Lepton Photon 2015 – Into the Dragon’s Lair

This was my first time in Ljubljana, the capital city of Slovenia – a nation rich with forests and lakes, and the only country that connects the Alps, the Mediterranean and the Pannonian Plain. The slight rain was not an ideal welcome, but knowing that such an important conference that was to be held there – together with a beautiful evening stroll – relaxed my mind.

The guardian.

The guardian.

At first, I thought I was somewhere in Switzerland. The beauty of the city and kindness of the local people just amazed me. Similar impressions overwhelmed me once the conference started – it was extremely well organized, with top-level speakers and delicious food. And though I met several colleagues there that I already knew, I felt as though I knew all the participants – so the atmosphere at the presentations was nothing short of enthusiastic and delightful.

Before the beginning of the conference, the ATLAS detector just started getting the first data from proton collisions at 13 TeV center-of-mass energy, with a proton bunch spacing of 25 ns. The conference’s opening ceremony was followed by two excellent talks: Dr. Mike Lamont presented the LHC performance in Run 2 and Prof. Beate Heinemann discussed the ATLAS results from Run 2.

Furthermore, at the start of the Lepton Photon 2015 conference, the ALICE experiment announced results confirming the fundamental symmetry of nature (CPT), agreeing with the recent BASE experiment results from lower energy scale measurement.

The main building of the University of Ljubljana

The main building of the University of Ljubljana

The public lecture by Prof. Alan Guth on cosmic inflation and multiverse was just as outstanding as expected. He entered the conference room with a student bag on his shoulder and a big, warm smile on his face – the ultimate invitation to both scientists and Ljubljana’s citizens. His presentation did an excellent job at explaining, to both experienced and young scientists, the hard work of getting to know the unexplored. While listening to Prof. Guth’s presentation, it seemed like the hour passed in only a few minutes – so superb his talk was.

I was also impressed by some of the participants. Many showed great interest in the lectures, and asked tough, interesting questions.

To briefly report on the latest results, as well as the potential of future searches for physics beyond the Standard Model, the following achievements were covered during the conference: the recent discovery by the LHCb experiment of a new class of particles known as pentaquark;, the observed flavor anomalies in semi-leptonic B meson decay rates seen by the BaBar, the Belle and the LHCb experiments; the muon g-2 anomaly; recent results on charged lepton flavor violation; hints of violation of lepton universality in RK and R(D(*)); and the first observation and evidence of the very rare decays of Bs and B0 mesons, respectively.

The conference centre.

The conference center.

The second part of the conference featured poster sessions, where younger scientists were able to present their latest working achievements. Six of them were selected and offered the opportunity to give a plenary presentation, where they gave useful and well prepared talks.

The ending conference lecture was given by Prof. Jonathan Ellis, who provided an excellent closing summary and overview of the conference talks and presented results, with an emphasis on future potential discoveries and underlying theories.

To conclude, I have to stress that our very competent and kind colleagues from the Josef Stefan Institute in Ljubljana (as well as other international collaborative institutes) did a great job organizing this tremendous symposium. They’ve set a high standard for the future conferences to come.

pic_tatjana_jovin1 Tatjana Agatonovic Jovin is research assistant at the Institute of Physics in Belgrade, Serbia. She joined ATLAS in 2009, doing her PhD at the University of Belgrade. Her research included searches for new physics that can show up in decays of strange B mesons by measuring CP-violating weak mixing phase and decay rate difference using time-dependent angular analysis. In addition to her fascination with physics she loves hiking, skiing, music and fine arts!

Getting ready the next discovery

I’m just on my way back home after a great week spent in Ljubljana where I joined (and enjoyed!) the XXVII edition of the Lepton-Photon conference.


Ljubljana city center (courtesy of Revital Kopeliansky).

During the Lepton-Photon conference many topics were discussed, including particle physics at colliders, neutrino physics, astroparticle physics as well as cosmology.

In spite of the wide spectrum of scientific activities shown in Lepton-Photon, the latest measurements by the experiments at the Large Hadron Collider (LHC) based on 13 TeV proton-proton collision data were notable highlights of the conference and stimulated lively discussions.

The investigation of the proton-proton interactions in this new, yet unexplored, energy regime is underway using new data samples provided by LHC. One of the first analyses performed by ATLAS is the measurement of proton-proton inelastic cross section; this analysis has a remarkable relevance for the understanding of cosmic-ray interactions in the terrestrial atmosphere, thus offering a natural bridge between experiments in high-energy colliders and astroparticle physics.

Dragon sculpture in the Dragon Bridge in Ljubljana.

Dragon sculpture in the Dragon Bridge in Ljubljana.

While we are already greatly excited about the new results based on the 13 TeV collisions provided by LHC, it is also clear that the best is yet to come! As discussed during the conference, the Higgs boson discovered in 2012 by the ATLAS and CMS collaborations still has many unknown properties; its couplings with quarks and leptons need to be directly measured. Remarkably, by the end of next year, the data provided by LHC will have enough Higgs boson events to perform the measurements of many Higgs-boson couplings with good experimental accuracy.

Precision measurements of the Higgs boson properties offer a way to look for new physics at LHC, complementary to direct searches for new particles in the data. Direct searches for new particles, or new physics, at LHC will play a major role in the coming months and years.

A few “hints” of possible new-physics signals were already observed in the data collected by ATLAS at lower energy in 2011 and 2012. Unfortunately such hints are still far from any confirmation and the analysis of the 13 TeV proton-proton collision data will clarify the current intriguing scenarios.

Although LHC is in its main running phase, with many years of foreseen operation ahead of us, the future of particle physics is already being actively discussed, starting from the future world-wide accelerator facilities.

During Lepton-Photon, many projects were presented including proposals for new infrastructure at CERN, in Japan and in China. All these proposals show a strong potential for major scientific discoveries and will be further investigated, posing the basis for particle physics for the next fifty years to come.

Social dinner during the Lepton-Photon conference.

Social dinner during the Lepton-Photon conference.

Without a doubt one of the most inspiring moments of this conference was the public lecture about cosmological inflation given by Alan Guth. It attracted more than one thousand people from Ljubljana and stimulated an interesting debate. In his lecture, Alan Guth stressed the relevant steps forward taken by the scientific community in the understanding of the formation and the evolution of the Universe.

At the same time, Alan Guth remarked on our lack of knowledge of many basic aspects of our Universe, including the dark matter and dark energy puzzles. Dark energy is typically associated to very high energy scales, about one quadrillion times higher than the energy of protons accelerated by LHC; therefore, it is expected that dark energy can’t be studied with accelerated particle beams. On the other hand, dark matter particles are associated with much lower energy scales, and thus they are within the reach of many experiments, including ATLAS and CMS!

miapittura_new Nicola joined the ATLAS experiment in 2009 as a Master’s student at INFN Lecce and Università del Salento in Italy, where he also contributed to the ATLAS physics program as PhD student. He is currently a postdoctoral researcher at Aristotle University of Thessaloniki. His main research activity concerns the ATLAS Standard Model physics, including hard strong-interactions and electroweak measurements. Beyond particle physics, he loves traveling, hiking, kayaking, martial arts, contemporary art, and rock-music festivals.

BOOST Outreach and Particle Fever

Conferences like BOOST, which my colleagues Cristoph and Tatjana have written about already, are designed to bring physicists to think about the latest results in the field. When you put 100 experts from around the world together into a room for a week, you get a fantastic picture of the state of the art in searches for new physics and measurements of the Standard Model. But it turns out there’s another great use for conferences: they’re an opportunity to talk to the general public about the work we do. The BOOST committee organized a discussion and screening of the movie “Particle Fever” on Monday, and I think it was an enormously successful event!


For those who haven’t seen it, Particle Fever is excellent. It is the story of the discovery of the Higgs Boson, and its consequences on the myriad of theories that we are searching for at the LHC. It presents the whole experience of construction, commissioning, turning on, and operating the experiments, from the perspective of experimentalists and theorists, young and old. People love it – it has a 95% rating on Rotten Tomatoes – and nearly all my colleagues loved it as well. It’s rare to find a documentary that both experts and the public enjoy, so this is indeed a real achievement!

Getting back to BOOST, not only did we have a screening of the movie, but also a panel discussion where people could ask questions about the movie and about physics in general. One question that an audience member asked was really quite excellent. He asked why physicists think that movies like Particle Fever, and events like this public showing, were important. Why did we go to the trouble of booking a room, organizing people, and spending hours of our day on a movie we’ve already seen many times before? And let’s not forget that David Kaplan, a physicist and a producer of the movie, spent several years of his life on this project full time. He essentially gave up research for a few years in order to make a movie about doing research – not an easy task for a professor!

So why do we do it? Why is Particle Fever important?

The answer, to me, is that we have a responsibility to share what we know about the Universe. We study the fundamental nature of the Universe not so that we as individuals can understand more, but so that humanity as a whole understands more. On an experiment as big as ATLAS, you quickly become extremely aware of how much you depend on the work and experience of others, and on the decades and centuries of scientists who came before us. Doing science means contributing to this shared knowledge. And while some details may only be important to a few individuals (not many people are going to care about the derivation of the jet energy scale via numerical inversion), the big picture is something that everyone can appreciate.

And Particle Fever helps with that. The movie is funny, smart, and understandable – all things that we strive to be as science communicators, but which we sometimes fail at. Every particle physicist owes David Kaplan and the director Mark Levinson a tremendous debt, because they have done such a tremendous job of communicating the excitement of fundamental knowledge and discovery. CERN has always sought to unite Europe, and the world, through a quest for understanding, and Particle Fever helps the rest of the world join us on that quest.

Conferences like BOOST are a great time to focus on the details of our work, but they’re also an opportunity to consider how our physics relates to the rest of the world, and how best we can communicate our understanding. Particle Fever has made me realize just how much work it takes to do a really wonderful job, and I’m extremely happy that such a great guide is available to the public. With any luck, we’ll have more movies coming out soon about the discovery of supersymmetry and extra dimensions!

“Max Max is a postdoctoral fellow at the Enrico Fermi Institute at the University of Chicago, and has worked on ATLAS since 2009. His work focuses on searches for supersymmetry, an exciting potential extension of the Standard Model which predicts many new particles the Large Hadron Collider might be able to produce. When not colliding particles, he can be found cycling, hiking, going to concerts, or playing board games.

A boost for the next discovery

I arrived in Chicago for my first conference after the first long LHC shutdown, where new results from the two big experiments ATLAS and CMS were to be shown. Before the beginning of the conference on Monday, I had one day to fight against jetlag and see the city – certainly not enough time to see everything!


Chicago at night.

The focus of the BOOST conference is to discuss the physics of objects produced at very high momenta. New, very heavy particles can be produced at LHC. Such particles decay very quickly and we only observe their daughter particles, or their granddaughter particles in the detector. These decay products are special – they get the boost from the mother particle and have very high momenta.

The reconstruction of such highly boosted particles is a big challenge. Around 100 experts from different institutes around the world meet for one week to discuss the discovery techniques and strategies for these new heavy particles at LHC. Compared to some other much larger conferences, it is a very familiar atmosphere!


Boost 2015 in Chicago: Many fruitful discussions among theorists and experimentalists from ATLAS and CMS.

We had many interesting discussions during the presentations and coffee breaks. For me, it was a great opportunity to meet colleagues from around the world that I’d known for a while but had never met in person. Theorists and experimentalists from ATLAS and CMS exchanged new ideas on the reconstruction and identification of high momenta particles, and discussed not only the discovery potential of both experiments for the next run period but also the prospective designs of new very high energy machines that could be built in 20-30 years.

The University of Chicago organised a public event during the conference: a screening of the Particle Fever movie and a discussion panel. For me, it was like going back in time before the Higgs boson discovery – feeling once again the excitement about the first beam at LHC. It was a great time and I am sure we will have more great moments aheard. It’s time to boost for a new discovery!

F00062 Tatjana Lenz is research assistent at the University of Bonn, Germany. She joined ATLAS in 2005, doing her Master’s at the University of Wuppertal. Her research includes searches for new physics which can show up in decays of top quark pairs and studies of Higgs boson properties like spin and parity. Currently she focuses on the measurement of the Higgs boson couplings to bottom quarks and new physics searches involving this topology. In addition to her fascination for physics she loves diving, climbing, hiking, skiiing and working in her garden!

Boost and never look back

Seen in Chicago the day before the start of the BOOST conference.

Seen in Chicago the day before the start of the BOOST conference. (Photo: Christoph Anders)

When I arrived in Chicago this last Sunday for the BOOST conference I had a pretty good idea what new results we were going to show from ATLAS. I also had some rough ideas of what our friends from the other experiments and theory groups would be up to. What I didn’t expect was to see an ad that would fit the conference so nicely!

Now, why do we care about “boost” and what is it?

Let’s say we want to find a pair of top quarks in our detector. You need enough energy in the collision to produce the top quark pair, and if it is just enough they will be “at rest”, i.e. just sit there. Now let’s picture the decay of the two top quarks as two water balloons exploding. The splashes you see are what we would see in the ATLAS detector. But imagine you want to understand which splashes came from which of the two water balloons… This is hard, as there are many different combinations, the water mixes, etc.

That is where “boost” will help!

If we have more energy, we can give both top quarks/balloons a kick – we call them “boosted”. They will fly away from each other and when they decay/explode, the splashes will go into two different directions! Now we can tell them apart! Of course it is more complicated in real life. We have other processes that look similar to the “splashes” the two boosted top quarks make, but we can distinguish them by analyzing the inner structure of the splashes.

This is what the BOOST conference is about, in essence: understanding how we can use the boost to our advantage when searching for new phenomena.

It actually does work and it is a lot of fun!
Boost and never look back!

Christoph Anders Christoph is a postdoc at the University of Heidelberg’s physics institute in Germany. He has been working in ATLAS since 2007. His research is currently focussed on the identification of very energetic heavy particles, e.g. top quarks. When he is not looking for physics beyond the Standard model, he likes reading, listening to music, photography, cooking, traveling with his wife, playing board games with friends and sports.

A summer evening in the ATLAS control room

The sun has already set over Geneva when I finally walk out from the ATLAS control room. We have been waiting for beams to be injected into the machine since the early hours of the afternoon, but without much success so far. First a issue with high voltage in one of the accelerator sectors, then some problems in controlling the cooling temperature, and finally a UFO dumping the beams (not what you are thinking of – rather a microscopic dust particle in the beam pipe, creating instabilities in the beam orbits). Just a regular day for the most ambitious particle accelerator mankind has ever built, but a pretty boring afternoon for our entire shift crew.

Don't feed physicists peanuts!

Don’t feed physicists peanuts!

With the 50 ns data-taking now half-way over, the ATLAS control room is no longer crowded as it was back in early June, when rivers of champagne were flowing out to celebrate the first Run 2 milestones and Discovery Channel cameras were filming physicists in their natural habitat. Now that more routine data-taking has been established, only the six shifters are there permanently, plus a few experts to assist them… and the Run Manager, which is me this week.

The Run Manager acts as a layer between the Run Coordinators and the rest of the team, making sure the plan of the day is respected and steering ATLAS operations towards a happy ending. But what if there are no operations to be steered? The excitement for us starts with the first hint of proton collisions – before that, we need to get ready and then wait patiently.

Luckily the messages from the LHC team keep us awake: they regularly announce beams “very soon”… and we always believe it. Under the vigilant eye of the Shift Leader, the trigger shifter keeps on checking constant particle rates, the shifters from the sub-detectors (the inner detector, the calorimeters and the muon systems) stare at green flags, the shifter at the Run Control desk enjoys the flux of harmless warning messages, and the Data Quality shifter gets ready to monitor the goodness of the data we might be collecting tonight.

Two more hours, and they will all be released, while the next shift crew comes in. Only the Run Manager – now sitting at the CERN restaurant nervously checking her phone – had better stay, to make sure all parameters are set correctly before a long fruitful run starts. In such a complex detector as ATLAS, every configuration has to be checked by multiple pairs of eyes; we can’t afford the luxury of making mistakes.

Long hours spent staring at the screen of LHC Page 1.

Long hours spent staring at the LHC Page 1 screen.

I am always surprised by how little competition reigns here in the control room. We are all part of this huge wonderful mechanism, that wouldn’t work without the tiniest piece – and we feel it. We are always happy to help new people getting started (so that they may eventually cover some night shifts, a privilege often reserved for students…) and ensure that they are never ashamed to ask trivial questions. I would say it’s like being part of a funny, weird family… if only it would not certainly condemn me to the eternal mockery of my colleagues! Friendships have been built over coffee, eating the Sunday croissants together (a small reward for being here over the weekend), and during the daily rushes to get our slides ready for the next presentations. Long days and long nights that we hope will bring new exciting discoveries.

The sunset has now made room for a warm summer night, but still no beams are circulating in the machine. I will need to call the CERN Control Center to ask what their plans are. It’s late but I don’t feel that tired. With a sigh and a smile I walk back to the control room, while the sky over the Alps turns into pink and then lilac and then blue.

Manuela Venturi Manuela Venturi is a research assistant at the University of Victoria (British Columbia). She is originally from Florence (Italy). She joined ATLAS in 2009, while doing her Master’s at the University of Roma Tor Vergata, and has been happy of that choice ever since. Together with the rest of the team, she searched for and discovered the Higgs boson. She likes to walk, run, dance, cook, write, read and the colour pink.

From ATLAS Around the World: Brief history of Morocco in ATLAS

In 1996, Morocco officially became a member of the ATLAS collaboration. The eagerly awaited day had finally arrived, and the first Arabic and African country signed a collaborative agreement with CERN to participate in the great scientific adventure of particle physics. This achievement was possible thanks to the efforts of a small group of physicists that recognised the potential benefits of collaborating with large accelerator centres.

Motivated to improve science, technology and innovation, the Moroccan High Energy Physics Cluster (RUPHE) founded in 1996 to enhance the scientific training of young people and advances in pure scientific knowledge. RUPHE includes ATLAS collaborators from University of Hassan II Casablanca, Mohammed V University (Rabat), Mohamed I University (Oujda), Cadi Ayyad University (Marrakech) and the National Energy Centre of Science and Nuclear Techniques (CNESTEN) in Rabat.

 John Ellis, Fairouz Malek and Farida Fassi enjoying afternoon tea during their visit to Fez after successfully training PhD students during the School of High-Energy Physics in Morocco.

John Ellis, Fairouz Malek and Farida Fassi enjoying afternoon tea during their visit to Fez after successfully training PhD students during the School of High-Energy Physics in Morocco.

Morocco’s participation in ATLAS started even before its membership was approved in 1996. In 1992, Moroccan researchers contributed to the construction of a neutron irradiation station. After that, they continued boosting their contribution by playing a key role in the construction, testing and commissioning of the ATLAS Electromagnetic Calorimeter (ECAL) presampler during 1998-2003 period. Since then, Moroccan researchers have been working to strengthen the long-standing cooperation with CERN. Currently, there are 27 faculty members and research assistants, including 9 active PhD students.

The research interests focus on these topics: the search for new physics phenomena in association with top physics, Higgs physics and B physics, including a significant participation on the detector performance studies. During the LHC’s Run 1, Moroccan researchers contributed to the success of the ATLAS experiment. This success has motivated our researchers to look forward to a very successful Run 2.

John Ellis visiting Fez during the Advanced School of Physics in the Maghreb in 2011 in Taza.

John Ellis visiting Fez during the Advanced School of Physics in the Maghreb in 2011 in Taza.

In addition, we are involved in the distributed computing effort. During ATLAS data taking periods, user support becomes a challenging task. With many scientists analysing data, user support is becoming crucial to ensure that everyone is able to analyse the collision data distributed among hundreds of computing sites worldwide. The Distributed Analysis Support Team (DAST) is a team of expert shifters who provide the first direct support for all help requests on distributed data analysis. Alden Stradling (University of Texas, Arlington) and I (Mohammed V University) coordinate the overall activity of this team.

In terms of building local expertise, several schools and workshops have been organized. Outstanding worldwide experts have participated, giving lectures on particle physics, nuclear physics, applied physics and grid computing. Most participants are master’s degree or PhD students already working in these fields, or in related fields and seeking a global dimension to their training. Such schools include: “L’Ecole de Physique Avancée au Maghreb 2011” in Taza, “tutorial training on statistics tools for data analysis” and the “Master of High-Energy Physics and Scientific Computing” in Casablanca. High school students from Oujda participated in the International Masterclasses in March 2015, which aimed to encourage them in doing science, and gave them an introduction to what we do in ATLAS and why it is interesting and exciting.

ATLAS Overview Week in Marrakech in 2013.

ATLAS Overview Week in Marrakech in 2013.

After the success of the ATLAS Liquid Argon Week organized in Marrakech in 2009, the ATLAS Overview Week for 2013 was hosted in Morocco. It was our great pleasure to invite our ATLAS colleagues to this important event in Marrakech. There were many interesting talks and discussions at the event. We took a brief time out to watch the announcement of the 2013 Nobel Prize in Physics. To our delight, it was awarded to François Englert and Peter Higgs for their pioneering work on the electroweak-symmetry-breaking mechanism in 1964. It was a very exciting moment for me.

The ATLAS Collaboration reacts to the 2013 Nobel Prize in Physics announcement during ATLAS Week in Marrakech.

The ATLAS Collaboration reacts to the 2013 Nobel Prize in Physics announcement during ATLAS Week in Marrakech.

Farida Fassi Farida Fassi is a research assistant professor at Mohammed V University in Rabat. She started working in ATLAS in 1996 doing her PhD at IFIC in Valencia, Spain. She worked in the online and offline test beam data analysis of the first prototypes of the Hadronic Tile Calorimeter modules. This was in addition to top physics analysis. In 2003, she began working in Grid Computing and Distributed Data Analysis. She had a CNRS post-doctoral research fellowship working on the CMS experiment while based in Lyon, France. She was the coordinator and contact person of the French CMS Tier-1, and continued her search for new physics phenomena. In 2011, she came back to ATLAS focusing on the search for the ttbar resonances. Farida is the co-coordinator of the Distributed Analysis Support Team.

From ATLAS Around the World: Triggers (and dark) matter

To the best of our knowledge, it took the Universe about 13.798 billion years (plus or minus 37 million) to allow funny looking condensates of mostly oxygen, carbon and hydrogen to ponder on their own existence, the fate of the cosmos and all the rest. Some particularly curious specimens became scientists, founded CERN, dug several rings into the ground near Geneva, Switzerland, built the Large Hadron Collider in the biggest ring, and also installed a handful of large detectors along the way. All of that just in order to understand a bit better why we are here in the first place. Well, here we are!

CERN was founded after World War II as a research facility dedicated to peaceful science (in contrast to military research). Germany is one of CERN’s founding members and it is great to be a part of it. Thousands of scientists are associated with CERN from over 100 countries, including some nations that do not have the most relaxed diplomatic relationships with each other. Yet this doesn’t matter at CERN, as we are working hand-in-hand for the greater good of science and technology.

Monitoring and analysing events provided by the first beam of the LHC since the first run. (Picture by R. Stamen)

Monitoring and analysing events provided by the LHC. (Picture by R. Stamen)

In the ATLAS collaboration, Germany has institutes from 14 different cities contributing to one of the largest and most complex detectors ever built. My institute, the Kirchhoff-Institut für Physik (KIP) in Heidelberg, was (and is) involved in the development and operation of the trigger mechanism that selects the interesting interactions from the not so interesting ones. Furthermore, we are doing analyses on the data to confirm the Standard Model of Particle Physics or – better yet – to find hints of excess events that point to dark matter particles (although we are still waiting for that…).

But let’s start with the trigger. The interaction rate (that is the rate at which bunches of LHC protons collide within the ATLAS detector) is way too high to save every single event. That is why a selection process is needed to decide which events to save and which to let go. This trigger mechanism is split up into several stages; the first of which handles such high rates that it needs to be implemented using custom hardware, as commercial PCs are not fast enough.

This first stage (also called the level-1 trigger) is what we work on here at KIP. For instance, together with a fellow student, I took care of one of the first timing checks after the long shutdown. This was important, because we wanted to know if the extensive maintenance that started after the Run 1 (wherein we had personally installed new hardware) had somehow changed the timing behaviour of the level-1 trigger. Having a timed system is crucial, since if you are off by even a few nanoseconds, your trigger starts misbehaving and you might miss Higgs bosons or other interesting events.

In order to determine the timing of our system we used “splash” events. Instead of collisions at the centre of the detector, a “splash” is an energetic spray of a huge number of particles that comes from only one direction (more information on splashes here). They are great for timing the system, because they light up the entire detector like a Christmas tree. Also, they came from the first LHC beam since Run 1 – so it was the first opportunity to see the detector at work. This work was intense and cool. The beam splashes were scheduled over Easter, but we did not care. We gladly spent our holiday together in the ATLAS control room with other highly motivated people who sacrificed their long weekend for science. To see the first beams live in the control room after a long shutdown was a special experience. Extremely enthusiastic!

Murrough Landon (r.) and Manuel (l.) discussing results from the beam splashes. (Picture by R. Stamen)

Murrough Landon (right) and Manuel (left) discussing results from the beam splashes. (Picture by R. Stamen)

But of course, timing is not the only thing that has to be done. We also write the firmware for our hardware, code software (for instance, to monitor our system in real time), plan future upgrades (in both hardware and software) and do even more calibration. Each of these items is important for the operation of the detector and also very exciting to work on. I find it cool to know that the stuff I worked on helps keep ATLAS running.

Once we have the data – what do we do with it? Each student at KIP can choose which topic he or she wants to work on, yet the majority of us study processes that are related to electroweak interactions. This part of the Standard Model has become even more interesting after the discovery of the Higgs boson and has potential for the discovery of new physics. For example, dark matter. Many models predict dark matter interacts electroweakly, which is what I am working on. We can search for this in the data by looking for events from which we know that particles escaped the detector without interacting with it (leaving “missing transverse energy“; neutrinos do this too) and than comparing the results to models of electroweak coupling to dark matter. The discovery of dark matter would be awesome. The cosmological evidence for dark matter is convincing (for instance galactic rotation curves or the agreement between observations from the Planck satellite and models such as ΛCDM). It is just a matter of finding it…

Going back to the beginning – literally. I am extremely curious to see what we – those funny-looking condensates of mostly oxygen, carbon and hydrogen – will find out about the Universe, its beginning, end, in-between, composition, geometry, behaviour and countless other aspects. And CERN, and especially the ATLAS collaboration, is a great environment in which to do so.

doc01069020150318091345_001 Manuel is a PhD student at the Kirchhoff-Institut für Physik at the University of Heidelberg, Germany. He joined ATLAS in 2014 and has since been working on both the level-1 calorimeter trigger and an analysis searching for dark matter. He did his Bachelor’s and Master’s degrees in Physics in Bielefeld, Germany, in the fields of molecular magnetism theory and material science. For his PhD he decided to switch fields and become an experimental particle physicist.

From ATLAS Around the World: Working with Silicon in Japan

I joined the ATLAS experiment in 2012 after graduating from the University of Tokyo, however my previous experience was completely different from collider physics. During my Master’s course, I focused on the behaviour of a kind of silicon detector operated in Geiger mode. In my Doctoral course, I designed and developed a gaseous detector called a Time Projection Chamber used for neutron lifetime measurements. These studies were done with very few colleagues in Japan. At that time, the experiments at CERN looked like a “castle” to me.


Workers assembling the ATLAS SemiConductor Tracker (SCT) at CERN.

Right after I came to ATLAS, I was surprised that more than 3000 people had operated the well-established ATLAS detector system and analysed the data so quickly. At that time, we were in the last year of Run 1, and I began investigating the performance of the SemiConductor Tracker (SCT), which is one of the inner tracking detectors in ATLAS. Through this study, I realised that there were many new things for me.

For the SCT, 44 institutes from 17 countries have contributed so far. The SCT consists of 4088 modules, which have two planes of silicon with 768 strips, so that we have six million channels. The details have been described by our project leader, Dave Robinson. Since 2014, I have filled the role of SCT Data Quality coordinator, who promptly checks the data to see whether or not the SCT has a problem. For this purpose, strong communication among the people responsible for various activities in the SCT is very important. In addition, a good understanding of the other inner detectors is needed in order to evaluate the performance of the SCT. With the help of many experts, we have prepared for stable data taking during Run 2.

Now I’m considering how to discover new physics. Almost all the analyses done by ATLAS and CMS assumed the decay of new particles at the collision point of the proton beams. Alternatively, I would like to target new particles with flight lengths longer than a millimetre and up to a few metres, which is favoured from the existence of relic dark matter in the Universe (for an example, see our results from Run 1). For this search, the high performance of the SCT will be essential. This is also my motivation for contributing the SCT operation.

I hope we will report something new from ATLAS in the next few years!!

Hidetoshi Otono Hidetoshi Otono is an assistant professor at the Kyushu University in Japan, who joined the ATLAS experiment in 2012. He has contributed to operation of the SemiConductor Tracker (SCT) as a data quality coordinator and searched for long-lived particles by making full use of the SCT.

From ATLAS Around the World: Faster and Faster!

Simon Ammann from Switzerland starts from the hill during the training jump of the second station of the four hills ski jumping tournament in Garmisch-Partenkirchen, southern Germany, on Thursday, Dec. 31, 2009. (AP Photo/  Matthias Schrader)

Simon Ammann from Switzerland starts from the hill during the training jump of the second station of the four hills ski jumping tournament in Garmisch-Partenkirchen, southern Germany, on Thursday, Dec. 31, 2009. (AP Photo/ Matthias Schrader)

Faster and Faster! This is how it gets as soon as LS1 ends and the first collisions of LHC Run 2 approaches. As you might have noticed, at particle physics experiments we LOVE acronyms! LS1 stands for the first Long Shutdown of the Large Hadron Collider.

After the end of Run 1 collisions in March 2013 we had two full years of repairs, consolidations and upgrades of the ATLAS detector. Elevators at P1 (that is Point 1, one of the 8 zones where we can get access to the LHC tunnel located 100 m underground) were once again as crowded as elevator shafts in a coal mine. Although all the activities were well programmed, during the last days the activity was frenetic and we had the impression that the number of things in our t0-do lists was increasing rather than reducing.

Finally, last week I was sitting in the ACR (Atlas Control Room) with experts, shifters, run coordinators, and the ATLAS spokesperson for the first fills of the LHC that produced “low luminosity collisions”. You might think that, for a collider that is designed to reach a record instantaneous luminosity (that is the rate of collisions in a given amount of time), last week’s collisions were just a warm up.

Well, this is not entirely true.

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Racks in USA15 (100m underground) hosting trigger electronics for the selection of minimum bias collisions (rack in foreground with brown cables). In background (with thick black cables), electronics for the calorimetric trigger. (Picture by the author.)

Last week we had the unique opportunity to collect data with very particular beam conditions that we call “low pile-up”. That means that every time the bunches of protons cross one through the other, the protons have a very small probability of actually colliding. What is important is that the probability of having two or more collisions at the same time is negligible, since we are only interested in collisions that are produced once for each bunch crossing. These data are fundamental for performing a variety of physics measurements.

Just to cite a few of them:

  • the measurement of the proton-proton cross section (“how large are the protons?”) at the new center of mass energy of 13 TeV;
  • the study of diffractive processes in proton-proton collisions (YES, protons are waves also!); and
  • the characterization of “minimum bias” collisions (these represent the overwhelming majority of collisions and are just the “opposite” of collisions that produce top quarks, Higgs and eventually exotic or supersymmetric particles) which are key ingredients for tuning our Monte Carlo simulations that will be used for all physics analysis in ATLAS (including Higgs physics and Beyond Standard Model searches).

Over the past few months, I’ve been coordinating a working group with people around the world (Italy, Poland, China, UK, and US) – none of them resident full time at CERN – who are responsible for the on-line selection of these events (we call this the trigger). Although we meet weekly (not trivial due to the different time zones), and we regularly exchange e-mails, I had never met with these people face to face. It was strange to finally see their faces in a meeting room at CERN, although I could recognize their voices.

Clint Eastwood in "Per Qualche Dollaro in piu`" movie (Director: Sergio Leone)

Clint Eastwood in “Per Qualche Dollaro in piu`” movie (Director: Sergio Leone) ( Produzioni Europee Associate and United Artists)

We have worked very hard for the last week of data-taking trying to be prepared for all possible scenarios and problems we might encounter. There were no room for mistakes that could spoil the quality of data.

We cannot press the “replay” button.

It was like “one shot, one kill”.

Luckily everything ran smoothly, and there weren’t too many issues and none of them severe.

This is only one of the activities where my institution, the Istituto Nazionale di Fisica NucleareSezione di Bologna, and the University of Bologna and the other 12 ATLAS Italian groups were involved during the Run 2 start up of LHC.

doc01069020150318091345_001 Antonio Sidoti is a physicist in Bologna (Italy) at the Istituto Nazionale Fisica Nucleare. His research include top quark associated with Higgs production searches, upgrade studies for the new inner tracker and trigger software development using Graphical Processing Units. He is coordinating the ATLAS Minimum Bias and Forward Detector Trigger Signature group and is now deputy coordinator of the physics analysis for the Italian groups in ATLAS. When he is not working he plays piano, runs marathons, skis or sails with a windsurf.