Ghosh, Dipak

Mallick, Asok Kumar

Purkait, Krishnadas

Sarkar, Sharmila

English

IACS Institutional Repository

Indian J. Phvs. 71A (6 ), 657-667 (1997)I J P  A— an international journalAzimuthal asymmetry of black particles in high-energy interactions—evaporation model revisitedDipak Ghosh, Sharmila Sarkar, Krishnadas Purkait and Asok Kumar MallickHigh Energy Physics Division, Department of Physics, Jodavpur University. Calcutta-700 032. IndiaReceived 2 May 1997, accepted 22 August 1997Abstract : Azimuthal anisotropy of target fragments in C12-Em interactions at 4.5 GeV/c/n and O l6-Em interactions at 60 GeV/c/n is investigated here. The evaporation model fuils to explain the experimental data. The model of local healing is found to describe the data satisfactorily.Keywords : Azimuthal anisotropy, target fragments, local heating model l'ACS No. : 25.75.-q1. IntroductionIn the cases of relativistic nucleus-nucleus inelastic interactions at high energies a large part of the total cross section is due to multiparticle production. It is also found that the characteristics of disintegration are functions of number of interacting nucleous of the projectile and the target nuclei and therefore, also functions of the mass of the colliding nuclei. After interaction, a spectator piece of the target is formed and if the impact parameter is sufficiently large, a spectator piece of the projectile is also formed f 1-4].According to Additive Quark model, two incoherent 'wounded' quarks are responsible for particle production phenomena in nucleus-nucleus inelastic interactions at high energies [5], In the Dual-Parton model, exchange of colours is the first step in inelastic hadronic collisions at high energies. In the intermediate state, two chains are formed for every exchange of colours. These chains which fragment into hadrons7 1 A(6)-6© 19971ACS658 Dipak Ghosh et alare attached to different objects in the projectile and the tatget nuclei [51. According to evaporation model, black particles are emitted from a system in statistical equilibrium and the distribution of those particles are expected to be isotropic in the angular range | 6 |.Here, we mention a few deficiencies of evaporation model. Sullivan e t  a l  |7], in their plastic detector experiment Kullberg and Otterlund [8 ], in their cosmic ray experiment showed deviations from evaporation model. Warwick e t  a l - [9] and Gossel e t  a l  \ 1 0 ] also observed deviations from conventional evaporation scenario.It is also found from the study of the energy spectrum of slow pqriiclcs that the existence of inequilihrium states exist in the system of nucleons insiVie an excited nucleus | 6 - l  I]. \Powell e t  a l  [121 supposed local heating of the target nucleus. During collisions, some part or the whole of the target nucleus is affected. This affected part of the residual target nucleus is heated due to absorption of a part of the energy ol the projectile. This is known as local heating model (LHM). In the cases of nonccnirul collisions, the residual target nucleus is an assembly of inhomogencouslv heated nucleons which arc in statistical equilibrium. In the cases of central collisions, the degree of homogeneity in heating of the nucleons of the residual target is. significant and hence the statistical equilibrium in the excited residue is also significant. According to LHM, in the cases of noncentral collisions, those black particles which aie near the surface of locally heated region and moving towards the surface ol that icgmn may escape residual target easily, whereas those black particles which arc interior to the residual target after encountering a number of collisions, either can escape residual target or cannot escape residue due to lack of energy. In the cases of central collisions, as the affected region of the target nucleus is increased, the number of black tracks is also increased [ 1 2 ].The recent revival of interest in studying azimuthal asymmetry in detail is connected with the observation of an iniermitlency effect in nucleus-nucleus inelastic interactions at high energies 113].This paper reports an extensive study of the azimuthal asymmetry of black particles in Cl2-Em and Ol6-Em interactions at incident beam-momenta 4.5 GcV/c/n and 60 GcV/c/n respectively, in the light of LHM (local heating model).2. Experimental dataThe required data is obtained from NIKF1BR2 nuclear research emulsion plates (25 cm x 1 0  cm x 600 pm) irradiated horizontally with C1 2  or Olft beam from JINR synchrophasotron. Primary inelastic events of Cl2-Em interactions and primary inelastic events of Ol6-Em interactions are investigated here. We have classified the secondary particles in b,  g,  s, particles following the usual nuclear emulsion methodology.Azimuthal asymmetry of black particles etc 659(i) The emission tracks having a range < 3 mm and ionisation l  > 6 / 0  where / 0  is the plateau of ionisation value of the singly charged particles in the emulsion pellicle, are known as black ( b )  tracks.(ii) The emission tracks having a range > 3 mm and ionisation l .4/ 0  < / < 6 / 0  are known as grey (#) tracks.(iii) The tracks having ionisation / < 1 .4/ 0  and very long ranges are known as shower ( s)  tracks. The tracks with emission angle greatei than 3° are considered here to exclude the contamination of projectile associated fast fragments.Absemetova e t  a l  [14) showed from the data of the energy of the evaporated slow particles and the degree of excitation of the residual target nucleus that the maximum of the energy of the slow particles in the energy spectrum shifts towards the lower energies with the increase ol the number of black-grey tracks. This phenomenon cannot be explained by cascade evaporative model (CEM).3. Method of analysisWe have studied here the azimuthal asymmetry of black particles in non-overlapping equal width cos <9 bins and in the entire cos 0 range.If the number ol black tracks and grey tracks in an event be n h and respectively,thenN, ,  = n h +where N lt is the number of heavy ion tracks in the event. The events ate divided into a lew N h intervals which are ( I < N h < 5), ( 6  < N h < 10), ( I 1 < N h < 15), (16 < N h < 20). The non-overlapping cos 0  bins are ( - 1 . 0  to - 0 .6 ). (- 0 . 6  to - 0 .2 ). (- 0 . 2  to 0 .2 ). (0 . 2  to 0 .6 ), (0 . 6  to I 0 ).For the events in a N h interval, azimuthal asymmetry of black particles of the i-th event in the j-lh cos 0 hin is defined as.where .v(/ = number of black particles of the i-lh event in the j -th cos 0 bin whose azimuthal angles arc less than 180°.y lf = number of black particles of the /'-th event in the /'-th cos 0 bin whose azimuthal angles arc greater than 180°. For the events of a given N fl interval average azimuthal asymmetry in the_/-th cos 0 interval is_  X w ,W, = - S - V -  1 =  I to AT.' N *where N * is the total number of events in the 7 -th cos 0 bin lor a given N h interval. As the degree of excitation of the target nucleus depends on N , r  we have taken N h as a parameter of the event [14],660 DifHik Ghosh et alThe above formulae are applied for calculating average azimuthal asymmetry for the events of each N h interval in the entire cos# range.4. Results and discussionsFigures 1(a) to 1 (d) are asymmetry (V )^ v's c o s O  graphs of ,2 C-Em interactions at 4.5 GeV/n/c for different N h intervals. Figures 1 (e)to 1 (g) are asymmetry (W) vs cos0♦ i.o rw1 M ,1 1 1►X j-10 -0-5 03 . |♦ COSO — ♦-0 5 ♦-10 -U)10w 6 <Nk<tat os-1.0 -0 5* 05 ♦ '* COS • -  —♦ -05-l 0 -(b)I 0 w! 0<116 C Nh € 70♦  1 ^♦  -as 0 5 i♦ COS 0 --- --03-i n „( d )Figure 1. (a) to (d) are plots of W vs cos 0 graphs for l2C-Em  interactions al 4 5 GeV/c/nFigure I. (e) to (g) are plots of IV vs cos 0 graphs for ,60 -Em  mteiactions at 60 GeV/c/ngraphs of l6 0-Em interactions at 60 GeV/n/c for different N h intervals. It is seen from the graphs that with the increase of N h% average azimuthal asymmetry decreases lor both ,2 C-Em and ,6 Q-Em interactions. It is also seen from the graphs 1(a) to 1(d) thatAzimuthal asymmetry»of black particles etc 661average azimuthal asymmetry of black particles in the cos0  bins of forward emission angles (0 < 90°) are much lower than those of in the backward emission angles (6 >  90°).Figure 2. (a) and (b) are plots of W vs N ^  graphs l2C-Em interactions and ^ -E m  interactions at 4 5 GeV/c/n and 60 GeV/c/n respectivelyFigures 2(a) and 2(b) are average azimuthal asymmetry vs N h graphs for the entire cos0 range for l2 C-Em interactions and ,6 0-Em interactions at 4.5 GeV/c/n and 60 GeV/c/n respectively. Graphs 2(a) and 2(b) show that average azimuthal asymmetry of black particles decreases with the increase of N h for both 1 2C-Em and 1 6 0-Em interactions. Thus, this analysis shows that the average azimuthal asymmetry of black particles decreases withGRf Y TRACKS- I < IQI 0 < Ir1f.I fIhr0 too 200 300 360(a)<P000730 0030J 0075-h i a v y  tr a ck s  - i < C o « e  < 1_ ni— i— j_J—i__IOC 700 300 360<P(c)Figure 3. (a) to (c) are plots of p{0) (for grey, black and heavy tracks respectively) vs 0 graphs in the entire cos0 region for ,2C-Em interactions 4.5 GeV/c/n662 D ip a k  G h o sh  et al(c)Figure 4. (a) to (c) are plots of normalised p(0) (for grey, black and heavy tracks respectively) vs 0 graphs in the entire cos0 region for ,60-Em interactions at 60 GeV/c/n.(b) ♦Figure 5. (a) to (c) ore plots of normalised p{0) (for grey, black and heavy tracks respectively) vs 0 in the forward emission angles (0  < 90°) region for 12C- Em interactions at 4.5 GeV/c/nthe increase of N h and the observations speak in favour of local heating model of target nucleus. From graphs 2(a) and 2(b), any significant dependence of average azimuthal asymmetry of the black particles on the incident projectile energy is not found. Our data is also consistent with the results of Absemetova e t a l  [14] where similar study was made for proton-nucleus interactions at 67-400 GeV.Here, we added a few more graphs to substantiate our results. We drew normalised azimuthal angle ( 0 ) distribution of tracks p(0 ) v s  0  graphs of grey, black and heavy tracks in the entire cos0 region for ,2 C-Em interactions [Figures 3(a) to 3(c)] and , 6 0-Em interactions [Figures 4(a) to 4(c)] at 4.5 GeV/n/c and 60 GeV/n/c respectively./"!*>) /*(*■) /»(0IAzimuthal asymmetry o f black particles etc 663Figure 6. (a) to (c) ore plots of normalised p{Q) (for grey, black and heavy tracks respectively) vs 0 in the forward emission angles (0 < 90°) region for '^O-Em interactions at 60 GeV/c/n.Figure 7. (a) to (c) are plots of normalised p (f)  vs 0 graphs for grey, black and heavy tracks respectively in the backward emission angles (0 > 90°) region for ,2C-Em interactions at 4.5 GeV/c/n.664 D ip a k  G hosh  et al040A0 •Figure 8. (u) to (c) are plots of normalised p(0)vx <p graphs for grey, black and heavy tracks respectively in the backward emission angles (0 > 90°) legion for 1 V)-Em interactions at 60 GeV/c/n0 0150 16 O.Oioo 2 00050G R E Y  TRACKS- l < C o » 0  < 10  1 0 0  200 300 360 (a) *(a) <P(b) *0025000200— 0 0150 *±z 001000-00500 100 200 300 360(b) $SLACK t r a c k s- K C o i K lU jnA j I L ___Figure 9._ (a) to (c) are plots of normalised N ( 0 ) v s $  (of grey, black and heavy tracks respectively of an event) in the entire cos0 range for '^C-Em interactions at 4.5 GeV/c/n.Figure HI. (a) to (c) are plots of normalised N ($ )v s 0  (of grey, black and'heavy tracks respectively of an event) in the entire cos 9 range for 160-Em interactions at 60 GeV/c/n.Azimuthal asymmetry o f black particles etc 665' ±20 0150 00(00  0  0030(a)00150E l00,00(b)o ic v  t i a c hC « » 0 > 02000BLACK TRACKS C*» i >  0100 200 500 540000130-500 140 0 0100-Z  0  0030-(c)HEAVY TRACKS C o i O >  0y " v ti/k100 100 500 3600Figure 11. (a) to (c) are plots of normalised /V(0) w 0 (of grey, black and heavy tracks respectively of an event) in the forward emission angles (0  < 90°) region for ,2C-Em interactions at 4.5 GeV/c/nZoooso-GREY TRACKS Cp i 0 > 05=c—1-------* kfa)(b)z100 200*0  0130' 0  0 1 0 0  z  0 0050 -GREY TRACKS Co i B < 0500 540100 200 500 5400(a)0  0140-fooioo-j Z  0  0030 -• i a c k  t r a c k s  Co»4 < 0A100 200 500 560$ 0(b)Figure 12. (a) to (c) are plots of normalised N( 0 ) vs 0 Figure 13. (a) to (c) are plots of normalised 0) vs 0 (of grey, black and heavy tracks respectively of an (of grey, black and heavy tracks respectively of an event) in the forward emission angles (Oc 90°) region event) in the backward emission angles (0 > 90°) region for ,60-Em interactions at 60 GeV/n/c. for t2C-Em interactions at 4.5 GeV/c/n.71 ATM-7666 Dipak Ghosh et alWe drew similar plot of p(0) vs  0  graphs of gre>, black and heavy tracks for 0  < 90° (forward emission angles) region [Figures 5(a) to 5(c) for ,2 C-Em interactions at 4.5 GeV/n/c; Figures 6 (a) to 6 (c) for ,6 0-Em interactions at 60 GeV/n/c] and for 6  > 90° (backward emission angles) region [Figures 7(a) to 7(c) for ,2 C-Em interactions at 4.5 GeV/n/c; Figures 8 (a) to 8 (c) for l6 0-Em interactions at 60 GeV/n/cJ.Then we drew normalised 0 (averaged over all tracks of the event) distribution N(<p)  of event for grey, black and heavy tracks of the event vs 0 [Figures 9(a) to 9(c) for ,2 C-Em interactions at 4.5 GcV/n/c; Figures 10(a) to 10(c) for , 6 0-fem interactions at 60 GeV/n/c] in the entire cos#region.1^ 0 0 1 0 0 -(a) 0 02000 0150-— 0  0 1 0 0  z0 0050(b)GREY T R A C K SC o » 0 < T O/ V ^ - N - ^ r ^ P - n  n r0 0200 -) 100 ? 0 0  $3 0 0  360  — 0 0150-z  o oioo -B L A C K  T R A C K S0 0050-C o i 0  < 00( c )1 0 0 200*300  360h e a v y  t r a c e s  C o i 0 < 0100 200*300  3 6 0Figure 14. (a) to (c) are plots of normalised N{0)  vs0  (of grey, black and heavy tracks respectively of an event) in the backward emission angles (0 > 90°) legion for *60-Hm  interactions at 60 GeV/n/c,Then wc plotted N ( Q )  vs 0 graphs for grey, black and heavy tracks of event for forward emission angles ( 0  < 90°)' [Figures 1 1 (a) to 1 1 (c) for ,2 C-Em interactions al4.5 GeV/n/c; Figures 12(a) to 12(c) for ,6 0-Em interactions at 60 GeV/n/c| and for backward emission angles 6  > 90° [Figures 13(a) to 13(c) for 1 2 C-Em interactions at4.5 GeV/n/c; Figures 14(a) to 14(c) for l6 0-Em interactions at 60 GeV/n/c] regions.AcknowledgmentsWe are grateful to Prof. K D Tolstov of JINR, Dubna, Russia and Prof. P L Jain (SUNY, New York) for supplying us exposed plates for measurements. Authors are grateful to the University Grants Commission for its financial help under COSIST program. Authors acknowledge the contribution of Dr. Tapas Kumar Ballabh, Department of Physics, Jadavpur University, Calcutta in computation. S Sarkar acknowledges the receipt of aAzim uthal asymmetry o f  b lack particles etc 667Senior Research Associateship awarded by the Council of Scientific and Industrial Research, Government of India, during the tenure of this work.References|1] E S Basova el til Sov. J Nud Phys 30829(1979)[2] V A Antonchik el ul Sov J Null Plm  46 790(1987)13] G D Westfall etui Pliys Rev l.ell 37 1202 (1976)|4| William 0  Myres Nut I Pliys A296 177 (1978)[5| A Bialas Quark Mutter Formation and Heavy ton Collisions (Proteedmus of Bielfeld Workshop, May I9R2) eds M Jacob and H Sal/ (Singapore ■ World Scientific) p 139 (1982)J6J 17 Ghosh el al J Phys G20 1077 (1974)17] James D  Sullivan er al Phys Rev Leu 30 136 (1973)[8] R Kullberg and l Otterlund Z Phys 259 245 (1973)(9] A I Warwick et al Phys Rev C27 1083 ( 1983)[10] J Cosset e ta lP /m  Rev C16 629 (1977)| IIJ TEiieson/U/r Phw 9 425 ( I960). N Dulkhazhaev et ul Sov J Nud Phys 23643 (19/6)[I2[ C  F Powell. F Fowler and D  H Perkins Study of Elementary Particles by Photographic Method (NewYoik Pcigamon) (I960)[131 D Ghosh et al Hadron J 18 599 ( 1995)114[ Zh A Absemetova et al Sov J Nui l. Phys. 42 909 ( 1985)

Azimuthal Asymmetry of Black Particles in High-Energy Interactions — Evaporation Model Revisited

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Azimuthal Asymmetry of Black Particles in High-Energy Interactions — Evaporation Model Revisited

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