- Email: [email protected]
c
-~
Nuclear Physics B21 (1970) 505-514. North-Holland Publishing Company
INELASTIC PN INTERACTIONS AT 3.7 GeV/c* H. O. C O H N Oak Ridge National Laboratory, Oak Ridge, Tennessee R. D. M c C U L L O C H Central Data Processing Facility, Union Carbide Nuclear Division, Oak Ridge, Tennessee W. M. BUGG a n d G. T . CONDO University of Tennessee, Knoxville, Tennessee and Oak Ridge National Laboratory, Oak Ridge, Tennessee Received 9 F e b r u a r y 1970 (Revised manuscript received 26 May 1970)
Abstract: Cross sections for N*(1238} production arising from various inelastic r e actions of 3.7 GeV/e protons with deuterons are presented. We find that N* production in the reaction pn --* pnrr+rr- is considerably s m a l l e r than in the pp and ~p analogue reactions. An upper limit of 350/zb is found for the N*(1400) production c r o s s section.
1. I N T R O D U C T I O N A l t h o u g h i n e l a s t i c pp a n d pp i n t e r a c t i o n s h a v e b e e n e x t e n s i v e l y i n v e s t i g a t e d , v e r y l i t t l e e x p e r i m e n t a l i n f o r m a t i o n i s a v a i l a b l e on p r o t o n - n e u t r o n i n t e r a c t i o n s i n the GeV r a n g e . I n p a r t i c u l a r , w h i l e the high e n e r g y p n t o t a l a n d e l a s t i c c r o s s s e c t i o n s h a v e b e e n a c c u r a t e l y d e t e r m i n e d , t h e d a t a on r e s o n a n c e f o r m a t i o n f r o m pn i n t e r a c t i o n s are somewhat m e a g r e . In the p r e s e n t n o t e we p r e s e n t o u r r e s u l t s f o r the r e a c t i o n s :
(A) p + n - ~ p + p + ~ "
,
(B) p + n - , p + p + ~ . -
+~o ,
(C) p + n - - ~ p + n + ~ + + ~ "
.
T h e d a t a w e r e o b t a i n e d f r o m a n e x p o s u r e of t h e 20 i n c h BNL d e u t e r i u m b u b b l e c h a m b e r to 3oq G e V / c p r o t o n s . S i n c e o u r goal i s to s t u d y p n r e a c t i o n s , o u r s a m p l e w a s r e s t r i c t e d to * Research jointly sponsored by the US Atomic Energy Commission under contract with the Union Carbide Corporation and by the University of Tennessee, UT Contract No. AT-40-1-3956.
506
H.O. COHN et 8/.
e v e n t s c o n t a i n i n g a t l e a s t one p r o t o n of k i n e t i c e n e r g y l e s s t h a n 60 MeV. T h e i n c l u s i o n of p e r i p h e r a l p p i n t e r a c t i o n s w a s m i n i m i z e d b y i m p o s i n g t h e r e q u i r e m e n t , when a p p l i c a b l e ( r e a c t i o n C), t h a t t h e f i n a l s t a t e n e u t r o n b e m o r e e n e r g e t i c t h a n t h e s l o w e r p r o t o n . F o r e v e n t s w h e r e t h e r e w a s a n ambiguity in i d e n t i f i c a t i o n b e t w e e n p r o t o n a n d ~+ on t h e s c a n n i n g t a b l e , b o t h f i t s w e r e t r i e d w i t h t h e e v e n t t y p e s e l e c t i o ~ b a s e d on t h e c h i - s q u a r e p r o b a b i l i t y . O u r s a m p l e , s o s e l e c t e d , c o n t a i n s 438 e v e n t s of t y p e A, 497 e v e n t s of t y p e B a n d 880 e v e n t s of t y p e C. T o d e t e r m i n e t h e c r o s s s e c t i o n s c o r r e s p o n d i n g t o t h e s e e v e n t s , we h a v e a s s u m e d t h e p d t o t a l c r o s s s e c t i o n a t 3.7 GeV/c to b e 81.5 m b f o u n d b y B u g g e t al° [1] in a h i g h - p r e c i s i o n c o u n t e r e x p e r i m e n t ( o u r m e a s u r e d v a l u e i s 83.4 ± 3.0 m b ) . D e t e r m i n a t i o n of t h e n e u t r o n t a r g e t c r o s s s e c t i o n in a d e u t e r i u m e x p e r i m e n t a l s o r e q u i r e s an e s t i m a t e of t h a t f r a c t i o n of n e u t r o n i n t e r a c t i o n s f o r w h i c h t h e s p e c t a t o r p r o t o n i s t o o s h o r t to b e i d e n t i f i e d . By a s s u m i n g t h a t a l l e v e n t s of t h e t y p e p d ~ n s p p + (ky) h a v e two v i s i b l e p r o t o n s a n d b y r e f e r e n c e to t h e pp f o u r p r o n g c r o s s s e c t i o n s r e p o r t e d b y H a r t et a l . [2] a t a s i m i l a r e n e r g y , we f i n d t h a t 64 ± 4% of a l l s p e c t a t o r p r o t o n s a r e i n v i s i b l e in o u r e x p e r i m e n t . I n c o r p o r a t i o n of a 5% c o r r e c t i o n t o c o m p e n s a t e f o r s c r e e n i n g of t h e t a r g e t n e u t r o n b y t h e p r o t o n in t h e d e u t e r o n ( ' G l a u b e r c o r r e c t i o n ' [3]) y i e l d s t h e s i z e of o u r e x p e r i m e n t t o b e 7.2 + 1.1 ~ b p e r e v e n t . T a b l e 1 s u m m a r i z e s our data and lists, for comparison, some closely allied quantities from pp a n d ~p r e a c t i o n s . Table 1 P a r t i a l c r o s s section for pn, pp and ~p at 3.7 GeV/c. Reaction
Momentum
C r o s s section
pn ~ ppTr-
3.7 GeV/c
3.2 ± 0.6 mb
pp--~ ppyO
3.67 GeV/v
° 2.9 * 0.3 mb
Ref. This experiment Smith et al. [3]
pp---, pmr +
3.67 GeV/c
11.4 :~ 0.7 mb
Smith et al. [3]
~p __. ppyO
3.66 GeV/c
2.3 4- 0.5 mb
F e r b e l et al. [4]
~p--~ pf~r-
3.66 GeV/c
2.0 + 0.4 mb
F e r b e l et al. [4]
pn ~ pnff+;r-
3.7 GeV/c
6.3 4- 1.0 mb
This experiment
pp--~ ppTr+~r-
3.67 GeV/c
2.67 ~- 0.13 mb
Hart et al. [2]
~p ~ ~p;r+~ -
3.66 GeV/c
3.67 ~- 0.30 mb
F e r b e l et al. [4]
pn ~ pplr-Tr°
3.7 GeV/c
3.6 • 0.7 mb
This experiment
9.. R E S O N A N C E
PRODUCTION
Figs. I-4 present the various pion-nucleon and di-pion mass combinations w h i c h a r e a v a i l a b l e t h r o u g h r e a c t i o n s A, B a n d C in t h i s e x p e r i m e n t . F o r r e a c t i o n (A) o r (B), w i t h two p r o t o n s in t h e f i n a l s t a t e , a f o u r f o l d a m b i g u i t y e x i s t s w i t h r e s p e c t t o i d e n t i f i c a t i o n of t h e y - n u c l e o n c o m b i n a t i o n
INELASTIC PN INTERACTIONS
507
~0
8060 F~~ 4O
M(nTr-)
60
M (p~r)
Iz
z
+
X
o
t.0
t.t
I.~'
t.3
1.4 t.5 1.6 MASS (C-eV/c2 )
"%%-
1.7
t.8
1.9
2.0
Fig. 1. Pion-nueleon mass distributions for T z = ±~ states in the np?~-y- final state.
with a p r o d u c t i o n vertex. Only those combinations with lowest m o m e n t u m t r a n s f e r a r e plotted. It is seen that, in the uncut data, the only c l e a r r e s o r,ance f o r m a t i o n is limited to the N*(1238) i s o b a r and that this i s o b a r m a n i f e s t s itself m o s t c l e a r l y in the Tz = ~-{ states. We f u r t h e r note the a b s e n c e of p - p r o d u c t i o n in both di-pion channels. By fitting the u n s e l e c t e d p i o n - n u cleon m a s s s p e c t r a to a combination of phase space, adjusted for r e f l e c t i o n of i s o b a r s in other c h a r g e s t a t e s , and B r e i t - W i g n e r for the N*(1238), F = 120 MeV, we deduce the following c r o s s sections at 3.7 G e V / c . ( ; ( p + n - - , N * + + + n + y -) = 9..52 ± 0.4 mb ,
(I)
~ ( p + n - ~ N * ' + p + ~ +) = 3.31 + 0.5 m b ,
(2)
( ; ( p + n - ~ N * ° + n + ~ +) = 0.94 ± 0.15 m b ,
(3)
(r(p+ n - . N * + + p + I r ") = 0.63 ± 0.06 m b ,
(4)
( r ( p + n - ' N * ° + p + ~ °) = 1.26 ± 0.24 mb ,
(5)
( ~ ( p + n - ~ N * + + p + ~ ") = 0.72 ± 0.14 mb ,
(6)
(r(p+n ~ N * ° + p ) = 0.80 ± 0.15 mb.
(7)
508
H.O.COHN et al.
>
0
-
-
JIJS,I
": z
50
l
MIpT-)
i
0 1.0
t.t
t2.
t3
1.4
t.5
1.6
L7
IS
1.9
2.0
MASS~v/c2~ Fig. 2. Pion-nucleon m a s s distributions for T z = ~:½ states in the npTr+~- final state.
T h e s e c r o s s s e c t i o n s a r e only f o r e v e n t s v i s i b l e in o u r e x p e r i m e n t s o t h at , f o r e x a m p l e , ~(p + n ~ N *o + p + ~o) s h o u l d b e a d j u s t e d to a c c o u n t f o r N * ° d e c a y i n t o t h e n~ o c h a n n e l . I n s p e c t i o n of t h e a p p r o p r i a t e t r i a n g l e p l o t s (fig. 5) y i e l d s f o r t h e d o u b l e i s o b a r p r o d u c t i o n c r o s s s e c t i o n s : ~(p+n~N*+++N
*-) = 1.55 ± 0 . 2 5 m b ,
¢ r ( p + n ~ N *+ + N *°) --< 0.35 + 0.10 m b .
INELASTIC PN INTERACTIONS
509
4o
I pn--~pp~-
:30
~.
I0 0
' ~ ~
......
co! ' I.O
1.2
t.4
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A2min< '~c m~
"L.. LJ
1.6 M (p~r-) (GeV/c:;}
__ 1.8
2.0
RO
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I
pn..., ppTr_TrO
60 (.n Ira 50
"
i (p~r-)
w h O40 hi
= ~3o
F
2O ,o 0 80
(b)
~
M (p~O) oo
a~
A
|.0
t.2
t.4
t.6 M (p~') (GeV/c 2 )
1.8
2.0
F i g . 3. (a) P i o n - n u c l e o n m a s s d i s t r i b u t i o n f o r t h e r e a c t i o n p n ~ pp?r-. T h e p~'- m a s s c o m b i n a t i o n p l o t t e d i s t h a t f o r w h i c h A2 b e t w e e n t h e p~ a n d i n c i d e n t n u c l e o n i s s m a l l e s t . T h e d a s h e d c u r v e f u r t h e r r e s t r i c t s ~ 2 to b e l e s s t h a n 1 2 m 2. (b) a n d (c) p i o n - n u c l e o n m a s s d i s t r i b u t i o n f o r t h e r e a c t i o n pn ---* pp?rTr ° , w i t h t h e r e s t r i c t i o n t h a t A 2 i n b e l e s s t h a n 1 2 m 2. E a c h e v e n t i s p l o t t e d o n l y o n c e a c c o r d i n g to w h i c h combination has the lower A2.
510
H.O.COHN et al.
60
[7
pn ---~ on T * T--
Mly%'-)
o
,
> 20 ' LL O
® z
7_00
40
I
I
on - - ~ ppTr- vr°
N
30
~o ~r~l_l
M (T-T °)
LI
=',
'°
0.25
0.35
0.45
0.55
0.65
0.75 0.85 MASS (GeV/c2)
0.95
1.05
I.t5
t.25
Fig. 4. Pion-pion m a s s distributions for the final states np~-~r- and ppy-~o.
If w e a l l o w f o r u n o b s e r v e d d e c a y m o d e s , a ( p + n - - * N * + + N *°) b e c o m e s 1.5 rob. We n o t e t h a t d o u b l e i s o b a r p r o d u c t i o n a c c o u n t s f o r only a b o u t ~ of t h e t o t a l pnTr+~ - f i n a l s t a t e c r o s s s e c t i o n , w h i l e in p p r e a c t i o n s , t h e d o u b l e i s o b a r p r o d u c t i o n c r o s s s e c t i o n (pp ~ N*++N * - - ) a c c o u n t s f o r 50-95% of t h e t o t a l pp ~ pp~+Tr- c r o s s s e c t i o n a t s i m i l a r e n e r g i e s [4]. We h a v e p r e v i ously reported momentum-transfer distributions for double isobar product i o n f r o m reacb_'on (C) in c o n n e c t i o n w i t h p o s s i b l e e v i d e n c e f o r Q= 2 e x c h a n g e e f f e c t s in p n c o l l i s i o n s [5].
INELASTIC PN INTERACTIONS
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2.2
t
--
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•
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t.6
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÷
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2.0
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F i g . 5. T r i a n g l e p l o t s f o r t h e f i n a l s t a t e s pn'1r+Tr- a n d pp~r-~To. T h e d i f f e r e n t s y m b o l s in t h e u p p e r f i g u r e c o r r e s p o n d to d i f f e r e n t s a m p l e s o f t h e d a t a a n d a r e w i t h o u t s i g nificance.
512
H.O. COHN et al.
3. SEARCH FOR N*(1400) The existence of a pion-nucleon i s o b a r of m a s s ~ 1.4 GeV was f i r s t sugg e s t e d by p h a s e - s h i f t a n a l y s e s of 7rN elastic s c a t t e r i n g [6]. Verification of such an enhancement has often been achieved by m e a n s of m i s s i n g m a s s s p e c t r o m e t e r e x p e r i m e n t s [7]. The e x p e r i m e n t a l situation, however, is not c l e a r . Bubble c h a m b e r e x p e r i m e n t s [8-13] employing pp, pn, ~p and ~+p r e a c t i o n s have r e p o r t e d o b s e r v i n g this r e s o n a n c e , but its m a s s and width s e e m to be r a t h e r widely v a r y i n g quantities. F u r t h e r m o r e the enh a n c e m e n t has been explained as having a kinematic origin [14], as being a diffractively p r o d u c e d r e s o n a n t state in b a r y o n - b a r y o n collisions [10, 11], and as being a consequence of a double R e g g e - p o l e exchange [15]. Recently F e r b e l et al. [16] have suggested that e n h a n c e m e n t s o b s e r v e d , in pp ~ pp~+~r-, in this r e g i o n a r e due to a kinematic r e f l e c t i o n a r i s i n g f r o m simultaneous a++~ - - production. Since the r e p o r t e d inelasticity of the N*(1400) state is l a r g e r [10] N* -~ 7r~N/N* --. IrN ~ ~, t h e r e a r e s e v e r a l possibilities of o b s e r v i n g it in this experiment. We focus f i r s t on the dipion production channels. Fig. 6a shows the N~r s p e c t r a for channels (B) and (C), where each event is plotted twice to account for the two combinations possible in either case. It is seen that s m a l l enhancements a r e p r e s e n t in both s p e c t r a ; for N~r+Tr-, a ~ 400 t~b and for NTr'~r°, cr ~ 100 t~b. However, both of these enhancements a p p e a r to be p r i m a r i l y a s s o c i a t e d with double i s o b a r (A) production. Fig. 6b is the NlrTr s p e c t r u m for each of these channels with the r e s t r i c t i o n to double isob a r events. It is apparent that most, if not all, of the enhancement obs e r v e d in fig. 6a can be accounted for by this overlap. We also note that Mlp~Tr'Tr°+pzlr-~r )
80
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z 30
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+lr + nlr+tr - )
d
2.25 1.25 t.50 MASS ( GeV/c 2)
~
I1
U - L" r 1.75
2.00
2.25
F i g . 6. (a) NrrTr s p e c t r a f o r pn -~ pnTr+rr- and pn -~ p p y - y o . R e s t r i c t i o n to A2 l e s s than
12rn~ is shown as shaded regions. (b) N#Tr spectra for pn ~ pn/~-#- and pn -* ppTr-lr° restricted to double N* events.
INELASTIC PN INTERACTIONS
513
c o n s i d e r a b l y m o r e 'N*(1400)' p r o d u c t i o n is p r e s e n t in the pny+y- final state than in the pp~-~o final state. This s a m e behavior is o b s e r v e d in the m a g nitude of the o v e r l a p c r o s s s e c t i o n s given above. If the N*(1400) is p r o duced by P o m e r o n exchange, it should appear p r e f e r e n t i a l l y at l o w - m o m e n tum t r a n s f e r to the N ~ s y s t e m . The shaded a r e a s in fig. 6 p r e s e n t the data with the a p p r o p r i a t e m o m e n t u m t r a n s f e r r e s t r i c t e d to values l e s s than 12m 2. No e n h a n c e m e n t is observed. Thus, we find no evidence for the N*(1400) in either of the dipion p r o d u c t i o n channels available in this e x p e r iment. Finally, since the N*(1400) d e c a y s ~ 60% of the time to ~N, if it is p r o duced in pn i n t e r a c t i o n s at 3.7 GeV/c, it should be p r e s e n t in r e a c t i o n (A) ( p p - . ppy-). In other bubble c h a m b e r studies, Tan et al. [10] find an N*(1400) p r o d u c t i o n c r o s s section of 0.38 ± 0.22 mb in 6.07 G e V / c pp coll i s s i o n s while at 7 G e V / c , Shapira et al. [11] r e p o r t that in pn collisions the N*(1400) p r o d u c t i o n c r o s s section is about 1.5 mb (for d e c a y s into both p~- and taro). To r e m o v e the ambiguity between which f i n a l - s t a t e p r o t o n is a s s o c i a t e d with the y- we have plotted, in fig. 3, that py- m a s s for which the s q u a r e of the invariant f o u r - m o m e n t u m t r a n s f e r between each py- c o m bination and each incident nucleon is least. A f u r t h e r r e q u i r e m e n t that this A2 be l e s s than 12m 2 is indicated by the dashed h i s t o g r a m in the s a m e figu r e . We see that, at m o s t , a s m a l l signal r e m a i n s in the data. C o r r e c t i n g for the N*(1400) d e c a y into n~ °, the o b s e r v e d c r o s s section for N*(1400) p r o d u c t i o n in pn c o l l i s i o n s at 3.7 G e V / c is l e s s than 350 pbo T h e s e r e s u l t s a r e in a g r e e m e n t with a diffraction production m e c h a n i s m for N*(1400) since the r e l a t i v e l y l o w - b o m b a r d i n g m o m e n t u m in our e x p e r i m e n t should s e v e r e l y r e s t r i c t diffraction phenomena. By c o n t r a s t , if pion exchange were the production m e c h a n i s m , N*(1400) production at 3.7 G e V / c would be expected to exceed its value [ i i ] at 7 GeV/c, which r e s u l t is c l e a r l y not observed.
REFERENCES
[1] D.V.Bugg, D.C.Satter, G.H.Stafford, R.F.George, K.F.Riley and R.J. Tapper, Phys. Rev. 146 (1966) 980. [2] E. L. Hart, R.I. Louttit, D. Luers, T.W. Morris, W.J. Willis and S. S. Yamamoto, Phys. Rev. 126 (1962) 747. [3] V.Franeo and R.J.Glauber, Phys. Rev. 142 (1966) 1195. [4] G.A. Smith, H. Courant, E.C. Fowler, H.Kraybill, J. Sandweiss and H. Taft, Phys. Rev. 123 (1961) 2160; T. Ferbel, A. Firestone, J. Sandweiss, H.D. Taft, M. Gailloud, T.W. Morris, W.J.Willis, A.H.Bachman, P.Baumel and R.M.Lea, Phys. Rev. 138 (1965) B1528. [5] H.O.Cohn, R.D.MeCulloeh, W.M.Bugg and G.T.Condo, Phys. Letters 26B (1968) 598. [6] L.D.Roper, Phys. Rev. Letters 12 (1964) 340. [7] I.M.Blair, A.E.Taylor, W.S. Chapman, P.I.P.Kalmus, J.Litt, M.C.Miller, D.B.Seott, H.J.Sherman, A.Astbury and T.G.Walker, Phys. Rev. Letters 17 (1966) 789.
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H . O . COHN et al.
E.W.Anderson, E.J.Bleser, G.B.Collins, T.Fujii, J.Menes, F.Turkot, R.A. Carrigan, R.M. Edelstein, N.C. Hien, T.J. McMahon and I.Nadelhaft, Phys. Rev Letters 16 (1966) 855; K. J. Foley, R.S. Jones, S.J. Lindenbaum, W.A. Love, S. Ozaki, E.D. Platner, C.A.Quarles and E. H,Willen, Phys. Rev. Letters 19 (1967) 397. [8] R.A.Jespersen, Y.W.Kang, W.J.Kernan, R.A.Leacock, J.I.Rhode, T.L. Schalk and L.S.Schroeder, Phys. Rev. Letters 21 (1968) 1368. [9] R.B.BelI, D.J.Crennell, P.V.C.Hough, U. Karshon, K.W.Lai, J.M.Scarr, T. G. Schumann, J.O. Skillicorn, R.C. Strand, A.H. Bachman, P. Banmel, R.M. Lea and A.Montwill, Phys. Rev. Letters 20 (1966) 164. [10] T.H. Tan, M. L. Perl, F. Martin, W. Chinowsky, R. Kinsey, S. Klein, P. Sehmidt, M. Mandelkern and J.Schultz, Phys. Letters 28B (1968) 195. [11] A. Shapira, O. Benary, Y. Eisenberg, E.E. Ronat, D. Yaffe and G. Yekutieli, Phys. Rev. Letters 21 (1968) 1835. [12] R.Ehrlich, R.Nieporent, R.J.Plano, J.B.Whittaker, C.Baltay, J.Feinman, P. Franzini, R . N e w m a n and N. Yeh, Phys. Rev. Letters 21 (1968) 1839. [13] T.C.Bacon, F.Bomse, T.B.Borak, T.B.Cochran, W.J. Fiekinger, E.R.Goza, H.W.K. Hopkins and E.O.Salant, Phys. Rev. Letters 22 (1969) 43. [14] E.Gellert, G.A.Smith, S.Wojcicki, E.Colton, P.Schlein and H.K.Ticho, Phys. Rev. Letters 17 (1966) 884. [15] E. L. Berger, E.Gellert, G.A. Smith, E. Colton and P. E. Schlein, Phys. Rev. Letters 20 (1968) 964; E.L.Berger, Phys. Rev. Letters 20 (1968) 964. [16] T.Ferbel, R.Holmes and S.Stone, Phys. Rev. Letters 22 (1969) 1141.
Nuclear Physics B21 (1970) 505-514. North-Holland Publishing Company
INELASTIC PN INTERACTIONS AT 3.7 GeV/c* H. O. C O H N Oak Ridge National Laboratory, Oak Ridge, Tennessee R. D. M c C U L L O C H Central Data Processing Facility, Union Carbide Nuclear Division, Oak Ridge, Tennessee W. M. BUGG a n d G. T . CONDO University of Tennessee, Knoxville, Tennessee and Oak Ridge National Laboratory, Oak Ridge, Tennessee Received 9 F e b r u a r y 1970 (Revised manuscript received 26 May 1970)
Abstract: Cross sections for N*(1238} production arising from various inelastic r e actions of 3.7 GeV/e protons with deuterons are presented. We find that N* production in the reaction pn --* pnrr+rr- is considerably s m a l l e r than in the pp and ~p analogue reactions. An upper limit of 350/zb is found for the N*(1400) production c r o s s section.
1. I N T R O D U C T I O N A l t h o u g h i n e l a s t i c pp a n d pp i n t e r a c t i o n s h a v e b e e n e x t e n s i v e l y i n v e s t i g a t e d , v e r y l i t t l e e x p e r i m e n t a l i n f o r m a t i o n i s a v a i l a b l e on p r o t o n - n e u t r o n i n t e r a c t i o n s i n the GeV r a n g e . I n p a r t i c u l a r , w h i l e the high e n e r g y p n t o t a l a n d e l a s t i c c r o s s s e c t i o n s h a v e b e e n a c c u r a t e l y d e t e r m i n e d , t h e d a t a on r e s o n a n c e f o r m a t i o n f r o m pn i n t e r a c t i o n s are somewhat m e a g r e . In the p r e s e n t n o t e we p r e s e n t o u r r e s u l t s f o r the r e a c t i o n s :
(A) p + n - ~ p + p + ~ "
,
(B) p + n - , p + p + ~ . -
+~o ,
(C) p + n - - ~ p + n + ~ + + ~ "
.
T h e d a t a w e r e o b t a i n e d f r o m a n e x p o s u r e of t h e 20 i n c h BNL d e u t e r i u m b u b b l e c h a m b e r to 3oq G e V / c p r o t o n s . S i n c e o u r goal i s to s t u d y p n r e a c t i o n s , o u r s a m p l e w a s r e s t r i c t e d to * Research jointly sponsored by the US Atomic Energy Commission under contract with the Union Carbide Corporation and by the University of Tennessee, UT Contract No. AT-40-1-3956.
506
H.O. COHN et 8/.
e v e n t s c o n t a i n i n g a t l e a s t one p r o t o n of k i n e t i c e n e r g y l e s s t h a n 60 MeV. T h e i n c l u s i o n of p e r i p h e r a l p p i n t e r a c t i o n s w a s m i n i m i z e d b y i m p o s i n g t h e r e q u i r e m e n t , when a p p l i c a b l e ( r e a c t i o n C), t h a t t h e f i n a l s t a t e n e u t r o n b e m o r e e n e r g e t i c t h a n t h e s l o w e r p r o t o n . F o r e v e n t s w h e r e t h e r e w a s a n ambiguity in i d e n t i f i c a t i o n b e t w e e n p r o t o n a n d ~+ on t h e s c a n n i n g t a b l e , b o t h f i t s w e r e t r i e d w i t h t h e e v e n t t y p e s e l e c t i o ~ b a s e d on t h e c h i - s q u a r e p r o b a b i l i t y . O u r s a m p l e , s o s e l e c t e d , c o n t a i n s 438 e v e n t s of t y p e A, 497 e v e n t s of t y p e B a n d 880 e v e n t s of t y p e C. T o d e t e r m i n e t h e c r o s s s e c t i o n s c o r r e s p o n d i n g t o t h e s e e v e n t s , we h a v e a s s u m e d t h e p d t o t a l c r o s s s e c t i o n a t 3.7 GeV/c to b e 81.5 m b f o u n d b y B u g g e t al° [1] in a h i g h - p r e c i s i o n c o u n t e r e x p e r i m e n t ( o u r m e a s u r e d v a l u e i s 83.4 ± 3.0 m b ) . D e t e r m i n a t i o n of t h e n e u t r o n t a r g e t c r o s s s e c t i o n in a d e u t e r i u m e x p e r i m e n t a l s o r e q u i r e s an e s t i m a t e of t h a t f r a c t i o n of n e u t r o n i n t e r a c t i o n s f o r w h i c h t h e s p e c t a t o r p r o t o n i s t o o s h o r t to b e i d e n t i f i e d . By a s s u m i n g t h a t a l l e v e n t s of t h e t y p e p d ~ n s p p + (ky) h a v e two v i s i b l e p r o t o n s a n d b y r e f e r e n c e to t h e pp f o u r p r o n g c r o s s s e c t i o n s r e p o r t e d b y H a r t et a l . [2] a t a s i m i l a r e n e r g y , we f i n d t h a t 64 ± 4% of a l l s p e c t a t o r p r o t o n s a r e i n v i s i b l e in o u r e x p e r i m e n t . I n c o r p o r a t i o n of a 5% c o r r e c t i o n t o c o m p e n s a t e f o r s c r e e n i n g of t h e t a r g e t n e u t r o n b y t h e p r o t o n in t h e d e u t e r o n ( ' G l a u b e r c o r r e c t i o n ' [3]) y i e l d s t h e s i z e of o u r e x p e r i m e n t t o b e 7.2 + 1.1 ~ b p e r e v e n t . T a b l e 1 s u m m a r i z e s our data and lists, for comparison, some closely allied quantities from pp a n d ~p r e a c t i o n s . Table 1 P a r t i a l c r o s s section for pn, pp and ~p at 3.7 GeV/c. Reaction
Momentum
C r o s s section
pn ~ ppTr-
3.7 GeV/c
3.2 ± 0.6 mb
pp--~ ppyO
3.67 GeV/v
° 2.9 * 0.3 mb
Ref. This experiment Smith et al. [3]
pp---, pmr +
3.67 GeV/c
11.4 :~ 0.7 mb
Smith et al. [3]
~p __. ppyO
3.66 GeV/c
2.3 4- 0.5 mb
F e r b e l et al. [4]
~p--~ pf~r-
3.66 GeV/c
2.0 + 0.4 mb
F e r b e l et al. [4]
pn ~ pnff+;r-
3.7 GeV/c
6.3 4- 1.0 mb
This experiment
pp--~ ppTr+~r-
3.67 GeV/c
2.67 ~- 0.13 mb
Hart et al. [2]
~p ~ ~p;r+~ -
3.66 GeV/c
3.67 ~- 0.30 mb
F e r b e l et al. [4]
pn ~ pplr-Tr°
3.7 GeV/c
3.6 • 0.7 mb
This experiment
9.. R E S O N A N C E
PRODUCTION
Figs. I-4 present the various pion-nucleon and di-pion mass combinations w h i c h a r e a v a i l a b l e t h r o u g h r e a c t i o n s A, B a n d C in t h i s e x p e r i m e n t . F o r r e a c t i o n (A) o r (B), w i t h two p r o t o n s in t h e f i n a l s t a t e , a f o u r f o l d a m b i g u i t y e x i s t s w i t h r e s p e c t t o i d e n t i f i c a t i o n of t h e y - n u c l e o n c o m b i n a t i o n
INELASTIC PN INTERACTIONS
507
~0
8060 F~~ 4O
M(nTr-)
60
M (p~r)
Iz
z
+
X
o
t.0
t.t
I.~'
t.3
1.4 t.5 1.6 MASS (C-eV/c2 )
"%%-
1.7
t.8
1.9
2.0
Fig. 1. Pion-nueleon mass distributions for T z = ±~ states in the np?~-y- final state.
with a p r o d u c t i o n vertex. Only those combinations with lowest m o m e n t u m t r a n s f e r a r e plotted. It is seen that, in the uncut data, the only c l e a r r e s o r,ance f o r m a t i o n is limited to the N*(1238) i s o b a r and that this i s o b a r m a n i f e s t s itself m o s t c l e a r l y in the Tz = ~-{ states. We f u r t h e r note the a b s e n c e of p - p r o d u c t i o n in both di-pion channels. By fitting the u n s e l e c t e d p i o n - n u cleon m a s s s p e c t r a to a combination of phase space, adjusted for r e f l e c t i o n of i s o b a r s in other c h a r g e s t a t e s , and B r e i t - W i g n e r for the N*(1238), F = 120 MeV, we deduce the following c r o s s sections at 3.7 G e V / c . ( ; ( p + n - - , N * + + + n + y -) = 9..52 ± 0.4 mb ,
(I)
~ ( p + n - ~ N * ' + p + ~ +) = 3.31 + 0.5 m b ,
(2)
( ; ( p + n - ~ N * ° + n + ~ +) = 0.94 ± 0.15 m b ,
(3)
(r(p+ n - . N * + + p + I r ") = 0.63 ± 0.06 m b ,
(4)
( r ( p + n - ' N * ° + p + ~ °) = 1.26 ± 0.24 mb ,
(5)
( ~ ( p + n - ~ N * + + p + ~ ") = 0.72 ± 0.14 mb ,
(6)
(r(p+n ~ N * ° + p ) = 0.80 ± 0.15 mb.
(7)
508
H.O.COHN et al.
>
0
-
-
JIJS,I
": z
50
l
MIpT-)
i
0 1.0
t.t
t2.
t3
1.4
t.5
1.6
L7
IS
1.9
2.0
MASS~v/c2~ Fig. 2. Pion-nucleon m a s s distributions for T z = ~:½ states in the npTr+~- final state.
T h e s e c r o s s s e c t i o n s a r e only f o r e v e n t s v i s i b l e in o u r e x p e r i m e n t s o t h at , f o r e x a m p l e , ~(p + n ~ N *o + p + ~o) s h o u l d b e a d j u s t e d to a c c o u n t f o r N * ° d e c a y i n t o t h e n~ o c h a n n e l . I n s p e c t i o n of t h e a p p r o p r i a t e t r i a n g l e p l o t s (fig. 5) y i e l d s f o r t h e d o u b l e i s o b a r p r o d u c t i o n c r o s s s e c t i o n s : ~(p+n~N*+++N
*-) = 1.55 ± 0 . 2 5 m b ,
¢ r ( p + n ~ N *+ + N *°) --< 0.35 + 0.10 m b .
INELASTIC PN INTERACTIONS
509
4o
I pn--~pp~-
:30
~.
I0 0
' ~ ~
......
co! ' I.O
1.2
t.4
.
A2min< '~c m~
"L.. LJ
1.6 M (p~r-) (GeV/c:;}
__ 1.8
2.0
RO
.o
I
pn..., ppTr_TrO
60 (.n Ira 50
"
i (p~r-)
w h O40 hi
= ~3o
F
2O ,o 0 80
(b)
~
M (p~O) oo
a~
A
|.0
t.2
t.4
t.6 M (p~') (GeV/c 2 )
1.8
2.0
F i g . 3. (a) P i o n - n u c l e o n m a s s d i s t r i b u t i o n f o r t h e r e a c t i o n p n ~ pp?r-. T h e p~'- m a s s c o m b i n a t i o n p l o t t e d i s t h a t f o r w h i c h A2 b e t w e e n t h e p~ a n d i n c i d e n t n u c l e o n i s s m a l l e s t . T h e d a s h e d c u r v e f u r t h e r r e s t r i c t s ~ 2 to b e l e s s t h a n 1 2 m 2. (b) a n d (c) p i o n - n u c l e o n m a s s d i s t r i b u t i o n f o r t h e r e a c t i o n pn ---* pp?rTr ° , w i t h t h e r e s t r i c t i o n t h a t A 2 i n b e l e s s t h a n 1 2 m 2. E a c h e v e n t i s p l o t t e d o n l y o n c e a c c o r d i n g to w h i c h combination has the lower A2.
510
H.O.COHN et al.
60
[7
pn ---~ on T * T--
Mly%'-)
o
,
> 20 ' LL O
® z
7_00
40
I
I
on - - ~ ppTr- vr°
N
30
~o ~r~l_l
M (T-T °)
LI
=',
'°
0.25
0.35
0.45
0.55
0.65
0.75 0.85 MASS (GeV/c2)
0.95
1.05
I.t5
t.25
Fig. 4. Pion-pion m a s s distributions for the final states np~-~r- and ppy-~o.
If w e a l l o w f o r u n o b s e r v e d d e c a y m o d e s , a ( p + n - - * N * + + N *°) b e c o m e s 1.5 rob. We n o t e t h a t d o u b l e i s o b a r p r o d u c t i o n a c c o u n t s f o r only a b o u t ~ of t h e t o t a l pnTr+~ - f i n a l s t a t e c r o s s s e c t i o n , w h i l e in p p r e a c t i o n s , t h e d o u b l e i s o b a r p r o d u c t i o n c r o s s s e c t i o n (pp ~ N*++N * - - ) a c c o u n t s f o r 50-95% of t h e t o t a l pp ~ pp~+Tr- c r o s s s e c t i o n a t s i m i l a r e n e r g i e s [4]. We h a v e p r e v i ously reported momentum-transfer distributions for double isobar product i o n f r o m reacb_'on (C) in c o n n e c t i o n w i t h p o s s i b l e e v i d e n c e f o r Q= 2 e x c h a n g e e f f e c t s in p n c o l l i s i o n s [5].
INELASTIC PN INTERACTIONS
2.2 2.0
I --
~
I
I
I
511
I
,
..~~.-. +,
I
:." •
t.4
bO
04.
q~9 •
i~
~.
÷' '<.
I
I
tO
t.2
t.4
I
I
2.2
.
"" .,+.÷+~" e "'+ "'+'"
~
+.o +co)
I
I
t6 t.8 M(n~r-) (GeV/¢ 2) ~
I
I 2.0
2.2
t
--
NU
•
÷ ÷+
t.6
÷ +
÷
* * - 7 .++ "., v ,, ~ ÷
..4: ~.÷ +
'.~;.~, ~ ÷ q e ' Z ~ , ÷ +2"
'.2
~.o
"
. : ~ - ~.~..
,.2-.,
2.0
•
:: ,.;~1~..., • " 'T__~'a~ :~.~* ?,? ? ,
_
~ ,
(~'] +.0
.
1 ~.2
e +÷
+ [~'xT%+ ÷ w +o,+. + +.
~ , ~ ~,+-v
~ ~..dt
I t4
I
~1~ . ~ •
I
~.8 M ( p T O) (GeV/,¢ 2) t6
~." +t.++ee.e 4+. <"
--
I 2.0
2.2
F i g . 5. T r i a n g l e p l o t s f o r t h e f i n a l s t a t e s pn'1r+Tr- a n d pp~r-~To. T h e d i f f e r e n t s y m b o l s in t h e u p p e r f i g u r e c o r r e s p o n d to d i f f e r e n t s a m p l e s o f t h e d a t a a n d a r e w i t h o u t s i g nificance.
512
H.O. COHN et al.
3. SEARCH FOR N*(1400) The existence of a pion-nucleon i s o b a r of m a s s ~ 1.4 GeV was f i r s t sugg e s t e d by p h a s e - s h i f t a n a l y s e s of 7rN elastic s c a t t e r i n g [6]. Verification of such an enhancement has often been achieved by m e a n s of m i s s i n g m a s s s p e c t r o m e t e r e x p e r i m e n t s [7]. The e x p e r i m e n t a l situation, however, is not c l e a r . Bubble c h a m b e r e x p e r i m e n t s [8-13] employing pp, pn, ~p and ~+p r e a c t i o n s have r e p o r t e d o b s e r v i n g this r e s o n a n c e , but its m a s s and width s e e m to be r a t h e r widely v a r y i n g quantities. F u r t h e r m o r e the enh a n c e m e n t has been explained as having a kinematic origin [14], as being a diffractively p r o d u c e d r e s o n a n t state in b a r y o n - b a r y o n collisions [10, 11], and as being a consequence of a double R e g g e - p o l e exchange [15]. Recently F e r b e l et al. [16] have suggested that e n h a n c e m e n t s o b s e r v e d , in pp ~ pp~+~r-, in this r e g i o n a r e due to a kinematic r e f l e c t i o n a r i s i n g f r o m simultaneous a++~ - - production. Since the r e p o r t e d inelasticity of the N*(1400) state is l a r g e r [10] N* -~ 7r~N/N* --. IrN ~ ~, t h e r e a r e s e v e r a l possibilities of o b s e r v i n g it in this experiment. We focus f i r s t on the dipion production channels. Fig. 6a shows the N~r s p e c t r a for channels (B) and (C), where each event is plotted twice to account for the two combinations possible in either case. It is seen that s m a l l enhancements a r e p r e s e n t in both s p e c t r a ; for N~r+Tr-, a ~ 400 t~b and for NTr'~r°, cr ~ 100 t~b. However, both of these enhancements a p p e a r to be p r i m a r i l y a s s o c i a t e d with double i s o b a r (A) production. Fig. 6b is the NlrTr s p e c t r u m for each of these channels with the r e s t r i c t i o n to double isob a r events. It is apparent that most, if not all, of the enhancement obs e r v e d in fig. 6a can be accounted for by this overlap. We also note that Mlp~Tr'Tr°+pzlr-~r )
80
]:1
60
LJU
40
,=, m
.
n
.r-i L,... "l.I
,
4°
,
,
n
~
'°'
1.50
t.75
2.00
,
RESTRICTED T() N ~'++ + N ~t-
RESTRICTED T() N* + + N ~°
z 30
O 1.25
+lr + nlr+tr - )
d
2.25 1.25 t.50 MASS ( GeV/c 2)
~
I1
U - L" r 1.75
2.00
2.25
F i g . 6. (a) NrrTr s p e c t r a f o r pn -~ pnTr+rr- and pn -~ p p y - y o . R e s t r i c t i o n to A2 l e s s than
12rn~ is shown as shaded regions. (b) N#Tr spectra for pn ~ pn/~-#- and pn -* ppTr-lr° restricted to double N* events.
INELASTIC PN INTERACTIONS
513
c o n s i d e r a b l y m o r e 'N*(1400)' p r o d u c t i o n is p r e s e n t in the pny+y- final state than in the pp~-~o final state. This s a m e behavior is o b s e r v e d in the m a g nitude of the o v e r l a p c r o s s s e c t i o n s given above. If the N*(1400) is p r o duced by P o m e r o n exchange, it should appear p r e f e r e n t i a l l y at l o w - m o m e n tum t r a n s f e r to the N ~ s y s t e m . The shaded a r e a s in fig. 6 p r e s e n t the data with the a p p r o p r i a t e m o m e n t u m t r a n s f e r r e s t r i c t e d to values l e s s than 12m 2. No e n h a n c e m e n t is observed. Thus, we find no evidence for the N*(1400) in either of the dipion p r o d u c t i o n channels available in this e x p e r iment. Finally, since the N*(1400) d e c a y s ~ 60% of the time to ~N, if it is p r o duced in pn i n t e r a c t i o n s at 3.7 GeV/c, it should be p r e s e n t in r e a c t i o n (A) ( p p - . ppy-). In other bubble c h a m b e r studies, Tan et al. [10] find an N*(1400) p r o d u c t i o n c r o s s section of 0.38 ± 0.22 mb in 6.07 G e V / c pp coll i s s i o n s while at 7 G e V / c , Shapira et al. [11] r e p o r t that in pn collisions the N*(1400) p r o d u c t i o n c r o s s section is about 1.5 mb (for d e c a y s into both p~- and taro). To r e m o v e the ambiguity between which f i n a l - s t a t e p r o t o n is a s s o c i a t e d with the y- we have plotted, in fig. 3, that py- m a s s for which the s q u a r e of the invariant f o u r - m o m e n t u m t r a n s f e r between each py- c o m bination and each incident nucleon is least. A f u r t h e r r e q u i r e m e n t that this A2 be l e s s than 12m 2 is indicated by the dashed h i s t o g r a m in the s a m e figu r e . We see that, at m o s t , a s m a l l signal r e m a i n s in the data. C o r r e c t i n g for the N*(1400) d e c a y into n~ °, the o b s e r v e d c r o s s section for N*(1400) p r o d u c t i o n in pn c o l l i s i o n s at 3.7 G e V / c is l e s s than 350 pbo T h e s e r e s u l t s a r e in a g r e e m e n t with a diffraction production m e c h a n i s m for N*(1400) since the r e l a t i v e l y l o w - b o m b a r d i n g m o m e n t u m in our e x p e r i m e n t should s e v e r e l y r e s t r i c t diffraction phenomena. By c o n t r a s t , if pion exchange were the production m e c h a n i s m , N*(1400) production at 3.7 G e V / c would be expected to exceed its value [ i i ] at 7 GeV/c, which r e s u l t is c l e a r l y not observed.
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