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STAR Physicists Track Sequential 'Melting' of Upsilons

The STAR (Solenoidal Tracker at RHIC) collaboration has been studying the behavior of quark-gluon plasma (QGP) at the Relativistic Heavy Ion Collider (RHIC) for over two decades. Recently, they have made a breakthrough in understanding the sequential "melting" of upsilons, a type of heavy quarkonium, in QGP. This article will explore the significance of this discovery and its implications for our understanding of QGP.

What is Quark-Gluon Plasma?

Before delving into the specifics of the STAR collaboration's research, it is important to understand what quark-gluon plasma is. QGP is a state of matter that existed in the early universe, just microseconds after the Big Bang. It is created by colliding heavy ions, such as gold or lead nuclei, at high energies. These collisions cause the ions to break apart into their constituent quarks and gluons, which then interact with each other to form a hot and dense soup-like substance.

The Role of Heavy Quarkonia in QGP

Heavy quarkonia, such as upsilons and charmoniums, are bound states of heavy quarks and their anti-quarks. They are important probes for studying QGP because they are sensitive to its temperature and density. In particular, upsilons are useful because they are relatively long-lived compared to other heavy quarkonia, which allows them to travel through QGP and interact with it before decaying.

The STAR Collaboration's Research

The STAR collaboration has been studying upsilon production in heavy ion collisions at RHIC for many years. In their recent study, they looked specifically at sequential suppression, which refers to the phenomenon where higher excited states of upsilons are more strongly suppressed than lower excited states.

To study this phenomenon, the STAR collaboration used data from collisions between gold nuclei at energies of 200 GeV per nucleon pair. They measured the production of different excited states of upsilons and compared their yields to what would be expected in the absence of QGP. They found that the suppression of higher excited states was indeed stronger than that of lower excited states, consistent with sequential suppression.

Implications for Our Understanding of QGP

The STAR collaboration's discovery has important implications for our understanding of QGP. Sequential suppression was predicted by theoretical models, but until now it had not been observed experimentally. The fact that it has now been observed provides strong evidence that QGP behaves as expected based on these models.

Furthermore, the STAR collaboration's results suggest that upsilons "melt" sequentially as they travel through QGP. This means that the higher excited states "melt" at lower temperatures and densities than the lower excited states. This information can be used to refine our theoretical models of QGP and improve our understanding of its properties.

Conclusion

The STAR collaboration's recent discovery of sequential "melting" of upsilons in quark-gluon plasma is an important breakthrough in our understanding of this exotic state of matter. By studying the behavior of heavy quarkonia in QGP, we can gain insights into its temperature and density, as well as refine our theoretical models. This research has important implications for both particle physics and cosmology, and we can expect further breakthroughs in the coming years.

FAQs

1. What is quark-gluon plasma?

Quark-gluon plasma is a state of matter that existed in the early universe, just microseconds after the Big Bang. It is created by colliding heavy ions at high energies.

2. What are heavy quarkonia?

Heavy quarkonia are bound states of heavy quarks and their anti-quarks. They are useful probes for studying quark-gluon plasma because they are sensitive to its temperature and density.

3. What is sequential suppression?

Sequential suppression is the phenomenon where higher excited states of heavy quarkonia are more strongly suppressed than lower excited states in quark-gluon plasma.

4. Why is the STAR collaboration's discovery important?

The STAR collaboration's discovery of sequential "melting" of upsilons provides strong evidence that quark-gluon plasma behaves as expected based on theoretical models. It also allows us to refine our understanding of its properties.

5. What are the implications of this research?

This research has important implications for both particle physics and cosmology, as it provides insights into the behavior of matter in extreme conditions. It also has practical applications, such as improving our understanding of nuclear fusion and developing new materials for high-temperature environments.

This abstract is presented as an informational news item only and has not been reviewed by a subject matter professional. This abstract should not be considered medical advice. This abstract might have been generated by an artificial intelligence program. See TOS for details.

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qgp (4), plasma (3), quark-gluon (3), star (3)