AND K0s PRODUCTION IN pC COLLISIONS AT 10 GeVc Petros Aslanyan 1,2, et.al. 1 Joint Institute for Nuc - PowerPoint PPT Presentation

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AND K0s PRODUCTION IN pC COLLISIONS AT 10 GeVc Petros Aslanyan 1,2, et.al. 1 Joint Institute for Nuc

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Title: AND K0s PRODUCTION IN pC COLLISIONS AT 10 GeVc Petros Aslanyan 1,2, et.al. 1 Joint Institute for Nuc


1
AND K0s PRODUCTION IN pC COLLISIONS AT 10
GeV/cPetros Aslanyan 1,2,? et.al. (1) Joint
Institute for Nuclear Research.(2) Yerevan
State University . paslanian_at_jinr.ru.
Low Energy Antiproton Physics, Institute of
Nuclear Physics Research Centre Juelich,
16-22 May, Germany
  • Introduction
  • Method
  • Cross sections ? and K0s
  • Conclusion

2
Introduction
The experimental data from heavy ion collisions
show that the K /? ratio is larger at BNL-AGS
energies than at the highest CERN-SPS energies
and even at RHIC. This behavior is of particular
interest as it could signal the appearance of new
dynamics for strangeness production in high
energy collisions. Strangeness enhancement has
been extensively discussed as a possible
signature for the quark-gluon plasma (QGP)
1,2. Strange particle production has also been
analyzed regarding such reaction mechanisms as
the multinucleon effect 3, the fireball effect
4, or as the deconfiment signal, within the
context of thermal equilibrium of hadron
statistical model 5,6,7,8. The statistical
approach has been very successful in describing
particle yields from low energies starting with
SIS and AGS all the way up to SPS (see figure).
In particular, strange particles have been
observed extensively on hadron - nucleus and
nucleus-nucleus collisions 4-15 Gev regions
9-14. Experiments on SiAu and AuAu
collisions at 11.6 and 14.6 A GeV/c a K / ?
ratio in heavy-ion reactions was measured which
is four to five times larger than the K / ?
ratio in pp reactions at the same
energy13,14.
3
The strange hyperon yields 6 ,9, 10, 11 are
therefore of great interest as an indicator of
strange-quark production(see in figure). Figure
shows the energy dependence of the ? / ? , ?- /
? and the ?- / ? . As can be seen from the
figure there is a very clearly pronounced maximum
especially in the ? / ? ratio. The number of
?s produced in antiproton Ta reaction at 4
GeV/c was 11.3 times larger than that expected
from the geometrical cross section (KEK, Japan)
9. However, there have not been sufficient
experimental data concerning strange-hyperon
production over 10-40 GeV/c momentum range. In
this paper the new results are presented for the
measured inclusive cross sections for ?(K0s)
production and ? / ? ratio in the reaction
pC are presented.
AGS Si-Au
1J.Rafaelski et al., PL. 91B,281,1980 PRL 48,
066,1982. 2 P.Koch et. al., PL
123B,151.1983. 3 J.Rundrup and C.M.Ko,
Nucl.Phys. A343, 519, 1980. 4 F.Asai, H.Sato
and M.Sano, Phys. Lett. 98B, 19, 1981. 5 J.
Cleymans and K.Redlich, Phys.Rev. C60(1999). 6
P. Braun-Munzinger et al.,NPA697902-912,2002 hep
-ph/0106066,2001. 7 F. Becattini et al, PR
C24,024901,2001. 8 M. Gazdzicki,
hep-ph/0305176v2,2003. 9 K. Miyano et al.,
Phys. Rev. C38 (1988). 10 M. Anikina et al.,
Phys. Rev. Lett. 50 (1971). 11 S. Albergo,et.
al.,Phys. Rev. Lett. 88,v.6, 2002. 12 B. Back
et al.,E866, E917 Collab., nucl-ex/9910008
Figure Prediction for the ? / ? (note the
factor 5) ?- / ? and the ?- / ? ratios as
a function of s1/2. For compilation of data see
6 ,7.
13 L. Ahle et al., PR C60 (1999), PL
B476(2000)1. 14 T. Abbott et al., PL B 291,
341 (1991) T. Abbott et al.,PR C 50, 1024 (1994).
4
?
A reliable identification of the above
mentioned resonance needs to use 4?-detectors and
high precision measurements of the sought
objects. The bubble chamber is the most suitable
instrument for this purpose . The experimental
information of more than 700000 stereo
photographs are used to select the events with V0
strange particles . The GEOFIT based on the
Grind-CERN program is used to measure the
kinematics parameter of tracks momenta(P), tg?(?
- depth angle) and azimuthal angle(?) in the
photographs. The relative error of measuring
momentum p and the average track length L of
charged particles are found to be ?P/P2.1,lt
Lgt12 cm for stopped particles and ?P/Pgt9.8 ,
ltLgt 36 cm for nonstopped particles. The mean
values of measurement errors for the depth and
azimuthal angles are equal to ?tg? 0.0099
0.0002 and ?? 0.0052 0.0001 (rad.). The
estimation of ionization, the peculiarities of
the end track points of the stopped
particles(protons, K? ) allowed one to identify
them. Protons can be identified over the
following momentum range 0.150? P ? 0.900 GeV/c.
In the momentum range P gt 0.900 GeV/c
protons couldn't be separated from other positive
charged particles.
5
The events with V0 (? and Ks0) were identified
by using the following criteria 20-21 1) V0
stars from the photographs were selected
according to ?? ?-p,Ks0 ??-? or ??ee-
hypothesis. A momentum limit of Ks0 and ? is
greater than 0.1 and 0.2 GeV/c, respectively 2)
V0 stars should have the effective mass of ? or
of Ks0 3) these V0 stars are directed to some
vertices(complanarity) 4) they should have one
vertex, a three constraint fit for the MK or M?
hypothesis and after the fit,?2should be
selected over range less than 12 5) The
analysis has shown21 that the events with
undivided ?Ks0 were assumed to be events as ?.
As a result of this analysis we have lost 8.5
of events with Ks0 s and 4.6 events with Ks0
mixed with ? events.
Distributions of ? (Armenteros parameter) and
cos??- are used for correctly identification
of the undivided V0s. ? (P?? - P - ??)/(P
?? P- ??). Where P ?? and P- ?? are the
parallel components of momenta positive and
negative charged tracks. cos ? ?- - is the
angular distribution of ?- from Ks0 decay.
Distributions of ? and cos ? ?- were
isotropic in the rest frame of Ks0 when
undivided ? Ks0 were assumed to be events as ?
.

6
Each V0 event weighted by a factor
wgeom1/et, where et is the probability of
observing the V0 , it can be expressed as et
exp(-Lmin/L)- exp(-Lmax/L), where L (cpt/M) is
the flight length of the V0, Lmax the path length
from the reaction point to the boundary of
fiducial volume, and Lmin(0.5 cm) is an
observable minimum distance between the
reaction point and the V0 vertex. M, t , and P
are the mass, lifetime, and momentum of the V0
.The average geometrical weight(wgeom) was
1.340.02 for ? and 1.22 0.04 for Ks0.
Lifetime c? was deduced from the t / (??)
distributions (? - the lifetime V0) to be
(3.50.6)cm for Ks0 and (7.9 0.2)cm for ?.
These data are in good agreement with PDG data.
Examine a possibility backgrond from neutron
stars of imitating ? and Ks0 the using model
FRITIOF for the hypotheses reaction pC?nX, nn
? ?- p(or ?- ?) X0 with including fermi motion
in carbon. Then, these background events were
analyzed by using the same experimental condition
for the selection of V0 events. The 2 verteces
analysis have shown that the background from
neutron stars is equal to 0.1 for ? and 0.001
for Ks0 events.
7
Figures (a,c) and (b,d) show the effective mass
distribution of 8657-events with ?, 4122-events
with Ks0 particles and their ?2 from kinematics
fits, respectively. The expected functional form
for ?2 is depicted with the dotted histogram.
The measured masses of these events have the
following Gaussian distribution parameters
ltMKs0gt 497.7 3.6, s.d. 23.9 MeV/c2 and ltM ?gt
1117.0 0.6, s.d.10.0 MeV/c2. The masses of
the observed ? and Ks0 are consistent with their
PDG values.
8
Figure compares the momentum, cos? in the c.m.
nucleon-nucleon system, transverse momentum (pt)
and longitudinal rapidity distributions of ?
and K0s for experimental events (solid line) and
those simulated by the FRITIOF model (broken
line) in pC interactions. From Fig. one can see
that the experiment is satisfactorily described
by the FRITIOF model.
9
2.2.The selection of carbon nucleus interactions
The criteria for selection of interaction with
carbon has shown in article G.N.Agakashiev et.
al., Yad. Fiz.,1986,43(2),p.366,373. The
pC??(Ks0 )X reactions were selected by the
following criteria 1. Q n- n- gt 2 2. npn?
gt1 3. npb n?b gt0 4. n-gt2 5. nch odd number
6. E p (?) -P p (?) cos?p (?) )/mtgt1. n
and n- are the number of positive and negative
particles on the star np and n? are the number
of protons and ? hyperons with momentum P lt0.75
GeV/c on the star. npb and n?b are the nuber of
protons and ? emitted in backward direction. E p
(?),P p (?)and ? p (? ) are an energy, a momentum
and a emission angle of protons(or ?s) in the
Lab. system. mt is the mass of target. Using
these criteria we have 83 of all inelastic
pC interactions (D. Armutljski et al., JINR
Commun, ?1-87-423, 1987). The pC events were
selected by the above criteria using FRITIOF
model. Results of the simulation have lost 18
and 20 from interactions pC? ?X and pC ? Ks0 X
,respectively. The contribution from pp ? ?X and
pp ? Ks0 X to pC interactions is equal to 1.0
and 0.3, respectively.
10
3. Cross sections ? and K0s
The cross section is defined by the formula ?
(?t NV0 /Nr ) w? wgeomwintwkin/e1e2e3,
(3.1) where e1 is the
efficiency of search for V0 in the photographs,
e2 is the efficiency of measurements, e3 is
the probability of decay via the channel of
charged particles (???-p,Ks0??-?), ?t is the
total cross section for the registered events,
Nr is the total number of registrated
interactions of beam protons over the effective
range of chamber. NV0 is the total number of
registered events with ? or K0s . The w is
the weight for lost events with V0 for ( w? )
the required isotropy for V0 in the azimuthal
(XZ) plane the interaction of V0 C3H8 ( wint )
the V0 decay outside the chamber (wgeom) the
kinematic conditions which have obtained by
FRITIOF model (wkin ) .
Table 2 Weight of the lost experimental
events with ? and Ks0 for pC and pp interactions
11
Table 3 Cross sections ? hyperons and Ks0
mesons for pp and pC ineractions at beam
momentum 10 GeV/c.

Table 4 Ratios of average multiplicities ?
hyperons and Ks0 mesons to multiplicities ?
mesons for pC interaction at beam momenta 4.2
GeVc and 10 GeV/c. .
12
Conclusion
The experimental data from the 2 m propane bubble
chamber have been analyzed for pC? ? (K0s) X
reactions at 10 GeV/c.The estimation of
experimental inclusive cross sections for ? and
K0s production in pC collisions is equal to ? ?
13.31.6 mb and ?K0s 3.8 0.5 mb,
respectively. The measured ?/? anv K0s /?
ratios in pC reaction is equal to (5.3
0.8)10-2 and (1.8 0.3)10-2, respectively.
The experimental ? / ? ratio in the pC
reaction is two times larger than the ? / ?
ratio from pp reactions The multiplicity
of ? and ? production in CC reaction at 10
GeV/c have been used the Glauber approach
based on the experimental cross section for pC
? ?X. As can be seen from experimental data in
the Table 5 and thermal statistical model
(Figure) there is a very clearly pronounced
enhancement specially in the ? / ? ratio for
hadron-nucleus and nucleus collissions at 10-15
A.GeV/c.
AGS Si-Au
Table 5 Ratios of average multiplicities ? /
? for CC interactions at beam momentum 4.2
and 10 GeV/c.
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