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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72 views

LEP vs. LHC for Higgs production?

Now that we know the mass of the Higgs boson, which system would be better for the production of Higgs bosons, the LEP ramped up or the LHC?
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1answer
67 views

Asteroid collision debris calculation

I wonder how to determine the directions, in which the collision debris is launched when 2 asteroids collide. I am aware of: m1*v1 + m2*v2 = m*v = m3*v3 + m4*v4 + m5*v5 + ... and this works just fine ...
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1answer
113 views

Matter Waves Interference

When an EM wave diffracts, I can imagine that its EM field interacts with the charges in a certain obstacle thus inducing a wave behaviour on the charges of the matter that will interact with the EM ...
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1answer
52 views

What defines the interaction strength of a particle (massless or not) with matter?

Generally, talking about photons, the shorter the wavelength, the higher the interaction with matter. I doubt that I really understand why this happens. What about other massless particles? And ...
6
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1answer
406 views

Why decay of neutral Rho meson into two neutral Pions forbidden?

Why neutral rho meson decay into two neutral Pion forbidden? Can someone explain me in bit more detail? Although, other modes of decay are possible. Is it something with conservation of Isospin ...
10
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1answer
122 views

The delay between neutrinos and gammas in a supernova, and the absolute mass scale of neutrinos

In a supernova explosion (of some type), there is a huge amount of neutrinos and gamma rays produced by a runaway nuclear reaction at the stellar core. In a recent comment, dmckee noted that the ...
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3answers
141 views

Are all elementary particles of the same type exactly the same?

Are all elementary particles of the same type EXACTLY the same? Is there some variation in what an electron is, for example, or are they all the same?
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2answers
456 views

Why Cronin Effect Happens?

I'm looking for explanation on Cronin effect but unfortunately there's no Wikipedia entry or self-contained paper to start from. The statement of this effect is that: "At leading order, multiple ...
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0answers
46 views

What will happen to matter if there is a Higgs metastability decay?

Previously, on Save us from swallowing baby universes, please!, I pointed out the dangers associated with false vacuum decay. I wish to be more specific here. Suppose the Standard Model remains a ...
9
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1answer
85 views

More forces at low energy?

Just a quick question: In high energy experiments, the fundamental forces are thought to merge into a single force. My question is, in very low energy experiments (very low), do the forces we know ...
1
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1answer
48 views

Possibility of stable muonic structures?

In an analogy to the neutron, which decays rapidly as a free particle, but when bound in a nucleus it is stable, would it be possible to crease a structure that permits the stability of muons - be it ...
2
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0answers
76 views

Partial waves and the velocity expansion of a scattering cross section

I'm confused about the relation between the velocity expansion of a scattering cross section and the angular momentum (partial wave) expansion. For example, for dark matter annihilation, we write ...
8
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1answer
149 views

Charge of the muon

In the Wikipedia article of Muon, it says ...with unitary negative electric charge of roughly -1 and a spin of 1/2, What are they trying to convey with the "roughly"? Aren't the allowed values ...
0
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1answer
90 views

Is the Higgs particle the final one predicted by the Standard Model? [duplicate]

Are there any other particle predictions by the standard model?
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0answers
78 views

Anomaly cancellation and fermion number violation

In the standard model, an axial $SU(3)$ currents has anomaly which after quantization leads to the fermion number violation. However, taking all the fermions into account we note that the anomalies ...
6
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1answer
120 views

Importance of MHV amplitudes

Why are MHV amplitudes so important? How/where are they used and why do people keep trying to rederive them in many different ways?
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0answers
63 views

Running chargino/neutralino masses in MSSM

Consider the plot below, showing the running of different masses due to renormalization for a certain point of the (c)MSSM. I am able to exactly reproduce the plot, including the running of M1, M2, ...
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1answer
52 views

What is the chemical symbol for Mu-mesic atoms?

Is there a convention for chemical symbols of mu-mesic atoms, at least for ones bound to light atomic nuclei?
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1answer
97 views

Mass is rigidity?

In General Relativity, a totally rigid body cannot be accelerated. It will behave like something of infinite mass. Similarly a body of two separated particles which connected to each other with a ...
5
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1answer
90 views

What sorts of complications do massive neutrinos bring to the Standard Model?

Naively, I'd just think of considering them as any other massive fermions (but without electric charge), including the appropriate chiralities (and neutrino-higgs coupling when necessary). ...
0
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0answers
34 views

Yan - Drell process

I'm looking for more information about Yan - Drell process but didn't manage to find a good place to learn from (still looking for one). I understood that this process can help us to understand the ...
0
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1answer
81 views

Why do arrows point backwards in time for Feynman Diagrams?

I've been looking into Feynman Diagram for quite some time, and the fact that anti-particles point backwards in time after an interaction has been puzzling me. I understand this to be some convention ...
7
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2answers
241 views

Anti-matter as matter going backwards in time? (requesting further clarification upon a previous post)

I understand this question has already been asked here, however, I don't have enough reputation points to place a comment (I suppose that's the reason) on a specific answer to request a reference. A ...
7
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1answer
654 views

Why do we need to find 5 Higgs Bosons to prove the existence of the dark matter?

I was recently watching a show that say we need at least 5 Higgs Boson to prove the existence of the dark matter because it will strengthen the concept of symmetry. Why is that so? Because, I am not ...
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0answers
28 views

Lower bound bound on the mass of scalar bosons

Is there any lower bound bound on the mass of scalar bosons in nature. I know that a massless scalar boson would lead to a fifth force which would violate the equivalence principle. But is there any ...
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5answers
170 views

Do the particles made in a collider exist outside the collider?

Below is the transcript of a section from Demystifying the Higgs Boson with Leonard Susskind. Around 1:02:23 Susskind says that the heaviest of the fermions is called the top quark. Top quark is ...
2
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1answer
57 views

Might HEP production of “exotic” particles like superparners and dark matter be impossible?

In reading a lot of articles about HEP and what the LHC could detect or what it has excluded (like low-mass superpartners) it seems every author essentially assumes that things like low-mass ...
2
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2answers
86 views

How can the Higgs have so many different Yukawa couplings?

How can the Higgs have so many Yukawa couplings? Isn't this about the same as saying the Higgs has a force or charge for each different coupling? Is this some indication of substructure for the ...
6
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2answers
97 views

Deciding what to collide at particle accelerator

Different particle accelerators use different types of collisions. For instance at the LHC they investigated p Pb collisions while its predecessor (LEP), used to collide electrons with proton and at ...
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2answers
203 views

Bathroom photons from the edge at the universe [duplicate]

I was looking through my bathroom window this night and I was wondering if any of the photons my retina is hit with are from 13 (40) billion light years away ?! I was looking through it a few ...
3
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1answer
89 views

What determines the shape of the WIMP cross-section vs mass limit curves?

In figure 5 of http://arxiv.org/abs/arXiv:1310.8214 (PDF: http://arxiv.org/pdf/1310.8214v1.pdf), the experiments all seem to reach the lowest cross-sections when the WIMP is in the $40-100\, ...
5
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1answer
139 views

Charge neutrality of the Universe: evidences and theories

I've always wondered why the number of protons in the Universe exactly matches the number of electrons. They are such different particles with totally different cross sections. So, first of all, is ...
2
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0answers
55 views

What determines the probability of a pair of photons interacting, and producing a positron and an electron?

The second answer to this question describes how this process might occur, and I'm curious for more details about it: What is the probability distribution of the interaction producing ...
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0answers
123 views

Is total angular momentum conserved in particle interaction?

Imagine that two electrons interact by exchanging a virtual photon. I know that the total energy and linear momentum of the two electrons is conserved by the interaction. Is the total (orbital) ...
4
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1answer
68 views

Spinor representation restricted under subgroup, a formula from Polchinski

The question is about the spinor representation decomposed under subgroups. It's a common technique in string theory when parts of dimensions are compactified and ignored, and we are only interested ...
2
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1answer
104 views

Particles from String theory

I understand that the strings in string theory are posited to be many, many orders of size smaller than say, a quark, electron or any other particle. But if this is so, how does the string "expand" to ...
5
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1answer
128 views

Number of decays in a chain reaction

It is widely known that the probability of $n$ decays from one system to another $A \rightarrow B$ (e.g., electrons decaying from one atomic energy level to another or muons decaying into neutrinos ...
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1answer
66 views

Any known relationships among quark masses?

Here is some numerology: Gen 1 Mass(d)/Mass(u) = 2 = 2 * 1 Gen 2 Mass(c)/Mass(s) = 12 = 4 * 3 Gen 3 Mass(t)/Mass(b) = 40 = 8 * 5 Does standard model make any predictions of relations? Do any GUT ...
2
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1answer
66 views

momentum conservation and gluons

The process is the following: $$e^-e^+ \rightarrow photon \rightarrow quark + antiquark$$ Regarding the momentum conservation law, how come we have a photon of spin 1 and at the end some meson with ...
2
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0answers
74 views

Møller scattering: twisted?

I am studying the Møller scattering, but I don't know how to get the twisted diagram from the S-matrix. Has anybody a good explanation?
5
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1answer
84 views

Classical EM neglects electron recoil?

Imagine two electrons $A$ and $B$ at rest. Electron $B$ is at a vertical distance $r$ above electron $A$. Let us assume that the electrons are constrained to move on horizontal rails. At time $t=0$ ...
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0answers
33 views

Fermi's weak interaction theory

In Fermi's theory, we have energy squared in the numerator of the cross-section which makes it diverge as energy increases. But isn't that the Fermi constant suppresses it with increasing order?
2
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2answers
190 views

Have we found a Higgsino?

In supersymmetry, for each particle (boson/fermion), there is a symmetric particle which is a fermion/boson. The MSSM predicts five Higgs bosons: two neutral scalar ones (H and h), a pseudo-scalar ...
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1answer
63 views

Simple photon recoil question

Imagine two charges A and B separated by some distance. Charge A emits a photon which is absorbed by charge B. Is the recoil momentum received by charge A always equal and opposite to the momentum ...
11
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1answer
269 views

Operator that describes particle detector

In non-relativistic QM, the position of a particle is an observable. In QFT, fields are the observables. However, particles must have some sort of position, otherwise we wouldn't see pictures like the ...
4
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2answers
136 views

Pair production of neutrinos

I learned that neutrinos have a much lower energy than electrons. Pair production of electrons occurs when the photon energy is above 2 times the energy of an electron. So I am wondering if pair ...
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1answer
56 views

Statistics followed by Neutrinos [closed]

What does the neutrino particles follow- Dirac or Majorana Statistics?
2
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1answer
239 views

Can two photons annihilate?

This is a question about definitions. When two photons interact to create an electron/positron pair, does this process 'count' as annihilation of the photons? I've struggled to find a good ...
22
votes
1answer
256 views

Identification of particles and anti-particles

The identification of an electron as a particle and the positron as an antiparticle is a matter of convention. We see lots of electrons around us so they become the normal particle and the rare and ...
5
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1answer
127 views

Photon particle/wave question

Imagine a source of photons at the center of a spherical shell of detectors at radius $R$. Assume the photons are emitted one at a time. Now if photons are particles that are highly likely to travel ...