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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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 $...
3
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0answers
75 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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0answers
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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0answers
16 views

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 ...
3
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1answer
926 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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2answers
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
97 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
53 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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1answer
33 views

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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1answer
84 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.
3
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1answer
49 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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1answer
97 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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0answers
45 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 $X$ ...
3
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1answer
45 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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1answer
68 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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0answers
19 views

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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0answers
67 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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0answers
37 views

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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1answer
91 views

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 = ...
3
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0answers
70 views

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 ...
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2answers
35 views

time of flight between two scintillators

I found this page on Wikipedia about finding distance between time of flight of two particles passing past two scintillators, https://en.wikipedia.org/wiki/Time_of_flight_detector, but I can't find ...
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1answer
42 views

Does our Universe reside in the smallest particle? [closed]

I do not know where to ask this question in the first place, but I think here would be a start. Is there a possibility that if we go inside the smallest particle (which we have not discovered yet; ...
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2answers
62 views

Neutrinoless double beta decay: annihilation of neutrinos or nucleon absorption?

I've a question regarding the interpretation of the neutrinos in neutrinoless double beta decay: The basic issue that I have is with papers that regard the decay as a neutrino-neutrino ...
3
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1answer
100 views

Can I catch a particle (such as electron) and say it's left hand

Why is only the left hand electron coupled to weak interaction? How can I tell the chirality of an electron?
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0answers
35 views

Proton-Proton collision [duplicate]

How are the people at CERN able to exactly collide protons head on? What about the HUP? Do they accelerate many particles and smash them so that at least some of them collide head on?
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1answer
34 views

Massive spin one pseudovector decay?

Suppose you have a massive spin one pseudo-vector particle. Is it allowed to decay into an electron-positron pair? I'm thinking it might be disallowed because of parity conservation. If it is ...
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4answers
210 views

Why do we say that photons are particles? [closed]

This question may appear stupid but I really do have to understand. Maybe it's just semantic and nothing else. Why do we say that photons are (elementary) particles? They are pure radiation, since ...
3
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1answer
91 views

How can neutrinos have both mass and helicity?

If a neutrino has mass it must travel at less than the speed of light. So how can it possess helicity, which can change depending on relative velocity?
2
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0answers
50 views

What are the essential pure mathematics branches applied in theoretical high energy physics [closed]

I am a physics graduate student.I am interested in theoretical high energy physics.Very often people say that to be a good theoretical physicist you need to know mathematics very well.Now although we ...
4
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0answers
25 views

Physical inituition for axial and vector form factors of a hadron

I often see a decomposition of the matrix element $\langle V|\bar{q}\Gamma^{\mu} Q |P\rangle$, where $V$ is a vector particle, for example a vector meson or a photon, $P$ is a pseudoscalar meson, and $...
7
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133 views

Do photons generate gravitational waves since they affect with their energy the stress tensor?

The gravitational waves are fact. They are produced in a way predicted 100 years before by Einstein. Anything with energy affecting stress tensor of space time produces them. What does it happen with ...
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2answers
52 views

Questions about particles and their forces

Consider the hypothetical scenario where 2 particles are headed for each other in a collision course but neither interact with a common force. Do these particles simply pass through each other?
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37 views

A question relating to the Higgs boson scalar field

Just wondering. The potential for the Higgs boson is given by: $$ V(\varphi)=\lambda(\varphi^{2}-v^{2})^{2} $$ where $v≃$ 246 GeV is the vacuum expectation value required to explain mass in the ...
0
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1answer
26 views

How to calculate the decay rate of Higgs to lepton pair?

In class, the generic formula we've been given for calculating scattering amplitudes for the weak decay (at low energies so that the interaction is effectively point-like) is $$ M= <f|L_{eff}|i&...
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3answers
128 views

How can we conciliate the structure of a proton and Coulomb/strong force? [closed]

I was told in answers to my questions that the schematic picture at wikipedia is misleading, that the 3 (valence) quarks are point particles, sit in on the outer edge of a proton (r = .85 ftm) and ...
0
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0answers
44 views

What causes certain particles to have charge? [duplicate]

The three major measurements for the elementary particles are mass, spin and charge, mass is supposedly achieved through interaction within the Higgs field due to the Higgs effect, spin is the angular ...
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0answers
14 views

What is the meaning of the minimum separation requirement?

In this work, BHsearch done by CMS, they reconstructed and identified objects using certain conditions. And finally, in Page 3, the last paragraph requires that the minimum separation between any two ...
4
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0answers
43 views

What is the difference between Breit-Wigner mass and pole mass in PDG?

In Review of Particle Physics 2014, page 81, in the baryon summary table, there are usually noticeable differences between Re(pole position) and Breit-Wigner mass, for example, for $N(1440)$, $M_{BW}=...
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0answers
69 views

Do all particles have radiative transitions?

Everybody knows that excited electrons can emit photons upon relaxation. A nucleus too (which is not an elementary particle), can be in an excited state and emit gamma rays upon relaxation: (source) ...
2
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0answers
25 views

Ideas for experiments on the Beamline for Schools at CERN? [closed]

I'm thinking of participating in CERN's Beamline for schools competition. To those who do not know, they offer a batch from a school to conduct their own experiment on a small scale particle ...
1
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1answer
33 views

Particle lifetime doesn't depend upon longitudinal momentum

I am writing a report on an analysis of the $B_{s}$ meson from CDF data, and as part of the lifetime analysis, I have noted down that: $$\tau = \frac{l_{xy} m_{B_{s}}}{p_{T}}$$ Where $l_{xy}$ is the ...
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1answer
39 views

What is the likelihood of pair production for a high energy photon?

Wikipedia says that pair production is the dominant form of light-matter interaction for photons with a mass equivalence of at least twice the rest mass of the target particle, implying that not all ...
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0answers
39 views

Decay rate and differential cross-section

If I have a $pp-$beam producing an on-shell particle $A$, which then decays into particle $B+C$, then I can find the total cross-section $pp \to A \to B+C+Y$ ($Y$ being inclusive particle which should ...
3
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1answer
177 views

Confirming an inconsistency of the Balitsky-Kovchegov equation between references

I'm comparing the form of the Balitsky-Kovchegov equation, which describes the splitting of low-momentum gluons, between different references, and I'm finding an inconsistency: most sources (1, 2, 3, ...
3
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2answers
100 views

Proof that 1d lattice displacement by phonons is given $u_{n\pm 1}(t) = A_ke^{i\omega_k t} e^{i knd}e^{\pm i k d}$

I looked in «Kittel - Introduction to solid state physics», Wikipedia and Google for the derivation that: A phonon of wavenumber $k$ displaces the $s$-th atom in a monoatomic 1d crystal lattice by a ...
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0answers
87 views

Electric field inside the “Dees” of a Cyclotron and why no “Cups”

I read about cyclotron and how does it work. Several references say that the particle to be accelerated is only accelerated when it is between the gaps of the "Dees" or the semicircular disc like ...
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1answer
61 views

Is Electron decay period less than stated?

Phys. Rev. Lett. 115, 231802 – Published 3 December 2015 sets a limit on the stability of the electron for decay into a neutrino and a single monoenergetic photon in $\tau\ge6.6\ 10^{28}\ \mathrm{yr}$....
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31 views

Cloud chamber and observations [closed]

What are the best ways to use a cloud chamber to study particles. What would you gain from observations done in a cloud chamber.
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1answer
45 views

Understanding wave functions of matter waves

The wave functions of matter waves give the probability density of the particle being at a certain location. Does this arise because as an outside observer, we have incomplete information about the ...