# Tagged Questions

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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### Can you tell if a particle is in superposition?

This may be an easy answer for anybody. Is it possible to detect if a particle A is still in a superposition via the sending a group of particles B through a box containing particle A?
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### Conservation laws in mSUGRA model

Can somebody list all the quantum numbers (beside R-parity) that are conserved in vertex for SUSY particles in mSUGRA model?
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### Is there a simple way to compute some physical constant from Feynman diagram statistics?

I've been playing around writing some software to generate Feynman diagrams for QED, respecting the vertex "rules" described here, and avoiding creating isomorphic duplicates. So from a starter ...
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### Do all the particles acquire mass in the Standard Model due to the Higgs mechanism only?

I know that a mass term for an intermediate boson is not compatible with the gauge symmetry. But in principle a mass term for the electron field does not violate a gauge symmetry. However to build an ...
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### Can the mass of a SUSY particle depend on the process it participates in?

I believe that mass is property of every particle,as well as spin etc.Now I'm interested in SUSY particles in cMSSM model.Can it be,that mass of a SUSY particle (at one point in five parameter space) ...
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### Hamiltonian of the charged current in SM (related to the lorentz invariance)

recently when I was studying the scatterings which involves a vector boson (like W boson) as an intermediate particle, I saw that the propagator is not Lorentz invariant, I read that there is another ...
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### Parity of a decay

If a particle of unknown intrinsic parity decays into 2 particles each with negative intrinsic parity, does that necessarily imply that the original particle also has negative parity?
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### Lower bound for the spin in particle decay process

Is my logic right? Suppose there is a particle $p$ that can either decay into $\{$a spin-1 and a spin-0 particle$\}$ or two spin-0 particles, then the lowest possible spin of $p$ is 2. This is ...
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### What is the spatial mode of light or the spatial mode of a massive particle?

I'm extremely confused by what physicists mean by the spatial mode of light. I am also equally if not more confused by what the spatial mode of a massive particle is. Can anyone help me out by ...
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### Identification of extended quantum objects?

In some physics theories like string theory we have notion of spatially extended quantum objects - strings, membranes etc. Assuming that such objects exist, how would they appear in experiments ? More ...
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### How do I start learning particle physics? [closed]

I am 16 at the moment. I am really interested in physics. Especially particle physics. Can someone please tell me how to start learning the subject. like what to learn first. like which fundamental ...
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### Assuming that extra dimensions will not be visible at LHC, what motivation will still remain to study them?

Many physicists believe that there is little possibility of observing extra dimensions at LHC so that some extra dimension models originally designed to solve hierarchy problem (ADD/Randall-Sundrum) ...
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### Measuring nucleons using electron beams

sorry if the question is too elementary. From: The Britannica Guide to Particle Physics: The sizes of atoms, nuclei, and nucleons are measured by firing a beam of electrons at an appropriate target. ...
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### Mechanisms of mass generation for Dirac neutrinos

If neutrinos are Majorana particles, one way of explaining their small masses is the seesaw mechanism. Now say I'd like my neutrinos to be Dirac, for symmetry to the quark sector. What mechanisms ...
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### Origin of lepton/quark generations?

What theoretical explanations exist for the fact that there are three generations of leptons and quarks? I'm not so much asking why there are exactly 3 generations, but rather what makes electron, ...
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### How to deduce E=(3/2)kT?

It says in my course notes that a particle has so-called "kinetic energy" $E=\frac{3}{2}kT=\frac{1}{2}mv^²$ Where does this formula come from? What is k?
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### Will Randall-Sundrum extra dimension scenario become defunct if not supported by LHC?

The Randall-Sundrum extra dimension scenario had been one of the most extensively studied class of theories. This offered a solution to the hierarchy problem. However, if this picture is not supported ...
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### What is the meaning of the word “particle” in particle physics?

I want to use Matt Strassler's definition of the word "particle" as a specific example: Matt Strassler writes: (1) "...all the elementary “particles” (i.e. quanta) of nature are quanta of waves ...
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### What is difference between the different 'flavours' of neutrinos?

Moreover, how-come scientist know that muon-neutrino are different from electron-neutrino when they didn't even know what the difference was? Did they interact differently with other particles?
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### About free quarks and confinement

I simply know that a single free quark does not exist. What is the reason that we can not get a free quark? If we can't get a free quark then what is single-top-quark?
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### SUSY, ways to boost Chargino/Neutralino production?

Does anybody know a good reference that works out the equations for the Chargino/Neutralino production cross section in SUSY? I'm trying to understand if there are any tricks for boosting the ...
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### Which pion is mediator in nucleon-nucleon interaction

In nucleon-nucleon interactions of n-n, p-p, n-p how do you determine which pion is the mediator?
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### why is the modelisation of elementary particle as a two dimensional object in contradiction with General Relativity?

This is asserted by Trinh Xuan Thuan in his book "Chaos & Harmony" chapter String theory.
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### Dynamical supersymmetry breaking and Witten index

Witten index, defined as ${\rm Tr}(-1)^F$, determines if supersymmetry is spontaneously broken or not for a given model. However, it is also known that supersymmetry can be dynamically broken. One ...
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### What maintains quark spin alignments in baryons?

What maintains quark spin alignments in baryons? The $uud$ proton and $udd$ neutron are both spin 1/2, implying that two of their spin 1/2 quarks are always parallel and the other is always opposed. ...
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### How can some-one independently do research in particle physics? [closed]

I'm not affiliated with a physics department and I want to do independent research. I'm working my way through Peskin et. al. QFT now. Let's say that I've finished Peskin et. al. and Weinberg QFT ...
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### Difference between Quark-Gluon Plasma and Color-Glass Condensate?

From the news. Apparently they are very similar, yet different.
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### How was the Oh-My-God particle observed?

How exactly was the Oh-My-God particle (ultra-high energy cosmic ray) observed and its energy measured?
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### Higgs boson in LHC

Recently,the higgs bosons are discovered in LHC. My question is How did they come to know that the particle that are created are actually Higgs boson? On the basis of which properties,they ...
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### Why isn't Hydrogen's electron pulled into the nucleus? [duplicate]

Possible Duplicate: Why do electrons occupy the space around nuclei, and not collide with them? Why don’t electrons crash into the nuclei they “orbit”? From what I learned in chemistry, the ...
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### Would it be possible to create a hadron collider in space?

Would it be theoretically possible to create a hadron collider in space by orbiting particles around a planet?
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### About interchange phase of identical particles in Weinberg's QFT book

In Weinberg's textbook on QFT(google book preview), he discussed the phase acquired after interchanging particle labels in the last paragraph of page 171 and the footnote of page 172. It seems he's ...
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### Is There Any Difference Between Strong Quarks Force and Strong Nuclear Force?

the spectrum of quarkonium and the comparison with positronium potential for the strong force is: $V(r) = - \frac{4}{3} \frac{\alpha_s(r) \hbar c}{r} + kr$ (where the constant $k$ determines the ...
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### How does Delta baryon decay conserve angular momentum?

I'm a chemist so bear with me: I understand the Delta baryons $\Delta^{+}$ and $\Delta^{0}$ to be in some sense spin (and isospin) quartet states of the proton and neutron. These can decay straight ...
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### Center Of Mass Troubles

I understand the concept of Center Of Mass(com), but I am having a difficult time interpreting the equation of the simplified case of one-dimension. The book I am reading defines the position of the ...
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### How exactly are the different motions of only one kind of fundamental string assumed to give rise to the spectrum of elementary particles we observe?

In string theory, it is assumed that all particles can be described as quanta corresponding to the excitations of only one kind of fundamental string. How can in principle the different motion ...
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### Is it really a particle?

Forgive the stupid question but when colliding particles together, how does one know that a particle is actually a new form of sub-atomic matter and not simply just some shattered fragment of the ...
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### Unstable particles and quantum field theory

I am searching for not too old literature on the quantum description of unstable particles. I am referring to something beyond the ad-hoc S-matrix description based on the optical theorem common to ...
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### What is the $\mu$ problem in SUSY?

I need a little bit of help in understanding the mu problem in SUSY. As I understand it, the gist of the problem is that $\mu$ must be on the same order of magnitude as the electroweak scale (246 GeV)....
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### should the Z0 decay at the same rate that the neutral pion?

The original title of the question was "In a composite Higgs..." and so the sub-questions were done around this theme: Should the decay rate of Z0 be related to the decay of the "higgs" composite ...
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### Isn't a single Quantum one single string? [duplicate]

In physics, a quantum (plural: quanta) is the minimum amount of any physical entity involved in an interaction. In Quantum Mechanics There is no difference between one Quantum to another one. ...
my question concerns the kinematics of 2 to 2 particle scattering. I refer to Peskin and Schroeder eq.17.59 going from this expression $\frac{d^3\sigma}{dy_3dy_4dp_T}=x_1f_1(x_1)x_2f_2(x_2)\;2p_T\... 1answer 232 views ### Definition of scattered particle? Compare the number of scattered particles:$N_s=Fa\int\sigma(\theta)d\Omega$With the total number of incident particles:$N_{in}=Fa$Here, F is the flux of incoming beam, a the area. sigma the ... 1answer 486 views ### What does the latest$B_s^0\rightarrow \mu^+\mu^-$results mean for SUSY? A paper from the LHCb collaboration just came out last week, stating basically that the$B_s^0\rightarrow\mu^+\mu^-\$ decay matches standard model predictions, and people are already shouting that SUSY ...
Could it be possible that the mass of the proton can be calculated by a series of integer sequences? Or is this just a curiosity? $$\sum_{m=1}^{\infty } \frac{1}{10^{26}(m^2+1)_{2m}}=$$ ...