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Double charmonium production in e + e - annihilation

Double charmonium production in e + e - annihilation. P.Pakhlov ITEP, Moscow (for Belle collaboration). e+e- collision from  to  Novosibirsk, BINP, 2006. Theory introduction. Last 30 years NRQCD serves to calculate charmonium production:

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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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