Research Reports in Physics Research Reports in Physics Nuclear Structure of the Zirconium Region Editors: J. Eberth, R. A. Meyer, and K. Sistemich Ecodynamics Contributions to Theoretical Ecology Editors: W. Wolff, C.-J. Soeder, and F. R. Drepper Nonlinear Waves 1 Dynamics and Evolution Editors: A. V. Gaponov-Grekhov, M. I. Rabinovich, and J. Engelbrecht Nonlinear Waves 2 Dynamics and Evolution Editors: A. V. Gaponov-Grekhov, M. I. Rabinovich, and J. Engelbrecht Nonlinear Waves 3 Physics and Astrophysics Editors: A. V. Gaponov-Grekhov, M. I. Rabinovich, and J. Engelbrecht Nuclear Astrophysics Editors: M. Lozano, M. I. Gallardo, and J. M. Arias Optimized LCAO Method and the Electronic Structure of Extended Systems By H. Eschrig Nonlinear Waves in Active Media Editor: J. Engelbrecht Problems of Modern Quantum Field Theory Editors: A. A. Belavin, A. U. Klimyk, and A. B. Zamolodchikov Fluctuational Superconductivity of Magnetic Systems By M. A. Savchenko and A. V. Stefanovich Nonlinear Evolution Equations and Dynamical Systems Editors: S. Carillo and O. Ragnisco Nonlinear. Physics Editors: Gu Chaohao, Li Yishen, and Tu Guizhang Nonlinear Waves in Waveguides with Stratification By S. B. Leble Quark-Gluon Plasma Editors: B. Sinha, S. Pal, and S. Raha Symmetries and Singularity Structures Integrability and Chaos in Nonlinear Dynamical Systems Editors: M. Lakshmanan and M. Daniel Modeling Air-Lake Interaction Physical Background Editor: S. S. Zilitinkevich Bikash Sinha Santanu Pal Sibaji Raha (Eds.) Quark-Gluon Plasma Invited Lectures of Winter School, Puri, Orissa, India, December 5-16, 1989 With 164 Figures Springer-Verlag Berlin Heidelberg New York London Paris Tokyo Hong Kong Barcelona Dr. Bikash Sinha Dr. Santanu Pal Variable Energy Cyclotron Centre, 1/AF, Bidhan Nagar, 700 064 Calcutta, India Professor Sibaji Raha Fachbereich Physik der Philipps Universitat Marburg, Mainzer Gasse 33, 0-3550 Marburg, Fed. Rep. of Germany ISBN-13: 978-3-540-51984-3 e-ISBN-13: 978-3-642-75289-6 001: 10.1007/978-3-642-75289-6 This work is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in other ways, and storage in data banks. Duplication of this publication or parts thereof is only permitted under the provisions of the German Copyright law of September 9, 1965, in its current version, and a copyright fee must always be paid. Viola tions fall under the prosecution act of the German Copyright law. © Springer-Verlag Berlin Heidelberg 1990 The use of registered names, trademarks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protectiv laws and regulations and therefore free for general use. 2157 13140-543210 - Printed on acid-free paper Preface This volume contains the notes of the main lectures presented at the Winter School on Quark-GIuon Plasma (QGP) held at the Toshali Sands resort near Puri, India, 5-16 December, 1989. The format of the volume can be considered as a compre hensive synthesis of introductory lectures dealing with the essential fundamentals of the field and the frontier level ideas, directly relevant for an in-depth understand ing of the state of the art. The degree of enthusiasm and involvement displayed by the participants of the School convinced us that a permanent record in the form of this book would be appropriate. This text begins with a discussion of experiments and experimental tech niques: Roberto Salmeron relates the history of the search for signs of QGP in ultrarelativistic heavy ion collisions, after an exposition of relativistic kinematics. Michael J. Tannenbaum's contribution is primarily concerned with QGP activities at Brookhaven National Laboratory. We continue with several chapters on the theoretical models and formalism. Jitendra Parikh covers Quantum Chromodynarnics (QCD) and QCD plasma, in particular, perturbative QCD in many-body systems at finite temperatures, to study QGP thermodynamics. Frank Close discusses the properties of a single ground state nucleon in a nuclear medium, and in a volume of high energy density. This problem is of direct relevance to the phase transition from hadronic to QGP behaviour. A more detailed knowledge of the glue and its distribution inside hadrons is a pressing goal. Narayan Rana and Charles Alcock present the very exciting developments in our understanding of the Universe a microsecond after its creation - an area of physics where QCD/QGP related ideas can be applied with some confidence. Narayan Rana focuses on the geometry and dynamics of the early universe going over to Big Bang nucleosynthesis; Charles Alcock covers the very recent work of possible changes in the relative abundances of various nuclei essentially due to the inhomogeneity introduced by QCD phase transition. The need to invoke dark matter, its possible origin and its relevance to QCD phase transition is discussed. It is implicit that previous knowledge of QGP is not essential to understand the contents of this book. It is hoped that the material gathered here, like the .lectures on which it is based, will inspire the reader to the same degree of enthusiasm as experienced by the participants of the Puri School. Calcutta, Marburg Bikash Sinha June, 1990 Santanu Pal Sibaji Raha v From the Editors A little over two years ago, the International Conference on Physics and Astro physics of Quark-GIuon Plasma (lCPA-QGP'88) organised by us at Tata Institute of Fundamental Research, Bombay, seemed to have enjoyed a satisfactory measure of success. To sustain the excitement and motivation generated in that conference and especially to introduce the young graduate students and fresh post-docs to this new and rapidly evolving discipline, we decided to organise a more intense school on the same subject, covering extensively, if not exhaustively, the experimental and theoretical scenario related to the physics of QGP, starting from the very early universe to the laboratory experiments of the present generation as well as the next generation. To many of us, the study of QGP is all the more stimulating, because it forges, as it were, a bridge between the microcosmos and the macrocosmos. The Winter School on QGP, December 5-16,1989, was organised at the glo riously enchanting and picturesque surroundings of Toshali Sands, a spot near Puri, a famous pilgrimage and sea resort in Orissa, situated in the eastern part of India. The setting and the surroundings helped a great deal in cementing a sense of intense involvement and eager anticipation both among the students and the lecturers. The format of the school was neither entirely pedagogic nor synoptic but rather a synthesis of the two. Each lecturer started with an introduction to his subject accessible to a graduate student generally well prepared but without any prior expertise in the area of QGP. From there, he brought the students along to the very forefront of the discipline with remarkable clarity and lucidity. It was indeed a pleasure to witness at the end of the school the young participants hitherto unfamiliar with the field converse knowledgeably about the current issues and bubbling with enthusiasm to start contributing to this growing subject. It is our firm belief in editing these proceedings that a large share of that enthusiasm will filter through in the printed pages too, and that this volume will prove to be of immense help to the beginners and the practising experts in QGP. On the experimental side, Roberto Salmeron covered single-handedly the entire area of searches for the signals of QGP in ultrarelativistic heavy ion collisions. His remarkable set of lectures started very appropriately with a lucid introduction to the relativistic kinematics of high energy collisions, concepts which are often glossed over in the usual curricula, leaving room for immense confusion in the minds of beginners. Salmeron thus rendered yeoman service not only to the students of the school but to the entire community through his clear enunciation of the concepts every theorist and experimentalist must know by heart. From there on, he covered in an inspiring set of lectures the entire state of the art of experimental VII QGP searches - from direct photons to hadrons, from two particle interference (Bose-Einstein correlations) to intermittency, the resonance states of J/psi and the possible sources of its suppression, the changes in the slope of the average energy density deposition as a function of the average transverse momentum indicating a phase transition. Behind all these signals, however, there still remains the enigma of FRITUOF, somehow managing to get things almost right, hinting that there are as yet no clear signals of QGP. Robert Brockman, along with Salmeron, helped to "demystify" the mythology of the large scale detectors which are part and parcel of ultrarelativistic heavy ion physics research. He concentrated mainly on the CERN detectors, from TCP to ZDC, streamer chambers to nuclear emulsions, dimuon spectrometers, BGO crystals, massive on line data acquisition systems and so on. It was extremely useful for the Indian participants, especially as India is on the verge of becoming a full partner in one of the CERN experiments (WA80), where involvement with the hardware is a must. Is it then possible for us to build a calorimeter or indeed a TPC - how about drift chambers? It is indeed unusual to delve deep into the hardware of detectors in a school not solely dedicated to instrumentation, but Brockman's and Salmeron's attempts were instrumental in stimulating many young minds at the school to get their hands dirty while keeping the physics goals firmly in sight. For reasons beyond our control, however, we had to leave the write-up of Brockman's lectures out of this volume. The other scheduled lecturer in the experimental section, Mike Tannenbaum, could not attend at the very last minute. He had planned to cover the features of the Brookhaven activities in this area, emphasising in particular the role of transverse energy measurements as a tool for QGP diagnostics. In his absence, Salmeron gave the students an introduction to this area too. But we are also including the write-up of Tannenbaum's contribution in this volume for the benefit of the readers. On the theoretical side, Jitendra Parikh covered the essential area of QCD and QCD plasma. His discussion on how to avoid the pitfalls of perturbative QCD in many-body systems at finite temperature in order to study thermodynamics and other collective properties of QGP was incisively instructive. Quite clearly, the young (and often the initiated too) can embark on a rather elaborate and involved calculation using perturbative QCD, without fully appreciating the fact that unless one takes into account the collective modes semi-phenomenologically (at the present state of our understanding of strong interaction physics), one might end up throwing the baby away with the bath water. The essential foundation of thermodynamics (or the lack of its validity!) for studying the evolution of the reaction volume after the collision of two nuclei at ultrarelativistic energies was also discussed in detail. Frank Close contributed greatly in bridging the two seemingly (but then again, why indeed?) uncorrelated areas, the properties of a single nucleon embedded in a nuclear medium in its ground state on the one hand and on the other hand, what happens to them when they are in a volume where sufficient energy density has been pumped in. The very important recent developments in our understanding of a baryon in a nucleus and exactly how important the glue distribution is for predicting the structure of a baryon was emphasised. Needless to say, these con- VIII siderations can have profound consequences for our understanding of the QGP signals as well as the phase transition from the hadronic to QGP sector. It is felt that whether it is the EMC effect involving the hadronic structure in a nucleus in terms of the QCD degrees of freedom (quarks and gluons) or the study in volving the QCD phase transition, a more detailed knowledge of the glue and its distribution inside hadrons or in the fireball is a central issue. Thus, a more comprehensive study of the atomic nucleus revealing the quark structure of hadrons (through lepton-nucleus interactions) and its logical extension to high density/high temperature hadronic matter, eventually dissolving into a QGP, needs to be performed in a careful and self-consistent manner. The physics of CEBAF (Continuous Electron Beam Acceleration Facility) and the physics of RIDC (Relativistic Heavy Ion Collisions) should be mutually complementary, fitting into the wonderful goal of searching for a unified picture of the ultimate constituents of the hadronic world. So what exactly is the message at this time for our search for QGP in the laboratory and the related theoretical questions? It is probably correct to say that no definitive signals are yet at hand, the central problem being the pollutants of the hot hadronic matter, evolving with time beyond the critical temperature of the phase transition and eventually to freeze-out. All the signals proposed so far fall short of the acid test, implying that most of the data can perhaps be explained without necessarily invoking the existence of a QGP, notwithstanding the unnatural assumptions often needed to make the mundane explanations work. But it is heartening to note that to date not a single set of data has been found which would rule out the formation of QGP. Perhaps the theorists have not yet succeeded in asking sufficiently discerning questions on QGP diagnostics, but there is always a hint for the future. Is there enough energy deposited? Is the statistics good enough? This last point is particularly relevant for the direct photon signals of QGP - a 30% effect will correspond to one direct photon for every thousand charged particles, not an easy task and one which certainly demands much longer running time. Strange and anti-strange mesons may help to an extent but so little is known about the process of hadronisation, final state interactions and/or the scattering of hadrons from the neighbouring hadrons in a hot dense medium! Indeed, while we are looking for a novel state of matter, it is imperative to realise that very little really is known about the properties of hadronic matter (the background, to wit) at high density and/or temperature. It is high time that the initiated take a harder look at this issue. If signals relating to anyone particular species of detected particles may not be truly clinching; what about their ratios? Yes, it may be difficult to do, involving the measurement of several different kinds of particles in the same experiment, but the dividends certainly justify the effort. The ratio of photons to dileptons is an apt example. Naively, direct photons from QGP arise from the annihilation of quarks and anti-quarks as well as from the so-called generalised Compton effect (q+g going to q+photon), a channel absent for diphotons in the lowest order. So the ratio will clearly provide an all-important "clue" to the elusive glue distribution. It is felt that looking for several signals in the same experiment and studying their ratios will clarify many cloudy issues. IX Similarly for two particle interferometry! Pion interferometry has been tradi tionally done for the past 30 years, starting with the epoch-making discovery of the GGLP effect. As can be gleaned from the lectures of Salmeron, such mea surements have now become a mainstay of RIDC processes, not to mention also electron-positron and hadronic collisions at high energy. The enormous impor tance of these measurements notwithstanding, one has to realise that extracting physically meaningful information from them is still not an unambiguous endeav our, what with the final state interactions, parametrisation dependence of the source distributions and so on. Moreover, pions being predominantly final state products, pion interferometry measures the size of the reaction volume at or near freeze-out, at any rate in its hadronic phase. It will thus be most important to devise interfer ometric experiments which could yield information about the volume of the initial stage of the evolution. On the theoretical side, the study of non-equilibrium dynamics and its appli cation to RHIC processes, especially at the early times of formation, must be addressed. The efforts of the past few years in unravelling the subtleties of a ki netic theory with QCD ingredients appear not to have borne the fruit they initially seemed to promise, the difficulties of formulating a gauge-invariant prescription being the root cause. We cannot help thinking that there is scope for a break through there and perhaps some ingenious theorist will take a fresh look at the problem in the near future. What concerns the signals, a simultaneous analysis of the central rapidity regime and the fragmentation regime seems important to understand the role of the baryonic chemical potential, especially in suppressing the anti-quarks. The evaluation of the production rates of J/psi in hadron-nucleus and nucleus-nucleus collisions within the framework of a bound state equation (e.g. Bethe-Salpeter) is an urgent task. We believe that the experimental results obtained from the runs with sulphur will decide the course theoretical activities should take, with an eye to the forthcoming lead runs. The message is quite clear. It is simply not possible to detect QGP by a short run without elaborate controlled experiments, be that for higher statistics, be that for scanning for the signals event by event, be that for the study of correlation experiments. The results obtained at CERN and AGS so far have proved beyond doubt that there is interesting physics to be learnt from the search for QGP and it is absolutely imperative to design more detailed experiments to iron out some of the prejudices and unclarities in our search for the truth. Going over from the microcosmos to the macrocosmos, the most relevant issue is the possible consequences of a QCD phase transition on the evolution of the very early universe, approximately several microseconds after the Big Bang. Narayan Rana introduced the students to the language, the techniques and the subtleties of the geometry and the dynamics of the early universe. In an excellent series of talks, both in terms of thoroughness and pedagogy, he elaborated from a classical point of view the issue of the observed abundances of the elements and its deep connection with the inhomogeneity produced in the early universe by the (presumably) first order QCD phase transition. The lectures covered the basic concepts of the Standard Big Bang cosmology; the question of the dark matter whether it is necessary - was discussed. The students were given a taste of the intricacies involved in the study of primordial nucleosynthesis. Rana paved the x way for the students to ask: What are the ingredients that go into the cosmic soup? How is the latent heat associated with the QeD phase transition taken away to the ambient hadronic universe? How many layers conducting heat away from one another exist in the early universe? What is the mechanism of this conduction? How sensitive are the results to the parameters of the phase transition, the critical temperature, for example? Charles Alcock dealt with these questions at length, in a brilliant set of lectures. The prospect of the first order phase transition leading to a cosmic separation of the QGP and the hadronic phases, which eventually allow diffusion of baryons among them, as Alcock expounded, can have very important effects on primordial nucleosynthesis and on the overall picture of the evolution of the early universe. The stretching of the time scale associated with nucleosynthesis as a consequence of the QeD transition is a scenario decidedly absent in the Standard Big Bang cosmology. The central issue of the dark matter came into focus again. As was argued by Witten some time ago, a QeD phase transition may perhaps produce stable configurations of strange quark matter (called strange nuggets in the literature) which would be opaque and thus be plausible baryonic candidates for dark matter. While in recent times the existence of nuggets has been called into question, it is undeniable that an understanding of the dark matter within the framework of known physics, without having to invoke exotics like axions or massive neutrinos, would indeed be a great step forward. Alcock told the students about the results of detailed calculations done by himself and collaborators on nucleosynthesis in the presence of a first order QCD transition, where the observed abundances of all light elements with the singular exception of 7Li come out to be within ac ceptable limits even when one insists on a baryonically closed universe. The intriguing question about the reliability and the accuracy of the astrophysical ob servation of abundances of elements was also discussed, with the conclusion that the uncertainties are rather large. Having argued that the QeD phase transition allows the universe to be closed by baryonic matter, Alcock then addressed the second part of the issue. If the dark matter is not to be the strange nuggets, could they be Jupiter-like planets? They would indeed be non-luminous; how can one search for them? Alcock gave the students an introduction to his group's future project, setting up optical telescopes in the southern hemisphere to look for the brightening of distant stars in the Magellanic cloud by the gravitational lensing action of these Jupiter-like objects. All of us look forward to the results of this experiment. In addition to the lectures, there were also some specialised seminars delivered by more initiated participants. We decided not to include those write-ups in this volume, as the format of those talks would not match the style followed in the regular lectures where no previous knowledge about the subject was assUmed. The two weeks at Toshali Sands were a feast, a gourmet meal where each course was different from the others, yet complementing one another in a way we had not imagined possible. We are grateful to Springer-Verlag for letting the whole community savour that taste to some extent. The School was sponsored by the Department of Science and Technology and the Department of Atomic Energy, Government of India. XI