Photoproduction of Heavy Vector Mesons at the LHC

Photoproduction of Heavy Vector Mesons at the LHC Joakim Nystrand Department of Physics and Technology, University of Bergen, Norway In collaboration with Spencer Klein, LBNL, Berkeley 13 -17 July 2004 Physics at LHC, Vienna Joakim Nystrand

Photoproduction of heavy Vector Mesons A probe of the nucleon/nucleus gluon density The photon wave function can be written as a Fock decomposition: | > = Cbare | bare> + C | > + … + Cq |qq> A photon is not always a photon… With a certain probability it will appear as a qq– flucutuation Conservation of quantum numbers ( : JP = 1–) The photon tend to fluctuate to a vector meson ( , , , J/ ). Vector Meson Dominance. 13 -17 July 2004 Physics at LHC, Vienna Joakim Nystrand

A photon in the vector meson state will interact strongly (hadronically). The hadronic component can materialize if the virtual qq-pair is knocked on mass shell. The probability to find the photon in the vector meson state V: f. V – photon-vector-meson coupling Vector Meson Dominance: 13 -17 July 2004 Physics at LHC, Vienna Joakim Nystrand

Studied at HERA in ep collisions: W p : photon-proton CM energy t: (momentum transfer from proton) 2 -Q 2 : virtuality of the photon; for protons or nuclei, Q 2 0. 13 -17 July 2004 Physics at LHC, Vienna Joakim Nystrand

Summary of HERA Results • W p up to 200 Ge. V • 0 10% of TOT • Light mesons: W p 0. 22 • J/ : W p 0. 80 • a few tens of seen 13 -17 July 2004 Physics at LHC, Vienna Joakim Nystrand

Electromagnetic field An equivalent flux of photons. (Fermi 1924, Weizsäcker-Williams 1935) Equivalent photon luminosity The photon spectrum extends to /R W p 1000 Ge. V in Pb+Pb collisions (Q 2 0) 13 -17 July 2004 Photon energy spectrum: dn /dk (k photon energy) + Beam luminosity, LAA Equivalent photon luminosity, d. L /dk Physics at LHC, Vienna Joakim Nystrand

Ultra-peripheral Interactions Menu 1. Purely electromagnetic, two-photon 2. Photonuclear a) direct Example: gamma+gluon b) resolved Vector Meson Dominance 13 -17 July 2004 Physics at LHC, Vienna Joakim Nystrand

Calculation of Vector Meson cross sections in Heavy-Ion Interactions Phenomenological model based on scaling data of p to A. J. Nystrand, S. Klein PRC 60(1999)014903 The ingredients: Photon spectrum: Weizsäcker-Williams Input photon-nucleon data: parameterized from results at HERA and fixed target Scaling p A: 1) Neglecting cross terms - fluctuates into V which scatters elastically 2) Shadowing through a Glauber model 3) nuclear momentum transfer from Form factor 13 -17 July 2004 Physics at LHC, Vienna Joakim Nystrand

The model predicts cross sections, rapidity and p. T distributions of vector mesons at RHIC and LHC. For Au+Au 200 Ge. V at RHIC: —————— [mb] (prod. rate) —————— 590 (120 Hz) 59 (12 Hz) 39 (7. 9 Hz) J/ 0. 29 (0. 058 Hz) —————— Cross sections in the 1 -600 mb range! The p. T distribution determined by the nuclear Form Factor, p. T 1/R 50 Me. V/c 13 -17 July 2004 Physics at LHC, Vienna Joakim Nystrand

Data on Au+Au+ 0 at RHIC in good agreement with calculations [mb] Theory: A. Baltz, S. Klein J. Nystrand Pre lim ina ry STAR Collaboration, Quark Matter 2002 Triggering + Analysis techniques work; photon spectrum and basic photonuclear cross sections well understood. 13 -17 July 2004 Physics at LHC, Vienna Joakim Nystrand

p data from HERA J/ : = 1. 5 W p 0. 80 [nb, W in Ge. V] Extrapolate this to LHC energies Too little data on , QCD predicts Ryskin 1993 Further developments: Martin, Ryskin, Tubner Phys. Lett B 454 (1999)339 and Frankfurt, Mc. Dermott, Strikman JHEP 02(1999)002. Can be parameterized as : = 0. 06 W p 1. 7 [pb, W in Ge. V] 13 -17 July 2004 Physics at LHC, Vienna Joakim Nystrand

in ultra-peripheral Pb+Pb collisions at the LHC A 2 scaling of QCD prediction A 2 scaling of exp. data from HERA. Mid-rapidity y=0 Uncertainty in measured cross section (mainly poor statistics). p CM energy W p = 230 Ge. V, x=2· 10 -3 13 -17 July 2004 Physics at LHC, Vienna Joakim Nystrand

What can one expect in pp/pp ? Equivalent photon spectrum of a proton: Drees and Zeppenfeld (1989) RHIC =108 Point charge, b>0. 7 fm 13 -17 July 2004 Physics at LHC, Vienna Joakim Nystrand

(pp pp+V) Drees&Zeppenfeld photon spectrum point charge, b>1 fm Uncertainty in experimental cross section (mainly poor statistics). 13 -17 July 2004 Physics at LHC, Vienna Joakim Nystrand

(pp pp+V) Kinematics at mid-rapidity (y=0) Tevatron J/ W p = 80 Ge. V x 1 · 10 -3 W p = 130 Ge. V x 5 · 10 -3 LHC W p = 210 Ge. V x 2 · 10 -4 W p = 350 Ge. V x 6 · 10 -4 Lower x can be reached away from y=0, but separation of photon-emitter and photon-target non-trivial. 13 -17 July 2004 Physics at LHC, Vienna Joakim Nystrand

Transverse momentum spectrum Dominated by proton form factor Low p. T < 1 Ge. V/c 13 -17 July 2004 Physics at LHC, Vienna Joakim Nystrand

Transverse momentum spectrum Dominated by proton form factor with Low p. T < 1 Ge. V/c without 13 -17 July 2004 Physics at LHC, Vienna interference Joakim Nystrand

Transverse momentum spectrum At very low p. T (p. T << 1/<b>), not possible to distinguish photon-emitter and photon-target. Add amplitudes (not cross sections) with correct sign. VM p 13 -17 July 2004 b p Physics at LHC, Vienna Joakim Nystrand

Exchanging photon-emitter and photon-target VM p b VM p P p b VM p b p VM p P p b p VM C p b p JPC = 1– – Destructive interferenc in pp (AA), constructive interference in pp. 13 -17 July 2004 Physics at LHC, Vienna Joakim Nystrand

Comparisons with hadronic production mode (pp) J/ RHIC, s=200 Ge. V: = 2. 70 0. 40 b Photoproduction: 7 nb S. S. Adler et al. (PHENIX Collaboration) PRL 92(2004)051802, p+p J/ + X Tevatron, s=1. 96 Te. V: Photoproduction: d /dy|y=0 = 30. 4 3. 1 nb d /dy|y=0 = 10 -25 pb 13 -17 July 2004 Physics at LHC, Vienna Joakim Nystrand

Comparisons with hadronic production mode at LHC pp : hadronic: 0. 15– 0. 28 b* photo: 3. 5 nb ratio: ~ 2· 10– 2 *ALICE PPR / R. Vogt Pb. Pb : Total hadronic (all centralities) AA A 2 pp hadronic: 6. 5– 12. 1 mb photo: 170 b ratio: ~ 2· 10– 2 Much better background rejection in Pb. Pb: a) Higher multiplicities (hadronic interactions) b) Coherence photoproduced w/ very low p. T 13 -17 July 2004 Physics at LHC, Vienna Joakim Nystrand

In pp, hadronic ’background’ must be suppressed by a factor 103! Rapidity gaps: <dnch/dy> 4 - 6 in pp at Tevatron/LHC Probability of having a gap of width y: exp( - <dnch/dy> · y ) y 2 will be sufficient Further rejection from p. T distribution, p. T < 1 Ge. V/c 13 -17 July 2004 Physics at LHC, Vienna Joakim Nystrand

Some indication of J/ at the Tevatron Presented at ”Small-x and Diffraction”, Fermilab, September 2003 (CDF Collaboration, Angela Wyatt) Searched for pp pp+ c via Pomeron-Pomeron, c J/ + Found also a sample of J/ ’s without ’s ! p. T distribution of exclusive J/ : s: 13 -17 July 2004 Physics at LHC, Vienna Joakim Nystrand

Kinematics at mid-rapidity - pp vs. Pb W p – photon-proton CM energy x - Bjorken-x of gluon y=0 J/ Tevatron W p = 80 Ge. V x 1 · 10 -3 W p = 130 Ge. V x 5 · 10 -3 LHC pp W p = 210 Ge. V x 2 · 10 -4 W p = 350 Ge. V x 6 · 10 -4 LHC Pb. Pb W p = 130 Ge. V 13 -17 July 2004 x 6 · 10 -4 Physics at LHC, Vienna W p = 230 Ge. V x 2 · 10 -3 Joakim Nystrand

Note: AA and pp competitive for selected reaction channels/final states. Not suitable for measuring tot( ) or tot( p), for example. • Tagging of beam-nuclei not possible. • Q 2 ħ/R 0. • The corresponding QCD processes must suppressed. 13 -17 July 2004 Physics at LHC, Vienna Joakim Nystrand

Summary • Some more details in PRL 92(2004)142003 (hep-ph/0311164). • Interesting possibility to study exclusive production of heavy vector mesons in pp and pp collisions, and in Ultra-peripheral AA collisions. • A probe of the nucleon/nucleus gluon density at low Bjorken-x. • Extends the energy range studied at HERA. 13 -17 July 2004 Physics at LHC, Vienna Joakim Nystrand