The Fermilab E760/E835 experiments (JETFNAL) Study of Charmonium Spectroscopy in pp Annihilations Ferrara, Genova, Torino, Fermilab, UC Irvine, Northwestern, Penn State
The Charmonium System The cc system is a powerfool tool for the study of the strong interaction. NR potential models + relativistic corrections + PQCD allow prediction of masses and widths to compare with experiment. All states can be formed directly in pp annihilations. The resonance parameters are determined from the beam parameters and do not depend on the detector energy and momentum resolution.
Experimental Method The accumulated beam of antiprotons (up to 51011p) is decelerated from the injection momentum of 8.9 GeV/c to the formation energy of the resonance to be studied. The beam momentum is then varied in small steps ( 150 KeV/c)and a scan across the resonance is made. The formation of charmonium is detected through e+ e – X and final states.The resonance parameters (MR, R, BinBout) are extracted from the excitation curve using a maximum likelihood fit
The E835 Detector
E760/E835 Data Taking Runs E760 run I (june – september 1990) J/, , c1, c2 E760 run II (july 1991 – january 1992) Ldt = 16 pb-1. J/, , c, c, c1, c2, hc. E835 run I (october 1996 – september 1997) Ldt = 143 pb-1. J/, , c, c, c0, c1, c2, hc. E835 run II (january – november 2000) Ldt = 113 pb-1. , c0, c1, c2, hc.
The c(11S0) pp c
J/(13S1) and (23S1) masses and widths Mass (MeV/c2) Width (KeV) J/ 3096.87 0.03 0.03 99 12 6 3686.0 0.1 (input) 306 36 16
The c0(13P0), c1(13P1), c2(13P2) masses and widths 0 Mass (MeV/c2) Width (MeV) 0 3415.4 0.4 0.2 9.8 1.0 1 3510.53 0.10 0.07 0.88 0.14 2 3556.15 0.11 0.07 1.98 0.18
The Singlet P State hc(1P1) pp hc(1P1) J/+0 e+e-+ pp hc(1P1) c+
c0,c2 (c0) = 2.6 0.5 keV (c2) = 0.49 0.05 keV c0
Proton Form Factors in the Timelike Region The proton e.m. form factors can be extracted from the cross section for the process: pp e+e- Data at high Q2 are crucial to test the QCD predictions for the asymptotic behavior of the form factors (dashed line in the figure). E760 and E835 have carried out the measurement at the highest Q2. Q2 (GeV2)
Summary of E760/E835 Results First direct measurement of J/ and total width. Most precise measurement of cJ masses and widths (first and only measurement of c1 width). First observation of the singlet P state hc(1P1). Precise measurement of c mass and total width. Only direct measurement of two-photon decays of charmonium states. Highest Q2 measurement of the electromagnetic form factor of the proton in the timelike region.