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## Forward Physics at the LHC SM discoveries with early LHC data UCL, March 30th –

Ward, Kory, On-Air Personality has reference to this Academic Journal, PHwiki organized this Journal Forward Physics at the LHC SM discoveries with early LHC data UCL, March 30th – April 1st 2009 1. Exclusive/diffractive Higgs signal: pp p + H + p Alan Martin, IPPP, Durham Properties of soft interactions ( as long as ward/diffractive physics at the LHC) Return to the exclusive processes (at the Tevatron in addition to the LHC) 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) Very clean environment, even with pile-up–10 ps timing Unique chance to study Hbbbar: QCD bbbar bkgd suppressed by Jz=0 selection rule S/B~1 as long as SM Higgs M < 140 GeV SUSY Higgs: parameter regions with larger signal S/B~10, even regions where conv. signal is challenging in addition to diffractive signal enhanced-h, H both observable Azimuth angular distribution of tagged ps spin-parity 0++ FP420 ATLAS + CMS Is the cross section large enough How do we calculate s(pp p + H + p) What price do we pay as long as an exclusive process with large rapidity gaps

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unintegrated skewed gluons fg given in terms of g(x,Qt2) in addition to Sudakov factor which exponally suppresses infrared region no emission when (l ~ 1/kt) > (d ~ 1/Qt) i.e. only emission with kt > Qt s > 100 fb !! but . can use pQCD QCD mechanism as long as pp p+H+p but soft scatt. can easily destroy the gaps gap gap eikonal rescatt: between protons enhanced rescatt: involving intermediate partons soft physics at high energies H soft-hard factorizn conserved broken Model as long as soft high-energy interactions needed to – underst in addition to asymptotics, intrinsic interest – describe underlying events as long as LHC jet algorms – calc. rap.gap survival S2 as long as 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 (Dark age)

Optical theorems High mass diffractive dissociation at high energy use Regge triple-Pomeron diag but screening important gN3g3P but screening important so stotal suppressed gN2 so (g3P)bare increased M2 2 elastic unitarity e-W is the probability of no inelastic interaction diagonal in b ~ l/p Must include unitarity DL parametrization: Effective Pomeron pole aP(t) = 1.08+0.25t KMR parametrization includes absorption via multi-Pomeron effects

Low-mass diffractive dissociation include high-mass diffractive dissociation Elastic amp. Tel(s,b) bare amp. introduce diffve estates fi, fk (combns of p,p, ) which only undergo elastic scattering (Good-Walker) multichannel eikonal (-20%) (SD -80%) (-40%) g3P PPP PPR PPR ppP RRP RRR RRP ppP PPP triple-Regge analysis of ds/dtdx, including screening x x fit: c2 = 171 / 206 d.o.f. Tevatron CERN-ISR (includes compilation of SD data by Goulianos in addition to Montanha) g3P=l gN l~0.2 g3P large, need to include multi-Pomeron effects LKMR g3P=l gN l~0.2 M2dsSD/dM2 ~ gN3 g3P ~lsel M2 2 large ln s so at collider energies sSD ~ sel gN g3P

Multi-compt. s- in addition to t-ch analysis of soft data 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 KMR 2008 model: Use four exchanges in the t channel a = Plarge, Pintermediate, Psmall, R 3 to mimic BFKL diffusion in ln qt soft pQCD average qt1~0.5, qt2~1.5, qt3~5 GeV VRP1 ~ gPPR,gRRP VPiPj ~ BFKL solve as long as Waik(y,b) by iteration sec. Reggeon bare pole absorptive effects evolve up from y=0 evolve down from y=Y-y=0 (arXiv:0812.2407) Parameters All soft data well described g3P=lgN with l=0.25 DPi = 0.3 (close to the BFKL NLL resummed value) aP1 = 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 as long as secondary Reggeon) Results 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, in addition to t dep. from dsel/dt D = a(0) – 1

f1: large f3: small ~ g, sea more valence f1f1 f3f3 LHC (x0.1) elastic differential ds/dt Description of CDF dissociation data no ppP no ppP stotal (mb) pppX parton multiplicity soft, screened, little growth, partons saturated All Pom. compts have Dbare=0.3 hard ~ no screening much growth, s0.3 Predictions as long as LHC stotal = 91.7 mb sel = 21.5 mb sSD = 19.0 mb see also Sapeta, Golec-Biernat; Gotsman et al.

soft Pomeron hard Pomeron Multi-Pomeron effects at the LHC Each multi-Pomeron diag. simultaneously describes several different processes Example 8 different cuts AGK cutting rules Long-range correlations at the LHC cutting n eikonal Pomerons multiplicity n times that cutting one Pomeron long range correlation even as long as 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

Calculation of S2eik as long as pp p + H +p average over diff. estates i,k over b survival factor w.r.t. soft i-k interaction hard m.e. i k H prob. of proton to be in diffractive estate i S2eik ~ 0.02 as long as 120 GeV SM Higgs at the LHC s ~ 2 – 3 fb at LHC

model has 4 t-ch. exchanges a = Plarge, Pintermediate, Psmall, R 3 to mimic BFKL diffusion in ln qt soft pQCD average qt1~0.5, qt2~1.5, qt3~5 GeV VRP1 ~ gPPR,gRRP VPiPj ~ BFKL ~ solve with in addition to without abs. effects bare pole absorptive effects evolve up to y2 evolve down to y1 enh. abs. changes P3 distribn P3 P1 y2 y1 p1t p2t H

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, in addition to infrared Qt region not so suppressed by Sudakov factor KMR cross section predictions are consistent with CDF data 3 events observed (one due to p0gg) s(excl gg)CDF ~ 0.09pb s(excl gg)KMR ~ 0.04pb s(gg) = 10 fb as long as ETg>14 GeV at LHC KMR Observation of exclusive prodn, pp p + A + p, at Tevatron y=0 The KMRS predn is reduced by S2enh ~ 1/3 in addition to by 1.45 due to a revised Gtot(cc(0)) cb

soft analysis allows rapidity gap survival factors to be calculated as long as any hard diffractive process Exclusive central diffractive production, ppp+H+p, at LHC has great advantages, S/B~O(1), but s ~ few fb as long as 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 as long as pp(bar) p + A + p(bar) with A = dijet in addition to A = gg in addition to A = cc More checks with higher MA valuable. Processes which can probe all features of the as long as malism used to calculate s(ppp+A+p), may be observed in the early LHC runs, even without proton taggers Conclusions exclusive processes at the LHC

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