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Double charmonium production in e + e - annihilation

This text discusses the production of double charmonium in e+e- annihilation and the different theoretical models used to explain the observed phenomena. It also explores the experimental results from Belle and BaBar collaborations, as well as new ideas and predictions for future studies.

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Double charmonium production in e + e - annihilation

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  1. Double charmonium production in e+e- annihilation P.Pakhlov ITEP, Moscow (for Belle collaboration) e+e- collision from  to  Novosibirsk, BINP, 2006

  2. Theory introduction • 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 appears (1994) • Color Octet Model was believed can solve the Tevatron problem • Purely phenomenologic approach: free parameters -- Oncc, to tune to the data • If tune parameters to the observed p((2S)) spectra, still have problem to predict polarization P.Pakhlov

  3. Charmonium production in e+e- Big surprise #1 • 1990 CLEO: e+e- J/ X exists! • 15.2  4.6 J/ events above kinematical limit for B-decays (p>2.0 GeV/c) in (4S) data • (e+e- J/ X )~2 pb • Was not predicted by theory, but first observed experimentally L~1fb-1 P.Pakhlov

  4. Theory: production in e+e- • 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~1-2 pb Cho-Leibovich (1996) P.Pakhlov

  5. 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- E J/ )2 - P J/2 ) • 2002, Belle found large cross-sections for: • e+e- J/ c • e+e-J/ c0 • e+e-J/c‘ L~45fb-1 P.Pakhlov

  6. Belle’s first result • Not the whole story! • In addition, also observed associated production • e+e-J/ D(*+) X • e+e-J/ D0 X • Immediately demonstrates large e+e- J/ cc unlike theory prediction • Based on LUND cc D*+/D0 fragmentation rates calculated: (e+e-→ J/cc)/(e+e-→ J/X) =0.590.140.12 P.Pakhlov

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

  8. Cross-sections Born cross-sections:  * BR (recoil charmonium  >2charged) • Interesting: • Orbital excitations are not suppressed! • Only S,P states are seen recoiling to V charmonium! R e c o i l Reconstructed P.Pakhlov

  9. Can theory adopt this result • The first NRQCD estimates: R=J/c/~s2(mcv/Ebeam)6 • (e+e-→J/c)=2.31.1 fb ~10 times lower! • matrix elements are fixed from annihilation constants using J/→ e+e-, c Bodwin-Braaten-Lee 2003; confirmed by Liu-He-Chao, Brodsky-Ji-Lee • Double photon annihilation also can not resolve the disagreement: • experimentally e+e-→ J/ J/ is not seen; • theoretically (after correcting mistake) e+e-→  →J/ cc is small. P.Pakhlov

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

  11. New ideas • We need to solve an order of magnitude disagreement • Kaydalov 2003. NRQCD is wrong! Use instead Redge trajectories approach – tune free parameters from D meson production  get reasonable agreement for e+e-→ J/cc (~1 pb) and predict ~10%of J/cc are double charmonium (Mcc <2MD) • Bondar Chernyak 2005. Try to save NRQCD! Light cone expansion formalizm. Use wider wave functions. Manage to “predict”  (e+e- J/ c )~30 fb • Braguta Likhoded Luchinsky 2006. Similar approach to BC applied for all final states: reasonable agreement • All approaches are phenomenological. Need to predict something that can be checked. P.Pakhlov

  12. Angular analysis • Fit Mrecoil(J/) in bins of J/ production and helicity angles • Correct on efficiency • Fit with ~(1+cos2) • production and helicity angles separately • simulteneously: prod=hel -1.01+0.38-0.33 P.Pakhlov

  13. Angular analysis • Measure: L=1 for J/ c and J/c‘ as expected • L=0 is measured for J/ c0 ; NRQCD expects L=0,2 with similar fractions (c0 is a P-wave) • Can be used to check BC & BLL models. We pay their attention to this measurement P.Pakhlov

  14. New state • Add more data and extend searching region above DD threshold • New peak at M~3.9 GeV, Temporary called X(3940) • Two peaks are not excluded, but the second is not significant with the present statistics • Significance 5.0  • =39  26 MeV (< 93MeV @ 90%C.L.) L~450fb-1 P.Pakhlov

  15. X(3940) decays • Expect XDD or DD* • Try to find these decays: • Reconstruct J/ & two D’s – no chance • J/ & one D & see the unreconstructed D in Mrecoil(D J/) -- challenging • D and D* are well • separated ~2.5 • Clearly seen in the data P.Pakhlov

  16. X(3940)  DD(*) X (3940)DD*: Clear peak N=24.5 6.9 (5.0) =15.110.1 MeV M=3.9430.006 GeV B (X(3940)DD*)=(96+45-32±22)% X(3940)DD: no signal N = 0.2+ 4.4-3.5 < 8.1 B (X(3940)DD)<41%@ 90 C.L. P.Pakhlov

  17. Summary • Double charmonium production is interesting and still not completely understood phenomena • Belle luminosity & theory’s wisdom grow! • Hope to have more interesting results soon. P.Pakhlov

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