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Double Charmonium Production in e+e- Collisions with the Belle Detector

Double Charmonium Production in e+e- Collisions with the Belle Detector. Tom Ziegler  GHP 2004  Fermilab, Batavia, USA 24-26 th Oct 2004. Introduction, Motivation Event selection Angular distributions and cross sections Recent update, evidence for X(3940) state

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Double Charmonium Production in e+e- Collisions with the Belle Detector

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  1. Double Charmonium Production in e+e- Collisions with the Belle Detector Tom Ziegler  GHP 2004  Fermilab, Batavia, USA 24-26th Oct 2004 • Introduction, Motivation • Event selection • Angular distributions and cross sections • Recent update, evidence for X(3940) state • Summary and Conclusion

  2. Charmonium Charmonium states as testing ground for QCD -> clear experimental signature -> non-relativistic QCD (NRQCD) -> exclusive charmonium modes even simpler -> no unknown non-perturbative parameters e.g. E.Braaten and J.Lee, PRD D67, 054007 (2003) cross section for 'e+e- --> J/ + c': 2.31  1.09 fb J/ e+ * e- c

  3. Double cc production in e+e- annihilation l+ l- reconstruct 46.2 fb-1 -> PRL 142001-2 (2002) J/ e+ e- X Define the 'recoil mass' of X: Mrecoil = (ECMS - E*J/ )2 - p*2J/ c(2S) c0 c Invariant mass of X is taken from J/ kinematics cross section: s(exp.) > 10 x s(theor.)

  4. * * J/ J/ e+ e+ * * e- e- J/ c, J/ Possible explanations Double J/ production via 2- annihilation(this mode is forbidden by C conjugation conservation for 1- annihilation)=> See G.T. Bodwin et al., Phys. Rev. Lett. 90, 162001 (2003)=> if there is a problem with momentum scale bias there might be contribution from J/ to hc peak Associated glueball production=> See S.J. Brodsky et al., Phys. Rev. Lett. 91, 112001 (2003) andS. Dulat et al., arXiv:hep-ph/0402230

  5. The KEK-B collider 3.5 GeV e+ on 8 GeV e- +- 11 mrad crossing angle 1.6 A x 1.2 A Y(4S)

  6. Peak luminosity: 1.39 1034 cm-2 s-1 June 3rd, 2004 Integrated luminosity per day: 944.2 pb-1/day May 23rd, 2004 Excellent operation: L dt = 285 fb-1 255 fb-1 on-resonance 30 fb-1 off-resonance

  7. The Belle Detector  and KL detection system Aerogel Cherenkov Counter 3.5 GeV e+ 3(4) layer Silicon Vertex Detector Electromagnetic. Cal.(CsI crystals) 8 GeV e- Central Drift Chamber 1.5 T SC solenoid ToF counter

  8. J/ e+ e- X Event selection • 140 fb-1 on-resonance • 15 fb-1 off-resonance • J/  l+l- reconstruction: • dr < 2 cm, dz < 4 cm • Pe = Le / (Le + Lnon-e) > 0.01 • P = L / (L + LK + L) > 0.5 • Add Bremsstrahlung photons closer than 50 mrad around e+/e- • |Mll - MJ/| < 30 MeV => 2.5 (sidebands = 100-400 MeV) • Background suppression • Nch > 4 suppresses QED background • P*J/ > 2 GeV suppresses BB background => 155 fb-1 total l+ l-

  9. The recoil mass spectrum K. Abe et al., hep-ex 0407009 set * to 0 set * to 90% C.L. upper limits c(2S) c c0 Yields for cc = J/, c1/2 and (2S) are compatible with 0 *: masses fixed at PDG value  = -ln(L0/Lmax)

  10. Calibrate Mrecoil with e+e- -> (2S)  Very clean sample -> < 1% background from non-(2S) Fit M2recoil(J/) with free peak position -> M2recoil = 0.010  0.009 GeV2/c4 (data/MC) -> Mrecoil (J/) < 3 MeV/c for Mrecoil(J/)  3 GeV/c (2S) --> J/ +- => Momentum scale is OK

  11. Check: full reconstruction of J/ c c KsKp, 2(K+K-) For Nch = 63 events reconstructed(> 4 s) 2.6 events expected(based on Mrecoil fit yieldin MC) With Nch = 4 no (J/ J/) signal is found MC MC => We really see the (J/ hc) events  no ISR  ISR >10MeV

  12. Production and helicity angles Fit Mrecoil(J/) in bins of J/ production and helicity angles

  13. Angular analysis Correct for efficiency and fit 1 + cos2 NRQCD (s-/d-wave): *) prod / hel = +0.25/+0.25 Glueball: prod / hel = -0.9 /-0.9

  14. Look for e+e- -> (2S) cc K. Abe et al., hep-ex 0407009 Reconstruction same as above, (2S) --> J/ + - c (2S) c0 c set * to 0 set * to 90% C.L. upper limits • 5.3  observation of sum of c, c0, c(2s)

  15. Cross sections for J/ (cc) and (2s) (cc) * At 90% C.L. Reminder from theory: (e+e- --> J/ c)  2 fb, see E.Braaten and J.Lee, PRD D67, 054007 (2003)

  16. Recent update Extend the studied region • No signal of X(3872) • significant peak at M=3.9400.011 GeV/c2 • N=14833 (4.5) Use whole Belle data set collected by July 2004 L=285 fb-1 X(3872)

  17. Search for X(3940)  D(*)D(*) Reconstruct J/ + D: Investigate Mrecoil(J/ D) Use only cleanest modes D0  K-p+ and D+  K-p+p+ e+e-  J/ D(*) D(*) + nothing can be clearly seen Investigate Mrecoil(J/) with: Mrecoil (J/ D)  M(D*) N = 9.9  3.3 (4.5 s) Mrecoil (J/ D)  M(D) N = 4.1  2.2 (2.1 s)

  18. Summary and conclusion • e+e- J/ (cc)res was studied in detail: • (cc)res = c, c0, c(2s) are confirmed; angular analysis is done • (cc)res = J/, c1, c2, (2S) not seen, • Experimental cross section is 1 order of magnitude larger than theoretical calculations • e+e- --> (2s) (cc)res seen for first time, the cross sectionhas same order of magnitude as for J/ (cc) • Strong evidence for new charmonium state X(3940)decaying into D(*)D(*)

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