And hear my voice Yes.
Okay, thanks. Oh, I will be talking about the uhm particle identification using silicon em
timing detectors.
I'm talking on behalf of the Alice collaboration. So the precision timing has
always been a prominent topic in the instrumentation for high energy physics
experiment both for applications ehm
to trigger detectors, but also for for particle identification via time of flight
detectors. And in the last two decades, resistive clay chambers have been widely
used for applications of large area detector, kind of replacing the scintillators
for this type of use. But recently, the silicon sensors have become very popular
for timing and notably for pile-up rejection at the high lumi LHC and there
is also rapid progress for consumer application.
In the field of imaging the leader are 3D scanners. So let me introduce the Alice
experiment which is dedicated to heavy ion physics at the LHC. It's currently being
upgraded for Run three and run four and is designed on purpose for heavy ion physics
such to cope with high multiplicity be able to tracking down to very low pT. And
particle identification identification is an essential feature it uses all the known
PID technique, but in particular among the PID detectors in the central barrel,
there is a large time of flight array.
So, the time of fly detector of Alice is designed for the identification of
hadrons up to five GeV in pT. It consists of multigap resistive, multigap RPC
strip detectors that provide excellent timing and performance with better than 50
picoseconds time resolution measured in beam tests.
Better than 60 Pico seconds deliver for physics. Now the detector is doing physics
at the LHC since 10 years with impact on a large and diverse set of physics
measurements and will be running for the next 10 years at higher rates in tun
three and run four.
I said the ALICE experiment is being upgraded for operation in run three and
run four with luminosity is a factor of ten a hundred larger than then so far. And eventually
this will be the maximum rate that TPC based the experiment can can operate. And
in fact, if if we want to do another step in luminosity, the TPC should be abandoned
and a new technology should should be used. And for this reason, it has been
proposed
to have a completely new detector to be installed in the long shut down for these
proposals.
is discussed in this paper that has been submitted as input to the European
strategy. It would consist of full silicone detector with very high spatial
and time resolution and that will enable to fulfill a rich heavier in physics
program in the 2030. Going from studies of heavy flavors and quarkonia, low mass
dileptons, soft and ultra soft photons and so on and so forth. Now, of course,
those ambitious physics goals are the main drivers for the requirements for such a
detector that must be low in material budget, it should be fast and high
precision as well.
Now, you see in this slide the concept of the proposed em,
detector for after LS4 it consists of a barrel plus and endcap tracking with
approximately 10 layers and has
a time of flight
silicone detector that will provide hydron identification and electronic
identification at low pT. So it's a compact layout detector features very low mass
tracking layers, I mean down to zero point zero point five porcent of radiation length for the vertex in layers.
This thanks to the current R&D for the ITS three upgrade or at least it would be a
large accessed acceptance down to very low pT. And it will be capable to reach very
high luminosity is up to 10 to the 34, nuclear nuclear average luminosity.
So the performance is excellent with high resolution board for position and for time
of flight. So the expectation is to have a time of flight layer with 20 picosecond
time resolution.
Now the technology for doing timing in the time of flight layers are multiple if you
want to. So here's a list of some of them.
LGAD are devices that have been developed for high energy physics and they are going
to be part of the LS3 upgrades of ATLAS and CMS. The good news is that
already now, they have been proved to be able to, em,
provide a very good time resolution 20 or 30 Picoseconds with radiation loads
pretty high up to 10 to the 30, 10 to the 14 neutron equivalent. SPAD are also another
possibility for timing.
There is a bit of a limitation because of the fact that you have to quench them and
this will reduce the fill factor which has to be
taken care in a different way. They are also high dark count rates devices, but as a
matter of fact, that might be options to lower the gain and operate them in a more
that would not be, let's say sensitive to single photons anymore.
still be okay for MIPS. The problem SPAD is that they have been produced in quite
some time in the industrialized facilities and therefore a possibility to have them
integrated in a monolithic sensor is also quite attractive.
There are also timing sensors without gain. An example is this
monolithic pixel prototype that has been developed by the University of Geneva that
has reached a time resolution of 50 picoseconds. And now the team is exploring
the path doors the one picosecond approximately device adding gain to
this sensor. Now, one point to be
to be added here is that the fact that we expect to have a lower radiation load than
ATLAS and CMS opens some new possibilities such that we could explore new technology
options for timing and therefore perform a complimentary R&D.
From the physics point of view, there are
many points where the TOF will will provide the em
extremely good information just to list a few the measurement of low mass dileptons
in the plus and minus invariant mass, which is where we need high purity
for electron ID at low momentum or the measurement of multi heavy flavored barions
or mesons, many of them have not been seen notably, the Omega Triple C is a
state that is expected to be hugely enhancement in nucleus nucleus collisions.
So giving rise to spectacular phenomena. And in this case, PID is of course, very
useful to enhance the significance in the in the environment massively construction
of these things. Many more measurements from nuclear exotic hyper nuclear can be
performed and down to very ultra low pT in the measurement of coherent pion
production would benefit from this time of flight system.
Now I'm going to show you an example study of the performance of the time of fligth
detector that it has to be taken just as initial study to guide future
optimizations with the detector towards the achievement of the requirements for
for physics
one start from an analytical estimate of the performance you can plot the
separation power as a function of transverse momentum for electrons, kaons
and protons in an approximation that uses straight tracks and an idea of tracking
performance. And and and this plus here, sure your what would be the expected
performance of a 20 picoseconds time of flight they are at at one meter from the
beam pipe. When you can you can read from the plus the number for simplicity they
are written here, this system would give you a three sigma separation for the
electrons and pions up to 750 GeV
K to pi up to 2.5, GeV and proton to K up to about four GeV oversee.
Now, to have a more realistic estimate of the performance of the full system one has
to follow the in also the performance of the tracker. So, what we have done was
to estimate the, em,
the efficiency of momentum resolution of the tracker via studies with a fast MonteCarlo
tool. This take into account the detector configuration material effects and the
occupancy of the detector and therefore provides a reliab a reliable estimate of the
performance, you see the plots here on the left hand side, the efficiency on the on
the top part for electrons, pions and protons as a function of pT. And in the
lower part, the momentum resolution for electron, pions and protons as well. So
these are examples for magnetic field configuration of point two Tesla,
which is what would enable the measurement of particles down to low pT. And em as a
matter of fact, with this configuration electrons could be measured down to about
50 MeV over c.
So, these curves have been used for input as an input for the simulations of the
time of flight said to get a more realistic performance estimate of the
particular identification
and, and they have been fed to the Delphes fast simulation tool for the following results.
Now, if you look at the performance of a time of flight detector, you might
generally plot the measured velocity as a function of the particle momentum which is
on the x axis on this plot. And there you can see the separation power and the and the
different particle IDs that show up quite nicely. Now, the truth is that the TOF by
itself is an a, it's a layer
that measures only the time of arrival of the particle. And if
you want to have a performance as good as the one shown in this plot, you have to
know the start time of the particle to be able to measure the time of flight. And in
an environment where the collision time has a jitter of about three, 300 picoseconds,
you have to find a solution. But the good thing is that the TOF detector itself can
measure the event time. This can be done with a combinatorial algorithm, you just
need the two tracks. And eventually you measure the event time resolution, which
scales as one over the square root of the number of tracks that enter into your
algorithm. And you see in this plot the distribution foreseen and seen on
collision of the event time resolution that has a mean better than four
picoseconds, that means being negligible, compared to the 20 picoseconds of the
timing resolution of the array itself, and with a tiny fraction
of events below point five porcent, where the event time cannot be measured,
because only one track has reached the time of flight.
Now, eventually, if you want to quantify the particle identification performance a
bit more, em
you want to try to see what is the efficiency of the, em
detector system and the purity in the in the identification. So, this is shown in this
plot is the blue curves, you see the efficiency for the electrons, kaons and
protons they are primary particles, em,
and in and in red the purity for the particle identification. Now, this plot
here and this study include all the detector effects: start time, resolution,
time resolution, tracking, decays,
everything, and the particle identification strategy which is being
applied here to estimate the purity of the sample is a very simple three sigma cut selection.
So, something that would allow you to have 100% roughly particle
identification efficiency. And you can see that for instance in the electron case,
electron identification is very clean better than 90% up to pT or 500 MeV over c
and the coincide if you want it in very nicely agreement with what you would
expect from the Six Sigma separation from the analytical calculation, you see the
same case also for the kaons and and the protons in this case. So, this Yeah.
Just two minutes left. Yeah, I'm almost done.
So, this system would give you a clean particle identification better than with a better
than 90% purity up to 500 MeV for electrons 1.9 were about two GeV four kaons
and three GeV for protons.
Now this brings me to my summary. There is significant interest in precision in
precision timing with silicone sensors. This is of quickly evolving field. And
there are several interesting developments in in
ongoing that are promising and that the timing capabilities of silicone are
still to be fully exploited.
I've shown you the proposal for our next generation LHC experiment for heavy
ion physics. This is the detector conceived for running at about a factor of
50 higher luminosity than they currently upgraded the ALICE experiment and
therefore will enable a rich physics program in 2030s. This detector
will be equipped with a time flight layer
for particle identification made of silicon sensors. The time
resolution is expected to be of the 20 picosecond level, which is something that
is already achieved so far for MIPS. The point is that given the fact that the flux
and the radiation is different, different requirements with respect to ATLAS and CMS
apply for this case, and therefore, this opens the possibility to explore new
technologies, like the use of SPAD or monolithic sensors. Thank you very much
for your attention.
Thank you, Roberto.
Do we have any questions
so I
don't see any raised hands.
So, I have a question just from a technology like feasibility standpoint,
which do you think of these newer technologies is more feasible? Let say.
Well, I cannot I cannot really answer now, I must say, well, for sure, LGADs are
kind of already proven as a as a technology for for a timing layer with
with these capabilities. But I I believe that there is quite a good let's say,
perspectives in in the use of SPAD, these are devices that can be in principle quite
nicely coupled, in a,
in a sensor that will also embed the circuitry, using CMOS technology.
So I would say that,
the the fact that one can move to perform a new R&D that can be complimentary with
respect to the ones that have been carried out for Atlas and CMS timing layers, will
be for sure something to try to to to achieve in order to you know, move forward the field
like the the the field of timing, precision timing with silicone even further, as I
was also discussing, there are these these developments also on monolithic sensors
that are quite, quite promising. And these type of devices, if they are eventually
prove, if you can prove that these devices are really going to be,
you know, capable to give you
picoseconds level high resolution that could be exploited for physics in the
future experiment, that
that is definitely going to be the the most promising one that
would be a game changer I mean a factor of 10 in time resolution would be really ...