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Blast from the past: Constraints on the dark sector from the BEBC WA66 beam dump experiment
by Giacomo Marocco, Subir Sarkar
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Submission summary
| Authors (as registered SciPost users): | Giacomo Marocco · Subir Sarkar |
| Submission information | |
|---|---|
| Preprint Link: | scipost_202011_00018v1 (pdf) |
| Date submitted: | 2020-11-27 12:52 |
| Submitted by: | Marocco, Giacomo |
| Submitted to: | SciPost Physics |
| Ontological classification | |
|---|---|
| Academic field: | Physics |
| Specialties: |
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| Approach: | Phenomenological |
Abstract
We derive limits on millicharged dark states, as well as particles with electric or magnetic dipole moments, from the number of observed forward electron scattering events at the Big European Bubble Chamber in the 1982 CERN-WA-066 beam dump experiment. The dark states are produced by the 400~GeV proton beam primarily through the decays of mesons produced in the beam dump, and the lack of excess events places bounds extending up to GeV masses. These improve on bounds from all other experiments, in particular CHARM~II.
Current status:
Reports on this Submission
Report #1 by Anonymous (Referee 2) on 2020-12-22 (Invited Report)
- Cite as: Anonymous, Report on arXiv:scipost_202011_00018v1, delivered 2020-12-21, doi: 10.21468/SciPost.Report.2320
Report
The paper considers the production of a pair of new Dirac fermions
chi through their coupling to the Standard Model photon either via
millicharge or through magnetic/electric dipole moments in fixed
target proton beam experiments. Decay yields from scalar and vector
mesons as well as Drell-Yan production are modeled using the
MadGraph plugin MadDump. The total number of scattering events in a
downstream detector is then estimated. Old data from the CERN BEBC
experiment are utilized to set the most stringent direct
constraints on the size of the aforementioned interactions.
The paper is a welcome and timely addition to the general ongoing
"intensity-frontier" efforts that seek to chart out the sub-GeV
landscape of new dark states coupled to Standard Model
particles. The paper is well-written, clear in its physics and I am
happy to recommend publication after the following remarks have been
addressed:
The authors make a point about the difference between charged
and neutral pion decay distributions, owed to their markedly
different lifetime and subsequent differing interactions with the
target. However, it did not become clear to me to what extend this
is actually taken into account? MadDump is used, but it appears its
primary purpose is to infer the angular and energy differential chi
distributions given the initial meson spectra? But what is assumed
for the latter? Finally, plots of the chi-distribution in angle and
energy would be helpful.