In particle physics, a pion (or a pi meson, denoted with the Greek letter pi: π) is any of three subatomic particles: π0, π+, and π−. Each pion consists of a quark and an antiquark and is therefore a meson. Pions are the lightest mesons and, more generally, the lightest hadrons. They are unstable, with the charged pions π+ and π− decaying after a mean lifetime of 26.033 nanoseconds (2.6033×10−8 seconds), and the neutral pion π0 decaying after a much shorter lifetime of 85 attoseconds (8.5×10−17 seconds). Charged pions most often decay into muons and muon neutrinos, while neutral pions generally decay into gamma rays.
The exchange of virtual pions, along with vector, rho and omega mesons, provides an explanation for the residual strong force between nucleons. Pions are not produced in radioactive decay, but commonly are in high-energy collisions between hadrons. Pions also result from some matter–antimatter annihilation events. All types of pions are also produced in natural processes when high-energy cosmic-ray protons and other hadronic cosmic-ray components interact with matter in Earth's atmosphere. In 2013, the detection of characteristic gamma rays originating from the decay of neutral pions in two supernova remnants has shown that pions are produced copiously after supernovas, most probably in conjunction with production of high-energy protons that are detected on Earth as cosmic rays.The pion also plays a crucial role in cosmology, by imposing an upper limit on the energies of cosmic rays surviving collisions with the cosmic microwave background, through the Greisen–Zatsepin–Kuzmin limit.
There are 36 hadron composites composed of 2 quarks selectable from the set ##[u, d, c, s, t, b, \bar u, \bar d, \bar c, \bar s, \bar t, \bar b]## satisfying the condition of having total charge = ##[-1, 0, 1]##. However, the superposition states of pure hadrons are sometimes also listed as new...
Below are the statements in the "David Griffiths, Introduction to Elementary Particles 2nd Edition, 147~148 p.":
Evidently, the long-lived neutral kaon is not a perfect eigenstate of CP after all, but contains a small admixture of K1. The coefficient epsilon is a measure of nature's departure...
Hello, I am trying to figure out the right way to approach this. First of all, other than the different Bohr radius value, does the change to a negative pion make any other difference to calculating the probability?
Also what would be the correct way to apply the "small volume"? What I'm...
I am studying the following process: pion decays (mediated by the charged ##W## boson) into a muon and anti-muon neutrino (i.e. ##\pi^- \to \mu + \bar{\nu}_{\mu}##). The Feynman diagram associated to it is
And its Feynman amplitude is (where we of course neglected...
π+ + π- → γ + γ
How do you represent this in a Feynman diagram showing the individual quark? I am very confused please help!
[Moderator's note: Moved from a technical forum and thus no template. Own effort below.]
So I worked out the first part and obtained ##E_1 = 478.8MeV##, ##E_2 = 459.4MeV## and ##p = 0.49 MeV/c## but I can't quite wrap my head around the second part. Normally, I'd use the equation for s but I'm confused since I don't know the angle between the gamma rays.
Hi guys,
Merry Christmas to you all!
I wanted to know whether a neutral pion can be made up of a strange quark and an anti-strange quark. I know that the kaon is the only strange meson and all variations contain an s quark but wouldn't the strangeness be zero in an s quark/anti-s quark pair as...
Homework Statement
I'm considering a non-linear chiral theory where the Lagrangian is in terms of the field #\Sigma = e^{\frac{2i\pi}{f}}# where #\pi# is my pion matrix containing pion, kaon, and #\eta#. I need to calculate the transformation of #\pi# up to order #\pi^2# under an axial...
The longer-range inter-nucleon force is not a direct result of the gluon field, but is indirectly affected by a quark-antiquark pair (meson).
If this ‘residual’ strong interaction between nucleons is mediated by a π-meson, then what is the maximum time period in which the interaction takes...
Homework Statement
I have a lambda decaying into a pion and a proton. The lambda is moving with velocity 0.9c and I know the mass of the lambda as well as the pion and proton (these are known constants). I need to find the momentum of the pion and the proton after the decay happens.
Homework...
Does anyone have a reference to a good explanation of this experiment. I am looking at https://quantummechanics.ucsd.edu/ph130a/130_notes/node323.html
I am unable to comprehend the reasoning by which it determines the parity of the two neutrons in the final state. Particularly when it says the...
Homework Statement
The reaction dd → απ0 (where α is the Helium-4 nucleus and d denotes the deuteron) has never been observed. Why?
Homework EquationsThe Attempt at a Solution
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So I checked first the masses to make sure energy/momentum are conserved and found out that mass of 2d is...
I have seen vague explanations and (to me) misleading diagrams, and I am still not completely sure what is supposed to be happening in pion+/- decay. This Feynman diagram is a starting point.
https://en.wikipedia.org/wiki/Pion#/media/File:PiPlus_muon_decay.svg
What is happening? What happens to...
I thought only strange particles were produced in pairs via the strong interaction, however in my textbook it states 'kaons, like pions are produced in pairs via the strong interaction'.
Can particles that are not strange also be produced in this way?
Homework Statement
We were supplied with several images of hydrogen bubble chamber tracks, from which we measured the length of the (invisible) K0 track, angles of departure from the K0 meson's track and curvature. As a way to limit the amount of data we're talking about, I'll only discuss the...
Homework Statement
After being produced in a collision between elementary particles, a positive pion (π+) must travel down a 1.00 km -long tube to reach an experimental area. A π+ particle has an average lifetime (measured in its rest frame) of 2.60×10−8s; the π+ we are considering has this...
Hello everyone,
I am currently trying to understand how we can use feynman diagrams to estimate the matrix element of a process to be used in fermi's golden rule so that we can estimate decay rates. I am trying to learn by going through solved examples, but I am struggling to follow the logic...
Homework Statement
The speed of a particle in Earth's frame is 0.4 c. A second particle goes away from the first one with speed 0.6 c. What is the speed of the second particle in Earth's frame?
Homework Equations
u=(u'+v)/(1+u'v/c^2)
The Attempt at a Solution
I think v=0.4 c and u'=-0.6, but...
Homework Statement
A ##\pi^0## meson decays predominantly to two photons. Suppose the energies (E1, E2) and angle (##\theta##) between the emitted photons are measured. Find an expression for the ##\pi^0## mass in terms of E1, E2, and ##\theta##.
Homework EquationsThe Attempt at a Solution...
I have been given the following problem on a homework sheet;
"The CMB has an (almost) uniform temperature of (almost) 3K. If we take the energy of a photon to be E=3kT, what minimum energy must a proton have in order to interact with a CMB photon in order to produce neutral Pi Mesons?"...
I'm a student in high school asking for suggestions for an experiment proposal.
So far, our idea has been to recreate Young's interference experiment, but instead of using electrons, we will use a heavier particle. Charged pions have been the first choice so far. Aluminum is the current delegate...
The pion decay constant f_{\pi} is defined by
<0|\overline{d}\gamma^{0}\gamma^{5}u|\pi^{+}>=f_{\pi}m_{\pi}
where I have set the momentum \boldsymbol{p}=0 (and used the temporal component of the axial vector).
Now, at the right-hand-side the dimension is two (the decay constant and the mass are...
Hi, I'm recently reading Krane's nuclear physics textbook, and in the meson physics chapter there is a section about the spin and parity of pions. He demonstrated a way to find out the parity of the pion by investigating a pion decay(as in the attached images). I think I understand what he's...
Hi everyone,
I am curious about how a neutral pion decays in two photons. I don't understand how it is possible since the pion has spin = 1 and the photons have spin = 1 as well: doesn't this mean that spin is not conserved in this decay? What am I missing?
Another question I have is about...
Homework Statement
I am trying to calculate the ratio of the density of states factor, ##\rho(p)##, for the two decays:
$$\pi^+\rightarrow e^++\nu_e~~$$ and $$\pi^+\rightarrow \mu^++\nu_{\mu}~~$$
Homework Equations
##\rho(p)~dp=\frac{V}{(2\pi\hbar)^3}p^2~dp~d\Omega##
Which is the number...
Homework Statement
For the reaction below draw three Feynman diagrams, one that proceeds through
exchange of a gluon, one through a photon and one exchanging a weak W-Boson.
##\pi^0+\pi^0\rightarrow \pi^++\pi^-##
Which diagram provides the dominant contribution for this reaction?
Explain how...
The decay
\rho^0 \rightarrow \pi^- \pi^+
occurs with a probability of 100\%, whereas the decay
\rho^0 \rightarrow \pi^0 \pi^0
does not occur in nature, due to isosphin conservation.
I don't understand this.
Looking at the Isospin and its third component ¦I,I_3\rangle we have in the first...
I was searching Dark Matter and I found this site is that can be true ? Dark matter can be a act like a pion ?
http://right.is/space/2015/07/deja-vu-new-theory-says-dark-matter-acts-like-well-known-particle-2117.html
Homework Statement
A beam of pion mesons travels down a tube at the CERN accelerator moving at v/c=0.95 with respect to the laboratory.
(i) Compute the γ factor for these pions.
(ii) The pion lifetime is 2.6 × 10−8 s, what is the lifetime measured at the laboratory?
(iii) The pions travel 50...
In the text-book example of CP violation in the kaon system, the usual statement is that the KS decays much faster than the KL because the phase space is larger for a decay into two pions, compared to three pions. (See, for example, Griffiths or "Modern Particle Physics" by Thomson.)
I was...
Hello, my problem is as follows
I've tried finding the invariant mass of the positron and pion as follows
M^2=(E_e+E_{\pi})^2-(\mathbf{p_e}+\mathbf{p_{\pi}})\\
=E_e^2+E_{\pi}^2+2E_eE_{\pi}-p_e^2-p_{\pi}^2-2\mathbf{p_ep_{\pi}}\\
=m_e^2+m_{\pi}^2-2(E_eE_{\pi}+\mathbf{p_ep_{\pi}})\\...
This may be a silly question, but what prevents the decay of a Pion into a (anti) Tau and (anti)Tau neutrino. I can see the process for the electron but not for the tau.
Homework Statement
A possible decay mode a of a positive Kaon in the production of three Pions as shown below:.
K+ → π+ + π+ + π−
Whats is the maximum Kinetic energy that anyone of the pions can have?
The kaon is a rest when...
Hello
The textbooks about nuclear physics I have read don't explain too much about the Yukawa's model. For example, the textbook Structure of the Nucleus -by Preston and Bhaduri- finish the Yukawa's model with open questions about the "mesonic effects" by virtual pions.
And my doubt: are the...
p -> e+ + pi°
is >10^33 years. what conservation law does this limit test?
p is uud
pi° is uu or dd where the second quark of each is an antiquark
baryon number is not conserved 1 = 0 + 0
charge is conserved
lepton number is not conserved 0 = -1 + 0
not sure what this...
How fast must a pion be moving, on average, to travel 9.0 m before it decays? The average lifetime, at rest, is 2.60 ✕ 10-8 s. (Answer in terms of c)
I'm not exactly sure what equations I have to use but I believe it relates to time dilation.
I originally didn't realize it was a time...
So i have a question regarding a homework question I'm working on which suggest a neutral pion traveling with velocity v decays into two gamma rays of equal theta to the normal and they of course have velocity c. It then asks to prove that
v= cos theta
Which kind of confuses me. I mean if...
Hi,
Given the initial energy of a pion is it possible to calculate the probability and mode of its decay?
Ive looked everywhere for a relevant formula but everywhere simply states the probability and mode...
Wiki "The primary decay mode of a pion, with probability 0.999877, is a purely...
The TOTAL energy of a pion is given, no other information is given so we don't know how fast it is moving, is it possible to calculate its mass? I'm assuming it's relativistic and we need GAMMA (the lorentz factor)
Also if E is it's total energy what would it's kinetic energy be? wouldn't its...
Apologies, this is going to be a bit disjointed, I don't want to write the full question down as I don't want anyone to give me a solution as its an assignment question.
1. am i correct in assuming when a pion decays at rest its energy will be given by:
E^2 = p^2 c^2 + m^2 c^4
which...
Particle Physics -- decay of a neutral pion
Homework Statement
Consider the decay of a neutral pion that has a momentum of 10 GeV/c into two photons. What is the minimum energy that a photon from this decay can have? In terms of the pion mass and pion momentum. What about Maximum Energy...
Homework Statement
We are the given the rare decay:
π+ → e+ + ve
Also, we are given mπ = 139.6 MeV/c2, mv ≈ 0, me+ = 0.511 MeV/c2
And we are given that the decay starts with the pion at rest, so I took that to mean that pπ = 0
Solve for the momentum of the positron.
Homework Equations...
Homework Statement
"(a) Draw a quark-flow diagram for the weak decay \pi^{-}\rightarrow\mu^{-}+\overline{\nu_{\mu}} . Explicitly include the appropriate intermediate vector boson. (b) By considering the production of \mu^{-} and \overline{\nu_{\mu}} in the rest frame of the vector boson...
Homework Statement
"Assuming that the incident deuteron has sufficient energy, why is the reaction d+d \rightarrow He^{4}_{2}+\pi^{0} not allowed?"
Homework Equations
The Attempt at a Solution
I've gone through the various conservation laws that apply in a strong reaction...
Homework Statement
Negative pion with kinetic energy 100 Mev decays to electron and antineutron. What is the kinetic energy of electron , which will move in the same direction as pion did?Homework Equations
##p^{\mu }=(\frac{E}{c},\vec{p})##
##E=T+mc^2=\sqrt{p^2c^2+m^2c^4}##The Attempt at a...
Homework Statement
If anyone could help me with this classical mechanics exercise I would be very grateful! The exercise is as follows:
The muon (μ) is a particle with mass mμ=207me, with me being the electron mass. The pion (∏) has a mass of m∏=273me. The pion can decay into a muon...
\pi^0s decay to two photons via the EM interaction. The J^{PC} of the pion is 0^{-+} and of a \gamma is 1^{--}.
\gamma\gamma therefore has J^{PC} = 0^{++}, 1^{-+}, 2^{++}.
This does not match the pion, so how can this decay occur?
Homework Statement
Calculate the energy for 1S->2P transition in lithium and carbon. We had to calculate the energy and eigenvalue equations (though I verified these are correct)
Homework Equations
E = mc^2/sqrt(1+(Za/lambda)^2)
lambda = n + 1/2 + sqrt((l+1/2)^2- (Za)^2)
The...