RHIC Run 25 - preparations
March 18, 2025
Preparations for RHIC Run 25 are in full swing. In the past week(s), the superconducting magnets are all lowered to the temperatures where we can start to use liquid helium for the last step to 4K. In the status plot, below, you can see how each of the sectors sequentially sees its temperatures lowered to about 70-80K. Liquid helium will do the rest, and by March 23 we expect to see the full RHIC ring at 4K operating conditions.
Meanwhile, we are preparing the detectors of the STAR experiment. For starters, we make sure that we can ramp up the solenoidal magnet (the S in STAR) and flow the flammable gas in our tracker (the T in STAR), called the TPC. Without actual beam collisions we are able to set up our detectors to trigger for cosmic rays, i.e. the muons that are the decay products of energetic protons hitting the earth's atmosphere, leading to large particle showers that include many pions (the lightest mesons). These pions subsequently decay into muons (and neutrinos, which the STAR detector does not see). Even muons don't have eternal life, but thanks to special relativity (and their high velocity) we can still see them as they zap through our detector before turning into electrons. The video below shows our detector registring single muons. If you look carefully then you can see some of the tracks have some curvature. That's the magnetic field acting upon the charged particles! You also see that some tracks appear broken up in pieces. Well, that's why we start this testing well ahead of our operations using beam collisions: we are using these tracks to check each and every piece of our detectors!
Click on the picture below to see a ~45second GIF of incoming cosmic rays.
Meanwhile, we are preparing the detectors of the STAR experiment. For starters, we make sure that we can ramp up the solenoidal magnet (the S in STAR) and flow the flammable gas in our tracker (the T in STAR), called the TPC. Without actual beam collisions we are able to set up our detectors to trigger for cosmic rays, i.e. the muons that are the decay products of energetic protons hitting the earth's atmosphere, leading to large particle showers that include many pions (the lightest mesons). These pions subsequently decay into muons (and neutrinos, which the STAR detector does not see). Even muons don't have eternal life, but thanks to special relativity (and their high velocity) we can still see them as they zap through our detector before turning into electrons. The video below shows our detector registring single muons. If you look carefully then you can see some of the tracks have some curvature. That's the magnetic field acting upon the charged particles! You also see that some tracks appear broken up in pieces. Well, that's why we start this testing well ahead of our operations using beam collisions: we are using these tracks to check each and every piece of our detectors!
Click on the picture below to see a ~45second GIF of incoming cosmic rays.
STAR Collaboration Meeting
March 08, 2025
The STAR collaboration meeting is a great opportunity to learn about the many exciting analyses that are performed by as many students and postdocs. Two days of parallel sessions, for each PWG, are followed by two days of plenary discussions on physics and our future endeavours were preceded by a dedicated workshop on the endcap TOF detector and a Junior's Day.
More details, including the agenda can be found on this page: https://indico.bnl.gov/event/26119/
No meeting without a group picture!
(courtesy BNL 2025)
More details, including the agenda can be found on this page: https://indico.bnl.gov/event/26119/
No meeting without a group picture!
(courtesy BNL 2025)
Confinement and Symmetries in the QCD Phase Diagram
February 16, 2025
I asked ChatGPT to summarize our current understanding of the Quark-Gluon Plasma, and this is what it wrote for me (see below). While I can understand that it blissfully “forgets” the foundational work that facilities like CERN’s SPS, BNL’s AGS, and GSI’s SIS have done, its description has a few other intriguing, let’s say, inaccuracies. Lattice QCD, a powerful tool in the theory community, still faces significant challenges in describing conditions that more realistically correspond to energy regimes, typically at and below those provided by RHIC. Additionally, the notion of two distinct phases, such as a gas of hadrons versus free quarks and gluons, remains a debatable and potentially inaccurate description of the so-called phase diagram of hot and dense nuclear matter.
So, workshops like this one attempt to address this from a purely theoretical perspective: “Confinement and symmetry from vacuum to QCD phase diagram.” I was fortunate enough be invited to this workshop as the sole experimentalist, presenting experimental observations that should provide theoretical guidance, although it often requires that as well. While it was undoubtedly a very technical workshop, and I must admit that I often lost track of most talks after their introductory slides, I thoroughly enjoyed listening to the discussions and their physical motivations and constructs. Of course, convincing experimentalists that there are more than three color charges in QCD, let alone an infinite number, will be challenging. Additionally, extracting an imaginary chemical potential from our particle yields and spectra may seem difficult. Nevertheless, the underlying physical reasoning and mathematical concepts are relevant and inspiring.
Unfortunately, I don't ski, so I did miss out as some of the discussions continued in ski lifts and, presumably, downhill slopes.
Current Understanding of Quark-Gluon Plasma (QGP)
Introduction:
Quark-Gluon Plasma (QGP) is a state of matter in which quarks and gluons, the fundamental constituents of protons and neutrons, are not confined within hadrons, but exist freely. This state is believed to have existed microseconds after the Big Bang and can be recreated in high-energy heavy-ion collisions in particle accelerators such as the Large Hadron Collider (LHC) at CERN.
Properties of QGP:
High Temperature and Energy: QGP is formed at extremely high temperatures, exceeding 2 trillion Kelvin, where quarks and gluons are free from the strong force that typically binds them inside protons and neutrons. Color Confinement and Deconfinement: In normal conditions, quarks are confined within hadrons. In QGP, they are deconfined, allowing quark-gluon interactions to be studied without confinement. Fluid-Like Nature: Experiments have shown that QGP behaves like a nearly perfect fluid with very low viscosity, unlike traditional gases or plasmas. Thermalization and Collective Motion: QGP undergoes rapid thermalization, leading to collective flow patterns, which are studied through observables like elliptic flow.
Experimental Observations:
Heavy-Ion Collisions: Experiments at the LHC and RHIC (Relativistic Heavy Ion Collider) have recreated QGP conditions by colliding heavy ions at near-light speeds. Jet Quenching: The suppression of high-energy jets in QGP serves as a probe of its density and the interactions within. Direct Photon and Dilepton Production: Photons and dileptons, unaffected by the strong force, provide insight into the initial conditions and temperature of the QGP.
Theoretical Developments:
Lattice QCD: Quantum chromodynamics (QCD) simulations on lattice frameworks provide theoretical insights into the properties of QGP at different temperatures and densities. Hydrodynamic Models: These models mimic the QGP's fluid-like behavior, aiding in understanding its evolution and observable phenomena in collisions.
Challenges and Future Directions:
Despite advances, understanding the precise mechanisms of QGP formation, its thermalization, and transition back to hadronic matter remains challenging. Future research aims to explore QGP properties at even higher temperatures, study its behavior in smaller systems, and understand the quark-hadron phase transition.
In summary, the study of QGP provides critical insights into the fundamental forces and early universe conditions. With ongoing experiments and theoretical advancements, our understanding continues to grow, revealing the complex dynamics of this unique state of matter.
So, workshops like this one attempt to address this from a purely theoretical perspective: “Confinement and symmetry from vacuum to QCD phase diagram.” I was fortunate enough be invited to this workshop as the sole experimentalist, presenting experimental observations that should provide theoretical guidance, although it often requires that as well. While it was undoubtedly a very technical workshop, and I must admit that I often lost track of most talks after their introductory slides, I thoroughly enjoyed listening to the discussions and their physical motivations and constructs. Of course, convincing experimentalists that there are more than three color charges in QCD, let alone an infinite number, will be challenging. Additionally, extracting an imaginary chemical potential from our particle yields and spectra may seem difficult. Nevertheless, the underlying physical reasoning and mathematical concepts are relevant and inspiring.
Unfortunately, I don't ski, so I did miss out as some of the discussions continued in ski lifts and, presumably, downhill slopes.
ChatGPT:
Current Understanding of Quark-Gluon Plasma (QGP)
Introduction:
Quark-Gluon Plasma (QGP) is a state of matter in which quarks and gluons, the fundamental constituents of protons and neutrons, are not confined within hadrons, but exist freely. This state is believed to have existed microseconds after the Big Bang and can be recreated in high-energy heavy-ion collisions in particle accelerators such as the Large Hadron Collider (LHC) at CERN.
Properties of QGP:
Experimental Observations:
Theoretical Developments:
Challenges and Future Directions:
In summary, the study of QGP provides critical insights into the fundamental forces and early universe conditions. With ongoing experiments and theoretical advancements, our understanding continues to grow, revealing the complex dynamics of this unique state of matter.