ap-3-10.dvi Acta Polytechnica Vol. 50 No. 3/2010 Physics on the Terascale J. Engelen The Terascale At an energy of order 1012 eV, i.e. 1 TeV, the funda- mental interactionsbetweenquarks, leptons andgauge bosons need an additional ingredient in order to pre- serve unitarity. This ingredient is naturally provided by the Brout-Englert-Higgs mechanism. This mecha- nism invokes a scalar field with a ‘Mexican hat’ type potential, inwhich the ground state of the vacuumoc- curs atafinite valueof thefield (‘symmetrybreaking’); the quantum of this field, the Higgs boson, provides a way of ‘generating’ massive gauge bosons whilst pre- serving renormalizability of the theory. The existence of the Higgs boson has not yet been demonstrated experimentally; in fact the elucidation of ‘the Higgs sector’ represents a huge experimental program – ar- guably including the ‘next large collider’ ILC-CLIC – that onlybeginswith thediscoveryof the (or ‘a’)Higgs boson. Furthermore, access to the Terascale holds the promise of more discoveries. A theoretically attrac- tive scenario, in which the electro-weak and strong in- teractions unify at a scale of 1015 GeV (‘Grand Uni- fication’), requires an additional ingredient to enter into the renormalization group equations on a scale of 1 TeV. This couldmark the scale onwhich ‘supersym- metry’ is revealed and a new world of supersymmetric partners of all known particles is discovered. Finally, and increasingly speculatively, the Teras- cale might give us access to ‘large’ (of the order of 0.1 mm) extra dimensions, only open to gravity: this would open up possibilities of the experimental study of quantum gravity well below the Planck scale (1019 GeV). An accelerator for the Terascale The Large Hadron Collider was approved by the CERNCouncil in December 1996. Initial ideas can be traced back to the late 1970’s, but even in 1996 an ex- tensiveR&Dprogramme still had to be completed be- fore the feasibility (and the cost) of the LHC could be established. The nominal energy of 14TeV, i.e. 7TeV per beam, requirednew superconductingmagnet tech- nology; the nominal luminosity of 1034 cm−2s−1 re- quired, among other things, a novel collimation sys- tem. Moreover, experiments able to cope with the in- teraction rate at this energy needed new concepts in detector technology and on-line selection of poten- tially interesting events (‘triggering’). This is the sub- ject of a separate presentation at this Symposium, by Peter Jenni (spokesman of the ATLAS collabora- tion). In addition, the huge amounts of data of 15 PetaBytes per year required a new approach to com- puting: the now operational worldwide LHC comput- ing GRID (wLCG), also serving as a platform for ap- plications outside high energy physics. The LHC dipole magnets have all now been suc- cessfully produced, and the last magnet was installed in the tunnel in March 2008. In total 1232 of these magnets and about 400 quadrupole magnets (and a large number of smaller, higher order correction mag- nets) form the LHC lattice. The LHC is a marvel of technology in all its facets, crowned by the super- conducting dipole magnets. They are 15 m in length, and feature two coils (for the two beams) in one ‘cold mass’ (flux return yoke). The coils consist of niobium- titanium cables (out of 7 micron filaments) and are operated at a temperature of 1.9 K, cooled by super- fluid helium. The LHC was successfully put into operation on September 10, 2008. In the period September 10– September 19, 2008 this very complexmachine proved to have been extremelywell designed: injecting, circu- lating and ‘capturing’ (by theRFacceleration system) the beam was achieved in a matter of days. Prepara- tions for first collisions were in full swingwhen an un- fortunate incident revealed a weakness in one of the joints between two superconducting cables between two magnets. There are more than 10000 such con- nections in the LHC, but one of themhad a resistance of ∼ 100 nano-ohm (instead of less than 1, as in the specifications – a few additional ‘suspect’ joints were identified during subsequent inspections). The dissi- pated energy (at a current of 10 kA) led to warm up and eventual failure of the joint. The loose cable sub- sequently discharged, burning a hole in the pipe car- rying the liquid helium. The helium escaping into the vacuum system caused a pressure wave that damaged (and in a number of cases dislodged) magnets over a distance of several hundred meters. The repairs and the implementation of additional diagnostics (and of some measures to limit the damage should such an event occur again, but it should not!) are estimated to take a full year, such that restart of the accelerator is foreseen for October 2009. (Note added: meanwhile the LHC has very successfully resumed operation in November 2009). Brief summary of a colloquium given in honor of Professor J. Niederle on the occasion of his 70th birthday 82 Acta Polytechnica Vol. 50 No. 3/2010 Conclusion Research into the interactions of elementary particles andfields is at the eve of a newera. TheLargeHadron Collider, a marvel of technology and a wonderful ex- ample of European leadership in worldwide collabora- tion will allow the exploration of new and uncharted territory, where exciting new phenomena are waiting to be discovered. Finally Jiri Niederle has contributed prominently to theEuro- pean leadership referred to in the previous paragraph: as the Czech delegate, he is a long-time member of the CERN Council; on the basis of his authority as a prominent scientist he has successfully helped to steer CERN in the right direction! References [1] The Large Hadron Collider: a Marvel of Technol- ogy. EPFL Press, 2009, edited by Lyndon Evans. Jos Engelen NIKHEF and NWO – the Netherlands Organisation for Scientific Research P/O BOX 93138 NL 2509 AC Den Haag, Netherlands 83