Hi,
thinking about the lead glass again, here are my considerations.
Pions above 200 MeV/c momentum (=100MeV kin. energy) are approx.
minimum-ionizing. Minimum-ionizing pions loose 1.1MeV/(g/cm^2) in lead or
1.6MeV/(g/cm^2) in Si, the density of lead (Si) is 11.35g/cm^3 (2.3). So,
pions would loose deltaE=190MeV in 15cm lead or 55MeV in 15cm Si. Probably
100MeV is realistic for 15cm leadglass. The pion energy loss
would be mostly independent of the incident energy for pions
faster than 200 MeV/c.
The radiation length in lead is 0.56cm, in Si 9.36cm. All electrons are
therefore likely to be stopped in the leadglass. Therefore, for
electrons of 200MeV and above the leadglass will distinguish between them
and pions.
While quasieleastically scattered electrons have energies of 600MeV and
more, the electrons corresponding to the delta excitation region have
energies of typically 300-600MeV. As shown above, here the 15cm leadglass
would help. The leadglass detector would be most useful for the inclusive
trigger channel which has fewer constraints than the exclusive channels.
The "tall" wall consists of 2x9=18 horizontal 16''-long bars with
single-sided readout, giving total measures of
TxWxH=6''x32''x54''=15x81x137cm^3.
The TOFs are 180cm high, so 43cm or 25% of the out-of-plane acceptance
would remain uncovered.
The leadglass signals would not be considered for any trigger decisions at
the hardware level, we would rather only record the signals with ADCs.
Gainmatching can be done with cosmics.
Regards,
Michael
On Wed, 22 Dec 2004, Douglas Hasell wrote:
> BLAST Weekly Meeting
>
> December 22, 2004
>
> General –
> - running for Tera-Hz measurements for the past week
>
> Mechanical – Jim
> - work for the shutdown includes adding 1” lead and 1” steel in front
> off the forward LADS in the right sector
> - 12 mm diameter target cell will be ready in January
> - discussion of adding the lead glass behind the TOF’s in the left
> sector to improve pion rejection
>
> § this would prevent the left sub-detector from moving (putting the
> rear WC covers would not be possible without removing the lead glass,
> putting front covers would require two people)
> § cabling and connectors would have to be found
> § need to calculate that this will in fact improve rejection
> § lower priority than other work
>
> Accelerator – Manouch
> - plan to have a 4 week shutdown in January then a week of beam the and
> startup beam to experiment 7 February
> - no major changes to the machine
> - Tera-Hz running, measured 45 ps bunch length, could get 8 ps with low
> momentum compaction, need 1 ps for tera-Hz and they are still working
> on it today and tomorrow (BLAST target cell and collimator had to be
> removed)
>
> Compton Polarimeter – Bill
> - plan to measure circular polarization of laser over the shutdown but
> will not open up to replace the mirror
>
> Atomic Beam Source – Genya
> - replace dissociator, measure holding field, improve cooling, install
> 12 mm target cell
> - measure 3 components of holding field along beam axis
> - also desirable to measure roughly the holding field away from the
> centre line (Karen says some data already exists)
>
> Unpolarised Gas System and Ion polarimeter –
> - no report
>
> Trigger and CODA – Karen
> - new processors will be shipped January 17 and will need 2 weeks to
> install and get running
> - will try buffering next week
>
> Wire Chambers – Douglas
> - gas flow at 1 l/min and will last until January
> - would need to be increased for a few days before running again
>
> Time of Flight Scintillators – John
> - repair RTOF3T PMT over shutdown
> - flasher RTOF6 needs to be repaired too
>
> Cerenkov Detectors –
> - no report
>
> Neutron Detectors – Michael
> - survey gains and thresholds using Sr90 source
> - will use a student to do this in January
>
> Backward Angle TOF’s –
> - no report
>
> Analysis – Michael
> - meeting at 10:00
>
> Run Plan – Doug
> -
>
>
> Miscellaneous
> -
>
>
> Cheers,
>
> Douglas
>
> 26-415 M.I.T.
> Tel: +1 (617) 258-7199
> 77 Massachusetts Avenue Fax: +1 (617)
> 258-5440
> Cambridge, MA 02139, USA E-mail:
> hasell@mit.edu
>
--+-------------------------------------+--------------------------+ | Office: | Home: | |-------------------------------------|--------------------------| | Dr. Michael Kohl | Michael Kohl | | Laboratory for Nuclear Science | 5 Ibbetson Street | | MIT-Bates Linear Accelerator Center | Somerville, MA 02143 | | Middleton, MA 01949 | U.S.A. | | U.S.A. | | | - - - - - - - - - - - - | - - - - - - - - -| | Email: kohlm@mit.edu | K.Michael.Kohl@gmx.de | | Work: +1-617-253-9207 | Home: +1-617-629-3147 | | Fax: +1-617-253-9599 | Mobile: +1-978-580-4190 | | http://blast.lns.mit.edu | | +-------------------------------------+--------------------------+
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