In
high-energy physics
Particle physics or high energy physics is the study of fundamental particles and forces that constitute matter and radiation. The fundamental particles in the universe are classified in the Standard Model as fermions (matter particles) a ...
, 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 fo ...
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. Particles currently thought to be elementary include electrons, the fundamental fermions ( quarks, leptons, ...
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
The chronology of the universe describes the history and future of the universe according to Big Bang cosmology.
Research published in 2015 estimates the earliest stages of the universe's existence as taking place 13.8 billion years ago, with ...
, 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 (; grc, ἁδρός, hadrós; "stout, thick") is a composite subatomic particle made of two or more quarks held together by the strong interaction. They are analogous to molecules that are held together by the ...
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 nuclei. All commonly ...
s and
gluon
A gluon ( ) is an elementary particle that acts as the exchange particle (or gauge boson) for the strong force between quarks. It is analogous to the exchange of photons in the electromagnetic force between two charged particles. Gluons bind ...
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 thermal (local kinetic) and (close to) chemical (abundance) equilibrium. The word ''plasma'' signals that free color charges are allowed. In a ...
(QGP). In this realm, the laws of physics that apply are those of
quantum chromodynamics
In theoretical physics, quantum chromodynamics (QCD) is the theory 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 ...
(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, quantum chromodynamics (QCD) is the theory 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 o ...
, 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) processe ...
produced in the initial stage of a nucleus-nucleus collision will undergo multiple interactions inside the collision region prior to
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 ...
. 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 by a ...
(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-mass energy of 2.76 and 5.02 TeV at the
Large Hadron Collider
The Large Hadron Collider (LHC) is the world's largest and highest-energy particle collider. It was built by the European Organization for Nuclear Research (CERN) between 1998 and 2008 in collaboration with over 10,000 scientists and hundr ...
(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 a northwestern suburb of Gen ...
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 maps of Earth or of a region of Earth.
Atlases have traditionally been bound into book form, but today many atlases are in multimedia formats. In addition to presenting geogra ...
,
CMS
CMS may refer to:
Computing
* Call management system
* CMS-2 (programming language), used by the United States Navy
* Code Morphing Software, a technology used by Transmeta
* Collection management system for a museum collection
* Color manage ...
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 ...
.
See also
*
Parity (physics)
In physics, a parity transformation (also called parity inversion) is the flip in the sign of ''one'' spatial coordinate. In three dimensions, it can also refer to the simultaneous flip in the sign of all three spatial coordinates (a point ref ...
References
External links
Jet Suppression in Heavy Ion CollisionsJetting through the Quark SoupReview of Jet Quenching (2017)Review of Jet Quenching (2009)
Experimental particle physics
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