A method of measuring the close to threshold meson production in
neutron-neutron collisions is described where the momenta of the colliding
neutrons can be determined with the accuracy obtainable for the proton-proton
reaction. The technique is based on the double quasi-free nn --> nn X^0
reaction, where deuterons are used as a source of neutronsComment: 6 pages, 2 figures, to be published in Phys. Lett. 

A Budzanowski

A Khoukaz

A Strzałkowski

Bachman

Balestra

Balewski

Bergdolt

Bilger

Bondar

Brauksiepe

Büscher

C Kolf

C Quentmeier

Calén

Chiavassa

D Grzonka

Daehnick

Drochner

Duncan

G Schepers

H.-H Adam

Hahn

Hardie

Hibou

Hutcheon

J Smyrski

K Kilian

Korkmaz

L Jarczy

M Siemaszko

M Wolke

Machleidt

Machner

Meyer

Moskal

N Lang

P Kowina

P Moskal

P Winter

P Wüstner

Prasuhn

R Santo

S Steltenkamp

Sewerin

Smyrski

T Götz

T Lister

T Sefzick

Tippens

W Oelert

W Zipper

Wilkin

Physics Letters B

English

arXiv

AbstractA method of measuring the close to threshold meson production in neutron–neutron collisions is described where the momenta of the colliding neutrons can be determined with the accuracy obtainable for the proton–proton reaction. The technique is based on the double quasi-free nn→nnX0 reaction, where deuterons are used as a source of neutrons

Moskal, P

Adam, H.-H

Budzanowski, A

Götz, T

Grzonka, D

Jarczy, L

Khoukaz, A

Kilian, K

Kolf, C

Kowina, P

Lang, N

Lister, T

Oelert, W

Quentmeier, C

Santo, R

Schepers, G

Sefzick, T

Siemaszko, M

Smyrski, J

Steltenkamp, S

Strzałkowski, A

Winter, P

Wolke, M

Wüstner, P

Zipper, W

Elsevier - Publisher Connector 

4 October 2001
Physics Letters B 517 (2001) 295–298
www.elsevier.com/locate/npe
On the close to threshold meson production
in neutron–neutron collisions
P. Moskal a,b, H.-H. Adam c, A. Budzanowski d, T. Götz b, D. Grzonka b, L. Jarczy a,
A. Khoukaz c, K. Kilian b, C. Kolf b, P. Kowina b,e, N. Lang c, T. Lister c, W. Oelert b,
C. Quentmeier c, R. Santo c, G. Schepers b, T. Sefzick b, M. Siemaszko e, J. Smyrski a,
S. Steltenkamp c, A. Strzałkowski a, P. Winter b, M. Wolke b, P. Wüstner f, W. Zipper e
a Institute of Physics, Jagellonian University, Cracow, Poland
b Institut für Kernphysik, Forschungszentrum Jülich, Germany
c Institut für Kernphysik, Westfälische Wilhelms–Universität, Münster, Germany
d Institute of Nuclear Physics, Cracow, Poland
e Institute of Physics, University of Silesia, Katowice, Poland
f Zentrallabor für Elektronik, Forschungszentrum Jülich, Germany
Received 6 July 2001; accepted 1 August 2001
Editor: L. Montanet
Abstract
A method of measuring the close to threshold meson production in neutron–neutron collisions is described where the
momenta of the colliding neutrons can be determined with the accuracy obtainable for the proton–proton reaction. The technique
is based on the double quasi-free nn→ nnX0 reaction, where deuterons are used as a source of neutrons.
 2001 Elsevier Science B.V.
PACS: 13.60.Le; 13.75.-ni; 13.75.Cs
In the last decade close to threshold production
of mesons has attracted a lot of experimental and
theoretical effort (see, for instance, [1,2]). Experi-
ments performed at the accelerators CELSIUS [3–7],
COSY [8–15], IUCF [16–19], SATURNE [20–25],
and TRIUMF [26–31] delivered precise data on the
pseudoscalar (π,η,η′,K) and vector (ω,φ) meson
production in proton–proton and proton–deuteron col-
lisions. A secondary neutron beam with a spread in en-
ergy smaller than 1 MeV focussed onto liquid hydro-
gen targets (∼ 1023 atoms/cm2) permitted also pre-
E-mail address: w.oelert@fz-juelich.de (W. Oelert).
cise investigations of the π meson production in the
neutron–proton reactions [26,27,29].
Close to threshold meson production in proton–
neutron collisions were also investigated by means of
a technique based on a quasi-free scattering of the
proton off the neutron bound in the deuteron. Thin
windowless internal deuterium cluster targets (∼ 1014
atoms/cm2) make a detection of an undisturbed spec-
tator proton and a precise determination of the reacting
neutron momentum — and hence of the excess energy
— possible.
Pioneering experiments of the π0 meson creation
in the proton–neutron reaction with the simultaneous
tagging of the spectator proton resulted in a resolution
0370-2693/01/  2001 Elsevier Science B.V.
PII: S0370-2693(01) 01 01 6- 4
Open access under CC BY license.
Open access under CC BY license.
296 P. Moskal et al. / Physics Letters B 517 (2001) 295–298
Fig. 1. Schematic depiction of the double quasi-free nn→ nnX reaction. During the collisions of deuterons (left hand side of the figure, with
the total momentum (solid arrow) resulting from the sum of the beam momentum (dotted arrow) plus the Fermi momentum (short arrow)) a
double quasi-free neutron–neutron reaction may lead to the creation of mesons (small gray circle). The spectator protons (black circles) leave
the reaction region with their initial momentum plus the Fermi momentum, which they possessed at the moment of the reaction. Neutrons are
plotted as open circles. Due to the large relative momenta between spectators and the outgoing neutrons (∼ 1 GeV/c close to the threshold for
the η meson production) a distortion of the nnX system by the accompanied protons can be neglected.
of the excess energy (σ ) equal to σ = 1.8 MeV [32].
Similar studies including the production of heavier
mesons will be continued at COSY [33,34].
Experimental investigations of the close to thresh-
old production in neutron–neutron collisions, how-
ever, have not yet been carried out. A realisation of
such studies — which are characterised by typical
cross sections of  µb — with high quality neutron
beams bombarding a deuterium target is not feasible
due to the low neutron beam intensities forcing to use
liquid or solid deuterium targets which make the pre-
cise determination of the momentum of the specta-
tor proton impossible. In this contribution a unique
possibility of the precise measurement of the close to
threshold meson production in neutron–neutron colli-
sions is pointed out. The technique is based on the dou-
ble quasi-free interaction of neutrons originating from
colliding deuterons as depicted in Fig. 1. Utilizing this
method, a precision of ∼ 1 MeV can be obtained for
determining the excess energy, since it depends only
on the accuracy of the momentum or angle reconstruc-
tion for the registered spectator protons. At present
cooled deuteron beams — available at the facilities
CELSIUS, COSY, and IUCF — give the possibility of
using this method for the studies of neutron–neutron
scattering. Moreover, the usage of a stored beam cir-
culating through an internal cluster target permits the
study with high luminosities (1031 cm−2 s−1) in spite
of very low target densities.
In the double quasi-free interaction, due to the small
binding energy of the deuteron (EB = 2.2 MeV), the
colliding neutrons may be approximately treated as
free particles in the sense that the matrix element
for quasi-free meson production from bound neutrons
is identical to that for the free nn→ nnX reaction
at the same excess energy available in the nnX
system. The measurements at CELSIUS [5,6] and
TRIUMF [30,31] have proven that the offshellness
of the reacting neutron can be neglected and that
the spectator proton influences the interaction only in
terms of the associated Fermi motion [30].
The registration of both spectator protons will al-
low for a precise determination of the excess energy.
A possible internal target facility based on the COSY-
11 setup [35] is presented in Fig. 2. The energy and
the emission angle of the “slow” spectator can be mea-
sured by an appropriately segmented silicon detector,
whereas the momentum of the “fast” spectator pro-
ton can be analysed by the magnetic spectrometer.
By means of the detection system shown in Fig. 2,
a resolution of the excess energy of 2 MeV can be
achieved for excess energies lower than 30 MeV as
demonstrated in reference [34]. The double quasi-free
nn→ nnX0 reaction can be identified by the reg-
istration of both outgoing neutrons. For example, in
order to measure the production of the η meson, a
four meter distance for the time of flight measurement
would be enough to obtain 8 MeV (FWHM) missing
P. Moskal et al. / Physics Letters B 517 (2001) 295–298 297
Fig. 2. Schematic view of the extended COSY-11 detection setup [35]. Only detectors needed for the measurements of the dd→ nnpsppspX
reactions are shown. D1, D2 denote the drift chambers used for the track reconstruction of the fast spectator proton; S1, S3 and V1, V2 are the
scintillation detectors used as time-of-flight and veto counters, respectively, N1, N2 the neutron detectors, and Si [32] the silicon strip detectors.
mass resolution [34] with a calorimeter segmented by
10 cm ×10 cm and providing a 0.5 ns (σ ) time resolu-
tion, which was obtained in test runs using a scintilla-
tor/lead sandwich type of detector.
The suggested meson production via a double
quasi-free neutron–neutron reaction with precisions
achievable for the proton–proton and proton–neutron
reactions, opens the possibility of studying, for ex-
ample, the charge symmetry breaking by comparing
cross sections for the pp→ ppη and nn→ nnη re-
actions, similarly to investigations performed via the
π -deuteron reactions [36]. The Dalitz-plot analysis
of the nn → nn meson would allow for the study
of the neutron–neutron and neutron–meson [37] scat-
tering lengths, the first being still not well estab-
lished [38] and the second being unknown. In prin-
ciple when studying the meson production in proton–
proton and in proton–neutron collisions one has access
to all possible isospin combinations, which can be de-
rived after the correction for the electromagnetic inter-
action. Exceptionally, close-to-threshold meson pro-
duction via the neutron–neutron scattering represents
a pure T = 1 isospin channel without accompanying
Coulomb interaction and consequently no need for
its correction. Investigations of neutron–neutron scat-
tering allow also for the production of K+K− pairs
in a system with only two charged particles in the
final state (nn→ nnK+K−), simplifying the theo-
retical calculations drastically, which in case of the
pp→ ppK+K− are not feasible due to the difficulty
of treating the electromagnetic forces in the system of
four charged particles [39].
298 P. Moskal et al. / Physics Letters B 517 (2001) 295–298
At present the COSY synchrotron can accelerate
deuterons up to 3.5 GeV/c [40] which, utilizing the
Fermi momentum, allows for the π and η meson
production in the nn→ nnX0 reaction. To investigate
the neutron–neutron interaction with the production of
heavier mesons like ω, η′, or φ, a deuteron beam of
∼ 7 GeV/c would be required.
Acknowledgements
We would like to thank V. Baru, A. Gasparyan,
J. Haidenbauer, Ch. Hanhart, A. Kudriavtsev, and
C. Wilkin for very helpful discussions.
References
[1] C. Wilkin, in: Baryons 98, Proceedings of the 8th International
Conference on the Structure of Baryons, World Scientific,
1999, p. 505, nucl-th/9810047.
[2] H. Machner, J. Haidenbauer, J. Phys. G 25 (1999) R231.
[3] A. Bondar et al., Phys. Lett. B 356 (1995) 8.
[4] H. Calén et al., Phys. Lett. B 366 (1996) 39.
[5] H. Calén et al., Phys. Rev. Lett. 79 (1997) 2642.
[6] H. Calén et al., Phys. Rev. C 58 (1998) 2667.
[7] H. Calén et al., Phys. Lett. B 458 (1999) 190.
[8] J. Smyrski et al., Phys. Lett. B 474 (2000) 182.
[9] P. Moskal et al., Phys. Lett. B 474 (2000) 416.
[10] M. Drochner et al., Nucl. Phys. A 643 (1998) 55.
[11] M. Drochner et al., Phys. Rev. Lett. 77 (1996) 454.
[12] S. Sewerin et al., Phys. Rev. Lett. 83 (1999) 682.
[13] R. Bilger et al., Phys. Lett. B 420 (1998) 217.
[14] J. Balewski et al., Phys. Lett. B 420 (1998) 211.
[15] P. Moskal et al., Phys. Rev. Lett. 80 (1998) 3202.
[16] H.O. Meyer et al., Phys. Rev. Lett. 65 (1990) 2846.
[17] H.O. Meyer et al., Nucl. Phys. A 539 (1992) 633.
[18] J.G. Hardie et al., Phys. Rev. C 56 (1997) 20.
[19] W.W. Daehnick et al., Phys. Lett. B 423 (1998) 213.
[20] A.M. Bergdolt et al., Phys. Rev. D 48 (1993) R2969.
[21] E. Chiavassa et al., Phys. Lett. B 322 (1994) 270.
[22] E. Chiavassa et al., Phys. Lett. B 337 (1994) 192.
[23] F. Hibou et al., Phys. Lett. B 438 (1998) 41.
[24] F. Balestra et al., Phys. Lett. B 491 (2000) 29.
[25] F. Balestra et al., Phys. Rev. C 63 (2001) 024004.
[26] D.A. Hutcheon et al., Phys. Rev. Lett. 64 (1990) 176.
[27] D.A. Hutcheon et al., Nucl. Phys. A 535 (1991) 618.
[28] E. Korkmaz et al., Nucl. Phys. A 535 (1991) 637.
[29] M.G. Bachman et al., Phys. Rev. C 52 (1995) 495.
[30] F. Duncan et al., Phys. Rev. Lett. 80 (1998) 4390.
[31] H. Hahn et al., Phys. Rev. Lett. 82 (1999) 2258.
[32] R. Bilger et al., Nucl. Instrum. Methods A 457 (2001) 64.
[33] M. Büscher et al., COSY Proposals #75 and #94,
http://ikpd15.ikp.kfa-juelich.de:8085/doc/Anke.html.
[34] P. Moskal, T. Johansson et al., COSY Proposal #100,
http://ikpe1101.ikp.kfa-juelich.de/.
[35] S. Brauksiepe et al., Nucl. Instrum. Methods A 376 (1996)
397.
[36] W.B. Tippens et al., Phys. Rev. D 63 (2001) 052001.
[37] A. Kudriavtsev, private communication.
[38] R. Machleidt, I. Slaus, J. Phys. G: Nucl. Part. Phys. 27 (2001)
R69.
[39] Ch. Hanhart, private communication.
[40] D. Prasuhn et al., Nucl. Instrum. Methods A 441 (2000) 167.


On the close to threshold meson production in neutron–neutron collisions 

A method of measuring the close to threshold meson production in neutron-neutron collisions is described where the momenta of the colliding neutrons can be determined with the accuracy obtainable for the proton-proton reaction. The technique is based on the double quasi-free nn → nnX0 reaction, where deuterons are used as a source of neutrons

Moskal, P.

Adam, H. H.

Budzanowski, A.

Gotz, T.

Grzonka, D.

Jarczy, L.

Khoukaz, A.

Kilian, K.

Kolf, C.

Kowina, P.

Lang, N.

Lister, T.

Oelert, W.

Quentmeier, C.

Santo, R.

Schepers, G.

Sefzick, T.

Siemaszko, Marek

Smyrski, J.

Steltenkamp, S.

Strzałkowski, A.

Winter, P.

Wolke, M.

Wüstner, P.

Zipper, Wiktor

Repozytorium Uniwersytetu Śląskiego RE-BUŚ

             Title: On the close to threshold meson production in neutron-neutron collisions  Author: P. Moskal, H.H. Adam, A. Budzanowski, T. Gotz, D. Grzonka, L. Jarczy, Marek Siemaszko, Wiktor Zipper i in.  Citation style: Moskal P., Adam H.H., Budzanowski A., Gotz T., Grzonka D., Jarczy L., Siemaszko Marek, Zipper Wiktor i in. (2001). On the close to threshold meson production in neutron-neutron collisions. "Physics Letters B" (Vol.517, iss. 3-4 (2001), s. 295-298), doi 10.1016/S0370-2693(01)01016-4  4 October 2001Physics Letters B 517 (2001) 295–298www.elsevier.com/locate/npeOn the close to threshold meson productionin neutron–neutron collisionsP. Moskala,b, H.-H. Adamc, A. Budzanowskid, T. Götzb, D. Grzonkab, L. Jarczya,A. Khoukazc, K. Kilian b, C. Kolf b, P. Kowinab,e, N. Langc, T. Listerc, W. Oelertb,C. Quentmeierc, R. Santoc, G. Schepersb, T. Sefzickb, M. Siemaszkoe, J. Smyrskia,S. Steltenkampc, A. Strzałkowskia, P. Winterb, M. Wolkeb, P. Wüstnerf, W. Zipperea Institute of Physics, Jagellonian University, Cracow, Polandb Institut für Kernphysik, Forschungszentrum Jülich, Germanyc Institut für Kernphysik, Westfälische Wilhelms–Universität, Münster, Germanyd Institute of Nuclear Physics, Cracow, Polande Institute of Physics, University of Silesia, Katowice, Polandf Zentrallabor für Elektronik, Forschungszentrum Jülich, GermanyReceived 6 July 2001; accepted 1 August 2001Editor: L. MontanetAbstractA method of measuring the close to threshold meson production in neutron–neutron collisions is described where themomenta of the colliding neutrons can be determined with the accuracy obtainable for the proton–proton reaction. The techniqueis based on the double quasi-freenn → nnX0 reaction, where deuterons are used as a source of neutrons. 2001 ElsevierScience B.V.PACS: 13.60.Le; 13.75.-ni; 13.75.CsIn the last decade close to threshold productionof mesons has attracted a lot of experimental andtheoretical effort (see, for instance, [1,2]). Experi-ments performed at the accelerators CELSIUS [3–7],COSY [8–15], IUCF [16–19], SATURNE [20–25],and TRIUMF [26–31] delivered precise data on thepseudoscalar (π,η,η′,K) and vector (ω,φ) mesonproduction in proton–proton and proton–deuteron col-lisions. A secondary neutron beam with a spread in en-ergy smaller than 1 MeV focussed onto liquid hydro-gen targets (∼ 1023 atoms/cm2) permitted also pre-E-mail address: w.oelert@fz-juelich.de (W. Oelert).cise investigations of theπ meson production in theneutron–proton reactions [26,27,29].Close to threshold meson production in proton–neutron collisions were also investigated by means ofa technique based on a quasi-free scattering of theproton off the neutron bound in the deuteron. Thinwindowless internal deuterium cluster targets (∼ 1014atoms/cm2) make a detection of an undisturbed spec-tator proton and a precise determination of the reactingneutron momentum — and hence of the excess energy— possible.Pioneering experiments of theπ0 meson creationin the proton–neutron reaction with the simultaneoustagging of the spectator proton resulted in a resolution0370-2693/01/ 2001 Elsevier Science B.V.PII: S0370-2693(01)01016-4Open access under CC BY license.Open access under CC BY license.296 P. Moskal et al. / Physics Letters B 517 (2001) 295–298Fig. 1. Schematic depiction of the double quasi-freenn → nnX reaction. During the collisions of deuterons (left hand side of the figure, withthe total momentum (solid arrow) resulting from the sum of the beam momentum (dotted arrow) plus the Fermi momentum (short arrow)) adouble quasi-free neutron–neutron reaction may lead to the creation of mesons (small gray circle). The spectator protons (black circles) leavethe reaction region with their initial momentum plus the Fermi momentum, which they possessed at the moment of the reaction. Neutrons areplotted as open circles. Due to the large relative momenta between spectators and the outgoing neutrons (∼ 1 GeV/c close to the threshold fortheη meson production) a distortion of thennX system by the accompanied protons can be neglected.of the excess energy (σ ) equal toσ = 1.8 MeV [32].Similar studies including the production of heaviermesons will be continued at COSY [33,34].Experimental investigations of the close to thresh-old production in neutron–neutron collisions, how-ever, have not yet been carried out. A realisation ofsuch studies — which are characterised by typicalcross sections of µb — with high quality neutronbeams bombarding a deuterium target is not feasibledue to the low neutron beam intensities forcing to useliquid or solid deuterium targets which make the pre-cise determination of the momentum of the specta-tor proton impossible. In this contribution a uniquepossibility of the precise measurement of the close tothreshold meson production in neutron–neutron colli-sions is pointed out. The technique is based on the dou-ble quasi-free interaction of neutrons originating fromcolliding deuterons as depicted in Fig. 1. Utilizing thismethod, a precision of∼ 1 MeV can be obtained fordetermining the excess energy, since it depends onlyon the accuracy of the momentum or angle reconstruc-tion for the registered spectator protons. At presentcooled deuteron beams — available at the facilitiesCELSIUS, COSY, and IUCF — give the possibility ofusing this method for the studies of neutron–neutronscattering. Moreover, the usage of a stored beam cir-culating through an internal cluster target permits thestudy with high luminosities (1031 cm−2 s−1) in spiteof very low target densities.In the double quasi-free interaction, due to the smallbinding energy of the deuteron (EB = 2.2 MeV), thecolliding neutrons may be approximately treated asfree particles in the sense that the matrix elementfor quasi-free meson production from bound neutronsis identical to that for the freenn → nnX reactionat the same excess energy available in thennXsystem. The measurements at CELSIUS [5,6] andTRIUMF [30,31] have proven that the offshellnessof the reacting neutron can be neglected and thatthe spectator proton influences the interaction only interms of the associated Fermi motion [30].The registration of both spectator protons will al-low for a precise determination of the excess energy.A possible internal target facility based on the COSY-11 setup [35] is presented in Fig. 2. The energy andthe emission angle of the “slow” spectator can be mea-sured by an appropriately segmented silicon detector,whereas the momentum of the “fast” spectator pro-ton can be analysed by the magnetic spectrometer.By means of the detection system shown in Fig. 2,a resolution of the excess energy of 2 MeV can beachieved for excess energies lower than 30 MeV asdemonstrated in reference [34]. The double quasi-freenn → nnX0 reaction can be identified by the reg-istration of both outgoing neutrons. For example, inorder to measure the production of theη meson, afour meter distance for the time of flight measurementwould be enough to obtain 8 MeV (FWHM) missingP. Moskal et al. / Physics Letters B 517 (2001) 295–298 297Fig. 2. Schematic view of the extended COSY-11 detection setup [35]. Only detectors needed for the measurements of thedd → nnpsppspXreactions are shown. D1, D2 denote the drift chambers used for the track reconstruction of the fast spectator proton; S1, S3 and V1, V2 are thescintillation detectors used as time-of-flight and veto counters, respectively, N1, N2 the neutron detectors, and Si [32] the silicon strip detectors.mass resolution [34] with a calorimeter segmented by10 cm×10 cm and providing a 0.5 ns (σ ) time resolu-tion, which was obtained in test runs using a scintilla-tor/lead sandwich type of detector.The suggested meson production via a doublequasi-free neutron–neutron reaction with precisionsachievable for the proton–proton and proton–neutronreactions, opens the possibility of studying, for ex-ample, the charge symmetry breaking by comparingcross sections for thepp → ppη andnn → nnη re-actions, similarly to investigations performed via theπ -deuteron reactions [36]. The Dalitz-plot analysisof the nn → nn meson would allow for the studyof the neutron–neutron and neutron–meson [37] scat-tering lengths, the first being still not well estab-lished [38] and the second being unknown. In prin-ciple when studying the meson production in proton–proton and in proton–neutron collisions one has accessto all possible isospin combinations, which can be de-rived after the correction for the electromagnetic inter-action. Exceptionally, close-to-threshold meson pro-duction via the neutron–neutron scattering representsa pureT = 1 isospin channel without accompanyingCoulomb interaction and consequently no need forits correction. Investigations of neutron–neutron scat-tering allow also for the production ofK+K− pairsin a system with only two charged particles in thefinal state (nn → nnK+K−), simplifying the theo-retical calculations drastically, which in case of thepp → ppK+K− are not feasible due to the difficultyof treating the electromagnetic forces in the system offour charged particles [39].298 P. Moskal et al. / Physics Letters B 517 (2001) 295–298At present the COSY synchrotron can acceleratedeuterons up to 3.5 GeV/c [40] which, utilizing theFermi momentum, allows for theπ and η mesonproduction in thenn → nnX0 reaction. To investigatethe neutron–neutron interaction with the production ofheavier mesons likeω, η′, or φ, a deuteron beam of∼ 7 GeV/c would be required.AcknowledgementsWe would like to thank V. Baru, A. Gasparyan,J. Haidenbauer, Ch. Hanhart, A. Kudriavtsev, andC. Wilkin for very helpful discussions.References[1] C. Wilkin, in: Baryons 98, Proceedings of the 8th InternationalConference on the Structure of Baryons, World Scientific,1999, p. 505, nucl-th/9810047.[2] H. Machner, J. Haidenbauer, J. Phys. G 25 (1999) R231.[3] A. Bondar et al., Phys. Lett. B 356 (1995) 8.[4] H. Calén et al., Phys. Lett. B 366 (1996) 39.[5] H. Calén et al., Phys. Rev. Lett. 79 (1997) 2642.[6] H. Calén et al., Phys. Rev. C 58 (1998) 2667.[7] H. Calén et al., Phys. Lett. B 458 (1999) 190.[8] J. Smyrski et al., Phys. Lett. B 474 (2000) 182.[9] P. Moskal et al., Phys. Lett. B 474 (2000) 416.[10] M. Drochner et al., Nucl. Phys. A 643 (1998) 55.[11] M. Drochner et al., Phys. Rev. Lett. 77 (1996) 454.[12] S. Sewerin et al., Phys. Rev. Lett. 83 (1999) 682.[13] R. Bilger et al., Phys. Lett. B 420 (1998) 217.[14] J. Balewski et al., Phys. Lett. B 420 (1998) 211.[15] P. Moskal et al., Phys. Rev. Lett. 80 (1998) 3202.[16] H.O. Meyer et al., Phys. Rev. Lett. 65 (1990) 2846.[17] H.O. Meyer et al., Nucl. Phys. A 539 (1992) 633.[18] J.G. Hardie et al., Phys. Rev. C 56 (1997) 20.[19] W.W. Daehnick et al., Phys. Lett. B 423 (1998) 213.[20] A.M. Bergdolt et al., Phys. Rev. D 48 (1993) R2969.[21] E. Chiavassa et al., Phys. Lett. B 322 (1994) 270.[22] E. Chiavassa et al., Phys. Lett. B 337 (1994) 192.[23] F. Hibou et al., Phys. Lett. B 438 (1998) 41.[24] F. Balestra et al., Phys. Lett. B 491 (2000) 29.[25] F. Balestra et al., Phys. Rev. C 63 (2001) 024004.[26] D.A. Hutcheon et al., Phys. Rev. Lett. 64 (1990) 176.[27] D.A. Hutcheon et al., Nucl. Phys. A 535 (1991) 618.[28] E. Korkmaz et al., Nucl. Phys. A 535 (1991) 637.[29] M.G. Bachman et al., Phys. Rev. C 52 (1995) 495.[30] F. Duncan et al., Phys. Rev. Lett. 80 (1998) 4390.[31] H. Hahn et al., Phys. Rev. Lett. 82 (1999) 2258.[32] R. Bilger et al., Nucl. Instrum. Methods A 457 (2001) 64.[33] M. Büscher et al., COSY Proposals #75 and #94,http://ikpd15.ikp.kfa-juelich.de:8085/doc/Anke.html.[34] P. Moskal, T. Johansson et al., COSY Proposal #100,http://ikpe1101.ikp.kfa-juelich.de/.[35] S. Brauksiepe et al., Nucl. Instrum. Methods A 376 (1996)397.[36] W.B. Tippens et al., Phys. Rev. D 63 (2001) 052001.[37] A. Kudriavtsev, private communication.[38] R. Machleidt, I. Slaus, J. Phys. G: Nucl. Part. Phys. 27 (2001)R69.[39] Ch. Hanhart, private communication.[40] D. Prasuhn et al., Nucl. Instrum. Methods A 441 (2000) 167.

On the close to threshold meson production in neutron-neutron collisions

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On the close to threshold meson production in neutron–neutron collisions

A method of measuring the close to threshold meson production in neutron-neutron collisions is described where the momenta of the colliding neutrons can be determined with the accuracy obtainable for the proton-proton reaction. The technique is based on the double quasi-free nn --> nnX(0) reaction, where deuterons are used as a source of neutrons. (C) 2001 Elsevier Science B.V. All rights reserved

Adam, H.-H.

Sefzick, N. Y.

Siemaszko, M.

Steltenkamp, A. L.

Strzalkowski, A.

Zipper, W.

Götz, T.

Jarczyk, L.

Juelich Shared Electronic Resources

arXiv:nucl-ex/0108005v1  3 Aug 2001On the close to threshold meson productionin neutron-neutron collisionsP. Moskal1,2, H.-H. Adam3, A. Budzanowski4, T. Go¨tz2, D. Grzonka2, L. Jarczyk1,A. Khoukaz3, K. Kilian2, C. Kolf2, P. Kowina2,5, N. Lang3, T. Lister3, W. Oelert2,C. Quentmeier3, R. Santo3, G. Schepers2, T. Sefzick2, M. Siemaszko5, J. Smyrski1,S. Steltenkamp3, A. Strza lkowski1, P. Winter2, M. Wolke2, P. Wu¨stner6, W. Zipper51 Institute of Physics, Jagellonian University, Cracow, Poland2 Institut fu¨r Kernphysik, Forschungszentrum Ju¨lich, Germany3 Institut fu¨r Kernphysik, Westfa¨lische Wilhelms–Universita¨t, Mu¨nster, Germany4 Institute of Nuclear Physics, Cracow, Poland5 Institute of Physics, University of Silesia, Katowice, Poland6 Zentrallabor fu¨r Elektronik, Forschungszentrum Ju¨lich, Germany(December 16, 2013)AbstractA method of measuring the close to threshold meson production in neutron-neutron collisions is described where the momenta of the colliding neutronscan be determined with the accuracy obtainable for the proton-proton reac-tion. The technique is based on the double quasi-free nn → nnX0 reaction,where deuterons are used as a source of neutrons.PACS: 13.60.Le, 13.75.-ni, 13.75.CsTypeset using REVTEX1In the last decade close to threshold production of mesons has attracted a lot of experi-mental and theoretical effort (see for instance [1,2]). Experiments performed at the accelera-tors CELSIUS [3–7], COSY [8–15], IUCF [16–19], SATURNE [20–25], and TRIUMF [26–31]delivered precise data on the pseudoscalar (pi,η,η′,K) and vector (ω,φ) meson productionin proton-proton and proton-deuteron collisions. A secondary neutron beam with a spreadin energy smaller than 1 MeV focussed onto liquid hydrogen targets (∼ 1023 atoms/cm2)permitted also precise investigations of the pi meson production in the neutron-proton reac-tions [26,27,29].Close to threshold meson production in proton-neutron collisions were also investigatedby means of a technique based on a quasi-free scattering of the proton off the neutron boundin the deuteron. Thin windowless internal deuterium cluster targets (∼ 1014 atoms/cm2)make a detection of an undisturbed spectator proton and a precise determination of thereacting neutron momentum – and hence of the excess energy – possible.Pioneering experiments of the pi0 meson creation in the proton-neutron reaction with thesimultaneous tagging of the spectator proton resulted in a resolution of the excess energy(σ) equal to σ = 1.8 MeV [32]. Similar studies including the production of heavier mesonswill be continued at COSY [33,34].Experimental investigations of the close to threshold production in neutron-neutron col-lisions, however, have not yet been carried out. A realisation of such studies – which arecharacterised by typical cross sections of ≤ µb – with high quality neutron beams bombard-ing a deuterium target is not feasible due to the low neutron beam intensities forcing to useliquid or solid deuterium targets which make the precise determination of the momentum ofthe spectator proton impossible. In this contribution a unique possibility of the precise mea-surement of the close to threshold meson production in neutron-neutron collisions is pointedout. The technique is based on the double quasi-free interaction of neutrons originating fromcolliding deuterons as depicted in Figure 1. Utilizing this method, a precision of ∼1 MeVcan be obtained for determining the excess energy, since it depends only on the accuracyof the momentum or angle reconstruction for the registered spectator protons. At presentcooled deuteron beams – available at the facilities CELSIUS, COSY, and IUCF – give thepossibility of using this method for the studies of neutron-neutron scattering. Moreover, theusage of a stored beam circulating through an internal cluster target permits the study withhigh luminosities ( 1031cm−2s−1) in spite of very low target densities.In the double quasi-free interaction, due to the small binding energy of thedeuteron (EB = 2.2 MeV), the colliding neutrons may be approximately treated as freeparticles in the sense that the matrix element for quasi-free meson production from boundneutrons is identical to that for the free nn→ NNX reaction at the same excess energy avail-able in the NNX system. The measurements at CELSIUS [5,6] and TRIUMF [30,31] haveproven that the offshellness of the reacting neutron can be neglected and that the spectatorproton influences the interaction only in terms of the associated Fermi motion [30].The registration of both spectator protons will allow for a precise determination of the ex-cess energy. A possible internal target facility based on the COSY-11 setup [35] is presentedin Figure 2. The energy and the emission angle of the ”slow” spectator can be measuredby an appropriately segmented silicon detector, whereas the momentum of the ”fast” spec-tator proton can be analysed by the magnetic spectrometer. By means of the detection2system shown in Figure 2, a resolution of the excess energy of 2 MeV can be achieved forexcess energies lower than 30 MeV as demonstrated in reference [34]. The double quasi-free nn → nnX0 reaction can be identified by the registration of both outgoing neutrons.For example, in order to measure the production of the η meson, a four meter distance forthe time of flight measurement would be enough to obtain 8 MeV (FWHM) missing massresolution [34] with a calorimeter segmented by 10 cm ∗ 10 cm and providing a 0.5 ns (σ)time resolution, which was obtained in test runs using a scintillator/lead sandwich type ofdetector.The suggested meson production via a double quasi-free neutron–neutron reaction withprecisions achievable for the proton-proton and proton-neutron reactions, opens the possi-bility of studying for example the charge symmetry breaking by comparing cross sectionsfor the pp → ppη and nn → nnη reactions, similarly to investigations performed via thepi-deuteron reactions [36]. The Dalitz-plot analysis of the nn → nn Meson would allow forthe study of the neutron-neutron and neutron-Meson [37] scattering lengths, the first beingstill not well established [38] and the second being unknown. In principle when studyingthe meson production in proton-proton and in proton-neutron collisions one has access toall possible isospin combinations, which can be derived after the correction for the electro-magnetic interaction. Exceptionally, close-to-threshold meson production via the neutron-neutron scattering represents a pure T = 1 isospin channel without accompanying coulombinteraction and consequently no need for its correction. Investigations of neutron-neutronscattering allow also for the production of K+K− pairs in a system with only two chargedparticles in the final state (nn → nnK+K−), simplifying the theoretical calculations dras-tically, which in case of the pp→ ppK+K− are not feasible due to the difficulty of treatingthe electromagnetic forces in the system of four charged particles [39].At present the COSY synchrotron can accelerate deuterons up to 3.5 GeV/c [40] which,utilizing the Fermi momentum, allows for the pi and η meson production in the nn→ nnX0reaction. To investigate the neutron-neutron interaction with the production of heaviermesons like ω, η′, or φ, a deuteron beam of ∼ 7 GeV/c would be required.We would like to thank V. Baru, A. Gasparyan, J. Haidenbauer, Ch. Hanhart, A. Ku-driavtsev, and C. Wilkin for very helpful discussions.3REFERENCES[1] C. Wilkin, Proceedings of the 8th International Conference on the Structure of Baryons(Baryons 98), World Scientific (1999) 505, e-Print Archive: nucl-th/9810047[2] H. Machner, J. Haidenbauer, J. Phys. G 25, R231 (1999).[3] A. Bondar et al., Phys. Lett. B 356, 8 (1995).[4] H. Cale´n et al., Phys. Lett. B 366, 39 (1996).[5] H. Cale´n et al., Phys. Rev. Lett. 79, 2642 (1997).[6] H. Cale´n et al., Phys. Rev. C 58, 2667 (1998).[7] H. Cale´n et al., Phys. Lett. B 458, 190 (1999).[8] J. Smyrski et al., Phys. Lett. B 474, 182 (2000).[9] P. Moskal et al., Phys. Lett. B 474, 416 (2000).[10] M. Drochner et al., Nucl. Phys. A 643, 55 (1998).[11] M. Drochner et al., Phys. Rev. Lett. 77, 454 (1996).[12] S. Sewerin et al., Phys. Rev. Lett. 83, 682 (1999).[13] R. Bilger et al., Phys. Lett. B 420, 217 (1998).[14] J. Balewski et al., Phys. Lett. B 420, 211 (1998).[15] P. Moskal et al., Phys. Rev. Lett. 80, 3202 (1998).[16] H. O. Meyer et al., Phys. Rev. Lett. 65, 2846 (1990).[17] H. O. Meyer et al., Nucl. Phys. A 539, 633 (1992).[18] J.G. Hardie et al., Phys. Rev. C 56, 20 (1997).[19] W.W. Daehnick et al., Phys. Lett. B 423, 213 (1998).[20] A. M. Bergdolt et al., Phys. Rev. D 48, R2969 (1993).[21] E. Chiavassa et al., Phys. Lett. B 322, 270 (1994).[22] E. Chiavassa et al., Phys. Lett. B 337, 192 (1994).[23] F. Hibou et al., Phys. Lett. B 438, 41 (1998).[24] F. Balestra et al., Phys. Lett. B 491, 29 (2000).[25] F. Balestra et al., Phys. Rev. C 63, 024004 (2001).[26] D. A. Hutcheon et al., Phys. Rev. Lett. 64, 176 (1990).[27] D. A. Hutcheon et al., Nucl. Phys. A 535, 618 (1991).[28] E. Korkmaz et al., Nucl. Phys. A 535, 637 (1991).[29] M. G. Bachman et al., Phys. Rev. C 52, 495 (1995).[30] F. Duncan et al., Phys. Rev. Lett. 80, 4390 (1998).[31] H. Hahn et al., Phys. Rev. Lett. 82, 2258 (1999).[32] R. Bilger et al., Nucl. Instr. & Meth. A 457, 64 (2001).[33] M. Bu¨scher et al., COSY Proposals#75 and #94,http://ikpd15.ikp.kfa-juelich.de:8085/doc/Anke.html[34] P. Moskal, T. Johansson et al., COSY Proposal#100,http://ikpe1101.ikp.kfa-juelich.de/[35] S. Brauksiepe et al., Nucl. Instr. & Meth. A 376, 397 (1996).[36] W. B. Tippens et al., Phys. Rev. D 63, 052001 (2001).[37] A. Kudriavtsev, private communication[38] R. Machleidt, I. Slaus, J. Phys. G: Nucl. Part. Phys. 27, R69 (2001).[39] Ch. Hanhart, private communication[40] D. Prasuhn et al., Nucl. Instr. & Meth. A 441, 167 (2000).4FIGURESafter the reactionreaction productsbefore the reactionbeam-deuterontarget-deuteronFIG. 1. Schematic depiction of the double quasi-free nn→ nnX reaction. During the collisionsof deuterons (left hand side of the figure, with the total momentum (solid arrow) resulting fromthe sum of the beam momentum (dotted arrow) plus the Fermi momentum (short arrow)) a doublequasi-free neutron-neutron reaction may lead to the creation of mesons (small gray circle). Thespectator protons (black circles) leave the reaction region with their initial momentum plus theFermi momentum, which they possessed at the moment of the reaction. Neutrons are plotted asopen circles. Due to the large relative momenta between spectators and the outgoing neutrons(∼ 1 GeV/c close to the threshold for the η meson production) a distortion of the nnX system bythe accompanied protons can be neglected.5DIPOLBEAMCLUSTER TARGETprotonBEXIT WINDOWD1D2S1S3VACUUM CHAMBERneutronsprotonSiN1V1N2V2~1 meterFIG. 2. Schematic view of the extended COSY-11 detection setup [35]. Only detectors neededfor the measurements of the dd→ nnpsppspX reactions are shown.D1,D2 denote the drift chambers used for the track reconstruction of the fast spectator proton;S1,S3 and V1,V2 are the scintillation detectors used as time-of-flight and veto counters, respectively,N1,N2 the neutron detectors, and Si [32] the silicon strip detectors.6

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On the close to threshold meson production in neutron-neutron collisions

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