Exploring QCD in the Charmonium System

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1 Exploring QCD in the Charmonium System Matthew Shepherd ndiana University September 27, 200 T(r)opical QCD -- Cairns, Australia

2 2 September 27, 200

3 Outline Key charmonium experiments: BES and CLEO-c Recent results: a sampler of various measurements the charmonium spectrum and radiative transitions radiative and electromagnetic decays of charmonium light meson spectroscopy in charm and charmonium decays Summary September 27, 200

4 The Charmonium System The -- states are easily populated in e + e - collisions -- well known and clean initial states All expected cc states below DD threshold have been experimentally verified c S 0 D S h c P DD Threshold 2 Provides an opportunity to explore the qq bound state in heavy quark regime Decays of cc into light hadrons proceed via glue-rich OZ suppressed channels c S S + 0 0,, September 27, 200

5 Charmonium Experiments CLEO-c Cornell Electron Storage Ring (thaca, NY) e + e - collisions at ψ, ψ(770), and Ecm = 460 MeV decommissioned in analysis still ongoing BES nstitute for High Energy Physics (Beijing) successor to BES world s largest sample of ψ and J/ψ decays (and still growing) vibrant current and future program SC Quadrupole Pylon SC Quadrupoles Rare Earth Quadrupole Magnet ron Solenoid Coil Barrel Calorimeter Ring maging Cherenkov Detector Drift Chamber Barrel Muon Chambers nner Drift Chamber / Beampipe Endcap Calorimeter ron Polepiece 5 September 27, 200

6 Spectrum and Transitions Mass of the hc: P-wave hyperfine splitting Multipole amplitudes in photon transitions through the χc states c S 0 D S h c P DD Threshold Measurements test cc quark model calculations lattice QCD predictions c S 0 S ,, September 27, 200

7 The P-wave singlet state: hc Last state below open charm threshold to be identified E85 (2005): σ CLEO (2005): 5σ c S 0 D S π 0 h c P DD Threshold 2 ts mass gives P-wave hyperfine splitting which is naively predicted to be zero γ 0 Production in isospin violating decay Predicted to have large radiative branching fraction to the ηc c S S + 0,, September 27, 200

8 hc Properties New high-stats study from BES Reconstruct specific hc γηc decays (a) or inclusively by just finding hc γηc photon (b) Recent precision results form BES: M(h c) = ± 0. ± 0.8 MeV Γ(hc) 90% C.L. agrees w/cleo-c (PRL 0, 8200); comparable precision P-wave hyperfine splitting is consistent with zero at 0.5 MeV level Branching fractions (first measured by BES ): B(ψ π 0 hc) = (8.4 ±. ±.0) x 0-4 B(hc γηc) = (54 ± 7 ± 5)% Dominant decay to γηc agrees with theoretical predictions BES: PRL 04, 2002 (200) 8 September 27, 200

9 Radiative Transitions to χcj Dominated by E (electric dipole) but M2 (magnetic quadrupole) provides sensitivity to anomalous magnetic moment of charm quark (κc) Leading order quark-model quadrupole amplitudes:.8 2MD.6!c(2 S0) "( D) "(2 S) b J=2 b J= MASS [GeV/c 2 ].4 hc( P) a J= #c( P) #c0( P0) a J=2 #c2( P2).2 J/"( S) E is zero in absence of S/D (ψ) or P/F (χ) mixing.0!c( S0) E-Dominated Transitions M-Dominated Transitions 0 $+ $$ +$ J PC September 27, 200

10 Evidence for M2 Contribution CLEO Collaboration PRD 80, 200 (2009) CLEO analysis reconstructs full decay chain; very clean (< 0.% background) χc ψ γχcj; χcj γj/ψ; J/ψ l + l - A five-dimensional fit to angular distributions of decay products is used to measure multipole moments Both the χc and χc2 are analyzed independently χc2 Poor fit without M2 (quadrupole) amplitudes E amplitudes are consistent with zero Example: angle between χcj decay γ and J/ψ decay lepton 0 September 27, 200

11 Quadrupole Amplitudes Precision greatly supersedes previous experimental results χ c γj/ψ Excellent agreement with leading order theory using mc =.5 GeV/c 2 κc = 0 (no anomalous charm quark magnetic moment) Agreement with recent lattice QCD calculations for Χc γj/ψ but not Χc2 γj/ψ (Dudek et al., PRD7, (2006) and PRD79, (2009)) Full numerical results available: PRD 80, 200 (2009) [CLEO Collaboration] ψ γχ c χ c2 γj/ψ ψ γχ c2 September 27, 200

12 Purely Electromagnetic Decays c S 0 D S γ h c P DD Threshold 2 χc(0,2) γγ 500 π + π c S 0 S J/ψ γγγ ,, September 27, 200

13 χcj(p) Two-Photon Widths Two-photon decays of χcj probe relativistic and radiative corrections likely to be significant in the charmonium system ψ γχcj; χcj γγ Γγγ(χc2) = 0.66 ± 0.07stat ± 0.04syst ± 0.05PDG kev Γγγ(χc0) = 2.6 ± 0.5stat ± 0.syst ± 0.9PDG kev Ratio = ± 0.050stat ± 0.08syst ± 0.0PDG CLEO Collaboration: PRD 78, 0950 (2008) n pqcd quark mass and wave function uncertainties cancel, making the ratio of widths R a key quantity -- at first order in αs: Γγγ(χc2) = 4( Ψ (0) 2 2 αem /mc 4 ) x [ -.70αS +...] R = = (4/5) [ - Γγγ(χc0) = 5( Ψ (0) 2 2 αem /mc 4.76αS +...] ) x [ αS +...] R. Barberi et al. Nucl. Phys. B 92, 26 (980) new world avg.: R = 0.22 ± 0.0 higher order corrections very significant prediction: αs = 0.2 R=0.2 September 27, 200

14 The only direct photon decay ever observed in nature is in the orthopositronium ( S) system J/ψ γγγ CLEO Collaboration PRL 0, 080 (2008) Kwong et al. (PRD 7, 20 (988)) predict a rate of order 0-5 Tag J/ψ in ππ transition from ψ and reconstruct γ decay -- greatly reduces backgrounds Kinematic fit used to separate signal from dominant background: γπ 0 π 0 (γfj) B(J/ψ γγγ) = (.2 ± 0. ± 0.2) 0 5 Agrees with leading order prediction, but second order correction takes rate negative! (Another test of higher order corrections?) 4 September 27, 200

15 J/ψ,ψ γ(η, η ) Measure: R n B(ψ(nS) γη) B(ψ(nS) γη ) Existing measurements of R consistent with expected mechanism and known η/η mixing R2 has only been limited, but expected to be equal to R J/ψ or ψ η or η Cut and count analysis in region of meson mass CLEO Collaboration PRD 79, 0(R) (2009) 5 September 27, 200

16 J/ψ,ψ γ(η, η ) Surprising Results: Why is ψ(2s) γη strongly suppressed? Reminiscent of the ρπ puzzle : B(ψ(2S) ρπ) B(J/ψ ρπ) 2%...somehow related? prediction from leptonic widths of J/ψ and ψ 6 CLEO Collaboration PRD 79, 0(R) (2009) September 27, 200

17 Radiative Decays of χcj D S γ c S 0 h c P DD Threshold 2 P χc γ S ρ,ω,ϕ c S 0 S Similar in structure to the often-cited glueball production channel: S γ P ,, 2 ++ J/ψ fj 7 September 27, 200

18 c c B ES preliminary!"#$$$% c B ES preliminary B ES preliminary Look for: ψ γ(low)χcj; χcj γ(high)(ρ,ω,φ) Events / ( 0.0 GeV/c2 ) Observation of χc γ(ρ,ω,φ) 0 25 BES Preliminary M Jȡ (Ge V/c2) 20 M J (Ge V/c2) Significant signals: χc γϕ, χc γρ, χc γω M JZ (G e V/c2) 5 T hese decays are important for evaluating theoretical techniques. C L E Oc pq CD Fc0 o J < 4.8 < Fc o J 27. ± 5.5stat < 26.6 Fc2 o J < 7.8 <. Fc0 o Jȡ0 < 9.5 < Fc o Jȡ0 24 ± 4stat 24 ± 9 ± 22 4 Fc2 o Jȡ0 < 9.7 < <.7 < Fc o JZ 7.5 ± 7.6stat 8 ± 5 ± 2.6 Fc2 o JZ < 5.8 < PRL 0, 580 (2008) B ES : O nly statistical er rors are shown A pqcd calculation, however, predicts rates that are over an order of magnitude lower for χc decays! (Gao,Zhang,Chao, Chin.Phys.Lett. 2, 276 (2006) [arxiv:hep-ph/ ]) M(a q) (GeV/c2) Fc o J observed for first time. p Q C D predictions u0 too low. Difference may be explained by non-shuwxuedwlyh 4&' ³ORRS FRUUHFWLRQV ' < &KHQ et al, ar X iv: v2[hep-ph].m(a l) (GeV/c ) Fc0 o JZ.4 H Events / ( GeV/c2 ) B ES H Events / ( 0.0 GeV/c2 ) B (0-6) C L E O c:60pr L 0, 580 (2008) p Q C D: Y.J. G ao et al., hep-ph/ M(a t) (GeV/c2) H September 27, 200

19 Light Hadrons cc annihilation provides a great laboratory to explore the light hadron spectrum J/ψ low background known initial state challenging multi-body decays a controlled environment to explore final state interactions? J/ψ Results light hadrons in J/ψ decays two-body interactions in D decays J/ψ X π π η ω 9 September 27, 200

20 J/ψ γη ππ Utilize large BES J/ψ sample to confirm X(85) observed at BES State confirmed! Apparent additional structures not consistent with phase space not visible in η sidebands J P unknown -- amplitude analysis is needed: likely + (f), 0 - (η), or 2 - (η2) Results of a Breit-Wigner fit (statistical errors only): ) Events/(0.02GeV/c BES Preliminary PS bkg. Known bkg M 2.2 (GeV/c ) State Mass (MeV/c 2 ) Γ (MeV/c 2 ) Est. Significance X(85) 88 ± 80 ± 9 huge X(220) 225 ± 6 0 ± 4 > 7.2 σ X(270) 27 ± 6 08 ± 5 > 6.7 σ 20 September 27, 200

21 J/ψ ωηππ Related channel: expect + (f), 0 - (η), or 2 - (η2) states BES Preliminary Clear signals for known f(285) and η(405) Additional state observed around 870 GeV/c 2 J P not known s X(870) the same as X(85)? Results of a Breit-Wigner fit (statistical errors only): State Mass (MeV/c 2 ) Γ (MeV/c 2 ) f(285) 285 ± 2 ± η(405) 400 ± 57 ± 8 X(870) 87 ± 82 ± 9 nitial results show great promise -- expect improvements with more statistics and more sophisticated analyses. 2 September 27, 200

22 D + K - π + π +...from e + e - ψ(770) DD Perform a fit to the Dalitz plot, including contributions from κ, K*(892), K0*(40), K2*(40), and K*(680) Asymmetry in K*(892) peak is a indicates interference with a scalar Kπ component CLEO Collaboration Phys. Rev. D 78, (2008) Additional =2 π + π + S wave is needed to achieve an adequate fit to the data sobar model description not sufficient for high precision analysis likely to be case for many future analyses is there a more model independent approach? 22 September 27, 200

23 D + K - π + π + Fit for amplitude and phase in bins of Kπ or ππ mass (quasi-model-independent PWA) [E79: PRD 7, 2004] Kπ S wave does not look like a Breit-Wigner resonance =2 ππ S wave consistent with ππ scattering data CLEO Collaboration Phys. Rev. D 78, (2008) Example: K - π + D wave K - π + S wave = 2 π + π + S wave 2 September 27, 200

24 Summary and Discussion Many opportunities for studying QCD using charmonium very high statistics and low backgrounds make almost any measurement possible have an idea for measurement? let us know! Some results seem to confirm expectations: e.g. radiative transitions between states, multipole amplitudes, and cc hyperfine splittings Some results are surprising: e.g. apparent suppression of ψ γη, enhancement of χc γ(ρ,ϕ,ω) Analysis of light hadron spectrum in multi-body charmonium decays shows extraordinary potential for exciting results need close collaboration with theory to develop analysis techniques: phenomenological systematic errors are likely to dominate clean charmonium environment can serve as a test bed for analysis techniques that can be extended to current and future dedicated light hadron experiments 24 September 27, 200