data, no energy dep. in n yield -- after including S2eik we are left with b > 0.6 fm, where Q2saturation < 0.3 GeV2 (Watt et al), so S2en ~ 1 Early LHC probe of S2en 

  26. inclusive diffractive A = dijet or W or U …. known from HERA

  27. Possibility for LHC to probe S2enhanced pp  diffve dijet pp  inclve dijet rough estimates of enhanced absorption S2en

  28. Exclusive U production as probe of odderon and fg odderon exch g exch comparable ? Bzdak, Motyka, Szymanowski,Cudell x 0.025 (br for Umm) can separate by pt of upper proton if it is tagged For small pt For pt > 1 GeV g exch dominates odderon should show up If |yU|<2.5, then sample fg(x1,x2) with xi in (10-4, 10-2)

  29. Conclusions – soft diffraction -- screening/unitarity/absorptive corrections are vital -- Triple-Regge analysis with screening  g3P increased by ~3  importance of multi-Pomeron diagrams -- Latest analysis of all available “soft” data: multi-ch eikonal + multi-Regge + compts of Pom. to mimic BFKL (showed some LHC predictions ….. stotal ~ 90 mb) soft-hard Pomeron transition emerges “soft” compt. --- heavily screened --- little growth with s “intermediate” compt. --- some screening “hard” compt. --- little screening --- large growth (~pQCD) -- LHC can explore multigap events  probe multi-Pomeron structure LHC is a powerful probe of models of soft processes SD DPE

  30. Conclusions – hard diffraction soft analysis allows rapidity gap survival factors to be calculated for any hard diffractive process Exclusive central diffractive production, ppp+H+p, at LHC has great advantages, S/B~O(1), buts ~ few fb for SM Higgs. However, some SUSY-Higgs have signal enhanced by 10 or more. Very exciting possibility, if proton taggers installed at 420 m Formalism consistent with CDF data for pp(bar)  p + A + p(bar) with A = dijet and A = gg andA = cc More checks with higher MA valuable. Processes which can probe all features of the formalism used to calculate s(ppp+A+p), may be observed in the early LHC runs, even without proton taggers

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