Search for axion-like particles produced in e_e- collisions at Belle II
https://authors.belle2.org/dir.pl?p=3
Submitter: Ezio Torassa on June 17th 2020
Dear authors,
our compliments for the analysis, interesting results were obtained despite the limited statistics recorded during phase 2.
Is not easy to describe all the details with only 4 pages, some suggestions are given trying to make the article easier to read.
(C means current version , N means new proposed version)
General Comments:
a) A Feynman diagram showing the ALP-strahlung production it would be useful
Are there other signal diagrams giving 3 photon final states ?
b) There is a sizable discrepancy between data and MC at very low Mγγ and M_recoil.
it would be nice to see the fit result compared with the data in that range.
It is likely that the discrepancy is due to the different resolution in data and MC of photon energy reconstruction at low energy,
quoted at lines 246-247. Do you smear MC photons before or after the selection cuts ?
If you smear them before, do you find a better agreement with data in the low mass region ?
Specific Comments:
Abstract Line 9-10
C - upper limits on the coupling strength gaγγ of ALPs to photons at the level of of 10-3 GeV-1
N - upper limits on the coupling strength gaγγ of ALPs to photons as a function of ma up to the level of 10-3 GeV-1
Line 11-12
C - Axion and axion-like particles (ALPs) are a generic feature of many extensions
N - Axion and axion-like particles (ALPs) are predicted by many extensions
Line 34
C - beam dump experiments and mono photon searches for light APLs [2,4]
N - beam dump experiments and invisible with single photon searches for light APLs [4,2]
(is better to recall in the text the term “invisible” used in Figure 5).
(is better to keep the same order for text and references)
Fig5 Caption
C - and invisible final states
N - and invisible with single photon final states
Line 41
C - The signature is a mono-energetic photon with energy ..
N - The signature is an ALP candidate with a recoil photon with energy
(the sentence “recoiling against a two photon system at the ALP mass ma” can be removed)
Line 48
Is better to explicitly write the formula for M2_recoil as a function of sqrt(s) and the recoil photon momentum to ease readers not familiar with e+e- jargon
Line 70-72
It will be useful to provide energy and time resolution of the ECL as they are important for this search, and the Belle2 detector is quite new.
Line 122-123
C - We check that each photon time t is compatible with the average weighted photon time
N - We check that each photon time t is compatible with the weighted average time among the three selected photons
Line 122-129
The definition of t, tbar, delta t is not easily understandable, a reference with a more exhaustive discussion can help.
Line 145-147
Are all the three possible photon permutations always accepted by the selection criteria ?
Line 149 / Figure 1
Is better to clarify the bump at the vertical line of the figure is due to the different selection criteria before and after ma=4 GeV/c2
Line 175
C - number of events in data is 3.6 +- 0.9 % (4.2+- 1.1 %) higher
N - number of events in data is 3.6 % +- 0.9 % (4.2 % +- 1.1 %) higher
Line 205
C - The resolution of Mγγ worsens
N - The resolution of M2γγ worsens
Line 240
C - ranging from 0
N - ranging from 0 %
Line 286
C - The local significances are
N - The local significance as a function of ma is