Feature Article

ATUL GURTU India’s Feature Article Feature ConnectionCERN Indian scientists have made concrete contributions to research at this “Mecca of high energy physics” and look toward an even more significant role in the future. Here is an account of how India’s collaboration with CERN has evolved over time. technologies, like particle detectors and (LHC), with over hundred times higher computing and information technology. energy than the ISR. “It’s the Mecca of high energy Experimental particle physics physics.” These words about CERN still ring attempts to answer questions about the in my ears, spoken to me by my senior basic building blocks of nature by firing colleague at Tata Institute of Fundamental particle beams against one another and Research (TIFR), P.K. Malhotra, a few months detecting the debris of the collisions. The before I was to embark on my first stint to particles are traveling at almost the speed CERN. This was late 1970 and I had recently of light and carry very high energy. In a joined the bubble chamber group at TIFR collision some of this energy gets as a postdoctoral researcher, having converted into new particles (good old completed my PhD work at Panjab Einstein’s E = mc2), which fly out in all HE “God-particle” laboratory! With University, Chandigarh. As luck would have directions. One tries to detect and the recent discovery of the new it, my thesis was on properties of measure the energies and directions of Tparticle, which appears to be exactly hypernuclei that are produced by all the particles in order to deduce the what the Higgs particle should be, the stopping K-minus mesons, the exposure to fundamental nature of the particles and laboratory where this experiment was K-minus mesons having come from CERN! the forces between them. LHC energies carried out is also very much in the news – It had been a TIFR-Panjab University are so high that it is like creating a mini big CERN! collaboration. bang at a millionth-millionth (10-12) second CERN was founded in 1954, is I was going to CERN in early 1971 to after the real big bang that created the headquartered in the outskirts of Geneva, participate in experimentation at the still- universe. Switzerland, and extends over the border being-commissioned proton-proton From the 1970s to the mid-80s, TIFR, into France. CERN or Conseil Europeen collider, the Intersecting Storage Rings (ISR). and later other Indian high-energy groups, pour la Recherche Nucleaire is the This was to be the first proton-proton collider participated in many CERN-based bubble European laboratory for particle physics. in the world and would provide interactions chamber experiments. A bubble chamber Its mandate is to carry out front-ranking at record high energies. TIFR had is a transparent chamber research in particle physics, a field that proposed an experiment at the ISR facility. filled with a liquid kept in a superheated delves into the nature of the fundamental The ISR became operational in 1971 and state by application of pressure. A beam constituents of matter and the forces our experiment was duly carried out and of particles is fired into it, and between them. Over its lifetime, CERN has yielded results on photon and pi-zero simultaneously the pressure is released. developed and hosted a succession of production. Forty years down the line, in Some beam particles collide with the state-of-the-art accelerators and has 2012, the discovery of the Higgs boson atomic nuclei in the bubble chamber and been the birthplace and development has come from another proton-proton new particles are created in this collision. cradle for related advanced collider at CERN, the Large Hadron Collider The release of pressure results in bubble SCIENCE REPORTER, NOVEMBER 2012 24 Feature Article The CERN Working Group as well as CERN management was very appreciative of these concrete proposals from the Indian scientists. In the June 2010 CERN Council meeting new rules for Associate Membership were adopted. Laureate Sam Ting of MIT, who was the co-discoverer of the charm quark. Participation in L3 collaboration provided new experience to the TIFR group. Modern particle detectors are hugely complex and expensive. It is normal, and actually mandatory, for tens of institutions from across the globe to collaborate in building different parts of the overall detector. TIFR’s responsibility was to build the forward-backward hadron calorimeter in sub-collaboration with the Aachen group. A hadron calorimeter detects and measures the energy of hadrons – strongly interacting particles, like the proton and neutron. The detectors were fabricated in TIFR with quite a bit of precision machining work for it done by the Mumbai industry and BARC workshop. These were tested and delivered at CERN in 1988 and integrated within the L3 detector. These hadron CERN Technician Urs Brotchi (left) and Dr. Atul Gurtu (right) at work inside the ISR tunnel. The intersecting pipes and the calorimeters performed perfectly from bar used for designing the stacks are visible. (Photo credit: CERN Official Photo no. 135-9-71) 1989, when LEP started operation, till 2000 when the LEP experimental program was formation along the paths of the charged helped to detect and measure high terminated. The TIFR group also provided particles. energy particles produced in interactions strong software support to this Photographs of the chamber are within the chamber. This experiment, NA27, collaboration. taken from three or four suitable angles studied properties of “charm” particles for An area where the TIFR group made for three-dimensional reconstruction of this the first time, the charm quark having the maximum impact was in the extraction interaction. The film is processed and been discovered just eight years back of the science from the experimental projected on a table where in 1974. results. The group was responsible for the measurements are made along the By mid 1980s, the days of the bubble analyses to determine the properties of bubble trajectories where the particles chamber were over, and the purely the Z boson particle, which was the main passed. Computers are then used to electronic experiments had taken over. goal of the first phase of the LEP project. reconstruct the interaction and the study In such experiments many cylindrical Group members were also instrumental in of tens of thousands (or more) of such layers of detectors surround the collision studying the properties of the strong interactions allows one to discover point. Each layer specializes in the interaction (that holds together atomic properties of the produced particles and detection of a particular type of particle, nuclei), mesons containing b-quarks, and their interactions. so that taken together all the particles in searches for the Higgs and super- The last such collaborative can be detected (except neutrinos, symmetric particles. experiment with TIFR participation in the which hardly interact with anything at all). The LEP experiments systematically early 1980s was a landmark experiment in In 1983, TIFR joined the L3 collaboration and comprehensively tested the validity which a very small bubble chamber (10 that would carry out experiments at LEP, of the Standard Model of particle physics, centimeters in length) called Lexan Bubble the Large Electron Positron collider, which which predicted the existence of the Chamber (LEBC) was placed upstream of started operation in 1989. This Higgs and the Z boson particles as a by- very sophisticated instruments, which collaboration was led by the Nobel product of the unification of the 25 SCIENCE REPORTER, NOVEMBER 2012 Feature Article heavier than the three already mUnit=152 GeV discovered), we can confidently say that we have already discovered ALL the Theory uncertainty Mass limit set on the Higgs Boson matter generations that exist in nature! set by the LEP and LHC During the 1990s, while the TIFR group experiments. The mass in GeV on 0.02750A0.00033 was involved in the LEP experiment, other 0.02749A0.00010 the - axis and theoretical Indian groups, led by Variable Energy incl. low Q2 data uncertainty on the Y–axis. The Cyclotron Centre (VECC), Kolkata, started participation in CERN-based band in white shows the mass collaborations in the area of high energy region that has not been heavy ion interactions. CERN accelerators excluded by the two could produce such beams, including experiments. lead beams, and Indian groups fabricated plastic scintillator based detectors to detect and study photon production in search for a new state of matter called quark-gluon plasma. They worked on WA93 and WA98 collaborative experiments and many interesting results on photon multiplicity and its energy and angular distributions were obtained. By this time the Indian Department of m =MGeVN H Atomic Energy (DAE), interested in accelerator related technologies, saw an electromagnetic and weak interaction fundamental constituents of matter that opportunity of collaborating with CERN, theories by Steve Weinberg and Abdus can be clubbed in three generations. which had been at the forefront of such Salam. The Z boson had been discovered The visible universe we see around us research for long. The first CERN-DAE at CERN in 1983-84 but detailed study of its needs only the first generation for its umbrella agreement for scientific co- properties needed a “Z boson factory” existence: the two quarks called up and operation was signed by Atomic Energy where millions of Z boson could be down quarks, which make up the protons Commission Chair P.K. Iyengar and CERN produced and studied. LEP was this and neutrons of atomic nuclei, the Director General Carlo Rubbia in 1991 and ambitious Z boson factory. The Higgs had electrons, which orbit the nuclei, and the a follow-up protocol in 1996 by not been discovered at all and LEP was to neutrino, which is necessary to explain the succeeding AEC Chair R.

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