[Halld-npp] Fwd: Sign conventions for polarizabilities

[Elton Smith]

Hi Jose,

I want to make sure I understand the signs of the polarizabilities. See 
slides 2 and 8 of my presentation. Please confirm the following two 
statements:

1. I am taking a plus sign for the polarization of p = + alpha * E, mu = 
+ beta * H, according to Holstein and Scherer Annual Rev. Nucl and Part 
Sci. 64 (2014), Eq. 1 and 2.

2. I assume the polarizability of the pi- is opposite of the pi+, namely 
alpha(pi-) = - alpha(pi+), where the formula above is for the pi+. 
However, I note that COMPASS quotes a positive sign to their 
polarizability. Is this inconsistent with 1 and 3?

3. With the convention of 1) the polarizability of the pi0 is negative.

I have changed my presentation (slide 2) according to #1 above.


Thanks, Elton.


-------- Forwarded Message --------
Subject: 	Draft presentation to the PAC
Date: 	Fri, 31 Jul 2020 14:16:06 -0400
From: 	Elton Smith <elton at jlab.org>
To: 	Halld-npp at jlab.org <Halld-npp at jlab.org>
CC: 	elton at jlab.org



Dear collaborators,

I have uploaded a draft version of the presentation to the PAC at
https://halldweb.jlab.org/doc-private/DocDB/ShowDocument?docid=4600. I
will give a practice talk next Friday. Comments and suggestions are welcome


I need to sort out the signs of the polarizability. (Perhaps Jose can
help out?):
First is the sign on the p = - alpha *E on page 2. I don't remember
where I got the graphic from, but I assume the minus came with it. I do
note that the pi0 polarizability is expected to the negative, whereas
the polarizability for the charged pion is positive, at least according
to our proposal and to the COMPASS paper. Does the sign change between
pi+ and pi-? I assume it does because of the charge.

Thanks, Elton.

-- 
Elton Smith
Jefferson Lab MS 12H3
12000 Jefferson Ave STE 4
Newport News, VA 23606
(757)269-7625
(757)269-6331 fax