CERN Alice Particle spectra behavior

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Discussion Overview

The discussion revolves around the behavior of particle spectra at the CERN ALICE experiment as a function of momentum. Participants explore the reasons behind the rising and falling nature of the particle spectrum, particularly in the low momentum range, and its potential connections to theories such as Fermi's theory of beta decay.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions the relationship between the particle spectrum and Fermi's theory of beta decay, suggesting a possible connection.
  • Another participant argues that the connection to beta decay is indirect and that weak processes are negligible for the spectra being discussed.
  • It is noted that at low momentum, the phase space is small, which limits the number of particles with very low transverse momentum, similar to Maxwell-Boltzmann statistics.
  • A participant seeks clarification on why low momentum particles have small phase space and how this relates to high energy scenarios, suggesting that medium momentum particles may have more options for decay.
  • One participant illustrates the concept of phase space by comparing the distribution of particles in a coordinate system, indicating that fewer particles are found closer to the center.
  • There is a discussion about whether the detection of low momentum particles is influenced by their proximity to "ground zero" and the implications of the coordinate system used for momentum representation.
  • Another participant asserts that low-energetic particles are harder to detect but that this has been accounted for in the calculations of the spectra.
  • Participants reference the Maxwell-Boltzmann distribution as a relevant concept for understanding the particle spectra.
  • There is a question about the relevance of the Gamow Peak, which is met with a negative response, indicating it is not applicable to this discussion.

Areas of Agreement / Disagreement

Participants express differing views on the connection between particle spectra and beta decay, as well as the implications of phase space on low and high momentum particles. The discussion remains unresolved with multiple competing perspectives on these topics.

Contextual Notes

Participants highlight limitations in understanding related to the assumptions about phase space and the nature of particle detection, but these remain unresolved within the discussion.

moso
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So i have a question regarding the nature of the particle spectre at alice as a function of momentum. The spectre in question can be seen here. http://cerncourier.com/cws/article/cern/48325. My question is, why is it that the particle in the low momentum range are rising and the reaching a maximum and then beginning to decrease again. From what I have understood it has something to do with the Fermi theory of beta decay or? It would be awesome it anyone knew and you give me a hint on it. thanks in advance.

Morten
 
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The connection to the energy spectrum of beta decays is very indirect, and weak processes (like for beta decays) are negligible for those spectra.

For very small momenta, the phase space is small. In the same way only a very small fraction of gas molecules in the atmosphere is very slow (see Maxwell–Boltzmann statistics), only a small fraction of the particles has a very low (transverse) momentum.
For high energies, the probability that a single particle gets so much energy drops again.
 
So to summarizes, at low momentum (transverse) the possibilities for particles being in different states, eq: phase space is low. Could you elaborate, why the low momentum particles have small phase space? and that for high energies gives it self, because there is limited energy available in a collision.

edit:
is it because the combination of the low moment particles has less options than the medium momentum particles? Because the collision is with pb-pb have the same phase space, they can decay to the same and the same momentum each time,
 
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Draw a coordinate system on paper, randomly fill it with points (particles). The amount of particles you'll find between 0 and 1 cm from the center will be smaller than the amount of particles between 5 and 6 cm away simply because the first set corresponds to a much smaller area.

If you look at each momentum component separately (like momentum in vertical and horizontal direction), you don't see this effect.

moso said:
Because the collision is with pb-pb have the same phase space, they can decay to the same and the same momentum each time,
I don't understand that part.
 
So has this assumption something to do with the detector and that low momentum particles are close to "ground zero" and high momentum particles travels faster and therefor are father away. Or do you coordinate system just states an idea, that the y and x-axis is momentum and the phase space is the area in-between. Do it have anything to do with Gamow Peak?
 
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moso said:
So has this assumption something to do with the detector and that low momentum particles are close to "ground zero" and high momentum particles travels faster and therefor are father away.
No. Low-energetic particles are harder to detect but that has been taken into account to calculate those spectra.

The coordinate system I suggested is momentum, right.

See the Maxwell-Boltzmann distribution. If you understand this, the particle spectra are a natural consequence.
moso said:
Do it have anything to do with Gamow Peak?
No.
 

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