The Fermilab E760/E835 experiments (JETFNAL)

Study of Charmonium Spectroscopy

in pp Annihilations

Ferrara, Genova, Torino,

Fermilab, UC Irvine, Northwestern, Penn State

The Charmonium System

The cc system is a powerfool tool for

the study of the strong interaction.

NR potential models + relativistic

corrections + PQCD allow prediction

of masses and widths to compare

with experiment.

All states can be formed directly in

pp annihilations. The resonance

parameters are determined from the

beam parameters and do not depend

on the detector energy and momentum

resolution.

Experimental Method

The accumulated beam of antiprotons

(up to 51011p) is decelerated from the

injection momentum of 8.9 GeV/c to the

formation energy of the resonance to be

studied. The beam momentum is then varied

in small steps ( 150 KeV/c)and a scan across

the resonance is made. The formation of

charmonium is detected through e+ e – X and final states.The

resonance parameters (MR, R, BinBout) are extracted from the

excitation curve using a maximum likelihood fit

4)(

4

)12(2

2

2

2

R

R

R

outin

BW

ME

BB

k

J

The E835 Detector

pppp

KKKKpp

multipp

ccpp

XeeXJccpp

eeccpp

/

4

1231

102

1051

beam

beam

p

p

scmL

E760/E835 Data Taking Runs

• E760 run I (june – september 1990)– J/, , c1, c2

• E760 run II (july 1991 – january 1992) Ldt = 16 pb-1.– J/, , c, c, c1, c2, hc.

• E835 run I (october 1996 – september 1997) Ldt = 143 pb-1.– J/, , c, c, c0, c1, c2, hc.

• E835 run II (january – november 2000) Ldt = 113 pb-1. , c0, c1, c2, hc.

The c(11S0)

pp c

2/)0.11.21.2984()( cMeVM c

MeVc )0.24.20()( 7.77.6

KeVc )8.3()( 9.11.10.10.1

J/(13S1) and (23S1)masses and widths

Mass (MeV/c2) Width (KeV)

J/ 3096.87 0.03 0.03 99 12 6

3686.0 0.1 (input) 306 36 16

The c0(13P0), c1(13P1), c2(13P2) masses and widths

0

Mass (MeV/c2) Width (MeV)

0 3415.4 0.4 0.2 9.8 1.0

1 3510.53 0.10 0.07 0.88 0.14

2 3556.15 0.11 0.07 1.98 0.18

The Singlet P Statehc(1P1)

E760 E835

pp hc(1P1) J/+0 e+e-+ pp hc(1P1) c+

2/3.08.3525)( cMeVhM c 2/3.02.3526)( cMeVhM c

c0,c2

c0 c2

(c0) = 2.6 0.5 keV (c2) = 0.49 0.05 keV

Proton Form Factors in theTimelike Region

The proton e.m. form factorscan be extracted from thecross section for the process: pp e+e-

Data at high Q2 are crucial to testthe QCD predictions for the asymptotic behavior of the form factors (dashed line in the figure).

E760 and E835 have carried outthe measurement at the highest Q2.

Q2 (GeV2)

Summary of E760/E835 Results

• First direct measurement of J/ and total width.

• Most precise measurement of cJ masses and widths (first and only measurement of c1 width).

• First observation of the singlet P state hc(1P1).

• Precise measurement of c mass and total width.

• Only direct measurement of two-photon decays of charmonium states.

• Highest Q2 measurement of the electromagnetic form factor of the proton in the timelike region.