Email from Vanderhaeghen

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Begin forwarded message:

From: "Vanderhaeghen, Univ.Prof.Dr. Marc" <vandma00@uni-mainz.de>
Date: March 29, 2020 at 5:51:11 PM EDT
To: "miskimen@physics.umass.edu" <miskimen@physics.umass.edu>
Cc: "Danilkin, Dr. Igor" <danilkin@uni-mainz.de>
Subject: Re:  Neutral pion polarizability

 Dear Rory,

Thanks for your mail. All fine with me, I hope you and your family are also in good health.
We are all doing home office since one week already, having meetings online and getting ready for online teaching 
(our summer semester starts only in the week after easter). 
I think we all will have to adjust to come through it in the safest way possible.
 You may know that we’re submitting a proposal to the upcoming JLab PAC to measure the neutral pion polarizability.    
 This is a new proposal, the charged pion polarizability   measurement was approved several years back, and we’re 
 planning to take data on the neutral pion the same time as the charged pion.   A while ago I contacted Barbara P. to see
 if she had an update to her dispersion calculation, and of course she referred me to the calculations you’re doing on 
 g*g* -> pi pi for hadronic LBL.  I think Svetlana also discussed with you the need for dispersion calculations to support 
 the neutral pion polarizability. 
  
Yes, Svetlana and Alex already told me about it a couple of weeks ago. 
We are surely very interested in this as I told them that this will be crucial input for better estimating the 
light-by-light contribution to the muon’s (g-2), which Fermilab aims to improve by a factor of 4, requiring 
a similar improvement in the standard model prediction. With my collaborator, Igor Danilkin (who I put in CC) 
as well as with the experimental group in Mainz (of Achim Denig) we have embarked already 8 years years ago 
on a detailed program to constrain this light-by-light contribution. On the theory side, we have e.g. worked out 
and published in the past few years an updated dispersion theory calculation for the gamma* gamma* -> pi+ pi- 
and pi0 pi0 contributions, see e.g. the following papers (second is a review paper)

10.1103/PhysRevD.101.054008
arXiv:1909.04158

10.1016/j.ppnp.2019.05.002
arXiv:1901.10346

10.1016/j.physletb.2018.12.047
arXiv:1810.03669
 We were wondering if you could provide a paragraph to be included in our proposal supporting the case for 
measuring the neutral (and charged) pion polarizabilities as a test of hadronic LBL corrections to muon g-2?  
This will be very helpful for us. There’s certainly no rush on this, the PAC submission deadline isn’t until June 1. 
We’ll probably be finalizing the PAC submission mid-May.  
We would surely be interested to include such a paragraph to support the physics case of this proposal.

Let us know once you have a draft,
Cheers,
Marc