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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If cathode rays travel from the cathode to the anode how do they make zinc sulphide glow?

So I basically learned about cathode rays today, and I had a lot of questions in mind. So my textbook says cathode rays travel from the cathode to the anode. So it further says that to observe ...
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2answers
25 views

Can you pass cathode rays in a non vacuumed tube

Is it possible to have a cathode ray discharge in a non vaccumed tube while having a low pressure?
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16 views

Non-zero spin meson have ever seen experimentally? [on hold]

Have been ever shown ( in experiment) none-zero spin meson? We should have it?
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1answer
22 views

Physical limits to number of particles per collider bunch

Currently, colliders work with around $\sim\!10^{11}$ particles per colliding bunch. Recently LHC has increased this number to $10^{13}$. I would like to know if there are, in principle, physical ...
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1answer
40 views

Which elementary particles have been seen up to now?

Which elementary particles have been shown up to now? which one except Graviton, haven't seen? I need an update one, I am searching but I couldn't find. If anyone could answer me, I am so thankful.
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10 views

Transverse momentum [duplicate]

I'm having an introduction on detector systems in particle physics. The sources I read constantly talk about the measurement of "transverse momentum". However, I cannot find a definition of what is ...
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0answers
46 views

Why is diproton unstable? [duplicate]

Diproton is an isotope of helium without any neutrons. It commonly forms in the Sun, where protons are fused constantly. However, it is extremely unstable, and will revert back to two protons almost ...
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106 views

What was Dirac's clear intuitive understanding of the electron? [closed]

There have been some recent questions concerning de-Broglie Bohm theory, such as this and this. The latter asked if Dirac's argument against classical mechanics stands in contradiction to Bohm's ...
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31 views

Schwartz QFT solution

Is there a way I Can find a solutions manual for Matthew Schwartz's "Quantum Field Theory and the Standard Model" book?
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18 views

Why can $\chi_{c}$ states not decay leptonically?

I am trying to understand why the $\chi_{c}$ states of charmonium cannot decay to $l\overline{l}$ pairs. I believe it is because they have positive parity, but I'm unsure why this prevents the decay?
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19 views

Particle interaction kinematics in lab frame

Attempting a question from a past paper on scattering kinematics, fixed particle mass $m$ is struck by another particle mass $m$ with kinetic energy $T$. By evaluating $s$, $t$ and $u$, and their sum ...
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0answers
11 views

Why is the bottom antibottom decay channel for the Higgs difficult to observe? [duplicate]

This is a question from a past paper on particle physics, it asks: Explain why experimentally it was easier to observe $h \to\gamma\gamma$ rather than $h \to b\bar b$ which has the highest ...
2
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1answer
79 views

Perturbativity of SM Higgs quartic coupling [closed]

I'm little confused about the maximal appropriate value for the SM Higgs quartic coupling. I know that the Higgs mass, $m_h= 125 \,\text{GeV}$ and that $ \lambda = m_h^2 / 2 v^2 \simeq 0.1 $ for $v = ...
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1answer
52 views

Inverse beta decay; energy of anti-neutrino

Assuming that the target protons are at rest, calculate the minimum energy of the anti-neutrino for this reaction to take place: $$\bar{\nu}_e+p\rightarrow e^++n$$ I know the answer is given by ...
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0answers
39 views

How do funnels hinder (help?) detection of dark matter?

I came across some a new (to me) bit of terminology at a seminar recently. In the context of dark matter scattering off of atomic nuclei (but I think it may apply more generally for any particle ...
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0answers
33 views

What is a “Scalar Manifold”?

I'm trying to understand a recent paper working within the context of $\mathcal{N}=8$ gauged supergravity with gauge group $\rm{SO}(6)$. There are a number of statements along the lines of: "...the ...
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3answers
76 views

How do particles get their charge?

How does an electron get its charge? And how can it maintain that charge for very long (infinite) periods of time? And how come a neutron has no charge since and a proton does? They are both made of ...
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21 views

Exercise: Calculating Q-value for $D_0 \to \chi_s^-e^+\nu_e$

Question Is the following methodology correct in calculating the Q-value (change in kinetic energy) for the $D^0 \to \chi_s^-e^+\nu_e$ decay process? Steps The change in kinetic energy is ...
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3answers
126 views

Why is this particle interaction forbidden?

Why is this interaction forbidden? $$\nu_e+\bar{\nu}_e\rightarrow K^+ + K^-$$ Lepton number is conserved, charge is conserved, baryon number is irrelevant since these are mesons. Energy is conserved ...
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1answer
1k views

Why do physicists say that elementary particles are point particles?

For example, an electron, it has mass and charge, but is considered to have point mass and point charge, but why? Why are they assumed to have charge and mass in a single infinitely small point in ...
2
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2answers
73 views

Why do particle physicists use the $h\rightarrow{\gamma\gamma}$ decay mode rather than $h\rightarrow{b\bar{b}}$?

Just wondering, the $h\rightarrow{\gamma\gamma}$ decay mode is often quoted as being most sensitive to measuring the mass of the Higgs particle, why isn't the $h\rightarrow{b\bar{b}}$ decay channel ...
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0answers
13 views

Difference between 'merging' and 'matching' procedure

For combining scattering processes with different jet-multiplicities in the final state, higher order corrections and parton shower, merging/matching procedures need to be applied to avoid ...
2
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1answer
35 views

How come two protons create top-antitop quark pair? (A question regarding CERN courier May 2016)

I am not very well versed in particle physics lingo but as much as I know $p$ stands for proton and $t$ stands for top-quark. Then, how could this be possible? I hope I am wrong about what is ...
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1answer
59 views

How are the particles produced at the very early universe?

We know that according the standard model of cosmology $\Lambda {\rm CDM}$, there is a primordial plasma after the inflation. And then we study the non-equilibrium evolution of this plasma such as ...
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2answers
262 views

From the viewpoint of field theory and Derrick's theorem, what's the classical field configuration corresponding to particle? Is it a wavepacket?

In the framework of QM, we have known that particle, like electron, cannot be a wavepacket, because if it is a wavepacket then it will become "fatter" due to dispersion and it's impossible. However ...
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2answers
78 views

What particles do these Feynman diagram lines represent?

What particles could be represented by A and B (labels I have added myself - this is not a homework question)? For A, it looks like it's supposed to be a photon, but I was under the impression that ...
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1answer
58 views

A few questions on quarks, gluons and the strong force

I wanted to answer for myself some pretty fundamental questions pertaining to the strong interaction, color charge and quarks, but I'm sort of stumbling on a few. So I wanted to find the ...
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23 views

Semileptonic decay amplitude

I'm trying to do past exam papers and I am absolutely failing understand some things. I would very much appreciate any insights/intuition you have. The part I'm struggling is here: In the first ...
2
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1answer
67 views

Supersymmetry and grand unification

I came across this diagram in my introductory particle physics class. Given the fact that SUSY can make the plot look suspiciously nice, what can we do with it? Also, electromagnetism has been ...
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0answers
31 views

Why can an electric chargeless Z-particle decay in three photons?

The Z-particle that is supposed to convey the weak force has no electrical charge. So how is it possible the particle can decay in three photons. Because the weak and e.m. force are more or less ...
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1answer
70 views

How to understand the idea of functional renormalization group?

I have been looking at how to use the functional RG method in many-body systems, but I don't quiet get the idea of it, it look different from Wilson's RG approach (eg. why shall we integrate out the ...
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0answers
20 views

B meson mixing and CP violation

From my understanding of CP violation in the weak interation only the $V_{ub}$ and $V_{td}$ terms in the CKM matrix contain the complex phase terms which introduce CP violation. In B meson mixing, ...
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0answers
31 views

Electromagnetic Field caused by accelerating and oscillating charge particles?

Will accelerating and oscillating charges will cause EM waves of different shapes ? As EM waves are always shown as sinusoidal Electric and Magnetic Fields perpendicular to each other. Does it mean ...
2
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2answers
137 views

The mass of the proton times its charge radius is very close to 4ħ/c. Is this a coincidence?

The claim is $r_p m_p = 4 L_0 M_0 = 4\hbar/c$, where $r_p$ and $m_p$ are the proton's charge radius and mass, and $L_0$ and $M_0$ are the Planck length and mass. Using the muon measurement ...
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31 views

Colliding beams vs static target

In this problem I need to find the threshold energy of a positron-electron collision that creates a Z boson (the reverse of the following picture; Z mass 92 GeV) in two distinct cases: collision ring ...
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0answers
43 views

Are quadrilinear weak boson couplings possible?

$ZZ\rightarrow ZZ$, $ZZ\rightarrow W^+ W^-$, etc. Are these interactions possible?
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31 views

Feynman Diagram of $\nu_\mu + p \rightarrow \nu_\mu + p + \pi^0$

According to my class notes, the following interaction is possible $$\nu_\mu + p \rightarrow \nu_\mu + p + \pi^0$$ I tried drawing a Feynman diagram and got the below, but don't know what happens ...
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0answers
16 views

Conversion from PPBV to PPBM [closed]

What is the conversion between PPBV and PPBM? I have a database that includes values of Parts-per-billion-by-volume (PPBV) as a function of altitude. I've been asked to convert this to ...
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1answer
30 views

For processes with multiple Feynman diagrams is the cross section increased?

For example in electron, positron annihilation $e^- + e^+ \rightarrow 2\gamma$ has 2 diagrams, whereas, $e^- + e^+ \rightarrow 3\gamma$ has 6 possible diagrams. This suggests, ...
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0answers
15 views

Decay kinematics of Higgs boson

So I'm looking at a two-body decay question for the $h\rightarrow\gamma\gamma$ decay channel for the Higgs Boson. I am asked to find the invariant mass of the Higgs boson. I'm not too sure how to ...
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0answers
9 views

Question pertaining to the branching ratio of Ka0ns

I'm a little lost for part c of this question: I understand the $\mathcal{BR}$ (branching ratio) for species $i$ is $\mathcal{BR}=\Gamma_{i}/\Gamma_{T}$ (total Decay width). I know that ...
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0answers
18 views

Invariant amplitude in QED in terms of Mandelstam variables [closed]

So I'm having a little trouble with this question: These are my workings thus far: I just can't seem to get certain terms to vanish. I have the 1/4 factor for going between $8e^4$ to $2e^4$. Is ...
1
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1answer
39 views

Why is the energy shift due to a 'sagging' potential negative and independent of box size?

Consider a box of width $L$ and the composed of the following potential $$V(x)=\frac{V_0x(x-L)}{L^2}, x\in[0,L]$$ and $V(x)=\infty$ elsewhere. Using perturbation theory - with a square box as the ...
0
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1answer
29 views

How would one go about drawing a Feynman diagram of color screening and anti-screening in QCD?

Title really explains this one. I'm not sure how to put together a diagram of the lowest order for colour screening and anti-screening in QCD. Seems to be a lack of diagrams for this in the ...
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0answers
42 views

How to draw Feynman diagram for K^- + p -> Sigma^0 + pi^0 — superposition in diagram

I'm trying to draw the Feynman diagram for the reaction $$K^- +p \rightarrow \Sigma^0 + \pi^0$$ I have two problems: How to draw the $\pi^0 = (u\bar u + d\bar d)/\sqrt 2$, a superposition of ...
3
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1answer
42 views

Pion decay: why is the positron electron neutrino decay suppressed?

I'm reading through M. Thomson's Modern Particle Physics to better understand why the positron electron neutrino decay channel is suppressed relative to the muon and muon neutrino decay route. I know ...
2
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1answer
35 views

What experimental measurement could be used to show that a neutrino is a Majorana and not a Dirac particle?

I've just been reading something on the concept that neutrinos could be Majorana particles and not Dirac fermions. I was wondering what experimental measurement could show/prove that neutrinos are in ...
2
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0answers
54 views

Explanation of graphs from CERN [closed]

I have a few questions about these kinds of graphs What is the name of this type of graph? What does the width of the peak mean? If the points are data points, how was the curve created/predicted? ...
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0answers
35 views

Gravitational entropy [duplicate]

In the beginning (big bang), mass was evenly distributed (if you consider an elementary particle as an extended object, like a circle on a very thin cylinder, with a radius near the Planck length, but ...
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1answer
16 views

Semileptonic decay of neutral D meson: branching ratios?

I am looking for the branching ratio of the semileptonic decay of the neutral $D^0$ meson: BR($D^0 \to \pi^+e^-\bar\nu_e$) = ? According to the PDG book the branching ratio for $D^0 \to ...