Laboratory for Nuclear Science, Massachusetts Institute of Technology, ... chambers comes from a bank of scintillation counters and lead-lucite sandwich.
SIX-m-1511 November 1.974 (T/E)
EXPERIMENTALUPPER LIMIT ON THE PHOTOPRODUCTION CROSSSECTION FOR THE 7443105)
J.F. Martin, C. Bolon, R.L. Lanza, D. Luckey, L.S. Osborne, and D.G. Roth Laboratory
for Nuclear Science, Massachusetts Institute Cambridge, Massachusetts O2l393C J.T.
Department
of Technology,
Dakin
of Physics and Astronomy, University Amherst, Massachusetts 01002+
of Massachusetts,
G.J. Feldman, G. Hanson D.E. Lyon, M.L. Perl, and T. Pun Stanford Linear Accelerator Center Stanford University, Stanford, California
94305*
ABSTRACT The experimental production
upper limit
for
the diffractive
of the $(3105) is 29 nb, with
photo-
9% confidence,
an average photon energy of 18.2 GeV. (Submitted
Work supported 'Work supported
to Phys. Rev. Letters)
by U.S. Atomic Energy Commission. by U.S. National
Science Foundation.
,,
at
-2-
Jr(3105)lJ2 and 9(369t$- particles
The newly discovered important
property
pro;ced
with
copiously
the p", cu, and Q vector
in e+e- annhilation.
how the photoproduction vector
meson photoproduction
that
the +(3105)
production
beam at the Stanford liquid
hydrogen or liquid
and any other
particles
superconducting the exiting reducing
tube
electron
Accelerator deuterium
through
for recording
shower counters
at the rear
at least
in a electron
pass through
an
chamber system.
the center
A
of the magnet shields
magnet, thus drastically
data from the proportional counters
is sensitive
duced in the target or a neutron.
a real
enter
i+eC+e-
by the incident
by the shower counters. scatters
sandwich requirement
the shower counters.
,
2 photon or a very low q virtual
The two electrons
generally
The trigger
chambers
to the reaction
y+N-+q+N, where y is either
and lead-lucite
of the apparatus.
one high energy electron
Hence the experiment
electron
The scattered
beam from the analyzing
comes from a bank of scintillation
identified
1, a 20.5 GeV electron
Center interacts
target.
smaller.
background.
The trigger
is that
is considerably
a 12,000 wire proportional passing
the
we are able to show
produced in the interaction
magnet into
analyzing
experiment,
experiment3 , Fig.
Linear
is
Using data from a just
cross section
In the electroproduction
question
for the IJ/'s compare with
cross sections.
completed hadron electroproduction
mesons -- they are
An interesting
cross sections
share an
electron
photon pro-
beam, and N is a proton
from the $ decay are detected In this
at a very small
reaction
and
the incident
angle and is not detected.
-3-
The data presented cident
here corresponds
and 3.6 x 10 13 electrons
on a 4 cm hydrogen target
a &>rn deuterium pairs
target.
as a function
to 4.2 x 10'3 electrons
The number of detected
of their
invariant
talizing
mass is shown in Fig.
mass of 3.090 f .045 GeV/c2.
and is produced with
positron.
The expected background
solid
of Fig.
lative
acceptance
for
1.
We calculate
carried
from this
the flux
the following
as well
former
to the latter
is about 5 to 1.
scalar
photons.
We assume that
cross section
steps:
photons
of real
in the target. We ignore
.
transverse
as the flux
the Jr is produced diffractively
photons
The ratio the flux
of the
of virtual
with
a differential
of the form
with b taken to be either in vector
4 (GeV/c)-'
= A e
-bp:
or 8 (GeV/c)-2,
the range en-
meson photoproduction.
We assume a decay angular
distribution
in the center
the 9 + e' -I- e- mode of the form 1 + cos 2 8. 4.
the re-
.i
kio(yN +$N)/dt
3.
2 indicates
of very low q2 virtual
bremsstrahlung
countered
as a
source is shown by the
on the photoproduction
we go through
along by the electrons,
cross section
R'
an average photon energy of 18 GeV.
produced by electron
2.
with being inclusive
The dashed curve on Fig.
To deduce an upper limit from these results
We
momentum squared of .O25 (GeV/c) 2 .
a transverse
2.
2.
it has the tan-
-ievents in which the 31 has been misidentified
electroproduction
on
It has an energy of 19.5 GeV
The events below 2.65 GeV/c2 are consistent
line
incident
electron-positron
only one event above a m&s of 2.65 GeV/c';
find
in-
We use a branching
ratio
of 0.06l
for $ + e+ + e-.
of mass for
-45.
We assume the cross section
The average relevant -
I spe&rum
photoproduction We can state
limit
of the photon energy.
photon energy is 18.2 GeV and the relevant
photon
extends from 14 to 20.5 GeV.
At an invariant
section
is independent
cross section with
the $(3105)
is less than 29 nb.
the photoproduction We see that
section
than that
photoproduction
A comparison
cross sections
given in Table I. is smaller
that
to a
7.5 nb for b = 4 (GeV/c)-2.
per nucleonof
9% confidence
per nucleon with
mass of 3105 MeV/c2, one event corresponds
of this
for vector
cross
upper
mesons4 is
the @(3105) photoproduction of the @ meson by at least
cross a factor
of
20. If we use a vector
dominance model for the photoproduction
the 4r(3105) we can set an upper limit the $ on a nucleon,
a(+N),
e/gv, -l-e e
[da(rN
of
-+VN)/dt] t=o
model the V couples
to the photon with
where e is the electric
charge and gG/k,
colliding
cross section
by using the relation
~2mo= 16a(g2/e2) In this
on the total
of
the coupling obtained
constant
from the
beam measurements 1,5 , is given in Table I.
We have
also used (1)
The upper limits quite that
on a(+N) are given in Table I.
dependent upon the value
assumed for b; nevertheless
a(jrN) is less than even the smallest
namely u(@N).
These limits
of the total
are
we observe
cross sections,
-5-
On the other -
hand the efe-
colliding
beam production
of the
jr(3105) may have nothing to do with vector meson dominance ideas. For example, one might speculate on a direct electron-electron-coupling. In that
llr(3105).
case one might expect some direct We find
an'upper
nucleon for
the direct
electrons.
In this
though there
limit
with
electroproduction
9% confidence
we have used steps 2, 3, and 4,
is no reason to assume step 2 in this
The branching
of the +(36~)
ratio
photoproduction
by the branching
ratio
into
e'e-,
into
al-
case.
e+e- is not yet known.
2, the 9% confidence
However, based on the data in Fig. on the diffractive
0.46 nb per
of the $(31@) by 20.5 GeV
electroproduction
calculation
of
of the
upper limit
of the q(3695) is 4.5 nb divided -2 . for b=4 (GeV/c)
REFERENCES 1.
J.-E.
Augustin
--et al.,
Phys. Rev. Letters; be published 2.
J.J.
G.S. Abrams --et al.,
MIT Laboratory
Aubert --et al.,
This apparatus for
earlier
(to be published
SLAC-PUB-1510 (1974)
in (to
in Phys. Rev. Letters).
COO-3069-271 (1974)
3.
SL4C-PUB-1504 (1974)
for Nuclear
(to be published
is an improved version
electroproduction
Science Report
in Phys. Rev. Letters). of the spectrometer
experiments.
See J.T.
used
Dakin -0 et al.,
Phys. Rev. D8, 687 (1973); Phys. Rev. DlO, 1401 (1974). 4.
J. Ballam -et al.,
5.
D. Benaksas -et al.,
Phys. Rev. 3, Phys. Letters
(1972); G. Cosme --et al.,
3150 (1973).
39B 289 (1972); --ibid,
Phys. Letters
48B, 155 (1974).
42B, 507
-6TABLE I.
Properties
cross section,
of the vector
do(yN -+VN)/dt
nan??e model coupling measurements "'; in the text.
mesons4 and i(3105)'
= A exp(-bltl);
constant
and the total
photoproduction
the vector +from e e
obtained cross section
For the 9 the cross sections
meson domicolliding
beam
a(VN) obtained
from Eq. 1
are 9% confidence
upper
limits.
Particle
(yN(;?)
Photon Energy (GeV)
b
n
(GeV/c)-2
0 P
9.3
13,500 I- 500
6.5 f 0.2
w
9.3
1,800 "r 300
6.6 : 1.1
18.4h.8
0
9.3
550 : 70
4.6 : 0.7
12:2fl.o
v(3105)
18.2
-=I29
4 (assumed)
13 r 4
~2.4
+(3105)
18.2
< 27
8 (assumed)
13 +J+
< 3.6
23 t 3
2.3 : 0.3
24f3 g"1
FIGURE CAPTIONS 1.
Schematic drawing
of apparatus.
Shaded region
A downstream gas Cherenkov counter acceptance 2.
Histogram
arbitrary
one eighth
field.
of the
is not shown. of e'e-
curve represents dashed line
covering
is magnetic
pair
than 1.5 GeV.
the expected background
indicates scale).
masses greater
the calculated
The solid
from nrfe- pairs.
relative
acceptance
The (to
TOP VIEW Superconducting
Tube -7
Magnet: 10.9 kG-m
SIDE VIEW Target: -Scintillation
LHz or LDz, 4cm- 1
Counters
e- Beam
*MWPC
(2mm
Spacing)
Shower Counters ( I5 r-0) t
0
I
lm
I
2m
-30
25 YN -
e+e-X
20
\
\ \
h
\
5 u I
0 1.5
2.0
2.5
3.0
M,e+e- ( GeV )
FIG. 2
,...
3.5
4.0 2622A2
