Particle physics is the study of the fundamental forces of nature as they are embodied in the interactions of elementary and composite particles at high energies and short time and distance scales.

learn more… | top users | synonyms (2)

18
votes
2answers
2k views

What the heck is the sigma (f0) 600?

At one point, I decided to make friends with the low-lying spectrum of QCD. By this I do not mean the symmetry numbers (the "quark content"), but the actual dynamics, some insight. The pions are the ...
7
votes
1answer
773 views

What does “tagging” mean in experimental high energy physics?

Could someone explain in details the meaning of the terminology "tagging" in experimental high energy physics and how is it used in the analysis?
10
votes
2answers
1k views

How are Monte Carlo simulations used in experimental high energy physics?

How are Monte Carlo simulations used in experimental high energy physics? Particularly in studying detectors limitations (efficiencies?) and data analysis. I will appreciate giving a simple example ...
3
votes
1answer
766 views

Fitting to a high density scatter plot

I am trying to do a crude particle identification, using a Bethe Bloch tenchnique. Here is a plot I made from the data that I have From what I've read, the standard method to identify charged ...
5
votes
2answers
503 views

How are the HEP experiments' invariant mass plots generated?

I am experimenting and playing around with some data, and I'm having trouble seeing how to generate invariant mass plots. The data I have has a bunch of events, and variables such as ...
1
vote
0answers
79 views

Scaling an electron microscope to fit within 1 cubic cm when running multiple parallel scans [closed]

Yes, I'm serious. What components correspond to an individual scan vrs what components can be cascaded across all objects? Ex: The vacuum chamber can be cascaded ( colocate the sample chambers ...
13
votes
1answer
593 views

How come random matrices can predict energy spectra of heavy atoms?

Some of the applications of random matrices is to find the spectra of heavy atoms in nuclear physics which are usually difficult to find otherwise. How can starting from randomness of some kind, ...
4
votes
1answer
72 views

Is accelerating particles through a chain of accelerators a continuous or batch process?

At the Advanced Photon Source, they use two accelerators before injecting the electrons into the large storage ring. Is the addition of particles to the storage ring done in "batches" (however ...
16
votes
2answers
3k views

Particle physics plots

I'm having a hard time understanding what some of the plots that are presented by ATLAS/CMS actually show. See for example: http://resonaances.blogspot.com/2011/07/higgs-wont-come-out-of-closet.html ...
4
votes
1answer
705 views

Cheat sheet of elementary particles

I am trying to teach myself some particle physics. There are too many particles and its too much for me. I hated biology just because of this sort of stuff. Too many names and it was all Greek to ...
2
votes
2answers
346 views

Question concerning Isospin symmetry

I'm currently taking an introductory course to particle physics and I'm now trying to understand the concept of isospin. However I do have some trouble. So let's write the up- and down Quark as a ...
1
vote
0answers
206 views

decay with initial velocity:

decay with initial velocity: All static particle decay to particles with momentum distribution in the same shape like that's implied by structure function and calculated by MG. but the decay of W ...
8
votes
7answers
667 views

Are the rest masses of fundamental particles certainly constants?

In particular I am curious if the values of the rest masses of the electron, up/down quark, neutrino and the corresponding particles over the next two generations can be defined as constant or if ...
13
votes
3answers
1k views

What are the mathematical problems in introducing Spin 3/2 fermions?

Can the physics complications of introducing spin 3/2 Rarita-Schwinger matter be put in geometric (or other) terms readily accessible to a mathematician?
5
votes
2answers
1k views

What is meant by “combinatorial background” in experimental high energy physics

My guess is that they find a certain tracks coming from a certain source by "combintaorially" selecting all track pairs and finding their invariant mass. If this is true, of which I am not sure, how ...
8
votes
3answers
676 views

Why muonium is unstable?

This question is closely related to my previous question Bound states in QED. Muonium is a system of electron and anti-muon. This article in wikipedia claims that muonium is unstable. QUESTION: Why ...
-1
votes
1answer
245 views

Transition of Electric Charge In Collision Between Proton And Antiproton

I know that $$p+\bar{p}\to 4\pi^++4\pi^-+(\gamma)$$ Before the collision, the sum of absolute electric charge value is $2$. $$\left | +1 \right |+\left | -1 \right |=2$$ After the collision, the ...
10
votes
2answers
2k views

How Did Paul Dirac Predict The Existence of Antiproton?

The existence of the antiproton with -1 electric charge, opposite to the +1 electric charge of the proton, was predicted by Paul Dirac in his 1933 Nobel Prize lecture. Quotation by Wikipedia. ...
16
votes
3answers
3k views

Decay of massless particles

We don't normally consider the possibility that massless particles could undergo radioactive decay. There are elementary arguments that make it sound implausible. (A bunch of the following is ...
13
votes
1answer
1k views

How to determine the mass of a quark?

As far as I know quarks are never found in isolation, so how can we determine their rest mass?
8
votes
1answer
294 views

A moderate introduction to Hanbury Brown Twiss interferometry in particle physics

For astronomy, as originally invented, the Hanbury Brown Twiss interferometer is good for finding the angular diameter of stars and is not a rapidly fluctuating observable like the amplitude in ...
10
votes
2answers
4k views

Why is pseudorapidity defined as $-\log \tan \theta/2$

Why the log? Is it there to make the growth of the function slower? As this is a common experimental observable, it doesn't seem reasonable to take the range from $[0,\infty)$ to $(-\infty,\infty)$ ...
12
votes
1answer
1k views

Cross-section in relativistic limit: Fermi's golden rule still valid?

In order to calculate the cross-section of an interaction process the following formula is often used for first approximations: $$ \sigma = \frac {2\pi} {\hbar\,v_i} \left| ...
3
votes
1answer
479 views

How large is the information collected from an inverse femtobarn of collisions?

I ran into this while looking at measures of humongous amounts of data. How does the information (data) collected in an inverse femtobarn exposure compare to a gigabyte of data ?
-2
votes
1answer
221 views

muon neutrino momentum distribution

muon neutrino momentum distribution I have read the public data of T2K ,KEK to find this subject, I'm curiously that it's coincides with my prediction perfectly: The neutrino get its momemtum by its ...
12
votes
3answers
2k views

Why does the weak force distinguish left and right handedness?

I'm wondering why the weak interaction only affects left-handed particles (and right-handed antiparticles). Before someone says "because thats just the way nature is" :-), let me explain what I find ...
19
votes
2answers
6k views

Are all electrons identical?

Why should two sub-atomic (or elementary particle) - say electrons need to have identical static properties - identical mass, identical charge? Why can't they differ between each other by a very ...
7
votes
3answers
425 views

why certain superpositions of quantum states are supressed?

it has been said that the electron is the fundamental representation of the Poincare group, with only two conmuting observables, $( \sigma , p_{\mu})$. This question regards what is usually called the ...
9
votes
1answer
763 views

Universality in Weak Interactions

I'm currently preparing for an examination of course in introductory (experimental) particle physics. One topic that we covered and that I'm currently revising is the universality in weak ...
0
votes
2answers
808 views

Iron Man repulsor question [closed]

Ignoring the whole movie situation along with the power demands, what do you think Iron Man's repulsors use to "repulse" his targets? I don't think they are lasers or electric beams, or "reverse ...
4
votes
2answers
1k views

Is nature symmetric between particles and antiparticles?

Is nature symmetric with respect to presence of particles? Do we have an antiparticle for every particle thought of? Are there any proven examples where we don't have an antiparticle? And what about ...
9
votes
2answers
923 views

What does the data in various stages of analysis from a particle collision look like?

I've been following the news around the work they are doing at the LHC particle accelerator in CERN. I am wondering what the raw data that is used to visualize the collisions looks like. Maybe someone ...
12
votes
2answers
463 views

Alejandro Rivero's correspondence: diquarks and mesons as superpartners of quarks and leptons

The idea of “hadronic supersymmetry” originated in the mid-1960s and derives from the observation that baryons and mesons have similar Regge slopes, as if antiquarks and diquarks are superpartners. ...
6
votes
1answer
255 views

Parametrisation of general MSSM/SUSY based on collider experiment observables

The full MSSM contains 120 parameters. In SUSY searches, one usually picks a model like MSUGRA which makes a few assumptions and only has 5 free parameters like $m_0$, $m_{1/2}$, .... Now, I'm ...
18
votes
2answers
2k views

How does one experimentally determine chirality, helicity, spin and angular momentum of a fundamental particle?

If I've got an instance of a fundamental particle, how can I separate out the measurements of these four quantities? (I think) I understand the theory behind them, and why the particles in the ...
0
votes
1answer
303 views

What happens when light moves perpendicular to a moving object?

Imagine the folllowing situation: A coherent light source is attached to a car such that the emitted light beam path is "being crossed over" by the car i.e. the long parallel light beams are struck by ...
12
votes
3answers
4k views

What does it mean that the neutral pion is a mixture of quarks?

The quark composition of the neutral pion ($\pi^0$) is $\frac{u\bar{u} - d\bar{d}}{\sqrt{2}}$. What does this actually mean? I think it's bizarre that a particle doesn't have a definite composition. ...
3
votes
1answer
329 views

Does kaon decay etc prove “CP violation” or just “CP or CPT violation”

Shlomo Sternberg (math professor at Harvard) wrote a book called "Group theory and physics". On p156 (link) there's a strange offhand comment: "Experiments done in 1964 by Fitch and Cronin seem to ...
8
votes
1answer
258 views

Is there literature on a continuous mass spectrum for the Higgs field?

Various masses for the Higgs field are compatible with experiment, but is it possible that the Higgs field is not observable because it has a continuous mass spectrum? Work in the 60s and 70s on free ...
8
votes
1answer
385 views

What properties of Germanium make it suitable for Dark Matter detectors?

What properties of Germanium make it suitable for Dark Matter detectors? I tried googling but there was too many results describing the use of Germanium Chrystals at low tempretures for Dark Matter ...
7
votes
1answer
650 views

Why are higher generation of matter unstable?

My secondary school physics textbook has mentioned that protons and neutrons are made up of down and up quarks in different amounts. It has also mentioned that other quarks exist. It states that ...
4
votes
1answer
1k views

Confusion between the de Broglie wavelength of a particle and wave packets

So I learned that the de Broglie wavelength of a particle, $\lambda = \frac{h}{p}$, where h is Planck's constant and p is the momentum of the particle. I also learned that a quantum mechanics ...
4
votes
1answer
591 views

Detection of W and Z bosons

What specific behaviour confirmed the existence of the W and Z bosons at the UA1 and UA2 experiments? Thanks!
18
votes
4answers
6k views

Is it pions or gluons that mediate the strong force between nucleons?

From my recent experience teaching high school students I've found that they are taught that the strong force between nucleons is mediated by virtual-pion exchange, whereas between quarks it's gluons. ...
6
votes
1answer
626 views

7 GeV dark matter particle: how particle accelerators missed it?

This posting is regarding the recent confirmation of the DAMA results that might be due to underlying differences in proton and neutron cross section with the dark matter particles, which reflect on ...
17
votes
2answers
970 views

Correlation between outstanding hints in experimental particle physics

The 115 GeV ATLAS Higgs with enhanced diphoton decays has gone away but there are several other recent tantalizing hints relevant for particle physics, namely CoGeNT's 7-8 GeV dark matter particle ...
2
votes
1answer
123 views

experimental setup to measure Center-Of-Momenta of products from spontaneous radiactive decay

This question is an attempt to complement this other question about fluctuations in radiactive decay. This question is completely experimental though: in general, suppose i have certain sample of a ...
8
votes
2answers
655 views

What is the fastest process or shortest time in nature?

We know about some events that happen very quickly. For example, the dielectric relaxation time is about $10^{-14}\, \mathrm{seconds}$. I'm interested in other processes that switch extremely fast ...
3
votes
6answers
1k views

Good book about elementary particles for high school students?

I need a good book about elementary particles. I am a high school student and don't want anything to technical. I read a brief history of time and the universe in a nutshell but I want something that ...
2
votes
1answer
195 views

Why are the third generation superpartners lighter than the other sfermions in MSUGRA

In the MSUGRA breaking scenario, the stop particle typically appears at energies reachable at the LHC. Other sfermions, notably the partners of up, down, strange and charm are assumed to be degenerate ...