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Review of E760/E835
Keith GollwitzerAntiproton Source Department
Accelerator DivisionFermi National Accelerator Laboratory
Project X 2nd Physics WorkshopJanuary 25, 2008
Charmonium Masses and Widths11
F i g u r e1 . 7 :Thecharmoniums pectrumbe l ow t h eopencharmt h r e s h o l dwitht h e1P1
l oc a t e da tt h es p i nwe i g ht e dave r a g eo ft h et r i p l e tP wave s t a t e s .Thick s o l i dl i n e s
d e n o t et h es t a t e swhich a r ed i r e c t l yp r oducedby e+e# a n n i h i l a t i o n ;s t a t e swhichwe r e
unseeno rneededt obe ve r i f i e dbe f o r et h i sexperiment a r er e p r e s e nt e dby t h i ckbroken
l i n e s .Theknown andexpe c t e dh a d r o n i cande l e c t r o m a g n e t i ct r a n s i t i o n sanddecay st h a tE760cand e t e c ta r es h own.
E760/E835 main purposes were to do precision measurements of the
Charmonium spectrum as well as the
discovery/confirmation of 1P1 and ηc
/
TechniqueThe 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 CernekovShower 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 Scans
PRECISION
PRECISION
PRECISION
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 In
terf
eren
ce n
ext
slid
e
Interference can be your friend
The continuum “amplifies” the resonance
E835 example in 4 photonspbarp c0 0 0 , , /
Should expand interference analyses to
more channels; in particular pbarp at 90o
in the center of mass system
Confirmations?
Searches?
Discoveries?
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 (e+e-) ()
Search for pbarp ηc/
PDGM = 3637 ± 4 MeVГ = 14 ± 7 MeV
Search using inclusive J/
c/ s
ear
ch f
or p
oss
ible
hin
dere
d M
1 tr
ansi
tion
to
J/
Max
imum
Acc
umul
ato
r E
nerg
y
Fav
orite
The
oris
t P
oint
of
the
mom
ent
The States
J PC
1 - -
2 + +
1 + +
? ? ?
/0 12
c c/hc
Other Physics Measurements
pbarp +
pbarp two neutral mesons
00 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
• 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