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.
3
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1answer
92 views
How to determine predicted CP violation for a given SUSY point?
I'm currently studying at the spectra of some supersymmetric models, and would like to know whether the parameter points I'm looking at are ruled out due to excessive CP violation.
I am using SPheno, ...
1
vote
1answer
84 views
Can 3 photons be combined to give a spin-0 projection?
Motivation: The neutral pion decays to 2 photons ($\pi^0\to\gamma\gamma$) most of the time. For the decay of the neutral to 3 photons ($\pi^0\to 3\gamma$) we have an upper limit on the branching ...
0
votes
1answer
86 views
can be exist the negative mass? [duplicate]
I'm not sure about this but I guess there must be negative masses in the universe because of the symmetry. If the gravity is one of the main forces in nature it must has negatives mass to be able to ...
1
vote
1answer
28 views
what is the magnetic quadrupole operator?
To find magnetic or electrical moments in quantum theory we must calculate the expectation value of an appropriate operator. the dipoles operator are similar and is easy to find but the magnetic ...
7
votes
3answers
103 views
Resonances in high energy physics
I still do not understand what a resonance precisely is. Is it exactly the same as a particle? Or only an excited state?
And why does it make a peak in some diagrams? And which diagrams?
4
votes
2answers
312 views
Will negatively charged strangelets be produced by the LHC?
Witten (and earlier, Bodner) hypothesized that strange matter (up, down, strange quarks) should be more stable than "regular" nuclear matter(The strange matter hypothesis). That is that the typical ...
16
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3answers
714 views
How do we know Dark Matter isn't simply Neutrinos?
What evidence is there that dark matter isn't one of the known types of neutrinos?
If it were, how would this be measurable?
1
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1answer
40 views
Interpreting the results
I have preformed the muon lifetime experiment at my uni's lab, and got the data. It's text file with 8190 numbers. My TDC unit was set so that the time gates were at 10 $\mu s$, and it has 8192 ...
2
votes
1answer
771 views
Does the Breit Wigner formula apply to intermediate virtual particles?
Breit Wigner Formula describes the cross section for interactions that proceed dominantly via a intermediate particle (O*) A+B → O* → C + D:
$$σ = \frac{2\Pi}{k^{2}}\frac{Γ_{i}Γ_{f}}{(E-E_{o})^{2} + ...
4
votes
1answer
75 views
Asymptotic Freedom - Qualitative Explanation
I am doing a (mostly qualitative) course on Particle Physics, and am confused about the concept of asymptotic freedom. The lecture notes basically say that a quark may experience no force/be "unbound" ...
4
votes
2answers
222 views
About free quarks and confinement
I simply know that a single free quark does not exist. What is the reason that we can not get a free quark?
If we can't get a free quark then what is single-top-quark?
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0answers
46 views
Are Gribov copies responsible for the observed Mass-gap and color confinement properties of Pure Yang-Mills Theory?
New solutions to the existing problems are presented by the quantum mechanics and Einstein's theory of special relativity when treated together. The creation of particle/anti-particle pairs by quantum ...
11
votes
2answers
395 views
What is the mass density distribution of an electron?
I am wondering if the mass density profile $\rho(\vec{r})$ has been characterized for atomic particles such as quarks and electrons. I am currently taking an intro class in quantum mechanics, and I ...
4
votes
2answers
795 views
Rigid body dynamics joints
I can't seem to find any info on connected rigid bodies by a joint. Can someone explain the basics to me? I'm trying to do a little research to find out how feasible it would be to implement 3d ...
9
votes
2answers
141 views
What happens in electron-electron collisions?
What are the results of high energy electron electron collisions? Are other particles created?
4
votes
1answer
75 views
Are electrons simple? Do they have any inner structure? [duplicate]
The plank length is far smaller than the classical electron radius. Could the electron have structure?
0
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1answer
66 views
Why Planck scale is so important?
I know that Planck scale is the scale where both, gravity and quantum effects are relevant simultaneously. Are there more reasons?
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1answer
206 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 ...
7
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0answers
339 views
+100
About defining “baryons” and “mesons”
I want to understand the proof of the claims (of the construction as well as of its uniqueness) of gauge singlet states given around equation 2.13 (page 10) of this paper.
Also does the listing of ...
3
votes
1answer
37 views
Parametrization of $U(N)$ non-linear sigma model
The motivation of this question actually comes from this (really old) paper of Weinberg. He considers a theory of massless pions. They have a chiral $SU(2)_{L} \times SU(2)_{R}$ symmetry. The pions ...
0
votes
0answers
20 views
What's the real value of screening length?
I know that the screening length (R) is an effective distance over which the nucleus of an atom is active, since it is screened by the orbiting electrons.Various derivations for R have been proposed, ...
3
votes
1answer
34 views
Caveats when using event-by-event reweightings?
A fairly common technique in experimental particle physics is event-by-event reweighting. The idea is that you have a sample of background-model events, either from a Monte Carlo simulation, or from a ...
3
votes
0answers
49 views
List of cross sections?
Sometimes I need to look up a certain cross section, say the inclusive Z production cross section at $\sqrt{s}$ = 7 TeV. Is there a place where 'all the' cross sections are tabulated ...
0
votes
1answer
233 views
Where to find experimental/theoretical value of (charge) radius of particles?
Where to find experimental/theoretical value of (charge) radius of particles like proton, neutron, $pi^+$, etc. ?
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2answers
181 views
Where to find cross section data for e- + p -> p + e-?
Where to find cross section data for e- + p -> p + e-?
PDG's cross section data listing does not include it.
0
votes
0answers
32 views
Lagrangian of electromagnetic tensor in light cone coordinates? [closed]
I have Lagrangian Density of Electromagnetic field Tensor in light cone coordinates using D'Alembertian operator and Lagrangian density in Cartesian coordinates. I couldn't figure out the way to ...
3
votes
2answers
72 views
Transfer of electron energy to atoms (heating up of matter by absorption of photons)
If an electron absorbs a photon to get exited to a higher energy level, it should either come back to same state or any other lower state by emitting the required photon. How then can there be a net ...
1
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0answers
52 views
Matrix element approximation
In the formula for the decay width of $\Upsilon(4S)$ to B-mesons from $\text{e}^+\text{e}^-$ collisions:
$$\Gamma_{\Upsilon(4S)\to B\bar{B}}=\frac{\left|\underline{P}_B \right|}{8\pi ...
4
votes
0answers
58 views
I am trying to calculate the branching ration of higgs goes to 2 photons using the standard model [closed]
I need to use the three lowest order feynman diagrams to first calculate the squared matrix element to put into fermis golden rule formula and then from there get the branching ratio of higgs decays ...
1
vote
1answer
45 views
Baryon wave function symmetry
If a baryon wavefunction is $\Psi = \psi_{spatial} \psi_{colour} \psi_{flavour} \psi_{spin}$,
and we consider the ground state (L=0) only.
We know that the whole thing has to be antisymmetric under ...
0
votes
1answer
82 views
Is the heat required to alter the Higgs field an 'absolute heat'?
I have read and heard that manipulating the Higgs field would require heating up a local geometry to ridiculous temperature. I am trying to understand if there are stars or places in the universe ...
-1
votes
0answers
48 views
What is the difference between various fields of physics? [closed]
what is the difference between the fields of physics? like high energy physics, particle physics, cosmology, quantum physics, quantum mechanics, experimental physics, theoretical physics, applied ...
4
votes
4answers
4k views
What are quarks made of?
So atoms are formed from protons and neutrons, which are formed from quarks.
But where do these quarks come from? What makes them?
2
votes
0answers
116 views
About the decay of Higgs into 2 Z bosons
I need to know if I understand this point.
The factor of HZZ vertex in the SM Lagrangian is half the value of the Feynman rule which appears in Diagrammatica.
When I calculate the decay of Higgs ...
6
votes
0answers
84 views
Status of experimental searches for tachyons?
Now that the dust has settled on the 2011 superluminal neutrino debacle at OPERA, I'm interested in understanding the current status of experimental searches for neutrinos. Although the OPERA claim ...
1
vote
1answer
66 views
is the nature of particle beam weapons in science fiction true to the reality of particle physics?
I am referring to the use of specific particle types such as an antiproton beam, positron beam, meson beam or muon beam for example in the likes of shows like star trek. I was curious if a beam of a ...
4
votes
2answers
74 views
Does it make a sense to speak about age of electron or atom?
It's possible that this question is too soft or even quite senseless for this forum, but I will ask nevertheless.
Everyday (macroscopic) things, like a grandfather's pendulum clock or the grandfather ...
3
votes
2answers
502 views
What Quark and Anti-quark are electrically neutral Pions made out of?
A positive pion is an up and an anti-down. A negative pion is a down and an anti-up. What's a pion with an electrical charge of 0?
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votes
1answer
171 views
What process could produce two neutral pions only?
Any examples?
$$? \rightarrow \pi^0 \pi^0$$
If such a process exist, could there be nonzero total orbital angular momentum in the final states of the two neutral pions? But then how to understand ...
9
votes
3answers
886 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. ...
1
vote
1answer
61 views
Which pion is mediator in nucleon-nucleon interaction
In nucleon-nucleon interactions of n-n, p-p, n-p how do you determine which pion is the mediator?
2
votes
1answer
282 views
Why the pion does not get mass under Spontaneus breaking of chiral symmetry, but the quarks do?
Some sources state that when the mass of a quark goes to zero, it allows for Spontaneous Breaking of Chiral Symmetry and gets a constituent mass of about $200\, \mathrm{MeV}$.
Other sources state ...
1
vote
2answers
249 views
Quark compositions in $\pi^+$ to $\pi^0$ pion decay
Pions can undergo a rare beta-like decay into leptons:
Pion beta decay (with probability of about $10^{−8}$) into a neutral
pion plus an electron and electron antineutrino (or for positive
...
5
votes
2answers
412 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 ...
8
votes
2answers
990 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. ...
9
votes
0answers
87 views
infrared free QED and Higgsless standard model phenomenology
This is one of those "what if" fantasy world type questions. I like hard sci-fi so please no "well, you changed one thing about the world so now anything goes." :)
What if the Higgs had no vev?
That ...
-3
votes
0answers
35 views
effect of gravity on chemical reaction rates [closed]
a chemical reaction is done on earth in very vacuum and that chemical reaction is also done in space so that gravity higgs field not affect that reaction.
Which reaction will be fast wrt gravity and ...
2
votes
1answer
64 views
Infinite reflection of light and the conservation of energy / momentum
First off, I confess I'm no physicist, but I have been asking people with a more extensive knowledge this one question, without a definitive answer so far.
Basically, I'm playing around with the idea ...
5
votes
1answer
100 views
Mechanisms of mass generation for Dirac neutrinos
If neutrinos are Majorana particles, one way of explaining their small masses is the seesaw mechanism.
Now say I'd like my neutrinos to be Dirac, for symmetry to the quark sector. What mechanisms ...
1
vote
1answer
74 views
Elementary question on pion-proton scattering cross-section
Is $E_k$ the energy of the outgoing or incoming pion?
The first peak is supposed to be a delta baryon.
What does the graph tell us, experimentally? A pion of kinetic energy x comes in, then we ...
