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

Double charmonium production Tom Ziegler GHP 2004 Fermilab, 24-26th Oct 2004 1

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

DetectorTom Ziegler

GHP 2004

Fermilab, Batavia, USA 24-26th Oct 2004

Introduction, MotivationEvent selectionAngular distributions and cross

sectionsRecent update, evidence for X(3940)

stateSummary and Conclusion


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

Charmonium

J/

c

*e+

e-


Double cc production in e+e- annihilation

reconstruct 46.2 fb-1 -> PRL 142001-2 (2002)

c

c(2S)c0

cross section: (exp.) > 10 x (theor.)

J/

X

e+

e-

l+ l-

Define the 'recoil mass' of X:

Mrecoil = (ECMS - E*J/ )2 - p*2J/

Invariant mass of X is taken from J/ kinematics


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 c peak

Associated glueball production=> See S.J. Brodsky et al., Phys. Rev. Lett. 91, 112001 (2003) and S. Dulat et al., arXiv:hep-ph/0402230

J/*e+

e- * J/

J/*e+

e- *c, J/


The KEK-B collider

3.5 GeV e+ on 8 GeV e-

+- 11 mrad crossing angle1.6 A x 1.2 AY(4S)


Excellent operation:

L dt = 285 fb-1

255 fb-1 on-resonance 30 fb-1 off-resonance

Peak luminosity:1.39 1034 cm-2 s-1

June 3rd, 2004

Integrated luminosity per day: 944.2 pb-1/dayMay 23rd, 2004


The Belle Detector

3(4) layerSilicon Vertex Detector

Central Drift Chamber

8 GeV e-

3.5 GeV e+

Aerogel Cherenkov Counter

ToF counter

Electromagnetic. Cal.(CsI crystals)

1.5 T SC solenoid

and KL detection system


Event selectiono 140 fb-1 on-resonanceo 15 fb-1 off-resonance

J/ l+l- reconstruction:o dr < 2 cm, dz < 4 cmo Pe = Le / (Le + Lnon-e) > 0.01 o P = L / (L + LK + L) > 0.5o Add Bremsstrahlung photons closer

than 50 mrad around e+/e-

o |Mll - MJ/| < 30 MeV => 2.5 (sidebands = 100-400 MeV)

Background suppressiono Nch > 4 suppresses QED backgroundo P*J/ > 2 GeV suppresses BB background

=> 155 fb-1 total

J/

X

e+

e-

l+ l-


The recoil mass spectrum

CC Mrecoil Nevt

c 2.972 0.007 235 26 10.7J/ Fixed @ PDG -14 20 *

c03.407 0.011 89 24 3.8

c1 + c2Fixed @ PDG 10 27 *

c(2S) 3.630 0.008 164 30 6.0(2S) Fixed @ PDG -26 29 *

*: masses fixed at PDG value

set * to 0set * to 90% C.L. upper limits

Yields for cc = J/, c1/2 and (2S)are compatible with 0

= -ln(L0/Lmax)

c

c(2S)

c0

K. Abe et al., hep-ex 0407009


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=> Momentum scale is OK

(2S) --> J/ +-


Check: full reconstruction of J/ c

c KsK, 2(K+K-) For Nch = 6

3 events reconstructed(> 4 )

2.6 events expected(based on Mrecoil fit yieldin MC)

With Nch = 4 no (J/ J/) signal is found

ISR >10MeV

MC MC

no ISR=> We really see

the (J/ c) events


Production and helicity angles

Fit Mrecoil(J/) in bins of J/ production and helicity angles


Angular analysisCorrect for efficiency and fit 1 + cos2

prod hel prod hel prod = hel

c +1.4 +1.1/-0.8 +0.5 +0.7/-0.5 +1 +1 +0.93 +0.57/-0.47

c0* -1.7 +0.5/-0.5 -0.7 +0.7/-0.5 -1 -1 -1.01 +0.38/-0.33

c(2S) +1.9 +2.0/-1.2 +0.3 +1.0/-0.7 +1 +1 +0.87 +0.86/-0.63

NRQCD (s-/d-wave):*) prod / hel = +0.25/+0.25

Glueball: prod / hel = -0.9 /-0.9


Look for e+e- -> (2S) cc

Reconstruction same as above,(2S) --> J/ + -

CC Nevt

c 36.7 10.4

4.2

J/ 6.9 8.9 *

c035.4 10.7

3.5

c1 + c16.6 8.0 *

c(2S) 36.0 11.4

3.4

(2S) -8.3 8.5 *

5.3 observation of sum of c, c0, c(2s)

c

c (2S)c0

set * to 0set * to 90% C.L. upper limits

K. Abe et al., hep-ex 0407009


Cross sections for J/ (cc) and (2s) (cc)

CC Born B((cc)res --> J/

> 2(0) charged [fb] (2s)

c 25.6 2.8 3.4 16.3 4.6 3.9J/ < 9.1* < 16.9*c0 6.4 1.7 1.0 12.5 3.8 3.1c1 + c2 < 5.3* < 8.6*c(2S) 16.5 3.0 2.4 16.0 5.1 3.8(2S) < 13.3* < 5.2*

Reminder from theory:(e+e- --> J/ c) 2 fb, see E.Braaten and J.Lee, PRD D67, 054007 (2003)

* At 90% C.L.


Recent update

Use whole Belle data set collected by July 2004 L=285 fb-1

Extend the studied region

No signal of X(3872) significant peak at M=3.9400.011 GeV/c2

N=14833 (4.5)

X(3872)


Search for X(3940) D(*)D(*)

Reconstruct J/ + D:Investigate Mrecoil(J/ D)

Use only cleanest modesD0 K- + and D+ K- + +

e+e- J/ D(*) D(*) + nothingcan be clearly seen

Investigate Mrecoil(J/) with:Mrecoil (J/ D) M(D*) N = 9.9 3.3 (4.5 )

Mrecoil (J/ D) M(D)N = 4.1 2.2 (2.1 )


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(*)

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

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