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Forward Physics at the LHC

Forward Physics at the LHC. 1. Exclusive/diffractive Higgs signal: pp  p + H + p. Properties of “soft” interactions (forward/diffractive physics at the LHC) Return to the exclusive processes ( at the Tevatron and the LHC). SM discoveries with early LHC data

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Forward Physics at the LHC

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  1. Forward Physics at the LHC 1. Exclusive/diffractive Higgs signal: pp  p + H + p • Properties of “soft” interactions • (forward/diffractive physics at the LHC) • Return to the exclusive processes • (at the Tevatron and the LHC) SM discoveries with early LHC data UCL, March 30th - April 1st 2009 Alan Martin, IPPP, Durham

  2. Advantages of pp p + H + p with H bbbar If outgoing protons are tagged far from IP then s(M) = 1 GeV (mass also from H decay products) Unique chance to study Hbbbar: QCD bbbar bkgd suppressed by Jz=0 selection rule S/B~1 for SM Higgs M < 140 GeV Very clean environment, even with pile-up---10 ps timing SUSY Higgs: parameter regions with larger signal S/B~10, even regions where conv. signal is challenging and diffractive signal enhanced----h, H both observable Azimuth angular distribution of tagged p’s spin-parity 0++  FP420  ATLAS + CMS

  3. Is the cross section large enough ? How do we calculate s(pp  p + H + p) ? What price do we pay for an exclusive process with large rapidity gaps ?

  4. QCD mechanism for pp p+H+p no emission when (l ~ 1/kt) > (d ~ 1/Qt) i.e. only emission withkt > Qt unintegrated skewed gluons fggiven in terms of g(x,Qt2) and Sudakov factor which exponally suppresses infrared region can use pQCD s > 100 fb !! but….

  5. …but “soft” scatt. can easily destroy the gaps gap H gap soft-hard factorizn conserved broken eikonal rescatt: between protons enhanced rescatt: involving intermediate partons  soft physics at high energies

  6. (Dark age?) Model for “soft” high-energy interactions needed to ---- understand asymptotics, intrinsic interest ---- describe “underlying” events for LHC jet algorms ---- calc. rap.gap survival S2 for exclusive prodn Model should: • be self-consistent theoretically --- satisfy unitarity •  importance of absorptive corrections •  importance of multi-Pomeron interactions • 2. agree with available soft data • CERN-ISR to Tevatron range • 3. include Pomeron compts of different size---to study effects of • soft-hard factn breaking

  7. at high energy use Regge Optical theorems but screening important so stotal suppressed gN2 High mass diffractive dissociation 2 M2 triple-Pomeron diag but screening important gN3g3P so (g3P)bare increased

  8. Must include unitarity diagonal in b ~ l/p elastic unitarity  e-W is the probability of no inelastic interaction

  9. DL parametrization: Effective Pomeron pole aP(t) = 1.08+0.25t KMR parametrization includes absorption via multi-Pomeron effects

  10. 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 g3P ?

  11. 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 g3P large, need to include multi-Pomeron effects g3P=l gNl~0.2 LKMR

  12. g3P=l gNl~0.2  large ? 2 gN M2 g3P M2dsSD/dM2 ~ gN3 g3P ~lsel ln s so at collider energies sSD ~ sel

  13. Multi-compt. s- and t-ch analysis of soft data KMR 2008 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

  14. 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 (arXiv:0812.2407)

  15. 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 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

  16. elastic differential ds/dt f1*f1 LHC (x0.1) ~ g, sea f3*f3 f1: “large” f3: “small” more valence

  17. Description of CDF dissociation data no ppP no ppP

  18. Predictions for LHC stotal (mb) stotal = 91.7 mb* sel = 21.5 mb sSD = 19.0 mb *see also Sapeta, Golec-Biernat; Gotsman et al. All Pom. compts have Dbare=0.3 parton multiplicity pppX “soft”, screened, little growth, partons saturated “hard” ~ no screening much growth, s0.3

  19. “soft” Pomeron “hard” Pomeron

  20. Multi-Pomeron effects at the LHC Each multi-Pomeron diag. simultaneously describes several different processes Example 8 different “cuts” AGK cutting rules 

  21. Long-range correlations at the LHC • cutting n eikonal Pomerons  multiplicity n times that • cutting one Pomeron • long range correlation even for large rapidity differences | ya – yb | ~ Y  R2 > 0 without multi-Pomeron exch. R2>0 only when two particles are close, e.g. from resonance decays

  22. Calculation of S2eik 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 S2eik ~ 0.02 for 120 GeV SM Higgs at the LHC  s ~ 2 - 3 fb at LHC

  23. <Senh>2 = ?? from g pJ/y p <Seik>2 ~ 0.02 0.6 fm Watt, Kowalski

  24. Calculation of S2enhanced for pp  p + H +p gap H gap soft-hard factorizn conserved broken eikonal rescatt: between protons enhanced rescatt: involving intermediate partons The new soft analysis, with Pomeron qt structure, enables S2enh to be calculated

  25. enh. abs. changes P3 distribn model has 4 t-ch. exchanges P1 y1 P3 3 to mimic BFKL diffusion in ln qt y2 a = Plarge, Pintermediate, Psmall, R soft pQCD average qt1~0.5, qt2~1.5, qt3~5 GeV VRP1 ~ gPPR,gRRP VPiPj ~ BFKL evolve up to y2 bare pole absorptive effects evolve down to y1 ~ solve with and without abs. effects

  26. Survival prob. for pp  p+H+p p1t <S2eik> ~ 0.02 consensus <S2enh> ~ 0.01 – 1 controversy KMR 2008  <S2>tot=<S2eikS2enh> ~ 0.015 (B=4 GeV-2) H p2t However enh. abs. changes pt behaviour from exp form, so 0.0015 LHC 0.0030 Tevatron KMR 2000 (no Senh) <S2>tot<p2t>2 = 0.0010 LHC 0.0025 Tevatron KMR 2008 (with Senh) see arXiv:0812.2413

  27. Comments on S2 1. Enhanced rescattering reduces the signal by ~30% 2. However, the quoted values of S2 are conservative lower limits 3. The very small values of S2enh in recent literature are not valid The arguments are given in arXiv:0903.2980 CDF observation of exclusive processes at the Tevatron offers the first experimental checks of the formalism

  28. Observation of exclusive prodn, pp  p + A + p, by CDF with A=gg or A = dijet or A = cc J/yg  m+m-g Same mechanism as pp  p+H+p tho’ predns become more unreliable as MA becomes smaller, and infrared Qt region not so suppressed by Sudakov factor

  29. Observation of exclusive prodn, pp  p + A + p, at Tevatron KMR cross section predictions are consistent with CDF data 3 events observed (one due to p0gg) s(excl gg)CDF ~ 0.09pb s(excl gg)KMR ~ 0.04pb KMR s(gg) = 10 fb for ETg>14 GeVat LHC

  30. y=0 The KMRS predn is reduced by S2enh ~ 1/3 and by 1.45 due to a revised Gtot(cc(0)) cb ?

  31. Early LHC runs can give detailed checks of all of the ingredients of the calculation of s(pp  p + A + p), sometimes even without proton taggers

  32. Early LHC checks of theoretical formalism for pp  p + A + p ? Possible checks of: (i) survival factor S2: W+gaps, Z+gaps (ii) generalised gluon fg : gp Up, 3 central jets (iii) soft-hard factorisation #(A+gap) evts (broken by enhanced #(inclusive A) evts absorptive effects) with A = W, dijet, U… (arXiv:0802.0177)

  33. W+gaps with Even without a proton tag can be measured by successfully used by CDF

  34. W+gaps cross section survival fac.  1 pb measure: W+gaps W inclusive S2 large, as large bt (small opacity)

  35. W+gaps has S2 large, as large bt for g exch (small opacity) Z+gaps has bt more like excl. Higgs s~0.2pb for Dhi>3 and ET(b)>50GeV but to avoid QCD bb backgd use Zl+l- expect S2~0.3 use track counting veto

  36. Exclusive U production as probe of fg odderon exch g exch comparable ? can separate by pt if a tag of upper proton is done (odderon has larger pt) x 0.025 (br for Umm) Bzdak, Motyka,Szymanowski,Cudell If |yU|<2.5, then sample fg(x1,x2) with xi in (10-4, 10-2)

  37. 3-jet events as probe of Sudakov factor T T is prob. not to emit additional gluons in gaps: pp  p + A + p T=exp(-n), where n is the mean # gluons emitted in gap 3 central jetsallow check of additional gluon emission System A must be colourless – so optimum choice is emission of third jet in high ET dijet production highest only highest ET jet used – stable to hadronization, final parton radiation…

  38. pp  p + jj + p pp  p + jjj + p study both dh and ET dependence of central 3-jet production (negligible DPE background)

  39. “Enhanced” absorptive effects (break soft-hard factorization) rescattering on an intermediate parton: can LHC probe this effect ?

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

  41. A = W or U …. A = dijet pp  AX pp  AX+p rough estimates of enhanced absorption S2en

  42. Conclusions – soft processes at the LHC -- 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 probe “soft” intns i.e. probe multi-Pomeron struct. via long-range rapidity correlations or via properties of multi-gap events etc.

  43. Conclusions – exclusive processes at the LHC 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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