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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194 views

Feynman diagram for $\overline{K}\,\!^0$ antimeson production on the quark-level

I've recently stumbled upon a physics problem concerning $\overline{K}\,\!^0$ antimeson production. In this particular example, colliding a $\pi^-$ meson with a stationary proton yields a $K^0$ meson ...
6
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2answers
1k views

Virtual photons, what makes them virtual?

The wikipedia page "Force Carrier" says: The electromagnetic force can be described by the exchange of virtual photons. The virtual photon thing baffles me a little. I get that virtual particles ...
1
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1answer
164 views

spin parity $J^P$ notation

In particle physics, when you read $J^P$, does it mean Spin parity or total angular momentum parity? I know that the letter $J$ is used for TOTAL angular momentum but I think I read somewhere that ...
2
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1answer
66 views

Elastic vs Inelastic vs isospin violating scattering particle physics models

I'm looking for a nice paper that explains the difference between three particle physics models for spin-independent dark matter interaction with nuclei: elastic, inelastic and isospin violating ...
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2answers
211 views

Neutrinos: how can they carry information about universe?

I know that neutrinos are particles with a very small mass and no electric charge. They infrequently interact with matter and so they can give us information about the "old" universe. But how can they ...
-2
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1answer
288 views

Why strong and weak forces are short range? [closed]

Why are the strong and weak nuclear forces short range? Are quarks confined or welded together? Why are elementary particles confined at short range? Or is color confinement color welding? the ...
2
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1answer
127 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
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0answers
274 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 ...
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2answers
451 views

Momentum of a particle? [closed]

I really need help to understand what is momentum of a particle (of a photon, proton, an electron...) I see so many definitions! My main questions are: •What exactly is momentum •What are the ...
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0answers
42 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
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2answers
7k 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
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1answer
222 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.
9
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1answer
269 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, ...
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1answer
112 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 ...
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0answers
43 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 ...
7
votes
1answer
169 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, ...
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3answers
1k 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 ...
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1answer
182 views

Plot of gauge coupling unification [closed]

(Zoom in here to see the scales.) 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 ...
2
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2answers
262 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 ...
3
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1answer
381 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
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1answer
239 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 ...
1
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1answer
764 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
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1answer
127 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
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1answer
108 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
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1answer
134 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 ...
6
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1answer
267 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 ...
5
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2answers
301 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 ...
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1answer
111 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 ...
4
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1answer
347 views

Pion production in proton-proton collision

Why is $\pi^0$ created in the high-energy collision $p+p\to p+p+\pi^0$?
5
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1answer
235 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 ...
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0answers
59 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 ...
11
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0answers
249 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
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1answer
169 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 ...
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0answers
51 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 ...
2
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0answers
40 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 ...
6
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1answer
559 views

What goes wrong when one tries to quantize a scalar field with Fermi statistics?

At the end of section 9 on page 49 of Dirac's 1966 "Lectures on Quantum Field Theory" he says that if we quantize a real scalar field according to Fermi statistics [i.e., if we impose Canonical ...
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1answer
177 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. ...
3
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1answer
206 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} + ...
7
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1answer
301 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
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2answers
395 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 ...
4
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0answers
108 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
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1answer
148 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
346 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
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1answer
66 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 ...
10
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3answers
603 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?
2
votes
1answer
324 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
162 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" ...
12
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2answers
3k 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
137 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
143 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?