1. L1 Track Trigger for ATLAS at HL-LHC
RAL seminar, 18/05/2011
L1 Track Trigger for ATLAS at HL-LHC
Nikos Konstantinidis
(University College London)

2. Track Trigger for ATLAS at HL-LHC
Outline
High Luminosity LHC (HL-LHC)
Motivation, physics potential, timelines, parameters
ATLAS upgrades for HL-LHC
Overview, focus on Level-1 Trigger upgrade
The ATLAS L1Track R&D programme
Motivation, challenges, studies, plans
Conclusions – Outlook
Nikos Konstantinidis
Track Trigger for ATLAS at HL-LHC

3. The HL-LHC project

4. Track Trigger for ATLAS at HL-LHC
HL-LHC idea
Upgrade the LHC to deliver O(3000fb-1) per experiment in the 2020s (x10 the LHC lumi)
O(250fb-1) per year, peak luminosity 5e34
Motivation:
Increased discovery potential
multi-TeV region, corners of SUSY parameter space…
Detailed studies of discoveries made with 250fb-1
e.g. Higgs couplings, SUSY properties etc
Probe the gauge structure of the SM
Vector Boson Fusion at 1TeV, triple gauge couplings…
Nikos Konstantinidis
Track Trigger for ATLAS at HL-LHC

5. Track Trigger for ATLAS at HL-LHC
Timelines for HL-LHC
Current dates for “Long Shutdown 3”:
Dates driven by two factors:
Integrated lumi “saturation”
Radiation damage of accelerator components
Two other long shutdowns in this decade:
LS1 ( ): work to prepare for 14TeV & 1e34
LHC will have delivered ~O(10fb-1) at 7TeV
LS2 (2017/18?): upgrades for peak lumi 2e3
LHC will have delivered ~O(50fb-1) at 14TeV
Nikos Konstantinidis
Track Trigger for ATLAS at HL-LHC

6. LHC int. luminosity evolution
50fb-1
250fb-1
10fb-1
If it takes many (>10) years to deliver integrated luminosity that halves
statistical errors, then it is not cost-effective.
Nikos Konstantinidis
Track Trigger for ATLAS at HL-LHC

7. LHC: Draft 10-year plan (03/2011)
Nikos Konstantinidis
Track Trigger for ATLAS at HL-LHC

8. How to deliver 250fb-1/year
Upgrade the machine to deliver 10e34 (5e34 with luminosity leveling
Higher current per bunch
Higher field magnets for stronger focusing
Superconducting crab cavities for lumi leveling
Extreme collimation in the collision points …
All these require a lot
of R&D
Nikos Konstantinidis
Track Trigger for ATLAS at HL-LHC

9. Lumi leveling with crab cavitiesqc
RF crab cavity deflects head and tail in opposite direction so that collision is effectively “head on” for luminosity and tune shift
bunch centroids still cross at an angle (easy separation)
First proposed in 1988, in operation at KEKB since → world record luminosity!
Nikos Konstantinidis
Track Trigger for ATLAS at HL-LHC

10. Lumi profile with leveling
Much more manageable for the detectors
~100 vs. ~200 pp collisions per bunch crossing
Also better for LHC
Reduced peak heat deposition in critical cold regions of the machine
Nikos Konstantinidis
Track Trigger for ATLAS at HL-LHC

11. Example HL-LHC parameters
symbol
nom.
nom.*
HL crab
HL sb + lrc
HL 50+lrc
protons per bunch
Nb [1011]
1.15
1.7
1.78
2.16
3.77
bunch spacing
Dt [ns] 25 50
beam current
I [A]
0.58
0.43
0.91
1.09
0.95
longitudinal profile
Gauss
rms bunch length
sz [cm]
7.55
5.0
beta* at IP1&5
b* [m]
0.55
0.15
full crossing angle
qc [mrad]
285
( )
508
Piwinski parameter
f=qcsz/(2*sx*)
0.65
0.0
1.42
2.14
tune shift
DQtot
0.009
0.0136
0.011
0.008
0.010
potential pk luminosity
L [1034 cm-2s-1] 1
1.1
10.6
9.0
10.1
events per #ing 19 40 95
189
effective lifetime
teff [h]
44.9 30
13.9
16.8
14.7
run or level time
trun,level [h]
15.2
12.2
4.35
4.29
4.34
e-c heat SEY=1.2
P [W/m]
0.2
0.1
0.4
0.6
0.3
SR+IC heat K
PSR+IC [W/m]
0.32
0.30
0.62
1.30
1.08
IBS e rise time (z, x)
tIBS,z/x [h]
59, 102
40, 69
38, 66
8, 33
18, 31
annual luminosity
Lint[fb-1] 57 58
300
Nikos Konstantinidis
Track Trigger for ATLAS at HL-LHC

12. ATLAS Upgrades for HL-LHC

13. ATLAS Upgrades this decade
At LS1 ( )
New Pixel barrel layer very close to the beam (+new beam pipe)
The existing innermost Pixel layer becomes inefficient above 1e34
At LS2 (2017/18?)
New Muon inner endcap Wheels
Too high rate in existing chambers above 1e34
New wheels will give sharper L1 muon thresholds in forward region
Trigger upgrades
L1 topological processor
Hardware track finder after L1 (FTK)
Nikos Konstantinidis
Track Trigger for ATLAS at HL-LHC

14. Track Trigger for ATLAS at HL-LHC
ATLAS upgrades for
Upgrades are necessary to retain performance at 5e34 or to withstand irradiation up to ~3000fb-1
New, all-silicon tracker (pixels + strips)
New calorimeter readout to provide higher granularity information for the L1 Calo trigger
Major redesign of the L1 Trigger hardware and other upgrades to Trigger-DAQ system
Changes in the very forward calorimeters
Present Calorimeters, Muon Chambers and Magnets don’t change
Nikos Konstantinidis
Track Trigger for ATLAS at HL-LHC

15. Current TDAQ architecture
L1 uses only Calo/Muon
40MHz L175kHz
Unlikely to change hugely, given material constraints
L2 accesses only ~10% of event data (in RoIs)
Rate to disk ~200Hz
Unlikely to change hugely, given increased event size
Nikos Konstantinidis
Track Trigger for ATLAS at HL-LHC

16. Track Trigger for ATLAS at HL-LHC
L1 Trigger upgrade for 5e34
Physics at HL-LHC will still require triggering on signatures at the electroweak scale (W/Z/H)
Raising the pT thresholds effectively cancels the benefits of upgrading the LHC luminosity!
L1 Trigger has to achieve 5x higher rejection in much more complex events
E.g. electron/muon isolation may be less effective
Reading out the tracker at ~500kHz not an option
Costly, wasteful and introduces a lot of material
Nikos Konstantinidis
Track Trigger for ATLAS at HL-LHC

17. Track Trigger for ATLAS at HL-LHC
Options for ATLAS
Upgrade L1Calo
Use finer granularity information from Calorimeters
Upgrade L1Muon
Sharpen pT thresholds, reject more fake triggers
Use tracking info at L1
Known to be a key element for rejection at L2
A combination of all of the above
Nikos Konstantinidis
Track Trigger for ATLAS at HL-LHC

18. ATLAS Trigger upgrade plans and activities
L1Calo upgrades for 5e34
Finer granularity info for L1Calo is the main physics driver for Calo readout upgrade
Currently 0.1x0.1 trigger towers
Studies ongoing to understand what info is most important for L1Calo
In depth or lateral shower profile
Which HLT Calo techniques can be ported to L1
Strips of Dh=0.003 in 1st LAr sampling are essential for rejecting p0s
Nikos Konstantinidis
ATLAS Trigger upgrade plans and activities

19. Track Trigger for ATLAS at HL-LHC
L1Muon rates at 5e34
Rates for muons from b/c/W can be extracted by convoluting pT resolution with physics x-section
pT resolution drives the physics rates: >50kHz for MU20, >25kHz for MU40
The above estimates do not include cavern background nor charged p/K decays in flight, hence they give a lower bound
Nikos Konstantinidis
Track Trigger for ATLAS at HL-LHC

20. Track Trigger for ATLAS at HL-LHC
L1Muon upgrades for 5e34
All L1 Triggers
New Small Wheels (to be installed at LS2) will provide in forward region
significant reduction of fake triggers
sharper pT thresholds
Barrel L1Muon is harder to improve, but less sensitive to fakes
Ongoing studies
Possible L1Mu barrel improvements
to characterize fully the L1Muon performance in MC and project from data to higher luminosities
Endcaps
L1 Triggers with offline muon
Endcaps
Nikos Konstantinidis
Track Trigger for ATLAS at HL-LHC

21. The ATLAS L1Track R&D

22. Track Trigger for ATLAS at HL-LHC
Why tracking at L1
Tracking is key for rate reduction at L2, so it would enhance the purity of the L1-accepted events
For electrons, muons, taus (high-pT tracks)
For double/multi-object triggers
(ensure that they come from the same pp collision)
Will provide additional flexibility, redundancy & robustness to the L1 trigger in the harsh and uncertain conditions of HL-LHC
Otherwise we’ll have to rely exclusively on pT thresholds for controlling the L1 rates
Nikos Konstantinidis
Track Trigger for ATLAS at HL-LHC

23. Track Trigger for ATLAS at HL-LHC
Nikos Konstantinidis
Track Trigger for ATLAS at HL-LHC

24. Possible L1Track designs
Cannot readout the whole tracker at 40MHz
Self-seeded L1Track: use closely-spaced (few mm) Si layers electrically connected and instrumented with coincidence logic that is satisfied only by high-pT tracks (the CMS idea)
Coincidences have to be sent off-detector at 40MHz and combined in a further step
The L0/L1 idea (or RoI-based L1Track)
L1Calo/L1Muon reduce the rate from 40MHz to ~500kHz and identify Regions of Interest (Level-0)
Tracker data from these RoIs are readout and processed by L1Track; L1Track info is added to the L1Calo/L1Muon info to form global L1 decision
Nikos Konstantinidis
Track Trigger for ATLAS at HL-LHC

25. Track Trigger for ATLAS at HL-LHC
The RoI-based L1Track
L0 is a synchronous pipelined trigger with latency ~3.2us (pretty much like current ATLAS L1 trigger)
Subsystems (e.g. Muons, Calorimeters) can either readout at the full L0 rate (~500kHz), ignoring L1, or have additional buffers (e.g. tracker) in their front-ends where L0-Accapted events are kept until the L1 decision arrives
L0 RoI information is converted into Regional Readout Requests that target specific modules in the tracker
From L0 to L1, the system is asynchronous; makes overall design more flexible
Depending on the size of the additional buffers, the L1 decision can take up to O(100us)
Nikos Konstantinidis
Track Trigger for ATLAS at HL-LHC

26. Track Trigger for ATLAS at HL-LHC
Example: strips readout chip design
Nikos Konstantinidis
Track Trigger for ATLAS at HL-LHC

27. Advantages of RoI-based L1Track
No impact on the tracker layout
Can be optimized for offline tracking performance
Full tracking information available (in principle)
For larger L1 latency, L1 rate can be significantly below 100kHz
Implications for the tracker’s material budget
Nikos Konstantinidis
Track Trigger for ATLAS at HL-LHC

28. Track Trigger for ATLAS at HL-LHC
ATLAS vs. CMS L1 upgrades
Conclusions depend on initial conditions
At least ~2 years ago, CMS had the constrain for L1 6.4us/100kHz (no change of ECAL electronics)
ATLAS has more options for improving L1Calo and L1Muon
High granularity of LAr calorimeter is an advantage
Muon Small Wheels
Of course, with more options it is harder to converge
Nikos Konstantinidis
Track Trigger for ATLAS at HL-LHC

29. A possible architecture: L0/L1
Calorimeters
Muon detectors
Inner detector
(Digitisation)
40MHz
Level-0 Calo
Level-0 Muon
e/γ
Jet ET μ R3
25 ns per
pipeline step
Pre-Trigger Processor
Level-1 MDT
Level-1 Track
~500kHz?
Tracks
ID Tracks
= 3.2 μs
Central Topology Processor
L1A
L0A
Trigger & Timing distribution
<100kHz?
= < μs
L0A, L1A
Nikos Konstantinidis
Track Trigger for ATLAS at HL-LHC

30. RoI-based L1Track parameters
Key parameters for the design of L1Track are
L0 rate
L1 rate
could be <100kHz if enough rejection is achieved
Number/size of RoIs
hence the fraction of the tracker to readout at L0 rate
Number of tracker layers to readout
not necessarily all
Ongoing simulation studies to determine these parameters
Nikos Konstantinidis
Track Trigger for ATLAS at HL-LHC

31. Regional Readout studies
RoI: Df=0.2, Dh=0.2 at Calo Dz=40cm at beamline
PIXEL
Module number in Z
STRIPS
Frequency (in %) inside an RoI
Nikos Konstantinidis
Track Trigger studies

32. RoI-based L1Track – issues
All ATLAS sub-detector should either be able to readout at the L0 rate (~500kHz) or change their readout electronics
Not an issue for tracker (new), Calorimeters (new electronics) and other small sub-detectors
BUT: potential problem with Muon system: max readout rate 100kHz (max latency 3.2us) and replacing all electronics is a very long operation – unlikely to fit in a 2-year shutdown
Alternatives are under investigation
Unlikely that any L1Track scheme can fit within 3.2us/100kHz
Nikos Konstantinidis
Track Trigger for ATLAS at HL-LHC

33. Track Trigger for ATLAS at HL-LHC
Conclusions – Outlook
The HL-LHC will dominate the high energy discovery frontier in the 2020s
Major upgrades of the detectors will be required to cope with the high-lumi environment (up to 200 pp collisions / bunch crossing)
ATLAS is evaluating a number of alternatives for the upgrades of L1Calo and L1Muon, as well as the use of tracking information at L1
An RoI-based L1Track appears to be an attractive solution for ATLAS, but more studies are needed to converge to the optimal L1 architecture
Nikos Konstantinidis
Track Trigger for ATLAS at HL-LHC