SLAC-PUB-625
(TH) and (mP)
July 1969
yp INTERACTIONSAT 5.25 GeV*
J. Ballam,
G. B. Chadwick,
Z, G. T. Guiragossi&,
A. Levy+
M. Menke, P. Seyboth tt , and G. Wolf ttt
Stanford
Stanford
Linear
Accelerator
Center
Stanford,
California
University,
ABSTRACT
Photoproduction
tion
radiation
Results
using positron
annihila-
on the nonstrange
particle
events and related
to the
Dominance Model.
The present
study represents
nucleon hadronic
interactions
been reported2'
a search for resonance production
using the SIX! monochromatic
beam1 in the SL,ACho-inch
already
using
has been studied
at 5.25 GeV in the SLAC!&O-inch hydrogen bubble chamber.,
are presented
Vector
tion
of resonances
HBC at 5.25 GeV.
' at this
energy and at 7.5 GeV.
the beam at 4.3 GeV has also been presented.
possible,
these results
Bremsstrahlung
streamer
4
results
A similar
Where comparison
agreement with
the CEA5 and DESY6 bubble
annihilation
experiments
radiahave
study
is
done in
chambers and the SLAC
chamber 7 .
Work supported
t Present
are in substantial
beams with
Preliminary
in phdton-
address,
by the U. S. Atomic Energy Commission.
Physics Department,
itOn leave from Max-Planck
Institute,
Tel Aviv University,
Munich,
Germany.
tttOn leave from DESY, Hamburg, Germany.
-l(Submitted
to Phys. Rev.Le-tters)
Tel Aviv,
Israel,
are based on about 260,000 pictures
The results
60 photons above 4 GeV per picture.
scanning
efficiency
elsewhere. 2r3
+ 105%, we have obtained
lowing
that
of which 3%
method are given
photon energy is known to
;vp + pfi+fl+n-n-
(4)
(2)
f-i---O
-+p7tEnflfl
+nfi+fi+rl-
(3)
--,nfln3-ccJ171
for
volume,
these reactions
and using a pair
reflections
fits
particle
The resulting
Reaction
p -tpn+fi-
The fi'x'
mass spectrum for
curve is a fit
were determined
production
was detected,
in other
pairs
cross section
combinations
cross sections
this
by counting
within
and
the event fidu-
of lg.8 mb.
6 Where
were made using a least
are swnmarized in Table I.
reaction
to the Ross-StodolsQ8
is shown in Fig.
l(a),
where the
form of the p" resonance,
as described
form for the spectrum is indistinguishable
and gives the same pop cross section
give nearly
(6)
to phase space plus resonances and
phase space and n++(l236) resonance reflection
using the &ding'
(5)
+++--
17,000 positron-electron
a sample of
squares method.
with
since the annihilation
(1)
resonance production
solid
of the analysis
- 0
-+pn+Jt fi
measuring
(1)
was double scanned at an overall
reactions:
Cross sections
their
of
at high energy a clean sample of events for the fol-
p +pfi+n-
cial
Details
photons.
We stress
an average flux
than 96%, and 10,000 events measured,
greater
are due to annihilation
The film
with
to within
along
below.
in spectral
5% (see Table I).
the same mean resonance mass of 764 2 3 MeV and width
A fit
shape
Both fits
of 136 + 8
MeV.
Figure
l(b)
displays
the squared momentum transfer
-2-
(t)
distribution
to
the proton
for the events
in the p band, normalized
HBC work, 4,5,6
near t = 0 has been seen in previous
ments".
We have observed that
the effect
is mainly
Therefore
we assume a purely
g
l(c)
due to a bias against
exponential
shows evidence
given in Table I.
agreement with
and a missing
for
decrease
but not in counter
of photon flux
experi-
and believe
seeing low energy recoil
protons.
form and find
the process
This value
those of Boyarski
--et al
ns + n-A*
with
and the t distribution
the cross
are in excellent
11 who used a single
arm spectrometer
mass technique.
The presence
of f and go are not required
the spectrum of Fig.
limit
is a function
The
(W -+PP') = (136 _+14 pb GeVB2) exp (7.14 + 0.4 G~v-~) t
Figure
section
it
to a(pp).
l(a),
although
for go (1650) production
to make an acceptable
up to 3% f(126O) is allowed.
is 1%.
When previously
fit
to
The upper
RBC data 4,5,6
published
= 3.5 and 5.8 GeV are combined with those of Fig. l(a),
the upper
Y
for go production remains about lsO If the g-meson is a Regge recur-
between E
limit
rence of the p it might be expected
scattering
process
to be produced by a diffractive
in a manner analogous
to the reaction
which occurs with
about 3% of the intensity
the same fraction
of go to p" would result.
Using the Vector
tions,
p" photoproduction
the coupling
do/dt
mb.
(s
These values
the p"- p elastic
cross section
constant,
+p"p)
pp -+p N* (1688)
of the elastic
scattering
Dominance Model l3 (VDM) and neglecting
one can calculate
implies
7:/&r,
that
and total
0el(pop)
cross sections
, and
using the
constant.
If
14,15,16 our measured value of
= 5.3 * .5 mb and otot(~'p)
are close to the mean of fl'p scattering
-3-
Id
u) and cp contribu-
at t = 0 and the y-p coupling
is taken to be 0.5
p meson
= 27.521.7
cross sections
(5,6 & 1 mb and 28 k
mb respe tively)
F
Using yE/ien = 1.1 rt .l 17~8 these values
required
0.5
by the simple
quark model.
become 7.7 _+ .8 and 40 + 4 mb re-
spectively.
(2)
Reaction
Figure
m + prr"n-no
l(d)
displays
the rlt.fi[-flo invariant
and shows cup production.
indicating
GeF,
The experimental
the mass resolution
the momentum transfer
$f
The ratio
(yp
+ pu)
of p" to w forward
Upper limits
absence is not unexpected
to q
cross sections
In the t region
and g
+ 1.4
is therefore
is apparent
production
GeVe2)t.
9 5 3.5.
in the n'n-fl"
are shown in Table I.
resonance
and neither
0.05 - 0.6
the form
for resonances
as neither
exchange because of isospin,
fits
reaction
of the LUpeak is + 15 MeV,
pb GeVm2) exp (8.2
+ 5
Other than cu, no evidence
spectrum.
width
of the experiment.
distribution
= (15
mass spectrum for this
mass
Their
can be produced under VDM by no
may be diffractively
produced because
of spin and C parity.
Evidence
this
channel.
agreement with
of p and of n production,
The upper limit
Ref.
for p-A++
as indicated
associated
(6) but not with Ref. (4).
in Table I, are found in
production
Assuming that
proceeds via the one pion exchange mechanism (OPE), with
mined in firp interactions
(3)
Reaction
19 , we find
-+ fir)
< 0.2
this
reaction
form factors
deter-
MeV.
9 + nfl+7c+n(-
This channel
is interesting
by OPE under the VDM assumption,
up to several
I'(p
is 0.5 pb, in
microbarns
in that
production
of f$ and A2f may proceed
for which photoproduction
have been predicted.
-L-
20
cross sections
No such relatively
strong
of
is seen, as is demonstrated
signal
A: production
is compatible
the cross section
expected
of Wolf 19 .
culations
with
for
by Fig.
2(a),
although
the presence of some
the data (see Table I).
the process pop +A:
We have calculated
using the OPE model cal-
The p" is taken to have zero mass and the VDM relation
c&y
+nA~,
= % 2Pll
a(pOp -+rl.$)
yP
is used, where p
is the usual
11
decay, a is the fine
PO- 7c- scattering
structure
spin density
entering
U(P'TC+ -+A -+p'~r+)
element for the p" from A+
and yp2/47r = 0.5.
constant
cross section
matrix
into
The on-mass-shell
the OPE formula
was put equal to
nH2
= 2.5
(m2-
mA = 1.32 GeV and PA = 0.03 GeV,assuming A2H production.
with
shell
corrections
value
of pll
particle
used the same r.m.s.
was taken to be 0.5,
decaying
into
0.3 pb, consistent
Following
pa.
with
radius
its
The resulting
= 0.5.
smaller
a similar
However, for
procedure
against
of q
the resonance
cross section
for the 5
for a 2'
is calculated
to be
production
meson (PA = 0.08 GeV, MA = 1.07
scattering,
the decay of a If
owing to a predominantly
non-observation
as expected
The
the data.
GeV), and assuming s wave pfi resonant
pll
the f-meson 19 .
as found for
maximum value,
The off-mass-
longitudinal
state
we find
into
pll
p" polarization
may not necessarily
interpretation
px,
oAl = 1.1 ub for
of the effect,
may be much
21 .
Hence the
be taken as evidence
contrary
to the suggestion
of Poe -et a12' .
(4)
Reaction
yp +prr+~+fi-rr-
This channel
indicates
p" production,
shaded events are in association
with
-5-
as shown in Fig.
the strong
n*
signal
2(b) where the
in the psrf system.
In addition,
Fig.
(unshaded)
and for
when associated
21(c)
those combinations
with
distribution
where the other
A three
the proton.
mass 1.32 GeV is apparent,
transfer
the sc+rl-~(- spectrum for
presents
and is mainly
show a fit
combinations
-His in the A region
-I-
deviation
associated
for events
to the A*
about 8% of events having
peripheral,
standard
fi
all
with
enhancement at
A++.
The momentum
in the enhancement region
t < 0.5.
The solid
curves in Fig.
for
"A2H."
The A2H may be produced under VDM by OPE, in a manner similar
discussed
(3).
under reaction
u (yp"A++
nearly
A;H)
it
cluded statistically,
A2L might be attributed
Although
is interesting
for a l-
to speculate
normal parity
of this
we find
that
leads to
that
ob-
leads to
is not actually
ex-
the suppression
of
p meson coupling.
assignment
enhancement,
with
spin parity
A2L production
again to a longitudinal
= 2' or other
Independent
value.
to that
of the OPE cross section
of the cross section
the same predicted
P
A calculation
N 0.4 pb, somewhat lower than but consistent
A calculation
case a J
2(c)
to phase space plus resonance with M = 1.32 GeV and I' = 0.03 GeV,
the parameters
served.
is
In suchja
to A2L would not be favored.
a contribution
from the reaction
yp 3 A++pOTT
which accounts
for 3% of reaction
A++z- or Affp"
spectra
(5)
- 0
fl -+pTC+~+~-fl 71
A strong
A*
2(d),
as well
However, no structure
is found in the
for these events.
Reaction
Pfi" system,
(4).
signal,
similar
to that
as cu" production
Most of the w" production
for B or g meson production
found in reaction
in the flffi-flo
is in association
mass spectrum shown in Fig.
with
the A*.
is found in the w"flc' combinations,
-6-
(4) is seen in the
No evidence
We wish to thank the SLAC Bubble Chamber operations
RAD personnel
P. Klein
ment.
for their
work during
the exposure,
Mr. A. Kilert
and T, H. Tan for much help in the preliminary
Miss M. Tartar
conscientious
efforts.
We are pleased
and Drs.
stages of the experi-
and our scanners and measurers deserve praise
F. Gilman for helpful
1.
fine
crew and the SLAC-
for their
to acknowledge Drs. Y. Eisenberg
and
discussions.
J. Ballam et al.,
SLAC-PUB 530, to be published
in Nuclear
Instruments
and Methods.
Phys. Rev. Letters
2.
J. Ballam -et sl.,
3.
Lot.
--
4.
Y. Eisenberg
5.
Cambridge Bubble Chamber Collaboration,
cit.,
g,
23, 1541 (1968).
1544 (1968).
et al.,
Phys. Rev. Letters
22, 669 (1969).
Phys. Rev. 146, 994 (1966); 155,
1468 (1967); 163, 1510 (1967); 169, 1081 (1968).
6.
Aachen-Berlin-Bonn-Hamburg-Heidelberg-Mtichen
D,
1669 (1968); Phys. Letters
7.
M. Davier
8.
M. ROSS and L. Stodolsky,
9.
P. Soding,
10.
et al.,
G. McClellan
et al..,
Phys. Rev. Letters
Phys. Letters
et al.,
A. Boyarsky et al.,
12.
The data are well
Theoretical
21, 841 (1968).
1172 (1966).
Phys. Rev. 9,
lg,
702 (1966), and private
g,
communications.
374 (1969); H. Blechschmidt
1348 (1967).
Phys. Rev, Letters
22, 148 (1969).
summarized by K. Fujimara,
Physics,
Phys. Rev.
54 (1968).
Phys. Rev. Letters
Nuovo Cimento s,
11.
G,
Collaboration,
-41 and 42, 282 (1967).
-7-
Suppl.
to Progress
of
13.
L. Stodolsky,
will
Phys. Rev. Letters
l8,
135 (1967); more recent
references
be found in Ref. 15.
14.
J. E. Augustin
15.
J. G. Asbury et al.,
Procedings
et al.,
Phys. Letters
28~, 503 (1969).
Phys. Rev. Letters
l.9, 865 (1967); S.C.C. Ting in
Physics,
of the Fourteenth International
Conference --on High Energy
-7
,
Vienna, Austria,
September, 1968 (CEFUVScientific
Information
Service,
Geneva, Switzerland,
16.
J. Ballam et al.,
17.
G. McClellan
18.
F. Bulos et al.,
19.
G. Wolf,
SLAC-PUB 618 (to be published).
et al,,
Phys. Rev. Letters
Phys. Rev. Letters
to be published
Argonne Conference
1968).
z,
in the Physical
on nfl and Kfi scattering
22, 377 (1969).
490 (1969).
Review, and presented
(1969).
20.
R. T. Poe et al.,
Phys. Rev. Letters
;12, 551 (1969).
21.
J. Ballam et al.,
Phys. Rev. Letters
2l,
H. Harari,
Phys. Rev. Letters
l8,
O-968).
-8-
to the
934 (1968); F. Gilman and
l.l.50 (1967) and Phys. Rev. 3,
1803'
22.4&l.
0
O(b)
0.3 zko.3
2.8 *l.O
A0
P+
A%
< 0.4
< 0.4
w -n37r+27r-
(4 'Corrected
(b) Corrected
for neutral
for forward
decay modes.
loss in scanning (see text).
4
A++WO
B-4 c!fn
g-+ 4fl
< means 90% C. L.
4.7io.
0.0 zto.5
A”p+
AP
PO
0.4 *to.4
A+p”
4
cd0
< 0.5
A++p-
10.3ztO.6
A++Ai
bi*po
go-+ 4n
A++
0.7 *0.6
PO
yp-pnt?r+n-T-Y+
Ai
1.7 *to.5
A+
A
PO
2.3 ho.7
.
P-
Az
A*
A+1
PO
A-
2.5 kO.8
6.4hO.5
10.2-10.6
A++
rp -p7r+7r+7nr-
++7r lr
Resonances
2.0 *o. 5(b)k
< 0.1
go+ 27(
yp-nn
Reaction
CROSS SECTIONS AT 5.25 GeV
cd0
< 0.5
1.7 zko.4
A++
fO-+ 2x
18.5 &O. 6(b)
u(pb) (4
PRODUCTION
p”
Resonances
AND RESONANCE
I
(a)Single resonance cross section included associated resonance production,
yp-p*+n-no18.4&l.
w--p7r+n-
Reaction
REACTION
TABLE
<0.4
<2.0
-2.8
+ .8
g2* 5-2.5
0.5rtO.2
1.5rto.4
< 1.0
3.9il.5
1.30.6
0.7zko.3
cl.4
1.2zkO.4
2.7&O. 8
3.3hO.8
0.4 + .2
co.1
0.8 + 0.4
Cl.0
d-4
Y
FIGURE: CAPTIONS
1.
a)
Invariant
best fit
mass spectrum of dipions
to the Ross-Stodolsky
space and n+"(u36)
b)
Differential
cross section
n'p invariant
production
The curve is the
form for p" production
four momentum transfer
using the fit
form described
values
plus phase
in (a).
squared from
The fitted
in the text.
mass spectrum for reaction
~++(1236), p" reflection
tifti-flo
versus
(l),
curve is the exponential
d)
resonance
(1).
reflection.
photon to p" for reaction
4
in reaction
(1) with
the best fit
curve
and phase space.
mass spectrum for
reaction
(2) with
and phase space plus reflections
the fit
curve for m"
of A and p in the amounts
shown in Table I.
2.
a)
space distribution
b)
normalized
to all
x'fl[- mass spectrum for reaction
per event)
flection
with
the best fit
fractions
association
with
~~(1236)
those opposite
events.
(4) for all
production
(four
combinations
shaded.
shows zCfxC-masses in
(two combinations
combinations
events of reaction
~~(1236)
events
The shaded histogram
two ~~(1236)
n+z-7~- masses for all
The curve is a pure phase
for the p" , phase space and the resonance re-
of Table I.
number of events with
4
(3).
nfx+fir- mass spectrum for reaction
per event).
The
is negligible,
(4) shown unshaded, with
The curves are for the fits
described
in
the text.
d)
tions
xlffl-xo mass distribution
for
are shown unshaded, while
~~(1236)
region
reaction
those recoiling
are shown shaded.
the resonance fractions
(5).
All
four possible
opposite
a pfl" pair
The curve again represents
shown in Table I.
- 10 -
combinain the
the fit
with
YP -p
0
U-J
;
I-
7T+ 7l-
(a)
60
$j 40
w
20
n
P
I I I 1 I I 1 1’ I’iIti-’ ’ ’ _m-,-p--’
1.0
M,+
0.5
1.5
r-
2.0
(GeV)
L3-l
(c)
0.4
0.6
ItI
(GeV2)
483
0.8
1.0
WEA
EVENTS
3
20 -
2
\
3;
lz
W
2
30
0.2
2
2
g
0
2.5
7T+ 7TYP -p
538 EVENTS
30 >W
0.1 ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ‘\r ’ ’
20
c
LLJ
=
IO-
0 IO‘“I ’ ’ ’1.5
’ ’ ” L2.0’ I I * 2.5c ’
..Mpr+
(GeV)
IO
u
3.0
0.5
1376~3
Fig. 1
1.0
1.5
M =+ r-,p
2.0
(GeV)
2.5
1376A4
p7T+ 7T+7T- 7T156 EVENTS
YPyp--nr+r+r-
(b)
50
266 EVENTS
> 4o
2
5: 30
P
= 20
z
IO
3.5
1.0 1.5 2.0
T+
1376/\S
M TT+,-(GeV)
YP -
30
r (Cl
0
0.5
p7r+7T+7T--7T156 EVENTS
n
1.0
I.5
2.0
M Tr+T- (GeV)
,yp-p71-+7T”7T-7r-TT”
Cd)
252 EVENTS
80
n
omb)
0
0.5
1.0 1.5 2.0
MTr+T-TT- (GeV) o-7
0
Fig. 2
0.5
1.0
1.5
2.0