Okay, I guess we should start. So good afternoon, morning or evening according to
your timezone and welcome to the upgrade session. We will have four presentations by
each of the LHC experiments. Each presentation with 25 minutes which is 20 minutes plus
five minutes for questions. I'd like to ask the speakers to be correct with their time. So
the first will be from ALICE. So yeah, Piotr.
You can start anytime.
Okay, good afternoon. Can you hear me? Yes, we can.
So I share my slides. And I would like to thank the organizers for the
opportunity of giving this talk, of showing you the status of the upgrades for
for Run 3, Run 4 and also beyond. ALICE, as it was already introduced today on
the highlight talk by Andrea, is a dedicated heavy-ion experiment at CERN LHC.
It consists of several detectors. The central Barrel detectors: the ITS, TPC
surrounding the interaction point and followed by the TRD, TOF detectors, all
installed within the magnetic field of 0.5 Tesla. And the muon spectrometer in forward
rapidities, and complimentary forward detectors for triggering, centrality
estimates. It showed great tracking and PID capabilities in large kinematic range.
It was successfully operated in Run 1 and Run 2, when we took a lot of data from
the collisions from the systems provided by the machine, and many of the fantastic
results will be discussed and presented during this conference.
We obviously continue, we plan to continue taking data in Run 3 and Run 4.
This is the pre-COVID timeline of LHC. And as I already said, in Run 3 and
Run 4, ALICE will continue operation. We have a rich physics program ahead of us
stemming from heavy-flavor mesons and baryons, charmonium states, di-leptons
and low-mass vector mesons and high-precision measurements of light- and hyper-nuclei.
All these observables will be used to characterize quark-gluon plasma in much more details.
And as you can see from this list of observables, we cannot run with a
dedicated trigger. We need a minimum-bias readout at highest possible rates.
And this will be accomplished with the major upgrades ALICE is
now undergoing. ALICE strategy for Run 3 and 4 is to increase minimum-bias
sample by a factor of up to 100 with respect to Run 2,
collecting integrated luminosity of 13/nb and write all Pb-Pb interactions at 50 kHz.
We will run without dedicated trigger and many of the detectors we want
in the continuous readout mode. We will improve tracking efficiency and resolution
especially at low pT and we need to preserve particle identification by
consolidating and speeding up main ALICE PID detectors.
The Run 3 upgrades were discussed and described in these technical design reports.
And I will discuss today the following: the new Inner Tracking System based on the new
MAPS technology. Also based on MAPS the new Muon Forward Tracker.
Also our TPC is undergoing a major upgrade. The old readout chambers are upgraded with the GEM technology.
We will also have new fast integration trigger detectors.
And the data from all these new and upgraded detectors will be read out, recorded and
analyzed by the new, integrated online-offline system, O-square.
In addition, we are also upgrading our readout of the all other, remaining detectors, including also
central trigger processor. So let's start with the upgrades.
ALICE TPC: is the main PID detector of ALICE. It is an almost 90 m3 tank, filled with gas.
Neon, or argon based gas mixture. It has five meter diameter and length of five meters.
And the central electrode in the middle defines two drift volumes: 2.5 m long each.
The maximum drift time\f around100 microseconds
for electrons which are then drifting towards the end plates on both sides and are read
and are read out by the multi-wire proportional chambers in Run 1 and Run 2.
The chambers are divided into sectors and further into inner and readout
and outer readout chambers, IROC and OROC. As I said, MWPCs were used in Run 1 and Run 2.
We have altogether 72 readout chambers with more than
half a million of pads for signal readout. And the MWPC technology
obviously was also using wire gating grid to minimize number of back-drifting
ions to the drift volume, and thus distorting the drift field. This, however,
this gating grid readout implies the rate limitation for the readout to only
a few kHz and, obviously, to operate the TPC at higher rates, 50 kHz or more,
we need to abandon this technology and run the TPC continuously. And this
will be realized using GEMs, gas electron multipliers. These are thin, polyimide foils
covered with with copper on both sides. In the photolithography process the
microscopic holes are etched. You apply high voltage across the foil and you
create high electric field inside these holes. And this is where the amplification
takes place. And the ions which are also created in this amplification are drifting
back and they are, most of them, they are collected on the top side of the GEM. So, this
intrinsic ion backflow suppression of GEM foils allows to abandon the gating grid
option and run TPC continuously. The TPC upgrade requirements were given in 2012
in the Letter of Intent. We will run these detectors at the nominal gain of 2000 in
Ne-CO2-N2 gas mixture, keeping ion backflow below 1%, which means only 20 ions
will leave the amplification stage per incoming electron. The energy resolution
of the system needs to be kept at the level below 12% measured for iron peak and
of course we need to assure the stable operation under LHC Run 3 conditions.
In the intensive R&D process, we found the solution for our new readout chambers.
The quadruple GEM stacks employing Standard and Large-Pitch GEM foils in this order:
Standard, Large-Pitch, Large-Pitch, Standard. And they are running, they will be operated with
highly optimized high-voltage configuration. On the right hand side you
can see a plot sigma (energy resolution) as a function of ion backflow.
Each data point corresponds to different high voltage settings. And you can see that
several high voltage settings fulfill our requirements. Later, also, our studies showed
that we can relax a little bit the requirements. Sigma up to 14% and ion backflow
up to 2%, so we have a lot of room for adjustment. The TPC readout chambers are
already built. IROCs consist of a single quadruple GEM stack and OROCs have
three quadruple GEM stacks. And in parallel tot he readout chamber upgrade we also
developed new front-end ASIC: SAMPA. This was a common development for both TPC and
MUON chambers.
This is 130 nm CMOS chip
providing 32 input channels and can be read out continuously
or in a trigger mode. It has an excellent noise figure of 670 electrons and the
front-end cards for the TPC will host five of such chips. And altogether we'll have almost
3300 front-end cards in the TPC which will continuously digitize signals at 5 MHz
so the data output will be around 3.3 TB/s.
The amount of data needs to be, of course, reduced and I will discuss that later
In the O2 part of my talk. The TPC upgrade is ongoing. Essentially, the TPC was extracted and
upgraded in the cleanroom already last year All chambers are installed. As you
As you can see here, in the middle bottom picture you can see the reflection of the GEM chambers
in the central electrode and also the front-end electronics is installed.And since
several months we take the pre-commissioning data, we are pre
We are pre-commissioning our detector, meaning that we test the two sectors at a time, measuring pulser,
noise, taking laser and cosmic runs and irritating our numbers chambers with X-ray sources.
Here you can see some examples of the laser tracks detected with GEMs. were
Our excellent noise figure of one ADC, so as designed. And also some nice examples of the cosmic tracks.
We start reinstallation in July 2020,
after this delay caused by the current health situation. I will discuss the timeline later.
Now, coming to the new ALICE detectors for Run 3.
This is: the Inner Tracking System, Muon Forward Tracker and FIT detectors.
The Inner Tracking System and Muon Forward Tracker are detectors based on the novel
monolithic active pixel sensor technology. These chips are produced in a Tower Jazz
180 nm technology, where the circuits are produced on an epitaxial layer
highly resistive epitaxial layer on the highly-doped p-substrates.
The epitaxial layer thickness is 25 micrometers which means that the minimum ionizing particle
will create around 1300 electron-hole pairs All electrons will be drifting towards the N-well sensing diodes
which are two by two micrometer squared large,
So - 100 times less than the pixel pitch and this gives very small input capacitance.
Thus relatively large input signal of 40 mV.
Taking into account the noise figure of 5 electrons we'll end up with very nice signal-to-background ratio
and all that, I think, justifies that MAPS are the great technology
to be used as a tracker, in the central tracker of such detectors
And it will be used for the first time on such a scale in the LHC experiment.
So MAPS were used to develop ALPIDE chip
ALICE Pixel Detector. This is, again, a common development for ITS and MFT, as I already said.
It hosts around 130,000 pixels/cm2 and can deal with particle rates up to 100 MHz/cm2.
In comparison to the old ITS, you can see on the bottom left side,
the old ITS system, which is already in ALICE exhibition,
the new ITS2 will have several advantages:
it will improve vertex and tracking precision, it will be installed closer to the interaction point,
it will have larger pseudorapidity coverage than the old ITS
and, the most important, it will be also thinner so the material budget will be more than 3 times less for the innermost layers
than the old ITS system.
With smaller pixel size and higher granularity, our spatial resolution figure will be around 5 micrometers.
And the readouts rate capabilities will reach around 100 kHz inPb-Pb and more than 1 MHz in pp collisions.
This is the layout: the ITS2 will consist of 7 layers three inner, two middle and two outer layers.
Altogether it consists of 192 so-called staves
This was a big engineering efforts to produce ultra-lightweight support for all these chips
which would not only support the chips but also provide cooling.
What's the status? The detector is produced, detector integration is finished.
It's ongoing on-surface commissioning, where we equilibrate thresholds, taking cosmic data and check its stability
It's, I think, worth to emphasize that we have extremely low noise figure and by masking only few pads we get the fake-hit rate
of below 10^(-10).
Now, we are testing the insertion of the ITS into the TPC.
After the TPC is pre-commissioned this test will will follow. And we are preparing for the installation of the ITS2 at the beginning of next year.
Now, building new ITS and having upgraded TPC we, obviously, foresee improvement in their performance.
So this improvement in the central barrel region means that the ITS tracking efficiency will increase, especially for the low pT,
Also we'll see improved tracking resolution and pointing resolution.
And if you consider the momentum resolution with the new TPC readout chambers we see, as required,
The momentum resolution will be preserved with the new TPC and ITS tracks.
This of course has an influence on the physics performance.
This is only one example of low-mass di-electron spectra
You can see with the 100 times more statistics, we will obviously improve our uncertainty figure.
And more about our future physics outcome with the new detectors, you will in other presentations in this conference and I will refer to that later.
Now, coming to the forward rapidity region: MFT - Muon Forward Tracker and FIT.
The main objective of the Muon Forward Tracker is to provide extra vertexing capabilities of our Muon Arm.
Our Muon System consists of tracking chambers, which are installed several meters away from the interaction point.
Also, they're installed behind this massive absorber.
So, obviously, the pointing resolution, vertexing resolution cannot be better than a millimeter.
And with this extra five layers of the muon tracker, close to the interaction point, we will improve figure, obviously.
The MFT is based on APIDE chips. We have five stations built out of 10 half-disks.
And assembly and integration of the detector is completed.
For the future performance, we we hope to get to the sub-millimeter for pointing accuracy, for the vertex reconstruction
This will, obviously, improve our reconstruction of the displaced J/Psi vertices from the b-hadron decays.
We'll also improve the J/Psi background and we hope to improve visibility of the Psi(2S) particles even in central Pb-Pb collisions.
Last but not least, the low-mass region of the di-muon spectrum will also be improved.
You can see the comparison before and after adding the MFT. These are, of course, simulations but we will soon be able to see eta mesons very nicely in the di-muon spectra.
Now, coming to the last new detector in this in this list:
FIT - Fast Interaction Trigger. It consists of several detectors. The new FIT will provide information to the Central Trigger of ALICE
It will be used for luminosity leveling, identification of the diffractive processes and also providing T0 for time-of-flight PID.
It consists of a large-acceptance scintillation detector, on one side of the interaction point.
Then we have Cherenkov detectors on both sides of the interaction point and then these forward diffractive detectors placed 17 to 19 meters from the interaction point.
It will improve our centrality resolution.
and also provide high-resolution T0 for our time-of-flight PID.
More on these detectors you can find in the posters presented on this conference.
Now, coming back to the reinstallation as you can see on this picture: ALICE is ready to host new and upgraded detectors.
The re-installation sequence, after this COVID-19 delay, will start around July 2020, (so in 2 months from now, or even less),
with re-installation of the TPC in the ALICE Cavern, followed by the installation of the cage and central beampipe, Miniframe,
and then, the new detectors FIT, MFT and ITS will be installed. We're supposed to be ready with the installation in May 2021
and this is when the global commissioning will start. We need around 16 weeks of global commissioning and we'll be ready for pp collisions end of August 2021.
Concerning the online offline data processing. As I said the new detectors will provide a lot of data.
This is just an example. This is a sub-timeframe 2 ms long. These are the MonteCarlo events overlaid on cluster level, using realistic bunch crossing structure.
This is a snapshot from what TPC and other detectors will deliver, and all that needs to be processed with our O2 system.
So around 3.3 or 3.5 TB/s of data in continuous mode will arrive to the first level processor.
And then the first data reduction and compression will take place.
Zero suppression, for example, and then the sub-timeframes of the length of 10 to 20 ms will be sent to the event processing nodes.
Here, the full online data processing will be done on GPUs.
We estimate that we need around 2000 or less GPUs.
And this will be nice efficiency increase with respect to the CPUs as a single GPU can replace more than 50 CPUs, in some configurations.
So this is ongoing. We are preparing for that. You can see the CR0 (Control Room 0) is ready
and the data will be further reduced in this stage
We'll save to disk, for further physics and data processing, around 100 Gbytes/s.
Now, coming to Run 4. As I said, we are also preparing upgrades for Run 4, after LS3.
One of the upgrades proposed recently is the Inner Barrel of theITS this will be called ITS3.
Fully cylindrical, almost massless inner barrel for the inner tracking system.
It will also consist of the new beam Pipe with smaller inner radius.
And the plan is to build three cylindrical wafer size layers based on curved, ultra-thin sensors with almost no material budget.
You can see the comparison of ITS2 (the new one) and ITS3 (the future new one)
Material budget will have only material budget of silicon to consider.
And the first tests of the ALPIDE sensor being curved to the radius of two centimeters are ongoing.
The project is accepted by LHCC and we are working towards the TDR in 2022.
The expected performance: again we expect further improvements:
Resolution improvement by a factor of two and efficiency improvement by a factor of two,
especially the low pT. It will obviously have impact on physics and more on that:
I would like to refer to the talk by Fabrizio on physics perspectives for ALICE in Run 4.
And he will also mention another upgrade, which is now, currently, under discussion.
It was accepted by our collaboration and it will be submitted to LHCC.
The forward calorimeter - FoCal.
It will have unique capabilities to measure direct photons in pp and p-pb collisions. It will allow us
to study the nucleon structure at small Bjorken-x scale and at low momentum
transfer. It will consist of to two calorimeters:
the hadronic and electromagnetic one, and the main challenge will be to separate gammas
and pi0s at high energies. So, for this electromagnetic calorimeters
we will use high-granularity\Si-W calorimeter with MAPS
layers, again. And as I said, the the project is accepted by the collaboration, and we can
expect a TDR end of 2021. Now, coming to the future in (like) 10 years from now:
after Long Shutdown 4 there's also some planning. Recently we submitted
an Expression of Interest for a all-silicon detector to be installed during LS4.
This was an input to the European Strategy Update and you can find more details under
this link. This all-silicon detector would increase rate capabilities
by a factor of 50 with respect to ALICE in Run 4. This will be
a detector not based on a TPC anymore. It will be based on silicon detectors. It would
consist of a tracker with 10 tracking barrel layers based of MAPS, with
great position resolution and almost no material budget.
for inner tracking layers. The TOF PID would be also given by silicon detectors
and then, electron-gamma identification would be done by a high-granularity shower
pixel detector. Physics goals stem from the
electromagnetic probes at ultra-low pT down to several tens of MeV/c,
to precision physics in charm and beauty sector. And again, to learn more
about the future and possibilities of building such a detector please
follow the talk which was was shown today. But you can still see the slides under the
link given here. So, this brings me to the summary and outlook. ALICE is undergoing a
major upgrade for the operation in Run 3. The major detector upgrades
involves TPC, ITS, MFT and FIT detectors. Also our readout system
will be upgraded and we're also working on the new online-offline O2 system,
for the data analysis. Installation of the upgraded and
new detectors will start in Summer 2020 and ALICE will be ready for pp
collisions end of August 2021. We also propose new upgrades in view of Run 4
and this is: inner barrel of the ITS and the forward calorimeter. And we are also
preparing a new generation of a heavy-ion detector - an all silicon experiment beyond LS4.
And with this, I would like to thank you for your attention!
Okay, thank you very much Piotr for giving so much information and staying in time. I'm
sure that must be questions. I remind people to raise their hands
and then we will unmute you. So the first question is from Ilya Gorbunov, please
state your name and institute.
Hello, I am Ilya
Gorbunov from JINR/Dubna
I have a question on slide number 29.
So here you say that
the GPU usage can replace up to 50 CPU models and what about the
software? Did you revisit all the software used by ATLAS to be able to run
on the GPUs? What's the situation with the offline software?
What's the situation with the offline software? Thank you.
First of all, concerning the number of 50. This of course, depends on
the unit you will choose and then, as I said, as it is written here, the final
choice will be done soon. Concerning the offline software, I would
prefer to advertise two other talks, where much more details on that will
be given. And especially the second talk on
the GPU analysis will, kind of, consolidate approach of all LHC experiments.
I don't see other questions. I have a question myself actually on slide 35.
Well, you stated that the material thickness would be less than 0.05% of the
radiation length per inner tracking layer. That looks exceedingly good. Is this wishful thinking
or is it something reality? What what is the thickness of the layers?
So, the current thickness of
ALPIDE chip is around 50 micrometers.
As you can see from the
this simulations, this
this consists of several layers of different materials. So, here you
can see already, based on our predictions for ITS3, removing all
these services, but also including other materials like glue and
aluminium, Kapton from the services, you can go down to
the bare silicon material. And this is where our material budget
improvement is coming from.
It's really what I see there: 20 to 40 micron thickness.
Yes, so 550 is currently
and then with further minimizing of this thickness, we can go to this 20-40 and this
is very small material budget. Okay, thank you.
There's still time for question two.
If there are no questions then, well, we thank virtually again Piotr.
There'd be the clapping of hands. That's also virtual. And then we move to the next.