Kärnfysikermötet, Umeå 1-2 November 2005 Agnes Lundborg, Uppsala Universitet

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1 Charmonium in e + e and pp Kärnfysikermötet, Umeå 1-2 November 2005 Agnes Lundborg, Uppsala Universitet

2 Raise a whole bunch of Questions Charmonium is a good tool for QCD studies: Why we want to understand QCD? Why is charmonium a good tool? How we understand charmonium presently? Why electron-positron? BES Radiative decays Preliminary results Why proton-antiproton? Charmonium hybrid search PANDA Relating cross sections to decay widths.

3 Why QCD? Self-interacting force carriers gluons - gives a nonabelian field theory. Theorists don t know how to deal with this. Can calculate AND measure perturbative. Can only measure nonperturbative through spectroscopy, formation and decay. We can find the right answer, we think we have the right equation - QCD - but we don t know the steps inbetween. We might encounter this kind of physics again

4 Why charmonium? mu md ms mc mb mt MeV c 4 8MeV c MeV c GeV c GeV c GeV c Very light, relativistic, most energy and mass comes from the strong force. Nonperturbative. Very difficult!! 2 Semirelativistic, halfperturbative Somewhat less difficult! Heavy and energetic, decays quickly through weak interactions Nonrelativistic. Already done but it only got us so far.

5 Charmonium spectrum like positronium Spectroscopic notation. Described by a Coulomb+linear confining potential In a Schrödinger equation. Spin-dependent perturbative Can calculate EM decays well using wavefunctions Strong using 3P0

6 Quarkonia Conventional states Quark model works well Baryon qqq Glueball gg Meson qq Hybrid qqg Explicit gluonic DOF Much discussed pentaquarks, molecules, fourquark states Gluonic excitations probes a new degree of freedom!

7 Why electron-positron? Easy initial state, definite energy. 1 = J ψ, Ψ' You pick an energy and where there s a resonance and you have a charmonium factory.

8 BES Linear accelerator, lab=cms system Barrel detector endcaps mainly for vetoing Modular: tracker, solenoid B-field, track calorimeter, muon chambers, TOF

9 World samples J ψ PWA many channels e e hadrons / e e Charmonium parameters, resonance scan ee ττ μ μ

10 Charmonium production decay An endstate can be produced through a resonance or non-resonant. Measure nonresonant background, estimate and simulate resonant. Radiative decay BR several %, source of glueballs, and lower charmonia. Radiative, K :0 1 X π + + X = 0,2 π, K :

11 J ψ γk + K, γπ + π [Earlier BES analysis] Resonances interfere. PWA from full fourvectors Global or bin-by-bin.

12 Ψ' γ K + K Signal f f 2 0 (1270) conventional (1710) glueball candidate f (2200) events above background PRELIMINARY Background ee e e ee hadrons, continuum ', ee ee + 0 π π 3π γφ γ K K K K π 0 Ψ' π π π Ψ 0 0 Ψ' Jψπ π mkk GeV c 2

13 Ψ ' γπ + π PRELIMINARY Signal f f f (1270) conventional (1710) glueball candidate f (2200) events above background Background ee e e ee ee (1370) asin J ψ hadrons, continuum I γρ γπ π Ψ' π π π + + Ψ' Jψπ π ππ 3π m ππ GeV c 2

14 Why proton-antiproton? J PC = 1 -- All (nonexotic) quantum numbers accessible in formation Energy resolution from beam not detector J = 0,2,.. C = CBall ev./2 MeV χ c1 CBall E E 835 ev./pb J = 1,.. C = MeV E CM

15 Gluon rich environment glueballs, hybrids o π, η J PC = 1 + cc H η χ π π 0 0 c c( ) s wave χ γ J ψ Lowest charmonium hybrid is predicted to be around 4.4 GeV. Exotic spin quantum numbers (production vs. formation). How can we detect this channel? J c ψ e e, μ μ + +

16 hypernuclei target and detectors target generator solenoid PANDA detector at FAIR muon counters TOF stop dipole EM and hadron calorimeters beam interaction point drift or wire chambers RICH Uppsala involved in EMC, Pellet target

17 Cross sections for associate charmonium production? p 0 0 pp cc + m m = π ηω ρ φπ + π,,,,,... Complicated QCD process Only theoretical guideline PCAC for only one channel J ψ p 0 π σ 0 ( ψπ ) 0.1 pp J nb at 3.5GeV offresonance Claudia Patrigniani E835 σ = 0.1 nb, BR = 4%, ε = 100% 70 events / day Annihilation background 7 10 / s

18 Use experimental data cc pp + m known amplitude A extrapolate A to pp cc + m [A.Lundborg, T.Barnes, U. Wiedner hep-ph/ , submitted to PRD.] π 0 p π 0 J/ψ A p A p We know this decay width and we want to know this cross section. p J/ψ It s a kinematical extrapolation, not very far..

19 Relating cross sections to decay widths Width proportional to Dalitz area Integrate here

20 Results Isoscalar η, η ' enhanced?

21 Constant amplitude?

22 Summary Charmonium spectroscopy, decay and production can probe QCD: semirelativistic, semiperturbative. ee Ψ' γ X γπ π, γk K Glueballs in e+e- at BES. Proton-antiproton can give all quantum numbers in formation beamwidth limits resolution, not detector Hybrids in the future experiment PANDA, EMC important. What rates? Relate decay widths to cross section indicates that production with could dominate. Resonances could change the result. η