INTERVIEW Peter Jenni (right) in the ATLAS cavern together with, from left to right, Fabiola Gianotti, Markus Nordberg, Marzio Nessi and Steinar Stapnes. ATLAS makes a smooth changeover at the top The ATLAS collaboration is experiencing our dreams and now it exists,” says Jenni. “I could lead the col- laboration for so long because I was supported by very good ATLAS the first major change of spokesperson management teams where the right people, such as Fabiola Gian- since it began. As Fabiola Gianotti takes otti, Steinar Stapnes, Marzio Nessi and Markus Nordberg over the past five years, were in the right places.” over from Peter Jenni, they spoke to As with most particle-physics experiments, the management of one of the two largest detectors at the LHC is a challenge that Antonella Del Rosso about being at changes during the lifetime of the collaboration: it starts with the the helm of one of the world’s largest design phase, continues with the R&D and the construction and ends up with the data-taking and analysis. “Over the years I tried particle-physics collaborations. to balance the emphasis given by the collaboration to the different aspects, that is, the hardware part (initially very strong), the data If you think that it might be time to retire after more than 15 years of preparation, computing and software,” confirms Jenni. leading a constantly growing international collaboration and of con- Originally “only” about 800-strong, the ATLAS collaboration today structing the world’s largest-volume particle detector, then Peter Jenni has almost 3000 members from all over the world. “Keeping the would disagree. Nicknamed the “father of ATLAS” by his colleagues, groups united, inviting new groups to join the collaboration, negoti- Jenni was there in 1992 when the ATLAS collaboration was born out of ating to find the funds necessary for the construction… these have two early proto-collaborations (CERN Courier October 2008 p42). Ini - been among my key tasks during the past 15 years,” he explains. tially co-spokesperson, he was spokesperson from 1995 until March “My efforts also went into keeping groups whose technologies were 2009, when he handed over to Fabiola Gianotti. Now he looks forward not retained in the collaboration. Most of the time we managed to to getting back to the main purpose of ATLAS: the physics. have everyone accept the best arguments, but unfortunately there “I am very proud to have helped the collaboration to construct were a few exceptions.” ATLAS. Twenty years ago we could only imagine the experiment in With such a vast amount of experience, what does Jenni regard s CERN Courier May 2009 31 CCMay09INTERVIEW.indd 31 9/4/09 13:20:21 INTERVIEW as the key element for managing a successful collaboration? “Talk- environment, share the excitement for the wonderful physics ing with as many people as possible is a key factor,” he says. “ATL AS opportunities and are given visibility and recognition,” she explains. members, even the youngest ones, knew that I was available to While the sharing of data relies mostly on the performance of the discuss all problems or issues at any time. With the exception Grid and the software and computing infrastructure put in place by of the Christmas period, I have tried to reply to all e-mails within the collaboration, it cannot occur without the other side of the coin 24 hours. By the way, that is why my son thinks physics is crazy – effective and open communication in real-time with all members and decided to study microtechnologies instead!” of the collaboration. “The solution we have envisaged is a web space While Jenni’s functions have changed, his engagement with ATLAS where ATLAS people will be able to find updated ‘on-line’ news about definitely has not. “A significant part of my work remains the same, the machine, the experiment, the physics results, anything that is particularly in the relationships of ATLAS with the outside world. My relevant to ATLAS’ life,” explains Gianotti. main duty is to help obtain a smooth transition, which is facilitated by Asked about the potential “competition” among many people the fact that Fabiola was one of my two deputies – and I have enjoyed working on the same analysis, she says: “I think it is healthy that peo- working with her before.” Indeed, having more freedom now, he can ple from different groups work on the same topic with a collaborative think of doing more than just sharing some management duties. “In and constructive spirit. This will allow us to produce solid, verified and the medium term I have the ambition to study physics with ATLAS,” fully understood results.” Regarding the relationship with CMS, the he says. “I am already ‘selling’ LHC physics in many public talks but I other general-purpose LHC experiment, she says, “ There is a healthy would like to contribute some real physics myself.” competition, but also collaboration. For instance, ATLAS and CMS The ATLAS collaboration is clearly appreciative of its father’s dedi- have set up a common group that works on statistics tools and how cation over the years. At the party organized in Jenni’s honour on to combine the information coming from both experiments.” 19 February, the Collaboration Board (CB) chairs directed by Katie The excitement about the restart of the LHC is growing again at McAlpine – the author and singer of the LHC rap (CERN Courier CERN and around the world, and the experiments all have their own December 2008 p25) – sang: “We’ve been CB chairs/and we’re plans and strategies. “Before undertaking the path towards discov- here to affirm /Peter’s time was more an era/ than just a few terms/ eries, we will need to understand the performance of our detector leading ATLAS to completion/ like no one else can/ Of course he did in all details and ‘rediscover’ the Standard Model,” says Gianotti. it/ Jenni is the man.” “I believe that we will be ready to start investigating new territories when we have observed top-quark production. Indeed, final states The changeover arising from the production of top quark–antiquark pairs contain Now with the construction complete, it’s Gianotti’s turn to fill the most of the interesting physics objects, from leptons to missing spokesperson’s many shoes, after Jenni passed her the leadership energy and light- and heavy-flavour jets. In addition, this process baton in March. At the very beginning she joined LHC R&D activities is the main background to many searches for new physics. Being and then the proto-ATLAS collaboration in 1990. “Heading such able to reconstruct these events successfully, and perform our first an ambitious scientific project, and a large and geographically dis- measurements of the top production cross-section and mass, will tributed collaboration, is certainly a big honour, responsibility and give us a clear indication that we are ready for discoveries.” challenge,” she says. “However, I have inherited a very healthy situ- When does Gianotti expect ATLAS to release the first results? “It ation from Peter: the experiment has already shown that it performs all depends on the performance of the machine – and its luminos- well, the collaboration is united and strong, and we can continue to ity and energy profile. If everything goes well we expect to have prepare for the first collisions without any major worry.” first results, mainly addressing the detector performance, for the Indeed, activity on ATLAS hasn’t stopped since the LHC incident on winter physics conferences early in 2010; then we hope to present 19 September 2008 (CERN Courier November 2008 p5). “The first the first interesting physics results at the summer conferences of single beams that circulated in the machine before the incident were the same year.” very useful for studying several aspects of the experiment, such as the timing of the trigger system. After the LHC stopped, we decided to Résumé focus on some repairs to the detector and on the optimization of the Transition en douceur à la tête d’ATLAS software and computing infrastructure, of the data distribution chain, and of the event simulation and reconstruction,” confirms Gianotti. Pour la première fois depuis sa naissance par fusion de deux An effective distribution of data to the worldwide community is proto-collaborations, en 1992, ATLAS a changé de porte-parole. a key point for the new ATLAS spokesperson because she thinks Peter Jenni a assumé cette fonction jusqu’en mars 2009 that this is the prime requisite for a motivated and successful et Fabiola Gianotti a maintenant pris sa succession. La collaboration. “The crucial challenge for me is to make sure that collaboration est passée de 800 à près de 3000 membres. Si each single member of ATLAS can participate effectively and suc- Peter Jenni a suivi la conception et la construction du détecteur cessfully in the adventure that this experiment represents. ATLAS ATLAS jusqu’au démarrage du LHC, Fabiola Gianotti conduira has a very exciting future ahead, with many possible discover- la collaboration à ses premières acquisitions de données et ies that will change the landscape of high-energy physics. I con- analyses de physique. Ils s’entretiennent ici avec Antonella Del sider it very important that each individual in this experiment can Rosso de leur rôle à la tête de la plus grande collaboration de actively participate in the data analysis, regardless of whether he physique des particules du monde. or she can physically be at CERN or not. In particular, we have to make sure the younger generations are nurtured in a stimulating Antonella del Rosso, CERN.