Review of E 760E 835 Keith Gollwitzer Antiproton

Review of E 760/E 835 Keith Gollwitzer Antiproton Source Department Accelerator Division Fermi National Accelerator Laboratory Project X 2 nd Physics Workshop January 25, 2008

Charmonium Masses and Widths E 760/E 835 main purposes were to do precision measurements of the Charmonium spectrum as well as the discovery/confirmation of 1 P and η / 1 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 Scan of ψ(2 S) Breit-Wigner line shape Convolution results in the observed cross section Beam Profiles Most precise measurement of the ψ(2 S) width despite much smaller statistics than e+e-

N O I S I C E PR 1 & 2 Scans N O I S I C E PR

0 Scan Could be more precise with more integrated luminosity Interference will be shown later

Two Photon Final States Takes work to understand the feeddown from multi-photon final states CCAL threshold of 5/20 Me. V pbarp 0 0 0 These data are from the c peak

The precision of the mass and width of the c needs to be improved E 760 & E 835 only reported pbarp Need to observe c in more channels

Interference next slide pbarp 0 & 2

Interference can be your friend The continuum “amplifies” the resonance E 835 example in 4 photons pbarp c 0 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 hc JPC = 1+- The hc mass is important to understanding hyperfine splitting. The hc width has not been measured pbarp hc c ( ) E 760: pbarp hc J/ 0 (e+e-) ( )

Search for pbarp ηc/ PDG M = 3637 ± 4 Me. V Г = 14 ± 7 Me. V

Maximum Accumulator Energy Favorite Theorist Point of the moment c/ search for possible hindered M 1 transition to J/ Search using inclusive J/

The States J PC -- 1 ++ 2 1 ++ ? ? ? c hc c/ 0 1 2 /

Other Physics Measurements

pbarp +

pbarp two neutral mesons 0 0 0

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 • E 760/E 835 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