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