Diffractive physics at LHC with rapidity gap trigger

1. Diffractive physics at LHC with rapidity gap trigger • LHCrap-gapNET: initiative to pursue diffractive physics at LHC with rapidity gap trigger • Experimental issue: diffractive gap trigger in ALICE • Physics interest: six contributions discussing possible diffractive physics program in ALICE

2. Diffractive physics at LHC • Surprise in HERA data: ~10 % of events show regions in rapidity without tracks gdiffractive events ( g color singlet gluon exchange) • Diffractive events characterized by leading proton and rapidity gap (g trigger on proton tagging, g trigger on rapidity gap) • Analysis of H1 data show that data from the two methods agree in detail (Frank-Peter Schilling, HERA-LHC workshop, june 2006, CERN) g high interest for rapidity gap trigger at LHC • CMS, ATLAS: L=1034cm-2s-1g 25 overlapping events/bunch crossing • CMS/TOTEM combined data taking is planned • ALICE: L=5x1030cm-2s-1g one event/80 bunch crossings

3. Acceptance LHC experiments • CMS/TOTEM LOI LHCC 2006-039 • ATLAS 0o calorimeter ZDC • ALICE 0o calorimeter ZDC

4. ALICE diffractive gap trigger gadditional forward detectors (no particle identification) 1 < h < 5 -4 < h < -1 g definition of gaps h+ , h_ Luminosity L = 5x1030cm-2s-1 : g one interaction/ 80 bunches diffractive L0 trigger (hardware): gap h+: 3 < h < 5 g Dh~ 0.5 gap h-: -2 < h < -4 g Dh~ 0.5 high level trigger (software): -3.7 < h < 5

5. Rapidity gap trigger in ALICE • two diffractive L0 trigger signals proposed to physics coordinator for day one data taking in ALICE: • TRDsgap AND PixelOR: diffractive trigger single gap • TRDdgap AND PixelOR: diffractive trigger double gap • TRDsgap, TRDdgap are generated in TRD pretrigger system g TOF multiplicity > 2, absence of signal in VOA,VOC • PixelOR asserts the multiplicity > 2 in central barrel

6. Diffractive production of vector mesons in pp, pA and AA collisions at LHC • L.Szymanowski, L.Motyka • pp gppV, pAgpAV, AAg AAV • Exclusive diffractive heavy vector meson production is sensititive to square of gluon density xg(x,M2V) of target in small-x region gstudy nuclear shadowing and gluon saturation • cross section for pp g pp J/Psi: ds/dy ~ 12 nb (at y=0) g photon-pomeron, odderon-pomeron contributions ( g look for odderon) • Diffractive production of heavy vector meson pairs • one J/Psi by electron decay in central barrel • one J/Psi by muon decay in muon arm needs further studies

7. Diffractive and electromagnetic processes with rapity gap trigger at LHC • A.Szczurek, W.Schäfer • Measurement of J/Psi photoproduction needs cc measurement due to BR(cc gg J/Psi) • Hadronic decays: cc gp+p- (0.7 %), cc gK+K- (0.5 %) • Work in progress on differential distributions which depend strongly on unintegrated gluon distributions • Double diffractive h‘ production, BR(h‘ gr0g) ~30 %

8. Time-like DVCS at LHC • D.Müller, K.Kumericki,. K.Passek-Kumericki • Deeply virtual compton scattering (DVCS) reveals information on generalized parton distributions (GPDs) in nucleon and nuclei • GPDs carry information on transverse parton distributions • Time-like DVCS in hadron-hadron collisions: pp g ppg*g ppl+l- DVCS amplitude Bethe-Heitler amplitudes

9. Ultra-Peripheral collisions at LHC • J.Nystrand • two photon, photo-nuclear reactions • Exclusive vector meson production gA gVA • D.d`Enterria, G.Baur, S.Klein, M.Strikman, J.Nystrand Trento workshop jan. 2007 „Photoproduction at collider energies“

10. Diffractive Dijet and cc production • A.D.Martin, M.G.Ryskin, V.A.Khoze, A.B.Kaidalov • pp g p + X + p • transverse energy ET of dijet selects events with soft/hard scale g applicability of perturbative QCD • Dijet ET > 10 GeV are dominately gluon jets g study structure of gluon jets, shape and flavour of secondaries as function of ETg perturbative/nonperturbative QCD • Uncertainties in diffractive Higgs production pp g p + H + p • rapidity gap survival factors, Sudakov factors • same uncertainties in dijet, cc production (large cross sections) • Check of uncertainties of diffractive signals of new physics

11. Multi-pomeron exchange dynamics and gap survival probability • A.D.Martin, M.G.Ryskin, V.A.Khoze, A.B.Kaidalov • Compare double diffractive events with min. bias inelastic events 1) glueball cross section is thought to be large in double pomeron fusion g study and compare resonances in central region 2) Slope α‘ of pomeron trajectory is small α‘ ~ 0.25 GeV-2, t-slope triple pomeron vertex < 1 GeV g mean trans. mom. kt in pomeron wave function large, kt > 1 GeV g mean trans. mom. of secondaries larger than in min. bias events 3) large kt > 1 GeV corresponds to large effective temperature gno suppression of strange quarks g K/π, η/π, η‘/π ratios enhanced

12. Multi-pomeron exchange dynamics and gap survival probability • A.D.Martin, M.G.Ryskin, V.A.Khoze, A.B.Kaidalov • Study Sudakov factors • Analyze events with full gap on one side, partial gap on the other • Partial gap due to Sudakov effect of QCD radiation • Test of perturbative formalism for exclusive diffraction

13. Conclusions • Rapidity gap trigger under construction in ALICE • Physics program complementary to CMS/Totem • ALICE unique in r,f,J/Y reconstruction by lepton decays • Rich physics potential