29
$\begingroup$

The name of the particle (resonance?) in the recent announcement Observation of the doubly charmed baryon $\Xi^{++}_{cc}$ is complicated. I'm sure it's standard notation but I don't know how to "decode" it.

Is it possible to explain the Xi and the two super-scripts and subscripts? A short description would be fine. I'm wondering if the two plus signs indicate a double charge or isospin or something else, but I'm guessing that the double c's are related to "doubly charmed" in the title.

$\endgroup$
37
$\begingroup$

The PDG naming scheme for hadrons is the authoritative source on this.

The easy bit is the superscript: that's just the charge. $++$ means a charge of $+2$.

The symbols for baryons are based on those chosen for the baryons formed of light quarks ($u$, $d$, $s$). They encode the isospin and quark content. The rules are relatively straightforward, but I'll refer you to the naming scheme for the full list.

A light-quark $\Xi$ has a quark content of $uss$ or $dss$. A heavy-quark $\Xi$ retains the single $u$ or $d$ and replaces one or both of the $s$ quarks with a $c$ and/or a $b$. This is denoted in the subscript: e.g. a $\Xi_c$ has $dsc$ or $usc$.

$\endgroup$
8
$\begingroup$

The +, - or 0 indicates the electric charge. The "c" stands for the charm quark indeed. Page 1 of the paper they give the three valance quarks of your baryon : ccu. They are all 2/3e as you can see on the wikipedia page of the quark, so you can check that you have a "++" baryon. For exemple the Xi baryon made of ccd has only one "+". https://en.wikipedia.org/wiki/Quark The Xi is for the family of baryon where you have at least one heavy quark. They are sometime called "cascade" https://en.wikipedia.org/wiki/Xi_baryon

dukwon is right, the PDG is a better source for particle physic.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.