Invisible decay

Idea

B(inivisible)/B(normalization)={N(upper limit)/efficiency(invisible)}/{N(normalization)/efficiency(normalization)} * {1/(1-sigma)}

• B(inivisible): branching ratio of the invisible decay
• B(normalization): branching ratio of the reference channel
• N(upper limit): upper limit of the yield of the invisible decay
• N(normalization): yield of the reference channel
• efficiency(invisible): acceptance of the invisible decay
• efficiency(normalization): acceptance of the reference channel
• sigma: systematic uncertainty

What applies here:

The channel we are using is : gamma p -> p eta_prime -> p pi+ pi－ （eta). The invisible decay of eta is eta -> xx. x is something like U boson, which could be dark photon or heavy photon.

B(normalization) is 1 when we obtain eta by requiring the missing mass.

efficiency(invisible)=efficiency(normalization) * efficiency (invisible decay of eta). efficiency(normalization) is the detection efficiency of p pi+ pi-. efficiency(invisible) is the product of efficiency(normalizaiton) and efficiency(invisible decay of eta). efficiency(invisible decay) is the detection efficiency of at least one photon from eta decay.

photon detection efficeincy

procedure

• collection events of p, pi+, pi- and one or two photons
• requiring the missing mass of p pi+ pi- to be pi0
• requiring the missing mass of p to be eta or omega
• events passing the above three conditions are called "all" events
• two-photon events are called "good" events
• the ratio of "good" events to "all" events is the detection efficiency of photon
• the ratio is binned in energy, theta, and phi angle in lab frame

result

Error creating thumbnail: File missing efficiency of photon in cosine theta vs. phi

Error creating thumbnail: File missing efficency of photon in momentum vs. phi after selection cosine theta between 0.7 and 0.98

Eta acceptance

File:Eta efficiency.pdf

partial statistics

The following is from 2% of the data.

Reference

arxiv:1209.2469