Are new nucleons formed in heavy-ion collisions?

  • Context: Undergrad 
  • Thread starter Thread starter hkyriazi
  • Start date Start date
  • Tags Tags
    Collisions Nucleons
Click For Summary

Discussion Overview

The discussion centers on whether new nucleons are formed during heavy-ion collisions that create a quark-gluon plasma (QGP). Participants explore the implications of energy added during these collisions and whether stable nucleons exist post-collision compared to pre-collision states. The conversation touches on experimental observations and theoretical interpretations related to nucleon formation and conservation laws.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants assert that heavy-ion collisions at high energies produce many new hadrons, including protons and neutrons, suggesting that new nucleons are formed.
  • Others question how it is determined that newly observed anti-protons or anti-neutrons are indeed new nucleons, raising concerns about the methods used to track nucleon numbers before and after collisions.
  • One participant emphasizes that all protons are indistinguishable, making it impossible to identify which protons existed prior to the collision.
  • Another participant notes that if the number of nucleons detected exceeds the initial count from the colliding lead ions, it indicates new nucleons were created, alongside corresponding anti-nucleons.
  • A discussion on beautiful mesons introduces the idea that baryons formed from their decay may not have existed before, raising questions about the clarity of nucleon origins in heavy-ion collisions.
  • Some participants argue that baryons can only form from the decay of beautiful mesons, suggesting a mechanism for nucleon formation that is observable in both proton-proton and lead-lead collisions.

Areas of Agreement / Disagreement

Participants express differing views on the formation of new nucleons in heavy-ion collisions. While some assert that new nucleons are created, others challenge the methods of determining nucleon origins and the implications of baryon conservation. The discussion remains unresolved regarding the specifics of nucleon formation and identification.

Contextual Notes

Limitations include the inability to track all particles due to detector constraints, and the reliance on conservation laws without definitive methods to verify the origins of individual nucleons.

hkyriazi
Messages
174
Reaction score
2
The subject heading says it all. In heavy-ion high energy collisions that form a quark gluon plasma (QGP), is it known whether new nucleons are formed from the added energy, or are all of the QGP's quarks ones that existed previously in the colliding heavy ion nuclei? More specifically, are there more nucleons (and not just their component quarks) after the collision--and after the QGP cools--than before? I'd like to know if stable nucleons are formed de novo in such experiments. I'm not familiar with the experimental details.
 
Physics news on Phys.org
Yes - many. Central collisions at LHC energies produce thousands of new hadrons. Most of them are pions and kaons but there are also many protons and neutrons (and their antiparticles) and various other particles.
The total number of baryons is conserved, for every new baryon there is also a new antibaryon.
 
Thanks, mfb! I'm curious how this is known. Is it assumed that any anti-proton or anti-neutron they see flying away out of such collisions must be new, and therefore the accompanying, ejected protons or neutrons must also be new (due to baryon number conservation)? Or are they able to do actual "housekeeping" on the numbers of nucleons present before and after?
 
All protons are the same. You can never point to a proton and say ”that one existed before the collision” or ”this proton is the partner of that antiproton”. There simply is no possible test that could verify this. What you can do is to check the number of protons (and other nucleons) before and after collision.
 
  • Like
Likes   Reactions: hkyriazi
Lead ions colliding in the LHC have 82 protons and 126 neutrons each, or combined 164 protons and 252 neutrons.
If you see more than that, then new nucleons were created, and all the antinucleons were created as well of course (where else would they come from?).

ALICE cannot measure particles that fly away close to the incoming beams (because there has to be space for the beams entering and leaving the detector, so counting everything doesn't work, but even the number of particles that hit the detector is much larger already.

This is not limited to heavy ion collisions, by the way. Proton proton collisions can produce new nucleons as well.
 
  • Like
Likes   Reactions: hkyriazi
A beautiful meson has rest mass sufficient to produce a pair of a baryon and antibaryon. Indeed, sufficient to produce two pairs.
And the lifetime of a beautiful meson is so long that t*c is 0.5 mm for a charged beautiful meson and 0.45 mm for neutral ones.
If a heavy ion collision is observed to produce, besides a number of antibaryons and baryons of which it is not clear which specific ones existed before, some beautiful mesons which can be tracked to decay to baryons and antibaryons, can you confidently specify that a baryon formed in decay of a beautiful meson did not exist before formation of that beautiful meson?
 
snorkack said:
can you confidently specify that a baryon formed in decay of a beautiful meson did not exist before formation of that beautiful meson?
Sure. Even more, the baryons only form when the B mesons decay.

This is easier to observe in proton-proton collisions where there are fewer other particles, but it works with lead-lead collisions as well.
 

Similar threads

  • · Replies 4 ·
Replies
4
Views
3K
Replies
8
Views
2K
  • · Replies 5 ·
Replies
5
Views
2K
  • · Replies 12 ·
Replies
12
Views
5K
  • · Replies 3 ·
Replies
3
Views
3K
  • · Replies 9 ·
Replies
9
Views
2K
  • · Replies 2 ·
Replies
2
Views
10K
  • · Replies 6 ·
Replies
6
Views
3K
  • · Replies 12 ·
Replies
12
Views
4K
Replies
1
Views
1K