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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Difference between particle-antiparticle decay and particle collision at high energy?

Can one show the difference between particle-antiparticle decay and particle collision at high energy? Is where a difference in the decay products? For example, could in both cases be a 5-pion or a ...
4
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1answer
224 views

Matter and antimatter differences?

I've heard (and after googling for a while, found) that the only difference between matter and anti-matter is simply charge. This bothers me when it comes to the neutron. Matter and anti-matter ...
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3answers
292 views

How did Pauli and Fermi deduce the existence of the neutrino? [duplicate]

From Wikipedia: The neutrino was postulated first by Wolfgang Pauli in 1930 to explain how beta decay could conserve energy, momentum, and angular momentum (spin). In contrast to Niels Bohr, who ...
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22 views

neutrons fission reaction [on hold]

If neutrons are uncharged particles then how they can be bombarded together and continue breaking into smaller and smaller neutrons? If they carry no charge then how it is possible that they can break ...
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2answers
140 views

Which is the lightest thing in this universe? Is that a photon or neutrino?

I hear a lot of people saying that neutrino is the lightest subatomic particle but according to me a photon must be the lightest as nothing can travel faster than light because it gets heavier and ...
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4answers
3k views

How is it possible to accelerate a neutron?

It is possible to accelerate a charged particle in an electric field, how is it possible to accelerate a neutron? How can we control its velocity?
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3answers
132 views

Detecting negative energy products in particle accelerators

Are the detectors in a typical particle accelerator experiment, either in Fermilab, or now in LHC, sensitive to negative energy particles? How would a negative energy particle, (say, a negative ...
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0answers
21 views

Conservation of charge on Higgs production by bremsstrahlung

The Higgs production channel $$q+\bar{q} \rightarrow W^++ H^0,$$ depicted below, seems to be violating charge conservation, or am I missing something? The quark and its antiquark have the same ...
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2answers
528 views

Why can the Euler beta function be interpreted as a scattering amplitude?

The Wikipedia article on the Veneziano Amplitude claims that the Euler beta function can be interpretted as a scattering amplitude. Why is this? In another word, when the Euler beta function is ...
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34 views

Is there a machine readable format of the data tables in Particle Data Group PDFs?

Is there a machine-readable format of the tables of data in PDG documents such as this one? http://pdg.lbl.gov/2011/download/rpp-2010-booklet.pdf Something such as JSON, XML, CSV, HTML, or anything ...
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1answer
35 views

How does the number of events per bunch collision scale (as function of energy, luminosity …)

Looking at Table 1 of Burton Richter's recent article High Energy Colliding Beams; What Is Their Future? I'm wondering how the number of events per bunch collision ("$N_b$") scales for the collider ...
4
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1answer
67 views

Understanding the Particle Data Group review documents

Would someone mind outlining what each piece of semi-structured data means in these images taken of some PDG documents? As a newcomer it is very difficult to interpret the tables. tl;dr This ...
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1answer
45 views

What does the first column in the “decay modes” table mean (in Particle Data Group documents)?

As a follow-up to this more general question, what are the values in the first column of each of the "decay tables" in a PDG document describing? What are those things in the first column? Are they ...
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2answers
63 views

Where can I find the datasets from LHC?

I know that most of the datasets from ATLAS or other particle physics experiments are terabytes, but I was just curious is there any place where one can find them to download? And one more question, ...
65
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2answers
10k views

Why doesn't matter pass through other matter if atoms are 99.999% empty space?

The ghostly passage of one body through another is obviously out of the question if the continuum assumption were valid, but we know that at the micro, nano, pico levels (and beyond) this is not even ...
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3answers
305 views

Why are there no elementary charged, spin-zero particles?

In the spirit of a related inquiry, I would like to know if there's a basis for understanding why there aren't any elementary particles that have non-zero electric charge but zero spin? Can such a ...
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1answer
34 views

A particle has $\overrightarrow{r}(0)=4m(\hspace{2pt}\hat{j}\hspace{2pt})$ and $\overrightarrow{v}(0)=(2m/s^2)\hat{i}$ [closed]

I am having trouble with these problems, and I want to gain a understanding of how to solve these. I'll put what I have tried at the end, even though I don't think it'll be of help. A particle has ...
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4answers
978 views

Why are neutrinos more weakly interacting than light?

When people describe neutrino interactions they describe them as rare/infrequent due to the fact that the neutrinos are electrically neutral and have little mass, if any. Well why then is the photon ...
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1answer
69 views

What does the size of an object have to do with it's color?

Stephen Hawking mentions in his book 'A Brief History of Time' that quarks are much smaller than the wavelength of visible light so they do not have any color in the normal sense. What exactly does ...
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2answers
49 views

What is the change in energy of $ \Delta e = h \nu $ in respect to?

I saw this equation today when calculating energies of photons of different frequencies, and noticed that the change in energy is a product of plank's constant and frequency. $$\Delta e = h * \nu $$ ...
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51 views

What's the value of the coupling constant in interacting field theories?

Consider this Lagrangian : $L = \frac{1}{2}(\partial_\mu \Phi)^2 - \frac{M^2}{2}\Phi^2 +\frac{1}{2}(\partial_\mu \phi)^2 -\frac{m^2}{2} \phi^2 -\mu\Phi\phi^2$ Its interaction term is given by : ...
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25 views

Inclusive and exclusive searches [duplicate]

Please, I would like to know what means inclusive and exclusive searches in High Energy Physics. Thanks in advance. Fábio.
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1answer
286 views

Why isn't the quark charge taken as primitive?

Why are electrons taken implicitly to be the elementary charge? It would save a lot of fractions in particle physics problems.
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3answers
195 views

Majorana Mass For Neutrinos In Standard Model

Neutrinos can't be given Dirac masses because there is no $SU(2)_L$ singlet right handed neutrinos in the standard model. But can neutrinos be given Majorana masses in the standard model? EDIT: Why ...
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0answers
60 views

Understanding the effective low-energy Lagrangian for hadrons

My course in Higgs Physics is discussing a two-nucleon low-energy effective theory of hadron interaction. With $\psi=(p,n)$, the pion is defined as $\vec{\pi}= i \bar{\psi}\vec{\tau} \gamma_5 ...
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38 views

Nuclear Interaction Stopping Power

Hello again question board. I'm in need of some help with my b) question for homework I have. Following question is verbatim: "How thick should a wall of shielding iron be to absorb a 10 GeV/c pion ...
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1answer
56 views

Scalar Particles, Flavor Changing Processes and Gauge Symmetries

Let's consider an extended version of the Standard Model (SM) with a new Yukawa operator of the form $$ \sum_\ell g_\ell\bar{\ell}\ell \phi ,$$ where $\ell$ is any lepton of the SM and $\phi$ is a new ...
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2answers
72 views

What is the reason for the $ i \tau_2 $ - factor in the higgs coupling with up-type quarks?

The quark mass term in the Standard Model Lagrangian looks like this: $$ L = - \lambda_d \bar{Q}\phi d_R - \lambda_u \bar{Q} i \tau_2 \phi^* u_R $$ What is the reason for the $ i \tau_2 $ - ...
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2answers
84 views

Is neutron decay a purely electromagnetic phenomena?

Until reading the Phys.SE post here about the neutron decay I never feel strange the fact about the antisymmetricity of this decay. But indeed why this decay is antisymmetric. The neutron is his own ...
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1answer
219 views

Gauge fermions versus gauge bosons

Why are all the interactions particle of a gauge theory bosons. Are fermionic gauge particle fields somehow forbidden by the theory ?
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2answers
121 views

Scalar field divergent mass correction interpretation question (hierarchy problem)

Simple power counting tells you that a scalar field coupled to some fermions at one-loop picks up a correction to the mass of the order $\Lambda^2$. Based on this people say things like "it's natural ...
2
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0answers
35 views

Is the left-handed neutrino, after seesaw, still the left-handed neutrino?

Reading this question and its answer Seesaw type-1 and integrating out heavy fields The diagonalization of the see-saw is described as going from "interaction basis" right (and left) handed ...
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4answers
547 views

Neutron to antiproton decay

Would it be possible for a neutron to lose a positron and become an antiproton? Or would would it need to be the decay of a antineutron to antiproton instead?
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379 views

Status of experimental searches for tachyons?

Now that the dust has settled on the 2011 superluminal neutrino debacle at OPERA, I'm interested in understanding the current status of experimental searches for neutrinos. Although the OPERA claim ...
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62 views

What does “P-wave” mean when referring to a particle?

In scattering theory, P wave means $l=1$, where $l$ is the azimuthal quantum number. However, what does P wave mean when referring to particle states? For example, in this paper (arXiv link), the ...
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2answers
103 views

Subatomic particle mass and Benford's Law

Nine out of 15 subatomic particle masses begin with the digit one. Benford's Law would imply 30% with one as the leading digit. Is there any significance to this frequency distribution, such as ...
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2answers
75 views

Is negative mass for a bound system of two particles forbidden?

Is there any theorem that forbids the bound system of two massive particles to have negative mass?
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1answer
136 views

Is the Higgs Boson a Force Carrier? [duplicate]

I am told there are four fundamental forces, and each of these forces has a boson that acts as its carrier. Reading this http://www.fnal.gov/pub/science/inquiring/questions/higgs_boson.html I find ...
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2answers
148 views

Increased likelihood of photon emission due to “nearby” absorber?

Is an excited atom more likely to emit a photon if there is a similar atom in the ground state nearby ready to absorb it? When I say "nearby" I guess I mean that the absorber has an approximately ...
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2answers
78 views

Does yukawa potential of two particles have effect on each other? [closed]

Okay,a novice here.Suppose two particle interact with Higgs field.Does The Yukawa potential created by each of them affect each other or the interaction in any way.If so,what is it physical ...
3
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2answers
514 views

Quarks as preons for the whole standard model

This is a sequel to an earlier question about Alejandro Rivero's correspondence, the "super-bootstrap". The correspondence itself was introduced in his "Supersymmetry with composite bosons"; see the ...
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0answers
76 views

General definition of vector spinor and spin

I am looking for basic and exact definitions of fundamental physical consepts in graduate level. I reach this following definitions. Could you please help to improve these definitions. Spin: ...
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1answer
33 views

Difference between Urca process and $\beta$-decay in neutron stars cooling

I was reading about the Urca process and its importance in the cooling of astrophysical compact objects. Indeed, it is supposed to be one of the major contribution to the cooling of neutron stars ...
2
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1answer
71 views

Fierz identity for Weyl spinors in tensor currents

Using Fierz identity I found that certain four-fermion operator with left $l_i$ and right-chiral $r_i$ Weyl spinors vanish $\bar{l}_1\sigma_{\mu\nu} r_2 \bar{r}_3 \sigma^{\mu\nu} l_4 =$ $ ...
2
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1answer
63 views

What are the quantum numbers of an exchange particle in the t channel?

i know that for an s channel reaction, the quantum numbers of the intermediate particle have to be the same as those of the particles coming in, for example in the reaction $\gamma \pi \rightarrow a_2 ...
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1answer
90 views

Do massive particles exchange Higgs bosons?

Do massive particles exchange virtual Higgs bosons between themselves? If they do does the resulting Higgs force decay exponentially with distance?
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1answer
461 views

Justification for new theories of Particle Physics and General Relativity

In reference to arxiv:1212.4893v3 and arxiv:1206.5078v2 papers of Ma and Wang, they have proposed new theories in particle physics, the weakton model where quarks and leptons are formed using these ...
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3answers
2k views

Can a third type of electrical charge exist?

Upon reading my book on physics, it mentions that there are only two discovered types of electric charges. I wonder if there could be a third type of elusive charge, and what type of effects could it ...
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2answers
89 views

Dashed lines in Feynman diagram

In this article, in e.g. figure 2, what does these dashed lines across the Feynman diagram mean?
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1answer
856 views

Does photon have size measurement because of its particle nature

Does photon have size measurement because of its particle nature like electron's 3.86*10^-13m etc..