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Showing posts with label Jet Quenching. Show all posts
Showing posts with label Jet Quenching. Show all posts

Friday, April 27, 2012

Particle Constructs

Several large experimental groups are hot on the trail of this elusive subatomic particle which is thought to explain the origins of particle mass.  Higgs Update Today

What use the Higg's Mechanism?

Just as one might look at GRB examples of motivation that come to us in natural cosmic particle collisions, by looking back in time is it not to strange to wonder how such compositions are given to the contacts  and explorations of where any beginnings may materialize. So we are given clues?

The structure is being detail as if in association to identifying the elements in between Mendeleev's elemental table components? Seaborg's octaves? It is an analogy in comparison as you might track LHC components of particle expressions?


this increases his resistance to movement, in other words, he acquires mass, just like a particle moving through the Higgs field

Latest research can pinpoint what I am saying yet it is through such expressions we might ask how is it an Einstein crossing the room can gather so many minds and ideas to it? Can we say then that consciousness is much the same, yet, it isn't the idea of a heat death that such notions are not palatable with what happens in the brain but the idea that new ideas can enter. You see?



See Also:

Tuesday, November 08, 2011

Elementary Particles in the Decay Chain

 The general theory of relativity is as yet incomplete insofar as it has been able to apply the general principle of relativity satisfactorily only to gravitational fields, but not to the total field. We do not yet know with certainty by what mathematical mechanism the total field in space is to be described and what the general invariant laws are to which this total field is subject. One thing, however, seems certain: namely, that the general principal of relativity will prove a necessary and effective tool for the solution of the problem for the total field.Out of My Later Years, Pg 48, Albert Einstein (bold added for emphasis by me)

What anchors me to reality is the understanding that what will be displayed in the particle chain and here there was some debate in my mind.....literately..... I seem to be questioning whether this decay chain or elementary connection should even be described as a chain. What had me thinking this way is how pervasive we could say energy is inclusive as a statement that we might say the chain of events lists all that is of value in that energy disposition. Cosmic Ray Spallation,  or Jet, seemed fitting to me that such articulation of the collision process would have amounted to so many descriptions of the one thing contained in the dissipation of energy.



I am not even sure of what I am talking about here.....but as most times my mind seems to be working even while I am suppose to be asleep. I catch the tail end of things and and do you think it is ever clear what it is I am after in my understanding to know that I could write it all down and be so perfecting clear. And as a layman to boot,  how confusing I could make it for others.

Once produced, the neutral Xi-sub-b (Symbol for Xi-sub-b) particle travels about a millimeter before it disintegrates into two particles: the short-lived, positively charged Xi-sub-c (Symbol Xi-sub-c^+) and a long-lived, negative pion (π-). The Xi-sub-c then promptly decays into a pair of long-lived pions and a Xi particle (Symbol pi^-), which lives long enough to leave a track in the silicon vertex system (SVX) of the CDF detector before it decays a pion and a Lambda (Λ). The Lambda particle, which has no electric charge, can travel several centimeters before decaying into a proton (p) and a pion (π). Credit: CDF collaboration and Fermi

Well such things start often by the exposure of the many pictures that I have captured on the internet in order to understand that such decay chains are relevant I think in how we see the development of the hierarchy of energy used to determine particle collisions. Of course I am not a scientist so I have to be really careful here.

Six of the particles in the Standard Model are quarks (shown in purple). Each of the first three columns forms a generation of matter.

***


So while I am never completely sure in my entirety the journey through science can I say has been with such consistency? Could I say my classroom has been all over the place and my enduring appeal for knowledge could have been the dissemination of so many wrong things.

I truly do not understand at what point that I started to be the convert to a relativistic discretion of the world as a legitimate expression of the universe contained in our undertaking of the decay chain. Is this what the debating is all about in my mind as I wrestle to explain where I have been and where I am going?

Foundations of Big Bang Cosmology




So for me what does this all have to do with the basis of how we might look at the cosmos and see such description will help us form a geometrical presence of the universe to know that we are using a relativistic interpretation to actually help us to describe the nature of expression of the universe as Omega.


Friedman Equation What is pdensity.
What are the three models of geometry? k=-1, K=0, k+1
Omega=the actual density to the critical density
If we triangulate Omega, the universe in which we are in, Omegam(mass)+ Omega(a vacuum), what position geometrically, would our universe hold from the coordinates given? See: Non Euclidean Geometry and the Universe

So while I am working to be consistent with the understanding of dimensional representation of the universe one may see how I have catapulted myself past the euclidean description of the world to move into the relativistic realm of expression based in  geometrical expressions. This allowed me to contained my views on Cherenkov as relativistic expressions detailed in an area that one may of assigned to missing energy events.


Further it may be of some help to understand that by "developing an theorem for particulate expression in relation to dimensional attribution" was significant to me (degrees of freedom) to have such development along side of the development of geometry as a viable approach to furthering our looking into the very nature of the world in which we live.  Genus figure descriptions contained in the valley have to be developed in relation to how we see possible expression, as a sign of the pencil falling one way or how a stone may roll down a hill, as a asymmetrical expression of the way in which the universe began and developed along the decay chain of energy dissipation?

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Friday, November 04, 2011

Jet Manifestation: A World Unto Itself.

The Landscape Again and again....

***

(September 20, 2010) Leonard Susskind gives a lecture on the string theory and particle physics. He is a world renown theoretical physicist and uses graphs to help demonstrate the theories he is presenting.

String theory (with its close relative, M-theory) is the basis for the most ambitious theories of the physical world. It has profoundly influenced our understanding of gravity, cosmology, and particle physics. In this course we will develop the basic theoretical and mathematical ideas, including the string-theoretic origin of gravity, the theory of extra dimensions of space, the connection between strings and black holes, the "landscape" of string theory, and the holographic principle.

This course was originally presented in Stanford's Continuing Studies program.

Stanford University:
http://www.stanford.edu/

Stanford Continuing Studies Program:
http://csp.stanford.edu/

Stanford University Channel on YouTube:
http://www.youtube.com/stanford

 Playlist

***
Quarks, gluons and anti-quarks are the constituents of protons, neutrons and (by definition) other hadrons.  It is a fascinating aspect of the physics of our world that when one of these particles is kicked out of the hadron that contains it, flying out with high motion-energy, it is never observed macroscopically. Instead, a high-energy quark (or gluon or anti-quark) is transformed into a spray of hadrons [particles made from quarks, antiquarks and gluons].  This spray is called a “jet.” [Note this statement applies to the five lighter flavors of quark, and not the top quark, which decays to a W particle and a bottom quark before a jet can form.] See: Jets: The Manifestation of Quarks and Gluons

***

See Also:

Tuesday, November 01, 2011

The Developmental Jet Process

As a layman I have been going through the research of those better educated then I in order to construct a accurate syntactically written developed scientific process as I have become aware of it. This is what I have been doing for the last number of years so as to get some idea of the scientific process experimentally driven to this point.

Theoretical development is important to myself,  as well as,   the underlying quest for a foundational perspective of how we can push back perspective with regard to the timeline of the universe in expression.

This has to be experimentally written in the processes we now use to help formulate an understanding of how the universe came into being by examining local events with the distribution of the cosmological data we are accumulating. A Spherical Cow anyone?


Jets: Article Updated An update here as well, "Two-Photons: Data and Theory Disagree"

I do appreciate all those scientist who have been giving their time to educating the public. This is a big thank you for that devotion to the ideal of bringing society forward as to what we as a public are not privy too. As too, being not part of that 3% of the population who are far removed from the work being done in particle research.

Almost a year ago, I had an e-mail exchange, and planned a phone call, with Maria Spiropulu of CMS. She looked particularly excited about something and the mortals may be learning what the cause was today.

CMS turned out to be much more "aggressive" relatively to the "conservative" ATLAS detector and it has already provided us with some hints. But what they published today, in the paper called: See:
CMS: a very large excess of diphotons
***

Measurement of the Production Cross Section for Pairs of Isolated Photons in pp collisions at sqrt(s) = 7 TeV
The integrated and differential cross sections for the production of pairs of isolated photons is measured in proton-proton collisions at a centre-of-mass energy of 7 TeV with the CMS detector at the LHC. A data sample corresponding to an integrated luminosity of 36 inverse picobarns is analysed. A next-to-leading-order perturbative QCD calculation is compared to the measurements. A discrepancy is observed for regions of the phase space where the two photons have an azimuthal angle difference, Delta(phi), less than approximately 2.8. 
 ***

Tscan

Tscan ("Trivial Scanner") is an event display, traditionally called a scanner, which I developed. It is a program that shows events graphically on the computer screen.

It was designed to be simple ("trivial") internally, and to have a simple user interface. A lot of importance was given to giving the user a large choice of options to display events in many different ways.

Tscan proved to be a very useful tool for the development of fitters. A particularly useful feature is the ability to show custom data for every photpmultiplier tube (PMT). Instead of the usual time and charge, it can show expected charge, scattered light, likelihood, chi-squared difference, patches, and any other data that can be prepared in a text format.
See:Trivial Scanner

Credit: Super-Kamiokande/Tomasz Barszczak Three (or more?) Cerenkov rings

Multiple rings of Cerenkov light brighten up this display of an event found in the Super-Kamiokande - neutrino detector in Japan. The pattern of rings - produced when electrically charged particles travel faster through the water in the detector than light does - is similar to the result if a proton had decayed into a positron and a neutral pion. The pion would decay immediately to two gamma-ray photons that would produce fuzzy rings, while the positron would shoot off in the opposite direction to produce a clearer ring. Such kinds of decay have been predicted by "grand unified theories" that link three of nature's fundamental forces - the strong, weak and electromagnetic forces. However, there is so far no evidence for such decays; this event, for example, did not stand up to closer scrutiny.
See:



Update

See Also:



  • 2010 ion run: completed!
  • What Does the Higgs Jet Energy Sound Like?
  • Monday, July 11, 2011

    ALICE Enters New Territory

    A computer screen in the ALICE control room shows an event display on the night of the first heavy-ion collisions in the LHC in November 2010.
    A basic process in QCD is the energy loss of a fast parton in a medium composed of colour charges. This phenomenon, "jet quenching", is especially useful in the study of the QGP, using the naturally occurring products (jets) of the hard scattering of quarks and gluons from the incoming nuclei. A highly energetic parton (a colour charge) probes the coloured medium rather like an X-ray probes ordinary matter. The production of these partonic probes in hadronic collisions is well understood within perturbative QCD. The theory also shows that a parton traversing the medium will lose a fraction of its energy in emitting many soft (low energy) gluons. The amount of the radiated energy is proportional to the density of the medium and to the square of the path length travelled by the parton in the medium. Theory also predicts that the energy loss depends on the flavour of the parton.

    Jet quenching was first observed at RHIC by measuring the yields of hadrons with high transverse momentum (pT). These particles are produced via fragmentation of energetic partons. The yields of these high-pT particles in central nucleus–nucleus collisions were found to be a factor of five lower than expected from the measurements in proton–proton reactions. ALICE has recently published the measurement of charged particles in central heavy-ion collisions at the LHC. As at RHIC, the production of high-pT hadrons at the LHC is strongly suppressed. However, the observations at the LHC show qualitatively new features (see box). The observation from ALICE is consistent with reports from the ATLAS and CMS collaborations on direct evidence for parton energy loss within heavy-ion collisions using fully reconstructed back-to-back jets of particles associated with hard parton scatterings (CERN Courier January/February 2011 p6 and March 2011 p6). The latter two experiments have shown a strong energy imbalance between the jet and its recoiling partner (G Aad et al. 2010 and CMS collaboration 2011). This imbalance is thought to arise because one of the jets traversed the hot and dense matter, transferring a substantial fraction of its energy to the medium in a way that is not recovered by the reconstruction of the jets.See: ALICE enters new territory in heavy-ion collisions

    Click no Image for larger viewing

    Friday, July 08, 2011

    QGP Advances

    Even the famous helium-3, which can flow out of a container via capillary forces, does not count as a perfect fluid.What black holes teach about strongly coupled particles by Clifford V. Johnson and Peter Steinberg....May of Last Year.

    If helium-3 is used in cooling energy containment and was to be considered within LHC, wouldn't such example be applicable as to thinking about capillary routes as holes? Energy loss attributed too?

    Layman wondering.


    The notion of a perfect fluid arises in many fields of physics. The term can be applied to any system that is in local equilibrium and has negligible shear viscosity η. In everyday life, viscosity is a familiar property associated with the tendency of a substance to resist flow. From a microscopic perspective, it is a diagnostic of the strength of the interactions between a fluid’s constituents. The shear viscosity measures how disturbances in the system are transmitted to the rest of the system through interactions. If those interactions are strong, neighboring parts of the fluid more readily transmit the disturbances through the system (see figure 1). Thus low shear viscosities indicate significant interaction strength. The ideal gas represents the opposite extreme—it is a system with no interactions and infinite shear viscosity.


    Perfect fluids are easy to describe, but few substances on Earth actually behave like them. Although often cited as a low-viscosity liquid, water in fact has a substantial viscosity, as evidenced by its tendency to form eddies and whorls when faced with an obstacle, rather than to flow smoothly as in ideal hydrodynamics. Even the famous helium-3, which can flow out of a container via capillary forces, does not count as a perfect fluid. What black holes teach about strongly coupled particles

    The interesting thing for me as a layman  was about the theoretic in String Theory research is the idea of pushing perspective back in terms of the Microseconds. So for me it was about looking at collision processes and see how these may be applied to cosmological data as we look out amongst the stars.


    At the recent seminar, the LHC’s dedicated heavy-ion experiment, ALICE, confirmed that QGP behaves like an ideal liquid, a phenomenon earlier observed at the US Brookhaven Laboratory’s RHIC facility. This question was indeed one of the main points of this first phase of data analysis, which also included the analysis of secondary particles produced in the lead-lead collisions. ALICE's results already rule out many of the existing theoretical models describing the physics of heavy-ions.
    See: 2010 ion run: completed!


    This is an important development in my view and I have been following for some time. The last contention in recognition for me was determinations of "the initial state" as to whether a Gas or a Fluid. How one get's there. This is phenomenologically correct as to understanding expressions of theoretic approach and application. Don't let anyone tell you different.

    While we understand Microscopic blackholes quickly dissipate, it is of great interest that if such high energy collision processes are evident in our recognition of those natural processes, then we are faced with our own planet and signals of faster then light expressions through the mediums of earth?We have created many backdrops (Calorimeters) experimentally for comparisons of energy expressions. ICECUBE.

    It is a really interesting story about the creation of our own universe in conjunction with experimental research a LHC


    Our work is about comparing the data we collect in the STAR detector with modern calculations, so that we can write down equations on paper that exactly describe how the quark-gluon plasma behaves," says Jerome Lauret from Brookhaven National Laboratory. "One of the most important assumptions we've made is that, for very intense collisions, the quark-gluon plasma behaves according to hydrodynamic calculations in which the matter is like a liquid that flows with no viscosity whatsoever."

    Proving that under certain conditions the quark-gluon plasma behaves according to such calculations is an exciting discovery for physicists, as it brings them a little closer to understanding how matter behaves at very small scales. But the challenge remains to determine the properties of the plasma under other conditions.

    "We want to measure when the quark-gluon plasma behaves like a perfect fluid with zero viscosity, and when it doesn't," says Lauret. "When it doesn't match our calculations, what parameters do we have to change? If we can put everything together, we might have a model that reproduces everything we see in our detector." See:Probing the Perfect Liquid with the STAR Grid





    Update:



    Wednesday, March 09, 2011

    Are There Extra Dimensions of Space?

    Are there Extra Dimensions of Space?

    A QGP is formed at the collision point of two relativistically accelerated gold ions in the center of the STAR detector at the relativistic heavy ion collider at the Brookhaven national laboratory.

    Some of these issues in relation to the LHC are what I tried to explain to Searosa.


    Brookhaven National Laboratory

    HOT A computer rendition of 4-trillion-degree Celsius quark-gluon plasma created in a demonstration of what scientists suspect shaped cosmic history.

    Here's what has to be considered. There is a calculated energy value to the collision process. You add that up as all the constituents of that process, and what's left is,  so much energy left to be discerned as particulate expressions as beyond that collision point. This may not be truly an accurate portrayal yet it is one that allows perspective to consider the spaces at such microscopic levels for consideration.

    The perspective of valuations with regard to the LHC is whether or not there is sufficient energy within the confines of LHC experiments in which to satisfy the questions about extra those dimensions. It seems the parameters of those decisions seem to be sufficient?


    Author(s)
    Alex Buche-University of Western Ontario / Perimeter Institute

    Robert Myers-Perimeter Institute
    Aninda Sinha-Perimeter Institute

     

    It is believed that in the first few microseconds after the Big Bang, our universe was dominated by a strongly interacting phase of nuclear matter at extreme temperatures. An impressive experimental program at the Brookhaven National Laboratory on Long Island has been studying the properties of this nuclear plasma with some rather surprising results. We outline how there may be a deep connection between extra-dimensional gravity of String Theory and the fundamental theories of subatomic particles can solve the mystery of the near-ideal fluid properties of the strongly coupled nuclear plasma.

    The QGP has directed attention to a method of expression with regard to that collision point.


    First direct observation of jet quenching.

     

    At the recent seminar, the LHC’s dedicated heavy-ion experiment, ALICE, confirmed that QGP behaves like an ideal liquid, a phenomenon earlier observed at the US Brookhaven Laboratory’s RHIC facility. This question was indeed one of the main points of this first phase of data analysis, which also included the analysis of secondary particles produced in the lead-lead collisions. ALICE's results already rule out many of the existing theoretical models describing the physics of heavy-ions.

    See: 2010 ion run: completed!


    The equations of string theory specify the arrangement of the manifold configuration, along with their associated branes (green) and lines of force known as flux lines (orange). The physics that is observed in the three large dimensions depends on the size and the structure of the manifold: how many doughnut-like "handles" it has, the length and circumference of each handle, the number and locations of its branes, and the number of flux lines wrapped around each doughnut.

    Early on looking at spaces, it was a struggle for me to understand how extra dimensions would be explained. It was easy using a coordinated frame of reference as x,y,z, yet,  how much did you have to go toward seeing that rotation around each of those arrows of direction would add greater depth of perception about such spaces?

    It's easier if you just draw the picture.

    A section of the quintic Calabi–Yau three-fold (3D projection)

    In superstring theory the extra dimensions of spacetime are sometimes conjectured to take the form of a 6-dimensional Calabi–Yau manifold, which led to the idea of mirror symmetry.

     

    The benefit of phenomenological approaches in experimental processes to attempt to answer these theoretical points of views.

     

    The first results on supersymmetry from the Large Hadron Collider (LHC) have been analysed by physicists and some are suggesting that the theory may be in trouble. Data from proton collisions in both the Compact Muon Solenoid (CMS) and ATLAS experiments have shown no evidence for supersymmetric particles – or sparticles – that are predicted by this extension to the Standard Model of particle physics. Will the LHC find supersymmetry Kate McAlpine ?


    Thank you Tommaso Dorigo

     

    Also see:

     

    Beautiful theory collides with smashing particle data."

    Implications of Initial LHC Searches for Supersymmetry"

    More SUSY limits"

    Monday, December 13, 2010

    2010 ion run: completed!

    First direct observation of jet quenching.

    At the recent seminar, the LHC’s dedicated heavy-ion experiment, ALICE, confirmed that QGP behaves like an ideal liquid, a phenomenon earlier observed at the US Brookhaven Laboratory’s RHIC facility. This question was indeed one of the main points of this first phase of data analysis, which also included the analysis of secondary particles produced in the lead-lead collisions. ALICE's results already rule out many of the existing theoretical models describing the physics of heavy-ions.
    See: 2010 ion run: completed!

    ***

    After a very fast switchover from protons to lead ions, the LHC has achieved performances that allowed the machine to exceed both peak and integrated luminosity by a factor of three. Thanks to this, experiments have been able to produce high-profile results on ion physics almost immediately, confirming that the LHC was able to keep its promises for ions as well as for protons.

    A seminar on 2 December was the opportunity for the ALICE, ATLAS and CMS collaborations to present their first results on ion physics in front of a packed auditorium. These results are important and are already having a major impact on the understanding of the physics processes that involve the basic constituents of matter at high energies.

    In the ion-ion collisions, the temperature is so high that partons (quarks and gluons), which are usually constrained inside the nucleons, are deconfined to form a highly dense and hot soup known as quark-gluon plasma (QGP). This type of matter existed about 1 millionth of a second after the Big Bang. By studying it, scientists hope to understand the processes that led to the formation of nucleons, which in turn became the nuclei of atoms. See:LHC completes first heavy-ion run

    See Also: Jets: Article Updated

    Tuesday, February 16, 2010

    Article From New York Times and More




    Brookhaven National Laboratory

    HOT A computer rendition of 4-trillion-degree Celsius quark-gluon plasma created in a demonstration of what scientists suspect shaped cosmic history.

    In Brookhaven Collider, Scientists Briefly Break a Law of Nature

    The Brookhaven scientists and their colleagues discussed their latest results from RHIC in talks and a news conference at a meeting of the American Physical Society Monday in Washington, and in a pair of papers submitted to Physical Review Letters. “This is a view of what the world was like at 2 microseconds,” said Jack Sandweiss of Yale, a member of the Brookhaven team, calling it, “a seething cauldron.”

    Among other things, the group announced it had succeeded in measuring the temperature of the quark-gluon plasma as 4 trillion degrees Celsius, “by far the hottest matter ever made,” Dr. Vigdor said. That is 250,000 times hotter than the center of the Sun and well above the temperature at which theorists calculate that protons and neutrons should melt, but the quark-gluon plasma does not act the way theorists had predicted.

    Instead of behaving like a perfect gas, in which every quark goes its own way independent of the others, the plasma seemed to act like a liquid. “It was a very big surprise,” Dr. Vigdor said, when it was discovered in 2005. Since then, however, theorists have revisited their calculations and found that the quark soup can be either a liquid or a gas, depending on the temperature, he explained. “This is not your father’s quark-gluon plasma,” said Barbara V. Jacak, of the State University at Stony Brook, speaking for the team that made the new measurements.

    It is now thought that the plasma would have to be a million times more energetic to become a perfect gas. That is beyond the reach of any conceivable laboratory experiment, but the experiments colliding lead nuclei in the Large Hadron Collider outside Geneva next winter should reach energies high enough to see some evolution from a liquid to a gas.
    See more at above link.

    ***

    Violating Parity with Quarks and Gluons
    by Sean Carroll of Cosmic Variance
    This new result from RHIC doesn’t change that state of affairs, but shows how quarks and gluons can violate parity spontaneously if they are in the right environment — namely, a hot plasma with a magnetic field.

    So, okay, no new laws of physics. Just a much better understanding of how the existing ones work! Which is most of what science does, after all
    .

    ***

    Quark–gluon plasma

    From Wikipedia, the free encyclopedia

    A QGP is formed at the collision point of two relativistically accelerated gold ions in the center of the STAR detector at the relativistic heavy ion collider at the Brookhaven national laboratory.


    A quark-gluon plasma (QGP) or quark soup[1] is a phase of quantum chromodynamics (QCD) which exists at extremely high temperature and/or density. This phase consists of (almost) free quarks and gluons, which are the basic building blocks of matter. Experiments at CERN's Super Proton Synchrotron (SPS) first tried to create the QGP in the 1980s and 1990s: the results led CERN to announce indirect evidence for a "new state of matter"[2] in 2000. Current experiments at Brookhaven National Laboratory's Relativistic Heavy Ion Collider (RHIC) are continuing this effort.[3] Three new experiments running on CERN's Large Hadron Collider (LHC), ALICE,[4] ATLAS and CMS, will continue studying properties of QGP.

    Contents

    • 1 General introduction


      • 1.1 Why this is referred to as "plasma"
      • 1.2 How the QGP is studied theoretically
      • 1.3 How it is created in the lab
      • 1.4 How the QGP fits into the general scheme of physics
    • 2 Expected properties


      • 2.1 Thermodynamics
      • 2.2 Flow
      • 2.3 Excitation spectrum
    • 3 Experimental situation
    • 4 Formation of quark matter
    • 5 See also
    • 6 References
    • 7 External links

    General introduction

    The quark-gluon plasma contains quarks and gluons, just as normal (baryonic) matter does. The difference between these two phases of QCD is that in normal matter each quark either pairs up with an anti-quark to form a meson or joins with two other quarks to form a baryon (such as the proton and the neutron). In the QGP, by contrast, these mesons and baryons lose their identities and dissolve into a fluid of quarks and gluons.[5] In normal matter quarks are confined; in the QGP quarks are deconfined.
    Although the experimental high temperatures and densities predicted as producing a quark-gluon plasma have been realized in the laboratory, the resulting matter does not behave as a quasi-ideal state of free quarks and gluons, but, rather, as an almost perfect dense fluid.[6] Actually the fact that the quark-gluon plasma will not yet be "free" at temperatures realized at present accelerators had been predicted already in 1984 [7] as a consequence of the remnant effects of confinement. 

    Why this is referred to as "plasma"

    A plasma is matter in which charges are screened due to the presence of other mobile charges; for example: Coulomb's Law is modified to yield a distance-dependent charge. In a QGP, the color charge of the quarks and gluons is screened. The QGP has other analogies with a normal plasma. There are also dissimilarities because the color charge is non-abelian, whereas the electric charge is abelian. Outside a finite volume of QGP the color electric field is not screened, so that volume of QGP must still be color-neutral. It will therefore, like a nucleus, have integer electric charge.

    How the QGP is studied theoretically

    One consequence of this difference is that the color charge is too large for perturbative computations which are the mainstay of QED. As a result, the main theoretical tools to explore the theory of the QGP is lattice gauge theory. The transition temperature (approximately 175 MeV) was first predicted by lattice gauge theory. Since then lattice gauge theory has been used to predict many other properties of this kind of matter. The AdS/CFT correspondence is a new interesting conjecture allowing insights in QGP.

    How it is created in the lab

    The QGP can be created by heating matter up to a temperature of 2×1012 kelvin, which amounts to 175 MeV per particle. This can be accomplished by colliding two large nuclei at high energy (note that 175 MeV is not the energy of the colliding beam). Lead and gold nuclei have been used for such collisions at CERN SPS and BNL RHIC, respectively. The nuclei are accelerated to ultrarelativistic speeds and slammed into each other while Lorentz contracted. They largely pass through each other, but a resulting hot volume called a fireball is created after the collision. Once created, this fireball is expected to expand under its own pressure, and cool while expanding. By carefully studying this flow, experimentalists hope to put the theory to test.

    How the QGP fits into the general scheme of physics

    QCD is one part of the modern theory of particle physics called the Standard Model. Other parts of this theory deal with electroweak interactions and neutrinos. The theory of electrodynamics has been tested and found correct to a few parts in a trillion. The theory of weak interactions has been tested and found correct to a few parts in a thousand. Perturbative aspects of QCD have been tested to a few percent. In contrast, non-perturbative aspects of QCD have barely been tested. The study of the QGP is part of this effort to consolidate the grand theory of particle physics.
    The study of the QGP is also a testing ground for finite temperature field theory, a branch of theoretical physics which seeks to understand particle physics under conditions of high temperature. Such studies are important to understand the early evolution of our universe: the first hundred microseconds or so. While this may seem esoteric, this is crucial to the physics goals of a new generation of observations of the universe (WMAP and its successors). It is also of relevance to Grand Unification Theories or 'GUTS' which seek to unify the four fundamental forces of nature.

    Expected properties

    Thermodynamics

    The cross-over temperature from the normal hadronic to the QGP phase is about 175 MeV, corresponding to an energy density of a little less than 1 GeV/fm3. For relativistic matter, pressure and temperature are not independent variables, so the equation of state is a relation between the energy density and the pressure. This has been found through lattice computations, and compared to both perturbation theory and string theory. This is still a matter of active research. Response functions such as the specific heat and various quark number susceptibilities are currently being computed.

    Flow

    The equation of state is an important input into the flow equations. The speed of sound is currently under investigation in lattice computations. The mean free path of quarks and gluons has been computed using perturbation theory as well as string theory. Lattice computations have been slower here, although the first computations of transport coefficients have recently been concluded. These indicate that the mean free time of quarks and gluons in the QGP may be comparable to the average interparticle spacing: hence the QGP is a liquid as far as its flow properties go. This is very much an active field of research, and these conclusions may evolve rapidly. The incorporation of dissipative phenomena into hydrodynamics is another recent development that is still in an active stage.

    Excitation spectrum

    Does the QGP really contain (almost) free quarks and gluons? The study of thermodynamic and flow properties would indicate that this is an over-simplification. Many ideas are currently being evolved and will be put to test in the near future. It has been hypothesized recently that some mesons built from heavy quarks (such as the charm quark) do not dissolve until the temperature reaches about 350 MeV. This has led to speculation that many other kinds of bound states may exist in the plasma. Some static properties of the plasma (similar to the Debye screening length) constrain the excitation spectrum.

    Experimental situation

    Those aspects of the QGP which are easiest to compute are not the ones which are the easiest to probe in experiments. While the balance of evidence points towards the QGP being the origin of the detailed properties of the fireball produced in the RHIC, this is the main barrier which prevents experimentalists from declaring a sighting of the QGP. For a summary see 2005 RHIC Assessment.
    The important classes of experimental observations are

    Formation of quark matter

    In April 2005, formation of quark matter was tentatively confirmed by results obtained at Brookhaven National Laboratory's Relativistic Heavy Ion Collider (RHIC). The consensus of the four RHIC research groups was that they had created a quark-gluon liquid of very low viscosity. However, contrary to what was at that time still the widespread assumption, it is yet unknown from theoretical predictions whether the QCD "plasma", especially close to the transition temperature, should behave like a gas or liquid[8]. Authors favoring the weakly interacting interpretation derive their assumptions from the lattice QCD calculation, where the entropy density of quark-gluon plasma approaches the weakly interacting limit. However, since both energy density and correlation shows significant deviation from the weakly interacting limit, it has been pointed out by many authors that there is in fact no reason to assume a QCD "plasma" close to the transition point should be weakly interacting, like electromagnetic plasma (see, e.g., [9]).

    See also

    References


    External links