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What kinds of particles can decay to Lambda hyperons?

by Chenkb
Tags: decay, hyperons
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Chenkb
#1
Jun10-14, 08:32 AM
P: 27
Such as ##\Sigma^0 \to \bar{\Lambda}\gamma\gamma##.

I want to make a complete collection of all these decay modes, i.e.

##X \to \Lambda / \bar{\Lambda} + \cdots##.

At least some major channels.
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ChrisVer
#2
Jun10-14, 10:12 AM
P: 914
wouldn't the pdg help you?
Chenkb
#3
Jun10-14, 07:59 PM
P: 27
Quote Quote by ChrisVer View Post
wouldn't the pdg help you?
Ok, it's easy to find the ##\Lambda## decay mode in PDG, but not so easy to do it inversely I think.

If there isn't a ready-made collection, I'll try to search one by one in PDG.

Thanks all the same.

Vanadium 50
#4
Jun10-14, 08:55 PM
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What kinds of particles can decay to Lambda hyperons?

Any baryon weighing more than 1115 MeV.
Any other particle weighing more than 2230 MeV.
Chenkb
#5
Jun11-14, 01:24 AM
P: 27
Quote Quote by Vanadium 50 View Post
Any baryon weighing more than 1115 MeV.
Any other particle weighing more than 2230 MeV.
Really?
mfb
#6
Jun11-14, 01:35 PM
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Quote Quote by Chenkb View Post
Really?
Those numbers are not exact, but yes. As long as conservation laws can be conserved, a decay is possible. Many of them are very unlikely, however.

I guess you look for particles that frequently produce Lambdas? Then look for baryons with two light quarks (up/down) and one heavier quark (especially strange and charm, but also bottom). In addition, some B-mesons can decay to lambda+X.

Z and W can produce lambdas as well, but those are quite rare. For very high-energetic lambdas, they might be relevant.

Where/how do you want to use such a collection?
Vanadium 50
#7
Jun11-14, 08:11 PM
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Quote Quote by mfb View Post
Z and W can produce lambdas as well, but those are quite rare.
Not as much as you think. The mean number of lambdas in a Z-decay is about 0.4.
Chenkb
#8
Jun11-14, 08:21 PM
P: 27
Quote Quote by Vanadium 50 View Post
The mean number of lambdas in a Z-decay is about 0.4.
What did you mean by 0.4?
##\frac{\sum Z \to {\Lambda}/\bar{\Lambda} + X}{\sum Z \to X}## = 40% ?
Vanadium 50
#9
Jun11-14, 09:06 PM
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No, I mean that in a sample of a million Z decays there are 400,000 Lambdas. It's a statistical statement, not event by event.
Hepth
#10
Jun12-14, 03:24 AM
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If you are looking for things beside short-distance production and the Z production just look at any heavier baryonic resonance and see what can give you the most Lambdas. Your end goal is a [uds]. So you can have some

##[uds]^* \to [uds] + (f \bar{f},\pi \pi, \gamma)## Resonant decays ##[\Lambda^*]##
##[udc] \to [uds] + \left(f \bar{\nu}_f, \pi^{+}, \rho^{+}, etc\right) ## electroweak decays ##[\Lambda_c, \Sigma_c, \Xi_c]##
##[udb]-> [uds] + f \bar{f}## (FCNC, highly suppressed) ##[\Lambda_b, \Sigma_b, \Xi_b]##
mfb
#11
Jun14-14, 11:42 AM
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Quote Quote by Vanadium 50 View Post
Not as much as you think. The mean number of lambdas in a Z-decay is about 0.4.
I meant Z and W are rare. Even with a branching fraction of 100% they would be a small contribution.

At the LHC, the cross-sections are 100nb for the W and 30nb for the Z (ATLAS result at 7 TeV).

I didn't find a proper cross-section measurement of the lambda at the LHC, but an approximate number of 100Áb given here (note: those lines are "100 events"), and I think this is restricted to the LHCb acceptance - that means the total cross-section is significantly higher. For the total number of lambdas, W and Z contribute less than .1%. That number could be larger for large transverse momentum.

For all other accelerators, the energy is lower, and the W/Z cross-section goes down faster than the other production modes, so there the contribution is even smaller (unless you run an electron-positron collider at the Z peak, of course).

I found a master thesis with a collection of (predicted) mother particles for Lambdas at LHCb.


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