Scientists crash lead nuclei together to create the hottest and densest nuclear material ever

Dec 06, 2010 By Phillip F. Schewe
A computer display taken from the first lead collisions. Credit: CERN | iSpy and Fireworks, CMS

The thousand-degree temperatures reached in the hottest of industrial furnaces is nothing compared to the equivalent temperatures achieved when particles traveling near the speed of light slam into each other.

On December 2 several scientists at the laboratory in Geneva, Switzerland reported the first results of an experiment in which the nuclei of atoms were shot around the 17 mile racetrack called the and then smashed into each other to create, for an instant, a speck of matter at a temperature of trillions of degrees.

Although the miniature fireballs that occur at the lead-lead collision points only last a fleeting moment -- about a trillionth of a trillionth of a second -- the immense detectors poised nearby are designed to act rapidly and sort through the myriad debris particles streaming outwards.

"This is the hottest nuclear matter ever created in a lab," said Bolek Wyslouch of the Ecole Polytechnique near Paris who spoke at the CERN gathering. He is a representative of the Compact Muon Solenoid collaboration, which uses one of the giant detectors at LHC to observe the lead-lead collisions.

"I like to call this the Little Bang," said Juergen Schukraft, also speaking at the CERN colloquium, suggesting that the violent collisions of heavy ions at the LHC were smaller cousins of the Big Bang explosion that ushered in the visible universe some 14 billion years ago. Indeed, the conditions of the mini-fireballs at LHC resemble the as it was only microseconds after the Big Bang in terms of energy density and temperature. Schukraft represented a second CERN detector group called Alice.

Never before has so much energy -- in this case hundreds of trillions of electron volts abbreviated as TeV -- been deliberately deposited in a volume of space only a few times the size of a proton. A proton is one of the constituents of the nucleus inside each atom, and is some 10,000 times smaller than the atom itself. Scientists who work at accelerators often use the electron volt as their unit of energy since it is precisely the energy gained by an electron accelerated by an electric force difference of one volt.

What happens when two lead nuclei containing hundreds of protons and neutrons, each of which have an energy of 1.4 TeV, smash into each other in an almost head-on collision? As they meet and interact the protons and neutrons melt into even more basic constituents, called quarks and gluons. What you get is a seething liquid of hundreds of strongly interacting particles, called by physicists a quark-gluon plasma.

Earlier this year scientists at the Relativistic Heavy Ion Collider at Brookhaven National Laboratory in New York reported on RHIC's collision measurements from a quark-gluon plasma made by colliding gold nuclei. They reported the temperature of the plasma to be 4 trillion degrees, the hottest temperature ever carefully measured in an experiment.

The LHC scientists haven't yet directly measured the temperature of their quark plasma. Schukraft said that since the of the collisions is some three times larger at LHC than at RHIC, the temperatures will be higher also.

In following weeks, a series of specific results from the LHC heavy ions will appear in scientific journals. Scientists from the Atlas collaboration -- which operates a third large detector at LHC -- report on their observations of huge jets emerging sideways from the collisions. A jet is a powerful cone of energy, in the form of flying particles that emerges from the fireball shortly after the collision. Scientists expect that if a powerful jet shoots out of the collision on one side, there should be a complementary jet on the other side that balances momentum.

In many collision events, however, only one jet is observed. In an article about to appear in the journal Physical Review Letters, the Atlas scientists report the first such examples of the imbalance between jets in the lead-lead collisions. But what happened to the missing jet?

Brian Cole, speaking at CERN on behalf of the Atlas team, said that the quark-gluon plasma itself is probably absorbing part or all of the jets on their way outwards. This process doesn't have to be symmetric.

"The more central the collision," Cole said, referring to how head-on the collision, "the more asymmetric the jets are."

Another Atlas scientist, Peter Steinberg, said that scientists expected that some of the jet energy would be absorbed, but were surprised that in some events the jet seemed to be completely absorbed.

The asymmetric appearance of jets, the scientists hope, can be used to understand the unprecedented nature of this densest matter ever observed in a lab.

Explore further: It's particle-hunting season! NYU scientists launch Higgs Hunters Project

Provided by Inside Science News Service

5 /5 (31 votes)

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User comments : 29

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El_Nose
3.4 / 5 (11) Dec 06, 2010
" i like to call it the little bang "

- HA HA -- thats what SHE said !!!

oh my - that will be my laugh for the whole week
hexmat1233
2.3 / 5 (3) Dec 06, 2010
Lol remember stay on topic lol that is funny tho
Ratfish
3 / 5 (5) Dec 06, 2010
I'm surprised that we humans, at this somewhat early stage in technological development, are able to both create, as well as contain, such reactions. Is there some portion of the device that is destroyed with each reaction?
tigger
5 / 5 (6) Dec 06, 2010
@Ratfish... we don't contain the reaction... it's literally a head on collision, we study the results of the head on collision, looking at the bits and pieces that spray out from the point of collision.
shavera
4.7 / 5 (6) Dec 06, 2010
Also @Ratfish: some of the detector components do degrade from the radiation over time. Generally we build them to withstand as much as possible, but there's only so much you can do.
Ratfish
3.7 / 5 (3) Dec 06, 2010
Oh OK, so it's just a matter of slow degradation due to the ionizing radiation over time? I figured that trillions of degrees for a fraction of a second must create many thousands of degrees on the surrounding components which much also be delicate instruments. Perhaps that's not the case.
lexington
5 / 5 (13) Dec 06, 2010
You're confusing temperature and heat. The plasma has a very high temperature (energy per unit of mass) but a very low amount of heat (total energy) because there is so little of it.
RaphaelH
2.5 / 5 (2) Dec 07, 2010
The size of the collision is of the atomic scale so i guess we can compare that to a nuclear explosion in a ball of radius equal to that of the earth.
chandram
1 / 5 (1) Dec 07, 2010
A remarkable measurement. The assymetric jets that result need a closer investigation, as detectors to sense such jets may not be operating in such an environment. One needs to be careful in the interpretation of results, based on unsatisfactory working of the detection apparatus. Naredra Nath
enter_name_here
5 / 5 (1) Dec 07, 2010
Oh OK, so it's just a matter of slow degradation due to the ionizing radiation over time? I figured that trillions of degrees for a fraction of a second must create many thousands of degrees on the surrounding components which much also be delicate instruments. Perhaps that's not the case.


Like those sparklers you had on fireworks night when you were a kid - white hot metal, small mass, so you didn't burn your hand when the sparks hit!
Jarek
1.5 / 5 (2) Dec 07, 2010
(...)there should be a complementary jet on the other side that balances momentum.
In many collision events, however, only one jet is observed

Reading it, I've scared that there is a problem with momentum conservation ... fortunately seeing the ATLAS pictures:
http://atlas.ch/i...ies.html
it looks that the asymmetry is only that one jet is more spread than the other - like there was some additional delayed explosion inside one jet, spreading it ...
There will probably return hypothesis that it was a micro black hole ... my candidate for source of energy of such additional delayed explosion is PROTON DECAY (also breaks baryon number conservation) - which should be expected not in room temperature water as is today, but to destroy baryon's internal structure, there should be rather required extreme conditions, like in LHC or in neutron star core...
shavera
5 / 5 (4) Dec 07, 2010
again Jarek, when a jet passes through a medium it dissipates its energy and momentum to the medium. That's what causes the spread. It's a strong signal of deconfined strong nuclear matter because it means that as the quark causing the jet passes through the deconfined nuclear matter it interacts/radiates strongly.
The explanation that a QGP is formed is far more likely and supported by other evidence rather than the formation of a micro black hole.
Jarek
1 / 5 (2) Dec 07, 2010
To spread many particles of many GeV a few dozens of degree, I don't think dissipation to medium (and: what medium? I thought it's near vacuum there?) would be enough - there is needed quite large energy to change their momentum - we need to understand its source ...
I also don't take micro black holes seriously, but proton decay (effect of QGP?) is needed in many particle theories (supersymmetric), to explain matter-antimatter asymmetry, baryon number conservation is broken in black hole theories (Hawking radiation) ...

Do you treat proton decay seriously?
Isn't QGP a perfect phenomenon to search for it?
Have you a better way to explain this very large momentum change in one jet?
gwrede
1 / 5 (3) Dec 07, 2010
Never before has so much energy -- in this case hundreds of trillions of electron volts abbreviated as TeV -- been deliberately deposited in a volume of space only a few times the size of a proton.
What happens when two lead nuclei containing hundreds of protons and neutrons, each of which have an energy of 1.4 TeV, smash into each other in an almost head-on collision?
The first thing a scientific journalist should do is learn magnitudes, right, Phillip?
genastropsychicallst
1 / 5 (5) Dec 07, 2010
The and bang never fits did I proved on my little website, Albert
Aristoteles
not rated yet Dec 07, 2010
Not only barion, but olso LEPTON-NUMBER ...
shavera
5 / 5 (5) Dec 07, 2010
@Jarek, there's actually a very hot dense medium nearby. All of the nucleons involved in the collision create (presumably) a quark-gluon plasma. This can be confirmed by several measurements. I think perhaps you might have an incorrect 'picture' of jet formation. Generally when we talk about suppressed jets, we mean that a quark-antiquark pair is produced near the surface of the QGP medium. One quark escapes easily off the surface and makes an unsuppressed jet. The other quark necessarily must pass through the bulk of the medium. As it passes through the medium it will exchange gluons with the quark/gluon plasma it passes through. Particularly, because the quarks and gluons are deconfined, it will exchange even more gluons than it would if it were to pass through a 'cold' nucleus of a similar size (cf deuterium-gold collisions). Each of these gluon exchanges smear the momentum magnitude and direction and effects on the order of several GeV are possible (strong nuclear force).
shavera
5 / 5 (5) Dec 07, 2010
Proton decay could exist... hasn't been observed yet, and there are pretty fantastic limits on its existence, but it could. The fact is, in a QGP there is no such thing as a proton or neutron anymore. Just free quarks and gluons for that brief period of time that it's sufficiently hot. Moments later it 'freezes out' (imagine melting a bunch of lead balls in a jar, then exploding the whole thing: you'll get new balls of lead, but they'll all be mixed up together)
Jarek
1 / 5 (1) Dec 07, 2010
Ok, so please explain where while symmetric collisions, comes from 'Eye-Catching' energy imbalance between jets:
http://atlas.ch/i...ies.html

About proton decay - the main question is if there was possible baryogenesis which created more baryons than anti-baryons - is baryon number conserved - or in other words: can baryons be created of pure energy and so: can their structure be completely destroyed, releasing its energy - or in energetic picture: 'tunneling' from deep energy well of proton's structure into the vacuum ...
Such hypothetical destruction would involve quarks - and so freeing them into QGP seems to be good step towards completely releasing energy hold in proton's structure ... ?
shavera
4.2 / 5 (5) Dec 07, 2010
Right, so if you look at the peak around phi=3, there's a similar but highly suppressed peak around phi=0. While the collision is symmetric with regards to lead-lead, all of the constituent particles have no real symmetry. Thus, there were two jets, one facing phi=0 and one facing phi=pi. Back-to-back. The pi jet didn't have to fly through the medium while the 0 jet did. Draw a circle, and place two back-to-back jets at position pi, one with direction out at pi and one with direction inward at angle 0. You can see for yourself that it must pass through the circle before exiting. As the quark passes through that 'circle' it radiates energy and momentum to the stuff around it.
So while the collision is "symmetric" with regards to lead on lead. The lead is each made up of protons and neutrons in a random configuration, each of these made up of quarks and gluons in another random configuration. The only thing symmetric about the collision is the mass-energy and momentum terms.
shavera
5 / 5 (4) Dec 07, 2010
As for proton decay: there is some discussion about making measurements of CPT violation in the QGP that would favor baryogenesis. You've that much correct. But I know FAR less about this than jet quenching.
It's a subtle misconception of physics that there is some 'pure' energy. Energy is always present in one form or another. Within the QGP it's predominantly the binding energy of gluons, so you're usually looking at gluon-to-hadronic processes and seeing if they favor baryon processes over anti-baryon ones.
Jarek
5 / 5 (1) Dec 08, 2010
I have to admit that I don't understand what 'medium' which could make that one of lead jets has 'Eye-Catching' more energy than the other you are talking about? Collision is made in vacuum in the center of symmetric detector: http://www.atlas....tor.html

About random configurations of nucleus, I think you overestimate such randomness (see e.g. http://www.physor...721.html ) - sure, there are thermal fluctuations, but generally nucleus is some relatively stable configuration near energy minimum of some potential well and quickly deexcitate when excited (in higher local minimum) - has rather fixed structure.

About proton decay, directly it has nothing to do with CPT violation - favoring matter is one thing, but the most essential question is: can baryon be destroyed - converted mainly into (massless) photons?
By 'pure energy' I've meant massless: not part of rest energy(mass) of a particle - not 'prisoned' in a structure of e.g. baryon.
shavera
5 / 5 (5) Dec 08, 2010
So the collision occurs in a vacuum, yes. The medium that's referred to is the colliding matter itself. All of the nucleons that collide together form a new state of hot dense 'nuclear' matter consisting of deconfined quarks and gluons.

Sure, let's even suppose that every atom has its nucleons arranged in the exact same physical way. We don't have the precision to make sure that each atom hits dead center each other atom, at the same rotation and everything. Many collisions are glancing blows and certainly there's a monte carlo distribution of hits. Furthermore, within the nucleons all we know of the structure is the probability of a quark or gluon to carry a certain amount of momentum. Nothing is known about their "position" within the nucleon (if something could be known).
shavera
5 / 5 (5) Dec 08, 2010

To the best of our knowledge the baryon is "disintegrated" but baryon 'conservation' is only a proxy value for maintaining certain rules about quark content and decays. Does the whole baryon turn into photons and gluons? No. The quarks are free to combine with whatever quarks are around, free to transmute into other quarks provided they follow the rules, etc. That's where CPT violation comes in. CPT might allow quarks to break the rules from time to time and favor matter quarks rather than anti-matter.
Jarek
not rated yet Dec 08, 2010
Clear argument that stable nucleses have usually (not known, but) the same structure is that photons created while nuclear processes have extremely similar energies - it's the difference between two local energy minimals.
I agree that there still are degrees of freedom which break symmetry, like rotation ... but it's difficult for me to imagine large energy imbalance between jets created this way - not using kind of 'delayed explosion' ...

About proton decay: http://en.wikiped...on_decay
CPT conservation says that anti-proton has quite analogous decay possible ... and yes - quarks can recombine, but what is essential is the final balance: is there a missing baryon? if yes, there should be 1GeV more energy there ...
shavera
5 / 5 (2) Dec 08, 2010
ah perhaps this is the core of our mutual misunderstanding: the jets are created perfectly symmetrically. And the QGP exists for a short, but non-zero amount of time. Thus it takes time for the jet to pass through the QGP and it is in this time that it loses energy. Again, the processes are very brief, but powerful. Imagine you have a twin and the two of you are at a party and you're standing right inside the front door and the cops come to bust up the party. By a weird rule you must also run in the opposite direction from your twin, at least at first. He can pass straight out the front door, but you've got to push and shove your way through the crowd to get out the back door. Each time you bump into someone your direction changes a little, your speed changes a little. You push on the crowd as they push back on you. By the time you get out, you'll be moving much differently than your twin.
shavera
5 / 5 (2) Dec 08, 2010
As for Baryon number, consult the wiki article on that. You can see it's defined as the difference between quarks and anti-quarks. A signature you might look for in a QGP is like a single quark to decay into only leptons and no quarks. When you consider the mass of a quark is only like 3 MeV, that's a much harder deficit to notice.
Proton Decay in a non-QGP would definitely be like a 1GeV energy gap. But again, there are no protons in the QGP. Only quarks and gluons.
jolson
not rated yet Dec 10, 2010
14 billion years and 1 day ago a young physicist reached the apex of scientific achievement as he was on the brink of discovering exactly how his universe was created. It had been widely known that the only way to exactly identify the complexity of the creation was, in fact, to re-create this 'big bang' in a laboratory environment. Small scale big-bangs were developed which gave rise to new insight and new theories, but left many more questions. It wasn't until this day, 14 billion years and 1 day ago, that the young physisist was able to create a Big Bang large enough to true understand the nature of their origin. the rest, they say, is history
Pkunk_
1 / 5 (1) Dec 13, 2010
14 billion years and 1 day ago a young physicist reached the apex of scientific achievement as he was on the brink of discovering exactly how his universe was created. It had been widely known that the only way to exactly identify the complexity of the creation was, in fact, to re-create this 'big bang' in a laboratory environment. Small scale big-bangs were developed which gave rise to new insight and new theories, but left many more questions. It wasn't until this day, 14 billion years and 1 day ago, that the young physisist was able to create a Big Bang large enough to true understand the nature of their origin. the rest, they say, is history


Said physicist called Gawd is worshiped today as the creator GOD . ;)

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