Hard probes of heavy-ion collisions

Project Information

HPOFHIC

Grant agreement ID: 101030031

DOI

10.3030/101030031

Project closed

EC signature date 15 March 2021

Start date 1 April 2021

End date 31 March 2023

Funded under

• EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions

Total cost

€ 156 980,64

EU contribution

€ 156 980,64

Coordinated by

UNIVERZITA KARLOVA
Czechia

Periodic Reporting for period 1 - HPOFHIC (Hard probes of heavy-ion collisions)

Reporting period: 2021-04-01 to 2023-03-31

Summary of the context and overall objectives of the project

In the big picture, the project tries to help understand the behavior of our nature at the most fundamental level. The obtained results improve our understanding of the matter that is believed to have existed during the first microseconds after the Big Bang or in the cores of neutron stars. Heavy ion collisions are currently the only way to create and study such extreme conditions on Earth. Secondly, the project results should help us understand the process of how heavy particles, like protons and neutrons, are formed from quarks, which are the most fundamental building blocks of matter we know.

More specifically, this project aims to improve our understanding of properties and states of matter at extremely high temperatures and pressures that existed shortly after the Big Bang. Such conditions can be created by collisions of two heavy nuclei at ultra-relativistic energies. The project also tries to improve our knowledge of one of the four fundamental forces in nature, the strong interaction. This is done by measurement of hard processes like jets, collimated sprays of particles that are born in collisions and penetrate the hot and dense plasma.

In conclusion, the result of this project provides a new perspective for understanding the role of jet structure, jet mass, jet flavor, and path length in jet suppression in the hot and dense medium, quark-gluon plasma. This can be further used by theorists in constraining plasma properties as we ll as improve our understanding of the strong force.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The researcher was elected to be the leader of the whole heavy ion (HI) physics group at the ATLAS collaboration for two years from September 2021. As the leader of the HI group at the ATLAS experiment, the researcher was responsible for the coordination of a group of approximately 70 physicists from various institutes across the globe, working on various aspects of heavy-ion physics, starting from physics of hard processes, through physics of correlations and fluctuations, and ending by physics of ultra-peripheral collisions. This work involved overseeing and coordinating 28 different analyses leading to 14 publications. Furthermore, the researcher was responsible for planning the future HI physics program and preparing data taking.

Overview of scientific work:

The researcher finalized the measurement of large-R jets in HI collisions and the dependence of their suppression on the sub-structure. This resulted in the manuscript "Measurement of suppression of large-radius jets and its dependence on substructure in Pb+Pb collisions at 5.02 TeV with the ATLAS detector". This result provides important information about the role of jet structure in the process of jet quenching.

The researcher followed up on a similar measurement while using tracks to define the jet structure that would allow increased precision. The results are expected to be published in 2023.

The result above was further extended beyond the expected scope and used in measurement in the publication "Measurement of the nuclear modification factor of b-jets in 5.02 TeV Pb+Pb
collisions with the ATLAS detector". This measurement provides important information about the role of parton flavor and mass in the process of jet suppression.

The researcher pursued the work on the use of hadronic decays of boosted W and Z bosons. The feasibility study was performed as part of a project and later bachelor thesis with a student at Charles University who was supervised by the researcher. The feasibility study showed that this measurement is not possible with the existing data set but might be possible with the larger dataset taken in fall 2023. The research coordinated the preparation of the jet trigger that will be used in the upcoming data-taking.

A researcher was involved in the measurement of dijets in Xe+Xe collisions. This resulted in the publication "Measurements of the suppression and correlations of dijets in Xe+Xe collisions
at 5.44 TeV" which will be the first publication of measurement of jets in that collision system. Additionally to this, the work on the measurement of dijet acoplanarity in Pb+Pb is ongoing. The
acoplanarity distribution in Pb+Pb and proton-proton data for comparison was been prepared ready, and the shape analysis was done.

Development was done on the EQ model and Pythia8 and JEWEL MC samples were generated and are available on the project's public website.

The researcher presented his work at international conferences, workshops, and seminars. This includes an invited plenary at the most important conference in the field, Quark Matter 2022.

List of presentations
1. March 2023, Jet quenching studies with new jet substructure and suppression measurements in ATLAS, Hard Probes 2023
2. June 2022, Heavy Ion Working Group Report, ATLAS collaboration week, Geneve, Switzerland
3. June 2022, Experimental results on intra-jet softening and large-angle energy flow, conference: ECT* Jet quenching workshop
4. May 2022, Jet substructure in heavy ions (experiment), conference: LHCP 2022
5. April 2022, Experimental overview on jet substructure and medium response (EX), conference: Quark Matter 2022
6. June 2021, Hard probes of heavy ion collisions with ATLAS, conference: ISMD2021
7. October 2021, Probing QCD matter with Jets, seminar at AGH Krakow
8. September 2021, Jets in Heavy Ion collisions, Hadronic Calibration Workshop

The researcher also organized a virtual HI trigger workshop (22/6 - 23/6 2021)

Outreach activities
The researcher was involved in 27 outreach activities:
- Main organizer of "The Big Bang Stage" at the Colours of Ostrava festival (3000 visitors).
- Public lectures on various topics from physics of elementary particles at SCIENCE Meetup in Paralelní Polis (September 2021), Patecnici (July 2022), Mensa meeting for talented kids (June 2022), Ostrava observatory (October 2021), festival Technology in Society (November 2022), Summer School of Astronomy (2021, 2022), and festival WOMAD (July 2022)
- Experiment with cloud chambers particle detector for high school students (2021, 2022)
- Lectures about particle physics as part of the Science to Go project in Blansko and Prague (October 2021, February 2022)
- Science is Wonderful in 2021 (three lectures)
- Two podcasts - "Sedmikrasky" by Observatory in Brno and X-challenge podcast
- Talk about extreme states of matter for high school students in Litomerice
- Moderating CERN Masterclasses for high school students (2021 and 2022)

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The three scientific publications that resulted from this project report 1) the first measurement of the substructure of large-radius jets in heavy-ion collisions 2) the first jet measurement in the Xe+Xe collisions and 3) a significant improvement of precision in the study of b-jet production in heavy-ion collisions.

Researcher giving a public lecture

Supression of jet production expressed through nuclear modification factor RAA

Event display of Pb+Pb collision with a jet production