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.
2
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1answer
59 views
Anti-symmetric 2 particle wave function
Suppose we want to construct a wave function for 2 free (relativistic) fermions. As we are dealing with fermions the total wave function has to be antisymmetric under interchange of the coordinates,
...
7
votes
0answers
98 views
Possible implications of Quark Quartet
Today on Nature's website appeared a news about the discovery of a quark quartet (formed from two quarks and two antiquarks). They say that this particle containing four quarks is confirmed. This is ...
0
votes
0answers
36 views
Why aren't there more than three generations of the leptons and quarks? [duplicate]
There are three generations of electrons, neutrinos, and quarks. The second and third generations of electrons and quarks are unstable and decay into lighter particles.
Why are there exactly three ...
2
votes
2answers
150 views
Is there anything smaller than a quark? [duplicate]
I've gotten interested in physics recently due to the many educational channels on YouTube such as sixtysymbols and minutephysics. They talk about quarks sometimes, and I was wondering if there is ...
4
votes
1answer
35 views
N=1 v N=2 supermultiplets
I read that the chiral nature of SM fields is an indication that they must be realized in a N=1 supermultiplet (and not N=2). I don't quite understand how so. Please enlighten.
8
votes
1answer
132 views
Gauge symmetries and elementary particles
The Weinberg-Witten theorem (disclaimer: I don't know this wikipedia entry) is usually mentioned as the reason why gravitons may not be composite particles. I do understand the proof of the theorem, ...
1
vote
1answer
43 views
Relationships between different measure of opacity
I'm reading some papers that compare different values for a materials opacity to a particular particle. The first is given as $\frac{dE}{dX}$, a single particles energy loss per unit column depth (X ...
1
vote
0answers
21 views
Can TOTEM's T2 detector measure differential cross sections?
My current research involves making a prediction for data collected by the TOTEM experiment at the LHC. The experiment is primarily designed to measure the total inelastic and elastic scattering cross ...
6
votes
1answer
67 views
Is broken supersymmetry compatible with a small cosmological constant?
I understand that we can find the energy of a bosonic field in its vacuum state via
$E_{vac}^{(B)} = \sum_{\vec{k},s} \frac{1}{2}\hbar\omega_{\vec{k},s}^{(B)}$
and a fermionic one similarly,
...
0
votes
3answers
81 views
If subatomic particles pop into existence all the time, why don't I gain weight?
Watching Discovery's first episode of the first season of Curiosity (entitled "Did God Create the Universe?" by Stephen Hawking), I heard this information:
[...] you enter a world where conjuring ...
1
vote
1answer
65 views
Plot of gauge coupling unification [closed]
About the result of plotting running of 3 coupling constant, we think that we should get the correct one(MSSM).
But we get discontinuity at $ M_{susy}$.
If there something wrong in our formulae?
If ...
1
vote
1answer
47 views
Matter and anti-matter collision energy problem
From Beyond Einstein, by Michio Kaku and Jennifer Thompson, Chapter 13, Antimatter :
Dirac, also focused on the fact that Einstein's equation $E=mc^2$ wasn't totally true. (Einstein was aware that ...
-1
votes
0answers
12 views
secondary electron gain and secondary electron yield [duplicate]
The context of the question is an electron microscope. Can someone explain me the difference between secondary electron gain and secondary electron yield?
-3
votes
0answers
81 views
Constructive physics more important than colliders? [closed]
Much of modern partcle physics concerns colliders. Some research involves creating particles using photons.
For example, low energy lasers can produce electron / positron pairs.
Soon after the big ...
-2
votes
0answers
30 views
What is the minimum amount of energy/mass? [duplicate]
is there a minimum amount of matter? perhaps the smallest elementary particle?
what about energy? Is there a minimum amount of energy or can this amount be infinitely small?
1
vote
1answer
91 views
Why no fundamental force from the Higgs? [duplicate]
I wish to ask whether I understand the following correctly. This universe seems to have six fundamental elementary bosons namely photon $(\gamma),\ W$-bosons$(W^+,W^-),$ gluon$(g),\ Z$-boson $(Z)$, ...
4
votes
1answer
204 views
Imaginary masses
While watching this video, at around 5:00, the man mentions a certain type of particle having imaginary mass. He also says that these kind of particles can go faster then light. But how it is possible ...
0
votes
1answer
69 views
From where do the permanent magnets get energy from? [duplicate]
I have a doubt about permanent magnets. If a magnet is permanent it can attract some materials permanently.
Attracting something involves energy. If a permanent magnet can do this forever, from where ...
4
votes
0answers
54 views
Fermion annihilation amplitude
Is there a physical reason why annihilation of 2 identical fermions with mass m to 2 scalars amplitude for $s=4m^2$ (fermions at rest) is zero? For example we can have 2 scalars annihilating in 2 ...
3
votes
1answer
40 views
What is the $t\bar{t}$ production supposed to bring up
The $t\bar{t}$ production, I've read, that will somehow confirm the QCD and might bring up new physics. Why are we studying $t\bar{t}$ production from $p-p$ collisions at the LHC?
What are we trying ...
1
vote
1answer
50 views
Quarks and anti-quarks forming particles [duplicate]
As I know, when particles and anti-particles come close, they anihilate. So somthing caused me a big trouble : how can particle formed by quarks and anti-quarks can exist? I've just found some mesons ...
4
votes
1answer
128 views
Could electrons be a form of antimatter?
I've played with this idea for years, and haven't really been able to eliminate it. So, perhaps someone here can point to simple experimental evidence that would do so.
Here's the issue: Antimatter ...
3
votes
1answer
59 views
What is the role of the color-anticolor gluons?
Ignoring for the moment the experimental necessity of eliminating the gluon singlet state, the nine "raw" gluon color components form two quite distinct sets. The first set consists of the six ...
0
votes
1answer
67 views
Is everything in the physical world composite?
In philosophy there is a principle that anything composite cannot have existed eternally, since it is preceded by its parts and whatever forces assembled it.
Is everything in the physical world ...
1
vote
0answers
32 views
Pion production in proton-proton collision
Why is $\pi^0$ created in the high-energy collision $p+p\to p+p+\pi^0$?
4
votes
1answer
55 views
Pileup subtraction for event reconstruction
In particle physics experiments, pileup occurs when two particles hit the same detector (say a calorimeter) at roughly the same time, resulting in what looks like a single event with higher energy ...
3
votes
0answers
38 views
Helicity dependence in loop diagrams
I am trying to evaluate a diagram that looks like
The middle of the diagram is a fermion loop. I know that the coupling between the $Z^0$ and fermions depends on the fermions' helicities, so it ...
8
votes
0answers
144 views
“S-duality” between confinement and the Higgs mechanism?
I feel picked by the second to last sentence in this answer to a question about what would happen if EM and QCD were spontaneously broken, which says
"In fact, there is a sense in theoretical ...
3
votes
0answers
45 views
Non-existence of gluon singlets: Any recent theoretical progress?
An unanswered question from last year (2012) on gluon singlets asked whether there is any theoretical explanation for the experimental absence of the ninth or colorless (singlet) gluon. This is the ...
0
votes
0answers
44 views
the effects of an ln-prime transformation to physical models
I have rather a "toy" type of modelling-problem that appeared to me along a book I am writing on number theory. I would be outmost thankful for any concrete or inspirational answers, including ...
1
vote
0answers
27 views
Limits on stable charged particles
Are there generic model-independent limits on massive stable charged particles (say 10-500GeV)? I mean SU(2)/color singlets with just a hypercharge.
For example the LEP search (CERN-EP/99-075) was ...
1
vote
1answer
65 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.
...
8
votes
0answers
103 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 ...
2
votes
1answer
87 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, $$ \mathcal{L} = \text{kinetic} +
...
-2
votes
0answers
33 views
calculate distance in feet using time interval from iphone camera [duplicate]
i am working on iPhone application to achiever the below functionality.
i want the distance in feet between Two Points from the below information.
i am standing at one position with iPhone (Camera ...
6
votes
1answer
115 views
Precise statement of Mermin–Wagner theorem
Roughly speaking, Mermin-Wagner theorem states that continuous symmetries cannot be spontaneously broken at finite temperature in systems with sufficiently short-range interactions in dimensions ...
4
votes
2answers
83 views
How to directly calculate the infinitesimal generator of SU(2)
We commonly investigate the properties of SU(2) on the basis of SO(3). However, I want to directly calculte the infinitesimal generator of SU(2) according to the definition $$X_{i}=\frac{\partial ...
3
votes
0answers
63 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 ...
0
votes
1answer
100 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
54 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 ...
1
vote
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 ...
9
votes
3answers
151 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?
1
vote
1answer
109 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 ...
4
votes
1answer
91 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" ...
11
votes
2answers
200 views
What happens in electron-electron collisions?
What are the results of high energy electron electron collisions? Are other particles created?
4
votes
1answer
81 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
votes
1answer
75 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?
3
votes
1answer
42 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
25 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
0answers
58 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 ...
