1. Diego BettoniCharmonium1 The Charmonium Spectrum Spectroscopic Notation n 2S+1 L J

2. Diego BettoniCharmonium2 The J/  (1 3 S 0 ) and the  (2 3 S 0 ) The masses of the triplet S states have been measured very precisely in e + e - collision (using resonant depolarization) and in  pp annihilation at Fermilab (E760) Accuracy of 11 keV/c 2 for the J/  and of 34 keV/c 2 for the . The widths of these states were determined by the early e + e - experiments by measuring the areas under the resonance curves. Direct measurement by E760 at Fermilab, which found larger values. PDG92PDG04 J/  68  1091.0  3.2  243  43277  22 Triplet S states total widths (keV)

3. Diego BettoniCharmonium3 The  puzzle Within the framework of PQCD the decay widths for both 3 S 1  e + e - and 3 S 1  hadrons are proportional to the square of the wavefunction at the origin |  (0)| 2. If this is true for each individual hadronic channel one finds the following universal ratio (12 % rule): This holds experimentally for many hadronic decays of the 3 S 1 states, but it is badly violated for several final states. The first violation to be observed was for the  decay, for which the latest result by BES is R  <0.0023. Many explanations have been proposed (vector glueball, intrinsic charm,...): the  -  puzzle must still be understood.

4. Diego BettoniCharmonium4 The  c (1 1 S 0 ) It is the ground state of charmonium, with quantum numbers J PC =0 -+. Knowledge of its parameters is crucial. Potential models rely heavily on the mass difference M(J/  )-M(  c ) to fit the charmonium spectrum. The  c cannot be formed directly in e + e - annihilations: –Can be produced in M1 radiative decays from the J/  and  (small BR). –Can be produced in photon-photon fusion. –Can be produced in B-meson decay. The  c can be formed directly in  pp annihilation. Many measurements of mass and  c width (6 new measurements in the last 2 years). However errors are still relatively large and internal consistency of measurements is rather poor. Large value of  c width difficult to explain in simple quark models. Decay to two photons provides estimate of  s.

5. Diego BettoniCharmonium5 The  c (1 1 S 0 ) Mass and Total Width M(  c ) = 2979.6  1.2 MeV/c 2  (  c ) = 17.3  2.6 MeV

6. Diego BettoniCharmonium6  c  In PQCD the   BR can be used to calculate  s :   (  c ) = 7.0  1.0 keV Using  s =0.32 (PDG) and the measured values for the widths:

7. Diego BettoniCharmonium7 Expected properties of the  c (2 1 S 0 ) The mass difference  between the  c and the  can be related to the mass difference  between the  c and the J/  : Various theoretical predictions of the  c mass have been reported: –M(  c ) = 3.57 GeV/c2 [Bhaduri, Cohler, Nogami, Nuovo Cimento A, 65(1981)376]. –M(  c ) = 3.62 GeV/c2 [Godfrey and Isgur, Phys. Rev. D 32(1985)189]. –M(  c ) = 3.67 GeV/c2 [Resag and Münz, Nucl. Phys. A 590(1995)735]. Total width ranging from a few MeV to a few tens of MeV: –  (  c )  5  25 MeV Decay channels similar to  c.

8. Diego BettoniCharmonium8 The  c (2 1 S 0 ) Crystal Ball Candidate The first  ´ c candidate was observed by the Crystal Ball experiment: By measuring the recoil  they found:

9. Diego BettoniCharmonium9 The  c (2 1 S 0 ) E760/E835 search Both E760 and E835 searched for the  c in the energy region: using the process: but no evidence of a signal was found. Crystal Ball  2 

10. Diego BettoniCharmonium10  c (2 1 S 0 ) search in  collisions at LEP The  c has been looked for by the LEP experiments via the process: L3 sets a limit of 2 KeV (95 %C.L.) for the partial width  (  c  ). DELPHI data (shown on the right) yield:

11. Diego BettoniCharmonium11 The  c (2 1 S 0 ) discovery by BELLE The Belle collaboration has recently presented a 6  signal for B  KK S K  which they interpret as evidence for  c production and decay via the process: with: in disagreement with the Crystal Ball result.

12. Diego BettoniCharmonium12    c (2 1 S 0 ) M(  c ) = 3637.7  4.4 MeV/c 2 BaBar BaBar:  (  c ) = 17.0  8.3  2.5 MeV

13. Diego BettoniCharmonium13 Estia Eichten – BaBar workshop on heavy quark and exotic spectroscopy Effect of Coupled Channel on the Mass Spectrum

14. Diego BettoniCharmonium14 The  cJ (1 3 P J ) States 00 First observed by the early e + e - experiments, which measured radiative decay widths, directly for  1 and  2, indirectly for  0. Radiative decay important for relativistic corrections and coupled channel effects. Precision measurements of masses and widths in  pp experiments (R704, E760, E835).  1 width measured only by E760, most precise measurement of  0 width by E835. Mass (MeV/c 2 )Width (MeV) 00 3415.19  0.3410.2  0.9 11 3510.59  0.120.88  0.14 22 3556.26  0.112.00  0.18 1 ++ 0 ++ 2 ++

15. Diego BettoniCharmonium15 PDG Global Fit Following a method proposed by Patrignani, the Particle Data Group has carried out a global fit to all available data for the  and  cJ decays using each experimentally measured quantity (e.g. product of branching ratios) to extract individual branching ratios and partial widths. This method minimized the propagation of systematic effects from one measurement to the other. The results of the global fit have been implemented in the PDG 2002 and 2004 Reviews of Particle Properties. As a result of this new procedure, many values of branching ratios and partial widths have changed, and some of the discrepancies between different measurements in  pp and e + e - have been eliminated.

16. Diego BettoniCharmonium16  cJ   pp The  pp decay of the  cJ states has been measured both in e + e - collisions and in  pp annihilation. Historically the two methods gave results which were barely compatible with each other. The situation has changed drastically after the global fit to all  and  cJ data carried out by the PDG. The  c0  pp BR is almost 4 times as large as that of the  c1 and  c2 !!!

17. Diego BettoniCharmonium17 Two-Photon Decay of  c0 and  c2  c0  c2   (  c0 ) = 2.6  0.5 keV   (  c2 ) = 0.49  0.05 keV

18. Diego BettoniCharmonium18 Radiative transitions of the  cJ ( 3 P J ) charmonium states The measurement of the angular distributions in the radiative decays of the  c states provides insight into the dynamics of the formation process, the multipole structure of the radiative decay and the properties of the c  c bound state. Dominated by the dipole term E1. M2 and E3 terms arise in the relativistic treatment of the interaction between the electromagnetic field and the quarkonium system. They contribute to the radiative width at the few percent level. The angular distributions of the  2 and  2 are described by 4 independent parameters:

19. Diego BettoniCharmonium19 The coupling between the set of  states and  pp is described by four independent helicity amplitudes: –  0 is formed only through the helicity 0 channel –  1 is formed only through the helicity 1 channel –  2 can couple to both The fractional electric octupole amplitude, a 3  E3/E1, can contribute only to the  2 decays, and is predicted to vanish in the single quark radiation model if the J/  is pure S wave. For the fractional M2 amplitude a relativistic calculation yields: where  c is the anomalous magnetic moment of the c-quark. Angular Distributions of the  c States

20. Diego BettoniCharmonium20  c1 (1 3 P 1 ) AND  c2 (1 3 P 2 ) ANGULAR DISTRIBUTIONS

21. Diego BettoniCharmonium21 Predicted to be 0 or negligibly small Interesting physics. Good test for models  c1 (1 3 P 1 ) AND  c2 (1 3 P 2 ) ANGULAR DISTRIBUTIONS

22. Diego BettoniCharmonium22 McClary and Byers (1983) predict that ratio is independent of c- quark mass and anomalous magnetic moment  c1 (1 3 P 1 ) and  c2 (1 3 P 2 ) Angular Distributions

23. Diego BettoniCharmonium23 The angular distributions in the radiative decay of the  1 and  2 charmonium states have been measured for the first time by the same experiment in E835. While the value of a 2 (  2 ) agrees well with the predictions of a simple theoretical model, the value of a 2 (  1 ) is lower than expected (for  c =0) and the ratio between the two, which is independent of  c, is  2  away from the prediction. This could indicate the presence of competing mechanisms, lowering the value of the M2 amplitude at the  1. Further, high-statistics measurements of these angular distributions are clearly needed to settle this question. Angular Distributions of the  c states

24. Diego BettoniCharmonium24 The h c (1 1 P 1 ) Precise measurements of the parameters of the h c give extremely important information on the spin-dependent component of the q  q confinement potential. The splitting between triplet and singlet is given by the spin-spin interaction (hyperfine structure). If the vector potential is 1/r (one gluon exchange) than the expectation value of the spin-spin interaction for P states (whose wave function vanishes at the origin) should be zero. In this case the h c should be degenerate in mass with the center-of-gravity of the  cJ states. A comparison of the h c mass with the masses of the triplet P states measures the deviation of the vector part of the q  q interaction from pure one-gluon exchange. Total width and partial width to  c +  will provide an estimate of the partial width to gluons.

25. Diego BettoniCharmonium25 Quantum numbers J PC =1 +-. The mass is predicted to be within a few MeV of the center of gravity of the  c ( 3 P 0,1,2 ) states The width is expected to be small  (h c )  1 MeV. The dominant decay mode is expected to be  c + , which should account for  50 % of the total width. It can also decay to J/  : J/  +  0 violates isospin J/  +  +  - suppressed by phase space and angular momentum barrier Expected properties of the h c ( 1 P 1 )

26. Diego BettoniCharmonium26 A signal in the h c region was seen by E760 in the process: Due to the limited statistics E760 was only able to determine the mass of this structure and to put an upper limit on the width: The h c ( 1 P 1 ) E760 observation

27. Diego BettoniCharmonium27 The h c ( 1 P 1 ) E835 search E835 took the following data in 2 running periods: –90 pb -1 in the  cJ c.o.g. region. –data taken outside this energy region for background studies, providing 120 pb -1 for the  c  mode and 80 pb -1 for the J/  0 mode. Very careful beam energy studies. All single  c1 and  c2 stacks taken in E835 have been preliminarly analyzed, to find  (E cm ) run/run better then 100 keV in both data taking periods. Not just a cross check: new measurements of the  cJ parameters :  c1 E835(PRELIM)E760 M(MeV/c 2 ) 3510.64  0.10  0.073510.53  0.10  0.07  (MeV)0.88  0.090.88  0.14 B(p  p)  (J/  )(eV)18.8  0.7  0.621.8  2.7  1.2  c2 E835(PRELIM)E760 M(MeV/c 2 ) 3556.10  0.15  0.073556.15  0.11  0.07  (MeV)1.93  0.221.98  0.18 B(p  p)  (J/  )(eV)25.8  1.9  0.828.2  2.9  1.5

28. Diego BettoniCharmonium28 Claudia Patrignani – BEACH 04 – Chicago 6/28-7/3 E835 Preliminary results for h c  J/  0 PRELIMINARY conclusion: no evidence for h c  J/  0.

29. Diego BettoniCharmonium29 Claudia Patrignani – BEACH 04 – Chicago 6/28-7/3 E835 Preliminary results for h c   c  We observe a total of 23  c  candidates 13 of them in 30 pb -1 within 0.5 MeV/c 2 of the  cJ c.o.g. The statistical significance is ~ 0.001 If interpreted as h c  c  the best fit resonance parameters are:

30. Diego BettoniCharmonium30 Other h c ( 1 P 1 ) Searches The E705 experiment at Fermilab observed an enhancement in the J/  0 mass spectrum at 3527 MeV/c 2 in   -Li interactions at 300 GeV/c incident momentum. The magnitude of this effect is 42  17 events above background, corresponding to a 2.5  significance. Due to its vicinity to M cog E705 interpreted this signal as due to the production of the h c and its decay to J/  0. The BaBar collaboration has recently reported on a search for the h c in the B decay process B  K+h c  K+J/  +  + +  -. The absence of a signal allowed the collaboration to set the following upper limit on the product of branching ratios (at 90 % C.L.):

31. Diego BettoniCharmonium31 Charmonium States above the D  D threshold The energy region above the D  D threshold at 3.73 GeV is very poorly known. Yet this region is rich in new physics. The structures and the higher vector states (  (3S),  (4S),  (5S)...) observed by the early e+e- experiments have not all been confirmed by the latest, much more accurate measurements by BES. This is the region where the first radial excitations of the singlet and triplet P states are expected to exist. It is in this region that the narrow D- states occur.

32. Diego BettoniCharmonium32 The D wave states The charmonium “D states” are above the open charm threshold (3730 MeV ) but the widths of the J= 2 states and are expected to be small: forbidden by parity conservation forbidden by energy conservation Only the  (3770), considered to be largely 3 D 1 state, has been clearly observed. It is a wide resonance (  (  (3770)) = 25.3  2.9 MeV) decaying predominantly to D  D. A recent observation by BES of the J/  +  - decay mode was not confirmed by CLEO-c.

33. Diego BettoniCharmonium33 The D wave states The only evidence of another D state has been observed at Fermilab by experiment E705 at an energy of 3836 MeV/c 2, in the reaction: This evidence was not confirmed by the same experiment in the reaction and more recently by BES

34. Diego BettoniCharmonium34 The X(3872) New state discovered by Belle in the hadronic decays of the B-meson: B   K  (J/  +  - ), J/  µ + µ - or e + e - M = 3872.0  0.6  0.5 MeV/c 2  2.3 MeV (90 % C.L.)

35. Diego BettoniCharmonium35 The X(3872) BaBar CDF D0

36. Diego BettoniCharmonium36 Experimental Evidence on the X(3872) - I The mass (3871.9  0.5 MeV/c 2 ) is very close to the D 0  D* 0 threshold (3871.1  1.0 MeV/c 2 ). This value differs from the simplest prediction for the 3 D 2 mass, however coupled channel effects might change masses considerably. In a calculation by Eichten et al the 3 D 3 state falls very close to 3872. The state is very narrow. The present limit by Belle is 2.3 MeV, compatible with a possible interpretation as 3 D 2 or 1 D 2.With a mass of 3872 MeV/c 2 both could decay to D 0  D* 0, but the widths would still be very narrow. The 3 D 3 could decay to D  D, but its f-wave decay would be strongly suppressed. In the only decay mode detected so far, J/  +  -, the  +  - mass distribution peaks at the kinematic limit, which corresponds to the  mass. The decay to J/  would violate isospin and should therefore be suppressed.

37. Diego BettoniCharmonium37 The decays X(3872)  c1 and X(3872)  c2 have been unsuccessfully looked for by Belle. This makes the 3 D 2 and 3 D 3 interpretations problematic. The decay X(3872)  J/  has been unsuccessfully looked for by BaBar. This is a problem for the charmonium hybrid interpretation. CLEO did not find this state in Initial State Radiation, which rules out the assignment J PC =1 --. Results from BaBar expected in the summer. Angular distribution measured by Belle incompatible with the J PC =1 +- assignment for this state. Experimental Evidence on the X(3872) - II

38. Diego BettoniCharmonium38 Possible X(3872) Interpretations If X(3872) is a charmonium state, the most natural hypotheses are the 1 3 D 2 and 1 3 D 3 states. In this case the non-observation of the expected radiative transitions is a potential problem, but the present experimental limits are still compatible with these hypotheses. Due to its closeness to the D 0  D* 0 threshold the X(3872) could be a D 0  D* 0 molecule. In this case decay modes such as D 0  D 0  0 might be enhanced. The charmonium hybrid (c  cg) interpretation has been proposed by Close and Godfrey. However present calculations indicate higher mass values (around 4100 MeV/c 2 ) for the ground state. Absence of J/  mode a potential problem. Further experimental evidence is needed to establish the nature of the X(3872): spin-parity, search for charged partners, search for further decay modes, in particular the radiative decay modes.

39. Diego BettoniCharmonium39 Outlook All 8 states below threshold have been observed, but only 7 of them of them are supported by strong experimental evidence. The study of the h c remains a very high priority in charmonium physics. The agreement between the various measurements of the  c mass and width is not satisfactory. New, high-precision measurments are needed. The large value of the total width needs to be understood. The study of the  c has just started. Small splitting from the  must be understood. Width and decay modes must be measured. The angular distributions in the radiative decay of the triplet P states must be measured with higher accuracy. The entire region above open charm threshold must be explored in great detail, in particular the missing D states must be found. Decay modes of all charmonium states must be studied in greater detail: new modes must be found, existing puzzles must be solved (e.g.  -  ), radiative decays must be measured with higher precision.

40. Diego BettoniCharmonium40 The Future For the near future, new results in charmonium spectroscopy will come from existing e + e - machines: –BES at BEPC in Beijing will collect data at the  (3770) resonance –CLEO-c at Cornell will run for at least 5 years at the  and especially above threshold. –BaBar and Belle at the existing B-factories will continue to provide first rate results in charmonium spectroscopy. For the future beyond 2010 it will be again the turn of  pp annihilation to take the lead in charmonium physics: the PANDA experiment at the FAIR facility in GSI will take data with a rich program of hadron spectroscopy, of which the study of charmonium will be a major part.

41. D. Bettoni - Charmonium at GSI 41 The GSI p Facility HESR = High Energy Storage Ring Production rate 2x10 7 /sec P beam = 1 - 15 GeV/c N stored = 5x10 10 p High luminosity mode Luminosity = 2x10 32 cm -2 s -1 dp/p~10 -4 (stochastic cooling) High resolution mode dp/p~10 -5 (el. cooling < 8 GeV/c) Luminosity = 10 31 cm -2 s -1

42. D. Bettoni - Charmonium at GSI 42 The detector Detector Requirements: –(Nearly) 4  solid angle coverage (partial wave analysis) –High-rate capability (2×10 7 annihilations/s) –Good PID ( , e, µ, , K, p) –Momentum resolution (  1 %) –Vertex reconstruction for D, K 0 s,  –Efficient trigger –Modular design For Charmonium: –Pointlike interaction region –Lepton identification –Excellent calorimetry Energy resolution sensitivity to low-energy photons

43. D. Bettoni - Charmonium at GSI 43 Panda Detector Concept target spectrometer forward spectrometer micro vertex detector electromagnetic calorimeter DIRC straw tube tracker mini drift chambers muon counter Solenoidal magnet iron yoke