[Halld-physics] Comments on all abstracts

[Jozef Dudek]

Dear all,

I still get these emails, so let me briefly summarise what the lattice calcs have said about what you call the b_1(1650), the first excited isovector 1+- state. ( BTW where does the mass 1650 come from? )


The spectrum for the lightest quark mass (pion mass near 400 MeV) we’ve so far considered is shown below.



Look at the blue boxes (isovector) in the  1+- column. The low-lying guy is the b_1(1235) — obviously it’s too heavy because the quarks are too heavy. Above that there are two boxes basically on top of each other and then another box above that. This indicates there might be two nearby states?


Quark-model like assignments for these states are discussed in  
https://journals.aps.org/prd/pdf/10.1103/PhysRevD.84.074023
where the first excited state in the isovector 1+- channel is identified (as Curtis has it) as likely a radial excitation of the qqbar P-wave

With respect to the second 1+- state that is very close to the first excitation -- this guy isn’t identified in the paper referenced above. It wasn’t totally clear what this guy is. You can see from the quark mass dependence shown below (focus on the blue)


(figure 16 in   https://journals.aps.org/prd/pdf/10.1103/PhysRevD.88.094505 <https://journals.aps.org/prd/pdf/10.1103/PhysRevD.88.094505>) 
that the splitting with the state you’re interested in probably grows with increasing quark mass. 

In a charmonium calculation (heavy quarks!) the splitting would have gotten quite large, and you’ll see in 
figure 16 of https://link.springer.com/content/pdf/10.1007%2FJHEP07%282012%29126.pdf
that there is a large splitting, but that the state can now be identified as a non-exotic hybrid meson, in the ‘first excited’ (quarks in a P-wave) set of hybrids. SO if you see two close-by states in your experiment, you might be seeing the radial excitation plus a non-exotic hybrid.

Hope this is helpful. If you have any questions, get in touch,

Thanks,
Jo.


> On Jun 27, 2017, at 9:49 AM, Curtis Meyer <cmeyer at cmu.edu> wrote:
> 
> With regard to the b2(1650) mentione din Ahmed’s abstract, this should be the b1(1650), which 
> is a radial excitation of the b1(1235) and you can see it in the lattice calculation. A b2 is exotic, and
> while expected, the mass is probably above 2GeV.
> 
> Curtis
> ---------
> Curtis A. Meyer MCS Associate Dean for Faculty and Graduate Affairs
> Wean:    (412) 268-2745  Professor of Physics
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> 
>> 
>> 
>> Ahmed Foda
>> 
>> - How are the b1(1235) and b2(1650) related? (Same branch modes?) What is the b2? Is it predicted by lattice?
>> - Why is the -t dependence important in this context?
>> 
>> 
>> 
>> 
>> -- 
>> Elton Smith
>> Jefferson Lab MS 12H3
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