Review of E760/E835

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Review of E760/E835

• Keith Gollwitzer
• Antiproton Source Department
• Accelerator Division
• Fermi National Accelerator Laboratory
• Project X 2nd Physics Workshop
• January 25, 2008

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Charmonium Masses and Widths
E760/E835 main purposes were to do precision
measurements of the Charmonium spectrum as well
as the discovery/confirmation of 1P1 and ?c/
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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

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Precision Measurements
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Clean electron/positron Signals
?/ ? J/? X ? ee- X
?/ ? ee-
Threshold Cernekov Shower shape
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1-- State Scans (1990-1)
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Beam Scan of ?(2S)
Breit-Wigner line shape
Convolution results in the observed cross section
Beam Profiles
Most precise measurement of the ?(2S) width
despite much smaller statistics than ee-
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?1 ?2 Scans
PRECISION
PRECISION
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?0 Scan
Could be more precise with more integrated
luminosity Interference will be shown later
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Two Photon Final States Takes work to
understand the feed-down from multi-photon final
states CCAL threshold of 5/20MeV
pbarp ? ?0 ?0 ?0 ? ? ?
These data are from the ?c peak
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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
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pbarp ? ?0 ?2 ? ??
Interference next slide
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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 90o in the center of
mass system
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Confirmations?Searches? Discoveries?
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1P1 or hc JPC 1- The hc mass is important to
understanding hyperfine splitting. The hc width
has not been measured
pbarp ? hc ? ? ?c ? ? (??)
E760 pbarp ? hc ? J/? ?0 ? (ee-) (??)
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Search for pbarp ? ?c/ ? ??
PDG M 3637 4 MeV ? 14 7 MeV
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Search using inclusive J/?
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The States
J PC 1 - - 2 1 ? ? ?
?c
?c/
hc
?
?/
?0
?1
?2
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Other Physics Measurements
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pbarp ? ?? ??
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pbarp ? two neutral mesons
?0?0
?0?
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Scaling Rule?
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pbarp ? two neutral particles
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Proton Magnetic Form Factor
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pbarp ? 6?
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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