Double charmonium production in e e annihilation

1
Double charmonium production in ee- annihilation

• P.Pakhlov
• ITEP, Moscow
• (for Belle collaboration)

ee- 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

3
Charmonium production in ee-

• Big surprise 1
• 1990 CLEO ee- ? J/? X exists!
• 15.2 ? 4.6 J/? events above kinematical limit for
  B-decays (pgt2.0 GeV/c) in ?(4S) data
• ?(ee- ? J/? X )2 pb
• Was not predicted by theory, but first observed
  experimentally

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4
Theory production in ee-

• Color-Singlet ee- ? 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-octet ee- ? (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 ee- ? J/? gg is the best
  candidate! Predicted ?CS1-2 pb Cho-Leibovich
  (1996)

5
Belles 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

• ee- ? J/? ?c
• ee- ? J/? ?c0
• ee- ? J/? ?c

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Belles first result

• Not the whole story!
• In addition, also observed associated production
  
• ee- ? J/? D() X
• ee- ? J/? D0 X
• Immediately demonstrates large ee- ? J/? cc
  unlike theory prediction
• Based on LUND cc? D/D0 fragmentation rates
  calculated

?(ee-? J/?cc)/?(ee-? J/?X) 0.59?0.14?0.12
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

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Cross-sections

• Born cross-sections
• ? BR (recoil charmonium ? gt2charged)

R e c o
i l
Reconstructed

• Interesting
• Orbital excitations are not suppressed!
• Only S,P states are seen recoiling to V
  charmonium!

9
Can theory adopt this result

• The first NRQCD estimates R?J/??c/????s2(mcv/Eb
  eam)6
• ?(ee-?J/??c)2.3?1.1 fb 10 times lower!
• matrix elements are fixed from annihilation
  constants using J/?? ee-, ?c???
• Bodwin-Braaten-Lee 2003 confirmed by
  Liu-He-Chao, Brodsky-Ji-Lee
• Double photon annihilation also can not resolve
  the disagreement
• experimentally ee-? J/? J/? is not seen
• theoretically (after correcting mistake) ee-? ??
  ? J/? cc is small.

10
BaBars confirmation

• 2005, BaBar also see double charmonium events
• ee- ? J/? ?c
• ee- ? J/? ?c0
• ee- ? J/? ?c

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
  ee-? J/?cc (?1 pb) and predict 10 of J/?cc
  are double charmonium (Mcc lt2MD)
• Bondar Chernyak 2005. Try to save NRQCD! Light
  cone expansion formalizm. Use wider wave
  functions. Manage to predict ? (ee- ? 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.

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

-1.010.38-0.33
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Angular analysis

• Measure L1 for J/? ?c and J/? ?c as expected
  
• L0 is measured for J/? ?c0 NRQCD expects L0,2
  with similar fractions (?c0 is a P-wave)
• Can be used to check BC BLL models. We pay
  their attention to this measurement

14
New state

• Add more data and extend searching region above
  DD threshold
• New peak at M3.9 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 (lt 93MeV _at_
  90C.L.)

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X(3940) decays

• Expect X?DD or DD
• Try to find these decays
• Reconstruct J/? two Ds 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
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X(3940) ? DD()

• X (3940)?DD
• Clear peak
• N24.5 ?6.9 (5.0?)
• ?15.1?10.1 MeV
• M3.943?0.006 GeV
• B (X(3940)?DD)(9645-3222)

• X(3940)?DD no signal
• N 0.2 4.4-3.5 lt 8.1
• B (X(3940)?DD)lt41_at_ 90 C.L.

17
Summary

• Double charmonium production is interesting and
  still not completely understood phenomena
• Belle luminosity theorys wisdom grow!
• Hope to have more interesting results soon.