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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173 views

How should we understand the value of a recent theory published on Phys. Rev. D? [closed]

I would like to know what to make of this paper, published on Phys. Rev. D on the 11$^{th}$ of January: Quantum field theory of gravity with spin and scaling gauge invariance and spacetime ...
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1answer
28 views

The magnetic moments of Hadrons

So I am very confused about how to find the magnetic moment of a arbitrary hadron. I have found out that the magnetic moment of a quark is given by: $\mu_q = \frac{e_qM_p}{m_q}\mu_N$ Where: $e_q, ...
3
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1answer
51 views

Why is the top quark mass reconstructed too high when the bottom quarks were swapped (semileptonic decay of a ttbar pair)?

I use a dataset containing simulated events of semileptonic $t\bar{t}$ decays ($t\bar{t} \rightarrow W⁺b W⁻ \bar{b} \rightarrow q\bar{q}bl\nu_l\bar{b}$) at CMS, LHC. For each event, the four-momenta ...
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0answers
34 views

Conservation of quantum information [duplicate]

Bosons occupy the same quantum states, even if fermions obey Pauli's Exclusion Principle. Heisenberg's Uncertainty Principle rules out determining the quantum states occupied by two close fermions, ...
66
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3answers
6k views

Why do we need to “create our own” Higgs boson in order to see one?

I understand that the LHC found the Higgs boson by pumping so much energy into a tiny space (via near light speed proton-proton collisions) that a Higgs boson appeared momentarily, then instantly ...
3
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0answers
42 views

The mass of X Boson (and Y Boson too)

I was reading an article on Wikipedia about the hypothetical particles called $X$ and $Y$ Bosons. Looking at their "calculated" masses, I felt quite weirded. Their mass should be $$m = 10^{15}\ ...
3
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1answer
134 views

Why are the elements of the periodic table stable? [duplicate]

I apologize in advance for the stupid question, but I was wondering about neutron decay and elements. Taking for example one of the most simple elements, Helium. Helium is made by 2 neutrons and 2 ...
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1answer
49 views

Four momentum in particle physics

I have seen four momentum defined in two different ways. One is $P =(E,\vec{p}c)$ and the other is $P =(E/c,\vec{p})$. Which one is correct and if they both are then why and when is it more convenient ...
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1answer
43 views

Can an atom be formed from a combination of subatomic particles other than electron, proton and neutron (or their antiparticle)?

I have read that there are plenty of elementary particles. Can some of them form some species other than proton and neutron that are able to form a stable atom together with an electron or an electron ...
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1answer
26 views

Is there any Higgs Model that has 4 Charged Higgs and 1 Neutral?

There is a 2HDM that predicts 3 neutral and 2 charged Higgs particles. There are also many more models out there. I already did some searching, but there is a large body of work here, and various ...
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0answers
24 views

Why do mesons like the J/Psi or Y exist? Shouldn't the quark/anti-quark pair annihilate? [duplicate]

q/qbar->photon is part of Drell Yan, so it's kinematically allowed. Is this somehow related to the difference in speed phenomenologically between a strong and a weak decay? As in is this annihilation ...
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3answers
250 views

Does quantum mechanics break causality? [duplicate]

If quantum mechanics is probabilistic, there is no reason for a particle to be in one place and not the other, but particles do make up their minds... but how?
3
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5answers
281 views

Could the universe be accurately simulated with an infinitely powerful computer? [duplicate]

This would mean that every event happens because of what has hapened before it and there is no randomness factor. At a microscopic level, the motion of atoms is a result of the motion of other atoms ...
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4answers
5k views

Why is 7 TeV considered as a big amount of energy?

Considering that $7$ TeV is more or less the same kinetic energy as a mosquito flying, why is it considered to be a great amount of energy at the LHC? I mean, a giant particle accelerator that can ...
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0answers
18 views

W boson recontruction

How we can reconstruct the W boson, when decays leptonically because there is MET (W-->lepton+neutrino). Need a theoretical description in detail. Can any one explain this or point me to a good link?
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2answers
64 views

Why is a nearby nucleus required for Pair Creation?

I was recently studying Pair Production and Annihilation. The author mentions that a nearby nucleus is required when the photon materialises into a particle and an anti-particle. The explanation given ...
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1answer
28 views

Can we have Bremsstrahlung emission of particles which are heavier than the initial radiating particle?

Lets consider a light particle in a high-energy process. Can this light particle radiate "Bremsstrahlung particles" which are heavier than the initial light particle? In this context I don't refer ...
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1answer
27 views

Doesn't the subsequent change in effective nuclear charge and atomic radii disrupt the standing wave in which electron moves?

Electrons move in standing waves around the nucleus. However, as the Atomic No. along a period increases, the effective nuclear charge on the valence electrons increases and the atomic radii decrease. ...
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0answers
91 views

How would you build a small cyclotron (particle accelerator)? [closed]

I heard Michio Kaku built a small cyclotron when he was young. I bought a book called "Principles of charged particle acceleration" where it explains the basic functioning of particle accelerators. ...
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0answers
28 views

zee model of radiative neutrino mass

Without computing the expression for radiatively generated neutrino mass matrix $M_{\alpha\beta}$, in Zee model, is it possible to guess that the diagonal elements of the mass matrix vanishes? I ...
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1answer
73 views

Baryon - Anti Baryon scattering

Is it possible, for a strong interaction of the above described type (baryon - anti baryon), to exist? $$B + \bar B \to \ldots $$ (Where $B$ is a generic baryon and $\bar B$ the anti-) Namely like ...
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1answer
113 views

A doubt in special relativity

I read in the Feynman Lecs about muons. They are created in the upper atmosphere and hav a lifespan of about 2.2 micro seconds and if there was no relativity, they can travel as much as 600 metres ...
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0answers
71 views

Is $PT$ always a symmetry in (2+1)D?

Is the combination of parity $P: (x,y,t)\to (-x,y,t)$ (sometimes also called reflection $R$) and time reversal $T: (x,y,t)\to (x,y,-t)$ always a symmetry in (2+1)D theories with Lorentz or Galilean ...
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0answers
19 views

How to introduce symmetry of particles to a layperson? [closed]

I want to introduce the concept of special unitary symmetry and how it is important in particle physics to a layperson. Without being technical, is there a way to explain the fundamental concept?
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1answer
37 views

Polarization in high energy vacuum non-linearity?

I heard that the vacuum becomes nonlinear at high energies. What is an intuitive explanation as to why this happens? For example, in classical optics non-linearitiy comes from material field ...
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0answers
18 views

Mass difference in particle oscillation from weak lagrangian

Looking for an answer to how an expression to $\Delta M = M_2 - M_1$ arise in QFT I have found the approximation \begin{equation} \Delta M_K \approx \frac{G_F^2}{4\pi} m_K f_K^2 \sum_{q=u,c,t} m_q^2 ...
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1answer
84 views

Strangeness of elementary particles

What is the property, whose violation led to the assumption of strangeness? Prior to the discovery of strangeness was it assumed that particles that are produced by strong interactions can decay only ...
3
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1answer
120 views

How the LHC bump can be a mere coincidence?

Speaking of http://www.nature.com/news/lhc-sees-hint-of-boson-heavier-than-higgs-1.19036. I understand that such a bump can be a statistical fluctuation. What troubles me is that the bump has been ...
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1answer
40 views

Resource recommendation for jet physics

I'm doing an undergrad research project in jet physics. I have enough algorithms / machine learning background to understand what jet clustering algorithms are doing, and analyze their performance, ...
0
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1answer
74 views

Magnetic field felt by an observer “orbiting” a proton

Classically, if one has an electron orbiting a proton, how can the magnetic field felt by an observer with the same instantaneous velocity as the electron be calculated? It seems that I may find the ...
0
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1answer
141 views

Fusion, Magnets and Quantum Generators [closed]

I cannot even play like I'm even at this level, but this is the fusion reactor in Germany called the Wendelstein 7-X stellarator. These doughnut-shaped magnets (often seen on Physic Exchange) are ...
2
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1answer
314 views

Do magnetic fields exist beyond the gravity of a black hole?

http://www.sciencealert.com/the-magnetic-field-just-outside-our-black-hole-has-been-studied-for-the-first-time reported strong magnetic fields escape out of black holes. Does that rule out photons ...
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0answers
24 views

Can an electron change its spin between multiple Stern-Gerlach experiments?

If you run multiple Stern-Gerlach experiments on a single electron, can its spin change in between them? So, for example, could an electron have an up spin through one experiment then a down spin ...
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1answer
68 views

How are the protons for collisions in the LHC made?

I heard that the LHC smashes two protons together to research the universe. But how does it create the protons for collision? If we strip off the electrons won't there be neutrons along with protons? ...
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0answers
22 views

Package for flavour physics computation? [closed]

Which softwares one usually uses for flavour physics related calculations? I saw one called SUSY_FLAVOR. I haven't used it yet though. What in case of other BSM models other than SUSY? Is there any ...
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0answers
14 views

Book Recommendation for relativistic scattering theory [duplicate]

I am looking for books on relativistic scattering theory with particular emphasis on application to experimental high energy physics. Does anyone have excellent recommendation?
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1answer
43 views

Number of spectral lines

In case of single isolated atom if electron makes transition from nth state to the ground state then maximum number of spectral lines observed $ = ( n — 1)$. Is the above statement true? If yes, then ...
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0answers
29 views

Ratio of decays rates for $\rho \to \pi + \gamma$ and $\omega \to \pi + \gamma$

How easily are the ratio of decays rates for $\rho \rightarrow \pi + \gamma$ and $\omega \rightarrow \pi + \gamma$ obtained? I know we should use somehow flavors and quark model, but I don't ...
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3answers
61 views

Are atoms elementary? [closed]

I'm reading wikipedia about Real neutral particle. I know, there are many different particles discovered in the background of atom, which was ( Neutrons + Protons + Electrons ) before. For example, ...
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0answers
23 views

electricity and magnetism [duplicate]

A charge Q is distributed uniformly on the surface of a spherical conducting shell of radius 5 cm.The magnitude of electric field on the surface is 106 V/m. What is the magnitude of electric field20 ...
4
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1answer
75 views

Why particles with certain properties can't exist

This is inspired by a recent post on why a free electron can't absorb a photon, though my question below is about something considerably more general. The argument in the accepted answer goes (in ...
0
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1answer
90 views

Could the Large Hadron Collider accelerate one kilogram of protons at once?

Is it possible to accelerate a very large number of protons in a particle accelerator as opposed to only a few as is regularly done? What's to keep someone from accidentally dumping too many particles ...
2
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1answer
46 views

How would the CLIC accelerator work?

After reading what I could find about the CLIC accelerator, I still don't understand how it would work. If someone could explain how the CLIC would work, I would greatly appreciate it.
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58 views

What sorts of problems does asymptotically safe gravity face as a potential quantum gravity solution?

I've recently read an article by Ethan Siegel over at Forbes (he also blogs at Starts with a Bang) on asymptotically safe gravity as a possible alternative to string theory. I read the author's blog ...
1
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2answers
39 views

In typical decay experiments what range of energies do electron neutrinos and muon neutrinos exhibit?

in experiments over decay of particles, what are the typical range of energies of electron neutrinos and muon neutrinos? I would guess I need to specify in the inertial frame of a lab here on earth? ...
3
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2answers
90 views

Questions regarding the Feynman-Stueckelberg interpretaion

I am studying for an introductory particle physics exam, and I am having some problems with the Feynman-Stueckelberg interpretation of antiparticle states. Background: The course was being thaught ...
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0answers
86 views

Mathematical form of the de facto repulsive “force” associated with the Pauli Exclusion Principle [duplicate]

One of the principles of General Relativity is that test objects follow a geodesic unless otherwise acted upon by a force. From this perspective, it is clear that physicists, consciously or ...
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2answers
66 views

Do light particles come in different sizes? [duplicate]

Do light particles come in different sizes if it makes sense to even think about them that way?
2
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1answer
49 views

Do muon neutrinos have more energy than electron neutrinos?

I saw an answer to "how to identify a muon neutrino and electron neutrino" as being "Weak interaction conserve not only the global lepton number, but the lepton flavor numbers as well. And that is ...
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2answers
43 views

If two very small and smooth particles collide at perfect right angles, is there friction?

If two perfectly round particles collide at perfect right angles, is there friction between them? If so, Is the friction in the form of heat (average kinetic motion), because if it is, where is this ...