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Production of helium projectile fragment in 84Kr-emulsion collisions at 1.7 A GeV
Radiation Measurements 50 (2013) 50e55
Contents lists available at SciVerse ScienceDirect
Radiation Measurements journal homepage: www.elsevier.com/locate/radmeas
Production of helium projectile fragment in
84
Kr-emulsion collisions at 1.7 A GeV
Dong-Hai Zhang* Institute of Modern Physics, Shanxi Normal University, Linfen, Shanxi 041004, China
h i g h l i g h t s < Multiplicity distribution can be well represented by two Gaussian distributions. < Projected angular distributions can be well fitted by two Gaussian distributions. < Transverse momentum distribution can be well explained by two Gaussian distributions. < The temperature of emission sources is obtained from pt2 distribution. < The temperature parameter is independent of the target size.
a r t i c l e i n f o
a b s t r a c t
Article history: Received 10 February 2012 Received in revised form 27 September 2012 Accepted 15 October 2012
Multiplicity, projected angular and transverse momentum distributions of helium projectile fragment (HPF) produced from 1.7 A GeV 84Kr induced different type of emulsion targets (H, CNO and AgBr) interactions are studied. It is found that the distributions of HPF from 84KreH, CNO, AgBr and emulsion interactions can be well explained by two Gaussian distributions. These imply the existence of two distinct emission sources (cold and hot source) of HPF in 84KreH, CNO, AgBr and emulsion interactions. The dominant source is the cold one (projectile spectator source) with lower temperature and the other is hot one (projectile participant source) with higher temperature. The temperature parameters of cold and hot source are obtained from p2t distribution fitting using two Rayleigh distribution, which is independent of the target size within experimental errors. Ó 2012 Elsevier Ltd. All rights reserved.
Keywords: Relativistic heavy-ion collision Helium projectile fragment Projectile fragmentation Nuclear emulsion
1. Introduction The particle production in relativistic nucleusenucleus interactions have been extensively studied in recent years. Most of the studies have concentrated on particle production in participant region with the goal of examining possible signals of quark gluon plasma (QGP). Based on the participant-spectator concept (Bowman et al., 1973) and the simple fireball model (Westfall et al., 1976) the projectile and target sweep out cylindrical cuts through other. Raha et al. (1984) proposed that during the separation of the spectator from the participants, there must be some intercommunication between them which results in the excitation of the spectators. Since this communication is strongly dependent on whether or not the participants form a QGP, the energy imparted in terms of temperature to the spectators may carry characteristic information in regard to the formation of a QGP in the participant region. They have proposed that observation of two obviously different temperatures in the projectile fragmentation region would be explained as a possible signal for the production of a QGP. * Tel./fax: þ86 3572051347. E-mail address: [email protected]. 1350-4487/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.radmeas.2012.10.006
Helium projectile fragments (HPFs), produced from projectile spectator, have been studied experimentally by many groups in recent years (Sengupta et al., 1989; El-Nadi et al., 1993, 2002; Jilany, 2004; Song et al., 2005; Kamel, 1999; Cherry et al., 1997; Singh and Jain, 1994; Singh et al., 1991; Jain and Aggarwal, 1986; Ganssauge et al., 1985; Joseph et al., 1989; Aggarwal et al., 1983; Adamovich et al., 1993; Ghosh et al., 1988; Bhalla et al., 1981). It is found that the multiplicity distribution of HPFs can be well explained by the Koba-NielseneOlesen (KNO) scaling hypothesis (Koba et al., 1972). The angular distribution or transverse momentum distribution of HPFs from heavy projectile has a long tail which cannot be represented by a single Gaussian distribution. Most of these distributions imply the existence of two distinct emission sources of HPFs. The dominant one is the cold source with an average excitation energy of about 7e10 MeV and the other is assumed to be of a fireball type at a high temperature of 40e70 MeV (Joseph et al., 1989; Ganssauge et al., 1985; Aggarwal et al., 1983; Ghosh et al., 1988; Bhalla et al., 1981). Two source emission of HPFs seem to support the idea of the formation of QGP proposed by Raha et al. (1984), but there are two experimental results cannot be explained by two emission sources. One of them can be explained by only one emission source
D.-H. Zhang / Radiation Measurements 50 (2013) 50e55
51
Table 1 Single Gaussian fitting parameters of HPFs multiplicity, projected angular and transverse momentum distributions in 1.7 A GeV 84Kr-emulsion interactions. Dis. type
Target
Average
Multiplicity
H CNO AgBr Emulsion H CNO AgBr Emulsion H CNO AgBr Emulsion
1.77 1.54 1.84 1.05 1.34 20.38 12.34 11.52 116.47 100.38 138.77 120.84
Projected angle
Trans. momentum
c2 /DOF
Error 0.15 3.74 0.32 0.33 0.26 2.69 1.55 0.98 5.88 15.44 8.50 6.37
1.25 3.94 2.53 2.71 1.49 7.02 6.25 5.77 67.68 132.58 132.04 122.95
0.17 1.36 0.28 0.20 0.22 0.51 0.38 0.24 7.13 15.81 11.94 8.94
2.92 1.56 1.11 0.57 0.96 1.49 1.14 3.10 1.25 4.03 5.50 10.97
(Adamovich et al., 1993) and another can be explained by three emission sources with different temperatures (Cherry et al., 1997). So emission of HPFs in relativistic nucleusenucleus collisions is not conclusive. In this paper we present a systematic investigation of multiplicity distribution, projected angular distribution and transverse momentum distribution of HPFs produced in 1.7 A GeV 84Kr induced different types of emulsion targets (H, CNO and AgBr). The transverse momentum distribution is compared with Maxwelle Boltzmann distribution, a clearly signature of two temperature is observed in the experimental data, and both of them are independent of the target size within experimental errors.
Fig. 1. Photograph of different kinds of 84Kr-emulsion interacting events, (a)Nh 1, (b) 1 < Nh < 8, and (c)Nh 8.
Fig. 2. Multiplicity distribution of HPFs produced from different kinds of
84
Kr-emulsion interaction, (a)Nh 1, (b)1 < Nh < 8, (c)Nh 8, and (d)Nh 0.
52
D.-H. Zhang / Radiation Measurements 50 (2013) 50e55
Table 2 Double Gaussian fitting parameters of HPFs multiplicity, projected angular and transverse momentum distributions in 1.7 A GeV Type of distribution
Target
Multiplicity
H CNO AgBr Emulsion H CNO AgBr Emulsion H CNO AgBr Emulsion
First Gaussian distribution Average
Projected angle
Trans. momentum
1.29 0.27 1.66 1.47 1.34 0.23 0.31 0.53 173.19 69.44 250.12 200.36
Kr-emulsion interactions.
c2 /DOF
Second Gaussian Distribution Error
0.83 0.86 0.90 0.21 0.26 0.65 0.46 0.30 524.27 43.61 152.25 109.84
84
Average
0.34 0.45 0.36 0.33 1.49 1.83 1.82 1.76 159.98 180.46 132.90 153.10
0.71 0.83 0.93 1.38 0.22 0.66 0.50 0.41 140.30 25.38 46.83 32.70
Error
1.99 2.82 1.82 1.04
0.25 0.52 0.38 0.25
1.45 2.09 2.73 2.76
0.26 0.36 0.26 0.25
5.51 4.25 5.26 112.00 112.75 113.61 108.66
4.83 3.85 2.91 9.33 6.32 12.03 4.14
2.42 2.82 2.44 56.24 34.95 66.82 60.47
2.56 1.38 1.14 21.55 7.74 21.93 14.73
0.55 0.35 0.49 0.71 0.96 0.38 0.66 0.51 0.23 1.15 2.30 1.99
within 30 mm from the top or the bottom surface of the emulsion plates were not considered for final analysis. For each interaction, the number of shower particles (Ns) and slow-moving (velocity b < 0.7) heavily ionizing particles (Nh) is determined. Shower particle is corresponding to single charged relativistic secondary with velocity b 0.7 and ionization less than 1.4 times of the plateau ionization of single charged minimum ionizing particle. The heavily ionizing tracks are classified into gray tracks Ng (0.3b < 0.7 and range in emulsion R > 3 mm) and black tracks Nb (b < 0.3 and range in emulsion R < 3 mm). Projectile fragments with charge Z 2 are emitted from the breakup of the projectile, essentially travel at the same speed as that of the beam. HPFs that are emitted in the forward
2. Experimental details A stack of nuclear emulsion pellicles 10 10 10 0.06 cm3 in volume, provided by EMU-01 Collaboration (Adamovich et al., 1993), was used in this experiment. The emulsion stack was exposed horizontally to 84Kr beam at an energy of 1.7 A GeV at the Bevatron at Lawrence Berkeley Radiation Laboratory (LBL). The density of the beam was about 103 nuclei/cm2. Interactions were found by along-the-track scanning method with an oil immersion objective of 100 magnification. The nuclear tracks were picked up at 5 mm away from the edge of the plate and carefully followed until they either interacted with emulsion nuclei or escaped from any surface of the emulsion plates. Interactions which took place
Fig. 3. Projected angular distribution of HPFs produced from different kinds of
84
Kr-emulsion interaction, (a)Nh 1, (b)1 < Nh < 8, (c)Nh 8, and (d)Nh 0.
D.-H. Zhang / Radiation Measurements 50 (2013) 50e55
53
cone with respect to the beam direction have grain density ga z 4gmin (where gmin is the grain density of the minimum ionizing particle and it is about 12 grains/100 mm for present experiment) and not charged within 2 cm away from its production point. The emission angle (q) and projected angle (Qproj ) have been measured for each track by taking readings of the coordinates of the interaction point (x0,y0,z0), the coordinates (xi,yi,zi) at the end of the linear portion of each secondary track and the coordinates (x1,y1,z1) of a point on the incident beam. 3. Experimental results and discussions There are 558 84Kr-emulsion unbiased inelastic events are used in present investigation. Based on the number of Nh, the events are classified into three categories. Events with Nh 1 are mainly interactions with H target (interactions with free and quasi-free nucleon) and peripheral interactions with CNO or AgBr targets. Events with 1 < Nh < 8 are mostly with CNO targets and with some admixture of peripheral AgBr interactions. Events with Nh 8 are only interactions with AgBr targets. Fig. 1 shows the photograph of different kinds of 84Kr-emulsion interacting events. Fig. 2 shows the multiplicity distribution of HPFs from 1.7 A GeV 84 Kr induced different type of emulsion targets (H, CNO, AgBr and emulsion) interactions, where Na means the multiplicity of HPFs. It is found that the width and the position of maximum of the distribution increase with the increase of the target mass. The distribution is fitted by single and double Gaussian distribution respectively. The fitting parameters including c2 /DOF are
Fig. 4. Transverse momentum distribution of HPFs produced from different kinds of
Fig. 5. The cumulated transverse momentum distribution of HPFs produced in 1.7 A GeV 84Kr induced different type of emulsion targets interactions.
84
Kr-emulsion interaction, (a)Nh 1, (b)1 < Nh < 8, (c)Nh 8, and (d)Nh 0.
54
D.-H. Zhang / Radiation Measurements 50 (2013) 50e55
Table 3 Values of the two temperatures from transverse momentum distributions of HPFs produced in 1.7 A GeV Target
C1
H CNO AgBr Emulsion
11.87 38.73 63.73 48.38
s21
5.56 4.41 3.45 2.47
2
(A MeV/c)
41576.0 35323.0 31992.0 32713.0
11116.0 1846.4 857.6 779.4
T1 (MeV) 165.9 140.9 125.2 130.5
pt ¼ p sin q;
Kr induced different type emulsion targets interactions.
s22 (A MeV/c)2
C2
44.3 7.4 3.4 3.1
presented in Tables 1 and 2 respectively, where DOF means the degree of freedom of simulation. Comparing the fitting parameters and the values of c2 /DOF it is clear that the distribution can be well represented by two Gaussian distributions. The multiplicity distributions of the produced fragments have been regarded as a potentially useful source of information of the underlying production mechanism. Fan (Fan and Liu, 2008) have studied the multiplicity distributions of HPFs in relativistic nucleusenucleus collisions using the two source emission picture, each source is represented by the exponential function. The projected angular distribution of HPFs from 1.7 A GeV 84Kr induced different type of emulsion targets (H, CNO, AgBr and emulsion) interactions is shown in Fig. 3. The distribution from Kre H interaction can be well fitted by a single Gaussian distribution, but the distributions from KreCNO, Kr-emulsion and KreAgBr interactions have a long tail, which cannot be fitted by a single Gaussian distribution and need two Gaussian distribution to fit the data. The fitting parameters of single and double Gaussian fit are presented in Tables 1 and 2 respectively. It is evident that double Gaussian fit can well represent the experimental data. From results in Table 2 we can see that the angular widths of the first Gaussian fit and the second Gaussian fit is independent of the target size. This target-independent behavior of angular widths is a characteristic feature of the hypothesis of limiting fragmentation. Heckman and Aggarwal (Heckman et al., 1978; Aggarwal et al., 1983) have studied the projected angular distributions for HPFs produced in Nh ¼ 0 type of relativistic nucleusenucleus interactions. The distributions can be well described by a single Gaussian, and the standard deviations of s(qproj) are in reasonable agreement with the theory of Lepore and Riddell (1974), they treated the fragmentation of high energy nuclei by using a quantum mechanical sudden approximation. The transverse momentum per nucleon (pt) of a projectile fragment was calculated on the basis of its emission angle q,
84
90.72 61.22 36.62 52.28
7.93 5.30 5.00 3.36
8161.4 7818.8 5652.4 6837.5
1149.1 1184.5 1264.8 704.6
T2 (MeV) 32.6 31.2 22.5 27.3
4.6 4.7 5.0 2.8
c2 /DOF 0.10 0.16 0.61 0.41
mass heats the swept-out nucleons leading to a quasi-equilibrium fireball. This fireball can be described by a statistical (Maxwelle Boltzmann) distribution in the projectile rest frame. The transverse momentum of a projectile fragment is given by
1=2 pt ¼ Am0 g2 1 sin q;
(2)
where A is the atomic number and g the Lorentz factor of the projectile. If we assume that the emission of HPFs is Maxwelle Boltzmann distribution in the projectile rest frame with a certain temperature T, the integral frequency distribution of the square of the transverse momentum per nucleon is
A p2 : ln F >p2t ¼ 2m0 T t
(3)
The linearity of such a plot would be strong evidence for a single temperature. Fig. 5 shows the cumulative plots of Fð> p2t Þ as a function of p2t for HPFs from 1.7 A GeV 84Kr induced different kind of emulsion targets (H, CNO, AgBr and emulsion) interactions. All of the plots can be well fitted by two Rayleigh distribution of the form
F
p2t
¼ C1 exp
p2 t2 2s1
!
þ C2 exp
! p2t 2 ; 2s2
(4)
where si ¼ (2/p)1/2i(i ¼ 1,2), which is related the temperature of HPFs emission source. The evidence of two temperatures is found in all of the data sets. The temperature and c2 /DOF of simulation for different kinds of events are listed in Table 3. The experimental results show that the percentage of HPFs from hot source increases with the increase of target size, and the percentage of HPFs cold source decreases with the increase of target size. The temperature of cold and hot sources is the same with experimental errors for different targets, no obvious dependence of target size is found in our data sets.
(1)
where p is the momentum per nucleon of beam which can be calculated from beam energy per nucleon (E), p ¼ (E2 þ 2m0E)1/2. m0 is the nucleon rest mass and q the emission angle of the projectile fragment with respect to the beam direction. Fig. 4 shows the transverse momentum distribution of HPFs from 1.7 A GeV 84Kr induced different type of emulsion targets (H, CNO, AgBr and emulsion) interactions. The width and the position of maximum of the distribution increase with the increase of the target mass. The distribution can be well represented by two Gaussian distributions. The fitting parameters of single and double Gaussian distribution are presented in Tables 1 and 2 respectively. According to the participant-spectator model, with the increase of the target size the overlapped region and also the contacted area increases, the communication between participant and spectator increases. This results in the increase of the excitation energy of HPFs, so the average of transverse momentum of HPFs is increased. Based on the fireball model (Westfall et al., 1976) of relativistic nucleusenucleus collisions, the available energy in the center of
4. Conclusions From the study of HPFs distributions in 1.7 A GeV 84Kr induced different kinds of emulsion targets (H, CNO, AgBr and emulsion) interactions, we can conclude that the multiplicity distributions and transverse momentum distributions can be well represented by two Gaussian distributions, the width of the distribution increases with the increase of the target size. The projected angular distribution of HPFs from KreH collisions can be fitted by a single Gaussian distribution, but the distribution of HPFs from KreCNO, AgBr and emulsion collisions need two Gaussian distribution to fit. The cumulated transverse momentum distribution can be well fitted by two Rayleigh distribution, which indicate that the HPFs is emitted from two emission source. The dominant source is the cold one (projectile spectator source) with lower temperature and the other is hot one (projectile participant source) with higher temperature. No obvious dependence of the temperature of emission source on the target size is found in our data sets.
D.-H. Zhang / Radiation Measurements 50 (2013) 50e55
Acknowledgment This work has been supported by the Chinese National Science Foundation under Grant No. 11075100, the Natural Science Foundation of Shanxi Province under Grant No. 2011011001-2, and the Shanxi Provincial Foundation for Returned Overseas Chinese Scholars, China (Grant No. 2011-058). We are grateful to Professor L. Otterlund of Lund University in Sweden for providing the emulsion stack. References Adamovich, M.I., Aggarwal, M.M., Alexandrov, Y.A., Amirikas, R., Andreeva, N.P., Anzon, Z.V., Arora, R., Avetyan, F.A., Badyal, S.K., Basova, E., Bhalla, K.B., Bhasin, A., Bhatia, V.S., Bogdanov, V.G., Bubnov, V.I., Burnett, T.H., Cai, X., Chasnikov, I.Y., Chernova, L.P., Chernyavski, M.M., Eligbaeva, G.Z., Eremenko, L.E., Gaitinov, A.S., Ganssauge, E.R., Garpman, S., Gerassimov, S.G., Grote, J., Gulamov, K.G., Gupta, S.K., Gupta, V.K., Heckman, H.H., Huang, H., Jakobsson, B., Judek, B., Just, L., Kachroo, S., Kalyachkina, G.S., Kanygina, E.K., Karabova, M., Kaul, G.L., Kitroo, S., Kharlamov, S.P., Krasnov, S.A., Kulikova, S., Kumar, V., Lal, P., Larionova, V.G., Lepetan, V.N., Liu, L.S., Lokanatan, S., Lord, J., Lukicheva, L.S., Luo, S.B., Maksimkina, T.N., Mangotra, L.K., Marutyan, N.A., Maslennikova, N.V., Mittra, I.S., Mookerjee, S., Nasrulaeva, H., Nasyrov, S.H., Navotny, V.S., Nystrand, J., Orlova, G.I., Otterlund, I., Palsania, H.S., Peresadko, N.G., Petrov, N.V., Plyushchev, V.A., Qarshiev, D.A., Qian, W.Y., Qin, Y.M., Raniwala, R., Raniwala, S., Rao, N.K., Rappoport, V.M., Rhee, J.T., Saidkhanov, N., Salmanova, N.A., Sarkisova, L.G., Sarkisyan, V.R., Shabratova, G.S., Shakhova, T.I., Shpilev, S.N., Skelding, D., Soderstrom, K., Solovjeva, Z.I., Stenlund, E., Surin, E.L., Svechnikova, L.N., Tolstov, K.D., Tothova, M., Tretyakova, M.I., Trofimova, T.P., Tuleeva, U., Vokal, S., Wang, H.Q., Weng, Z.Q., Wilkes, R.J., Xia, Y.L., Xu, G.F., Zhang, D.H., Zheng, P.Y., Zhokhova, S.I., Zhou, D.C., 1993. Study of angular distribution of helium projectile fragments in interactions of 200 A GeV 32S ions with emulsion nuclei. Mod. Phys. Lett. A 8, 21e31. Aggarwal, M.M., Bhalla, K.B., Das, G., Jain, P.L., 1983. Angular distributions of relativistic alpha particles in heavy-ion collisions. Phys. Rev. C 27, 640e649. Bowman, J.D., Swiatecki, W.J., Tsang, C.F., 1973. Abrasion and Ablation of Heavy Ions. Lawrence Berkeley Laboratory Report, LBL-2908. Bhalla, K.B., Chaudhry, M., Lokanathan, S., Grover, R.K., Daftari, I.K., Kaul, G.L., Magotra, L.K., Prakash, Y., Rao, N.K., Jaipur-Jammu-Lund Collaboration, Garpman, S., Otterlund, I., 1981. Relativistic a-particles emitted in Fe-emulsion interactions at 1.7 A GeV. Nucl. Phys. A 367, 446e458. Cherry, M.L., Dabrowska, A., Deines-Jones, P., Dubinina, A.J., Holynski, R., Jones, W.V., Olszewski, A., Sengupta, K., Smirnitcki, V.A., Szarska, M., Trzupek, A.,
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Waddington, C.J., Wefel, J.P., Wilczyaska, B., Wilczynski, H., Wolter, W., Woseik, B., Wozniak, K., 1997. Transverse momenta of helium fragments in gold fragmentation at 10.6 GeV/nucleon. Z. Phys. C 73, 449e454. El-Nadi, M., El-Nagdy, S., Ali-Mossa, N., Abdelsalam, A., Abdalla, A.M., AbdelHalim, S., 2002. Multiple fast helium fragments production from 28Si-emulsion interaction at 14.6 A GeV. J. Phys. G 38, 1251e1258. El-Nadi, M., Sherif, M.M., Abdelsalam, A., Yasin, M.N., Bakr, A., El-Nagdy, M.S., Jilany, M.A., 1993. Some characteristics of multiple helium fragments produced in heavy ion collisions at Dubna energy. Intern. J. Mod. Phys. E 2, 381e395. Fan, S.H., Liu, F.H., 2008. Alpha emission in krypton-emulsion collisions at 1.7 A GeV. Rad. Meas. 43, S239eS242. Ganssauge, E., Kallies, H., Dressel, B., Muller, Ch, Schulz, W., 1985. Two distinct classes of alpha particles and a possible correlation of anomalously short mean free paths with the cold component. J. Phys. G 11, L139eL142. Ghosh, D., Roy, J., Sengupta, R., 1988. Observation of hot and cold events in the 12Cemulsion interaction at 4.5 GeV/c per nucleon e a signal for quark matter formation? J. Phys. G 14, 711e716. Heckman, H.H., Greiner, D.E., Lindstrom, P.J., Shwe, H., 1978. Fragmentation of 4He, 12 14 C, N, and 16O nuclei in nuclear emulsion at 2.1 GeV/nucleon. Phys. Rev. C 17, 1735e1747. Jain, P.L., Aggarwal, M.M., 1986. Onset of helium-fragment scaling in heavy-ion collisions. Phys. Rev. C 33, 1790e1792. Jilany, M.A., 2004. Fast helium production in interactions of 3.7 A GeV 24Mg with emulsion nuclei. Eur. Phys. J. A 22, 471e480. Joseph, R.R., Ojha, I.D., Tuli, S.K., Bhatia, V.S., Kaur, M., Mittra, I.S., Sahota, S.S., Bhalla, K.B., Bharti, A., Mookerjee, S., Kitroo, S., Rao, N.K., 1989. Two-source emission of relativistic alpha particles in 40Ar-emulsion collisions. J. Phys. G 15, 1805e1814. Kamel, S., 1999. Further study of helium production at large impact parameters in 6.4 TeV 32S emulsion reactions. Nuovo Cimento A 112, 733e741. Koba, Z., Nielson, H.B., Olesen, P., 1972. Scaling multiplicity distributions in high energy hadron collision. Nucl. Phys. B 40, 317e334. Lepore, J.V., Riddell, Jr., R.J., 1974. Fragmentation of Heavy Nuclei at High-energy. Lawrence Berkeley Laboratory Report No. LBL-3086. Raha, S., Weiner, R.M., Wheeler, J.W., 1984. Spectator temperature as a signal for quark-matter formation. Phys. Rev. Lett. 53, 138e140. Sengupta, K., Singh, G., Jain, P.L., 1989. On the production of helium fragments in ultra-relativistic heavy-ion collisions. Phys. Lett. B 222, 301e305. Singh, G., Ismail, A.I.M., Jain, P.L., 1991. Characteristics of helium fragments produced in 28Si emulsion interactions at 14.5 A GeV. Phys. Rev. C 43, 2417e2421. Singh, G., Jain, P.L., 1994. Production of helium fragments in 197Au-emulsion collisions at 10.6 A GeV. Z. Phys. A 348, 99e104. Song, F., Zhang, D.H., Li, J.S., 2005. Two-source emission of relativistic alpha particles in 16O-Em interactions at 3.7 A GeV. Chin. Phys. 14, 942e948. Westfall, G.D., Gosset, J., Johansen, P.J., Poskanzer, A.M., Meyer, W.G., Gutbrod, H.H., Sandoval, A., Stock, R., 1976. Nuclear fireball model for proton inclusive spectra from relativistic heavy-ion collisions. Phys. Rev. Lett. 37, 1202e1205.
Contents lists available at SciVerse ScienceDirect
Radiation Measurements journal homepage: www.elsevier.com/locate/radmeas
Production of helium projectile fragment in
84
Kr-emulsion collisions at 1.7 A GeV
Dong-Hai Zhang* Institute of Modern Physics, Shanxi Normal University, Linfen, Shanxi 041004, China
h i g h l i g h t s < Multiplicity distribution can be well represented by two Gaussian distributions. < Projected angular distributions can be well fitted by two Gaussian distributions. < Transverse momentum distribution can be well explained by two Gaussian distributions. < The temperature of emission sources is obtained from pt2 distribution. < The temperature parameter is independent of the target size.
a r t i c l e i n f o
a b s t r a c t
Article history: Received 10 February 2012 Received in revised form 27 September 2012 Accepted 15 October 2012
Multiplicity, projected angular and transverse momentum distributions of helium projectile fragment (HPF) produced from 1.7 A GeV 84Kr induced different type of emulsion targets (H, CNO and AgBr) interactions are studied. It is found that the distributions of HPF from 84KreH, CNO, AgBr and emulsion interactions can be well explained by two Gaussian distributions. These imply the existence of two distinct emission sources (cold and hot source) of HPF in 84KreH, CNO, AgBr and emulsion interactions. The dominant source is the cold one (projectile spectator source) with lower temperature and the other is hot one (projectile participant source) with higher temperature. The temperature parameters of cold and hot source are obtained from p2t distribution fitting using two Rayleigh distribution, which is independent of the target size within experimental errors. Ó 2012 Elsevier Ltd. All rights reserved.
Keywords: Relativistic heavy-ion collision Helium projectile fragment Projectile fragmentation Nuclear emulsion
1. Introduction The particle production in relativistic nucleusenucleus interactions have been extensively studied in recent years. Most of the studies have concentrated on particle production in participant region with the goal of examining possible signals of quark gluon plasma (QGP). Based on the participant-spectator concept (Bowman et al., 1973) and the simple fireball model (Westfall et al., 1976) the projectile and target sweep out cylindrical cuts through other. Raha et al. (1984) proposed that during the separation of the spectator from the participants, there must be some intercommunication between them which results in the excitation of the spectators. Since this communication is strongly dependent on whether or not the participants form a QGP, the energy imparted in terms of temperature to the spectators may carry characteristic information in regard to the formation of a QGP in the participant region. They have proposed that observation of two obviously different temperatures in the projectile fragmentation region would be explained as a possible signal for the production of a QGP. * Tel./fax: þ86 3572051347. E-mail address: [email protected]. 1350-4487/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.radmeas.2012.10.006
Helium projectile fragments (HPFs), produced from projectile spectator, have been studied experimentally by many groups in recent years (Sengupta et al., 1989; El-Nadi et al., 1993, 2002; Jilany, 2004; Song et al., 2005; Kamel, 1999; Cherry et al., 1997; Singh and Jain, 1994; Singh et al., 1991; Jain and Aggarwal, 1986; Ganssauge et al., 1985; Joseph et al., 1989; Aggarwal et al., 1983; Adamovich et al., 1993; Ghosh et al., 1988; Bhalla et al., 1981). It is found that the multiplicity distribution of HPFs can be well explained by the Koba-NielseneOlesen (KNO) scaling hypothesis (Koba et al., 1972). The angular distribution or transverse momentum distribution of HPFs from heavy projectile has a long tail which cannot be represented by a single Gaussian distribution. Most of these distributions imply the existence of two distinct emission sources of HPFs. The dominant one is the cold source with an average excitation energy of about 7e10 MeV and the other is assumed to be of a fireball type at a high temperature of 40e70 MeV (Joseph et al., 1989; Ganssauge et al., 1985; Aggarwal et al., 1983; Ghosh et al., 1988; Bhalla et al., 1981). Two source emission of HPFs seem to support the idea of the formation of QGP proposed by Raha et al. (1984), but there are two experimental results cannot be explained by two emission sources. One of them can be explained by only one emission source
D.-H. Zhang / Radiation Measurements 50 (2013) 50e55
51
Table 1 Single Gaussian fitting parameters of HPFs multiplicity, projected angular and transverse momentum distributions in 1.7 A GeV 84Kr-emulsion interactions. Dis. type
Target
Average
Multiplicity
H CNO AgBr Emulsion H CNO AgBr Emulsion H CNO AgBr Emulsion
1.77 1.54 1.84 1.05 1.34 20.38 12.34 11.52 116.47 100.38 138.77 120.84
Projected angle
Trans. momentum
c2 /DOF
Error 0.15 3.74 0.32 0.33 0.26 2.69 1.55 0.98 5.88 15.44 8.50 6.37
1.25 3.94 2.53 2.71 1.49 7.02 6.25 5.77 67.68 132.58 132.04 122.95
0.17 1.36 0.28 0.20 0.22 0.51 0.38 0.24 7.13 15.81 11.94 8.94
2.92 1.56 1.11 0.57 0.96 1.49 1.14 3.10 1.25 4.03 5.50 10.97
(Adamovich et al., 1993) and another can be explained by three emission sources with different temperatures (Cherry et al., 1997). So emission of HPFs in relativistic nucleusenucleus collisions is not conclusive. In this paper we present a systematic investigation of multiplicity distribution, projected angular distribution and transverse momentum distribution of HPFs produced in 1.7 A GeV 84Kr induced different types of emulsion targets (H, CNO and AgBr). The transverse momentum distribution is compared with Maxwelle Boltzmann distribution, a clearly signature of two temperature is observed in the experimental data, and both of them are independent of the target size within experimental errors.
Fig. 1. Photograph of different kinds of 84Kr-emulsion interacting events, (a)Nh 1, (b) 1 < Nh < 8, and (c)Nh 8.
Fig. 2. Multiplicity distribution of HPFs produced from different kinds of
84
Kr-emulsion interaction, (a)Nh 1, (b)1 < Nh < 8, (c)Nh 8, and (d)Nh 0.
52
D.-H. Zhang / Radiation Measurements 50 (2013) 50e55
Table 2 Double Gaussian fitting parameters of HPFs multiplicity, projected angular and transverse momentum distributions in 1.7 A GeV Type of distribution
Target
Multiplicity
H CNO AgBr Emulsion H CNO AgBr Emulsion H CNO AgBr Emulsion
First Gaussian distribution Average
Projected angle
Trans. momentum
1.29 0.27 1.66 1.47 1.34 0.23 0.31 0.53 173.19 69.44 250.12 200.36
Kr-emulsion interactions.
c2 /DOF
Second Gaussian Distribution Error
0.83 0.86 0.90 0.21 0.26 0.65 0.46 0.30 524.27 43.61 152.25 109.84
84
Average
0.34 0.45 0.36 0.33 1.49 1.83 1.82 1.76 159.98 180.46 132.90 153.10
0.71 0.83 0.93 1.38 0.22 0.66 0.50 0.41 140.30 25.38 46.83 32.70
Error
1.99 2.82 1.82 1.04
0.25 0.52 0.38 0.25
1.45 2.09 2.73 2.76
0.26 0.36 0.26 0.25
5.51 4.25 5.26 112.00 112.75 113.61 108.66
4.83 3.85 2.91 9.33 6.32 12.03 4.14
2.42 2.82 2.44 56.24 34.95 66.82 60.47
2.56 1.38 1.14 21.55 7.74 21.93 14.73
0.55 0.35 0.49 0.71 0.96 0.38 0.66 0.51 0.23 1.15 2.30 1.99
within 30 mm from the top or the bottom surface of the emulsion plates were not considered for final analysis. For each interaction, the number of shower particles (Ns) and slow-moving (velocity b < 0.7) heavily ionizing particles (Nh) is determined. Shower particle is corresponding to single charged relativistic secondary with velocity b 0.7 and ionization less than 1.4 times of the plateau ionization of single charged minimum ionizing particle. The heavily ionizing tracks are classified into gray tracks Ng (0.3b < 0.7 and range in emulsion R > 3 mm) and black tracks Nb (b < 0.3 and range in emulsion R < 3 mm). Projectile fragments with charge Z 2 are emitted from the breakup of the projectile, essentially travel at the same speed as that of the beam. HPFs that are emitted in the forward
2. Experimental details A stack of nuclear emulsion pellicles 10 10 10 0.06 cm3 in volume, provided by EMU-01 Collaboration (Adamovich et al., 1993), was used in this experiment. The emulsion stack was exposed horizontally to 84Kr beam at an energy of 1.7 A GeV at the Bevatron at Lawrence Berkeley Radiation Laboratory (LBL). The density of the beam was about 103 nuclei/cm2. Interactions were found by along-the-track scanning method with an oil immersion objective of 100 magnification. The nuclear tracks were picked up at 5 mm away from the edge of the plate and carefully followed until they either interacted with emulsion nuclei or escaped from any surface of the emulsion plates. Interactions which took place
Fig. 3. Projected angular distribution of HPFs produced from different kinds of
84
Kr-emulsion interaction, (a)Nh 1, (b)1 < Nh < 8, (c)Nh 8, and (d)Nh 0.
D.-H. Zhang / Radiation Measurements 50 (2013) 50e55
53
cone with respect to the beam direction have grain density ga z 4gmin (where gmin is the grain density of the minimum ionizing particle and it is about 12 grains/100 mm for present experiment) and not charged within 2 cm away from its production point. The emission angle (q) and projected angle (Qproj ) have been measured for each track by taking readings of the coordinates of the interaction point (x0,y0,z0), the coordinates (xi,yi,zi) at the end of the linear portion of each secondary track and the coordinates (x1,y1,z1) of a point on the incident beam. 3. Experimental results and discussions There are 558 84Kr-emulsion unbiased inelastic events are used in present investigation. Based on the number of Nh, the events are classified into three categories. Events with Nh 1 are mainly interactions with H target (interactions with free and quasi-free nucleon) and peripheral interactions with CNO or AgBr targets. Events with 1 < Nh < 8 are mostly with CNO targets and with some admixture of peripheral AgBr interactions. Events with Nh 8 are only interactions with AgBr targets. Fig. 1 shows the photograph of different kinds of 84Kr-emulsion interacting events. Fig. 2 shows the multiplicity distribution of HPFs from 1.7 A GeV 84 Kr induced different type of emulsion targets (H, CNO, AgBr and emulsion) interactions, where Na means the multiplicity of HPFs. It is found that the width and the position of maximum of the distribution increase with the increase of the target mass. The distribution is fitted by single and double Gaussian distribution respectively. The fitting parameters including c2 /DOF are
Fig. 4. Transverse momentum distribution of HPFs produced from different kinds of
Fig. 5. The cumulated transverse momentum distribution of HPFs produced in 1.7 A GeV 84Kr induced different type of emulsion targets interactions.
84
Kr-emulsion interaction, (a)Nh 1, (b)1 < Nh < 8, (c)Nh 8, and (d)Nh 0.
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D.-H. Zhang / Radiation Measurements 50 (2013) 50e55
Table 3 Values of the two temperatures from transverse momentum distributions of HPFs produced in 1.7 A GeV Target
C1
H CNO AgBr Emulsion
11.87 38.73 63.73 48.38
s21
5.56 4.41 3.45 2.47
2
(A MeV/c)
41576.0 35323.0 31992.0 32713.0
11116.0 1846.4 857.6 779.4
T1 (MeV) 165.9 140.9 125.2 130.5
pt ¼ p sin q;
Kr induced different type emulsion targets interactions.
s22 (A MeV/c)2
C2
44.3 7.4 3.4 3.1
presented in Tables 1 and 2 respectively, where DOF means the degree of freedom of simulation. Comparing the fitting parameters and the values of c2 /DOF it is clear that the distribution can be well represented by two Gaussian distributions. The multiplicity distributions of the produced fragments have been regarded as a potentially useful source of information of the underlying production mechanism. Fan (Fan and Liu, 2008) have studied the multiplicity distributions of HPFs in relativistic nucleusenucleus collisions using the two source emission picture, each source is represented by the exponential function. The projected angular distribution of HPFs from 1.7 A GeV 84Kr induced different type of emulsion targets (H, CNO, AgBr and emulsion) interactions is shown in Fig. 3. The distribution from Kre H interaction can be well fitted by a single Gaussian distribution, but the distributions from KreCNO, Kr-emulsion and KreAgBr interactions have a long tail, which cannot be fitted by a single Gaussian distribution and need two Gaussian distribution to fit the data. The fitting parameters of single and double Gaussian fit are presented in Tables 1 and 2 respectively. It is evident that double Gaussian fit can well represent the experimental data. From results in Table 2 we can see that the angular widths of the first Gaussian fit and the second Gaussian fit is independent of the target size. This target-independent behavior of angular widths is a characteristic feature of the hypothesis of limiting fragmentation. Heckman and Aggarwal (Heckman et al., 1978; Aggarwal et al., 1983) have studied the projected angular distributions for HPFs produced in Nh ¼ 0 type of relativistic nucleusenucleus interactions. The distributions can be well described by a single Gaussian, and the standard deviations of s(qproj) are in reasonable agreement with the theory of Lepore and Riddell (1974), they treated the fragmentation of high energy nuclei by using a quantum mechanical sudden approximation. The transverse momentum per nucleon (pt) of a projectile fragment was calculated on the basis of its emission angle q,
84
90.72 61.22 36.62 52.28
7.93 5.30 5.00 3.36
8161.4 7818.8 5652.4 6837.5
1149.1 1184.5 1264.8 704.6
T2 (MeV) 32.6 31.2 22.5 27.3
4.6 4.7 5.0 2.8
c2 /DOF 0.10 0.16 0.61 0.41
mass heats the swept-out nucleons leading to a quasi-equilibrium fireball. This fireball can be described by a statistical (Maxwelle Boltzmann) distribution in the projectile rest frame. The transverse momentum of a projectile fragment is given by
1=2 pt ¼ Am0 g2 1 sin q;
(2)
where A is the atomic number and g the Lorentz factor of the projectile. If we assume that the emission of HPFs is Maxwelle Boltzmann distribution in the projectile rest frame with a certain temperature T, the integral frequency distribution of the square of the transverse momentum per nucleon is
A p2 : ln F >p2t ¼ 2m0 T t
(3)
The linearity of such a plot would be strong evidence for a single temperature. Fig. 5 shows the cumulative plots of Fð> p2t Þ as a function of p2t for HPFs from 1.7 A GeV 84Kr induced different kind of emulsion targets (H, CNO, AgBr and emulsion) interactions. All of the plots can be well fitted by two Rayleigh distribution of the form
F
p2t
¼ C1 exp
p2 t2 2s1
!
þ C2 exp
! p2t 2 ; 2s2
(4)
where si ¼ (2/p)1/2
(1)
where p is the momentum per nucleon of beam which can be calculated from beam energy per nucleon (E), p ¼ (E2 þ 2m0E)1/2. m0 is the nucleon rest mass and q the emission angle of the projectile fragment with respect to the beam direction. Fig. 4 shows the transverse momentum distribution of HPFs from 1.7 A GeV 84Kr induced different type of emulsion targets (H, CNO, AgBr and emulsion) interactions. The width and the position of maximum of the distribution increase with the increase of the target mass. The distribution can be well represented by two Gaussian distributions. The fitting parameters of single and double Gaussian distribution are presented in Tables 1 and 2 respectively. According to the participant-spectator model, with the increase of the target size the overlapped region and also the contacted area increases, the communication between participant and spectator increases. This results in the increase of the excitation energy of HPFs, so the average of transverse momentum of HPFs is increased. Based on the fireball model (Westfall et al., 1976) of relativistic nucleusenucleus collisions, the available energy in the center of
4. Conclusions From the study of HPFs distributions in 1.7 A GeV 84Kr induced different kinds of emulsion targets (H, CNO, AgBr and emulsion) interactions, we can conclude that the multiplicity distributions and transverse momentum distributions can be well represented by two Gaussian distributions, the width of the distribution increases with the increase of the target size. The projected angular distribution of HPFs from KreH collisions can be fitted by a single Gaussian distribution, but the distribution of HPFs from KreCNO, AgBr and emulsion collisions need two Gaussian distribution to fit. The cumulated transverse momentum distribution can be well fitted by two Rayleigh distribution, which indicate that the HPFs is emitted from two emission source. The dominant source is the cold one (projectile spectator source) with lower temperature and the other is hot one (projectile participant source) with higher temperature. No obvious dependence of the temperature of emission source on the target size is found in our data sets.
D.-H. Zhang / Radiation Measurements 50 (2013) 50e55
Acknowledgment This work has been supported by the Chinese National Science Foundation under Grant No. 11075100, the Natural Science Foundation of Shanxi Province under Grant No. 2011011001-2, and the Shanxi Provincial Foundation for Returned Overseas Chinese Scholars, China (Grant No. 2011-058). We are grateful to Professor L. Otterlund of Lund University in Sweden for providing the emulsion stack. References Adamovich, M.I., Aggarwal, M.M., Alexandrov, Y.A., Amirikas, R., Andreeva, N.P., Anzon, Z.V., Arora, R., Avetyan, F.A., Badyal, S.K., Basova, E., Bhalla, K.B., Bhasin, A., Bhatia, V.S., Bogdanov, V.G., Bubnov, V.I., Burnett, T.H., Cai, X., Chasnikov, I.Y., Chernova, L.P., Chernyavski, M.M., Eligbaeva, G.Z., Eremenko, L.E., Gaitinov, A.S., Ganssauge, E.R., Garpman, S., Gerassimov, S.G., Grote, J., Gulamov, K.G., Gupta, S.K., Gupta, V.K., Heckman, H.H., Huang, H., Jakobsson, B., Judek, B., Just, L., Kachroo, S., Kalyachkina, G.S., Kanygina, E.K., Karabova, M., Kaul, G.L., Kitroo, S., Kharlamov, S.P., Krasnov, S.A., Kulikova, S., Kumar, V., Lal, P., Larionova, V.G., Lepetan, V.N., Liu, L.S., Lokanatan, S., Lord, J., Lukicheva, L.S., Luo, S.B., Maksimkina, T.N., Mangotra, L.K., Marutyan, N.A., Maslennikova, N.V., Mittra, I.S., Mookerjee, S., Nasrulaeva, H., Nasyrov, S.H., Navotny, V.S., Nystrand, J., Orlova, G.I., Otterlund, I., Palsania, H.S., Peresadko, N.G., Petrov, N.V., Plyushchev, V.A., Qarshiev, D.A., Qian, W.Y., Qin, Y.M., Raniwala, R., Raniwala, S., Rao, N.K., Rappoport, V.M., Rhee, J.T., Saidkhanov, N., Salmanova, N.A., Sarkisova, L.G., Sarkisyan, V.R., Shabratova, G.S., Shakhova, T.I., Shpilev, S.N., Skelding, D., Soderstrom, K., Solovjeva, Z.I., Stenlund, E., Surin, E.L., Svechnikova, L.N., Tolstov, K.D., Tothova, M., Tretyakova, M.I., Trofimova, T.P., Tuleeva, U., Vokal, S., Wang, H.Q., Weng, Z.Q., Wilkes, R.J., Xia, Y.L., Xu, G.F., Zhang, D.H., Zheng, P.Y., Zhokhova, S.I., Zhou, D.C., 1993. Study of angular distribution of helium projectile fragments in interactions of 200 A GeV 32S ions with emulsion nuclei. Mod. Phys. Lett. A 8, 21e31. Aggarwal, M.M., Bhalla, K.B., Das, G., Jain, P.L., 1983. Angular distributions of relativistic alpha particles in heavy-ion collisions. Phys. Rev. C 27, 640e649. Bowman, J.D., Swiatecki, W.J., Tsang, C.F., 1973. Abrasion and Ablation of Heavy Ions. Lawrence Berkeley Laboratory Report, LBL-2908. Bhalla, K.B., Chaudhry, M., Lokanathan, S., Grover, R.K., Daftari, I.K., Kaul, G.L., Magotra, L.K., Prakash, Y., Rao, N.K., Jaipur-Jammu-Lund Collaboration, Garpman, S., Otterlund, I., 1981. Relativistic a-particles emitted in Fe-emulsion interactions at 1.7 A GeV. Nucl. Phys. A 367, 446e458. Cherry, M.L., Dabrowska, A., Deines-Jones, P., Dubinina, A.J., Holynski, R., Jones, W.V., Olszewski, A., Sengupta, K., Smirnitcki, V.A., Szarska, M., Trzupek, A.,
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