Dear Klaus.
Thanks for making the study. We need studies like this to help us understand the parameter optimization. The beam parameters will likely be chosen to balance luminosity, machine operation, backgrounds and detector performance and it is very difficult to predict exactly what these will be - this is the motivation for maintaining a parameter range. For example, if the luminosity is limited by the total beam power (for example there is a problem with the beam dumps), the luminosity for the LowP case could be more than 2x higher than in the nominal parameter case. If I understand you results, this would favor the lowP parameters even when considering a narrow resonance.
Anyway, since we do not have this information, could you normalize these results to the design luminosity for the different parameters - I think this will make the highL case look better - and could you also consider the low charge case since this has the lowest beamstrahlung? Are there other comparisons which are less dependent on the beamstrahlung energy spread and where the total luminosity might be more important? This also might make the highL parameters look more attractive.
Finally, I am confused - you state that these studies are made assuming a measurement at 350 GeV but I thought that the nominal run scenario was to operate at full energy which I think should be assumed to be 500 GeV -- see http://sbhepnt.physics.sunysb.edu/~grannis/runplan_korea.pdf. Are these results calculated assuming the 500 GeV or 350 GeV cms energy? If they are assuming a 350 GeV cms energy, did you scale the 500 GeV parameters to 350 GeV cms - I don't know what the beamstrahlung would be in this case. Do you also need to include the beam energy spread as this may smear out the differences or is it too small to have any impact?
Thanks.
Tor
I think that if you are assuming a 350 cms energy, you should choose parameters consistent with 350 GeV operation - did you scale the parameters accordingly? Finally,
-----Original Message-----
From: Klaus Moenig [mailto:[log in to unmask]]
Sent: Wednesday, December 07, 2005 7:55 AM
To: [log in to unmask]
Subject: [bds 231] Physics effects of ILC parameters
Dear colleagues,
to get a first idea of effect the ILC parameters on physics I looked into the Higgs recoil mass measurement at 350 GeV. The attached file shows the sqrt{s} spectrum for nominal (solid) lowP (dashed) and highL (dotted) in the upper plot and the reconstructed recoil mass in the lower plot. The plot contains neither beam spread nor detector. However since, as you see, the additional smearing moves the events from the peak to far away, this doesn't matter for a crude estimate of the effect.
For lowP and highL there is a factor 0.7 less events in the peak for the same luminosity, so for zero background the statistical error gets larger by a factor 1/sqrt(0.7). Taking the TESLA TDR as reference and integrating over the relevant region the signal/background is about 1/1. Since the background should be little effected by the beam parameter also this value goes to 0.7/1. Since the statistical error in presence of background has to be divided by
sqrt(purity) you need in the end a factor 1.8 more luminosity for lowP and highL compared to norm to arrive at the same statistical error. For the systematics you can only guess that it increases as well with the beamstrahlung.
Of course this applies to exactly this one analysis and has to be redone for every channel of interest. However the factor 0.7 comes from the number of events in the peak at nominal beam energy, so it should be roughly applicable for all channels where narrow resonances are involved.
Best wishes,
Klaus
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