The Charmonium SpectrumSpectroscopic Notationn2S+1LJ

Charmonium

The J/(13S0) and the (23S0)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/c2 for the J/ and of 34 keV/c2 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.Triplet S statestotal widths (keV)

PDG92 PDG04J/681091.0 3.2243 43277 22

Charmonium

The puzzleWithin the framework of PQCD the decay widths for both 3S1 e+e-and 3S1 hadrons are proportional to the square of the wavefunctionat the origin |(0)|2. If this is true for each individual hadronic channelone finds the following universal ratio (12 % rule):

This holds experimentally for many hadronic decays of the 3S1 states,but it is badly violated for several final states. The first violation to beobserved was for the decay, for which the latest result by BES isR

The c(11S0)It is the ground state of charmonium, with quantum numbers JPC=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.

Charmonium

The c(11S0) Mass and Total WidthM(c) = 2979.6 1.2 MeV/c2(c) = 17.3 2.6 MeV

Charmonium

cIn PQCD the BR can be usedto calculate s:(c) = 7.0 1.0 keVUsing s=0.32 (PDG) and themeasured values for the widths:

Charmonium

Expected properties of the c(21S0)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 Mnz, Nucl. Phys. A 590(1995)735].Total width ranging from a few MeV to a few tens of MeV: (c) 5 25 MeVDecay channels similar to c.

Charmonium

The c(21S0)Crystal Ball CandidateThe first c candidate wasobserved by the Crystal Ball experiment:

By measuring the recoil they found:

Charmonium

The c(21S0)E760/E835 searchBoth E760 and E835 searched for the c in theenergy region:

using the process:

but no evidence of a signalwas found.Crystal Ball2

Charmonium

c(21S0) search in collisions at LEPThe c has been looked for by theLEP 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:

Charmonium

The c(21S0) discovery by BELLEThe Belle collaboration has recentlypresented a 6 signal for BKKSKwhich they interpret as evidence forc production and decay via the process:

with:

in disagreement with the Crystal Ballresult.

Charmonium

c(21S0)M(c) = 3637.7 4.4 MeV/c2BaBarBaBar: (c) = 17.0 8.3 2.5 MeV

Charmonium

Effect of Coupled Channel on the Mass SpectrumEstia Eichten BaBar workshop on heavy quark and exotic spectroscopy

Charmonium

The cJ(13PJ) States0First 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 E835.1++0++2++

Mass (MeV/c2)Width (MeV)03415.19 0.3410.2 0.913510.59 0.120.88 0.1423556.26 0.112.00 0.18

Charmonium

PDG Global FitFollowing a method proposed by Patrignani, the Particle Data Group has carried out a global fit to all available data for the and cJ decaysusing 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 effectsfrom one measurement to the other. The results of the global fit have been implemented in the PDG 2002 and 2004 Reviews of ParticleProperties. As a result of this new procedure, many values of branchingratios and partial widths have changed, and some of the discrepanciesbetween different measurements in pp and e+e- have been eliminated.

Charmonium

cJ ppThe pp decay of the cJ states has been measured both in e+e- collisionsand in pp annihilation. Historically the two methods gave results which werebarely compatible with each other. The situation has changed drastically afterthe global fit to all and cJ data carried out by the PDG.The c0pp BR is almost 4 times as large as that of the c1 and c2!!!

Charmonium

Two-Photon Decay of c0 and c2c0c2(c0) = 2.6 0.5 keV(c2) = 0.49 0.05 keV

Charmonium

Radiative transitions of the cJ(3PJ) charmonium statesThe measurement of the angular distributions in the radiative decaysof the c states provides insight into the dynamics of the formationprocess, the multipole structure of the radiative decay and theproperties of the cc bound state.

Dominated by the dipole term E1. M2 and E3 terms arise in therelativistic treatment of the interaction between the electromagneticfield and the quarkonium system. They contribute to the radiativewidth at the few percent level. The angular distributions of the 2 and 2 are described by 4independent parameters:

Charmonium

Angular Distributions of the c StatesThe coupling between the set of states and pp is described by four independent helicity amplitudes:0 is formed only through the helicity 0 channel1 is formed only through the helicity 1 channel2 can couple to bothThe fractional electric octupole amplitude, a3E3/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.

Charmonium

c1(13P1) AND c2(13P2) ANGULAR DISTRIBUTIONS

Charmonium

c1(13P1) AND c2(13P2) ANGULAR DISTRIBUTIONSPredicted to be 0 or negligibly small Interesting physics. Good test for models

Charmonium

c1(13P1) and c2(13P2) Angular DistributionsMcClary and Byers (1983) predict that ratio is independent of c-quark mass and anomalous magnetic moment

Charmonium

Angular Distributions of the c statesThe angular distributions in the radiative decay of the 1 and2 charmonium states have been measured for the first timeby the same experiment in E835.While the value of a2(2) agrees well with the predictions ofa simple theoretical model, the value of a2(1) is lower thanexpected (for c=0) and the ratio between the two, which isindependent 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 angulardistributions are clearly needed to settle this question.

Charmonium

The hc(11P1) Precise measurements of the parameters of the hc give extremely important information on the spin-dependent component of the qq 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 ofthe spin-spin interaction for P states (whose wave function vanishes at theorigin) should be zero. In this case the hc should be degenerate in mass withthe center-of-gravity of the cJ states. A comparison of the hc mass with themasses of the triplet P states measures the deviation of the vector part of theqq interaction from pure one-gluon exchange.

Total width and partial width to c+ will provide an estimate of the partial widthto gluons.

Charmonium

Expected properties of the hc(1P1) Quantum numbers JPC=1+-.The mass is predicted to be within a few MeV of the center of gravity of the c(3P0,1,2) states

The width is expected to be small (hc) 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

Charmonium

The hc(1P1) E760 observation A signal in the hc region was seen by E760 in the process:

Due to the limited statistics E760 was only able to determine the massof this structure and to put an upperlimit on the width:

Charmonium

The hc(1P1) 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 (Ecm)run/run better then 100 keV in both data taking periods.Not just a cross check: new measurements of the cJ parameters:

c1E835(PRELIM)E760M(MeV/c2)3510.64 0.10 0.073510.53 0.10 0.07(MeV)0.88 0.090.88 0.14B(pp)(J/)(eV)18.8 0.7 0.621.8 2.7 1.2c2E835(PRELIM)E760M(MeV/c2)3556.10 0.15 0.073556.15 0.11 0.07(MeV)1.93 0.221.98 0.18B(pp)(J/)(eV)25.8 1.9 0.828.2 2.9 1.5

Charmonium

E835 Preliminary results for hc J/0Claudia Patrignani BEACH 04 Chicago 6/28-7/3PRELIMINARY conclusion: no evidence for hc J/0.

Charmonium

Claudia Patrignani BEACH 04 Chicago 6/28-7/3E835 Preliminary results for hc cWe observe a total of 23 c candidates 13 of them in 30 pb-1 within 0.5 MeV/c2 of the cJ c.o.g.The statistical significance is ~ 0.001If interpreted as hc c the best fit resonance parameters are:

Charmonium

Other hc(1P1) SearchesThe E705 experiment at Fermilab observed an enhancement in the J/0 mass spectrum at 3527 MeV/c2 in -Li interactions at 300 GeV/c incident momentum. The magnitude of this effect is 4217 events above background, corresponding to a 2.5 significance. Due to its vicinity to Mcog E705 interpreted this signal as due to the production of the hc and its decay to J/0.The BaBar collaboration has recently reported on a search for the hc in the B decay process B K+hc 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.):

Charmonium

Charmonium States abovethe DD thresholdThe energy region above the DDthreshold at 3.73 GeV is very poorlyknown. Yet this region is rich in newphysics.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.

Charmonium

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 conservationforbidden by energy conservationOnly the (3770), considered to be largely 3D1 state, has been clearly observed. It is a wide resonance (((3770)) = 25.3 2.9 MeV) decayingpredominantly to DD. A recent observation by BES of the J/+- decaymode was not confirmed by CLEO-c.

Charmonium

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/c2, in the reaction: This evidence was not confirmed by the same experiment in the reaction and more recently by BES

Charmonium

The X(3872)New state discovered by Belle in the hadronicdecays of the B-meson: BK (J/+-), J/+- or e+e-

M = 3872.0 0.6 0.5 MeV/c2 2.3 MeV (90 % C.L.)

Charmonium

The X(3872)BaBarCDFD0

Charmonium

Experimental Evidence on the X(3872) - IThe mass (3871.9 0.5 MeV/c2) is very close to the D0D*0 threshold (3871.1 1.0 MeV/c2). This value differs from the simplest prediction for the 3D2 mass, however coupled channel effects might change masses considerably. In a calculation by Eichten et al the 3D3 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 3D2 or 1D2.With a mass of 3872 MeV/c2 both could decay to D0D*0 , but the widths would still be very narrow. The 3D3 could decay to DD, 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.

Charmonium

Experimental Evidence on the X(3872) - IIThe decays X(3872) c1 and X(3872) c2 have been unsuccessfully looked for by Belle. This makes the 3D2 and 3D3 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 JPC=1--. Results from BaBar expected in the summer.Angular distribution measured by Belle incompatible with the JPC=1+- assignment for this state.

Charmonium

Possible X(3872) InterpretationsIf X(3872) is a charmonium state, the most natural hypotheses are the 13D2 and 13D3 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 D0D*0 threshold the X(3872) could be a D0D*0 molecule. In this case decay modes such as D0D00 might be enhanced.The charmonium hybrid (ccg) interpretation has been proposed by Close and Godfrey. However present calculations indicate higher mass values (around 4100 MeV/c2) for the ground state. Absence of J/ mode a potential problem.Further experimental evidence is needed to establish the nature of theX(3872): spin-parity, search for charged partners, search for further decay modes, in particular the radiative decay modes.

Charmonium

OutlookAll 8 states below threshold have been observed, but only 7 of them of them are supported by strong experimental evidence. The study of the hc 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.

Charmonium

The FutureFor 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) resonanceCLEO-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.

Charmonium

The GSI p FacilityHESR = High Energy Storage Ring

Production rate 2x107/sec Pbeam = 1 - 15 GeV/c Nstored = 5x1010 p

High luminosity mode Luminosity = 2x1032 cm-2s-1 dp/p~10-4 (stochastic cooling)

High resolution mode dp/p~10-5 (el. cooling < 8 GeV/c) Luminosity = 1031 cm-2s-1

Charmonium

The detectorDetector Requirements:(Nearly) 4 solid angle coverage (partial wave analysis)High-rate capability (2107 annihilations/s)Good PID (, e, , , K, p)Momentum resolution ( 1 %)Vertex reconstruction for D, K0s, Efficient triggerModular designFor Charmonium:Pointlike interaction regionLepton identificationExcellent calorimetryEnergy resolutionsensitivity to low-energy photons

Charmonium

Panda Detector Concepttarget spectrometerforward spectrometermicro vertex detectorelectromagnetic calorimeterDIRCstraw tube trackermini drift chambersmuon counterSolenoidalmagnetiron yoke

Charmonium