Supersymmetry reviewed from the past to the future

Some 400 theorists and experimentalists gathered at DESY in June 2002 for the SUSY02 conference to discuss aspects of supersymmetry and the prospects for unification physics. Jan Louis and Peter Zerwas report the conference highlights.

The DESY laboratory in Hamburg, Germany, hosted the 10th Inter­ national Conference on Supersymmetry and Unification of Funda­ Above: Julius Wess (centre) - mental Interactions (SUSY02) in June 2002, providing a forum for one of SUSY'S founding discussing the present status and future developments of super- fathers - registers for the symmetry (SUSY). In the week-long meeting - organized by Pran Nath SUSY02 conference taking of Northeastern University, US, and Peter Zerwas of DESY - theoreti­ place in Hamburg, Germany. cal ideas, analyses of experimental data, the expectations for physics Left: the poster for SUSY02 at CERN's (LHC) and the proposed tera-elec- featured this painting of the tronvolt range electron-positron linear colliders were on the agenda. Bunte Kuh, a 16th century A lively and exciting atmosphere prevailed, with established prac­ merchant ship from Hamburg titioners exchanging standard and not-so-standard views on the that sailed to Amsterdam and evolution of with enthusiastic youngsters. The excite­ London. ment had its roots in the fascinating prospect of addressing funda­ mental problems of physics in the new generation of accelerators, and in the well-founded hope of hearing about long-awaited break­ boson as predicted by supersymmetric theories derived from the throughs that would answer many of the outstanding questions. theoretical interpretation of precision data at LEP and the SLC. Ritva Kinnunen of Helsinki, Finland, explained how LHC experi­ Waiting for SUSY ments will be able either to establish or rule out the existence of a On the experimental side, the conference marked the transition from light within a few years - in nearly all scenarios as the experiments completed at CERN's LEP, DESY's HERA, 's pointed out byJackGunion of the University of California, Davis, US. and SLAC's SLC colliders, to those at Tevatron Run II and Looking further ahead, CERN's Marco Battaglia discussed how the HERA-II and to preparations for physics at future collider facilities. profile of this fundamental particle could be studied experimentally The experiments at LEP, reviewed by Eilam Gross of Israel's at a linear collider with very high precision to establish the Higgs Weizmann Institute, have covered a range of parameter space in mechanism for generating the masses of standard particles. the Higgs sector of the minimal supersymmetric extension of the Robert McPherson of Canada's Victoria University reviewed the , which was summarized by Howard Haber of the search for genuine supersymmetric particles at LEP. In its higher- University of California, Santa Cruz, US. The experiments seem to energy phase, LEP set lower limits on the masses of the scalar part­ have ruled out one of the two parameter ranges singled out previ­ ners of leptons close to the beam energy of 100 GeV. Similar limits ously by theoretical arguments (the so-called small tan(3 region). have been achieved for the fermionic partners of W bosons, while However, the large tan(3 region was not fully covered by LEP and, as the lightest supersymmetric particle has been constrained to a mass Fermilab's Marcela Carena pointed out, it is of great interest for of more than 50 GeV, albeit in a model-dependent way. The masses forthcoming Higgs searches at the Tevatron. On the other hand, of squarks and gluinos, on the other hand, have been increased by Wolfgang Hollik of Karlsruhe offered strong support for a light Higgs Tevatron analyses to more than 200 GeV, reported Teruki Kamon t>

CERN Courier January/February 2003 19 SUPERSYMMETRY

of Texas A&M University, US. This result is complemented by con­ Tell me where the straints on the stop mass in R-parity violating theories at HERA, dis­ SUSYs are: Robert cussed by Yves Sirois of the Ecole Polytechnique, France. McPherson (left) of The discovery range for SUSY will be extended by the LHC to val­ Victoria University, ues of up to 3 TeV, leaving little room in parameter space for super- Canada, and Eilam symmetric particles to hide, as analysed by Brookhaven's Frank Gross of the Weizmann Paige. In the future, the properties of such particles could be mea­ Institute, Israel, ask sured to an accuracy of parts per million in the several hundred Gordon Kane (centre) giga-electronvolt mass range by machines such as DESY's proposed of Michigan, US, for TESLA collider - presented by Hans-Ulrich Martyn of Aachen - theoretical advice. reducing to the percentage level in the multitera-electronvolt range that could be explored by CERN's CLIC. This allows the fundamental where decays of heavy Majorana neutrinos with masses close to the parameters in supersymmetric theories to be determined precisely, grand unification scale are the source for the observed asymmetry of as Jan Kalinowski of Warsaw, Poland, concluded. Abdel Djouadi of matter and antimatter in the universe. Montpellier, France, Walter Majerotto of Vienna, Austria, and Cosmological scenarios can cause problems for supersymmetric Michael Spira of the Paul Scherrer Institute, Switzerland, described models. However, as Hans Peter Nilles of Bonn, Germany, the high-precision theoretical calculations (sometimes to two-loop explained, in detailed analyses these often appear less severe. accuracy) that underpin all of these results and expectations. Recent data on energy fluctuations in the cosmic microwave back­ More information on supersymmetric scenarios, including the ground and measurements of the deceleration parameter via the CP-violating sector, examined by Nath, is offered by precision mea­ Hubble diagram of Type 1A supernovae suggest a positive cosmo­ surements at lower energies. B-decays are affected by supersym­ logical constant. Pierre Binetruy of Orsay, France, emphasized that metric particles through virtual-loop effects. Antonio Masiero of from a theoretical point of view, these results are more than puz­ Padova, Italy, pointed out that the agreement between present zling, prompting the suggestion from Edward Copeland of Sussex observations and the Standard Model is not at odds with the poten­ University, UK, that brane-world models may offer alternative sce­ tial intervention of supersymmetric particles, while Matthias Neubert narios for the cosmology of the early universe. of Cornell, US, discussed the consequences of rare decays. Errors are still too large to draw definite conclusions in multidimensional Connecting to the Planck scale SUSY parameter space on flavour physics. The most compelling argument in support of the supersymmetric Richard Arnowitt of Texas A&M showed how the discrepancy extension of the Standard Model is the unification of the three dif­ between the anomalous muon magnetic moment measurement and ferent gauge couplings - electromagnetic, weak and strong - at the the predictions of the Standard Model is compatible with wide areas percent level at a scale near 1016 GeV. After extrapolation over more of supersymmetric parameter space. New insight - as presented than 14 orders of magnitude in energy, the three couplings meet in by Isabella Masina of Saclay, France - might soon be obtained from a tiny area with an accuracy that is much better than expected in studying lepton-flavour-violating processes, such as radiative muon many scenarios. This surprisingly successful prediction cannot be decays into electrons. CERN's Concha Gonzales-Garcia and matched easily in alternative theories. Rabindra Mohapatra of Maryland, US, discussed the recent obser­ Although certain aspects of minimal versions are sometimes prob­ vation of neutrino oscillations that has prompted new interest in the lematic, such as too-rapid proton decay, even conventional super- search for such phenomena in the charged-lepton sector, with novel symmetric grand unified theories are still in agreement with data, conversion processes enhanced by virtual SUSY contributions. said Stuart Raby of Ohio State University, US. Graham Ross of Oxford, UK, discussed the possible origin of quark and lepton mass Giving mass and energy to the universe textures in this context. Lawrence Hall of the University of California, It has long been speculated that the observation of cold dark matter Berkeley, US, and John March-Russell of CERN showed how higher in the universe is related to SUSY. If, as in many scenarios, the light­ dimensions offer additional freedom in building models, and thus est supersymmetric particle is stable, it would be a perfect candi­ are more flexible in removing the stumbling blocks of traditional date for this new kind of matter. The signals of such particles, grand unified theories. While Jon Bagger of Johns Hopkins University, accounting for most of the mass of the universe, may be identified US, discussed questions of SUSY breaking within such models, in dedicated searches or astrophysics experiments, as described Edward Witten of Princeton, US, addressed how these models deal by Keith Olive of Minnesota, US. with the doublet-triplet splitting of the Higgs field. Riccardo Barbieri Cosmological problems are an excellent test ground for physics at of the Scuola Normale Superiore in Pisa, Italy, covered aspects of very-high-energy scales. - crucial for our own existence electroweak symmetry breaking. - can be explained by SUSY mechanisms if stop and Higgs masses Peter Mayr of CERN showed how studying the phenomenological are tightly constrained to barely above the present experimental aspects of supersymmetric theories in string theory has been exclusion limits, claimed Carlos Wagner of Argonne National improved by extending the powerful techniques of mirror symmetry Laboratory and Chicago University, US. A different picture emerges to theories with only N=l SUSY. Furthermore, Jan de Boer of from leptogenesis, presented byTsutomu Yanagida of Tokyo, Japan, Amsterdam, the Netherlands, showed how string theory can also

20 CERN Courier January/February 2003 SUPERSYMMETRY

The quest for unification

At SUSY02, DESY launched a series of and strong electromagnetic interactions annual lectures with the aim of conveying merge to form a single unified interaction. the fascination of particle physics to a However, the evolution of the couplings wider audience at the university and in of the individual interactions approach a the city of Hamburg, Germany. Edward single point accurately only if the Witten of the Institute for Advanced Study Standard Model is extended to a at Princeton, US, presented the first DESY supersymmetric theory. This may also Heinrich Hertz Lecture on Physics. open the door to unifying the genuine DESY director-general, Albrecht Wagner, Left: DESY director-general Albrecht particle physics interactions with gravity. introduced the series with a description of Wagner introduced his lecture in front of This last step may require the expansion Hertz's great theoretical and experimental a portrait of Heinrich Hertz. Right: of our four-dimensional space-time world achievements. Born in 1857 in Hamburg, Edward Witten captivated his audience to one of higher dimensions as required Hertz developed an outstanding talent for with his talk "Quest for unification". by superstring theories. physics early in life. After becoming Forthcoming experiments at the LHC professor of physics at the Karlsruhe It was fitting, therefore, that Witten's and future linear colliders will determine Polytechnicum in 1886, he carried out lecture covered the quest for unification. the truth of these ideas. Positive evidence one of the most important experiments of He described the steps and arguments would provide a more comprehensive the 19th century - demonstrating the leading us from the Standard Model of picture of matter and forces in nature - existence of electromagnetic waves. This particle physics to grand unified theories the "ultimate unification" sought by the confirmed Maxwell's theory, in which at 1016GeV. An extrapolation of precise most eminent theorists in history. electricity and magnetism are unified to experimental data on the three gauge Witten's presentation is available on electromagnetism. couplings suggests that at this scale, weak video at www.desy.de/susy02/.

be exploited to shed new light on strongly coupled gauge theories, aspects of extra dimensions on a tera-electronvolt scale are impor­ such as quantum chromodynamics, by means of the so-called tant for experiments at the next generation of particle accelerators. AdS/CFT correspondence between string and field theory. These were discussed by James Wells of the University of California, If SUSY is realized in nature, high-precision experiments at a linear Davis, and Greg Landsberg of Brown University, US, who focused on collider such as TESLA followed by a second phase in a multitera- the radiation of black holes from high-energy particle collisions. electronvolt collider such as CLIC, could determine the properties of It is likely that the structure of space-time is modified at ultrashort new particles with very high precision. This is a necessary prerequi­ distances. An interesting aspect of this is the potential non-commu- site for reconstructing the fundamental supersymmetric theory at tativity of space (and time). This would mean, for example, that mea­ the scale where SUSY breaking is localized, emphasized Gordon surements of the x and y co-ordinates of an event would affect each Kane of Michigan, US. If the SUSY parameters are transmitted at other in a similar way to the position and momentum measurements this scale from a hidden world to our visible eigen-world by gravita­ in standard quantum mechanics, albeit with the interference being tional interactions, these machines could be used as powerful tele­ characterized by a very-small-scale parameter. Volker Schomerus of scopes to view a domain where particle physics and gravity are Potsdam, Germany, showed that such an idea can be developed linked directly - a vision for the future. within string theory, while Julius Wess of Munich, Germany, devel­ A big step into the new experimental domain of high energy linked oped similar ideas from a field-theoretical point of view. with high accuracy - successfully pioneered by LEP and the SLC - The possibility that additional strongly coupled gauge groups on a was outlined by DESY's director-general, Albrecht Wagner, who pre­ tera-electronvolt energy scale could have a significant impact on sented the well-advanced plans for the TESLA machine, which has the pattern of electroweak symmetry breaking and the Higgs sector an energy target that is close to ITeV. If preparations continue as was covered by Savas Dimopoulos of Stanford, US, Stefan Pokorski they are now, the particle physics community could be operating of Warsaw and Lisa Randall of Harvard, US. This possibility is also this unique tool for SUSY particle diagnostics by 2012. suggested by reducing elegant theoretical structures in higher dimensions to the standard 3+1 space-time dimensions. Living in higher dimensions The physics programme discussed at the conference focused on The idea of the Standard Model being localized on a four-dimen­ the innermost structures of the microcosm, for matter as well as sional brane that is embedded in a higher dimensional space-time space-time, but it found them deeply connected with the structure can be formulated in string theories. Ignatios Antoniadis of CERN, of the universe at large - the final step of ultimate unification. Mirjam Cvetic of Pennsylvania, US, and Luis Ibanez of Madrid's Institute forTheoretical Physics, Spain, presented models where con­ Jan Louis, Martin-Luther University, Halle, Germany, and Peter structions of this type are carried out explicitly. Phenomenological Zerwas, DESY, Hamburg, Germany.

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