I've been reading about initial state radiation (ISR) and beamstrahlung and I am not sure whether one can measure the photon or not. Some say that it is possible for ISR, but I understand that in most of the events the photon(s) would be outside the detector acceptance. Besides that the calculations of ISR that I know are done considering the electrons as having some sort of structure.
For beamstrahlung it is said it could be possible to measure its effects, using for example the lumi detector, considering the effect as a collective effect of the particles of the beam. But the nature of the effect is statistical. What if the particle participating in the hard scattering were affected? Moreover, no photon should be possible to be measured because the radiation is emitted as the beam moves along the tunnel.
Does anybody understand these issues better? I believe that understanding this things better we could try to do something to improve the measurements in a long term.
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2 comments:
I agree that beamstrahlung is statistical and so cannot be accounted for by e.g. finding photons in forward detectors and adding them in. It may be possible to do something clever with a kinematic fit, maybe by measuring the total Z-momentum, but I doubt that it will give you any more information.
ISR photons may or may not show up in the detector. If they don't, it will just be the same as the beamstrahlung with missing energy and Z-momentum.
Clare is currently looking at how ISR photons appear. Most are very forward, and it will probably help to add them into the kinematic fit and recoil mass calculation.
There are a small number of ISR photons that end up at larger angles and will be basically indistinguishable from FSR or other (hadronic decay) photons. We will have to figure out whether this is important and how to deal with it.
Joel
Thanks for the clarifications.
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