- Email: [email protected]
η Production by proton-nucleon and proton-nucleus interactions from 800 MeV to 1.5 GeV
Prof. Part.N~cLPhys.,Vol.30, plx 101-102, 1993. Pdutedin CheatBritain.Allrishtsreserved.
0146--6410/93$7,4~0 O 1993,"~/~ma PtmsLtd
Production by Proton-Nucleon and Proton-Nucleus Interactions from 800 MeV to 1.5 GeV E. CHIAVASSA, G. Db'1J ACASA, N. DE MARCO, M. GALLIO, P. GUAITA, A. MUSSO, A. PICCOTFI, E. SCOMPARIN and E. VERCEI~IN Dipartimento di Fisica Sperimentale dell' Universit~ and lNFN, Via P. Giuria I, 10125 Tortno, Italy
In the last years both theoretical and experimental efforts has been done to study the production of ,1 on nuleous &ud nuclei [1], [2]; "in particular great interest has been a~sed to measure these processes near the threshold, where it seems to be dominated by the N'(1535) resonance production. Moreover the measurement of the 7/production in nucleusnucleus co]]Lsions has been indicated as a tool for studing the Equation of State in compressed nuclear matter and it is a necessary datum to understanding dilepton production in nuclei. Focusing our attention on the experimental aspects of this research, recently we have undertaken a program aiming to study the production of the meson on nucleons and nuclei by protons at Saturne. The ~ mesons are identified by PINOT, a neutral meson spectrometer which detects in coincidence the two 7 rays coming from the ~ --, ~ decay (BR 39%) and measures, for each, the energy and the direction. Starting from these quantities it is possible to reconstruct the 77 invar~nt mass spectrum, in which the q are recognised, and to determine their kinetic energy and production ansle [3]. Until now we have measured the doubly d~erential cross section d=cr/dt3dT for the ~ production in the following cases: a) as a function of A at 1 GeV and 900 MeV, detecting ~ mesons in the kinematical ranges 30 < Tn < 100 MeV and 0° ~ 8n ~ 40°; b) as a function of the projectile energy on a Carbon target, for ~ mesons in the same kinematical ranges as at point (a); c) as a function of the ~ kinetic energy on a Boron target and at ~xed beam energy (1 GeV), for ~ produced in the angular region 0 ° ~ 0n ~ 200 and in the complete klnematical range 0 ~ T,~ ~ 430 MeV, where the upper limit is given from the two-body reaction p + l l B --* ~+12C. The results are shown in figures 1, 2, 3 and 4 (open circles). In the same figures the close squares show
T. = 1 0 0 0 MeV II O 01
.P
16=
o) I,
I
II
''''I
,
I0
.
.,.,,.I
102
Figure 1: Doubly differential crou section at Tp=l GeV.
the results of calculation= performed by the Oiessen group [4] induding the ~ reabtozbtion in the target [5]. The model takes into ~count two production mechanisms, a primary one via the N N --. N~'~ interaction and a secondary one v ~ the f N -.-, UN process, the plon coming from a previous N N interactlon. Baaing a subthreshold production, the nuo cleon= Fermi motion plays an important role. The distribution is calculated in the mean field limit (Hartee-Foch method) neglecting the high momanturn tail. Evidently an essential input for the theoretical prevision is the knowledge of the pp ---, cross section; in the figure 5 we present our preliminary results for the o ' ~ . ~ , I total cross section at Tp=l.3 aad 1.5 OeV, which are in good ab~eement whit a parametrkation performed by De Paoli et al. [6]. In figure 5 the calculation= by Laget et al. [7] and Vetter et el. [8] are also presented. The ratio bewteen pn --. pn~ and pp -* ppr/moss sections has been chosen equal to 8, according to our preliminary data [9].
101
E. Chiavassa et ol.
102 1
~0.28
T, = 900 MeV
~0.24
:-El Prelimlnory doto ...
__
0.2
-. ....
Loget De Pvoli Vetter , / ° . . . . . °" - - - , .
0.16 0.12
~o
0.08
b) ,
, I,IHII
0.04 0
,
~0
I02
~ J
e
..-"
,..
I.."
1.2
1.6
Figure 2: Doubly differential cross section at Tp=900 MeV. 1
p C --> ~ X
2 T.(GeV)
A
Figure 5: Total cross section pp --, ppr/. This study will be continued in the near future by measuring the pp and pd (for the pn) reactions at energies between 1.5 and 2 GeV; we will also extend the measurements on nuclei at energies above the nucleon-nucleon ~zee threshold.
~
References
-2
10 !
O
[1] J.F.Germond and C.WgH-,
I°~
c) I,,,,W
. . . .
1000
750
I
. . . .
1250
I , ,
1500
T, O~ev) Figure 3: Doubly differential cross section versus proton energy on Carbon target. p B --)' W X T,,,, 1 GeV, "3,~< 20"
: •0.5
[2] E.Chlavassa et aL, Nucl. Phys. A538, 121c
(1992).
[3] E.Chiavassa et al,, Z. Phys. AS42, 107 (1992). [4] W.Cassing et al., Z. Phys. A340, 51 (1991). [5] E.VerceUin e~ ai., submitted for publication on Nuovo Cimento.
[6] A.De Paoli et al., Phys. Left. B219, 194
0989).
<>
"~ 0.4
Nucl. Phys.
Aslg, 30s (199o).
[7] J.M.Laget et al., Phys. Lett. B257, 254 (1991).
-0-
[8] T.Vetter et al., Phys. Lett. B263, 153 (1991).
o.3 ¢-W 0.2
u 0.1
[9] E.Chiavassa et aL, to be published on the Proceedings of "Sixi~mes Journe~ de Saturne", Mont St.Odile, may, 18-23, 1992.
-W-o~)
b 0
,,-'~7", ,--~.' , 200 ~00
T, (,J, ev) Figure 4: ~ kinetic energy distribution for mesons produced with 8, < 200 in p l l B -~ ~TX reaction at Yp=l GeV.
0146--6410/93$7,4~0 O 1993,"~/~ma PtmsLtd
Production by Proton-Nucleon and Proton-Nucleus Interactions from 800 MeV to 1.5 GeV E. CHIAVASSA, G. Db'1J ACASA, N. DE MARCO, M. GALLIO, P. GUAITA, A. MUSSO, A. PICCOTFI, E. SCOMPARIN and E. VERCEI~IN Dipartimento di Fisica Sperimentale dell' Universit~ and lNFN, Via P. Giuria I, 10125 Tortno, Italy
In the last years both theoretical and experimental efforts has been done to study the production of ,1 on nuleous &ud nuclei [1], [2]; "in particular great interest has been a~sed to measure these processes near the threshold, where it seems to be dominated by the N'(1535) resonance production. Moreover the measurement of the 7/production in nucleusnucleus co]]Lsions has been indicated as a tool for studing the Equation of State in compressed nuclear matter and it is a necessary datum to understanding dilepton production in nuclei. Focusing our attention on the experimental aspects of this research, recently we have undertaken a program aiming to study the production of the meson on nucleons and nuclei by protons at Saturne. The ~ mesons are identified by PINOT, a neutral meson spectrometer which detects in coincidence the two 7 rays coming from the ~ --, ~ decay (BR 39%) and measures, for each, the energy and the direction. Starting from these quantities it is possible to reconstruct the 77 invar~nt mass spectrum, in which the q are recognised, and to determine their kinetic energy and production ansle [3]. Until now we have measured the doubly d~erential cross section d=cr/dt3dT for the ~ production in the following cases: a) as a function of A at 1 GeV and 900 MeV, detecting ~ mesons in the kinematical ranges 30 < Tn < 100 MeV and 0° ~ 8n ~ 40°; b) as a function of the projectile energy on a Carbon target, for ~ mesons in the same kinematical ranges as at point (a); c) as a function of the ~ kinetic energy on a Boron target and at ~xed beam energy (1 GeV), for ~ produced in the angular region 0 ° ~ 0n ~ 200 and in the complete klnematical range 0 ~ T,~ ~ 430 MeV, where the upper limit is given from the two-body reaction p + l l B --* ~+12C. The results are shown in figures 1, 2, 3 and 4 (open circles). In the same figures the close squares show
T. = 1 0 0 0 MeV II O 01
.P
16=
o) I,
I
II
''''I
,
I0
.
.,.,,.I
102
Figure 1: Doubly differential crou section at Tp=l GeV.
the results of calculation= performed by the Oiessen group [4] induding the ~ reabtozbtion in the target [5]. The model takes into ~count two production mechanisms, a primary one via the N N --. N~'~ interaction and a secondary one v ~ the f N -.-, UN process, the plon coming from a previous N N interactlon. Baaing a subthreshold production, the nuo cleon= Fermi motion plays an important role. The distribution is calculated in the mean field limit (Hartee-Foch method) neglecting the high momanturn tail. Evidently an essential input for the theoretical prevision is the knowledge of the pp ---, cross section; in the figure 5 we present our preliminary results for the o ' ~ . ~ , I total cross section at Tp=l.3 aad 1.5 OeV, which are in good ab~eement whit a parametrkation performed by De Paoli et al. [6]. In figure 5 the calculation= by Laget et al. [7] and Vetter et el. [8] are also presented. The ratio bewteen pn --. pn~ and pp -* ppr/moss sections has been chosen equal to 8, according to our preliminary data [9].
101
E. Chiavassa et ol.
102 1
~0.28
T, = 900 MeV
~0.24
:-El Prelimlnory doto ...
__
0.2
-. ....
Loget De Pvoli Vetter , / ° . . . . . °" - - - , .
0.16 0.12
~o
0.08
b) ,
, I,IHII
0.04 0
,
~0
I02
~ J
e
..-"
,..
I.."
1.2
1.6
Figure 2: Doubly differential cross section at Tp=900 MeV. 1
p C --> ~ X
2 T.(GeV)
A
Figure 5: Total cross section pp --, ppr/. This study will be continued in the near future by measuring the pp and pd (for the pn) reactions at energies between 1.5 and 2 GeV; we will also extend the measurements on nuclei at energies above the nucleon-nucleon ~zee threshold.
~
References
-2
10 !
O
[1] J.F.Germond and C.WgH-,
I°~
c) I,,,,W
. . . .
1000
750
I
. . . .
1250
I , ,
1500
T, O~ev) Figure 3: Doubly differential cross section versus proton energy on Carbon target. p B --)' W X T,,,, 1 GeV, "3,~< 20"
: •0.5
[2] E.Chlavassa et aL, Nucl. Phys. A538, 121c
(1992).
[3] E.Chiavassa et al,, Z. Phys. AS42, 107 (1992). [4] W.Cassing et al., Z. Phys. A340, 51 (1991). [5] E.VerceUin e~ ai., submitted for publication on Nuovo Cimento.
[6] A.De Paoli et al., Phys. Left. B219, 194
0989).
<>
"~ 0.4
Nucl. Phys.
Aslg, 30s (199o).
[7] J.M.Laget et al., Phys. Lett. B257, 254 (1991).
-0-
[8] T.Vetter et al., Phys. Lett. B263, 153 (1991).
o.3 ¢-W 0.2
u 0.1
[9] E.Chiavassa et aL, to be published on the Proceedings of "Sixi~mes Journe~ de Saturne", Mont St.Odile, may, 18-23, 1992.
-W-o~)
b 0
,,-'~7", ,--~.' , 200 ~00
T, (,J, ev) Figure 4: ~ kinetic energy distribution for mesons produced with 8, < 200 in p l l B -~ ~TX reaction at Yp=l GeV.