Jet quenching

In ultra-relativistic heavy-ion collisions at center-of-mass energy of 5.5 TeV at the Large Hadron Collider (LHC), interactions between the high-momentum Parton and the hot, dense medium produced in the collisions, are expected to lead to jet energy loss, the so-called jet quenching, resulting in changes in the jet fragmentation functions as compared to the unquenched case.
High-energy nucleus–nucleus collisions allow us to change the scene of parton fragmentation from vacuum to a QCD medium, the Quark gluon plasma (QGP), and to studythe properties of this medium through modifications of the jet structure. High-momentum partons produced in the initial stage of a nucleus–nucleus collision are expected to undergo multiple interactions inside the collision region prior to hadronisation. Hereby, the energy of the partons is reduced through collisional energy loss [1] and medium-induced gluon radiation [2] , the latter being the dominant mechanism in a QGP. The effect of jet quenching in QGP is the main motivation for studying jets as well as high-momentum particle spectra and particle correlations in heavy-ion collisions.
First evidence of parton energy loss has been observed at RHIC from the suppression of high-pt particles studying the nuclear modification factor [3] and the suppression of back-to-back correlations [4] .
Accurate jet reconstruction will allow measurements of the jet fragmentation functions and consequently the degree of quenching and therefore provide insight on the properties of the hot dense medium (QGP) created in the collisions.

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References

[1] D. H. Perkins, Introduction to High Energy Physics, Cambridge University Press (2000);
[2] D. Gross and F. Wilczek, Phys. Rev. Lett. 30, 1343 (1973)
[3] Adcox K et al (PHENIX Collaboration) 2002 Phys. Rev. Lett. 88 022301
[4] Adler C et al (STAR Collaboration) 2003 Phys. Rev. Lett. 90 082302