Submitted to Palermo Meeting June, 1975
Decay Properties of pir~ Systems Produced in Neutron Dissociation
at Fermi lab Energies
J. Biel*, E. J. Bleser1", D. Duke*, T. Ferbel*,
D. Freytag , B. Gobbil, L. Kenahf, J. RosenI, R. Ruchtil,
P. Slattery*, and D. Underwood*
We have examined the decay distributions of (pit") systems produced in the reaction n + p -> (pir~) + p for neutron momenta between
120 GeV/c and 300 GeV/c. Preliminary analysis.of decay moments indicates the
presence of large he!icity-flip amplitudes even for small (pir~)
mass values.and does not support the hypothesis that the helicity
non-flip (piT) states are produced peripherally in impact parameter.
These results are in approximate agreement with predictions of the
Deck mechanism. The experiment was performed at the M-3 neutral
beam of Fermi lab.
-NOTICEThb report was prepared as in account of work
sponsored by the United States Government. Neither
the rnited States nor the United States Energy
Reaezich and Development Administration, nor any of
their employees, nor any of their contractors,
subconiiactnn, at their employees, makes any
warranty, express or implied, or assumes any legal
lubjjily or responsibility for the accuracy, completeness
*.<r usefulness of any information, apparatus, product or
process diKlosrd, or represents tiut its use would nor
infringe privately owned riehts.
Research supported by the U. S. Energy and Research Development Administration
University of Rochester, Rochester, N.Y. 14627
+
Fermilab, Batavia, 111. 60510
*SLAC, Stanford, Calif. 94305
Northwestern Univ.s Evanston, 111. 60201
-2The origin of the observed correlation between the mass M of an
inelastic system produced in diffraction dissociation and the square
of the four-momentum transferred to that system (t) has been the object
of extensive investigation.
'
One model for understanding the t-M
interdependence in these highly peripheral reactions is based on the
assumption that s-channel heiicity amplitudes for small masses
(M < 1.3 GeV)
are dominantly helicity non-flip.K ' Consequently
one expects a steep differential cross section (DCS) for small t and
a dip or sharp break near -t ~ 0.2-0.3 if the helicity non-flip
system is produced peripherally (i.e., near an impact parameter
b - 1 Fermi)- The contributions from the helicity flip amplitudes
are hypothesized to become more important as the mass and spin of
the diffractively produced system increases, thus leading to a substantial broadening of the t-distributions with increasing M values. (2)
'
(3}
v
In a paper submitted to this conference
features of dissociation reaction
' we displayed the main
n + p -*• (pif) + p .
(1)
Here we address ourselves to the decay angular distributions of the
(pir~) system in order to study the properties of the dissociation
helicity amplitudes for H < 1.55 GeV.
It is expected that the spin
structure for these masses is sufficiently simple to allow an analysis
of the (pir~) system production amplitudes. Processes such as reaction
(1) have been discussed in the past in the frameworkvof a Deck-like
model. ' In this paper we will also compare our data with the Deckproduction model indicated in Fig. 1. The square of a simple Decktype matrix element can be written as
-3|H|2
=
(V/,
M
W
^
.u
where t, and t are four-momentum transfers squared;s
and s~ are squares
of the irp invariant masses as indicated in Fig. 1; u, and u« are re-
1
spectively the squares of the four-momentun transfered to the pion
2
|
*
from the incident neutron and target proton; o^ = 0.9 (t-j-u ) is the
|
pion Regge trajectory, and u is the pion mass. The ir~p elastic DCS
|
is taken proportional to exp(lOt). The decay moments of the (piT)
|
system were extracted by numerical integration of the above expression.
|
Figure 2 displays the normalized low-order moments <Yj«> versus t for
fixad
mass
in the Gottfried-Jackson (GJ) frame and in the helicity
|
|
frame. The data are in rough agreement with the trend of the Deck
I
calculation. A similar level of agreement is available for other
I
(DTT~)
mass values. In Fig. 3 we display the variation of the same <Y |M >
versus mass
at fixed t in the GJ frame. Again, the data only
f
\
roughly follow the Deck calculations. The moment ^ - i ^ in the helicity-
f
frame consists of interference terms proportional to an helicity non-
j
flip amplitude and a unit helicity-flip amplitude.
|
In terms of the
(2)
I
s-channel peripheral model discussed above/ ' one therefore expects
|
<Y-ji> in the helicity frame to pass through zero at the t value where
J
the dip in the DCS is observed. Similarly, one also expects a zero in
|
<Y,,> near -t - 0.6 where the single he!icity-flip amplitudes are pre-
|
I
dieted to have a zero. The observed absence of these predicted zeroes
|
1
in <Y,,> implies that the s-channel peripheral model cannot be the
f
dominant production process.
|
Finally, in Fig. 4 we display the (preliminary) results of an
<
amplitude
(in the GJ analysis
frame) for
of Mthe> data.
2. Therefore
Y. > are
spins
negligible
up to J for
= 5/2L >and
4 and
|
|1
-4-
helicity-flips ±1 saturate the moments. The M < 2 cutoff in <Y.M>
is a consequence of Pomeron exchange in the s« subchannel of Fig. 1.
However, amplitudes calculated from the Deck expression (2) do not
agree even with the signs of the results in Fig. 4. Thus we conclude
that the simple Deck mechanism also does not agree in ultimate detail
with our data.
The presence of S' and P states is inconsistent
with the Morrison rule. '
We thank E.L.Berger and G.Fox for helpful discussions.
-5-
References
1.
See, for example, the following:
J. Bartsch et al., Phys. Letters 27B_, 336 (1968); B. Y. Oh and
W. D. Walker, Phys. Letters 28B, 564 (1969); M. S. Farber et al.,
Phys. Rev. Letters 22., 1394 (1969); H. I. Miettinen and P. Pirila,
Phys. Letters 40B, 127 (1972); the review of J. Rushbrooke,
Peoc. Ill Intl. Colloquium on Multiparticle Dynamics, Zakopane
(1972), A. Bialas et al., eds; H. Lubatti and K. Moriyasu,
Lett. Nuovo Cimento 12., 97 (1975).
2.
See, for example, G. Kane, Acta Phys. Pol. B3_, 845 (1972), and
S. Humble, CERN Report Th. 1827 (1974).
3.
J. Biel et al., paper submitted to this conference.
4.
See the recent comprehensive review of E. L. Berger, ANL Report
ANL-HEP-PR-75-06 (1975).
5.
D.R.O.Morrison, Phys. Rev. J65_, 1699 (1968).
I
1
2a-
1
-6-
Figure Captions
1.
The simple ir-exchange Deck diagram for reaction (1), (Nucleon
exchange has not been considered in this report.)
2.
The average <Y.M(6,<}>)> moments as a function of |t| for the piT
mass interval 1.300 - 1.375 GeV. The solid curves are predictions of equation (2). The dashed curves correspond to
2(t-u 2 )
equation (2) but without the (-t, e
) factor in front
of the expression. The latter can be thought of as a Deck
model with additional absorption.
3.
The low order Y,M(8,4>) moments as a function of pir~ mass for
the |t| interval 0.08 to 0.12 GeV2. The solid curves are predictions of equation (2). The dashed curves correspond to
2(try2}
equation (2) but without the (-t, e
) factor in front
of the expression. The latter can be thought of as a Deck
model with additional absorption.
4.
Preliminary t-channel helicity amplitudes compared with Deck
model predictions.
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