Tor, if you are working on something in the continuum well below the endpoint, all that counts to first order is luminosity.  For example, if you are looking at Z physics with Zs produced in the radiative tail of a high energy collision, you want maximum luminosity since that maximizes dn/dE at the point where you are looking.  The same applies if, for example, you want to study decays of top quarks - you would then set the beam energy well above the top mass to maximize the yield.  If you want to study a narrow resonance, what counts is the luminosity divided by the effective energy spread (incoming spectrum convoluted with beamstrahlung).  


Burton Richter
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-----Original Message-----
From: [log in to unmask] [mailto:[log in to unmask]] On Behalf Of Raubenheimer, Tor O.
Sent: Thursday, December 08, 2005 1:17 AM
To: Klaus Moenig
Cc: [log in to unmask]; lcd-l
Subject: RE: [bds 231] Physics effects of ILC parameters

Hi Klaus.

First, let me explain the rational for the parameter range.  The point of establishing the parameter range is to be able to deal with real life.  As an example, in the operating machine, it may be that the beam power or the number of bunches in a train is limited.  This could arise because of limits in the beam dumps.  It could arise because of limits in the damping rings, either the kickers or collective effects.  It also could arise if there is some reason that the detector or the beam instrumentation needs a larger bunch spacing.  The point of the lowP parameters is to have an operating path if one of these cases should arise.  

I think your study is great and the point of my previous email was two-fold.  First, if operation is limited as described above, your study shows that even in the narrow resonance case, one would want to use the lowP parameters and not simply chop the bunches in the main parameter set thereby reducing the luminosity by a factor of 2.1.  My point about normalizing by the design luminosity is just to understand whether there is a gain and justification for the high luminosity parameters.

This leads to my second point/question.  I would like to understand the balance between luminosity and precision.  I think the results that you are showing are emphasizing the precision  (as a side note, we may be able to optimize this further with tuning of the parameters within the parameter range and we should discuss this further).  Are there cases, where high luminosity with a larger beamstrahlung would be desired?  I had the impression from Paul Grannis' talk (linked in my earlier message) that, assuming some form of supersymmetry, you would want to operate at the maximum beam energy most of the time.  As I understand it, although the measurement of the Higgs suffers a bit at higher energy, such an operating scenario offers the greatest physics return per operating time.  Additional precision would be obtained with short dedicated lower energy runs.  In this scenario, what is the performance difference between the parameter sets?

Thanks again,

-----Original Message-----
From: Klaus Moenig [mailto:[log in to unmask]]
Sent: Thursday, December 08, 2005 12:46 AM
To: Raubenheimer, Tor O.
Cc: [log in to unmask]; lcd-l
Subject: RE: [bds 231] Physics effects of ILC parameters

Dear Tor et al.,

On Wed, 7 Dec 2005, Raubenheimer, Tor O. wrote:

> 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.

Now I am confused. I thought lowP has the same luminosity as norm, but with half the beam power. highL has 2.5 times the luminosity. If lowP has half the power, but you need to run 1.8 times longer, you would still save a little power but at the expense of a much longer running. highL would still help a little if systematics are the same.

> 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.

If Wolfgang can produce the GuinePig file for lowN I can run easily on that.

Of course we have taken an example where you expect effects and which is easy to study, since we wanted to start the discussion in time for Frascati.

Roughly speaking you expect similar effects for all threshold scans. For endpoint measurements, like the smuon mass, they should be of the same size as well, but this needs confirmation. For continuum measurements like W-couplings, Z' search, extra dimensions etc. I would expect much less dependence on the beamstrahlung.

> 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 
>  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?

A light Higgs you should study at 350GeV. Wolfgang sent around the scaled parameters as we used them. If you go to 500GeV the resolution in the recoil mass is much worse. You can combine this measurement with the top-threshold scan, so that you use the luminosity efficiently.

The beam energy spread smears the whole spectrum, it is, together with the detector resolution, responsible for the fact the signal/background is only 1/1. However, as you can see from the upper figure of my attachment, the events that you loose in the peak wrt. nominal are usually shifted by a percent or more. Since this is large compared to the energy spread it should not change my conclusions.

          Best wishes,


> 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
>          +------------------------------------------------+
>          | Klaus  Moenig     e-mail: [log in to unmask] |
>          | DESY, Zeuthen         or: [log in to unmask] |
>          |                                                |
>          | Tel.: +49 33762 77271   Fax:   +49 33762 77330 |
>          | Mob.: +49 160 8550906                          |
>          +------------------------------------------------+

           | Klaus  Moenig     e-mail: [log in to unmask] |
           | DESY, Zeuthen         or: [log in to unmask] |
           |                                                |
           | Tel.: +49 33762 77271   Fax:   +49 33762 77330 |
           | Mob.: +49 160 8550906                          |