The road ahead

CERN is fortunate to have a major accelerator project, the LHC, under active construction. This will take particle physics into a new energy regime, where we are confident that it will resolve many of the puzzles raised by the brilliant confirmation of the Standard Model by experiments at LEP and elsewhere. The LHC is the key to the future of high-energy physics and of CERN, and it offers bright prospects to the new generation of young particle physicists.

The LHC is a highly complex project, both technically and organizationally. The accelerator and the detectors involve sophisticated technologies, in many cases on industrial scales never attempted before in a scientific project.

Moreover, the LHC is truly a global project, with contributions to the accelerator from many countries outside Europe, as well as CERN and its member states, posing difficult problems of coordination and planning. One should also not forget that the long-term plan approved in 1996 left CERN with a reduced budget and no adequate contingency for the LHC.

There have already been unforeseeable delays in the civil engineering for the LHC. The industrialization of the successful prototype magnet technologies remains a challenge, and there are undoubtedly many more obstacles ahead.

Nonetheless, the LHC project is progressing steadily, contracts for a large fraction of subsystems have been adjudicated on schedule, and I consider it one of my primary responsibilities as director-general of CERN to  further it as best I can, and, as the doctors vow, avoid doing it any harm.

Weighing the implications

Over the past two years, dedicated work by CERN’s accelerator staff and the installation of advanced LHC cryogenics made it possible to run LEP at energies greater than design, and for one year longer than originally planned.

When data from LEP in the first part of 2000 revealed hints of new physics, the CERN management extended its run twice, in all from mid-September to the beginning of November, after first reassuring itself that these extensions would have no significant impact on the LHC. I was delighted to hear that the rapid and innovative combination of data from the four LEP experiments by their joint Higgs working group found that these early hints were strengthened, with the most likely interpretation being a Higgs boson weighing about 115 GeV.

In parallel with these extensions of the LEP run, the CERN directorate commissioned a study of the possible implications for the LHC, if LEP were to run in 2001. Two aspects needed to be considered. The LHC will be housed in the same tunnel as LEP, and the dismantling of LEP and modifications to the tunnel to accommodate the LHC are on the critical path. Also, the staff required for the operation of LEP would not be transferred as foreseen to LHC construction. Several ingenious ways to reschedule part of the essential work were tried, but finally we came to the conclusion that the LHC would inevitably be delayed by about a year if LEP was to run a full year in 2001.

Extra cost

There were also financial and personnel problems with a further LEP extension. It would have required around 100 million Swiss francs (about 40 million in running costs, and the rest in penalties for civil engineering contracts that are difficult to quantify a priori, additional expenses for rescheduling, etc).

I was grateful to see that some CERN delegations were willing to consider providing their share of these extra costs, but the bulk would inevitably have been borne by the regular CERN budget. Thus I came equally reluctantly to the conclusion that an LEP extension would be a major squeeze on the resources needed for the LHC project.

Projections of the signal seen at LEP in 2000 indicated that a year’s running might not lead to a conclusive result, particularly if the mass of the Higgs boson was in the upper part of the indicated range, namely around 116 GeV. This reflects the fact that the signal is seen at the very end of the LEP energy range.

To put this region under real scrutiny would require a significant energy increase, which in turn implies significant further expense and a prolongation of at least a two years, one year being approximately the time needed for the industrial production of new accelerating cavities. That would have led to a major disruption of the LHC project.

Overall

Putting all of these reasons together, and after consultation with the scientific committees, my colleagues in the CERN directorate and I became convinced that running LEP in the year 2001 would put the LHC under unacceptable pressure, and we decided that the CERN programme should not be changed to accommodate it. This decision had to be taken rapidly, precisely so as not to impact on the LHC schedule. I appreciated the efforts of the scientific review committees, which provided their advice and presented vigorously a variety of views, under the pressure of time.

Unlike the running of LEP in the year 2000, the issue of whether one should prolong LEP in 2001 divided the community and the scientific committees, and no consensus solution could be proposed. CERN management eventually cut the Gordian knot in favour of the LHC.

I understand the frustration and sadness of those who feel that they had the Higgs boson within their grasp, and fear that it may be years before their work can be confirmed.

Nevertheless, I am convinced that the best way forward for particle physics is the LHC. A Higgs boson as light as 115 GeV is most likely the signal of a rich supersymmetric particle spectrum at low energy, and the LHC will be the ideal instrument to put CERN and the physics community in a position to explore fully the new frontier in particle physics, which we may have glimpsed through the fascinating LEP events.

I hope that the high-energy physics community will join us in working wholeheartedly towards this exciting and challenging goal.