Diffraction at ALICE ALICE detector Diffractive gap trigger

Diffraction at ALICE ● ALICE detector ● Diffractive gap trigger in ALICE ● Pomeron signatures in p-p ● Odderon signatures in p-p ● Signature of gluon saturation in diffraction ● Conclusions, outlook Rainer Schicker, Uni Heidelberg EDS 09, jun 29 – july 3, 2009, CERN

The ALICE experiment Acceptance central barrel -0. 9 < h < 0. 9 Acceptance muon spectr. HMPID TRD ITS TPC TOF MUON SPEC. PHOS -2. 5 < h < -4. Rainer Schicker, Uni Heidelberg EDS 09, jun 29 – july 3, 2009, CERN

ALICE diffractive gap trigger → additional forward detectors (no particle identification) 1<h<5 -4 < h < -1 → definition of gaps h+ , h_ p-p luminosity L = 5 x 1030 cm-2 s-1 : → one interaction/ 80 bunches diffractive L 0 trigger (hardware): Pixel or TOF mult (central barrel) gap h : 3 < h < 5 → Dh ~ 0. 5 + gap h-: -2 < h < -4 → Dh ~ 0. 5 high level trigger (software): -3. 7 < h < 5 Rainer Schicker, Uni Heidelberg EDS 09, jun 29 – july 3, 2009, CERN

ALICE central barrel particle identification Particle identification by d. E/dx in central barrel as function of momentum In addition time of flight information for non-relativistic momenta Rainer Schicker, Uni Heidelberg Electron-pion separation in TRD as function of momentum →identify vector mesons by e+e- decay EDS 09, jun 29 – july 3, 2009, CERN

ALICE central barrel comparison to other LHC detectors h-pt acceptance low magnetic field Magn. PT cutoff Material field (T) Ge. V/c x/x 0 (%) ALICE 0. 2 -0. 5 0. 1 -0. 25 7 ATLAS 2. 0 0. 5 (0. 08) 20 CMS 4. 0 0. 75 (0. 2) 30 LHCb 4 Tm 0. 1 3. 2 → low p. T trigger ? →good ALICE acceptance for f, J/Psi, Y by electron decays (p. T > 0 Me. V/c) Rainer Schicker, Uni Heidelberg EDS 09, jun 29 – july 3, 2009, CERN

ALICE forward calorimeter • neutron calorimeter on each side – Placed at 116 m from interaction region – Measures neutral energy at 0 o • Diffractive events with and without proton breakup: – pp → pp. X : no energy in zero degree calorimeters – pp → p. N*X, N*N*X : energy in one or in both calorimeters Identify the three topologies: A B C → what are f(xi), g(xi), h(xi) ? Rainer Schicker, Uni Heidelberg EDS 09, jun 29 – july 3, 2009, CERN

ALICE diffractive physics • ALICE acceptance matched to diffractive central production: g -pomeron, double pomeron, odderon-pomeron central barrel Dh ~ 3 Data taking: pp @ L = 5 x 1030 cm-2 s-1 p. Pb @ L = 1029 cm-2 s-1 Pb. Pb @ L = 1027 cm-2 s 1 Rainer Schicker, Uni Heidelberg Dh ~ 4 f gap had gap h EDS 09, jun 29 – july 3, 2009, CERN

Pomeron signatures POMERON: C = +1 part of gluon color singlet exchange amplitude Compare pomeron-pomeron fusion events to min bias inelastic events 1) Enhanced production cross section of glueball states: study resonances in central region when two rapidity gaps are required 2) Slope pomeron traj. a‘ ~ 0. 25 Ge. V-2 in DL fit, a‘ ~ 0. 1 Ge. V-2 in vector meson production at HERA, t-slope triple pom-vertex < 1 Ge. V-2 → mean kt in pomeron wave function a‘ ~ 1/kt 2 probably kt > 1 Ge. V → <p. T> secondaries in double pomeron > <p. T> secondaries min bias 3) kt > 1 Ge. V implies large effective temperature Rainer Schicker, Uni Heidelberg → K/p, h‘/p ratios enhanced EDS 09, jun 29 – july 3, 2009, CERN

Central exclusive π+π- production at √s = 63 Ge. V Data taken by Axial Field Spectrometer at ISR √s = 63 Ge. V (R 807) very forward drift chambers added for proton detection p π+π- p f 0(600)=σ no ρ f 0(980) 3500 events/25 Me. V T. Akesson et al 1986: Flavour independence: equal numbers of π+π- and K+K- pairs for masses larger than 1 Ge. V Rainer Schicker, Uni Heidelberg M(π+π-) G(1710)? ? Structures not well understood beyond f(980) Not studied at higher √s EDS 09, jun 29 – july 3, 2009, CERN

Signature Odderon cross section ODDERON: C = -1 part of gluon color singlet exchange amplitude Look at exclusive processes with rapidity gaps Examples: diffractive pseudo scalar and tensor meson production: C = +1 states diffractive vector meson production: C = -1 states → measure cross sections Rainer Schicker, Uni Heidelberg EDS 09, jun 29 – july 3, 2009, CERN

The hunt for the Odderon • Production cross sections in pp at LHC energies – diffractive production: → contributions from Photon-Photon, Photon-Odderon, Odderon-Odderon – Look for diffractive J/Y production: → Photon-Pomeron, Odderon-Pomeron contributions → such an experimental effort is a continuation of physics programs carried out at LEP (gg) and HERA (g-Odderon) Rainer Schicker, Uni Heidelberg EDS 09, jun 29 – july 3, 2009, CERN

Diffractive J/Y production in pp at LHC ● ● First estimates by Schäfer, Mankiewicz, Nachtmann 1991 ds Motyka, Szymanowski, Cudell p. QCD estimate by Bzdak, dy y=0 – Photon: t-integrated ds dy y=0 Odderon: t-integrated At L = 5 x 1030 cm-2 s-1: – → s ~ 15 nb (2. 4 - 27 nb) ~ 0. 9 nb (0. 3 - 4 nb) 0. 15 J/Y in ALICE central barrel in 1 s, 150 k in 106 +e- channel in 106 s → 9000 in e → identify Photon and Odderon contribution by analysing p. T distribution ( Odderon harder p. T spectrum ) Rainer Schicker, Uni Heidelberg EDS 09, jun 29 – july 3, 2009, CERN

Signature Odderon interference ● Cross sections contain squared Odderon amplitudes → Odderon-Pomeron interference ! ds ~ Ag(AP + AO) 2 d. Nq ~ AP 2 + 2 Re(APAO*) + AO 2 → look at final states which can be produced by Odderon or Pomeron exchange → find signatures for interference of Codd and C-even amplitude Rainer Schicker, Uni Heidelberg EDS 09, jun 29 – july 3, 2009, CERN

Interference signal • Interference effects (relative contribution ) – Asymmetries in and pairs in continuum → charge asymmetry relative to polar angle of p+ in dipion rest frame → fractional energy asymmetry in open charm diffractive photoproduction → asymmetries in HERA kinematics estimated 10 % - 15 % Rainer Schicker, Uni Heidelberg EDS 09, jun 29 – july 3, 2009, CERN

Gluon saturation • Fits of parton densities xuv, xdv, xg, x. S to HERA data - How does gluon density behave at low x ? - Where does gluon saturation set in ? - Are there observables which are sensitive to gluon saturation ? Rainer Schicker, Uni Heidelberg EDS 09, jun 29 – july 3, 2009, CERN

Heavy quark photoproduction in pp @ LHC • Photoproduction of – photon fluctuates into , Golec-Biernat, – Interacts as color dipole Wuesthoff 1999 σ0, λ from fits of F 2 with x < 0. 01 → σdip saturates when r ~ 2 R 0 ● -production cross section in ppcollisions (LHC) Collinear p. QCD CGC model 16 mb 5 mb 230 nb 110 nb Rainer Schicker, Uni Heidelberg Goncalves, Machado Phys. Rev. D 71 (2005) EDS 09, jun 29 – july 3, 2009, CERN

Diffractive Photoproduction of heavy quarks • Advantage of diffractive photoproduction – Clear final state defined by two rapidity gaps pp p. Pb Pb. Pb 92 nb 54 mb 59 mb Goncalves, Machado 0. 2 nb 0. 09 mb 0. 01 mb Phys. Rev. D 75 (2007) p. Pb mode: L = 1029 cm-2 s-1 g R (cc) ~ 5 Hz Acceptance ~ 10 %, Efficiency ~ 50 % g R(cc)~20 k per day Heavy quarks can also be produced by central exclusive diffraction, ie two pomeron fusion g harder spectrum of quarks, hence could be disentangled in p. T spectrum Rainer Schicker, Uni Heidelberg EDS 09, jun 29 – july 3, 2009, CERN

Conclusions, outlook ● ● ALICE has unique opportunity to do soft diffractive physics @LHC Diffractive trigger defined by two rapidity gaps ● Neutral energy measurement at 00 ● Phenomenology of Pomeron/Odderon ● ● Gluon saturation in heavy-quark photoproduction Photon-Photon physics Rainer Schicker, Uni Heidelberg EDS 09, jun 29 – july 3, 2009, CERN