Status of E835 (CHARMONIUM)  2/29/2000

Goals:     
	Experiment E835 is a continuation of the studies of charmonium
states formed in pbar-p collisions performed in E760. The complete list of
goals of the 1996-1997 run were:
    	a) a search for the etac' and determination of its mass and width;
   	b) a precision determination of the mass and total width of the
etac and of the product of the branching fractions B(etac->pbarp) x
B(etac-> gamma gamma);
    	c) the confirmation of the 1P1 signal and a more precise
determination of the resonance parameters;
    	d) the determination of the mass and total width of the chi0 and
of the products of the branching fractions B(chi0->pbar-p)xB(chi0->gamma
gamma) and of B(chi0->pbar-p)xB(chi0->J/psi+gamma);
   	 e) the search for the 3D2 and 1D2 charmonium states.
   	 f) a measurement of the angular distributions in radiative decays
of  the chi1 and chi2.
Other measurements, including more precise measurements on the timelike
form-factor of the proton and the angular distributions of psi and psi'
production, could also be derived from the data-set.
	To achieve these goals an integrated luminosity of about 200 pb-1
was required based on the experience in E760.

Status:
	The experiment ran till September 1997 and received about 150 pb-1 of 
data. (See www-e835.fnal.gov for all sorts of details). 
The experiment was approved for another run of 3.5 months of data. This run 
will start in early March. The goals of the new run are in order of priority 
- investigation of the 1P1, measurements of the chi_c0, and if time permits 
a refined search for the eta-c'.



Results:
 	E835 has new preliminary results (which are superior in precision
 to the E-760 results) on, among other things:
 	1) the eta-c parameters (width, mass, branching ratio to two photons)
 	2) the angular decay distributions of the chi-1 and chi-2,
 	3) the two photon branching ratio of the chi-2,  
	4) the proton form-factor in the time-like region, 
	5) angular distributions of J/psi and psi' decays and
        6) the observation of a phi-phi signal in the eta-c region.

The reaction pbar-p to chi-0 to j/psi + X has been observed for the first
time. The search for the eta-c-prime did not yield any obvious signal, and 
the attempt to confirm the 1P1 state was confused by issues of the beam energy
measurement.

   Ph.D. theses have been presented on:
The chi_c2 angular distributions by Marta Ambrogiani, 
The proton form-factor in the time-like region by Giulio Stancari,
Search for phi-phi decays by Wander Baldini - 
all from the University of Ferrara.
Two Photon Decays of Charmonium.. by Todd Pedlar of Northwestern University
Two Photon Decay Widths of Charmonium.. by Michelle Stancari of UC Irvine
The Angular Distribution of Electron-Positron Pairs from Exclusive Charmonium
decays..by Robert McTaggart of Pennsylvania State University.

   Published physics papers so far are:
Measurements of the Magnetic Form Factor of the Proton in the Timelike 
Region at large momentum transfer. Phys. Rev. D 32002,60,3 (1 Aug 1999)

Study of the chi_c0 (1^3p_0) state of Charmonium Formed in Antiproton-proton 
Annihilations. Phys. Rev. Letters 83, 15, Page 2902.  (11 Oct 1999)

 In preparation are papers on the 2 gamma width of the chi_c2 and chi_c0,
on the angular distribution of the chi_c2 and chi_c1 radiative decays and
on the decay branching ratios for the psi'.

 Plans:

 Next Run:
	As mentioned, E835 has been approved to run again to resolve the 
issue with the 1P1 and to improve the measurements on the chi_c0.    
	The detector has been reinstalled as part of the antiproton 
accumulator as of jan 2000. The list of improvements to the apparatus 
discussed last year has been carried out.

1) The gas jet nozzle has been reconfigured to provide the optimal
temperature distribution along the inlet line, allowing the jet to operate
stably within 1 degree K of the gas-liquid transition where the cluster
density is high.
2) The scintillation counters and the straw chambers have been completely 
refurbished in Torino and reinstalled.
3) The new scintillating fiber tracker (500 channels) has been built and 
incorporated into the inner tracking volume. The VLPC cryogenic system has 
been recommissioned.
4) Mechanical modifications to maintain the correct geometry of the
Cerenkov counter mirrors have been successfully implemented.
5) The forward calorimeter counters were all calibrated in the recent test
beam run and the calorimeter has been reinstalled.
6) The Data Acquisition system has been upgraded with more powerful front-end
processing and faster tape-writing capability.
7) Perhaps most importantly, the antiproton source department has developed
a comprehensive set of deceleration ramps which move the transition energy 
as the beam is decelerated such that the beam does not have to cross 
transition. The beam can now be decelerated with well over 90% efficiency 
from injection energy to below the chi_c0. 

The experiment was recently given a two week commissioning run. This run
has proved invaluable in debugging the apparatus and very impressive
in the way the antiproton source was able to decelerate the beam and set
its energy. A scan of the psi' was performed to calibrate the accumulator
energy setting and further scans of the chi_c2 and chi_c1 showed that this
calibration was reproducible. 

The antiproton source is presently installing the stochastic cooling upgrades
for the debuncher and the experiment expects to start running in early
March.