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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6answers
562 views
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 ...
2
votes
2answers
108 views
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?
4
votes
2answers
224 views
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?
6
votes
1answer
167 views
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 ...
1
vote
1answer
62 views
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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0answers
36 views
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.
6
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2answers
210 views
Dynamical supersymmetry breaking and Witten index
Witten index, defined as ${\rm Tr}(-1)^F$, makes know if supersymmetry is spontaneously broken or not for a given model. But it is known that supersymmetry can be also broken dynamically and one can ...
5
votes
2answers
97 views
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.
...
4
votes
2answers
326 views
How can some-one independently do research in particle physics?
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 ...
2
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1answer
106 views
Difference between Quark-Gluon Plasma and Color-Glass Condensate?
From the news. Apparently they are very similar, yet different.
4
votes
2answers
408 views
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?
3
votes
1answer
223 views
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 ...
0
votes
1answer
222 views
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, ...
2
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3answers
109 views
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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1answer
137 views
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 ...
0
votes
1answer
65 views
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 ...
4
votes
1answer
264 views
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 ...
5
votes
1answer
178 views
Spin of Higgs boson 125 GeV
Can someone please explain to me why (according to decay of Higgs boson into 2 photons) Higgs boson cannot have s=1?
Thanks in advance
2
votes
1answer
113 views
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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5answers
472 views
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 ...
3
votes
1answer
155 views
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 ...
1
vote
1answer
169 views
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 ...
2
votes
0answers
54 views
In a composite Higgs, should the Z0 decay at the same rate that the neutral pion?
I am sorry to ask a question that obviously is a sum of separate questions about a process: Should the decay rate of Z0 be related to the decay of the "higgs" composite field it is eating? And, should ...
3
votes
0answers
309 views
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.
...
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0answers
80 views
Kinematics algebra, pT, Peskin Eq.17.59
my question concerns the kinematics of 2 to 2 particle scattering. I refer to Peskin and Schroeder eq.17.59 going from this expression
...
1
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1answer
73 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 ...
10
votes
1answer
291 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 ...
5
votes
3answers
2k views
Have I discovered how to calculate the proton's mass using only integers?
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?
$$\sum_{m=1}^{\infty } \frac{1}{10^{26}(m^2+1)_{2m}}=$$
...
4
votes
1answer
137 views
The use of Hall algebras in physics
I asked the same question in mo. I think maybe here there are more physics guys to help me.
I once read a statement (not memorized precisely) that a certain physics quantity between two states of ...
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votes
1answer
172 views
What process could produce two neutral pions only?
Any examples?
$$? \rightarrow \pi^0 \pi^0$$
If such a process exist, could there be nonzero total orbital angular momentum in the final states of the two neutral pions? But then how to understand ...
0
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0answers
37 views
Taylor-Slavnov Identity in spontaneously broken gauge theories
Where can I find a list of important Taylor-Slavnov identities in Spontaneously broken gauge theories? I am looking for not just the generating functional form, but rather a list of explicit ones ...
0
votes
0answers
113 views
Research in Quantum Physics [closed]
I am Suvankar, a student of engienering. My branch is Electrical & Electronics Engineering. Although this is a Physics oriented website, I want to know whether it is possible to do M.Sc. after ...
7
votes
1answer
141 views
Parton showering in Pythia 6 Monte Carlo generator
I have Pythia Monte Carlo (MC) samples where I can't understand the parton showering model. If I print out full decay chains from the events, each event contains multiple string objects with pdgId 92. ...
1
vote
1answer
50 views
Testing covariance of an expression?
This is something I've been unsure of for a while but still don't quite get.
How does one tell whether an expression (e.g. the Dirac equation) is covariant or not? I get it for a single tensor, but ...
4
votes
2answers
257 views
Basic question on experimental plots
On the following Higgs $\rightarrow$ Tau Tau plot, since we are plotting the ratio of $\frac{\sigma}{\sigma_{SM}}$ on the y axis, shouldn't the expected for this be 1? i.e., shouldn't the expected 68% ...
2
votes
1answer
90 views
$sss$ decay and violation of strangeness
Why can the hyperon $\Omega^{-}$ not decay by strong interaction? It seems that strangeness must be violated, but why is it the only way?
6
votes
1answer
186 views
Weinberg angle measurement methods
I was reading up on the history of $W/Z$ bosons today and I got a little puzzled. I always assumed that people measured $M_Z$ and $M_W$ and then derived the Weinberg angle. But it appears that they ...
1
vote
1answer
74 views
Do atoms have lifespans?
From A Short History of Nearly Everything by Bill Bryson:
Atoms, however, go on practically forever. Nobody actually knows
how long an atom can survive, but according to Martin Rees it is
...
2
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2answers
114 views
Compactness of spacetime: experiment and math
It is common to find models built on a compact spacetime. In mathematics, compactness is a very nice property $-$ and lot of powerful results depend on it.
But
how safe is assuming compactness of ...
8
votes
8answers
594 views
Why do physicists believe that particles are pointlike?
String theory gives physicists reason to believe that particles are 1-dimensional strings because the theory has a purpose - unifying gravity with the gauge theories.
So why is it that it's popular ...
1
vote
1answer
187 views
Missing transverse energy, exact definition
This might seem basic, but it is a bit confusing. You hear about missing transverse energy a lot in SUSY searches due to the LSP which cannot be detected.
Let's say I have the 4-vector for the LSP. ...
1
vote
2answers
134 views
how do we know that the base of entire universe is the proton (hydrogen) and not the antiproton?
It may be that the base of a part of the world is anti-proton, We've always been on the planet Earth and the Milky Way.
how do we know that the base of entire universe is proton (hydrogen atom)?
3
votes
1answer
123 views
Inverting an anisotropic distribution
I have come across a research problem where I need to solve an integral equation of the form
$\int A^{-1}(x,y) \nabla_z\cdot\left[\nabla_y\cdot\left(v(y) G(y-z) \right) v(z)\right]dy = \delta(x-z)$,
...
2
votes
1answer
170 views
Matrices order in dirac equations
The trace of matrix is always sum of its eigen values , which can be seen if $\hat{U}$ transforms the matrix $\alpha_i$ into it's diagonal form .
$$ \begin{pmatrix}
A_1 & 0 & \cdots & 0 ...
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votes
2answers
251 views
Was the Higgs mass correctly predicted by asymptotic safety of gravity?
This paper was published in Phys Lett B in 2009, and predicted the Higgs mass to be 126 GeV based on the asymptotic safety of gravity. Is this prediction taken seriously by the theory community, or is ...
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vote
1answer
85 views
Particle production channels [s,t] in HEP?
In high energy physics there are different channels of particle production: t-channel, s-channel. What do they mean? And are there any other channels besides "t" and "s"?
7
votes
1answer
110 views
Is the LEP B meson asymmetry evidence for higher dimensions and/or string theory?
According to this blog, new standard model calculations have changed the 3 sigma B meson forward and backward production asymmetry observed at LEP into two anomolies:
A 2.5 sigma B meson production ...
2
votes
2answers
213 views
Why do physicists think that the electron is an elementary particle?
When we first discovered the proton and neutron, I'm sure scientists didn't think that it was made up of quark arrangements, but then we figured they could be and experiments proved that they were.
...
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1answer
162 views
Matrix and exponential term problem
We know the Schrodinger equation for free Hamiltonian is :
$$
i\hbar\frac{\partial\psi}{\partial t} = H_f \psi
$$
the wave function could be written as
$$
\psi(x,t)=\hat{S}(t) \psi(x,0)
$$
$$
...
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votes
3answers
757 views
Would a spin-2 particle necessarily have to be a graviton?
I'm reading often that a possible reason to explain why the Nobel committee is coping out from making the physics Nobel related to the higgs could be among other things the fact that the spin of the ...
