LHC says quarks still elementary

In summary, the recent ATLAS experiment has published two papers looking for evidence of quark substructure in two different ways. One paper did not see any evidence of an excited quark, leading to the conclusion that if it exists, it must have a mass above 1.26 TeV. The other paper found no evidence of substructure below a scale of 3.4 TeV, extending the previous best limit. These results put new bounds on possible quark substructure and are the first exclusion of physics beyond the Standard Model by the ATLAS experiment. However, it is important to note that these results do not apply to all types of new physics, as theories such as GUT, SUSY, SUGRA, and
  • #1
Vanadium 50
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The ATLAS experiment has recently sent two papers for publication. Both look for evidence of quark substructure, in two different ways. http://arxiv.org/abs/1008.2461" , submitted to Physical Review Letters, looks for an excited quark, and does not see any evidence of one. Based on that, they conclude that such an excited quark, if it exists, must have a mass above 1.26 TeV. The previous best limit was 0.87 TeV.

http://arxiv.org/abs/1009.5069" , submitted to Physics Letters B, essentially repeats the Rutherford experiment with quarks, and sees no evidence of substructure below a scale of 3.4 TeV (corresponding to about 6 x 10-20 m). The previous best limit was 2.8 TeV.
 
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  • #2
Standard Model is still standing strong ;)
 
  • #3
...no evidence of substructure below a scale of 3.4 TeV (corresponding to about 6 x 10-20 m)

WHAT!? NO particles?

What about all those pretty theories that go to GUT scale or to PLANK scale?

Can't have that. It will cause too many layoffs!

jal
 
  • #4
jal said:
WHAT!? NO particles?

No quark substructure. Not the same thing.

Thanks for posting those papers, Vanadium 50. I really should keep a closer eye on hep-ex.
 
  • #5
Cough, cough!

http://cdsweb.cern.ch/record/1294718/files/CERN-PH-EP-2010-028.pdf

Search for New Particles in Two-Jet Final States in 7 TeV Proton-Proton Collisions
with the ATLAS Detector at the LHC
This result extends the reach of previous experiments and constitutes the first exclusion of physics beyond the Standard Model by the ATLAS experiment. In the future, such searches will be extended to exclude or discover additional hypothetical particles over greater mass ranges.
 
  • #6
jal said:
Cough, cough!

http://cdsweb.cern.ch/record/1294718/files/CERN-PH-EP-2010-028.pdf

Search for New Particles in Two-Jet Final States in 7 TeV Proton-Proton Collisions
with the ATLAS Detector at the LHC

These results put new bounds on possible quark substructure. Quark substructure is one possible type of new physics. There have previously been no new bounds on any type of new physics from the LHC. Thus, these are the first LHC results that put new bounds on new physics. You should not, however, take that to mean that these new bounds apply to every possible type of new physics. They don't.
 
  • #7
@jal: GUT, SUSY, SUGRA and superstrings do not predict any quark substructure.
 
  • #8
tom.stoer said:
@jal: GUT, SUSY, SUGRA and superstrings do not predict any quark substructure.

At least not at the TeV scale.
 
  • #9
I think though that there are some models where RS is used where the quarks are composite...

Maybe somebody with more knowledge on the subject can say something about it...
 
  • #10
@jal: GUT, SUSY, SUGRA and superstrings do not predict any quark substructure.

Are we playing with the definitions of quarks and substructures?

What I understood from those papers is that they have probed to 3.4 TeV (corresponding to about 6 x 10-20 m) and have found only quarks and nothing else, (no smaller particles, no other particles) that would indicate that there is anything else that makes up quarks.

I guess that I'll leave open the possibility that if there is anything else then it must be hiding in another dimension which we have no means of probing. (Lisa Randall can breath for a while longer) :smile:

jal
 
  • #11
jal said:
Are we playing with the definitions of quarks and substructures?

What I understood from those papers is that they have probed to 3.4 TeV (corresponding to about 6 x 10-20 m) and have found only quarks and nothing else, (no smaller particles, no other particles) that would indicate that there is anything else that makes up quarks.

I guess that I'll leave open the possibility that if there is anything else then it must be hiding in another dimension which we have no means of probing. (Lisa Randall can breath for a while longer) :smile:
We are not playing with definitions.

I can only repeat what I said: GUT, SUSY, SUGRA and superstrings do not predict any quark substructure. All these theories predict additional, new particles, but these particles are not substructures of quarks (superstring theory predicts a different high energy behavior of the amplitudes). So it is important to distinguish whether an experiment rules out a substructure or whether it rules out new particles.
 

Related to LHC says quarks still elementary

1. What is the LHC?

The LHC, or Large Hadron Collider, is a particle accelerator located at CERN (European Organization for Nuclear Research) in Switzerland. It is used to study the smallest particles that make up our universe, such as quarks.

2. What does it mean when the LHC says quarks are still elementary?

Elementary particles are particles that are believed to be the most basic building blocks of matter. The LHC has conducted experiments to try to break down quarks, but they have not been successful in finding any smaller particles. This means that quarks are still considered to be elementary particles.

3. How does the LHC study quarks?

The LHC accelerates protons and other particles to nearly the speed of light and then collides them with each other. These collisions create high-energy interactions that allow scientists to study the behavior and properties of quarks and other particles.

4. Why is it important to study quarks?

Quarks are fundamental to our understanding of the universe and play a crucial role in the structure of matter. By studying quarks, scientists can gain a deeper understanding of the fundamental forces that govern the universe and potentially uncover new insights into the nature of matter.

5. What are the potential implications of the LHC's findings about quarks?

The LHC's discoveries about quarks could have significant implications for our understanding of the universe, including the origins of matter and the fundamental forces that govern it. It could also potentially lead to advancements in technology and energy production.

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