[esa-t474] Your submission (fwd)

[stewart boogert]

Dear Eric, Mark and T474,

The reviewers comments are quite interesting and all quite beyond the
scope of the paper, which is principally machine physics.

1) The peak of the spectrum is the most important feature with regards  
the
physics program. The luminosity spectrum at the collision point  
bounded at the
top by the spectrometer measurement. In fact for M_t and M_h this is  
the most important
feature. The effect of the luminosity spectrum is convoluted with the  
threshold structure
being investigated, so the large energy loss beamstrahlung events are  
suppressed and
only the peak really contributes.

2) Absolutely no physics measurement (particle flow, or even more  
exotic for
any physics process ) can provide a precision energy measurement at any
reasonable time scale. It is possible to measure the beam energy using
radiative returns to the Z but this analysis is incomplete and  
provides energy
measurements at similar frequencies to physics rate.

3) The measurement of Bhabha scattering can provide information on
the momentum imbalance between the two colliding beams on a more rapid  
time
scale, but this method as formulated in all treatments does not  
reconstruct the collision
centre of mass energy, only the fractional energy loss from the  
maximum beam energy.
Of course then one requires the energy spread of the machine too. From  
Bhabhas the momentum
mismatch between the beams \Delta p can be measured not what p  
actually is.

4) I would think that more important comments are that the energy loss  
from the measurement
location and just before collision are more important as it is quite  
difficult to measure this
effect. Bino is simulating now, but we do not yet know the answer.

I can definitely add come text to the paper to this effect if the  
reviewer agrees.
There is little published in this area, something Eric. Mike and I  
have been trying
to correct for a while but without success.

I'll add a little more text to Mike's paragraph in a few hours and  
send around.

Cheers,
Stew


On 14 Dec 2007, at 18:02, Eric Torrence wrote:

> Hi Mark,
>
>   I think Mike has already given some good pointers
> on this, but just to reiterate it should be clearly
> stated that measuring the mean beam energy before
> collisions is a necessary (but certainly not sufficient)
> part of determining the collision spectrum needed for
> the ILC program.  For both direct reconstruction like
> M_H and threshold scans like M_t, the peak of the
> spectrum is the most important feature.  There are
> plenty of corrections, including energy loss in magnets
> and beamstrahlung, which need to be applied, but without
> a calibrated mean beam energy measurement you have no hope.
>
> Regards,
> -Eric
>
> On Dec 14, 2007, at 3:18 AM, Mark Slater wrote:
>
>> Dear All,
>>
>> Here are the first comments from the reviewer. Does anyone have a  
>> good
>> answer to this?
>>
>> Thanks,
>>
>> Mark
>>
>> ---------- Forwarded message ----------
>> Date: Thu, 13 Dec 2007 21:08:00 -0000
>> From: nim at lbl.gov
>> To: slater at hep.phy.cam.ac.uk
>> Subject: Your submission
>>
>> Nuclear Inst. and Methods in Physics Research, A
>> Title: Cavity BPM System Tests for the ILC Energy Spectrometer
>>
>> Dear Dr. Slater,
>>
>> Thank you for your recent submission to Nuclear Inst. and Methods in
>> Physics Research, A.
>>
>> Before proceeding further with the review process, I would like you  
>> to
>> address in detail the following issue.  Beamstahlung will spread the
>> energy of the electrons and positrons at the collision point by an  
>> amount
>> far greater than the precision of the instrument that you propose.  
>> Indeed,
>> for the purposes of data analysis new approaches, such as particle  
>> flow
>> analysis, must be developed because one cannot balance momentum in  
>> the
>> beam direction. Your treatment of this issue should speak to how the
>> information from the proposed instrument would be used as an input  
>> to the
>> new physics analysis approaches.
>>
>> Sincerely,
>>
>> William A. Barletta
>> Editor
>> Nuclear Inst. and Methods in Physics Research, A
>>
>>
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>
>
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