Double charmonium production in e + e – annihilation

1. Double charmonium production in e+e– annihilation Pavel Pakhlov ITEP, Moscow International Workshop on Heavy Quarkonia 2008 2-5 December 2008, Nara Women's University

2. Charmonium production in e+e– annihilation L~1fb-1 • Not expected by theory, but occasionally observed experimentally • 1990 CLEO: e+e–J/ X exists: • not from B-decays (p>2.0 GeV/c) • not from radiative return (Nch>4) • 15.2  4.6 J/ events in (4S) data • (e+e–J/ X ) ~ 2 pb • For more than 10 years these ~15 events served as the only information available to guess how charmonia can be produced in e+e–annihilation Is this suffucuent to identify the production mechanism?

3. Charmonium production at hadron machines • Last 30 years NRQCD serves to calculate charmonium production: • factorization perturbative (cc production) and non-perturbative (cc hadronization into charmonium)  = n(cc) Oncc • Color Singlet Model (ignore (cc)8) was ok before Tevatron ’ surplus problem was found (1994) • Color Octet Model was believed can solve the Tevatron problem (Braaten, Fleming) • Purely phenomenological approach: free parameters -- Oncc, to tune to the data • If tune parameters to the observed p((2S)) spectra, still have problem to describe polarization

4. Production in e+e–: which monsters give birth to charmonium? • Color-Singlet e+e–J/ cc was estimated to be very small by Kiselev et al.(1994) •  ~ 0.05 pb  should be unobservable even at high luminosity B-factories • Color-octete+e– (cc)8 g J/ g (with Oncc fixed to Tevatron and others data) should not be large as well (but can be significant around the end-point of J/ momentum) Braaten-Chen (1996) • Color-Singlet e+e–J/ gg is the best candidate! Predicted CS ~ 1 pb Cho-Leibovich (1996)

5. Double charmonium production

6. Belle’s first result • Idea is to study the recoil mass against reconstructed J/ using two body kinematics (with a known initial energy) Mrecoil = (Ecms– EJ/)2– PJ/2 ) • 2002, Belle found large cross-sections for: • e+e–J/ c • e+e–J/ c0 • e+e–J/c‘ L~45fb-1

7. Using more data L~155fb-1 • Belle 2004: Full analysis of double charmonium production • Reconstructed charmonium: • J/ • (2S) • Recoil charmonium: • All known charmonium states below DD threshold

8. Cross-sections Born cross-sections:  * BR (recoil charmonium  >2charged) • Interesting: • Orbital excitations are not suppressed! • Only 0+– and 0–– states are seen recoiling against reconstructed 1–– charmonium! ≈70% R e c o i l Reconstructed

9. Observation of e+e− J/ D(*)D(*) Reconstruct J/ and one of two D (or D*) Unreconstructed D(*) is seen as a peak Mrecoil (J/ D) D and D* recoiling against reconstructed J/ D are well separated (~2.5) DD* D*D* DD 693fb-1 D*D* DD* Phys. Rev. Lett. 98, 082001 (2007) All signals are > 5

10. BaBar’s confirmation • 2005, BaBar also see double charmonium events • e+e–J/ c • e+e–J/ c0 • e+e–J/c‘

11. NRQCD & light cone approximation bottomonium charmonium light mesons • The first calculations based on NRQCD gave 10 times smaller x-sections • Ma, Si pointed out that light cone approximation can help (but no idea how to fix the wave function) • Bondar, Chernyak used charmonium wave function parametrized by average charm-quark velocity in charmonium (the same parametrization gave correct result for light meson production) • NRQCD with NLO calculation+radiative+ RELATIVISTIC corrections (He, Fan, Chao; Bodwin, Lee,Yu; Gong, Wang) now also fits the data.

12. New states ine+e− J/ D(*)D(*) D* M = 3942 ±6 MeV tot =37 ±12 MeV +7 -6 D*π D +26 - 15 D* D +25 −20 M= 4156 15 MeV tot = 139 21 MeV +111 −61 X(3940) → DD* X(4160) → D*D* Two new states observed, both decay at open charm final states like “normal” charmonium. Possible assignments are hc(3S) and hc(4S). But in both cases the masses predicted by the potential models are ~100-150 MeV higher than observed. Theory probably needs more elaborated model to take into account interaction of charmonium with open charm.

13. J/ production with charmed hadrons с (e+e–J/cc) ───────────=0.590.140.12 с (e+e–J/X) с с (e+e–J/cc) ───────────~ 0.1 (e+e–J/gg) Looking for D0 and D*+ in J/ events to removeD from B-decays 5.3 Based onLUND predictions for cD(*) Perturbative QCD: Berezhnoy-Likhoded (2003) 3.5

14. New measurement of e+e–→J/ψ cc cross section ηc′ ηc′ hc hc χc0 χc0 J/ J/ ηc ηc Mrecoil(J/) Mrecoil(J/) Mrecoil(χc1) Mrecoil(χc1) ηc′ ηc′ χc0 χc0 ηc ηc hc hc J/ J/ Mrecoil((2S)) Mrecoil((2S)) Mrecoil(χc2) Mrecoil(χc2) e+e–→ J/ (cc) = e+e–→ J/ (cc) res + ½ e+e–→ J/ Hc Xc Hc=D0 Hc=D0 Hc=D+s Hc=D+s 12.4σ 3.6σ +½ Hc=D+ Hc=Λc+ 8.2σ Hc sb 2.2σ All double charmonium final states below open charm threshold All (except for Ξc/Ωc) ground state charmed hadrons preliminary

15. e+e–→J/ψ cc and non-cc cross sections (e+e–J/cc) ───────────~ 0.1 (e+e–J/gg) 673fb–1 e+e–→ J/ X J/ helicity ½ e+e– → J/ Hc Xc J/ production e+e–→ J/ cc dominant!!! Perturbative QCD (no relativisitc corrections): Kiselev et al. (1995) e+e–→J/ non-cc preliminary Model independent full cross sections (e+e–J/cc) ~0.05pb Perturbative QCD: Berezhnoy-Likhoded (2003) No correction on for Nch requirement! J/ from cascade decays included!

16. Summary • Charmonium production in e+e– annihilation: • Double charmonium production problem seems to be solved by taking into account relativistic corrections (charm quark motion in charmonium) • Still no quantative model to calculate e+e– → J/ cc production. The new experimental result (including angular and momentum study) is now available • e+e– → J/ non-cc is also observed: the kinematical features are quite different from e+e– → J/ cc • New charmonium states (and their decays): • Two new states X(3940) and X(4160) have been observed. Possible assignments are ηc(3S) and ηc(4S) in contradiction with mass predictions from potential models • Production of radially excited states is not suppressed: good chance to observe more states and to study the production kinematics and decays of X(3940) and X(4160)