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.
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2answers
84 views
What is the process that gives mass to free relativitic particles?
When a free particle move in space with a known momentum and energy then what is the physical process that gives mass to that free (relativistic) particle?
What is role does the Higgs field in that ...
2
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1answer
78 views
Complex masses for Dirac and Weyl spinors
I'm trying understand how to rotate Dirac fields to absorb complex phases in masses. I have a few related questions:
With Weyl spinors, I understand, $$ \mathcal{L} = \text{kinetic} +
...
8
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0answers
55 views
Does the existence of Higgs imply the existence of Magnetic Monopoles?
I am aware that in theories with spontaneous symmetry breaking, Magnetic Monopoles can exist as topological solitons. Can the same be done with the Standard Model gauge group. I am familiar with the ...
1
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1answer
41 views
Anti-particle problem for Dirac sea
According to the Dirac hole theory we know that Dirac sea is completely filled with negative energy, called vacuum. We will need $2mc^2$ or greater to get electron and a positron by incident photon.
...
6
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1answer
167 views
SUSY, ways to boost Chargino/Neutralino production?
Does anybody know a good reference that works out the equations for the Chargino/Neutralino production cross section in SUSY? I'm trying to understand if there are any tricks for boosting the ...
6
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1answer
86 views
Precise statement of Mermin–Wagner theorem
Roughly speaking, Mermin-Wagner theorem states that continuous symmetries cannot be spontaneously broken at finite temperature in systems with sufficiently short-range interactions in dimensions ...
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0answers
33 views
calculate distance in feet using time interval from iphone camera [duplicate]
i am working on iPhone application to achiever the below functionality.
i want the distance in feet between Two Points from the below information.
i am standing at one position with iPhone (Camera ...
4
votes
2answers
60 views
How to directly calculate the infinitesimal generator of SU(2)
We commonly investigate the properties of SU(2) on the basis of SO(3). However, I want to directly calculte the infinitesimal generator of SU(2) according to the definition $$X_{i}=\frac{\partial ...
2
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0answers
57 views
Categorizing solutions to Hierarchy problem
We know that no gauge symmetry can prevent a term $m_\phi^2|\phi|^2$ for a scalar field, and that, given the quadratic loop corrections, the natural scale is $m_\phi \sim M_P$. This is related to the ...
3
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1answer
98 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
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1answer
95 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 ...
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1answer
91 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
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1answer
31 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 ...
9
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3answers
120 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
717 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?
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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
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1answer
778 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
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1answer
79 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
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2answers
224 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
51 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
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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
798 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
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2answers
150 views
What happens in electron-electron collisions?
What are the results of high energy electron electron collisions? Are other particles created?
4
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1answer
76 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?
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1answer
67 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
208 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
353 views
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
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1answer
38 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 ...
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0answers
22 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.
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0answers
34 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
74 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 ...
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0answers
53 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
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1answer
48 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
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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 ...
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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
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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
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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
89 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
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1answer
67 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
75 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
511 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?
0
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1answer
173 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
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3answers
893 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. ...
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1answer
62 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?
