Review of E760/E835 Keith Gollwitzer Antiproton Source Department Accelerator Division Fermi National Accelerator Laboratory Project X 2 nd Physics Workshop January 25, 2008
Charmonium Masses and Widths E760/E835 main purposes were to do precision measurements of the Charmonium spectrum as well as the discovery/confirmation of 1 P 1 and η c /
Technique The Accumulator is the Spectrometer Annihilation of pbar p to form each state All quantum numbers can be formed Detector is a big scalar Scan beam energy to map out resonance
Precision Measurements
“Clean” electron/positron Signals / J/ X e + e - X / e + e - Threshold Cernekov Shower shape
1 -- State Scans (1990-1)
Beam Profiles Breit-Wigner line shape Beam Scan of ψ(2S) Convolution results in the observed cross section Most precise measurement of the ψ(2S) width despite much smaller statistics than e + e -
1 & 2 ScansPRECISION PRECISION
0 Scan Could be more precise with more integrated luminosity Interference will be shown later
pbarp 0 0 0 Two Photon Final States Takes work to understand the feed- down from multi-photon final states CCAL threshold of 5/20MeV These data are from the c peak
The precision of the mass and width of the c needs to be improved E760 & E835 only reported pbarp Need to observe c in more channels
pbarp 0 & 2 Interference next slide
Interference can be your friend The continuum “amplifies” the resonance E835 example in 4 photons pbarp c0 0 0, , / Should expand interference analyses to more channels; in particular pbarp at 90 o in the center of mass system
Confirmations? Searches? Discoveries?
1 P 1 or h c J PC = The h c mass is important to understanding hyperfine splitting. The h c width has not been measured pbarp h c c ( ) E760: pbarp h c J/ 0 (e + e - ) ( )
Search for pbarp η c / PDG M = 3637 ± 4 MeV Г = 14 ± 7 MeV
Search using inclusive J/ c / search for possible hindered M1 transition to J/ Maximum Accumulator Energy Favorite Theorist Point of the moment
The States J PC ? ? ? // 00 11 22 cc c/c/ hchc
Other Physics Measurements
pbarp +
pbarp two neutral mesons 0000 00
Scaling Rule?
pbarp two neutral particles
Proton Magnetic Form Factor
pbarp 6
Summary Direct formation of any Charmonium state (of any quantum numbers) is a unique advantage to making precision measurements of the mass and width E760/E835 utilized “clean” J/ inclusive and two photon final states to “count” the number of events at each beam energy setting against the very large hadronic interaction background It is hard to discover narrow states scanning a large energy range –Precision measurements possible once mass is nearly known Like ILC precision measurements will be possible once hadron machine(s) make discoveries