SIMULATION of CENTAURO EVENTS at CASTOR Introduction

ALICE/97{06

Internal Note/PHY

6 March 1997

SIMULATION OF CENTAURO EVENTS AT

CASTOR

1 2 3

E. Gladysz-Dziadu s ,Yu. V. Kharlov ,A.D.Panagiotou ,

S. A. Sadovsky

Institute of Nuclear Physics, Krakow, Poland

Institute for High Energy Physics, Protvino, Russia

University of Athens, Athens, Greece

Abstract

We present the rst Monte Carlo mo del of Centauro events based on the phe-

nomenological mo del of Panagiotou et al. and show the quantitative consequences

for kinematics, baryon numb er, mass and decay prop erties of the Centauro reball.

The simulation of Centauro events for the CASTOR detector is p erformed. The

signatures of these events are discussed in details.

Intro duction

In this pap er we present the rst Monte Carlo mo del of Centauro events based on the

phenomenological mo del [1, 2 , 3] and discuss results on MC simulations of Centauro events

for the CASTOR detector of the ALICE exp eriment at LHC [4]. Originally the mo del of

Centauro event pro duction was based on exp erimental facts from cosmic ray studies and

assumptions of some geometrical characteristics of the events; exp erimentally observed

transverse momenta, energies of di erent spices of secondary particles and scenario of

the Centauro reball evolution allow to calculate thermo dynamical parameters and the

lifetime of the Centauro reball. The extrap olation of this mo del to the higher energy

allowed to estimate some observables of Centauro events, when taking into account the

collider kinematics [5].

In this approachwe attempt to predict more precisely the characteristics of such

kind of events. In the current pap er we present this mo del of Centauro events in heavy

ion collisions on assumption of some fundamental characteristics of the Centauro reball

which lead to the predictions of observables in such kind of events. The mo del is for-

mulated in terms of impact parameter of ion collisions, two thermo dynamical parameters 1

baryochemical p otential and temp erature which are assigned to the Centauro reball

pro duced in the scenario of Centauro eventevolution, and the nuclear stopping p ower.

Since we construct the fully quantitative mo del wehave to formalize all assumptions of

the original mo del and intro duce some additional assumptions. The event generator cal-

culates the Centauro reball parameters and pro duces the full event con guration. Thus

the mo del predicts all kinematical parameters of the Centauro events whichwere observed

in cosmic ray exp eriments.

In section 1 we give the gradual thermo dynamical and kinematical description of

pro duction and evolution of Centauro-typ e events in relativistic heavy ion collisions and

showcharacteristic mass, energy and multiplicity distributions of these events.

In section 2 results of the detection simulation of these events with the CASTOR

apparatus are given. Centauro events are compared with minimum bias events pro duced

by the HIJING generator. Signatures of Centauro events are discussed.

1 Physics of Centauro events

Centauro reball evolution. The description of Centauro events [6] was intro duced

in pap ers [1, 2 , 3 ]. According to this mo del Centauro events o ccur in nuclear collision

in the pro jectile fragmentation region when the pro jectile nucleus p enetrating through

the target nucleus transforms its kinetic energy into heating and formats of a slightly hot

quark matter with high baryochemical p otential [2, 3]. We refer to this quark matter

as a primary Centauro reball. On the rst stage of its evolution it contains u and d

quarks and gluons. The high baryochemical p otential results in imp ossibil ity for gluons

to fragmentinto uu and dd pairs due to Pauli blo cking [2]. Therefore gluons quickly

fragmentinto ss pairs. The partial chemical equilibrium is achieved by couplings -quarks

+ 0

with u and d-quarks and emission of K and K from the primary reball which decreases

the temp erature and entropy. After this stage the Centauro reball b ecomes a slightly

strange quark matter SQM with relatively long lifetime 10 sec [3]. Finally the

SQM reball decays explosively into baryons and some light metastable strange matter

ob jects with A> 6 called as strangelets.

Baryon numb er of Centauro reball. We consider collisions of nuclei with atomic

numb ers A and A and charges Z and Z resp ectively with impact parameter b. The

1 2 1 2

impact parameter is roughly restricted by

1 2

1=3

fm i =1; 2 are radii of colliding nuclei. Centauro reball is where R =1:15A

pro duced in a region of the twonuclei overlapping. The baryon number N of the reball

can b e estimated from a simple geometrical consideration. We assume that all nucleons

of the pro jectile nucleus which o ccur in the overlapping region with the target nucleus

can interact. Really only the most central part of the overlapping region of the pro jectile 2 900

800

700 ), arbitrary units

b 600

f(N 500

Figure 1: Baryon numb er of the reball

400 pro duced in Pb-Pb collisions with impact

300

parameters 0

200

100

140 150 160 170 180 190

forms the reball. Assuming the uniform distribution of nucleons in a nucleus one can

nd N through the volume ratio of overlapping region V and the whole pro jectile

b ovrlp

nucleus V :

ovrlp

N =0:9 A : 1

b 1

Here the factor 0:9 gives the most central part of the overlapping region. In other words

the primary reball baryon number N is de ned bya number of nucleons of the pro jectile

nucleus which impacts in the interaction region.

It is naturally to assume that pro jectile and target nuclei are distributed uniformly in

the transverse plane, i.e. the squared impact parameter b is distributed uniformly. All

cosmic Centauro events were observed with rather high hadron multiplicityN > 70,

hence in our mo del we restrict the Centauro reball pro duction by N > 50. In our

quantitative mo del we use a simple assumption that eachnucleus collision with di erent

impact parameters results in Centauro reball pro duction with one and the same ther-

mo dynamical characteristics. In the real nature it is not so but it seems to b e reasonable

when the impact parameter varies a little. Central collisions are more likely to pro duce

the Centauro quark matter reball than p eripheral collisions are. Therefore we calculate

the distribution of the baryon numb er of the primary Centauro reball for Pb-Pb colli-

sions for impact parameters 0

plot is shown in Fig. 1. The form of the distribution f N is rough enough b ecause of

the motivation discussed ab ove. From the other hand this distribution gives the right

representation on the baryon number N range b ecause N is de ned strictly for the xed

b b

impact parameter. This remark also concerns shap es of other distributions given in the

pap er. 3

Mass of Centauro reball. The pro duced reball is a glob of decon ned quark matter

whichcharacterized by a temp erature T and baryochemical p otential of a nucleon .As

the basic phenomenological mo del [2, 3] predicts, the Centauro reball has a very high

baryochemical p otential which do es not p ermitu and d to b e pro duced. This phase of

the Centauro reball is unstable yet and after t 10 sec [3] gluons fragmentinto

ss pairs. After that a chemical equilibrium in the reball is achieved. In the rst-order

p erturbative QCD the energy density of the quark-gluon plasma containing u, d, s quarks

and gluons at the temp erature T around a critical one T is expressed by see, e.g. [7, 8 , 9]

and references therein

" = " + " + " :

g q s

Here q = u; d. Gluon and quark contributions " , " and " are

q q s

8 15

" = T ; 1

g s

15 4

2 50 3 7

4 4 2 2

1 1 T + 3 T + ; " =

s s q

q q

10 21 2

" !

18T m m T m m m

s s s s s

" = +6 K K :

s s 1 2

T T T T

Here K are i-order mo di ed Bessel functions. The strong coupling constant should b e

i s

taken at a scale Q 2T and equals =0:3 at a critical temp erature T = 170 MeV [8].

s c

The is the strangeness equilibration factor 0:4. The net energy density for all

s s

degrees of freedom is given by

37 110 3 2

4 4 2 2

" = T 1 T + 1 + 3 + " : 2

s s s

q q

30 37 2

Here baryochemical p otential of a quark can b e taken as = =3.

q q b

The other thermo dynamical quantities of interest, pressure P and quark numb er den-

sity n = N =V are obtained from equation 2:

q q fb

1 @P

P = "; n = ;

3 @

1 : 3 n =2 T +

s q q

Since the numb er of quarks N in the primary Centauro reball is de ned from the collision

geometry as N =3N one can obtain from 1 and 3 the volume of the reball V in

q b fb

the order O :

3N 2

V = : 4 1+

s fb

2 T +

4 T = 130 MeV 18000 T = 190 MeV 16000 T = 250 MeV 14000 ), arbitrary units fb 12000

f(M tauro re-

10000 Figure 2: Mass of the Cen

ball in Pb-Pb collisions at =

8000 b

1:8 GeV and T = 130, 190 and

6000 250 MeV.

4000

2000

100 200 300 400 500 600

Mfb, GeV

When the volume of the reball is de ned one can easily obtain the mass of the reball

from the energy density 2:

M = "V : 5

fb fb

The distribution of the Centauro reball mass pro duced in Pb-Pb collisions with =

1:8 GeV and T = 130, 190 and 250 MeV is shown in Fig. 2

Kinematics of the reball. Centauro events were observed in cosmic ray exp eriments

in the very forward region [6]. We supp ose that the longitudina l-momentum distribution

of the reball ob eys the scaling law of secondary particles pro duction which is describ ed

by empirical formula established at lower energies at large x :

dN =dx 1 x ; n 3:

F F

The transverse momentum of the reball should havea value of the order of the intrinsic

motion momenta of a nucleon inside a nucleus.

Each constituent quark of the pro jectile nucleus participating in the reball formation

comes though the scattering o the target nucleus. The transverse momentum distribution

of a quark in the fragmentation region can b e expressed by the form

dN =dp exp

with the slop e p =0:3 GeV=c.Vector summation of all transverse momenta of interacting

quarks gives the transverse momentum of the pro duced Centauro reball. 5

The rapidity range of the pro duced reball can b e obtained from the following consid-

eration. The maximum rapidity of the reball is reached when it carries the whole energy

of the pro jectile nucleus fragment, E = E N =A :

max b eam b b eam

max

: y =ln

max

for example for central Pb-Pb collisions at s =5:5TeV/nucleon N =0:9 A = 186,

b b eam

reball mass at T = 190 MeV and =1:8 GeV is M = 466 GeV=c and the maximum

b fb

rapidityis

y =7:69:

max

But the nuclear stopping is an essential e ect as it is exp ected in heavy ion collisions . The

nuclear stopping p ower shows the degree to which the energy of relative motion of the two

incidentnuclei can b e transferred into thermo dynamical degrees of freedom. The nuclear

stopping can b e expressed by the rapidity shift y of pro duced particles compared to

n:s:

NN collisions . Thus the actual rapidity of the Centauro reball is de ned by the equation

y = y y :

fb max n:s:

The value of y is a crucial parameter of the mo del which the observance of the

n:s:

Centauro events dep ends on. The average of HIJING [11 ] and VENUS [12] prediction

gives y =2:3 but values in the range 2:0 < y < 3:5 can take place [3].

n:s: n:s:

Recoil system. Since the kinematics of the reball is de ned one can calculate the

momentum of the recoil system which consists of secondaries from the target nucleus.

De ning the 4-momentum of the Centauro reball as p and the 4-momentum of the

recoil system as p wehave the momentum conservation lawas

rec

p + p = p + p :

pro j targ Cn rec

Let s to b e the c.m.s. collision energy of overlapping fragments of the b eam nuclei.

p p p

s wehave s = N s with N Obviously for the collision energy p er nucleon

NN aa b NN b

de ned by equation 1. Neglecting the mass of the Centauro reball in comparison with

s we get the mass of the recoil system M to b e de ned by the expression

aa rec

1=2

M = s 1 ;

rec aa

s .For the rapidity of the recoil system y the equation is where 2M coshy =

aa rec fb fb

as follows:

: sinh y

rec

1=2

For the values of the rapidity shift y of several units y =2 3 one can conclude

n:s: n:s:

that the recoil system carries almost the total energy of the nuclear collision s . In this

aa 6

approximation it is easy to obtain that value of vanishes, hence, the mass of the recoil

s and y is small. To feel the amountof system M is very close to the value of

aa rec rec

recoil mass and rapiditywe giveTable 1 which represents these values in central Pb-Pb

collisions at s =5:5TeV/nucleon, s = 1140 TeV when the Centauro reball mass is

M = 530 GeV=c , at di erentvalues of y .From this table it follows that the recoil

fb n:s:

y 2.0 2.5 3.0 3.5

n:s:

M = s 0.93 0.96 0.97 0.98

rec aa

y 0.07 0.04 0.03 0.02

rec

Table 1: Recoil system mass M and rapidity y in Pb-Pb collisions at di erent

rec rec

values of the rapidity shift due to nuclear stopping of the Centauro reball y .

n:s:

system is pro duced in the central rapidity region and, therefore, the secondary particles

can b e detected by the central detector of any exp eriment. The contents of the recoil

system is still unknown b ecause of the mechanism of the Centauro reball pro duction is

not understo o d well enough.

Strange quark matter reball. As it was mentioned earlier gluons in the primary

Centauro reball fragmentinto ss pairs to achieve the chemical equilibrium. The strange

quark numb er density is given by the equation [10 ]:

m T

3 3

K ; 6 n =1:37 10 GeV

2 s

200 MeV T

where K x is a mo di ed Bessel function of the second order. Being multiplied by the

Centauro reball volume V 4 the equation 6 gives the number of ss pairs inside the

reball and, hence, the numb er of emitted K -mesons:

+ 0

N = N K +N K = n V : 7

s s fb

Fig. 3 shows the distribution of kaon numb ers emitted from the Centauro reball with

=1:8 GeV and T = 130, 190 and 250 MeV. Before emitting kaons from the reball the

total numb er of quarks is N =3N +2N . Hence, the average energy p er a constituent

b s

quark at this stage is

= : 8

After 2N quarks have b een emitted with kaons the mass of the remaining SQM reball

is de ned by the average quark energy 8 and the numb er of quarks in the reball N :

0 0

: = M 1 = N M

fb q

q fb

The emission of anti-strangeness is describ ed as an isotropic decay of the primary reball

into N kaons and the SQM reball with the mass M . The average p of kaons is variated

s T

with the primary reball temp erature in the range 0:9 1:3 GeV/c. 7 30000 T = 130 MeV

25000 T = 190 MeV

T = 250 MeV

), arbitrary units 20000

f(N +

Figure 3: Number of K and K

15000

emitted from the Centauro reball

pro duced in Pb-Pb collisions at =

:8 GeV and T = 130, 190 and

10000 1 250 MeV.

5000

0204060

N(K+)+N(K0)

Decay of SQM reball. After emission of kaons the primary Centauro reball trans-

forms into a slightly strange quark matter which can have a long life-time, of the order

of 10 sec [3]. At the nal stage of its evolution the SQM reball decays into baryons

and strangelets. The latter are light drops of strange quark matter with A>6, high

strangeness-p er-baryon ratio S=A 1 and small charge-to-mass ratio Z=A 0. In our

mo del for simplicity the only one strangelet is pro duced in the SQM reball by random

cho osing u-, d- and s-quarks from all quarks of the reball. Not all strangeness of the SQM

reball can b e transferred to the strangelet, the rest of s-quarks forms strange hyp erons.

Baryons are formed in the reball by the random picking sets of three quarks from the

quarks of the reball matter. The priorityisgiven to the formation of nucleons and all

quarks which cannot b e coupled to nucleons pro duce strange hyp erons. The decay of the

SQM reball is p erformed isotropicall y.We use the well-known event generator Jetset

[13] to p erform further decays of kaons and strange baryons.

General characteristics of Centauro events. Table 2 shows characteristics of Cen-

tauro events in Pb-Pb collision at s =5:5TeV/nucleon. At a given impact parameter

b, temp erature T and baryochemical p otential we calculate baryon number N , energy

b b

density ", quark numb er density n ,volume of the reball V , mass of the primary re-

q fb

, strange quark numb er density n and number of ball M , mass of the SQM reball M

s fb

+;0

emitted kaons N K . With some initial parameters of the mo del, esp ecially for central

collisions b = 0 and high temp erature Centauro events are featured by a high mass

and a large numberofkaons. Nuclear collisions with large impact parameters could also

pro duce Centauro-typ e events but these events are characterized by a residual strange 8

0 +;0

b T N " n V M M n N K

b b q fb fb s

3 3 3 3

fm GeV MeV GeV/fm fm fm GeV GeV fm

0 1.8 130 186 4.3 6.7 83 357 344 0.13 11

190 186 7.7 9.2 61 466 423 0.48 28

250 186 13.6 12.5 45 607 515 1.14 50

1.5 130 186 2.7 4.4 125 334 316 0.13 16

190 186 5.3 6.5 86 460 402 0.48 40

250 186 10.4 9.2 60 626 503 1.14 68

5 1.8 130 114 4.3 6.7 51 219 212 0.13 6

190 114 7.7 9.2 37 286 260 0.48 17

250 114 13.6 12.5 27 372 315 1.14 31

8 1.8 130 53 4.3 6.7 24 102 98 0.13 3

190 53 7.7 9.2 17 133 120 0.48 8

250 53 13.6 12.5 13 173 147 1.14 14

Table 2: Centauro events prop erties at some xed impacts parameters, temp er-

ature and baryochemical p otential.

comp onent.

The Centauro events as they were observed in cosmic ray exp eriments are featured by

a total or almost total absence of photonic comp onent among secondary particles. Since

our mo del is based on the assumption that the Centauro reball mostly consists of u and

d quarks with a small amountofss pairs, the most of secondaries particles are baryons.

Kaons which are emitted from the primary reball can decay particular into neutral pions

which give, in turn, photons. But the neutral pion pro duction is suppressed due small

o o o o

factor N =N + N BRK ! K BRK ! 2 1=50. Therefore the amount

K b K

s s

of electromagnetic fraction of suchevent is suppressed very much. Fig. 4 shows the ratio

of hadron multiplicity to the total multiplicity hadrons + photons in Centauro events

with =1:8 GeV and T = 190 MeV pro duced at LHC in Pb-Pb collisions. The ratio

is very close to unity with mean value hN =N i =0:93 and the deviation of this value

h tot

from 1 is caused by electromagnetic particles. Fig. 5 gives the ratio of summary energy of

hadrons to the total energy in the same events. This value is close to 1 with average value

P P

h E = E i =0:99. Certainly these ratios dep end on thermo dynamical characteristics

h tot

of the Centauro reball, e.g. the higher the temp erature, the more kaons and therefore,

the more photons are pro duced and these ratios b ecome more di erent from 1.

Secondary particles in the Centauro events have a larger mean transverse momentum

in comparison with ordinary hadron interaction. The mean p observed in cosmic rays [6]

is hp i =1:75 GeV=c. Fig. 6 shows the transverse momentum distribution of hadrons

in Centauro events at LHC with 3 sets of baryochemical p otential and temp erature

T : =1:8 GeV, T = 190 MeV, =1:8 GeV, T = 250 MeV and =3:0 GeV,

T = 250 MeV. The average p in suchevents is hp i =1:34 GeV=c,1:47 GeV=c and

T T

1:75 GeV/c resp ectively. Usual hadron events, as the mo del HIJING predicts have the 9 5000 12000

4000 10000

8000 3000

6000 2000 4000

1000 2000

0 0 0.85 0.9 0.95 1 0.94 0.96 0.98 1 Σ Σ

Nh/Ntot Eh/ Etot

Figure 4: Ratio of hadron to total multi-

Figure 5: Ratio of hadron to total summary

plicities hadrons + photons. energies.

x 10 2 9000 16000 µ ∆ b=1.8 GeV, T=190 MeV yn.s. = 2.0 8000 14000 µ ∆ b=1.8 GeV, T=250 MeV yn.s. = 2.5 7000 µ 12000 ∆ b=3.0 GeV, T=250 MeV yn.s. = 3.0 ), arbitrary units

T 6000

f(y), arbitrary units 10000 f(p 5000 8000 4000 6000 3000 4000 2000

1000 2000

0 0 012345 468

pT (hadrons), GeV/c y (decay products)

Figure 6: Transverse momentum distribu- Figure 7: Rapidity distribution of decay

tion in Centauro event with =1:8 GeV, pro ducts of Centauro events for three val-

T = 130 MeV, = 1:8 GeV, T = ues of y =2:0, 2:5 and 3:0.

n:s:

190 MeV and = 3:0 GeV, T =

250 MeV. 10

average transverse momentum hp i =0:44 GeV=c whichis2 4 times smaller than that

in Centauro events.

Rapidity distribution of decay pro ducts of the Centauro reball certainly dep ends on

the nuclear stopping p ower y . In Fig. 7 rapidity distributions of secondary particles

n:s:

are shown for three values of y =2:0, 2:5 and 3:0. Obviously all secondaries are

n:s:

distributed in the very forward region as it was observed in cosmic rays.

2 Detection of Centauro events with CASTOR

Here we present a simple detection eciency calculation for the detector CASTOR of

the ALICE exp eriment at LHC. The detector is installed in a very forward region at the

distance 10:5 m apart from the interaction p oint of incoming nuclei. The detector has an

approximate central symmetry and installed as much as p ossible close to the b eam pip e,

i.e. it has a central hole with the radius R = 4 cm, the outer radius is R = 23 cm.

in out

Therefore, the detector covers pseudorapidities 4:5 < <6:2. The detector is capable to

measure charge particle and photon multiplicities and dep osited energy of hadronic and

electromagnetic comp onents.

The detection of Centauro events strongly dep ends on parameters of the mo del, namely

thermo dynamical variables and T which in uence the mass of the reball and rapidity

shift due to nuclear stopping y .We compare detection p ossibiliti es of the Centauro

n:s:

reball at di erent T and xed and y and at di erenty with xed thermo-

n:s: n:s:

dynamical parameters and 0

distribution in the detector with xed y =2:5 and =1:8 GeV and twovalues of

n:s:

the reball temp erature T = 190 and 250 MeV. The dep endence of the charged hadron

multiplicity on the rapidity shift at xed =1:8 GeV and T = 250 MeV is shown in

Fig. 9: curves corresp ond to y =2:0, 2:5 and 3:0. The numb er of detected charged

n:s:

hadrons at each set of parameters has to b e compared with the total number of charged

hadrons generated in event. The forth column of Table 3 shows the average eciency

of charged hadron detection in terms of , T and y . The charged hadron

ch:had: n:s:

, GeV T , MeV y

n:s: ch:had: str:

1.8 130 2.5 0.56 0.23

1.8 190 2.5 0.69 0.29

1.8 250 2.5 0.79 0.39

1.8 250 2.0 0.65 0.22

1.8 250 3.0 0.88 0.61

3.0 250 2.5 0.81 0.62

Table 3: Detection eciency of charged hadron and strangelets in terms

of , T and y .

n:s:

multiplicity of the Centauro-typ e events in the detector is rather small, not more that 120 11 20000 20000 ∆ T=190 MeV yn.s.=2.0 17500 T=250 MeV 17500 ∆ yn.s.=2.5 15000 15000 ∆ yn.s.=3.0 12500 12500

10000 10000

7500 7500

5000 5000

2500 2500

0 0 0 50 100 150 200 0 20 40 60 80 100 120 140 160 180 200

Ndet. ch.h. Ndet. ch.h.

Figure 8: Charged hadron multiplicityin Figure 9: Charged hadron multiplicityin

the detector at y =2:5, =1:8 GeV the detector at =1:8 GeV, T = 250 and

n:s:

and twovalues of T = 190 and 250 MeV. three values of y =2:0, 2:5 and 3:0.

n:s:

with the mean values 30 60. Photon multiplicityismuch smaller as it is seen from Fig.

Small multiplicity in the Centauro events seems to b e anomalous for nuclear collisions.

In ordinary hadron events the multiplicity is exp ected to b e of the order of some thousand.

Fig. 10 shows the charged hadron multiplicity in ordinary hadron events detected by

CASTOR as predicted by HIJING. The multiplicity in the minimum bias events is several

times higher that that in Centauro-typ e events, the mean detected multiplicity in hadron

events is 1500 which is ab out 30 times more in comparison with Centauro events.

Because of their higher mass strangelets are b o osted forward more than ordinary

hadrons are. Therefore strangelets have a tendency to y closer to the b eam. The

distribution of the radius of strangelet hits on the detection plane at =1:8 GeV,

T = 250 MeV and y =2:5isshown in Fig. 11. The shadowed area corresp onds to

n:s:

the detector surface. The eciency of strangelet detection at di erentvalues of the

str:

mo del parameters is given in the last column of Table 3.

Cosmic ray exp eriments observed also the high energy collimation in the forward region

in Centauro-typ e events [6]. As the degree of the collimation the ratio of multiplicity and

dep osited energy in the central core to those total values was taken:

N R

core core

= ; = :

N E

tot tot

Certainly the observed values of the multiplicity and energy collimation dep end of the

detector size. For the small CASTOR detector with radii 4

ultiplicityin

30 Figure 10: Charged hadron m

the detector in minimum bias events pre- y HIJING. 20 dicted b

0 0 500 1000 1500 2000 2500 3000 3500

Ndet. ch.h.

cho ose the central part of the detector, say, with R<10 cm to measure these values.

But if CASTOR can b e increased in the outer size, say,uptoR = 35cmorifit

out

can work along with the mid-rapidity detector covering central region, the collimation

measurementwould b e more signi cant. In Table 4 we show the collimations and

N E

with the central part of the detector of the radius R = 10 cm in Centauro events with

core

di erent sets of parameters and in hadron events predicted by HIJING. This table also

shows the observed in the detector ratios of hadron-to-total multiplicities and dep osited

energies in Centauro-like and hadron-likeevents. This table gives bright signatures to

P P

Eventtyp e N =N E = E

N E h tot h tot

Centauro events

, GeV T , MeV y

n:s:

1.8 130 2.5 0.70 0.83 0.95 0.99

1.8 190 2.5 0.62 0.77 0.93 0.99

1.8 250 2.5 0.54 0.70 0.90 0.98

1.8 250 2.0 0.64 0.79 0.89 0.98

1.8 250 3.0 0.42 0.55 0.91 0.98

3.0 250 2.5 0.52 0.68 0.95 0.99

Hadron events

0.38 0.58 0.58 0.75

Table 4: Degree of the multiplicity and energy collimation and and

N E

hadron-to-total multiplicity and energy ratios on Centauro and hadron minimum

bias events according the HIJING mo del.

observe Centauro events which are distinguished from the ordinary hadron events by the 13 7000

6000

5000

Figure 11: Distribution of hit radius of

4000

strangelets on the detection plane at =

:8 GeV, T = 250 MeV and y =2:5.

3000 1

n:s:

Shadowed area corresp onds to the detector

2000 surface.

1000

0 5 10 15 20

Rstr , cm

event collimation parameters and smallness of the electromagnetic comp onent.

Conclusion

We presented quantitative results of Centauro events observation in heavy ion collisions at

LHC energies. The phenomenological mo del of Centauro events was originall y intro duced

in pap ers [2, 3 ] and gives a transparent explanation of suchevents. On the basis of this

mo del we construct the quantitative mo del and the event generator which provides a to ol

to estimate detection eciency of Centauro events and strangelets.

Possibility to observe Centauro events dep ends strongly on the parameters of the

mo del such as thermo dynamical characteristics and the nuclear stopping p ower. Contrary

to hadrons emitted from the Centauro reball strangelets are harder to detect b ecause of

their higher mass in comparison with that of hadrons.

The signatures for Centauro events observation with the CASTOR detector can b e

summarized as follows:

small detected charged particles multiplicity, hN i = 50 compared to hN i =

ch: h: ch: h:

2000 in minimum bias hadron events;

small detected photon-to-hadron multiplicities ratio, hN =N i = 0:9 with

h tot

hN =N i =0:5 in hadron events;

h tot

P P

small photon-to-hadron energy dep osited in the detector, h E = E i =0:99

h tot

P P

with h E = E i =0:75 in hadron events;

h tot

large average transverse momentum, hp i > 1 GeV=c compared to hp i =0:44 GeV=c

T T

in hadron events; 14

higher multiplicity collimation with the core radius R = 10 cm, =0:4 0:7

core N

dep ending on mo del parameters; hadron events have =0:4 which is comparable

with Centauro events only at critical values of parameters;

high energy collimation, =0:6 0:8 while hadron events have =0:6 which

E E

is also at the lower limit of Centauro events. Both collimations di er much more

in Centauro-typ e and hadron-typ e events with increasing the detector acceptance,

say,upto R = 35 cm or with using the central detector.

out

Centauro events can b e accompanied by highly p enetrating ob jects with A>6,

which can b e connected with strangelets.

The authors would like to thank Zbigniew Wlo darczyk for useful remarks.

References

[1] A.D.Panagiotou et al., Z. Phys. A333 1989, 355.

[2] A.D.Panagiotou et al., Phys. Rev. D45 1992 3134.

[3] M.N.Asprouli et al., Asrtopart. Phys. 2 1994 167.

[4] ALICE Technical Prop osal, CERN/LHCC/95-71.

[5] E.Gladysz-Dziadu s, A.D.Panagiotou, Intern. Symp. on Strangeness and Quark Mat-

ter, Krete, 1994, p.265; Internal note ALICE/PHY/95-18.

[6] Chacaltaya and Pamir Collab orati on, Contributions to 23rd ICRC Calgary, 19{30

July, 1993, ICRR-Rep ort-295-93-7 1993; Nucl. Phys. B370 1992 365.

[7] B.Muller, Preprint DUKE-TH-92-36, e-print hep-th/9211010 .

[8] J.W.Harris, B.Muller, Preprint DUKE-TH-96-105, e-print hep-ph/9602235.

[9] Ask A.Panagiotou about this reference.

[10] T.S.Biro, J.Zimanyi, Nucl. Phys. A395 1983 241.

[11] M.Gyulassy, X.-N.Wang, Comput. Phys. Commun. 83 1994, 307; Preprint LBL-

34346; e-printnucl-th/950202 1.

[12] K.Werner, Phys. Rept. 232 1993, 87

[13] T.Sjostrand. Pythia 5.7 and Jetset 7.4 physics and manual. Comp. Phys. Comm.

82 1994 74. 15