ESTB TEST BEAM PROPOSAL
Submit proposal (2-5 pages) to: Carsten Hast hast@slac.stanford.edu
Date: June 10, 2013
Title: Tests of a small PbF2 Crystal Array
Principal Investigator: David W Hertzog
Institution: University of Washington
Email: hertzog@uw.edu
Telephone:
206 543 0839
Members: Pete Alonzi, Lawrence Gibbons, Tim Gorringe, Matthias Smith, (plus
others from the g-2 Detector Teams per availability and skill)
Description of Physics Goals:
We envision two tests periods at SLAC. This proposal refers to the Phase-I test for this summer.
Phase II will be requested following the initial test and should be scheduled for mid-year, 2014.
It will be considerably more elaborate and involve a more complete system of detectors,
electronics and DAQ. The physics goals of both phases are related to the new muon g-2
experiment at Fermilab, which is an approved Project now under some level of construction and
advanced design. Our subgroup is responsible for the central detector system, electronics and
DAQ and we would like to test these components in a realistic electron beam, which can mimic the
muon decay from the g-2 storage ring (energies up to 3.1 GeV).
The Phase-I test is intended to measure a few critical unresolved design parameters associated ith
our PbF2 (lead-fluoride) crystals. We have ordered four 2.5 x 2.5 x 15 cm3 PbF2 crystals and
will receive them this week. Each will be individually wrapped and stacks will be made in various
configurations. Additionally, we have larger 3 x 3 cm2 crystals that can be used for shower
containment in the array configuration.
The Phase-I test can use a 3 GeV electron beam impinging on the small array and crossed
scintillator trigger counters on a moveable X-Y table. If it is straight-forward to increase the
beam energy in a few steps up to 6 GeV, we would like the option to do so. For this first test, we
would request two roughly half-day long periods separated by time devoted to other users.
During the down time, we will rewrap the array, alternating between a white Millipore and black
Tedlar wrapping. For each configuration, we are interested in a program that can deliver the
following numbers
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pe/GeV yield
Resolution
Linearity vs. small incoming angle adjustment.
Pulse shape.
We will bring a very simple DAQ, consisting of a 4-channel 5 GSPS digitizer that can be triggered
by a scintillator start signal. For larger array configurations, we will have to multiplex using
delay cable to separate out pulses from different PMTs. We will require an X-Y translation table
with a range of approximately >5 cm in each dimension. The weight of our crystals is only a few
pounds. We will use calibrated 1-1/8” PMTs to read out the crystals. They require negative HV
up to 1700 V. We will need a multi-channel power supply located in the counting room and both
signal and HV runs from the experimental location to the counting room. We will need (or can
bring if it is not available), simple logic units (discriminators, AND/OR, PMT amp to split the
signals, and a gate generator).
Detailed Description of Experimental Apparatus:
Four PbF2 crystals, each wrapped and read out by a single PMT. A stack of these will be made
and housed in a light-tight box. A pair of crossed scintillator sticks will be used to form a trigger.
A jack stand will be required to hold these counters in place with respect to the PbF2 box. A more
complicated configuration can be made using additional PbF2 blocks and PMTs.
Preferred Beam Parameters:
Beam Parameters
Value
Comments
Particle Type
Energy (2-13 GeV)
3 – 6 GeV
3 is ideal
Rep Rate (1-5 Hz nominal, bursts up to 120 Hz) 5 Hz
Charge per pulse or number of electrons/pulse
1/pulse
Energy Spread
dP/P ~ 1%
2 or 3 okay
Bunch Length r.m.s.
Beam Spot size, x-y, emittance
Ideally 1-2 mm2
The way secondary particles are produced at ESTB has the inherent risk that the full power
beam might be delivered to your experiment. This can happen when the energies between
LCLS and the A-line are matched and/or the production target is removed. So suddenly,
instead of a single or a few particles it becomes possible that up to around 10^9 particles
per bunch might be delivered. Please evaluate the consequences for your experimental
apparatus and document them here.
This should be fine for a short test and could serve even as proof of the rad hard nature of the
crystals.
You will be required to document in writing your understanding and accepting of this risk.
We accept this risk
Logistics
Space Requirements (include sketch):
The 4 crystals will be packaged in a light-tight box. If we use the one we have built (see Fig. 1)
with outer dimensions ~ 10 x 10 x 30 cm3. The box can hold a variety of arrays. It is light tight
and has the required feed-throughs for HV and signal.
Figure 1. Left: Front view of 2 x 3 x 2 array tested in 2012 at Fermilab’s test beam. Right: Assembly
view of configurable box These crystals are all 3x3x14 cm3.
Figure 2. Simple array configuration #1 with slightly oversized 1-1/8th-inch PMT readout. The black dot
represents where we would focus the beam. The dashed circle is centered on the beam and corresponds to
1 Moliere radius. From Monte Carlo we can obtain the correct energy sharing and from the calibrated
PMTs, we can then assign the pe/GeV quantity.
The moveable table should be able to hold the light-tight box. We should have 8 – 10 HV and
signal cables available that run to the counting room. Additional details can be provided once we
are closer to the test time.
Special Requirements (cooling water, gasses, electricity, magnets, detectors, etc):
None.
Estimated installation time:
4 hours
Duration of Test and Shift Utilization:
Two 10-12 hour shifts desired with beam prepared at 3 GeV and after installation.
Desired Calendar dates:
June or early July, to be discussed per other users and our schedules.
Any other aspect of Importance:
Submit proposal (2-5 pages) to: Carsten Hast hast@slac.stanford.edu