Double charmonium production in e e

1
Double charmonium production in ee annihilation

• Pavel Pakhlov
• ITEP, Moscow

International Workshop on Heavy Quarkonia
2008 2-5 December 2008, Nara Women's University
2
Charmonium production in ee annihilation

• Not expected by theory, but occasionally
  observed experimentally
• 1990 CLEO ee ? J/? X exists
• not from B-decays (pgt2.0 GeV/c)
• not from radiative return (Nchgt4)
• 15.2 ? 4.6 J/? events in ?(4S) data
• ?(ee ? 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 ee annihilation

L1fb-1
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 ee which monsters give birth to
charmonium?

• 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 ?CS 1 pb Cho-Leibovich
  (1996)

5
Double charmonium production
6
Belles 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

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

L45fb-1
7
Using more data
L155fb-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 ? gt2charged)

70
R e c o
i l
?c J/? ?c0 ?c1?c2 ?c(2S) ?(2S)
J/? ?(2S) 25.6?2.8?3.4 16.3?4.6?3.9 lt9.1 lt16.9 6.4?1.7?1.0 12.5?3.8?3.1 lt5.3 lt8.6 16.5?1.7?0.4 16.3?5.1?3.8 lt13.3 lt5.2
Reconstructed

• Interesting
• Orbital excitations are not suppressed!
• Only 0 and 0 states are seen recoiling
  against reconstructed 1 charmonium!

9
Observation of ee- ? 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
DD
DD
693fb-1
DD
DD
Phys. Rev. Lett. 98, 082001 (2007)
All signals are gt 5?
10
BaBars confirmation

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

11
NRQCD light cone approximation

• 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 calculationradiative
  RELATIVISTIC corrections (He, Fan, Chao Bodwin,
  Lee,Yu Gong, Wang) now also fits the data.

12
New states in ee-? J/? D()D()
X(3940) ? DD
X(4160) ? DD
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
Looking for D0 and D in J/? events
to remove D from B-decays
5.3?
Based on LUND predictions for c?D() Perturbati
ve QCD Berezhnoy-Likhoded (2003)
3.5?
14
New measurement of ee?J/? cc cross section
ee ? J/? (cc) ee ? J/? (cc) res ½ ee ?
J/? Hc Xc
HcD0
HcDs
HcD0
HcDs
12.4s
3.6s
½
HcD
Hc?c
8.2s
Hc sb
2.2s
All double charmonium final states below open
charm threshold
All (except for ?c/Oc) ground state charmed
hadrons
preliminary
15
ee?J/? cc and non-cc cross sections
673fb1
ee ? J/? X
J/? helicity
½ ee ? J/? Hc Xc
J/? production
ee ? J/? cc dominant!!!
Perturbative QCD (no relativisitc corrections)
Kiselev et al. (1995)
ee?J/? non-cc
preliminary
Model independent full cross sections
?(ee?J/?cc) 0.05pb
s(ee?J/? cc),pb 0.740.080.090.08
s(ee?J/? non-cc), pb 0.430.090.09
Perturbative QCD Berezhnoy-Likhoded (2003)
No correction on for Nch requirement! J/? from
cascade decays included!
16
Summary

• Charmonium production in ee 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 ee ? J/?
  cc production. The new experimental result
  (including angular and momentum study) is now
  available
• ee ? J/? non-cc is also observed the
  kinematical features are quite different from
  ee ? J/? cc
• New charmonium states (and their decays)
• Two new states X(3940) and X(4160) have been
  observed. Possible assignments are ?c(3S) and
  ?c(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)