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Description
The primary objective of the project is to measure charm hadron production (mainly D mesons) in central Pb+Pb collisions with the upgraded NA61/SHINE detector at the CERN SPS. These will be the first direct measurements of charm production in heavy ion collisions in the CERN SPS energy domain. The objective can be achieved only by the upgrade of the read-out electronics of the Time Projection Chambers (TPC) of the NA61/SHINE experiment at the CERN SPS which will allow recording Pb+Pb collisions at a much larger interaction rate. This upgrade performed within the project is part of the NA61/SHINE detector upgrade programme to be conducted during the CERN accelerator Long Shutdown 2 period (2020 and 2021). The upgrades will be commissioned and tested in 2021 and are necessary to perform new measurements which will start at the end of 2021 and continue at least until 2024. The secondary objective of the project is to understand the charm production phenomenology, facilitated by the measurements proposed here and complemented by those at the higher RHIC and LHC energies, which will allow the disentangling of the hot and cold medium effects acting on the J/y production in an energy domain where the transition to a deconfined state of nuclear matter is expected. The project duration is 36 months from mid-2020 to mid-2023. The first part of the project is devoted for upgrade of the TPC, later the data taking campaign, calibration and data analysis will be carried out. The complexity of the physical goals of the project as well as upgrade of TPC and operational costs of the hardware and software systems require a collaboration of many institutions. The research group consists of 12 institutions: three Norwegian and nine Polish institutions. All these institutions have extensive and many years of experience in the field of nuclear physics and elementary particles. The number of research groups involved demonstrates the size of the project and its importance.
Summary of project results
The primary aim of this project was to measure the production of charm hadrons, predominantly D mesons, in central Pb+Pb collisions utilizing the upgraded NA61/SHINE detector at the CERN SPS. These measurements serve as a crucial avenue for investigating the properties of the phase transition to the relatively lesser-known phase of matter, Quark-Gluon Plasma. Notably, these measurements mark the pioneering direct observations of charm production in heavy ion collisions within the energy domain of the CERN SPS.
Achieving this objective necessitated enhancing the read-out electronics of the Time Projection Chambers (TPC) of the NA61/SHINE experiment, thereby enabling the recording of Pb+Pb collisions at significantly higher interaction rates. This upgrade constituted a pivotal component of the NA61/SHINE detector upgrade program undertaken during the CERN accelerator Long Shutdown 2 period (2020-2022).
Following its commissioning and testing in 2022, these upgrades became indispensable for conducting novel measurements, commencing towards the end of 2022 and persisting until 2024. Given the intricate nature of the project''s scientific goals, coupled with the technical upgrades to the TPC and the operational expenses associated with hardware and software systems, collaboration among numerous institutions was imperative.
The research consortium comprises 12 institutions, encompassing three Norwegian and nine Polish entities, all possessing extensive expertise in nuclear physics and elementary particles. The involvement of such a breadth of research groups underscores the scale and significance of the project.
The most important project deliverables are:
Upgrade of the NA61/SHINE detector, located at CERN, which allowed to increase of the data-taking rate, by factor 10, to about 1 kHz.
The very considerable effort invested in the detector upgrade opens new options for physics measurements and ensures the operation of the NA61/SHINE experiment for the next several years. The overall performance of the upgraded detection system employed during the data collection period was good. Operation of the upgraded TPC tracking system was stable. The new front-end electronic provided high-quality digitized signals from the chambers, allowing for the reconstruction of particle trajectories. Moreover, work on the new software has been completed. Primary efforts were dedicated to supporting the data acquisition system, reconstruction, and calibration, quality monitoring of the data collected with the upgraded detector, and software development for the data analysis.
These activities cover the following project tasks: • Design, construction and maintenance of readout chain • Maintenance, and further development of the detector control system • Software development • Maintenance and supervision of IT resources • Monte Carlo simulations • Preliminary data calibration and reconstruction for experimental data.
New world data for the open charm production in the heavy ion collision.
In November 2022, a significant milestone was reached as the NA61/SHINE experiment commenced data recording on charm production in Pb+Pb collisions following the reception of a 150A GeV/c Pb beam. Over the course of a week, approximately 30 million Pb+Pb interactions were meticulously gathered, marking the inaugural measurement of lead ion beams after a comprehensive hardware upgrade of the detector.
During the Pb+Pb data-taking period 2023, the experiment achieved a remarkable feat by recording 150 million Pb+Pb interactions. Presently, the collected data is undergoing thorough analysis. From the perspective of charm physics, the primary endeavors revolved around examining the pilot data amassed before the TPCs upgrade. Furthermore, rigorous analyses were conducted to ascertain the yield of open charm production, leveraging diverse statistical and string models alongside referencing previous measurements such as those undertaken by the other CERN experiments.
The NA61 experiment at CERN''s SPS (Super Proton Synchrotron) is a crucial fixed-target heavy-ion collision study. The recent upgrade of its main detector components, particularly the Time Projection Chambers, now enables the detection of open charm mesons, composed of charm and no-charm pairs, through precise measurements of Pb+Pb reactions. Although a well-established hypothesis suggests that the suppression in J/ψ production, compared to direct charm production, stems from the Quark-Gluon Plasma (QGP) medium, definitive evidence of the QGP state remains elusive. This conclusion has remained unchanged despite the wealth of precise data from RHIC and LHC heavy-ion programs.
The data collected will be pivotal for studying charm physics, providing a unique opportunity to explore particle production in heavy-ion collisions. Analyzing data from other channels, such as strange matter production, could bolster the case for the existence of QGP. Together with datasets spanning light to heavy systems collected by NA61, these data sets will facilitate investigations into the size and energy dependence of various phenomena in heavy-ion physics while also serving as an experimental foundation for theoretical models.
This ambitious charm program necessitated a tenfold increase in data-taking rates, prompting a significant upgrade to the TPC chambers. Coupled with the diverse beams and beam momentum available from the SPS accelerator, this enhancement creates a versatile platform for myriad hadron physics measurements. The device''s potential extends beyond heavy-ion collisions; it could measure cross-sections for various reactions, supporting experiments and models in neutrino and astrophysics domains, including neutrino beam production and investigations into cosmic ray propagation and dark matter.
Furthermore, the upgraded device and enhanced measurement capabilities will enable studying exclusive channels in nuclear reactions, such as strange and multi-strange particle production. This multifaceted approach promises to deepen our understanding of fundamental physics phenomena across various research domains.
The project, conducted within one of the world''s foremost particle physics laboratories, CERN, is a crucible for young talent. Its unique nature drew a predominantly youthful cohort, providing them with hands-on involvement at every stage. Beyond its scientific implications, the project carries significant sociological weight, affording participating teams the distinction of working within CERN, bolstering their visibility and institutional prestige. With data collected and cutting-edge experimental infrastructure, the project lays the groundwork for addressing a spectrum of physical inquiries over the coming years. This wealth of data and resources is poised to attract a new generation of researchers eager to carry out research related to them.
Summary of bilateral results
The large team consisted of 35 Polish members and 6 Norwegian participants, whose contribution to this project was meaningful and documented by publications.