I forgot to mention those estimates I quoted also used the target x-offset of +6.7 cm.


On Jul 29, 2015, at 16:31, Nathan Baltzell <[log in to unmask]> wrote:

> Hi Norman,
> 
> We took a look at this and I think this is due to lack of depth/position correction (since
> the one in the reconstruction code is for data with b-field).
> 
> There is an analytic correction that requires only geometry (track and crystal angles) and
> shower depth as inputs.  And we have a measure of the shower depth for these same crystals
> measured from a previous experiment (albeit with photons, average energy around 1.5 GeV).
> If we estimate the average geometry from the 2-d plot you showed and remember that target
> is 4m upstream from ecal, this gives average expected y-errors of -2.5 mm for top and +2.5 mm
> for bottom, and -3 mm for x.  This happens to be a good match with the residuals you measure.
> 
> Need to parameterize the crystal angles as function of x/y and then send a correction
> for you to try.
> 
> There also is a small x-rotation for top half of ecal from the survey which is not in lcsim.
> That could explain the difference in dx for top/bottom.
> 
> -Nathan & Holly
> 
> 
> On Jul 29, 2015, at 14:40, Graf, Norman A. <[log in to unmask]> wrote:
> 
>> Hello Stepan,
>> Yes, the residuals are cluster - track.
>> Norman
>> 
>> -----Original Message-----
>> From: Stepan Stepanyan [mailto:[log in to unmask]] 
>> Sent: Wednesday, July 29, 2015 11:38 AM
>> To: Graf, Norman A.; hps-software; [log in to unmask]
>> Subject: Re: SVT ECal relative alignment
>> 
>> Norman,
>> 
>> On X-axis, is it really cluster_position-track_postion?
>> 
>> Stepan
>> 
>> On 7/29/15 1:13 PM, Graf, Norman A. wrote:
>>> Hello All,
>>> I've taken the straight tracks from the field-off run 5784 and 
>>> projected them to the Ecal. The residuals are plotted in the 
>>> attachment using the z position of the cluster (which was essentially 
>>> constant at 1393.7). Although the accuracy is quite good (~2.5 to ~3 
>>> mm) there are clear systematic shifts in both x and y for both top and 
>>> bottom. Do these patterns make sense to anyone? I've also attached the 
>>> cluster x-y positions, showing the fiducial cuts imposed on the clusters.
>>> 
>>> I should note that these events were reconstructed using a 
>>> non-production steering file. The calorimeter positions were taken 
>>> from the uncorrected cluster collections pointed to by the 
>>> ReconstructedParticle objects. The reconstruction did use the
>>> 
>>> HPS-EngRun2015-Nominal-v2
>>> 
>>> detector which has the SVT survey incorporated. Have the ECal survey 
>>> numbers been incorporated into this detector? If not, are these shifts 
>>> commensurate with any of the measured offsets?
>>> Thanks,
>>> Norman
>>> 
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