NEWCHOD
construction ideas
I.M.
28/08/2013
Basic considerations:
• Ideally the NEWCHOD should be “ thin ”
and be contained in a light tight box,
occupying a limited longitudinal space.
It should be built with plastic scintillator
TILES of dimensions, dependent on the
position relative to the beam, such that
the maximum rate of particle crossing
is < 500KHz in any tile
with time resolution better than 1ns
• The active area should cover a ring
between the IRC, radius 140mm and
the inner radius 1070mm of the LAV12.
To limit interactions, the material seen by
the particles should be minimized and this
also in the ring (370mm radial width)from
1070 to 1440 occupied by the LAV12
crystals.
• It is proposed that the BASIC TILE be
of 30mm thickness and be read out
by two sets of 9 WLS FIBERS suitably
placed, so that any crossing particle would
produce with high efficiency a pulse in
each of the light sensors linked to the a
fiber set. The average time of the two
pulses would define the L0 time.
• As an example I have chosen the basic
TILE with dimensions:
Height = 1070/10 = 107mm
Width = 1070/4 = 265mm
• With this choice 37x4 = 148 tiles are
needed (with 2 SiPM or PM each, 296
electronic channels) of which 40 of half
size
• The two sets (let say TOP and BOTTOM)
of fibers could be separately brought
together with a common length of about
400mm. At this point a SiPM could be
attached to the TOP fibers and similarly
to the BOTTOM. Otherwise, possibly with
a junction of clear fibers), the light could
be brought to SiPMs (or PMs) placed at
the outside perimeter of NEWCHOD
• A single plane of such scintillator tiles
would be suitable for defining the ring
(140 to 1070mm in radius) crossed by
the charged particles for the L0 trigger
trigger. In principle the electronic chain
could be the same as for MUV3 (and by
chance… with the same 296 number of
channels with the chosen dimensions)
• It is proposed to accurately place the
TILES on SINGLE CENTRAL FOIL
e.g 2mm thick G10 glass fiber with thin Cu
lamination (thus allowing soft soldering),
surrounded for 1440>radius>1070mm by
a “ strong”, let say 30mm thick plate, with
honey comb structure, to minimize
interactions.
• The rows of tiles should be placed on each
side of the foil (e.g. the one seen by the
incoming beam) at a vertical distance
equal to their width. In this way the
WLS fibers equipping any given tile
would not significantly interfere with
other tiles.
• On the other side of the foil (e.g. the one
towards the LKr calorimeter) the tiles
will be placed vertically in the regions
not occupied by tiles on the entry side.
Considering the tiles on the two sides
of the supporting foil, any particle passing
through the annular region of interest
will produce a signal in one tile with its
two light detectors.
With a threshold at 1/3 Mip Spasimir
has calculated the rates in KHz on the
NEWCHOD surface, subdivided in either
the standard or the small tiles.
With the chosen example the maximum
total rate (multiple hits in a tile counted
as 1) in the standard tiles is 470KHz
For the validation of the NEWCHOD
a FULL test of a Standard TILE will
have to be carried out with cosmic rays
and afterwards with a beam at high rate.
The electronic chain up to the output
of Constant Fraction Dicriminators should
also be tested at the rate of > 500KHz.
Towards agreeing on the
NEWCHOD
requirements
I.M.
• Discussing with Augusto it was apparent
that we should aim at agreeing, by the
forthcoming June Collaboration Meeting,
on the requirements of the NEWCHOD
in term of:
1 maximum loss of triggers by accidentals
2 efficiency and geometrical coverage
3 time resolution
4 electronic chain including hardware trigger
1_ Spasimir’s rates calculation allows
to evaluate:
SUM(RSIG*REAL)/SUM(RSIG)
i.e. the average over the whole active
surface of rate of hits per cell (REAL)
weighted by the rate of signal (RSIG)
in the SAME cell.
• Taking e.g. the small cell subdivision
and the Kpai nu antinu signal, the
AVERAGE REAL is about 140KHZ.
The AVERAGE LOSS of signal by trigger
accidental vetoing (SAME cell)will hence
be:
TDEADns*140.000 = 1.0%
for a reasonable TDEAD=70ns
• More serious losses due to accidentals
could be due to MULTIPLICITY
requirements.
The logical OR of the NEWCHOD hits
(if reasonably well aligned in time) is
expected to have a rate of about 8MHZ.
This, for total vetoing time of 10ns, would
already mean 8.0% LOSS when requiring
no extra hit !
• The rate of the OR of the MUV3 hits
should be of about 4 MHZ and hence
the loss due to MUV3 accidental Vetoing
should be 50% of that caused by the
multiplicity requirement, assuming the
same accuracy in the time alignment
of the hits from the NEWCHOD and MUV3
tiles.
The hits due to backsplash, coming late
relative to the event, should not cause
rejection due to multiplicity requirements.
In order to reduce accidental losses it
will be necessary to improve the time
alignment of hits before defining the
multiplicity .
• In my view a HARDWARE trigger using
uncorrected hits and a linear OR cannot
be expected to do better than the 10ns
quoted as example.
It may nevertheless be useful to have it,
in particular while setting up the proper
SOFTWARE L0 trigger
At the level of the foreseen (but not yet
fully defined) Software TELL62 L0 trigger
the time alignment should be
actually only slightly worse than the
intrinsic time resolution of the signals
from the tiles.
It may thus be reasonable to aim at <1%
accidental losses with 1ns time resolution.
2_ The geometrical coverage for the
140< Radius<1070mm
should be easily of order <0.1%:
With tiles 100mm high a lack of overlap
of 1mm would result in 1% loss, but
this can be avoided by actually
overlapping a row in front with a row in
the back of the middle plane by a small
positive amount .
The electronic efficiency of the CFDs,
looking at the two light sensors from the
same tile, will be determined by the
fluctuactions in the number of photo
electrons (or of the exited pixels in case
of SiPMs. With threshold at 1/3Mip
for average N p.e.>16
Efficiency >.99% for both CFDs to be ON
(but probably better to require N p.e.>25)
3_ Time resolution of the average of the
two CFDs should be of the same
order as the time resolution obtained
with MUV3, i.e. about 0.5ns
This can probably be achieved by
using rather thick (but single plane)
scintillator giving enough light
e.g 30mm --> 30 p.e. or pixels ?
4_ There are at least two practically
available choices:
a) Use Frascati electronics, which digitizes
time (with normal discriminators) and time
over threshold of pulses . An on board
OR chain allows for a multiplicity based
L0 HARDWARE trigger.
b) Use the same MUV3 electronic chain
with CFD discriminators.
For each pair of light sensors the
mean time is provided and with a
suitable chain of ORs it can be used
for producing a multiplicity based
L0 HARDWARE trigger
.
Summary of exchange of views on the NEWCHOD
during the weekly Meetings May 16th and 23rd
a) single plane of scintillator with subdivision of
the active surface in TILES such that, following
Spasimir suggestion, it would be possible to
exclude from the trigger the region (roughly a
rectangol displaced towards negative X)where
less than a few per mille of K-->pai nu antinu
(with the z and p "standard" cuts) have the pai
crossing the scintillator plane.
b) whether PMs or SiPM are used the time
resolution for a tile should be better that 1ns.
• c) the losses due to geometrical coverage
should be << 1%
• d) the duration of the pulses reaching the
discriminators should not exceed 70ns
• e) the discriminators should be of the
Constant Fraction type
• f) from each pair of pulses from a tile the
Mean Time should be made available
towards providing a rough HARDWARE
trigger from multiplicity requirements.
• g) given the point e) the front end
the electronic chain (after necessary
amplification and shaping in case of SiPM)
could be practically identical to the one
existing for MUV3 ( the difference being
that for MUV3 the best time information
from the pair of pulses looking at one time
is the output of their overlap coincidence
rather than the mean time)
Since the beginning of July an intense
effort has been put by all groups involved
in the NEWCHOD i.e Mainz,Perugia,Pisa,
Protvino with the collaboration of Frascati
and the essential help of CERN in order
to build and test a Standard Tile and
TEST its RESPONSE.
After a (not so) BRIEF STORY (which
could be the subject of an after dinner
talk) FINALLY on 22 August a FIRST
test has been possible with a TILE
produced and machined in Protvino, sent
to Cern and equipped with Bicron 1mm
diameter fibers. The two bundle of fibers
have been then connected to 3x3mm
SiPMs by Hamamatsu.
Two typical examples of the response are
shown in the following two transparencies.
Keep in mind that the single pixel pulse
heigth is 15-20mV.
Also the preamplifiers were meant for
1x1mm2 SiPM and the output saturates
at about 600mV (i.e. 30-40 pixels)
Now a few slides with images of the
up to date preliminary design of the
proposed NEWCHOD structure