STAR (Solenoidal Tracker At RHIC)
STAR is a large acceptance multi-purpose experiment that is capable of performing a wide variety of measurements, each contributing uniquely to the overall picture of heavy-ion collisions at RHIC. RHIC is a versatile hadron collider which offers to study the phase diagram of nuclear matter in a large range of collision energies (7 - 200 GeV in the center-of-mass per nucleon pair) together with a possibility to collide various nuclei species (from protons to Uranium nuclei).
A schematic view of the STAR experiment at RHIC
In past years, the main physics focus in STAR was on exploration of hot and dense nuclear matter in collisions of gold (Au) ions at the top RHIC energy of 200 GeV together with measuring properties of “cold” nuclear matter in small collision systems such as proton+proton, proton+Au, and deuteron+Au, where no QGP is expected to be formed. In 2018, isobaric collisions of Ruthenium-96 (Ru+Ru) and Zirconium-96 (Zr+Zr) were studied to shed light on understanding of the chiral magnetic effect. This study has a fundamental impact beyond the field of high-temperature QCD.
In the upcoming years, the physics focus will primarily be on search for a critical point of the phase diagram of nuclear matter within the so called Beam Energy Scan (BES) program. After the very successful first phase of the BES completed in 2014 that provided promising hints at collision energies below 20 GeV, several observables with higher statistics and improved detector setup will be investigated in the energy range from 7.7 to 19.6 GeV in the collider and from 3 to 7.7 GeV in the fixed-target modes in the coming years. High data statistics at these low RHIC collision energies will be achieved by using a new low-energy electron cooling and longitudinally extended bunches improving the RHIC luminosity.
Phase diagram of nuclear matter
Credit: Image courtesy of Brookhaven National Laboratory
Besides the exploration of hot and dense nuclear matter, RHIC is also the only machine in the world capable of colliding beams of polarized protons to investigate the “missing” spin of the proton. Three quarks that built the proton account only for about 20 percent of proton's spin. The dedicated spin program carried out at RHIC and within the STAR experiment in parallel to its heavy-ion program is essential to try to find an answer to this fundamental question of modern particle physics.
The STAR group at NPI focused in past primarily on femtoscopic correlation measurements of the hot and dense fireball created in heavy-ion collisions. In last decade, the physics focus shifted toward exploration of hard probes – heavy quarks and jets, created early in the collision and ideally suited for tomography of the QGP matter.
Performing the maintenance of the ZDC detector of the STAR experiment at BNL
The Heavy Flavor Tracker of the STAR experiment prior to installation at BNL
(Credit: Roy Kaltschmidt, LBNL)
We are also active in participating in detector operations and maintenance. Since 2000, when the STAR experiment became operational, its detectors underwent important upgrades to be able to face new challenges of the rapidly developing field of heavy-ion physics and fully exploit excellent capabilities of RHIC. In 2014-2016 STAR was equipped with a high precision Heavy Flavor Tracker (HFT) to which we contributed with simulations, tests and calibrations. Currently we are helping to maintain the Zero Degree Calorimeter (ZDC) of STAR.
Team members of the STAR experiment:
Research scientists:
Jana Bielčíková (head of the STAR group)
Jaroslav Bielčík (part time)
Michal Šumbera
Ph.D. students:
Ing. Jitka Mrázková
Ing. Monika Robotková
Ing. Michal Svoboda
Contact person:
Jana Bielčíková, bielcikova@ujf.cas.cz
ALICE (A Large Ion Collider Experiment)
ALICE detector at CERN
ALICE is one of the four big experiments at the LHC. It is the only LHC experiment fully dedicated to the investigation of nuclear matter at extreme energy density and temperature. ALICE has a broad physics program in which physicists try to capture the properties of the elusive state of the QGP. At NPI, our physics focus is primarily on the analysis of jet properties in proton-proton, proton-lead, and lead-lead collisions. Jets are collimated sprays of particles created by the fragmentation of highly virtual quarks and gluons. Since jets are produced imminent to QGP formation, they are considered an ideal tool to study the properties of the QGP.
In terms of hardware, we have been from the very beginning of our participation in ALICE involved in various tasks related to the Inner Tracking System (ITS) detector. This detector is the closest one to the LHC beam. The ITS detector was completely upgraded and is formed by seven layers of Monolithic Active Pixel Sensors. The new detector is essential for performing high-precision measurements of particles containing heavy quarks c and b. The ALICE Collaboration works on a subsequent upgrade, which will replace the three innermost layers of the ITS with a new detector based on wafer-size, bent Monolithic Active Pixel Sensors. This will allow further reduction of the material close to the interaction point. At NPI, we employ a proton beam from the cyclotron U-120M to test the radiation hardness of various ITS electronic components and, in addition, we also analyze data from similar tests done at other irradiation facilities.
Irradiation of the ALPIDE silicon sensors at the NPI of the CAS cyclotron U-120M
Work on the setup for FPGA irradiation
ALICE Inner Tracking System detector after the upgrade
Our third activity in ALICE concerns Grid computing. The amount of data produced in the collisions at the LHC substantially exceeds the capacities of the CERN Computing Center for data processing and storage. As a solution, an infrastructure of worldwide distributed computing centers connected through a high-throughput network and operated by the local institutions involved in the LHC projects was created. Centers involved in this infrastructure called the LHC Computing Grid (LCG) provide sufficient resources for LHC data handling and storage. Our involvement in the LCG is realized by ensuring a flawless processing and storage of the ALICE data at the computing center at the Institute of Physics (IoP) of the CAS in Prague which is involved in the LCG. At IoP we host computing servers dedicated to ALICE. The data storage servers for ALICE are installed and operated at our institute. Our share in the total computing for ALICE has been significant since the beginning of the LHC Computing Grid operations.
One of the storage servers for ALICE at the NPI of the CAS with a capacity of 340 TB
Team members of the ALICE experiment:
Research scientists:
Filip Křížek (head of the ALICE group)
Dagmar Adamová
Jana Bielčíková
Svetlana Kushpil
Postdoc:
Mgr. Artem Kotliarov, Ph.D.
Ph.D. students:
Ing. Ekaterina Grecká
MSc. students:
Bc. Vojtěch Macháček
Contact person:
Filip Křížek, krizek@ujf.cas.cz
