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.

2015-06-11 17.16.49

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.

From ATLAS Around the World: The oldest observer state of CERN is no longer just observing!

If you have ever been to a bazaar in Turkey, you would know that (1) you have to bargain hard; (2) you have to carefully examine what you buy. But sometimes this attitude goes way too far. In our case about half a century…

Turkey had been an observer state of CERN since 1961 but as of 6 May 2015; we are associate members! And it seems that we like being the betatester of whatever status is available around. In ’61 this was observer status, and now it is associate membership[1].

Jokes aside, of course we have not just been watching from a distance in all that many years. Turkish teams have been involved in a number of past experiments, such as CHORUS, SMC, CHARM-II in the 80s and 90s and even going back to NA31/2, PS160 and WA17, the days when collaborations did not try to find fancy backronyms such as our beloved ATLAS! Nowadays Turkish teams are involved in AMS, CAST, CLIC, ISOLDE and OPERA in addition to the four major LHC experiments. Around 150 Turkish nationals are users of CERN, three-fourth of which are from Turkish institutes.

So if you are in ATLAS you should know quite a few of us, after all we have been collaborating since 1994, when late Professor Engin Arık[2] joined ATLAS with her team from Boğaziçi University of İstanbul.


Turkish teams meet at the national ATLAS workshop at Bogazici University on 23 June 2014. IMAGE: Serkant Çetin

Currently we are about 30 people from six different institutes clustered into two teams: Boğaziçi and Ankara, one in Europe one in Asia. We wonder if Engin could have imagined that we would one day be writing this blog article while sitting right under the bridge that connects Europe and Asia.


<Serkant|Bosphorus|Erkcan> IMAGE: selfie by Erkcan Özcan


Confident that our associate membership will add another bridge — a scientific and cultural one —  between Europe and Asia, we now proceed to have our drinks on the shore of Bosphorus in this beautiful summer night to celebrate. You are all welcome to join.



[1] Turkey becomes associate member of CERN:

[2] Turkish air crash is a great loss for physics:;

sev-cern2-12-2014a Serkant Çetin is the chair of the Physics Department at Doğuş University of İstanbul. He is a member of the ATLAS Collaboration since 1997 and is currently acting as the national contact physicist whilst running the national funding project for ATLAS. Serkant is also participating in the CAST experiment at CERN, BESIII experiment at IHEP and is a member of the Turkish Accelerator Center project.
erkcan-2 Erkcan Özcan is the current leader of the ATLAS Boğaziçi team. He is happy that a whole lot of the group’s administrative workload is being born by the deputy team leader (Serkant), and most of the analysis code is being written by the capable graduate students in the team. When he finds time to do actual physics himself, he is happier and can be considered a likeable chap.

From ATLAS Around the World: First Blog From Hong Kong

Part of the Hong Kong team in a group meeting at CERN.

Part of the Hong Kong team in a group meeting at CERN. Photo courtesy Prof. Luis Flores Castillo.

Guess who ATLAS’s youngest member is? It’s Hong Kong! We will be celebrating our first birthday in June, 2015. The Hong Kong ATLAS team comprises members from The Chinese University of Hong Kong (CUHK), The University of Hong Kong (HKU) and The Hong Kong University of Science and Technology (HKUST), operating under the umbrella of the Joint Consortium for Fundamental Physics formed in 2013 by physicists in the three universities. We have grown quite a bit since 2014. There are now four faculty members, two postdocs, two research assistants, and six graduate students in our team. In addition, five undergraduates from Hong Kong will spend a summer in Geneva at the CERN Summer Program. You can’t miss us if you are at CERN this summer (smile and say hi to us please)!

The humble telescope I used at high school pointed me both to the past and to the future.

The humble telescope I used at high school pointed me both to the past and to the future. Photo courtesy Tat Hung Wan.

While half of our team is stationed at CERN, taking shifts and working on Higgs property analysis, SUSY searches, and muon track reconstruction software, the other half is working in Hong Kong on functionality, thermal, and radiation tests on some components of the muon system readout electronics, in collaboration with the University of Michigan group. We have recently secured funds to set up a Tier-2 computing center for ATLAS in Hong Kong, and we may work on ATLAS software upgrade tasks as well.

I have also been actively participating in education and outreach activities in Hong Kong. In October last year, I have invited two representatives from Hong Kong Science Museum to visit CERN, so that they can obtain first-hand information on its operation and the lives and work of students and scientists. This will help them to plan an exhibition there on CERN and LHC in 2016. The timing is just right to bring the excitement with the restart of the LHC to Hong Kong. I have been giving talks on particle physics and cosmology for students and the general public. The latest one was just two weeks ago, for the 60th anniversary of Queen Elizabeth School, where I was a student myself many years ago. So many memories came back to me! I was an active member of the astronomy club and a frequent user of the very modest telescope we had. I knew back then the telescope is a time machine that brings images of the past to our eyes. How fortunate I am now, to be a user of the LHC and ATLAS, the ultimate time machine, and a member of the ATLAS community studying the most fundamental questions about the universe. Even though the young students in the audience might find it difficult to understand everything we do, they can certainly feel our excitement in our quest for the scientific truth.

Secondary school students in Hong Kong after a popular science talk on particle physics at the Chinese University of Hong Kong.

Secondary school students in Hong Kong after a popular science talk on particle physics at the Chinese University of Hong Kong. Photo courtesy Florence Cheung.



F00062 Ming-chung Chu is a professor at the Department of Physics, The Chinese University of Hong Kong. He did his undergraduate and graduate studies both at Caltech. After some years of postdoc at MIT and Caltech, he went back to Hong Kong in 1995, where he was born and grew up. h proud to have helped bring particle physics to Hong Kong.


From ATLAS Around the World: African Horizons

Greetings from, well CERN actually, I’m writing this while on a short trip here in order to attend two ATLAS meetings. One of these is focused on the physics and performance of our ATLAS detector after the two-year shutdown and the other focused on plans and improvements needed for the next shutdown in 2018[1]. It’s great being back at CERN and being able to immerse myself in the tangible atmosphere of excited anticipation for the first collisions at 13 TeV this June.

I am a South African, usually based in Durban — a city currently afflicted with xenophobically motivated riots and rolling blackouts. Being at CERN is really a different world right now, to a greater extent than usual.

South Africa has been officially represented on ATLAS since 2010 (co-incidentally the year that I joined the experiment as a post-doctoral fellow for the University of Witwatersrand group), and is now a cluster of three institutes: University of Witwatersrand (Wits), University of Johannesburg (UJ) (both in Johannesburg), and University of Cape Town (UCT) (in Cape Town, of course).

Inauguration of the High-throughput Electronics Laboratory at Wits

Inauguration of the High-throughput Electronics Laboratory at Wits. IMAGE: Erna Van Wyk. Wits press office.

During the shutdown the ATLAS community in South Africa has continued to grow, and been particularly busy with both analysis and detector development activities. To give you an idea, a small subset of our activities includes: Wits inaugurating their high-throughput laboratory  which is developing electronic components that can quickly process large volumes of data, and is currently focused on upgrades to the hadronic calorimeter readout electronics (particularly the ADC daughter board for the TileCal test stand which was designed and manufactured by South Africa); UJ developing local resources in order to perform radiation damage tests using our neutron facilities (we have reactor neutrons, and a neutron beam); and UCT investigating the use of ARM (mobile device) processors as a low cost alternative on which we can execute our software.

The 26th  Chris Engelbrecht Summer School at UCT

The 26th Chris Engelbrecht Summer School at UCT. IMAGE: Gregor Leigh, ATLAS Experiment © 2015 CERN

The Centre for High Performance Computing has made strides towards becoming a Tier-2 ATLAS (and ALICE) Grid site which is important since we’re one of the more remote locations collaborating on the LHC. In terms of building local expertise we have had many schools and workshops. The highlight of these was the 3rd installment of the Kruger International Workshop on Discovery Physics at the LHC, where our students were able to highlight their work and interact with leaders in the field chosen to represent their collaborations or, in the case of theorists, themselves. We’ve run both high level (The Chris Engelbrecht School), and introductory (International Workshop on Hot and Dense Nuclear and Astrophysical Matter ) schools for students, as well as a student focused conference (HEPP).

The International Workshop on Hot and Dense Nuclear and Astrophysical Matter at North-West University (Mahikeng). IMAGE: Simon Connell, ATLAS Experiment © 2015 CERN

Some of us have been part of the effort to wrap up analyses from the 7 TeV and 8 TeV data including: Higgs boson production rates where the Higgs decays to two photons[2][3] and Observation of the Higgs boson coupling to tau final states[4].

In addition to continuing this effort during Run 2 of the LHC we have also been investigating and planning new analyses for LHC Run 2, including both searches for well motivated but unobserved models of new physics, and extending current analyses to higher precision in order to test our understanding of the interactions that we are already aware of.

While at CERN, besides staying informed on things like the status of our simulation effort, flavour tagging, and planning for the next shutdown by trying to pick the best technology for different layers of the new tracker, it’s been great to see the local South African contingent – which reminds me – it’s time to run across to P1 and meet with the engineering students working on the NSW assembly…Sala kahle (Stay well).

Okay, actually let’s end with a gratuitous picture of a giraffe  (taken at the 2014 Kruger Workshop on Discovery Physics at the LHC):


Giraffe at Kruger National Park (2014). IMAGE: Sahal Yacoob, ATLAS Experiment © 2015 CERN



[1] The full schedule is available at

[2] Phys. Rev. D. 90, 112015 (2014).

[3] JHEP09 112 (2014).

[4] JHEP04 117 (2015).


SahalYacoob Sahal Yacoob is a lecturer at the University of Cape Town in South Africa (well, from July 2015 he will be). Sahal has been on ATLAS since 2010, and moved back to South Africa in 2012. He has worked on various tau-related analyses.

From ATLAS Around the World: A view from Down Under

While ATLAS members at CERN were preparing for Run 2 during ATLAS week, and eagerly awaiting the beam to re-circulate the LHC, colleagues “down under” in Australia were having a meeting of their own. The ARC Centre of Excellence for Particle Physics at the Terascale (CoEPP) is the hub of all things ATLAS in Australia. Supported by a strong cohort of expert theorists, we represent almost the entirety of particle physics in the nation. It certainly felt that way at our meeting: more than 120 people participated over five days of presentations, discussions and workshops. Commencing at Monash University, our youngest researchers were exposed to a one and a half day summer school. They then joined their lecturers on planes across the Bass Strait to Tasmania where we held our annual CoEPP general meeting.

CoEPP comprises ATLAS collaborators from the University of Adelaide, University of Melbourne and University of Sydney, augmented by theory groups, and joined by theory colleagues from Monash University. CoEPP is enhanced further by international partnerships with investigators in Cambridge, Duke, Freiburg, Geneva, Milano and UPenn to help add a global feel to the strong national impact.


Larry Lee of the University of Adelaide talks about his ideas for ATLAS Run 2 physics analyses.

Larry Lee of the University of Adelaide talks about his ideas for ATLAS Run 2 physics analyses.

Ongoing work was presented on precision studies of the Higgs boson, with a primary focus on the process where the Higgs is produced in association with a top-antitop quark pair (ttH) in the multilepton final state and the process where the Higgs decays into two tau leptons (H->tautau). Published results were shared along with some thoughts on how these analyses may proceed looking forward to Run 2. Novel techniques to search for beyond Standard Model processes in Supersymmetry and Exotica were discussed along with analysis results from Run 1 and prospects for discovery for various new physics scenarios. CoEPP physicists are also involved in precision measurements of the top-antitop (ttbar) cross-section and studies of the production and decay of Quarkonia, “flavourless” mesons comprised of a quark and its own anti-quark (Charmonium for instance is made up of charm and anti-charm quarks). It wasn’t just ATLAS physics being discussed though, with time set aside to talk about growing involvement in the plans to upgrade ATLAS (including the trigger system and inner detector) and how we can best leverage national expertise to have a telling impact.

A dedicated talk to outline our national research computing support for ATLAS proved very helpful to many people new to the Australian ATLAS landscape.

CoEPP director, Professor Geoffrey Taylor of the University of Melbourne, in deep discussion during the poster session.

CoEPP director, Professor Geoffrey Taylor of the University of Melbourne, in deep discussion during the poster session.

I was happy to spend time with colleagues from our collaborating institutes and also to meet the new cohort of students/postdocs and researchers who have joined us over the past year. It dawns on me how the Australian particle physics effort is growing, and how we are attract some of the brightest minds to the country. It is exciting to see the expansion and to be able to play a part in growing an effort nationally. The breadth of Australia’s particle physics involvement was demonstrated with a discussion of national involvement in Belle-II and the exciting development of a potential direct dark matter experiment to be situated in Australia at the Stawell Underground Physics Laboratory. The talks rounded out a complete week of interesting physics, good food, a few drinks and a lot of laughs.

As this was the first visit to Hobart for many of us it was particularly pleasing that the meeting dinner was held at the iconic Museum of Old and New Art (MONA), just outside the centre of the city. It proved a fitting setting to frame the exciting discussion, new and innovative ideas, and mixture of reflection and progression that the week contained. Although Australia’s ATLAS members are some of the farthest from CERN there is considerable activity and excitement down under as we plan to partake in a journey of rediscovery of the Standard Model at a new energy, and to see what else nature may have in store for us.

All the CoEPP workshop attendees outside MONA, Hobart.

All the CoEPP workshop attendees outside MONA, Hobart.


Dr Paul Jackson works in the Department of Physics at the University of Adelaide. His first involvement with ATLAS was in 2004, working on the construction of the optoboards of the pixel detector. He spent several years based at CERN during Run 1 before moving to Australia to start a new group in Adelaide. Dr Jackson receives funding from the Australian Research Council under the Future Fellowship scheme. He is affiliated with the ARC Centre of Excellence for Particle Physics and the Terascale and is the recipient of a 2015 Australia-Harvard Fellowship.

From ATLAS Around the World: Preparing for Run 2 from Colombia

I work at Universidad Antonio Nariño in Bogota, and I have been part of the ATLAS experiment since 2010. After a two-year stay at CERN, I moved back to Colombia in 2012 and since then, I have continued to do my work on ATLAS from here. Being involved in ATLAS and working from Colombia has been a great experience for me; I get to continue contributing to the physics searches I am involved in at ATLAS, and also do other things like teaching, giving seminars, and doing outreach activities.

A typical day for me starts with a videoconference meeting with one of the ATLAS groups I work with at CERN. The time difference means this is usually quite early, but things here in the city start quite early as well so it does not feel that strange anyway. After the meeting it is half way through the morning and some days I have to teach at the University at that time. Then I have all the afternoons to focus on my work on ATLAS, which is now starting to be all about preparing for Run 2 of the LHC.

For a couple of years I have been involved in a particular search for physics beyond the standard model, looking for a charged Higgs boson, different to the Higgs boson we already found at the LHC (which has zero charge). Our results with the Run 1 data are almost finished, and most of the people in the analysis group, me included, are moving to start preparing the search for the same particle with the Run 2 data. Although there is no data yet, it is important that we anticipate the issues that might arise with the new conditions of the LHC, and also that we prepare all our “machinery” (analysis software) for when the data arrives.

As one of the many improvements ATLAS has made for Run 2, the way in which we analyse and process our data has been changed, to improve its efficiency and compatibility across different analysis groups, so that we can more easily compare our results with other colleagues in a more efficient and faster way. So the first thing I am involved in for Run 2 is in understanding and adapting our Run 1 machinery to this new environment in order to be prepared when the new data arrives. This will help us get new updated results quickly, which for this search should be possible rather soon, hopefully just after the first year of data taking.

The other people in my group are also preparing themselves for Run 2. Our group also works on the system that chooses which events to keep and which ones to discard. This is called the Trigger, and here we are involved in developing a particular tool for identifying low mass particles reconstructed from electrons. Electron identification is in general something our group has been involved in for some time, and all this work will be very relevant as soon as we start taking data again, helping us identify where we need to improve and checking whether our algorithms are working as they should in the new conditions of the LHC.

Other than the research work on ATLAS, I also take remote computing shifts, where I monitor from here the behaviour of the ATLAS computing GRID for eight hours a day. This is part of the service work all of us in the collaboration do to share the load of all the different tasks needed to keep the experiment working properly all year long.

In the summer I will be in the ATLAS control room being part of the data taking

In the summer I will be in the ATLAS control room being part of the data taking

Another thing I enjoy doing here is outreach, trying to encourage young people in doing science and showing them a bit of what we do in ATLAS and why it is interesting and exciting. Just this month we hosted two international masterclasses, where school students come to the university one day and learn about the work that we do, and get to do a “mini” search for a particle with real ATLAS data. At the end of the day we have a video conference with other universities around the world where the same activity is being held, so that they can interact with other students in a different country and compare their results, sort of the way we do in real life in a collaboration like ATLAS.

We had a very special guest  at one of the International Masterclasses; Peter Jenni, one of the founding fathers of ATLAS came to visit us

We had a very special guest at one of the International Masterclasses; Peter Jenni, the first spokesperson of ATLAS.

These activities are important for us, because we are a rather small community here in Colombia doing experimental particle physics, so it is one of our “duties” to reach out to people and let them know about the potential of our research.

In the summer holidays I am usually able to go to CERN for a couple of months which is very nice: I can interact with many people there and hear about their ideas and get involved in new projects for when I return to my home country. This year the detector will already be taking data by the time I arrive, so it will be even better, since I will also take shifts in the control room and be part of the data taking process.

I feel very fortunate to be able to take active part in the very exciting things we do on ATLAS from my home country, and like all of us in the collaboration, looking forward to the new challenges that Run 2 will bring us.

CarlosSandoval Carlos Sandoval is a Lecturer at Universidad Antonio Nariño in Bogotá, Colombia, and is part of the ATLAS collaboration since 2010. His is currently involved in beyond standard model Higgs searches and has previously worked on jet physics and jet triggers in ATLAS.

A Week of Firsts

Me on skis!

Do I look nervous? I was nervous.

The annual conference, Moriond, is in its 50th edition this year, and I’ve had the pleasure of coming down to Aosta in Italy to participate in the QCD session for the first time. It’s actually a week of firsts for me. The conference organizers described it as being in a kind of “QCD confinement”: whereas most conferences are in big cities, where it’s easy to disappear into a museum or restaurant, stay in a hotel far from the conference, see friends, and so on, Moriond attempts to stay remote enough that the attendees are “forced” to discuss physics with each other for the week (it doesn’t take much encouragement, to be honest). Moriond has a funny schedule: talks from 8:30 to 12 in the morning, and from 5 to 7:30 in the evening, to leave a few hours in the middle of the day for skiing. Having never skied before, that’s been the most frightening first, but I am proud to say that I did manage to ski a couple of times while here, and I avoided breaking a leg this time. I even successfully got on and off a chairlift!

This was also the first time I’ve gotten to present the results of a physics analysis that I worked directly on at an international physics conference. And what a chance! That sounds a little funny, of course. ATLAS, like the other experiments, has to find a balance between getting the best, most knowledgeable speakers at each conference and ensuring that young students, people looking for jobs, and people who have been doing critical work for the experiment that isn’t a physics analysis (work we call “service work”, generally) get to go to conferences. That does sometimes mean people are asked to give talks on subjects that they’re familiar with, but the results that are ready to be presented may not be ones that they were deeply involved in producing. And that’s been the case for me – I’ve been to a couple of conferences, but up to this point it’s just not quite been at the right time or with the right topic to show something that I was working on.

Our little bump!

Our little bump. The data (black points) are about three sigma above the background (colored histogram). We have a couple of signal models (dashed histograms) on there for comparison. Is it SUSY? Or is it luck?

So what about those results? Well, one of the papers I worked on was submitted back in January, and while it was a great search covering lots of different possible signals, we didn’t really see anything. But some of you might have seen that CMS recently submitted a SUSY search that had a ~2.5 sigma excess, which caused a lot of stir. The week after, ATLAS submitted our version of the same search, which I also had the pleasure of helping out with, showing that with a signal region designed to be as close as possible to the CMS search region, we do not see a similar excess. But in the same paper, we pointed to another area with an apparent 3.0 sigma excess! There has been some discussion, both in the form of papers submitted by theorists and in the form of physics blogs.

It’s a fun possibility for the world to think about: have we seen the first hint of something really exciting, or have we just seen a rare fluctuation, expected because of the enormous number of searches we’ve performed? One wonderful talk given during the week was all about the “Fifth Force”, an interesting and extended saga of scientists trying to understand whether the data they had collected was the sign of something absolutely critical to understanding the universe, or just an unexpected manifestation of a well-known phenomenon. One of my favorites from that talk: in order to measure very small deviations in gravity, they needed to survey a large area around the (outdoors) experiment. The researchers failed at one point to account for the fact that graduate students carrying a $50,000 piece of equipment would not want to take it near a river or up a steep hill, and that led to a bias in their results.

We’ll have to wait for the next run to find out whether the small excess persists – but we should know soon! We got the good news that beam is expected back in the machine in a few days. Run 2 is not far off!

ZachMarshall Zach Marshall is a Divisional Fellow at the Lawrence Berkeley National Laboratory in California. His research is focused on searches for supersymmetry and jet physics, with a significant amount of time spent working on software and trying to help students with physics and life in ATLAS.

Moriond Electroweak: physics, skiing and Italian food

If you’re a young physicist working in high energy physics, you realize very soon in your career that “going for Moriond” and “going to Moriond” are two different things, and that neither of the two means that you’re actually going here:

The original location of the Moriond conference series

The original location of the Moriond conference series

“Les rencontres de Moriond” is one of the main Winter conferences for our field. Starting from its original location in Moriond, it has been held around the French and Italian Alps since 1966. In the 60s and 70s, there was a clear distinction between two branches of the same conference, as “electroweak” and “QCD” physics were still done in different labs and accelerators: in those years the former had to do for example with the discovery of the W and Z bosons and their interactions, while the latter saw the developments of a model to describe the “quarks” that compose protons and neutrons, and the discovery of these constituents themselves. Nowadays, both kinds of physics are studied at the LHC and in other experiments around the world, so the results presented in the two conferences are not necessarily divided by topic anymore.

This year I was lucky enough to be contributing some results that were “going for Moriond”, which means they’d be approved by the Collaboration to be presented at this conference for the first time, but I would also be “going to Moriond” in person. This year’s “Moriond Electroweak” was held in the Italian mountain resort of La Thuile, and had a special significance. In the session that celebrated the 50 years of the conference, the founder Jean Trân Thanh Vân reminded the audience of the two pillars of this conference:

  • encourage discussions and exchanges between theoretical and experimental physicists;
  • let young scientists meet senior researchers and discuss their results.
The official Moriond EW t-shirt and the announcement of the slalom competition

The official Moriond EW t-shirt and the announcement of the slalom competition

The first point was made when theorists and experimentalists alike were asked to take part in a slalom competition. The results were not categorized by subject of study, but certainly the cheering came from and towards both parties.

The latter took place almost every evening, in the dedicated “young scientists session”. Here, students and young post-docs can apply to give a short talk and answer questions on their research topic in front of an international audience of theorists and experimentalists.

The questions and answers can be then carried on to the (abundant) dinner. As an Italian, I do appreciate the long evenings dedicated to a mixture of excellent food combined with physics discussions (and where the two can be identified with each other, as in this snapshot from a talk by Francesco Riva).

New physics matched to Italian dinner choices at the conference, according to Francesco Riva

New physics matched to Italian dinner choices at the conference, according to Francesco Riva

Back to the physics: the results I contributed to were shown in the afternoon session, before the 50th anniversary talks. They’re in the top corner of one of the slides from the summary of the ATLAS and CMS new physics searches.

Beyond the Standard Model: New results presented at the Moriond EW conference

Beyond the Standard Model: New results presented at the Moriond EW conference

That’s only the tip of the iceberg of a search that looks for new phenomena that would manifest as an excess of collimated jets of particles in the central region of the detector, and it shows that there is no new physics to be found here, nor in any of the other searches shown in the conference so far. (What we didn’t know at that time was that there would be something not consistent with expectations in the LHCb results shown just one day after, as explained in this article). Given that so far we have not found much beyond what we consider Standard (as in belonging to the predictions made by the Standard Model of Particle Physics), the conference had a special focus on searches that look for the unexpected in unexpected places. “Stealthy” is how the physics beyond the Standard Model that is particularly hard to find is characterized, and as experimentalists we want to pay particular attention to the “blind spots” where we haven’t yet looked for the upcoming LHC runs. This was highlighted in the morning talks, describing searches for Supersymmetry in blind spots and searches for particles that leave no immediate signature after the collision because of their long lifetime. There were also other ideas of how to test the Standard Model with very high precision, as highlighted in another food-related slide by Francesco Riva.

Techniques to find new physics, according to Francesco Riva

Techniques to find new physics, according to Francesco Riva

No one in the audience forgot, however, that the new LHC run will bring more energy and more data. Both will allow us to investigate new, rare processes that were not accessible in the first run. Discoveries might be just around the corner!

Overall, the “Rencontres de Moriond” conferences have the effect of leaving everyone enthusiastic for the discussion and eager for more results: in particular, next year’s edition may see some of the first results of the upcoming LHC run. And of course, the results will be best discussed on skis and over dinner.

Caterina Doglioni Caterina Doglioni is a post-doctoral researcher in the ATLAS group of the University of Geneva. She got her taste for calorimeters with the Rome Sapienza group in the commissioning of the ECAL at the CMS experiment during her Master’s thesis. She continued her PhD work with the University of Oxford and moved to hadronic calorimeters: she worked on calibrating and measuring hadronic jets with the first ATLAS data. She is still using jets to search for new physics phenomena, while thinking about calorimeters at a new future hadron collider.