by Virginia Greco. Published: 25 September 2018

Professor at the National Autonomous University of Mexico, Antonio Ortiz Velasquez has been recently elected as a convener of the Monte Carlo generators and Minimum Bias physics (MM) working group, role that he will cover starting from October 1st. We talked with him about his career path and research interests.

Antonio found his call when he was still a Master’s student at the National Autonomous University of Mexico (UNAM). Already fascinated by high energy physics, he was particularly interested in pp collision research. However, he was invited by a professor of his to join the ALICE experiment, which indeed works mainly with heavy ions. He realized soon, though, that the study of high multiplicity pp collisions with the ALICE detector was a growing and attractive line of research. 

Therefore, during his PhD he joined the group led by Guy Paic, under whose supervision he worked on the characterization of high multiplicity pp collisions and performed one of the first measurements of their event structure. In this analysis, he could see early indications of unexpected behaviours of the high multiplicity pp collisions, which have been more extensively observed later and have opened up the quest for understanding whether droplets of QGP are formed in very high-multiplicity pp collisions as well.  

After receiving his PhD in 2011, he moved to Sweden to work as a postdoctoral research fellow at the University of Lund. There, he worked with Peter Christiansen on particle identification in different systems (pp, p-Pb, Pb-Pb) and he participated in the first measurement of pion, kaon and proton transverse momentum spectra up to 20 GeV/c. “The paper that we wrote about this analysis was quite successful and we can count more that 200 citations,” Antonio comments, highlighting that this is a work he is particularly proud of. As he also is of another study in which he participated while he was at Lund: “We discovered flow-like effects in PYTHIA Monte Carlo event generator, which encouraged us to look at alternative mechanisms to explain the new phenomena seen in small systems.

An important achievement in Antonio’s career was also having the idea of using a new quantity, called transverse spherocity, to disentangle soft and hard components of the pp collisions, in order to shed light on rare high multiplicity pp events and understand whether some droplets of QGP are formed in such collisions. “We need to isolate the jetty-like events from the isotropic ones, in which instead of observing the expected jet structure, we see many low pt particles uniformly distributed over the phi-eta range,” Antonio explains. “The transverse spherocity is a quantity that allows us to distinguish these two kinds of events. I proposed this idea in 2012 and I am happy to see that it is being exploited by many ALICE physics working groups.

In 2014, Antonio moved back to Mexico and started another stage of his career as an assistant professor at the Nuclear Science Institute (ICN) of UNAM. “Here I could combine my experience on the characterization of pp interactions using transverse spherocity and my expertise in particle identification with different detectors,” he comments. In the same year, he was also elected as a convener of the spectra physics analysis group, which is part of the light flavours physics working group. From that position, he could push forward his idea of the transverse spherocity and follow the analyses for measuring the mean pt versus multiplicity and spherocity as well as the pion, kaon and proton transverse momentum distributions in different collision systems. “We were able to split the high multiplicity pp collision sample in jetty-like and isotropic events for the first time,” he states enthusiastically. “We found indication that the isotropic events exhibit enhanced flow-like effects, as suspected from my previous studies. This is very encouraging and invites us to look at the details of the interaction by studying the extreme of the spherocity value – which means the very isotropic events – to see whether the effect increases as expected.

High multiplicity pp collisions represent a small percentage of events and only about 1% of them are the most isotropic ones. As a consequence, a big amount of data is required in order to have significant statistics. “We are now collecting many pp data and I think that, analysing them, we will be able to have a much clearer idea about what happens in the small systems,” adds Antonio.

Recently, he has been promoted to professor at the Nuclear Science Institute of UNAM, where he is now deputy team leader of the local ALICE group. With his students, he is working on developing new analyses using pp data: “Currently, we are using machine learning for data analysis and the results are promising; we are also exploring multidimensional unfolding methods to measure pt spectra as a function of multiplicity and spherocity; in addition, we are finally exploiting the physics of the so-called underlying event.

Antonio has already directed the thesis of two Bachelor’s and two Master’s students as well as of one PhD student. He particularly enjoys teaching and working with young researchers. “If I wish to do something for my country,” he explains, “I have to contribute to the training of young Mexicans. And I can also motivate them because I think that the research we are doing is important not only for my local group but also for the heavy-ion and high energy physics communities at large.

In the Collaboration Board meeting that took place during the summer ALICE week, Antonio was chosen as a convener of the Monte Carlo generators and Minimum Bias physics (MM) working group and his mandate will start on October 1st. “I believe that this is the natural group for studying the small system physics,” he declares, “and I will be very happy to cover this role. I am really grateful for all the support I have received from the Mexican Community, as well as from UNAM and CONACYT, and in particular from Guy Paic and Miguel Alcubierre (the Director of ICN).