What Do the Names and Numbers of Pseudovector Mesons Mean?

[Elmo]

TL;DR Summary

Looking for some sort of database/list on pseudovector mesons

I am looking for some detailed information on pseudovector mesons, mainly on their masses and quark contents. Also I am unfamiliar with the naming conventions of many of these mesons like
K1(1270), K1(1400), a1(1260), b1(1235), f1(1420), h1(1380).

What do these numbers and letters mean and ?
I can see that the numbers seem to give their approximate masses in MeV.
And I have no idea about their quark contents.

 

[Vanadium 50]

http://pdg.lbl.gov

 

[ohwilleke]

I have no idea about their quark contents.

For the a, b, f, and h mesons, nobody else does either.

Several dozen of these mesons have been observed. Determining their structure and quark content is one of the biggest open questions in high energy physics. Indeed, this is probably better described as one of the biggest set of open questions in high energy physics, as HEP research so far has made progress only on a case by case basis, finding unique answers (or at least unique solid hypotheses) for particular mesons, without finding some general rule that covers, for example, all h mesons.

Most of the naming conventions are standardized. But there are a couple of mesons whose names were established before this standardization system was in place that have stuck, and are simply irregular, like the sigma meson and the J/ψ meson.

Also, be aware that mesons generally have ground states, which are laid out in detail, and then multiple excited states (in theory, an infinite number of them), which are basically higher energy versions of ground state mesons. This is discussed, for example, at https://www.physicsforums.com/threads/quark-content-of-these-resonances.792591/

Wikipedia has a List of Mesons.

The Pseudo-Vector Mesons a.k.a. Isoscalar Vector Mesons a.k.a. Axial Vector Mesons, like the true scalar mesons, have quark content that is often not well understood, so they don't appear is a simple logical list based upon valence quark content the way the pseduoscalar mesons and vector mesons do. This article explains that:

Mesons named with the letter "f" are scalar mesons (as opposed to a pseudo-scalar meson), and mesons named with the letter "a" are axial-vector mesons (as opposed to an ordinary vector meson) a.k.a. an isoscalar vector meson, while the letters "b" and "h" refer to axial-vector mesons with positive parity, negative C-parity, and quantum numbers IG of 1+ and 0− respectively.

The, "f", "a", "b" and "h" mesons are not listed in the tables below and their internal structure and quark content is a matter of ongoing investigation. The particle described in the table above as f0(500) has historically been known by two other names: f0(600) and σ (sigma).

http://pdg.lbl.gov

The relevant article is entitled "Naming scheme for hadrons (rev.)". The most important part that is relevant to the question is Table 8.1:

Sections 8.2 and 8.3 which also pertain to meson are best just quoted and are short (I have added the emphasis indicated by italics below):

8.2 Remarks on “neutral-flavor” mesons with hidden charm or bottom not classified as qq

In the heavy-quark sector, there are several states with properties – such as masses, decay patterns, and widths – that are in disagreement with predictions from the naive quark model.

For example, the vector state at 4230 MeV (the ψ(4230)) apparently does not decay into DD, although within the naive quark model its quantum numbers would call for this decay channel to be dominant.

These states were originally named X, Y, or Z, with their masses added in parentheses. This nomenclature differs from the conventions outlined in the previous section, since the meson names are not related to their quantum numbers. However, these states have properties in conflict with the naive quark model and therefore deserve some special labeling. Since their original discovery, the properties of some of these states have become better understood and it has become possible to include them in the Listings as well as Summary Tables using the name assigned according to this review.

The X-, Y-, or Z-based names used at the time of the discovery are also reported in the Listings and Summary Tables from the 2018 edition onwards as a sub-header (listed are only some examples of the particles that appear in the Summary Tables),

•the state originally named X(3872) appears as ‘χc1(3872) also known as X(3872)’;
•the state originally named Zc(3900) appears <1> as ‘Tc ̄c1(3900) also known as Zc(3900)’;
•the state originally named Y(4260) appears <2> as ‘ψ(4230) also known as Y(4230)’;

<1> The name Tc ̄c1(3900) derives from the scheme outlined in a later section.
<2> This is one example where the mass label needed to be shifted given improved experimental information.

In addition, states with quantum numbers allowed by the naive quark model but showing some peculiarities, such as an unusual decay pattern, will have the following information in the header:

This state shows properties different from a conventional qq state. A candidate for an exotic structure. See the review on〈name of the proper review>.

8.3 Mesons with nonzero S, C and/or B

Mesons with nonzero strangeness S or heavy flavor C and/or B are not eigenstates of charge conjugation, and in each of them one of the quarks is heavier than the other (as above, states containing top quarks are not considered). The rules have been and remain:

1. The main symbol is an upper-case italic letter indicating the heavier quark as follows: s→K c→D b→B.

We use the convention that the flavor quantum number and the charge of a quark have the same sign. Thus the strangeness of the s quark is negative, the charm of the c quark is positive, and the bottomness of the b quark is negative. The effect of this convention is as follows: any flavor carried by a charged meson has the same sign as its charge. Thus the K+, D+, and B+ have positive strangeness, charm, and bottomness, respectively, and all have positive I3. The D+s has positive charm and strangeness. Furthermore, the ∆(flavor) = ∆Q rule, best known for the strange kaons, applies to every flavor.

2. If the lighter quark is not a u or a d quark, its identity is given by a subscript. The D+s is an example.

3. When the spin-parity is in the natural series, JP= 0+,1−,2+,···, a superscript “∗” is added.

4. The spin is added as a subscript except for pseudoscalar or vector mesons.

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There is additional discussion of some of the newer rules for naming hadrons at https://www.physicsforums.com/threa...he-lhc-lhcb-collaboration-paper-2022.1016538/

 

[Vanadium 50]

Going around correcting misinformation is getting to be a full time job.

For the a, b, f, and h mesons, nobody else does either.

That is wronger than wrong can be. Just because you don't know something doesn't mean nobody knows.

Let's start with the a's since they are the first in the list. They are isotriplets, so the a+ is y dbar, and the a- is d ubar. The neutral component is the isotriplet combination of u ubar and d dbar. The exception is the a0(980) which is almost surely not a meson in the conventional q qbar sense.

Netx the f's. They are isosinglets, so there is no f+ or f-. The neutral combination is the is the isosinglet combination of u ubar and d dbar. It is true that this can mix with other isosinglets like s sbar, but this is a statement that the pre-QCD model of mesons, the "naive quark model" breaks down. We know that hadrons are complex entities involving sea quarks and gluons, and they are not made of snapping quarks together the legos. The fact that different particles have the same "valence" quatk content demonstrates this.

If you want an analogy from chemistry, propyl alcohol and isopropyl alcohol have the same number of carbons, hydrogens and oxygens. But they are different chemicals. It would be just as wrong to say because of that "nobody knows what they are made of".

 

[berkeman]

El thread-o es cerrado para Moderation...

 

[berkeman]

Thread will remain closed pending results of a misinformation investigation...