Prof. Krzysztof Sliwa: research activities

conference presentations and invited talks : Krzysztof Sliwa's talks and presentations

Tufts ATLAS Group

The Tufts University Elementary Particles Group joined ATLAS in 1994. Together with Boston University, Brandeis University, Harvard University and Massachusetts Institute of Technology we decided to work as a single group, the Boston Muon Consortium (BMC), on the ATLAS muon system. After the decision to focus on the ATLAS end-cap muon system, the Tufts Group was very active in initial physics simulations and in construction and testing of the first MDT end-cap muon chamber, with Prof. Mann leading the latter effort. The Tufts Group's high precision computer-controlled machine shop served as a R&D lab for BMC, and later manufactured thousands of small, very precise and custom-designed pieces needed for the MDT chambers and for the entire muon alignment system. At the same time, the Tufts ATLAS Group was very active in studying and planning the world-wide data analysis and reconstruction, needed for the world-wide collaboration like ATLAS. MONARC, a very successful LHC project created jointly by Tufts and Caltech, provided the first realistic modelling of such a world-wide, distributed computer system.

The Tufts ATLAS Group currently consists of three faculty (Pierre-Hugues Beauchemin - who joined the group in 2011, Austin Napier and Krzysztof Sliwa), a research-associate (Vincent Croft), two graduate students (Alec Drobac and Colette Kaya) and a part-time consultant (Benjamin Whitehouse, a former Tufts graduate student). The Tufts Group was very active in the analysis of the muon test-beam data, and continued to work on the muon reconstruction software. The Tufts ATLAS Group developed the MuonTrackingGeometry, a completely new description of the entire muon system, including the active and the passive elements, which allows the use of ATLAS common tracking tools in muon reconstruction. The MuonTrackingGeometry is an essential component of FatRas, a new, fast ATLAS track simulation which models the detector response at the hit level. Tufts ATLAS Group was responsible for simulation of the entire muon system in FatRas, which became part of the Integrated Simulation Framework, a new fast simulation of the entire ATLAS detector.

Regarding physics studies, the Tufts ATLAS Group is interested in W+jets and Z+jets physics, top physics, Higgs boson studies, and physics beyond the Standard Model (non-standard Higgs searches, SUSY, extra dimensions et cetera). The main objective of the LHC analyses is to find out whether the new particle discovered in 2012 is the Minimal Standard Model Higgs, or some other kind. It would be really exciting if the latter were true. There is also a chance that with increased energy of the proton-proton collisions completely new particles will be found. Here, studies of top quarks are extremely important, as top quarks will constitute the most important background for almost any final states due to “new physics” and have to be understood very well.

Prof. Beauchemin, together with Dr Croft, Mr Drobac and Mrs Kaya and undergraduate students, is studying the production of W and Z electroweak bosons, accompanied by jets. They study the ratios of W+jets/Z+jets production rates. When taking the ratios, many of the systematic errors cancel, which leads to reduced uncertainties and allows more significant comparison with theoretical predictions. They also study the production of jets accompanied by large missing transverse energy, which could provide clues about dark matter.

The Tufts ATLAS Group has developed a new multidimensional and multiclass analysis technique - an event classifier based on Support Vector Machines (SVM). The method, originally developed by Dr. Ben Whitehouse when he was working towards his Ph.D. with Prof. Sliwa, allows to simultaneously take into account a large number of physics observables, including correlations between them. Although SVM were used in other research areas in the past, Tufts was the first group to apply it in collider physics. In contrast with other multivariate methods, SVM has a sound mathematical foundation - Mercer Theorem. Prof. Sliwa, together with Dr Whitehouse applied their new analysis technique in measurements of the production rate of top quarks in proton-proton collisons at 7 TeV and 8 TeV at LHC, and their ratio. Understanding top quark production is interesting on its own, but it is also crucial in studies of the Higgs boson in many difficult to analyse final states involving leptons, jets and missing transverse energy. Top quark is the main background in studies of Higgs bosons production via a WW* fusion mechanism, and in many Higgs decay modes.

Prof. Sliwa has decided not to take part in Run 3 at the LHC, and his involvement with the ATLAS Collaboration and the LHC Collider program will not extend beyond Fall 2021.

faculty: Pierre-Hugues Beauchemin, Austin Napier, Krzysztof Sliwa

past research associates: Dr Marcin Wolter, Dr Simona Rolli, Dr Sarka Todorova, Dr Federico Sforza

current research associates: Dr Vincent Croft

past graduate students: Samuel Hamilton (Ph.D. 2014, with Prof. Sliwa), Jeffrey Wetter (Ph.D. 2015, with Prof. Sliwa), Hyungsuk Son (Ph.D. 2019, Prof. Beauchemin)

current graduate students: Alec Drobac, Colette Kaya

Prof. Sliwa has won Tufts Faculty Research Awards in 2012 and 2013, and Prof. Beauchemin in 2014. They also jointly won in 2014 the Tufts International Research Award, which allowed both faculty and four students to spend 6 weeks at CERN in the summer of 2014.

other activities

I have been also studying topology, differential geometry and other areas of modern mathematics to gain better insight into the meaning of quantum gauge theories, the origin of mass and the structure of space-time, matter and all interactions, including gravity.

Recently, I embarked on studies of geometry and topology of the Universe. In the Standard Cosmological Model (SCM), the crucial starting point is the interpretation of observed increase of redshifts with the distance to far-away objects as a "Doppler" effect. Acceptance of this hypothesis led to the ideas of Big Bang and the expansion of the Universe. Universe locally looks flat, M_o=R1 x R3 - the flat Minkowski "world". Interestingly, there is another possibility. The same axioms of natural physical symmetries - global isotropy and homogeneity of space and time - and causality properties, which are satisfied by Minkowski spacetime, are also satisfied by another model, developed by a mathematician and a mathematical physicist Irwing Ezra Segal. In Segal's model, the geometry of Universe is M=R1 x S3, but locally it looks like flat Minkowski spacetime M_o. The redshift appears just a consequence of a distortion analogous to a known distortion when a stereographic projection is made from S2 onto R2, when making maps. Segal's model provides a verifiable prediction about how this geometric redshift depends on the propagation time (or geodesic distance on S3), if the Universe is M rather than M_o. I've decided in 2017 to take a look at the newest data from redshift catalogues available online and compare it with the predictions of Segal's cosmology and SCM. Surprisingly, although the data on supernovae prefer SCM, quasars agree better with Segal's model. This puzzling result is, of course, preliminary. The comparison, although in principle very simple, is highly not trivial, as for far-away objects one can only use proxies for the distance, it cannot be measured directly. I am now carefully analyzing the updated redshift data again. I am working on this fascinating study of the shape of the Universe with Maxwell Kaye, an undergraduate student at Tufts, who is majoring in mathematics, computer science and physics.

I am also a member of the MoEDAL Collaboration at CERN, a small, dedicated, experiment looking for magnetic monopoles. All searches so far were negative.