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Exclusive Production of Heavy Quark Mesons in pp and pp collisions

Exclusive Production of Heavy Quark Mesons in pp and pp collisions. Spencer Klein, LBNL & Joakim Nystrand, Bergen. Photoproduction of heavy vector mesons in pp/pp collisions Rates and rapidity distributions Interference and p T spectra Backgrounds Conclusions. Photoproduction.

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Exclusive Production of Heavy Quark Mesons in pp and pp collisions

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  1. Exclusive Production of Heavy Quark Mesons in pp and pp collisions Spencer Klein, LBNL & Joakim Nystrand, Bergen Photoproduction of heavy vector mesons in pp/pp collisions Rates and rapidity distributions Interference and pT spectra Backgrounds Conclusions

  2. Photoproduction • A photon from the electromagnetic field of one nucleus interacts with the other nucleus, producing a vector meson • Either nucleus can be photon source • The photon flux extends up to 0.1 Ep or higher • These photons can probe low-x gluons S. Klein,LBNL

  3. Photon Flux • From Weizsacker-Williams • b > 2Rp; • no hadronic interactions • Clean event signatures • Take bmin ~ 0.7 fm • Change to bmin = 1.0 fm is error estimate • Sensitive to proton form factor • Qmin2=k/g Drees and Zeppenfield, 1989 S. Klein,LBNL

  4. Vector Meson production ITheory • gg collision at lowest order • Need another gluon to conserve color • Refinements • Relativistic wave functions • Off diagonal parton dists. • NLO contributions • Sensitive to gluon distributions • Q2=MV2/4 Ryskin, 1993 S. Klein,LBNL

  5. ZEUS U Vector Meson production II Experiment • HERA data • J/Y: s~ W0.8 • agreement with theory • U: s ~ W1.7 • limited statistics • U(1), U(2), U(3) not separated • Estimate 80% U(1) • Alternately, use s~ W0.8 • So-so match with theory • Tevatron reaches slightly higher Wgp • Lower gluon x Wgp (GeV) H1/ZEUS J/y Wgp (GeV) Wgp (GeV) S. Klein,LBNL

  6. Cross Sections, Rates and ds/dy RHIC @ 500 GeV (top) • Photon energy -> rapidity • Y = ½ ln (2k/MV) • The U @ RHIC (500 GeV, 1031cm-2 s-1) • 0.4/hr • difficult • The U @ the Tevatron (1.8 TeV, 2*1032cm-2s-1) • 76/hr • Easy • J/Y rates are high The Tevatron (bottom) S. Klein,LBNL

  7. Interference • Either proton can act as emitter or target • Can’t differentiate between • How to transform diagram 1 into 2? • For pp -> parity transform • For pp -> CP transform • U and J/y are JPC = 1-- • pp: subtract amplitudes • pp add amplitudes S. Klein,LBNL

  8. pp --> ppU (RHIC) pp --> ppU (the Tevatron) dN/dpT2 dN/dpT2 Solid – interference Dashed – no interference pT spectra • pp & pp are very different! • <b> ~ few rp • pTP >> pTg • Different from AA • Interference is relevant for most of production pT range S. Klein,LBNL

  9. Interference or no interference? • Interference occurs when we can’t tell which nucleus emitted the photon • What if scattered proton is detected in a Roman pot? • Most of the VM pT comes from the target proton, so a measurement of the proton pT can determine where the photon came from. • But, what about timing? • What if the J/Y or U is detected before the proton hits the Roman pot? • If detection in a Roman pot destroys the interference, then this can be used to remove the 2-fold ambiguity and study gluons at very low x values S. Klein,LBNL

  10. Backgrounds • s(p(g)p --> (J/Y or U)pp) ~ 10-3 s(pp --> (J/Y or U)X). • Is the signal visible? • Cutting on pT < 1 GeV/c eliminates 94% of the hadroproduction. • Rapidity gaps eliminate the rest. • At the Tevatron dnch/dy ~ 3.9. • 3 units of rapidity gap --> exp(-3*3.9) ~ 10-5. • There are gaps on both sides. • The 3 units can be split between both sides. • 3 units of coverage is easy. • Similar numerology at RHIC; even easier at the LHC. • Quantum numbers wrong for Pomeron-Pomeron. S. Klein,LBNL

  11. Conclusions • Photoproduction of heavy vector mesons is substantial in pp and pp colliders. • The rates are sensitive to the gluon distribution in the proton. • Production at the two sources can interfere. The sign of this interference is different for pp and pp collisions. • The pT spectrum of produced mesons is very different for pp and pp collisions. S. Klein,LBNL

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