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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The highest photon energy ever measured and transplanckian energies

What is the highest energy of we have measured of a photon by any physical experiment? Has a transplanckian energy photon been measured? Can we study them -if they exist- with special relativity?
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90 views

Tree Level Feynman Diagrams of Electron Positron Interaction

Consider the interaction $$e^-+e^- \rightarrow e^-+e^-$$ The following is a tree level Feynman diagram for this: We can also make the paths of the two electrons on the right hand side cross over and ...
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Symmetry responsible for equality of masses of particles

During my studies of basic particle physics the following question came up. What symmetry is responsible for equality of masses of particles and their antiparticles? In particular, is this symmetry ...
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Topics important in electrodynamics for particle physics

Say I'm going to study Griffith's electrodynamics, what are the important topics in it, for particle physics? Like Maxwell equations etc.
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32 views

Helicity of massive particle at high enengy

We know that massless spin-1 particle like photon only has two helicity state (-1,1), what about the helicity of massive spin-1 particle (W boson) at very high energy? Does it have helicity 0 state ...
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How do single photons travel from here to there

I know there have been similar questions but I'm still unclear what the overall consensus is. (1) I assumed and have read that photons travel in straight lines unless deflected by gravity but there ...
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19 views

The energy of our universe [duplicate]

Is there a substantial basis for the claim that the total energy of our universe is zero? I just read a bit of Hawking's writing in which he comes to this conclusion through inflation theory, but i ...
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25 views

Finding the mixing angle for two-neutrinos

I am trying to answer the following question; Light Majorana neutrino masses can be generated by the see-saw mechanism. Consider a mass term which, in the simplest case of one active and one ...
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1answer
55 views

Why don't all the gluon's get converted into energy in an uranium atom undergoing fission?

I have following questions and arguments. why do only gluons get converted into energy in an uranium atom undergoing fission? why don't all the gluons get converted into energy? which conditions ...
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61 views

Appropriate fit function for $\phi$ meson mass from $K^{+}K^{-}$ pair

I am attempting to measure the mass of the $\phi$ meson using the decay mode $\phi \to K^{+}K^{-}$. I have isolated the $\phi$ meson candidates using this decay mode, and have constructed the graph ...
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1answer
102 views

Wave function of particle and antiparticle

The wave functions of particle and antiparticle are related by complex conjugation and wavefunction $Ψ$ must be complex for particle such as $n$, $p$. Is there way to prove this mathematically? Can we ...
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15 views

Is the back induced emf in inductive coil equal to the original? [duplicate]

I always thought that an inductor resists the change of magnetic flux to a CERTAIN EXTENT, that is it would generate a back emf that would provide only a percentage of obstruction to the original emf. ...
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45 views

What interaction shown in this Feynman diagram and is it possible?

I saw the following Feynman diagram in my textbook, not sure if a typo or something I don't know: Just to clarify, the "e" on the upper left does not have any superscript. I am not sure if such a ...
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33 views

DNA breaks with particles or photons (Radiation therapy)

When protons (or other particles) or photons are used in radiation therapy to treat cancer patients, the main effect is for it to make DNA breaks that hopefully will make the cancer cell die ...
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2answers
65 views

If dark energy is responsible for the expansion of the universe, is it possible that it is also the force which creates dark matter? [duplicate]

In a science fiction story I am writing humans travel through space (only our solar system) using dark energy. In my imagining of the future scientists discovered that dark energy exists in a field ...
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24 views

How to calculate probability of neutrino oscillation after a distance

I'm trying to calculate the probability of an detecting a muon neutrino after a certain distance, where the neutrino beam is entirely electron neutrinos as t = 0. I know I need to use the PMNS matrix ...
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184 views

Why do we need to build photon colliders? Since electron-position colliders are very “clean”

What's the advantage of gamma-gamma colliders? What new physics can be done with it? Reference: http://www.slac.stanford.edu/pubs/beamline/26/1/26-1-kim.pdf
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How do I go about understanding particle physics? [closed]

My science project has tasked me in creating a research paper on the standard model of particle physics, but I'm not in highschool yet. I don't know how to go about learning the math and the concepts ...
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448 views

What is the difference between “additive” quantum numbers and “multiplicative” quantum numbers?

What is the difference between "additive" quantum numbers and "multiplicative" quantum numbers? I think that this may have something to do with P and C Symmetry groups, but I may be mistaken. I’m ...
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42 views

Could we live if we were made of antimatter? If so, would there be any difference to experience?

Antimatter is material composed of antiparticles, which have the same mass as particles of ordinary matter but opposite charges, as well as other particle properties such as lepton and baryon numbers ...
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How can muons travel faster than light through ice?

When a neutrino traveling through ice hits and interacts with an oxygen atom, muons are created. Cherenkov radiation can be created when muons travel through ice faster than light and create a ...
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330 views

Why is there no fundamental force following from the $SU(4)$ symmetry?

I've understood that the three fundamental interactions described by the Standard Model (the electromagnetic, the weak and the strong force) are thought to correspond (roughly) to gauge invariances ...
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21 views

Trinification lepton Yukawa interactions

We have a trinification model of $SU(3)_c\otimes SU(3)_L\otimes SU(3)_R$, where the first is the usual colour group, the second a left $SU(3)$ and the third a right $SU(3)$. As usual, leptons and ...
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Higgs boson and dark matter.

In the standard model the Higgs boson gives the mass to other particles, but in the Universe we know that the 80% of mass is in form of dark matter, that is not constituted by known particles. The ...
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How do I form the four-momentum quantum operator?

I am trying to form the four-momentum quantum operator. These are the steps I have taken so far: The 3-momentum operator is given by $ \hat{p}_{i} = -i\partial_{i} $. This is covariant because it is ...
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64 views

Physics of tagging at B factories

At some B factories, mesons carrying $b/\bar{b}$ quarks are created by $e^-e^+$ collisions at $\gamma(4S)$ resonance. $\gamma(4S)$ decays into antisymmetric wavefunction given by $$ \frac{1}{\sqrt{2}}...
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Basic Quantum Entanglement

Quantum entanglement means that multiple particles are linked together in a way such that the measurement of one particle's quantum state determines the possible quantum states of the other particles. ...
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Why are there presently more electrons than positrons in the universe? [duplicate]

After the Big Bang, when the universe was extremely hot, there was a symmetry in the population of electrons and positrons. But in the present universe we observe a large number of electrons and ...
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33 views

What direction are the decay particles of muons emitted in?

If I were to run an experiment where I could measure the neutrino as well as the positron emitted when a muon decays, what direction should i be looking in?
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40 views

Why do the masses of decay products affect the branching ratio?

Consider a particle $P$ of mass $100m$ (where $m$ is some unit). It can decay into either of two particle-antiparticle pairs: $P\to P_1\bar{P}_1$ with branching ratio $BR_1$, where $P_1$ has mass $...
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76 views

Why do we say that elementary particles are pointlike? [duplicate]

When people discuss quantum field theory in a popular context, they say that fundamental particles, such as quarks and electrons, are pointlike, with zero size. However, I don't think this is what ...
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39 views

Why do Higgs decays depend on the production method?

I'm reading about Higgs phenomenology and I have come across the following table. I don't see why gluon fusion to $b \bar{b}$ is considered to be "impossible" in this table. As far as I can tell, ...
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Would the ultra high energy particle beam be scattered in plasma accelerators?

Plasma wakefield accelerators accelerate particles in hot plasma instead of cold vacuum chambers of superconductor linacs. Would the particle beam collide with ions, electrons or thermal photons in ...
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949 views

Why don't X-rays penetrate the bone?

My brother asked the simplest question ever: why do X-rays not penetrate the bone? I know it is something to do with the compact molecular structure of bone. What I really need to know is, what is ...
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246 views

What would have been the story of the Universe if there was no mechanism to produce massive fundamental baryonic particles? [duplicate]

Thanks for those of you who took their time answering my problem but it seems that there is a misunderstanding between us. Most answers are based on the assumption of Electroweak symmetry breaking ...
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1answer
102 views

What is a Parton Level Feynman Diagram?

I am studying elementary particle physics and I am wondering what a parton level Feynman diagram is? My understanding is that partons are representations of the quark and gluon substructure of hadrons,...
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1answer
56 views

The Space Between Atoms And Sub-Atomic Particles And More [closed]

I was wondering what the space between atoms or electrons is called. Is it Vacuum ? And what is in there ? Is it really free or empty space ? And if so, how can nothing exist ? It is a bit of an odd ...
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proton magnetism and repulsion [closed]

I am reading that it is proton magnetism that keeps us from falling through a bed if we land on it- That is to say that the proton magnetism in the bed repulses the protons in us, our clothes etc. If ...
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85 views

Do neutrinos have mass? [closed]

I'm really curious on this subject and I want to know if neutrinos have mass. I know they are a subatomic particle, but how much mass.
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50 views

How to determine if interaction is allowed?

I'm trying to determine if the reaction $$n\rightarrow p\pi^-$$ is allowed. First of, this doesn't list this as one of the decay modes of the neutron, so I suspect that it should not be allowed. ...
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98 views

What is the meaning of $\mathrm{d}^4k$ in this integral?

From Gerardus 't Hooft's Nobel Lecture, December 8, 1999, he states the following equation (2.1): $$ \int \mathrm{d}^4k \frac{\operatorname{Pol}(k_{\mu})}{(k^2+m^2)\bigl((k+q)^2+m^2\bigr)} = \infty ...
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23 views

is the earth's atmosphere positivly charged? [duplicate]

Is the earth's atmoshere charged with positive ions? What are the effects of positive verses negative ions?
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46 views

How is Spin experimentally determined?

I know what spin is and how theories determine it for particles. What I don't understand yet, is how people, through experiments and data analysis or whatever, reach to confirm/say that the $X$ ...
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1answer
46 views

Can glueball be created by electron-positron colliders?

Since electrons and positrons are leptons, which don't experience strong interaction, and glueballs are unadulterated entities of quantum chromodynamics. Does that mean hadron colliders are better at ...
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71 views

Why does antimatter and matter fuse to release energy even though they will cancel each other perfectly?

I have seen many physics people talk about antimatter as a evil twin of matter and when they come in contact with each other leave massive amount of energy instead of only void. If antimatter and ...
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Parent particles. Production modes of hyperon $\Lambda$

In the PDG are listed the decay modes of the known particles. I wonder if there exist lists with the production modes of particles. It is, lists with all the possible parent particles that decay into ...
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68 views

How the state of elementary particles change under lorentz transformation?

Let us take three observers namely Alice, Bob and Charlie. Bob is stationary with respect to Alice, but his axes are rotated from her's.We can get Bob's coordinate axes by rotating Alice's through 60 ...
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How do we know that A is a pseudoscalar (CP-odd) Higgs?

Starting from a model with two complex Higgs doublets (as e.g. in the MSSM) we arrive at 5 physical Higgs bosons (instead of 1 as in the Standard Model), 2 of which are charged and 3 are neutral. One ...
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Equivalence of nonlinear sigma model and the $CP^1$ model

While studying the non-linear sigma model, defined by the action $\mathcal{S} = \int dtd^2x (\partial_\mu n^a \partial^\mu n^a)$ along with the constraint $n^a n^a=1$, people often use the map $n^a = ...
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Why are spin-1/2 particles the simplest particles? [closed]

Paul Dirac, in his interview with Friedrich Hund, mentioned that it was to his surprise that his equation automatically incorporated spin. He said that he thought the simplest theory, for which he was ...