Introduction to this 14th International Symposium on Very High Energy Cosmic Ray Interactions

Introduction to this 14th International Symposium on Very High Energy Cosmic Ray Interactions Lawrence W. Jonesa aDept. of Physics, University of Michigan, Ann Arbor MI, U.S.A. The history of this conference series together with related cosmic ray conferences are reviewed. The historic role of emulsion chambers and the increasing liaison with the particle accelerator community are also discussed. 1. SYMPOSIUM HISTORY This symposium series on Very High Energy Cosmic Ray Interactions was formally begun in 1980. However before then, there had been other relevant conferences on the same general topics; i.e. the cosmic ray observations of high energy el- ementary particle interactions. The first in which I was involved was held at the Case Institute in Cleveland, Ohio (USA) in 1964, entitled “The In- teraction between Cosmic rays and High Energy Physics”. It was stimulated by discussions during the XII International Conference on High Energy Physics at Dubna, Russia earlier that year, and was organized by Fred Reines. In attendance were Luis Alvarez, Giuseppi Cocconi, Robert Thomp- son, Mel Schwartz, Ahud Pevsner, Yash Pal, my- self, and others; about 20 total. The discussions there centered on possible cosmic ray experiments with balloons, on mountain tops, in deep mines, etc. to study high energy particle physics; stim- ulated by the delay in decisions in Europe and America on when and where to construct the next 200 GeV generation of high energy accelerators. An interesting meeting was organized by Cesar Lattes in 1970; the “VI Inter-American Seminar on Cosmic Rays”, held in LaPaz, Bolivia and Rio de Janeiro, Brazil. I have no knowledge of the earlier five meetings, but indeed this meeting in- cluded emulsion chamber discussions. There were also two meetings in Tokyo, one on high energy interactions and the second on modulation (in- volving members of the emulsion chamber com- munity) during the 1970s, and a third meeting at the Bartol Research Institute in Delaware, USA. The International Emulsion Chamber Com- mittee organized a meeting in Nahodka, USSR (near Vladivostok, Siberia) in 1980 to discuss very high energy interactions. At the 1981 In- ternational Cosmic Ray Conference in Paris, the Cosmic Ray Commission of IUPAP authorized the Emulsion Chamber Committee to continue such meetings on a biennial basis, with the Na- hodka meeting the first. By 1990, the names of these meetings had become standardized to “International Symposium on Very High Energy Cosmic Ray Interactions”. The meetings follow- ing Nahodka were held as follows: LaPaz, Bolivia and Rio de Janeiro, Brazil (1982), Tokyo, Japan (1984), Beijing, China (1986), Lodz, Poland (1988), Tarbes, France (1990), Ann Arbor, USA (1992), Tokyo, Japan (1994), Karlsruhe, Ger- many (1996), Assergi (Gran Sasso), Italy (1998), Campinas, Brazil and LaPaz, Bolivia (2000), Geneva (CERN), Switzerland (2002), and Pylos (NESTOR), Greece (2004). As noted in paren- theses, some of the recent meetings have taken place at the sites of significant installations and facilities, for example, the Assergi meeting in 1998 was held at the site of the Gran Sasso deep underground laboratory; the Geneva meeting in 2002 was held at CERN (European Laboratory for Particle Physics), and the Pylos meeting in 2004 was held at the site of the shore facilities of the NESTOR underwater neutrino/muon de- tector. The Proceedings of all of these ISVHE- CRI symposia have been published, five of the last seven (plus these Proceedings) as Proceed- Nuclear Physics B (Proc. Suppl.) 175–176 (2008) 3–6 0920-5632/$ – see front matter © 2007 Elsevier B.V. All rights reserved. www.elsevierphysics.com doi:10.1016/j.nuclphysbps.2007.10.001 Figure 1. Participants in the 1982 II ISVHECRI visiting the Mt. Chacaltaya cosmic ray station near LaPaz, Bolivia. ings Supplements of Nuclear Physics B[1]. Fig- ures 1 and 2 are snapshots of some of the partic- ipants in past symposia; Figure 1 at the 5200m Mt. Chacaltaya, Bolivia cosmic ray station in 1982, and Figure 2 at the Fermi National Accel- erator Laboratory near Chicago, USA in 1992. 2. OTHER PAST MEETINGS AND THE ACCELERATOR PHYSICS INTER- FACE In addition to these biennial meetings, there have been other occasional meetings, generally covering related topics, in addition to the rel- evant discussions at the much larger regular, biennial International Cosmic Ray Conferences (held in years alternating with these ISVHE- CRI meetings). To be sure, the ICRC meet- ings also have sessions covering some of the same material discussed at these ISVHECRI meet- ings, but the smaller symposia on specific sub- jects of cosmic ray physics permit a more re- laxed, informal, and focused discussion of rele- vant topics. Other related meetings have been the 1991 “International Workshop on Super-High Energy Hadron Interactions” in Tokyo, the 1994 “First International Symposium on Cosmic Ray Physics in Tibet” in Lhasa, Tibet, the 2002 con- ference on “Needs from Accelerator Experiments for the Understanding of High-Energy Extensive Figure 2. Postconference tour of the US Fermi National Accelerator Laboratory following the 1992 VII ISVHECRI in Ann Arbor, USA. Air Showers” at Karsruhe, Germany, and the 2005 conference “From Colliders to Cosmic Rays” in Prague, Czech Republic. Again, the proceed- ings of many of these meetings are published [2]. The Karlsruhe “NEEDS” conference was orga- nized to bring together accelerator and cosmic ray physicists to discuss ways of improving the accelerator data on which the cosmic ray Monte Carlo models of primary interactions are based (e.g. QGSJET, DPMJET, SIBYLL, etc.). The Prague meeting also brought together compara- ble numbers of participants from the cosmic ray and accelerator communities, to share data and to improve the communication between these two groups. The regular European Cosmic Ray Sym- posia and other meetings on cosmic ray physics should also be noted. Indeed, 50 years ago, around the time of the cosmic ray discoveries of kaons, hyperons, etc., there was reasonably close interaction between these two communities. However, since the op- eration of accelerators of over 100 GeV, there has been relatively less communication. To be sure, there have usually been some accelerator physicists at these cosmic ray symposia. For ex- ample, at the 1984 Tokyo meeting, speakers in- cluded Karsten Eggert reporting on the observa- tion of the W and Z Intermediate Vector Bosons at CERN, Jean-Paul Repellin of the UA-2 collab- Introduction / Nuclear Physics B (Proc. Suppl.) 175–176 (2008) 3–64 oration at CERN, and Tom Kirk and myself dis- cussing recent Fermilab experiments [3]. At the 1992 meeting in Ann Arbor, J.D. Bjorken and Frances Halzen discussed a potential SSC detec- tor (of course, the SSC was never built), Samuel Ting presented data from the L3 experiment at the CERN electron-positron collider, LEP, and Lou Voyvodic showed recent Fermilab data [4]. And the 2002 meeting was held at CERN in order to further increase the interaction between these two communities. So, although there is still sig- nificant separation between the accelerator and cosmic ray communities, there is certainly closer interaction and communication now than was the case some years back. This close connection is probably nowhere as strong and obvious as in the current study of neutrino physics: neutrino masses, couplings, and interactions. 3. EMULSION CHAMBER OBSERVA- TIONS The historical focus of these meetings has been on emulsion chamber observations, as the 1981 organizers of this series came from that commu- nity. Thus, it is appropriate to note some of the particular phenomena which have been reported and discussed. The Centauro events are perhaps the oldest and among the most significant novel events reported from emulsion chambers. Chirons and Halo events have also been reported and di- cussed; due to lack of time, I will not explore them further here. Aligned events and the Long- Flying Component are two other interesting re- ported phenomena. These five phenomena have been observed in cosmic ray events in the PeV energy range, but have not been observed in ac- celerator data at fixed-target (e.g. sub-TeV) en- ergies. At one Tokyo meeting, Fujimoto said, in his closing remarks, “I am convinced that there is a fundamental change in the nature of Strong Interactions at energies above about 10 PeV”. The Centauro phenomenon, events displaying apparent reaction products with an anomalously low gamma content, has been a topic of discus- sion for over 30 years. There have been two ideas suggested to explain this. The first is the the- ory of “disoriented chiral condensates”, a model of strong interactions in which the final state dis- tributions of the charge states of pions would not peak at 2/3 charged, and 1/3 neutral, but would be much flatter, from 0% to 100% neutral, so that an event with almost no neutral pions in the fi- nal state would not be uncommon [5]. This was explored experimentally at the Fermilab Teva- tron Collider in a semi-parasitic experiment, T- 864 “Minimax”, headed by J.D. Bjorken and C.C. Taylor, and found not to be valid [6], i.e. the final state pion charge ratio was essentially statistical. The other concept whch has been discussed suggests that the origin of the Centauro events are “Strangelets” or “Nuclearites” in the primary cosmic ray flux. It has been conjectured that nu- clear matter made up of comparable numbers of up, down, and strange quarks may be stable, and might be a small component of primary cosmic rays. In the atmosphere, an energetic Strangelet might break up into component nucleons (or hy- perons containing an s quark), resulting in events with the Centauro characteristecs. Recently the Centauro I event has been re-analyzed, and has stimulated interest in this explanation [7]. There is a presentation at this Symposium by Edison Shibuya on this concept. An experiment at the CERN Large Hadron Collider (LHC), CASTOR, headed by Apostolos Panagiotou, is planned as a part of the CMS detector complex, specifically to seek evidence for Strangelets produced at this very high energy (14 TeV c.m., equivalent to a 100 PeV proton on a stationary proton) [8]. Another phenomenon discussed by the Lebe- dev group is the “Aligned Event” characteristic of high energy emulsion chamber events. They report that, as one goes to higher energies, the final state particle distributions, or the distribu- tions of jets or clusters of reaction products, is not azimuthally isotropic, but tends to become more aligned in a plane [9]. This could be a nat- ural consequence of quark-quark interactions in the high energy collisions; if the interaction was primarily between two quarks in the two collid- ing nucleons, it seems probable that the resulting jets would be coplanar with the incident nucleon and its resulting forward final state quark jets. If the scattered quark jet subsequently results in two or more separate jets, there will still be Introduction / Nuclear Physics B (Proc. Suppl.) 175–176 (2008) 3–6 5 an overall planar (e.g. azimuthally anisotropic) distribution. It seems that it would be relevant for the Lebedev group to interact with the CDF and D0 experiment groups at Fermilab to explore whether such azimuthal asymmetry is observed in the reaction products at the Tevatron Collider (with an energy equivalent to a 2 PeV proton on a stationary nucleon). The “Long Flying Component” is a phe- nomenon where some components of a hadron cascade appear to travel an anomalously long distance before initiating a nuclear cascade. Vladimir Yakovlev (of the Lebedev Institute) has championed this pheonmenon, and now, with I.M. Dremin, has proposed a solution [10]. They suggest that, at PeV energies, one final state re- action product might be a hyperon containing a “charm” (c) quark, for example with a quark com- position consisting of an up, down, and charm quark (udc), and that this hyperon might be pro- duced as a fast-forward reaction product. With an anomlously low interaction cross-section and a decay lifetime of the order of 100 ps, such hy- perons could have a decay mean free path of the order of a meter, with energies of the order of 100 TeV. Such charm-hyperons have been observed at accelerators, with the above decay lifetimes, and this argument of Yakovlev and Dremin bears fur- ther study. Indeed, there are other unexplained emulsion chamber phenomena, however those discussed above are perhaps the most interesting, in the context of this discussion of Very High Energy Cosmic Ray Interactions. 4. EULOGIES It is with sadness that we note the passing of three outstanding cosmic ray physicists, each of whom has contributed significantly to this field of science. Sergei Slavatinsky died earlier this year; he was a major contributor to these Symposia, and in fact was pivotal in intiating this Symposium series. He was an outstanding scientist and a wonderful gentleman; he will surely be missed. Alexander Borisov has a more substantive presen- tation in memory of Slavatinsky at this meeting. Eugene Loh died quite recently; he was a senior member of the Utah “Flys Eye” and “HiRes” pro- grams, and a contributor in many areas of cosmic ray physics. Again, a superb physicist, a fine fel- low, and a significant contributor to this area of science. We are sad to lose him. Pierre Sokolsky has a fine review here of Loh’s accomplishments and legacy. Cesare Lattes died in 2005; he was a major contributor to the emulsion chamber community, and the leader of the outstanding Brazilian cos- mic ray research program. Edison Shibuya recog- nizes Lattes’ many significant contributions in a memorial presentation here. REFERENCES 1. “Proceedings of the XIII International Sym- posium on Very High Energy Cosmic Ray In- teractions” Nuclear Physics B (Proc. Suppl.) 151 (2006). 2. “From Colliders to Cosmic Rays”, Czechoslo- vak Journal of Physics, Vol. 56, Suppl. 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