# Difference between nuclear, particle, and high energy physics?

1. Nov 18, 2011

### Nano-Passion

What is the difference in them? They all seem to be very similar at face value and they have some overlapping study.

Particle physics studies subatomic particle and its constituents, nuclear physics studies how they interact in the nucleus of a proton/proton and the quark-gluon force?

High energy physics includes both studies?

2. Nov 18, 2011

### Staff: Mentor

"Particle physics" and "high-energy physics" are pretty much synonyms in practice. You also see the term "high-energy particle physics" which wraps both of them together. Whatever you call it, it deals with interactions between individual particles at the level of protons / neutrons / electrons / quarks / pions / etc. Usually involves experiments at high-energy accelerators like CERN and Fermilab.

"Nuclear physics" is the study of the atomic nucleus as a system. It studies fission, fusion, nuclear reactions (shooting alpha particles, protons or neutrons at nuclei in order to transform them into something else or induce fission), nuclear decay (alpha, beta, gamma). A major goal is to understand the "structure" of the nucleus in terms of predicting its internal energy levels, etc. Also uses accelerators, usually with lower energies than the HEP folks use (you usually don't want to blast the target nucleus to smithereens).

There's some overlap, but the two fields are usually very distinct in practice. I was in HEP as a grad student, and couldn't get much out of the nuclear physics seminars. I'm sure the nuclear physics people felt the same way about us!

3. Nov 18, 2011

### mathman

One additional note. In practice the energies involved in nuclear physics tend to be lower than in particle physics.

4. Nov 18, 2011

### Nano-Passion

Hmm, thank you.

It seems to me that nuclear physics work on less exciting things except for the nuclear decay portion. But then again I know very little about nuclear physics I'm just stating a completely personal and biased opinion.

Doesn't nuclear physics also study the force between quarks and gluons? Because I find that very exciting!

5. Nov 19, 2011

### mathman

No. This is studied in particle physics.

Nuclear physics is concerned with protons and neutrons and their combinations, interactions, etc.

6. Nov 19, 2011

### Nano-Passion

Hmm, well what questions are out there for their combinations/interactions?

7. Nov 19, 2011

### cbetanco

I'm no nuclear physicist, but my understanding is that nuclear physics has been studied to death during the cold war. I think most research goes into getting a working fusion reactor to be made practical, but I think the main theoretical questions have all been answered. Someone correct me if I'm wrong.

8. Nov 19, 2011

### humanino

This is not correct. There are many laboratories in the world which fall under the classification "nuclear physics" and study the quark and gluon structures, in particular forces in cold nuclear matter, meaning the non perturbative low energy regime.

Now, I am not arguing the value of such a classification. It is one which is used in administrative offices. You can take a look at the Nuclear Science Advisory Commitee and its 2007 report for instance.

9. Nov 19, 2011

### humanino

In case someone would not be willing to pursue the NSAC link above, I can name a few open problems in nuclear physics.

Confinement : many high energy physicists take it for granted or even uninteresting after Wilson's work in particular, but this is old and changed largely over the last decade or so. In fact, although it is rather well established that confinement must happen in Yang-Mills theories, it is unclear what the real world mechanism for light quark is. The string tension is essentially irrelevant to the problem. There are indications that the light quarks undergo far weaker forces that 1 GeV/fm in semi-inclusive deep inelastic scattering. The relevant theoretical tools are under active developments and measurements are ongoing. What is the distribution of those forces ? How does the distribution of mass inside hadron compare with the distributions of charges, or the distributions of forces ?

How do the partonic constituents (quarks and gluons) combine to make up the spin of hadrons, such as the most ubiquitous one, the proton ? Amazingly enough, it is not the mere combination of 1/2+1/2-1/2 quark spins. We are unsure about the gluon spin contribution. We are unsure what is the best way to disentangle spin and orbital angular momentum, as there are ambiguities in an interacting gauge theory.

Is the NuTeV anomaly a reflection of the isovector part of the EMC effect ? The question may seem esoteric, but essentially the NuTeV anomaly has generated a plethora of speculation beyond the standard model, for months, while it may simply be that we do not understand nuclear corrections to the measurement.

The EMC effect (partonic) was recently linked to the old problem of short range correlations. This is another sign that Dokgarbagezer's quote is alive as ever$^{(1)}$
(1) QCD Phenomenology

10. Nov 20, 2011

### kloptok

This seems to assume that nuclear physics is only about nuclear power, which is wrong (nuclear power research is rather called applied nuclear physics). There are topics in nuclear physics which have nothing to do with fission or fusion but are more about theoretical issues such as the ones mentioned in the previous post above.

One big issue in nuclear physics I have heard about is the huge discrepancy between the individual masses of the quarks and the mass of the proton as a whole. As far as I know, that is not solved yet (as I'm not very well-read in this subject, perhaps someone could elaborate on this and explain more about what it is about).

Another thing which is not entirely understood are the nuclear processes which occur in a supernova, the r-process in particular is not entirely understood if I remember correctly.

Of course, the formation of heavier elements is a research topic in nuclear physics. This is done to further understand the stable elements and what it is making these stable, and also to investigate the possibility of an "island of stability" - that the stability of elements increase for some values of the number of neutrons and protons.

Read more about exotic nuclei and current research in nuclear physics in
http://physicsworld.com/cws/article/indepth/47639" [Broken] Note that you have to member of Physicsworld to be able to read (which I think is free).

Last edited by a moderator: May 5, 2017
11. Nov 20, 2011

### cbetanco

Ok, but I always considered the structure of the proton and questions about confinement to be areas of study in particle physics. But, it is a fuzzy line between the two disciplines.

12. Nov 30, 2011

### McCuack

well, the limists between nuclear physics and particle physics are very tiny and not always very clear.

Sometimes, nuclear physics we can say that they are restricted to low energies range even they work with "particles" (pions, kaons) because they try to understande QCD at low energy regime.

13. Nov 30, 2011

### Nano-Passion

There are still some things that are up for question. Our understanding isn't as encompassing as you think.

Agreed.