[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Main Index]

[lcdds 273] Re: draft CCR for muon walls posted for discussion

Subject:   [lcdds 273] Re: draft CCR for muon walls posted for discussion
From:   Ronald Dean Settles <settles@xxxxxxxxxxxx>
Date:   Sun, 17 Sep 2006 18:55:06 +0200 (CEST)

Hello Hitoshi and everybody,

               I started answering this a week ago but got interrupted by
our TPC endcap meeting in Paris.
               These effects are described in the DODs.  The ion density
over the TPC due to backgrounds (the real events contribute very
little) will not be uniform because the ions take 1 second to drift out
due to their low drift velocity (2-4mm/millisecond).  About 60cm of the
drift-stretch next to the gas-amplification plane integrates over 1 bunch
train, the next 60cm integrates over 2 bunch trains, the next over 3
bunch trains, and so on.  The overall space charge is small, at 1%
occupancy about 1 fC/cm^3 near the central membrane, so we don't expect
any problem here.  It is something we want to crosscheck with simulations
and mesurements.  There is also (see the DODs) an ion sheet built up at
the surface of the gas-amplification plane during a train which we also
expect to be no problem and this will be checked also.
         Similarly for the B-field gradient due to the anti-DID.  We think
that the level of correction needed can be achieved with the procedure
worked out by Dan and me at Snowmass: B-field mapped to 10^-4 plus Z-peak
calibration running plus radiation-return Zs.  The procedure developed for
Aleph (by Werner Wiedenmann) gave a correction accuracy (for B- and
E-fields) which is adequate for the ILC TPC.  This has to be checked but
simple calculations indicate this is o.k.
          By the way, every detector (not only the TPC) will have to
do careful calibration using such techniques if they want to achieve the
measurement-accuray we are striving for at the ILC detector.  For the TPC
we have learned how to do it at Lep; I hope the others have learned
how too...


On Mon, 11 Sep 2006, [ISO-2022-JP] »³Λά‘‘ΆΡ wrote:

> Dear Ron,
>     Thank you for your inputs.
>     By the way, I have one native question. The muon background hit the
> TPC more or less uniformly, but the distribution of the ionization
> seems to
> be linearly distributed. electrons toward the endcap and primary
> positive ions
> toward the center plane, correct? (electron density is zero at the
> center, and primary
> positive ion density is zero at the endcap)  Could such distribution
> cause
> any problem in terms of precision? We need to accomplish unprecedented
> precision, so even though TPC can operate with 10% occupancy for heavy
> ion experiment, I would like to convince myself that 5E-5 resolution
> can still
> be obtained. Do you think it would be OK with 1% occupancy, Ron?
> (Same can be said for the non-uniform field due to anti-DID)
>      Cheers
> - Hitoshi
> On 2006/09/07, at 22:32, Ronald Dean Settles wrote:
> >
> > Hello Andrei, Deepa and Hitoshi
> >
> >               Sorry if this feedback is late.
> >               I read your draft and Graham's reply to it, citing a
> > specific measurement that can be affected by this background.
> >               If I understood correctly, Graham is saying there could
> > be a
> > problem in the Ecal for the physics measurement he describes, and the
> > Ecal
> > should be designed with enough redundancy and hermeticity to handle it.
> >               For the TPC we are saying that we want to limit the
> > backgrounds, from all sources, below a total of 1% occupancy, since the
> > e+e- precision measurements will be very demanding and we want the
> > backgrounds to be as low as possible to make the analyses as efficient
> > as
> > possible.  The 0.15% TPC occupancy you give in your CCR for the muons
> > obviously satisfies this condition, and it must be remembered that
> > there
> > are other sources of backgrounds (neutrons, gammas, charged tracks),
> > and
> > each source has to yield much lower that 1%.  Therefore we should
> > not have much more than 0.15% from the muons.
> >               I agree with Graham (and as we also discussed
> > at Vancouver) that one of the most important points of your CCR is to
> > keep the option open of being able to add spoilers in case the muon
> > backgrounds are worse that expected (but that these additional spoilers
> > should not be part of the RDR costs).  So I agree with your CCR in this
> > form.
> >               Just a comment, as you say Reinhard Brinkman thinks the
> > muon
> > background should even be less, so your CCR is kind of a compromise
> > between worst and best cases.   But we will only know the truth when
> > our
> > ILC "gadget" is up and running.
> >               I would like to say a few words about the TPC occupancy,
> > since you mentioned it at Vancouver, Hitoshi.  The heavy-ion TPCs
> > (NA49,
> > Star, Alice) run or will run at occupancies of several 10s of %, from
> > the
> > many tracks in the events themselves.  (Also consider babar, belle,
> > the Atlas TRD or the VLHC.) We know that the heavy-ion
> > event-topologies are much different from the e+e- events: their events
> > our more like our background, in that they have a roughly isotropic
> > distribution of thousands of tracks, and our background will be roughly
> > isotropic filling up the detectors.  So the heavy-ion experience is
> > telling us more of a technical property, namely how much you can load
> > the
> > TPC with hits and still have it work properly.  Of course the muon
> > background is not isotropic in angle (the positions should be roughly
> > isotropic), but this should make them easier to recognize.  All this
> > has
> > to be checked with simulation.
> >               So our 1% limit for the total TPC occupancy should be
> > safe,
> > and, again, this has to be checked for our precision measurements.
> >
> >    Best wishes,
> >                  Ron
> >
> >
> > On Fri, 1 Sep 2006, Seryi, Andrei wrote:
> >
> >>
> >> Dear colleagues,
> >>
> >> A draft text of Configuration Change Request for
> >> going from 9+18m muon walls to 5m wall is posted here
> >>
> >> http://www-project.slac.stanford.edu/ilc/acceldev/beamdelivery/rdr/
> >> docs/CCR_muon/
> >>
> >> See the file CCR_muon_walls.doc and supporting documents.
> >>
> >> If there are any suggestions to the text or questions,
> >> please reply.
> >>
> >> We plan to submit this CCR to CCB in a few days.
> >>
> >>  Andrei for BDS area leaders
> >>
> >>
> >>