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The Charmonium Spectrum

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

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The Charmonium Spectrum

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  1. The Charmonium Spectrum Spectroscopic Notation n2S+1LJ Charmonium

  2. 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 states total widths (keV) Charmonium

  3. The  puzzle Within the framework of PQCD the decay widths for both 3S1 e+e- and 3S1 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 3S1 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. Charmonium

  4. 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 ccannot 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

  5. The c(11S0) Mass and Total Width M(c) = 2979.6  1.2 MeV/c2 (c) = 17.3  2.6 MeV Charmonium

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

  7. 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 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. Charmonium

  8. The c(21S0)Crystal Ball Candidate The first ´c candidate was observed by the Crystal Ball experiment: By measuring the recoil  they found: Charmonium

  9. Both E760 and E835 searched for the c in the energy region: using the process: but no evidence of a signal was found. The c(21S0)E760/E835 search 2 Crystal Ball Charmonium

  10. 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: c(21S0) search in collisions at LEP Charmonium

  11. The Belle collaboration has recently presented a 6 signal for BKKSK which they interpret as evidence for c production and decay via the process: with: in disagreement with the Crystal Ball result. The c(21S0) discovery by BELLE Charmonium

  12.   c(21S0) BaBar M(c) = 3637.7  4.4 MeV/c2 BaBar: (c) = 17.0  8.3  2.5 MeV Charmonium

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

  14. The cJ(13PJ) States • 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. 0++ 0 1++ 2++ Charmonium

  15. 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. Charmonium

  16. 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!!! Charmonium

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

  18. Radiative transitions of the cJ(3PJ) 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: Charmonium

  19. Angular Distributions of the c States • 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 • 2can couple to both • The fractional electric octupole amplitude, a3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. Charmonium

  20. c1(13P1) AND c2(13P2) ANGULAR DISTRIBUTIONS Charmonium

  21. c1(13P1) AND c2(13P2) ANGULAR DISTRIBUTIONS Interesting physics. Good test for models Predicted to be 0 or negligibly small Charmonium

  22. c1(13P1) and c2(13P2) Angular Distributions McClary and Byers (1983) predict that ratio is independent of c-quark mass and anomalous magnetic moment Charmonium

  23. Angular Distributions of the c states 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 a2(2) agrees well with the predictions of a simple theoretical model, the value of a2(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. Charmonium

  24. The hc(11P1) Precise measurements of the parameters of the hc 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 hc should be degenerate in mass with the center-of-gravity of the cJ states. A comparison of the hc 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. Charmonium

  25. 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

  26. 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 mass of this structure and to put an upper limit on the width: Charmonium

  27. 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: Charmonium

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

  29. E835 Preliminary results for hc c • We 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 ~ 0.001 • If interpreted as hc c the best fit • resonance parameters are: Claudia Patrignani – BEACH 04 – Chicago 6/28-7/3 Charmonium

  30. Other hc(1P1) Searches • The 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 4217 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

  31. Charmonium States abovethe 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. Charmonium

  32. 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 3D1 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. Charmonium

  33. 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

  34. 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/c2  2.3 MeV (90 % C.L.) Charmonium

  35. The X(3872) BaBar CDF D0 Charmonium

  36. Experimental Evidence on the X(3872) - I • The mass (3871.9  0.5 MeV/c2) is very close to the D0D*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 D0D*0 , but the widths would still be very narrow. The 3D3 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. Charmonium

  37. Experimental Evidence on the X(3872) - II • The 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

  38. Possible X(3872) Interpretations • If 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 D0D*0 threshold the X(3872) could be a D0D*0 molecule. In this case decay modes such as D0D0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/c2) 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. Charmonium

  39. 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 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

  40. 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. Charmonium

  41. The GSI p Facility • HESR = 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

  42. The detector • Detector Requirements: • (Nearly) 4 solid angle coverage (partial wave analysis) • High-rate capability (2×107 annihilations/s) • Good PID (, e, µ, , K, p) • Momentum resolution ( 1 %) • Vertex reconstruction for D, K0s,  • Efficient trigger • Modular design • ForCharmonium: • Pointlike interaction region • Lepton identification • Excellent calorimetry • Energy resolution • sensitivity to low-energy photons

  43. Panda Detector Concept forward spectrometer target spectrometer straw tubetracker mini driftchambers muon counter DIRC iron yoke Solenoidal magnet electromagneticcalorimeter micro vertexdetector

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