麻豆淫院

At the end of next year, CERN鈥檚 Large Hadron Collider (LHC) is scheduled to go online. Already, there are four major experiments planned and one of them, ALICE, is dedicated to the study of heavy-ion collisions. Rudolph Hwa, a professor at the University of Oregon, says that the objective of a heavy-ion collider is to produce quark-gluon plasma (QGP), which is thought to be the matter existent at the beginning of the universe, just after the Big Bang.

Hwa鈥檚 interest in the scheduled experiments at LHC is related to a Letter published July 26 in 麻豆淫院ical Review Letters. Together with his collaborator, Chunbin Yang at Hua-Zhong Normal University in the People鈥檚 Republic of China, Hwa has written a paper, titled 鈥淧roton Enhancement at Large pT at the CERN Large Hadron Collider without Structure in Associated-Particle Distribution,鈥� describing a way to determine how quarks and gluons turn into hadrons.

鈥淭here is no way to detect the quarks or gluons directly,鈥� Hwa explains to 麻豆淫院Org.com. 鈥淏ut they turn into hadrons 鈥� protons and pions 鈥� and these we can detect. That step in between is called hadronization.鈥�

Hwa says that 鈥渢here are two possible ways that hadronization can occur: fragmentation and recombination.鈥�

Hwa explains that fragmentation is the conventional wisdom. 鈥淚t鈥檚 been tested in other experiments where the colliding particles are electrons or protons and where no QGP has been produced. It鈥檚 been applied to heavy-ion collisions at LHC.鈥� He pauses. 鈥淏ut if a super-dense medium like a QGP can be created at LHC, fragmentation may not be the most important process in certain regions.鈥�

Hwa and Yang see a different possibility. 鈥淲e question whether another mechanism is more relevant 鈥� recombination.鈥� Explains Hwa: 鈥淭he paper attempts to correct a prejudice in the conventional thinking about multiparticle production in high-energy nuclear collisions. When the density of jets produced is high, the recombination of shower quarks in adjacent jets can be the dominant process in hadronization.鈥�

The Letter also explains how ALICE experimenters could possibly determine which mechanism is the correct explanation for hadronization. By analyzing the results of the experiment, it should be possible to determine the correct scenario by the ratio of pions to protons produced. 鈥淚n the case of fragmentation,鈥� says Hwa, 鈥測ou would see more pions than protons. In the case of recombination, the opposite is true. You would detect more protons than pions.鈥�

Hwa and Yang鈥檚 Letter also points out a notable lack of associated particles distinguished from the background in the recombination scenario: 鈥淲ith fragmentation, you see a particle coming out identified as a trigger and find that there are other particles associated with it. With recombination, we predict that the associated particles will be indistinguishable from the background.鈥�

鈥淥ur paper is mostly academic,鈥� explains Hwa, 鈥渨ith little significant societal impact. Hadronization is only the final part of the overall process in a heavy-ion collision. But it is necessary to understand it properly in order to determine what is going on in the middle of this small but very dense medium. We are trying to say that it is possible that something different may be happening in the last step. Something different from the conventional wisdom.鈥�

Hwa hopes that the ideas in his and Yang鈥檚 Letter will be considered when the data from the experiments at LHC are analyzed two or three years down the road. 鈥淭his is a technical point,鈥� explains Hwa, 鈥渂ut if you don鈥檛 know the process, how will you be able to know reliably what goes on inside the quark-gluon plasma?鈥�

And, after all, learning about quark-gluon plasma is the point of the experiments on heavy-ion collisions at the CERN LHC.

By Miranda Marquit, Copyright 2006 麻豆淫院Org.com