high-energy physics Particle physics or high-energy physics is the study of fundamental particles and forces that constitute matter and radiation. The field also studies combinations of elementary particles up to the scale of protons and neutrons, while the stu ...

, jet quenching is a phenomenon that can occur in the

collision In physics, a collision is any event in which two or more bodies exert forces on each other in a relatively short time. Although the most common use of the word ''collision'' refers to incidents in which two or more objects collide with great for ...

of ultra-high-energy particles. In general, the collision of high-energy particles can produce jets of

elementary particle In particle physics, an elementary particle or fundamental particle is a subatomic particle that is not composed of other particles. The Standard Model presently recognizes seventeen distinct particles—twelve fermions and five bosons. As a c ...

s that emerge from these collisions. Collisions of ultra-relativistic heavy-ion particle beams create a hot and dense medium comparable to the conditions in the early universe, and then these jets interact strongly with the medium, leading to a marked reduction of their energy. This energy reduction is called "jet quenching".

Physics background

In the context of high-energy

hadron In particle physics, a hadron is a composite subatomic particle made of two or more quarks held together by the strong nuclear force. Pronounced , the name is derived . They are analogous to molecules, which are held together by the electri ...

collisions,

quark A quark () is a type of elementary particle and a fundamental constituent of matter. Quarks combine to form composite particles called hadrons, the most stable of which are protons and neutrons, the components of atomic nucleus, atomic nuclei ...

s and

gluon A gluon ( ) is a type of Massless particle, massless elementary particle that mediates the strong interaction between quarks, acting as the exchange particle for the interaction. Gluons are massless vector bosons, thereby having a Spin (physi ...

s are collectively called partons. The jets emerging from the collisions originally consist of partons, which quickly combine to form hadrons, a process called

hadronization Hadronization (or hadronisation) is the process of the formation of hadrons out of quarks and gluons. There are two main branches of hadronization: quark-gluon plasma (QGP) transformation and colour string decay into hadrons. The transformation o ...

. Only the resulting hadrons can be directly observed. The hot, dense medium produced in the collisions is also composed of partons; it is known as a

quark–gluon plasma Quark–gluon plasma (QGP or quark soup) is an interacting localized assembly of quarks and gluons at Thermodynamic equilibrium#Local and global equilibrium, thermal (local kinetic) and (close to) chemical (abundance) equilibrium. The word ''plasm ...

(QGP). In this realm, the laws of physics that apply are those of

quantum chromodynamics In theoretical physics, quantum chromodynamics (QCD) is the study of the strong interaction between quarks mediated by gluons. Quarks are fundamental particles that make up composite hadrons such as the proton, neutron and pion. QCD is a type of ...

(QCD). High-energy nucleus–nucleus collisions make it possible to study the properties of the QGP medium through the observed changes in the jet fragmentation functions as compared to the unquenched case. According to

QCD In theoretical physics Theoretical physics is a branch of physics that employs mathematical models and abstractions of physical objects and systems to rationalize, explain, and predict List of natural phenomena, natural phenomena. This is in ...

, high-momentum

partons In particle physics, the parton model is a model of hadrons, such as protons and neutrons, proposed by Richard Feynman. It is useful for interpreting the cascades of radiation (a parton shower) produced from quantum chromodynamics (QCD) processes ...

produced in the initial stage of a nucleus–nucleus collision will undergo multiple interactions inside the collision region prior to

. In these interactions, the energy of the partons is reduced through collisional energy loss and medium-induced gluon radiation, 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. 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 QGP medium created in the collisions.

Experimental evidence of jet quenching

First evidence of parton energy loss has been observed at the

Relativistic Heavy Ion Collider The Relativistic Heavy Ion Collider (RHIC ) is the first and one of only two operating heavy- ion colliders, and the only spin-polarized proton collider ever built. Located at Brookhaven National Laboratory (BNL) in Upton, New York, and used ...

(RHIC) from the suppression of high-pt particles studying the nuclear modification factor and the suppression of back-to-back correlations. In ultra-relativistic heavy-ion collisions at center-of-momentum energy of at the

Large Hadron Collider The Large Hadron Collider (LHC) is the world's largest and highest-energy particle accelerator. It was built by the CERN, European Organization for Nuclear Research (CERN) between 1998 and 2008, in collaboration with over 10,000 scientists, ...

(LHC), interactions between the high-momentum parton and the hot, dense medium produced in the collisions, are expected to lead to jet quenching. Indeed, in November 2010

CERN The European Organization for Nuclear Research, known as CERN (; ; ), is an intergovernmental organization that operates the largest particle physics laboratory in the world. Established in 1954, it is based in Meyrin, western suburb of Gene ...

announced the first direct observation of jet quenching, based on experiments with ''heavy-ion collisions'', which involved

ATLAS An atlas is a collection of maps; it is typically a bundle of world map, maps of Earth or of a continent or region of Earth. Advances in astronomy have also resulted in atlases of the celestial sphere or of other planets. Atlases have traditio ...

CMS CMS may refer to: Computing * Call management system * CMS-2, a programming language implemented for and used by the United States Navy * Code Morphing Software, a technology used by Transmeta * Collection management system for a museum coll ...

and

ALICE Alice may refer to: * Alice (name), most often a feminine given name, but also used as a surname Literature * Alice (''Alice's Adventures in Wonderland''), a character in books by Lewis Carroll * ''Alice'' series, children's and teen books by ...

References

External links

Jet Suppression in Heavy Ion Collisions

Jetting through the Quark Soup

Review of Jet Quenching (2017)

Review of Jet Quenching (2009)
Experimental particle physics {{particle-stub

Physics background

Experimental evidence of jet quenching

See also

References

External links