According to the quark model, the masses of eta and eta' mesons should be
almost equal. However, the empirical values of these masses differ by more than
the factor of two. Similarly, though the almost the same quark-antiquark
content, the total cross section for the creation of these mesons close to the
kinematical thresholds in the pp --> ppX reaction differs significantly. Using
the COSY-11 detection setup we intend to determine whether this difference will
also be so significant in the case of the production of these mesons in the
proton-neutron scattering. Additionally, the comparison of the pp --> pp eta'
and pn --> pn eta' total cross sections will allow to learn about the
production of the eta' meson in the channels of isospin I = 0 and I = 1 and to
investigate aspects of the gluonium component of the eta' meson.Comment: Presented at LEAP05: International conference on Low Energy
  Antiproton Physics, Bonn - Juelich, Germany, May 16-22, 200

Adam, H. -H.

Budzanowski, A.

Czyzykiewicz, R.

Grzonka, D.

Janusz, M.

Jarczyk, L.

Kamys, B.

Khoukaz, A.

Kilian, K.

Klaja, P.

Moskal, P.

Oelert, W.

Piskor-Ignatowicz, C.

Przerwa, J.

Ritman, J.

Rozek, T.

Sefzick, T.

Siemaszko, M.

Smyrski, J.

Taeschner, A.

Wessels, J.

Winter, P.

Wolke, M.

Wuestner, P.

Zipper, W.

English

arXiv

J. Przerwa

Crossref

Isospin Dependence of the ηʹ Meson Production in Nucleon-Nucleon Collisions

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November 20, 2018 11:1 WSPC/INSTRUCTION FILE przerwa˙meson08
International Journal of Modern Physics A
c© World Scientific Publishing Company
ISOSPIN DEPENDENCE OF THE η′ MESON PRODUCTION IN
NUCLEON-NUCLEON COLLISIONS
J. Przerwa⋆,∗, P. Moskal⋆,$, A. Budzanowski#, E. Czerwiński⋆,$, R. Czyżykiewicz⋆, D. Gil⋆,
D. Grzonka$, L. Jarczyk⋆, T. Johansson@, B. Kamys⋆, A. Khoukaz%, P. Klaja⋆,
W. Krzemień⋆,$, W. Oelert$, C. Piskor-Ignatowicz⋆ , J. Ritman$, B. Rejdych⋆, T. Sefzick$,
M. Siemaszko&, M. Silarski⋆, J. Smyrski⋆, A. Täschner%, M. Wolke$, P. Wüstner$, J. Zdebik⋆,
M. J. Zieliński⋆, W. Zipper&
⋆Institute of Physics, Jagellonian University, Cracow, Poland
$IKP and ZEL, Forschungszentrum Jülich,Jülich, Germany
#Institute of Nuclear Physics, Cracow, Poland
@Department of Physics and Astronomy, Uppsala University, Sweden
%IKP, Westfälische Wilhelms-Universität, Münster, Germany
&Institute of Physics, University of Silesia, Katowice, Poland
A comparison of the close–to–threshold total cross section for the η′ production in
pp → ppη′ and pn → pnη′ reactions constitutes a tool to investigate the η′ me-
son structure and the reaction mechanism in the channels of isospin I = 0 and I = 1 and
may provide insight into the flavour-singlet (perhaps also into gluonium) content of the
η
′ meson.
In this contribution we present preliminary results of measurement of the quasi-free pro-
duction of the η′ meson in the proton-neutron collisions conducted using the COSY-11
facility.
Keywords: near threshold meson production; quasi-free reaction
1. Introduction
In the framework of the quark model the η′ meson is predominantly a flavour-
singlet combination of quark-antiquark pairs, and it is expected to mix with purely
gluonic states. Therefore, additionally to the production mechanisms associated
with meson exchange1,2 it is also possible that η′ meson is produced from excited
glue in the interaction region of the colliding nucleons, which couple to the η′ meson
directly via its gluonic component or through its SU(3)-flavour-singlet admixture3.
As suggested in reference4, the η′ meson production via the colour-singlet object
does not depend on the total isospin of the colliding nucleons and should lead to
the same amplitudes of the production for the pn → pnη′ and pp → ppη′ reactions.
In case of the η meson, the ratio of the total cross sections for the reactions pn → pnη
and pp → ppη was determined to be Rη ≈ 6.5
5, and Rη ≈ 3 at threshold
6, what
suggest the dominance of isovector meson exchange in the η production in nucleon-
∗E-mail address: j.przerwa@fz-juelich.de
1
November 20, 2018 11:1 WSPC/INSTRUCTION FILE przerwa˙meson08
2 J. Przerwa et al. – COSY–11 Collaboration
nucleon collisions. Since the quark structure of η and η′ mesons is similar, in case of
the dominant isovector meson exchange – by the analogy to the η meson production
– we can expect that the ratio Rη′ should be large. If however η
′ meson is produced
via its flavour-blind gluonium component from the colour-singlet glue excited in
the interaction region the ratio should approach unity after corrections for the
initial and final state interactions. The close–to–threshold excitation function for
the pp → ppη′ reaction has already been established7 and the determination of the
total cross section for the η′ meson production in the proton-neutron interaction
constitutes the aim of the work reported in this contribution.
2. Experiment
In August 2004 using the COSY–11 facility8 we have conducted a measurement of
the η′ meson production in the proton-neutron collision. The experiment has been
realized using a proton beam of the cooler synchrotron COSY 9 and a cluster jet
deuteron target 10. Proton and neutron outgoing from the pn → pnη reaction have
been registered by means of the COSY-11 facility. For the data analysis the pro-
ton from the deuteron is considered as a spectator which does not interact with the
bombarding proton, but escapes untouched and hits the detector carrying the Fermi
momentum possessed exactly at the time of the reaction. The experiment is based
on the registration of all outgoing nucleons from the pd → psppnX reaction
6. Fast
protons are measured in two drift chambers and scintillator detectors 8, neutrons
are registered in the neutral particle detector 11, and slow spectator protons mov-
ing upwords to the beam are measured by the dedicated silicon-pad detector 12.
Fig. 1(left) shows energy losses in the 1st layer of the spectator detector versus 2nd
layer. Slow spectator protons are stopped in the first or second layer of the detector
whereas fast particles cross both detection layers. Having the deposited energy and
the emission angle we calculate the kinetic energy of the spectator proton and its
momentum. Fig. 1(right) shows momentum distribution of protons considered as a
spectator as determined at COSY-11 with a deuteron target and a proton beam with
momentum of 3.35 GeV/c (points) compared with simulations taking into account
a Fermi motion of nucleons inside the deuteron (solid line).
Application of the missing mass technique allows to identify events with the
creation of the meson under investigation. The total energy available for the quasi-
free proton-neutron reaction can be calculated for each event from the vector of the
momenta of the spectator and beam protons. The absolute momentum of neutrons
is determined from the time-of-flight between the target and the neutron detector.
Fig.2(left) presents the time-of-flight distribution – for neutral particles – measured
between the target and the neutral particle detector. A clear signal originating from
the gamma rays is seen over a broad enhancement from neutrons. This histogram
shows that discrimination between signals originating from neutrons and gamma
quanta can be done by a cut on the time of flight. From the Monte Carlo simulations
of the pn → pnη′ reaction the largest expected momentum value of the neutron is
November 20, 2018 11:1 WSPC/INSTRUCTION FILE przerwa˙meson08
J. Przerwa et al. – COSY–11 Collaboration 3
eqaul to 1.4 GeV/c which corresponds to the time–of-flight value of 28.5 ns as it
is indicated by an arrow in Fig. 2(left). Neutrons having time–of–flight below this
value originate from pn → pn pions reactions and are not taken for the further
analysis.
0
1
2
3
4
5
6
7
8
9
10
0 1 2 3 4 5 6 7 8 9 10
energy loss in 2nd layer [MeV]
en
er
gy
 lo
ss
 in
 1
st
 la
ye
r 
[M
eV
]
0
1000
2000
3000
4000
5000
0 0.02 0.04 0.06 0.08 0.1 0.12 0.14
PF [GeV / c ]
Fig. 1. Left: Energy losses in the first layer versus the second layer as measured at COSY–11
with a deuteron target and a proton beam with momentum of 3.35 GeV/c. Right: Momentum
distribution of the proton spectator as reconstructed in the experiment (points) in comparison
with simulation taking into account Fermi momentum distribution of nucleons inside the deuteron
(solid histogram).
0
200
400
600
800
1000
1200
x 10 2
10 20 30 40 50 60
time of flight [ ns ]
co
un
ts
1
10
10 2
10 3
0 10 20 30 40 50 60
Q [ MeV ]
σ 
[ n
b 
]
PR
EL
IMI
NA
RY
Fig. 2. Left: Time–of–flight distribution between the target and the neutron detector as obtained
after the time walk correction under condition that in coincidence with neutral particle also two
charged particles were identified. Right: Total cross sections for the pp → ppη′ reaction as a
function of the excess energy (open symbols). Upper limit for the total cross section for the
pn → pnη′ reaction as a function of the excess energy (closed symbols).
Due to the smaller efficiency and lower resolution for the registration of the
November 20, 2018 11:1 WSPC/INSTRUCTION FILE przerwa˙meson08
4 J. Przerwa et al. – COSY–11 Collaboration
quasi-free pn → pn meson reaction in comparison to the measurements of the
proton-proton reactions, the elaboration of the data encounters problems of low
statistics. Therefore, the excess energy range for Q ≥ 0 has been divided only into
four intervals of 8 MeV width. For each interval we have calculated the missing mass.
Next, from events with negative Q value the corresponding background missing
mass spectrum was constructed, shifted to the kinematical limit and normalized
to the experimental distribution at the very low mass values where no events from
the η′ are expected. Detailed description of the method used for the background
subtraction can be found in the dedicated article13. After subtracting missing mass
distributions for the negative values of Q from spectra for Q values larger than 0 –
due to the very high signal–to-background ratio – at the present stage of the data
analysis, the signal from the η′ meson was found to be statistically insignificant.
Nevertheless, having the luminosity – established from the number of the quasi-
free proton-proton elastic scattering events 14 – and the detection efficiency of the
COSY-11 system we have estimated the upper limit of the total cross section for
the quasi-free pn → pnη′ reaction. The prelimnary result is shown in Fig. 2(right).
3. Acknowledgments
We acknowledge the support by the European Community under the FP6 pro-
gramme (Hadron Physics, RII3-CT-2004-506078), by the Polish Ministry of Science
and Higher Education under grants No. 3240/H03/2006/31, 1202/DFG/2007/03,
0082/B/H03/2008/34, and by the German Research Foundation (DFG).
References
1. K. Nakayama et al., Phys. Rev. C 61, 024001 (2000).
2. L. P. Kaptari, B. Kämpfer, e-Print: arXiv:0804.2019.
3. S. D. Bass, Phys. Scripta T 99, 96 (2002).
4. S. D. Bass, Phys. Lett. B 463, 286 (1999).
5. H. Calen et al., Phys. Rev. C 58, 2667 (1998).
6. P. Moskal et al., e-Print: arXiv:0807.0722 (2008).
7. P. Moskal et al., Phys. Lett. B 474, 416 (2000);
A. Khoukaz et al., Eur. Phys. J. A 20, 345 (2004);
F. Balestra et al., Phys. Lett. B 491, 29 (2000);
P. Moskal et al., Phys. Rev. Lett. 80, 3202 (1998).
8. S. Brauksiepe et al., Nucl. Instr. & Meth. A 376, 397 (1996);
P. Klaja et al., AIP Conf. Proc. 796, 160 (2005);
J. Smyrski et al., Nucl. Instr. & Meth. A 541, 574 (2005).
9. D. Prasuhn et al., Nucl. Instr. & Meth. A 441, 167 (2000).
10. H. Dombrowski et al., Nucl. Instr. & Meth. A 386, 228 (1997).
11. J. Przerwa et al., Int. J. of Mod. Phys. A 20, 625 (2005).
12. R. Bilger et al., Nucl. Instr. & Meth. A 457, 64 (2001).
13. P. Moskal et al., J. Phys. G 32, 629 (2006).
14. P. Moskal, R. Czyżykiewicz, AIP Conf. Proc. 950, 118 (2007).


According to the quark model, the masses of eta and eta' mesons should be almost equal. However, the empirical values of these masses differ by more than the factor of two. Similarly, though the almost the same quark-antiquark content, the total cross section for the creation of these mesons close to the kinematical thresholds in the pp --> ppX reaction differs significantly. Using the COSY-11 detection setup we intend to determine whether this difference will also be so significant in the case of the production of these mesons in the proton-neutron scattering. Additionally, the comparison of the pp --> pp eta' and pn --> pn eta' total cross sections will allow to learn about the production of the eta' meson in the channels of isospin I = 0 and I = 1 and to investigate aspects of the gluonium component of the eta' meson

Adam, H. H.

Täschner, A.

Wüstner, P.

Juelich Shared Electronic Resources

arXiv:hep-ex/0507076v1  18 Jul 2005Isospin dependence of the η ′ meson productionin nucleon–nucleon collisionsJ. Przerwa∗, H.-H. Adam†, A. Budzanowski∗∗, R.Czyz˙ykiewicz‡∗,D. Grzonka‡, M. Janusz∗, L. Jarczyk∗, B. Kamys∗, A. Khoukaz†,K. Kilian‡, P. Klaja∗, P. Moskal∗‡, W. Oelert‡, C. Piskor–Ignatowicz∗,J. Ritman‡, T. Roz˙ek‡§, T. Sefzick‡, M. Siemaszko§, J. Smyrski∗,A.Täschner†, J. Wessels†, P. Winter‡, M. Wolke‡, P. Wüstner¶ andW. Zipper§∗Nuclear Physics Department, Jagellonian University, 30-059 Cracow, Poland†Institut für Kernphysik, Universistät Münster, 48419 Münster, Germany∗∗Institute of Nuclear Physics, 31-342 Cracow, Poland‡Institut für Kernpfysik, Forschungszentrum Jülich, 52425 Jülich, Germany§Institute of Physics, University of Silesia, 40-007 Katowice, Poland¶ZEL Forschungszentrum Jülich, 52425 Jülich, GermanyAbstract. According to the quark model, the masses of η and η ′ mesons should be almost equal.However, the empirical values of these masses differ by more than the factor of two. Similarly,though the almost the same quark-antiquark content, the total cross section for the creation of thesemesons close to the kinematical thresholds in the pp→ ppX reaction differs significantly. Using theCOSY-11 detection setup we intend to determine whether this difference will also be so significantin the case of the production of these mesons in the proton-neutron scattering. Additionally, thecomparison of the pp → ppη ′ and pn → pnη ′ total cross sections will allow to learn about theproduction of the η ′ meson in the channels of isospin I = 0 and I = 1 and to investigate aspects ofthe gluonium component of the η ′ meson.INTRODUCTIONDespite the fact that the η ′ meson was observed fourty years ago, its structure is still notknown. According to the quark model, η and η ′ mesons can be described as the mixtureof the singlet (η1 = 1√3(uu¯ + d¯d + ss¯)) and octet (η8 = 1√6(uu¯ + d¯d − 2ss¯)) states ofthe SU(3) - flavour pseudoscalar meson nonet. Within the one mixing angle scheme, asmall mixing angle (Θ = −15.50) implies that the masses of η and η ′ mesons shouldbe almost equal. However, the empirical values of these masses differ by more than thefactor of two, and the mass of the η ′ does not fit utterly to the SU(3) scheme.More surprisingly the masses of all pseudoscalar mesons, vector mesons and baryonsare well described in terms of naive quark model.At present there is also not much known about the relative contribution of the possiblereaction mechanisms of the production of the η ′ meson. It is expected that the η ′meson can be produced through heavy meson exchange, through the excitation of anintermediate resonance or via emission from the virtual meson [11].Q [ MeV ]σ[nb]p p → p p ηp p → p p η′phase space   (arb. norm.)+ p p FSI + p η FSI 1 10 10210102103104FIGURE 1. Total cross section for the reactions pp → ppη ′ (circles) and pp → ppη (squares)as afunction of the centre–of–mass excess energy Q. Data are from references [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]However it is not possible to judge about the mechanism responsible for the η ′ mesonproduction only from the total cross section of the pp → ppη ′ reaction. Therefore onehas to investigate the η ′ production in proton-neutron scattering in order to impose theadditional constraint on the existing theoretical models. Moreover, there is also onesignificant aspect of these studies, viz the close–to–threshold production of η ′ meson inthe nucleon–nucleon collisions requires a large momentum transfer between nucleonsand occurs at distances in the order of 0.3 fm and this implies that the quark–gluondegrees of freedom may play a significant role in the production dynamics of this meson.Therefore it is possible that the η ′ meson is created from excited glue in the interactionregion of the colliding nucleons [12, 13, 14]. It is interesting to note that recently Bassand Thomas [15] argued that the strength of the interaction of η and η ′ mesons withnucleons is sensitive to the singlet-flavour component, and hence to the glue in thesemesons. This makes a connection in our endeavour to investigate the structure, theproduction dynamics, and the interaction of the η and η ′ mesons with nucleons.ISOSPIN DEGREES OF FREEDOMTreating proton and neutron as different states of nucleon distinguished only by theisospin projection, +12 for the proton and −12 for the neutron, we may classify theNN → NNX reactions according to the total isospin of the nucleon pair in the initialand final state. A total isospin of two nucleons equals 1 for proton–proton and neutron–neutron pairs, and may acquire the value 1 or 0 for the neutron–proton system. Sinceη ′ meson is isoscalar, there are only two pertinent transitions for the NN → NNXreaction, provided that it occurs via the isospin conserving interaction. It is enough tomeasure two reaction channels for an unambiguous determination of isospin 0 and 1cross section [16].As discussed in references [12, 13, 14] the comparison of the pp→ ppη ′ and pn→ pnη ′total cross sections will allow not only to learn about the production of the η ′ meson inthe channels of isospin I = 0 and I = 1 but also to investigate aspects of the gluoniumcomponent of the η ′ meson.Such investigations were already performed in case of η meson, and the total crosssection in both the proton–proton as well as the proton–neutron reactions has beenmeasured. The ratio Rη = σ(pn→pnη)σ(pp→ppη) was determined to be about 6.5 [17] in the excessenergy range between 16 MeV and 109 MeV. Since,σ(pp → ppη) = σI=1,σ(pn→ pnη) = σI=0 +σI=12we haveσI=0 = (2Rη −1)σI=1,where I denotes the total isospin in the initial and final state of the nucleon pair. Thismeans that the production of η meson with the total isospin I=0 exceeds the productionwith the isospin I=1 by a factor of 12. This large difference of the total cross sectionssuggests the dominance of isovector mesons exchange in the creaction of η in collisionsof nucleons.Since the quark structure of η and η ′ mesons is very similar, in case of the dominantisovector meson exchange – by the analogy to the η meson production – we canexpect that the ratio Rη ′ should be about 6.5. If however η ′ meson is produced via itsflavour-blind gluonium component from the colour-singlet glue excited in the interactionregion the ratio should approach unity after corrections for the initial and final stateinteractions [12].STATUS OF THE EXPERIMENTThe close–to–threshold excitation function for the pp → ppη ′ reaction (see fig.1) hasbeen already determined, whereas the total cross section for the η ′ meson productionin proton-neutron interaction is still unknown. Therefore we have performed the mea-surement of the quasi–free pn → pnX processes using a proton beam and a deuteroncluster target. In two separated runs we have measured the pn → pnX process close tothe η and η ′ production threshold. For the preliminary results on the pn→ pnη processthe interested reader is referred to reference [18]. The experiment is based on the regis-tration of all outgoing nucleons from the pd → psppnX reaction. Protons are measuredin two drift chambers and scintillator detectors [19, 20], neutrons are registered in theneutral particle detector [21, 22]. Protons considered as a spectators are measured bythe dedicated silicon-pad detector [23, 24]. Application of the missing mass techniqueallows to identify events with the creation of the meson under investigation and the totalenergy available for the quasi-free proton-neutron reaction can be calculated for eachevent from the vector of the momentum of the spectator proton. For more detailed de-scription of the experimental method see references [25, 26, 27].At present the analysis aiming for establishing the excitation function for the pn→ pnη ′reaction is in progress and will deliver the values for the total cross section in the excessenergy range between 0 and 20 MeV.ACKNOWLEDGMENTSThe work has been supported by the European Community - Access to Research In-frastructure action of the Improving Human Potential Programme, by the FFE grants(41266606 and 41266654) from the Research Centre Jülich, by the DAAD ExchangeProgramme (PPP-Polen), by the Polish State Committe for Scientific Research (grantNo. PB1060/P03/2004/26), and by the RII3/CT/2004/506078 - Hadron Physics-Activity-N4:EtaMesonNet.REFERENCES1. P. Moskal et al., Phys. Lett B 474 (2000) 416.2. A. Khoukaz et al., Eur. Phys. J. A 20 (2004) 345.3. J. Smyrski et al., Phys. Lett. B 474 (2000) 182.4. P. Moskal et al., Phys. Rev. Lett 80 (1998) 3202.5. H. Calén et al., Phys. Lett. B 366 (1996) 39.6. E. Chiavassa et al., Phys. Lett. B 322 (1994)270.7. A. M. Bergdolt et al., Phys. Rev. D 48 (1993) R2969.8. F. Hibou et al., Phys. Lett. B 438 (1998) 41.9. F. Balestra et al., Phys. Lett. B 491 (2000) 29.10. P. Moskal et al., Phys. Rev. C 69 (2004) 025203.11. K. Nakayama et al., Phys. Rev. C 61 (2000) 024001.12. S. D. Bass, Phys. Lett. B 463 (1999) 286.13. S. D. Bass, e-Print Archive: hep-ph/0006348.14. S. D. Bass, Phys. Scripta T 99 (2002) 96.15. S. D. Bass, A. W. Thomas, e-Print Archive: hep-ph/0507024.16. P. Moskal, e-Print Archive: hep-ph/0408162.17. H. Calén et al., Phys. Rev. C 58 (1998) 2667.18. P. Moskal et al., e-Print Archive: nucl-ex/0311003.19. S. Brauksiepe et al., Nucl. Instr. & Meth. A 376 (1996) 397.20. J. Smyrski et al., Nucl. Instr. & Meth. A 541 (2005) 574.21. J. Przerwa, e-Print Archive: hep-ex/0408016,Berichte des FZ-Jülich, Jül-4141 (2004).22. J. Przerwa et al., Int. J. of Mod. Phys. A 20 (2005) 625.23. R. Bilger et al., Nucl. Instr. & Meth. A 457 (2001) 64.24. M. Janusz, diploma thesis, Jagellonian University, Cracow (2004).25. P. Moskal, e-Print Archive: nucl-ex/0110001.26. P. Klaja et al., e-Print Archive: hep-ex/0507055, these proceedings.27. J. Stepaniak, H. Calén, e-Print Archive: nucl-ex/0412025.