by Virginia Greco. Published: 16 April 2018

A jubilee event was held at CERN on March 21 to celebrate the 25 years anniversary of the ALICE Collaboration. Highly attended, the event was an occasion to share personal recollections of the infancy of the experiment and retrace the milestones of its history.

Speakers of the jubilee event. Clockwise from the top left: Chris Fabjan, ALICE Technical Coordinator from 2001 to 2007, Emanuele Quercigh, the first chair of the Collaboration Board, Luciano Musa, project leader of the Inner Tracking System, and Jürgen Schukraft, ALICE Spokesperson from 1992 to 2010. [Credit: Virginia Greco/ALICE]

 

On March 1st, 1993, the recently-formed ALICE collaboration submitted a Letter of Intent to the CERN LHC Committee, proposing the construction of a heavy-ion experiment dedicated to the study of nucleus-nucleus collisions.  The aim was to shed light on the strong interaction and the quark-gluon plasma, the existence of which at that time was only speculated. It was also when the ALICE acronym for “A Large Ion Collider Experiment” was introduced. During the 25 years that followed, a collaborative effort has been put in conceiving, designing, building and commissioning the ALICE detector as well as in running the experiment, which is collecting a wealth of data and producing interesting results.

To celebrate this important anniversary, the ALICE Collaboration invited members and colleagues to a jubilee event, which took place on March 21 at CERN. After the opening by Spokesperson Federico Antinori, four speakers, Emanuele Quercigh, Jürgen Schukraft, Chris Fabjan and Luciano Musa, took the stage to recall the milestones of ALICE’s history as well as to present the plans for its future.

Emanuele Quercigh, who was the first Chair of the ALICE Collaboration Board, retraced the origin of heavy-ion physics as an independent research field. He recalled the first ion experiments at the SPS – which used oxygen ions at 60 and 200 GeV/nucleon, then sulphur at 200 GeV/nucleon and finally lead at 158 GeV/nucleon – and moved on to the birth and development of the ALICE experiment. As he reported, ideas on nucleus-nucleus collisions and a possible heavy-ion physics programme at the future Large Hadron Collider were discussed in the Aachen workshop, held in October 1990 to put the research case for the proposed LHC. A couple of months later, about 60 physicists met at CERN to initiate “a serious experimental effort towards a heavy ion detector capable of measuring ultra-relativistic heavy-ion collisions at LHC energies” and the so-called Heavy Ion Proto Collaboration (HIPC) was created. This would evolve later in the ALICE Collaboration.

From 1990 on, a group of about 20 scientists met at CERN regularly to work on a proposal for a dedicated heavy-ion experiment at the LHC and in March 1992, at the Evian Meeting called “Towards the LHC Experimental Programme”, an expression of interest for such an experiment was put forward. At the same workshop, as Quercigh reminded, physicists of the Brookhaven National Laboratory in the US presented the experimental programme for the Relativistic Heavy-Ion Collider (RHIC), which was under construction; at that time, the first core groups of the future STAR and PHENIX collaborations were working each on a Conceptual Design Report for the corresponding experiments.

Nobel Laurate physicist Samuel Ting, in turn, had proposed an upgrade of the LEP’s L3 experiment, which he led, to continue running with the LHC. This project, though, was turned down in 1992, thus he invited the HIPC to take the L3 magnet and part of its infrastructure and exploit it to build the new heavy-ion detector. This invitation was accepted and, in March 1993, a Letter of Intent was presented for a dedicated heavy-ion experiment that, since then, would be called ALICE. At the first official ALICE Collaboration Meeting, which took place in November 1993, Emanuele Quercigh was elected Chair of the Collaboration Board.

Evolution of the ALICE detector throughout the years, starting from its conception (design included in the Letter of Intent, 1993). Upgrade activities to prepare the experiment for the future high luminosity Run 3 are currently ongoing. [Credits: ALICE, CERN, Virginia Greco]

 

Once he had concluded his fascinating recollection of the first days of heavy-ion physics and of the ALICE experiment, Quercigh left the stage to Jürgen Schukraft, who was the first Spokesperson of the experiment and kept this role for 18 years (1992-2010). In his talk, Schukraft went through the history of the Collaboration and the making of the experiment. As he highlighted, in the early 90’s the heavy-ion physics community had to face a number of challenges to design a new experiment: the huge extrapolation from the SPS to the LHC – in which higher mass ions would run at 300 times higher energies –, limited experience in building large detectors, absence of previous examples of a truly ‘general purpose’ heavy-ion detector, and limitations in human and monetary resources. Nevertheless, between 1990 and 2002 a huge detector R&D programme was carried out to design a detector meeting the requirements of this physics research. In 1995, a Technical Proposal for the ALICE experiment was presented, which was approved in 1997 after the inclusion of an addendum for the muon spectrometer. Further addenda were included later, in 1999 (TRD) and in 2006 (EMCAL).

The phases of construction, installation and commissioning of the detector followed, starting from 2000, and this is when the contribution of Chris Fabjan became crucial. As he recalled in his presentation, which followed Schukraft’s one, his involvement in ALICE originated in the CERN cafeteria where, a few days before Christmas 2000, he met Ludovico Riccati – Chair of the Collaboration Board at that time – who proposed him to become ALICE Technical Coordinator. He accepted and, together with a ‘remarkable team’, he started the incredible adventure of putting together the detector and making it work.

The activities at the experimental site started with the cleaning of the cavern and the recuperation of the L3 magnet. Then, many years of coordinated work and numerous challenges to face followed. In his talk, Fabjan gave an overview through images of the milestones that signed the 7 years of his technical coordination and emphasized the very large variety of techniques employed to build the ALICE detector, often pushed to their limits; also the international collaborative effort put into each activity as well as the high level of dedication of all the people involved in the building and installation operations.

Since the LHC started running, ALICE has been collecting data with pp, Pb-p and Pb-Pb collisions at various energies and many novel results are being produced. But the R&D activities have not stopped. Programmes for future research are always under discussion and at the moment ALICE, as all other LHC experiments, are working on upgrading the detector to be able to exploit the higher luminosity that will be provided in the LHC Run 3, which will start in 2020. These developments and plans for a further future were reviewed by Luciano Musa, project leader of the Inner Tracking System, who gave an overview of the new challenges and strategies that the collaboration has and will have to deal with.

The presentation section was followed by a cocktail, during which historical pictures portraying the detector or the members of the collaboration were projected. All participants were also offered an anniversary box of chocolates, decorated with the ALICE logo. Attended by members of the collaboration and invited guests, the jubilee event was a pleasant occasion for long-time and recently joined collaborators to gather and recall memories and anecdotes of the history of the experiment, as well as to make a toast to a fruitful continuation of activities.

Present and past spokespersons of the ALICE collaboration toasting during the ALICE 25thanniversary celebration. From left to right: Paolo Giubellino (2010 – 2016), Jürgen Schukraft (1992-2010), Federico Antinori (current, since 2017). [Credit: Virginia Greco/ALICE]

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