by Hans H.Gutbrod. Published: 20 March 2013

In 1982 a MoU was signed by GSI, Darmstadt, CERN and LBL Berkeley to get heavy ions to CERN: GSI promised to bring an ECR-ion source and LBL a RFQ Linac to the CERN site. Rudolf Bock(GSI), Herrmann Grunder (LBL) and Reinhard Stock (Uni Marburg) and others proposed to have heavy ions in the CERN PS. Robert Klapisch, then research director of CERN, found SPS more adequate and this lead to heavy ion physic with Oxygen beams in 1986, sulphur beams in 1987 and lead beams in 1994

In 1983 at the relativistic heavy ion meeting at Brookhaven, I discussed with Carlo Rubbia topics of the future heavy ion collider at BNL, later called RHIC, when he told me: ‘You will get your collider at CERN, with enough energy for your physics case. At first it wasn’t clear for me what he was trying to tell me. He explained that physics signals became much clearer at the high energies of the SppbarS collider compared to the smaller ones at CERN-ISR.

A few years later, a proposal for a heavy-ion programme was submitted in the LHC project . Rubia, kept his promise and among many things he insisted on a two-in-one magnet solution for the LHC instead of a pp_bar mode with only one vacuum chamber. It should be noted that one vacuum chamber and one magnet is only good for ppbar, an option several persons preferred since it was also cheaper.

It was not before the Aachen meeting in 1990 that we had a clear picture of a detector suitable for heavy-ion physics at the new energy regime opened at the LHC. A small group (Ch.Fabian, H.Gutbrod, H.Specht, W.Willis et al.) sketched a detector concept comprised of a large solenoid, coupled with one dipole at each end and full tracking. This was similar to the smaller 4π detector the group had proposed several years earlier for RHIC.

From 1991 on, a group of about 20 persons met at CERN regularly to work on a proposal for a dedicated heavy ion experiment at the LHC. In parallel we had to build and run our lead beam experiments at the SPS. These were truly fulfilling times.

CERN research director Claude Détraz (left) with QM 2002 conference organizer Hans Gutbrod, who put the host town Nantes firmly on the heavy-ion physics map.

In the beginning of our discussions for a dedicated heavy ion experiment at the LHC we came up with two concepts: the first was based on a silicon tracker inside a superconducting thin solenoid,supported by Jürgen Schukraft while the other was to have all the detectors inside a large solenoid, pushed by myself. Our consensus was that the large magnet solution required a larger budget, but that the small magnet risked producing unwanted tracks in the detectors in the outside field free region with worse resolution due to multiple scattering in the magnet material.

It should be added that we didn’t have a clear picture about the multiplicity of produced particles. Theoretical models were predicting different numbers ranging from dN/dY = 2000 to 8000 charged particles. At the meeting at Evian-les-Bains in March of 1992, the concept of the small magnet was presented by Jürgen Schukraft. I tried to find a cost effective solution for a large magnet and looked at the DEPLPHI solenoid magnet, which was unfortunately too small for the track density that was anticipated in nuclear collisions. Then I focused my attention onto the L3 experiment with its huge magnet, which I found perfect for our purpose. Sam Ting was proposing at the same time his own L3P experiment, i.e. an upgraded L3 setup for the LHC program. For me it was obvious that the project should be named L3 HI so that we wouldn’t alienate the L3 team from the beginning. Alain Hervè from L3 helped me getting a nice drawing of L3 H.I.

On July 2nd 1992, in one of our Proto-collaboration meetings at CERN, the question was raised: Should we have 2 simulations, one for small magnet and one for large magnet? The decision was yes, we should follow still both ways.

In order to present my L3 H.I. concept to a wider public, I asked Paolo Giubellino to give a talk on heavy ion detector concepts for the LHC at the NATO Advanced Study Institute "Particle Production in Highly Excited Matter", Il Ciocco, Juli 1992 which I organized with J. Rafelski and G.Bellettini. Paolo presented there for the first time the drawings of L3 H.I., which foresaw an Inner Silicon Tracker, a TPC, a TOF barrel and an EM Calorimeter barrel and two Forward EM calorimeters outside of the L3magnet. Due to the off axis of the LHC beam with respect to the position of the LEP beam, a large, highly segmented crystal electromagnetic spectrometer was proposed at the bottom of the magnet at a distance of ca. 6m from the interaction point.

Sam Ting asked me to present this proposal only after a decision was clear about L3P. In Fall of 1992, the fate of L3P was clear and he invited me to give a talk to his collaboration. I started my presentation saying: ‘I feel somewhat awkward coming here wanting to steal your beautiful experiment.’ From then on we got strong support from the L3 team as well as from the CERN management.

On February 1st, the small magnet scenario was dropped and the L3H.I. concept was adopted which was then named: the ALICE detector. In March 1993, the Letter of Intent for ‘A Large Ion Collider Experiment’ was submitted as CERN/LHCC/93-16 – LHCC/I4 on the basis of L3 H.I.. Jürgen Schukraft pushed it over all the years to the successful operation. The transfer of ownership of the L3 magnet and the infrastructure of the L3 site from the L3 collaboration to the ALICE collaboration was performed at a seafood dinner hosted by Jürgen Schukraft in a restaurant at Ferney-Voltaire.

Finally, it should be noted that initially ALICE did not have a dimuon part. The LHCC requested from the collaboration to improve the coverage of ALICE to larger rapidities – which we never did- and to include dimuons in the programme. Karsten Eggert (CERN) and Andreas Morsch (CERN) and others were proposing a forward dimuon spectrometer with an additional dipole on one side of the L3 solenoid. Eggert’s intention was together with B.J. Bjorken (Fermilab) to join ALICE and to make it into a full 4π detector for soft pp physics.This option was not accepted by the ALICE collaboration and Eggert build up the TOTEM collaboration instead.

The ALICE collaboration followed the wish of the LHCC by submitting a letter of intent for a Foreard Dimuon spectrometer, and I took over as dimuon project leader when I left GSI in 1995 and went to Nantes. In 2001 when I returned to GSI to head the FAIR project, I handed over the project leadership of the dimuon spectrometer to Florent Staley who successfully led it to completion.

Figures from NATO ASI Series B: Physics Volume 303, page 138