Photoproduction of J/ψ on Nuclei

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1 Outline E.Chudakov SRC Workshop, Jlab 2007 Photoproduction of J/ψ on Nuclei 1 Photoproduction of J/ψ on Nuclei E.Chudakov 1 1 JLab SRC Workshop, Jlab 2007

2 E.Chudakov SRC Workshop, Jlab 2007 Photoproduction of J/ψ on Nuclei 2 JLab at 12 GeV Physics At 11 GeV γp η c (1S), J/ψ(1S), D 0 Λ + c, χ c1 (1P)... Cross sections are low: < 10 nb for D and < 1 nb for charmonia The only detectable particle seems J/ψ(1S) - decays to lepton pairs Photoproduction of J/ψ(1S) close to threshold Interaction of J/ψ(1S) - a long living particle - with matter Can we use J/ψ(1S) as a probe for the nucleon/nucleus?

3 E.Chudakov SRC Workshop, Jlab 2007 Photoproduction of J/ψ on Nuclei 3 J/ψ photoproduction at 10 GeV: Scales γ l c L l F ψ r 1 α s m c At E γ = 10 GeV: = 0.3 fm nuclear radius l coh = 2E γ 4m 2 c+q 2 l F = 2E γ m 2 ψ m2 J/ψ 0.4 fm 1 fm No coherent production on heavy nucleus: l coh R A No shadowing effects: l coh, l F < R A VMD not applicable: l coh < 1 fm

4 E.Chudakov SRC Workshop, Jlab 2007 Photoproduction of J/ψ on Nuclei 4 J/ψ photoproduction at 10 GeV: Dynamical models H x 1 x 2 GPD J/ψ Partonic soft mechanism Frankfurt Well tested at high energies 10 GeV: gluons x 1 x 2 1 t min > 0.4 GeV/c 2-gluon formfactor: (1 t/1.0gev 2 ) 4 dσ γp J/ψp dt Hard scattering mechanism Brodsky.., GeV: Quark counting rules 2-gluon exchange (1 x) 2 3-gluon exchange (1 x) 0 Unique probe of small-size gluon configurations in proton

5 E.Chudakov SRC Workshop, Jlab 2007 Photoproduction of J/ψ on Nuclei 5 J/ψ photoproduction at 10 GeV: Dynamical models σ(γn J/ψ elastic) nb Cornell 75 SLAC 75 SLAC 76 unpublished Both models fit the data at GeV: Frankfurt 2003 Brodsky 2001: 2-gluon exchange (red curve) b) (1-x) 2, 2-gluon exchange b fit to the data at GeV E γ GeV Brodsky 2001: 3-gluon exchange alone does not fit the data

6 E.Chudakov SRC Workshop, Jlab 2007 Photoproduction of J/ψ on Nuclei 5 J/ψ photoproduction at 10 GeV: Dynamical models σ(γn J/ψ elastic) nb Cornell 75 SLAC 75 SLAC 76 unpublished Both models fit the data at GeV: Frankfurt 2003 Brodsky 2001: 2-gluon exchange (red curve) b) (1-x) 2, 2-gluon exchange b fit to the data at GeV E γ GeV Subthreshold experiment E No J/ψ observed Spectral functions σ not large

7 E.Chudakov SRC Workshop, Jlab 2007 Photoproduction of J/ψ on Nuclei 6 Photoproduction on nucleons 1 Measure dσ dt (E) for γ+p J/ψ+p close to threshold, at E γ GeV Low energy sensitive to high-x gluons in the nucleon

8 E.Chudakov SRC Workshop, Jlab 2007 Photoproduction of J/ψ on Nuclei 7 ψn Interaction: Physics Small size color dipole r 1 α s m c = 0.3 fm interaction color dipole moment r cc (small) color transparency, σ ψn tot σ πn tot 30 mb Low energy: attractive potential (Luke,Manohar,Savage,1992) similar to Van der Waals, E binding 8 MeV Absorption: breakup to DD, ψ+n Λ + c D

9 ψn Interaction: Signature for QGP J/ψ suppression in AA collisions signature for QGP Range: s GeV deficiency found, using experiment σ ψn abs SPS 4.18 mb RHIC 3. mb g. 3. J/ψ production in d Au collisions at s = 200 GeV. er to convert the rates R Au Au into survival probabilhave to know what would be expected if only normal atter were present. At RHIC, this information is proough d Au studies [22]; the resulting nuclear modifictor, specifying the production rate relative to scaled isions, is shown in Fig. 3. Interpretation: not resolved yet mixture ψ, χ c...; regeneration at RHIC antify these RHIC results, with their presently rather tatistics, weinadopt different a description conditions similar to that used esults and apply the well-known simplified absorption Fig. 4. Impact parameter relation between p A and A A collisions. Fig. 5. J/ψ suppression as function of energy density. JLab experiment - measure σ ψn abs at lower energy s 5 GeV, For A A collisions at RHIC energy, we make use of th same simplified form (6). The geometry connecting the impa parameter b and path length L in p Au and Au Au collision is illustrated in Fig. 4; the relation between b and N part is agai E.Chudakov SRC Workshop, Jlab 2007 Photoproduction of J/ψ on Nuclei 8

10 E.Chudakov SRC Workshop, Jlab 2007 Photoproduction of J/ψ on Nuclei 9 ψn Interaction: σ ψn Theoretical Calculations Various models: VMD, exchange meson currents, etc. authors model s, GeV σ ψn, mb Brodsky,Miller,1997 Van-der-Waals potential small 7 Kopeliovich...,1994 GVMD, wave functions Gerland..., 1998 VMD, data for VM >7 3.6 Sibirtsev..., 2001 boson exchange >4 2.2 PHYSICAL REVIEW C Lattice

11 E.Chudakov SRC Workshop, Jlab 2007 Photoproduction of J/ψ on Nuclei 10 ψn Interaction: Experimental Access 1 Calculated from photoproduction on nucleons using VMD/GVMD γn >20 GeV σ ψn tot mb model dependent 2 Nuclear absorption: from A-dependence, Glauber model γa 20 GeV σ ψn abs = 3.5 ± 0.9 mb pa >100 GeV σ ψn abs = 4.2 ± 0.4 mb clean interpretation poor accuracy not ψn: l coh, l F R A contamination χ c, ψ We use arguments from Farrar et al.,1990, Kharzeev et al, 2007

12 E.Chudakov SRC Workshop, Jlab 2007 Photoproduction of J/ψ on Nuclei 11 ψn Interaction: Experiment at SLAC 1977 The cleanest method used so far: l coh, l F < R A Large experimental uncertainties 20 GeV e on Be and Ta targets Detecting only µ, through iron The background was calculated (decays, Bethe-Heitler) Nuclear coherence not measured σ(be)/σ(ta) = 1.21 ± 0.7 σ ψn = 3.5 ± 0.8 ± 0.6 mb Authors: syst. errors might be larger JLab: we can do a much more accurate experiment!

13 E.Chudakov SRC Workshop, Jlab 2007 Photoproduction of J/ψ on Nuclei 12 Photoproduction on Nuclei 1 Measure the A-dependence of σ(γ + A J/ψ + X), extract σ ψn abs at s 5 GeV Much improved accuracy and a cleaner interpretation.

14 E.Chudakov SRC Workshop, Jlab 2007 Photoproduction of J/ψ on Nuclei 13 Program at JLab PR for Hall C: conditionally approved. Objectives: 1 Accurate measurement of J/ψ-nucleon cross-section at s = 5 GeV Test theoretical ideas (color dipole model, Van-der-Waals force) Benchmark for future calculations Interest for heavy ion physics. 2 Measurement of J/ψ photoproduction cross section dσ dt (E γ) at E γ GeV Input for (1). Probes large-x gluon GPD / small-size gluon configurations in proton.

15 E.Chudakov SRC Workshop, Jlab 2007 Photoproduction of J/ψ on Nuclei 14 ψn Interaction: Proposed Experiment 1 Measure the A-dependence of γa J/ψX, extract σ ψn abs compared with SLAC 1977: low background for J/ψ no coherent production smaller effects from l coh,l F several targets used reconstructed kinematics of J/ψ steeper σ(e γ ) dependence stronger effect from Fermi motion (need σ(e γ ) to make correction) 2 Measure dσ dt (E) for γp J/ψp Provide Fermi-motion correction for the A-dependence Measurement in a new energy range

16 E.Chudakov SRC Workshop, Jlab 2007 Photoproduction of J/ψ on Nuclei 15 Experiment: Setup Use decays to e + e (6%), µ + µ (6%) to identify J/ψ mass Standard Hall C equipment High rate at various targets Low background: < 2%, scaled from Cornell, SLAC Reconstruction of E γ, identification of γ+p J/ψ+p Hall C Spectrometers HMS: e, µ at θ > 20 SHMS: e +, µ + at θ < 20 e +, e Gas Cher., Shower µ +, µ Gas Cher. Beam and target Bremsstrahlung by 50 µa beam 6 targets A = 9 197, 10% r.l. thick Each target: 3 plates 5 cm apart 20 cm LH 2 with a 7% radiator 20 cm LD 2 with a 7% radiator

17 E.Chudakov SRC Workshop, Jlab 2007 Photoproduction of J/ψ on Nuclei 16 Experiment: γa kinematics optimization dσ dt = C(E γ ) e b t, 2 gluon exchange, fit to data t-slope b varied in (GeV/c) 2 range Decay distribution (1 + cos 2 θ CM ) Fermi motion - spectral functions for C, Fe and Au used Beam energy 11 GeV Acceptance optimized for γa set HMS SHMS θ P, GeV/c θ P, GeV/c

18 E.Chudakov SRC Workshop, Jlab 2007 Photoproduction of J/ψ on Nuclei 17 Experiment: Rates on Nuclear Targets Acceptance ɛ 0.03% Internal Bremsstrahlung 1.6% No nuclear absorption is assumed for the moment 1 H 2 H Be C Al Cu Ag Au A Z T /T RL J/ψ per h Time, h * in order to detect 4000 events per target 200 hours on nuclear targets

19 E.Chudakov SRC Workshop, Jlab 2007 Photoproduction of J/ψ on Nuclei 18 Experiment: Counting rates, Backgrounds Cornell Rates Single arm: < 250 khz Coincidence t 100 ns: 200 Hz Resolutions Mass 7.4 MeV/c 2 For γ+p J/ψ+p: Photon energy 0.2% t: σ t (GeV/c) 2 Backgrounds Accidentals < 0.2 per hour Physics: Bethe-Heitler dominated Calculated Scaled using Cornell, SLAC < 2%

20 E.Chudakov SRC Workshop, Jlab 2007 Photoproduction of J/ψ on Nuclei 19 Fermi motion Correction and Hydrogen Measurements Fermi motion σ γn ψx (E γ ) : Au/C 1.10 sensitive to σ(e γ ) Need to measure σ(e γ ) Plan for σ γp ψp (E γ ) measurement 3 endpoints at 8.8, 10.2, 11.0 GeV Elastic γp ψp dominates Use reconstructed photon energy E γ E γ > E e 0.3 GeV: pure elastic Constraints from SLAC E γ > 15 GeV Simulation shows: δ(au/c) < 0.01 dn/de, arbitrary units C E photon (target nucleon at rest), GeV/c Measurements on LH 2 < E γ > GeV σ ψ (E) error % % %

21 E.Chudakov SRC Workshop, Jlab 2007 Photoproduction of J/ψ on Nuclei 20 Experiment: Expected Results on σ ψn Total error per target 3% beam flux 1% target thickness < 1.5% Fermi correction < 1.% statistics 1.5% acceptance: nearly cancels other 0.5% Glauber model used to extract σ ψn Expected transparencies T N (A) = σ A /Aσ N σ ψn A δ(σ ψn ) mb mb T σ ψn (3.5) ± 0.12 ± 0.20 mb at s 5 GeV SLAC: 0.80 ± 0.60

22 E.Chudakov SRC Workshop, Jlab 2007 Photoproduction of J/ψ on Nuclei 21 Experiment: Photoproduction 1 Main measurements on hydrogen 3 endpoints: 8.8,10.2 and 11.0 GeV expected accuracy σ ψ 3% for 10.2 and 11 GeV 2 Additional measurements at 11 GeV Increase the range of t to measure dσ dt Increase the range of θ decay to measure the absolute cross section LD 2 - for isoscalarity correction In total 290 hours are requested

23 E.Chudakov SRC Workshop, Jlab 2007 Photoproduction of J/ψ on Nuclei 22 Request Standard Hall C spectrometers New nuclear targets Radiators for cryo targets beam 11.0 GeV standard 16 days 10.8 GeV non-standard 2 days 8.8 GeV standard 3 days 21 days

24 E.Chudakov SRC Workshop, Jlab 2007 Photoproduction of J/ψ on Nuclei 23 Spectrometers spectr. P range P/P σp/p θ in range θ in θ out Ω σθ in σθ out GeV/c mrad mrad msr mrad mrad HMS % 0.1% ±24 ± SHMS % 0.1% ±20 ±

25 E.Chudakov SRC Workshop, Jlab 2007 Photoproduction of J/ψ on Nuclei 24 Settings for hydrogen measurements HMS SHMS selection rate J/ψ set θ P θ P P ψ P 2 t cos θ CM E γ per hour GeV/c GeV/c GeV/c (GeV/c) 2 GeV total elas. E e = 11 GeV E e = 10.2 GeV E e = 8.8 GeV

26 E.Chudakov SRC Workshop, Jlab 2007 Photoproduction of J/ψ on Nuclei 25 Photoproduction measurements

27 E.Chudakov SRC Workshop, Jlab 2007 Photoproduction of J/ψ on Nuclei 26 σ ψn Theoretical Calculations Various models used exchange meson currents, color dipole interactions etc. Low energy (Van-der-Waals): σ ψn tot 7 mb (Brodsky,Miller,1997), falling with energy Scaling from other VM: 3.6 mb (Gerland et al,1998) σ ψn abs GVMD, wave func, σ ψn tot 3 mb (Kopeliovich,Raufeisen,1994) Exclusive reactions

28 E.Chudakov SRC Workshop, Jlab 2007 Photoproduction of J/ψ on Nuclei 26 σ ψn Theoretical Calculations Various models used exchange meson currents, color dipole interactions etc. Low energy (Van-der-Waals): σ ψn tot 7 mb (Brodsky,Miller,1997), falling with energy Scaling from other VM: 3.6 mb (Gerland et al,1998) σ ψn abs GVMD, wave func, σ ψn tot 3 mb (Kopeliovich,Raufeisen,1994) Exclusive reactions σ (γ p J/ψ p) nb Kopeliovich H1 E401 E516 ZEUS BT COR LOG POW GBW H1 E401 E516 ZEU BT COR LOG POW s [GeV] 10 1

29 E.Chudakov SRC Workshop, Jlab 2007 Photoproduction of J/ψ on Nuclei 26 σ ψn Theoretical Calculations Various models used exchange meson currents, color dipole interactions etc. Low energy (Van-der-Waals): σ ψn tot 7 mb (Brodsky,Miller,1997), falling with energy Scaling from other VM: 3.6 mb (Gerland et al,1998) σ ψn abs GVMD, wave func, σ ψn tot 3 mb (Kopeliovich,Raufeisen,1994) Exclusive reactions σ [mb] 10 1 GBW ψ J/ψ Kopeliovich BT COR LOG POW s [GeV] 10 1 KST ψ J/ψ

30 E.Chudakov SRC Workshop, Jlab 2007 Photoproduction of J/ψ on Nuclei 26 σ ψn Theoretical Calculations Various models used exchange meson currents, color dipole interactions etc. Low energy (Van-der-Waals): σ ψn tot 7 mb (Brodsky,Miller,1997), falling with energy Scaling from other VM: 3.6 mb (Gerland et al,1998) σ ψn abs GVMD, wave func, σ ψn tot 3 mb (Kopeliovich,Raufeisen,1994) Exclusive reactions

31 σ ψn Theoretical Calculations Various models used exchange meson currents, color dipole interactions etc. Oh, Liu,Ko 2007 ψ+n Λ Low energy (Van-der-Waals): + c D σ ψn tot 7 mb (Brodsky,Miller,1997), (a) falling with energy 8.00 Scaling from other VM: 3.6 mb (Gerland et al,1998) σ ψn abs GVMD, wave func, σ ψn tot 3 mb (Kopeliovich,Raufeisen,1994) Exclusive reactions 6 σ J/ψ + p D 0 + Λc (mb) σ J/ψ + p D *0 + Λc (mb) s (GeV) FIG. 4: (Color online) Total cross section for (a) J/ψ + p D 0 + Λ c and (b E.Chudakov SRC Workshop, Jlab 2007 Photoproduction = In of (a), J/ψthe onu-channel Nuclei diagram 26 dominates and the contributi κ

32 E.Chudakov SRC Workshop, Jlab 2007 Photoproduction of J/ψ on Nuclei 27 J/ψ photoproduction at 10 GeV: Dynamical models S. Brodsky et al, 2001: Quark counting rules at x = s thresh mp 2 s mp 2 2-gluon exchange dσ dt dσ dt dσ dt = N 2g v (1 x)2 R 2 M 2 F 1 ( t 4 )(s m2 p) 2 3-gluon exchange = N 3g v (1 x)0 F R 4 M 4 1 ( t 9 )(s m2 p) 2 e b t from experiments 1 Different energy dependencies for 2,3-gluons Frankfurt, Strikman, Weiss dσ x 1 γp J/ψp dt Hg(x,t)2 H g(x,0) H g (x, t) (1 t/mg) gluon formfactor dσ γp J/ψp dt (1 t/1.0gev 2 ) σ(γn J/ψ elastic) nb Cornell 75 SLAC 75 SLAC 76 unpublished b) (1-x) 2, 2-gluon exchange b fit to the data at GeV E γ GeV

33 E.Chudakov SRC Workshop, Jlab 2007 Photoproduction of J/ψ on Nuclei 28 Spectra Produced Detected P ψ E γ