1. Tracking and L1 triggering in the ATLAS Muon spectrometer at sLHC
J. Dubbert, H. Kroha, R. Richter, P. Schwegler
Max-Planck-Institute für Physik, München
Topical Workshop on Electronics in Particle Physics
Vienna, 26th-30th Sept. 2011
Sept., 28th, 2011
Tracking and triggering in the Muon Spectrometer TWEPP2011, Vienna Robert Richter

2. Outline How to survive the harsh environment at the sLHC?
High particle rates and cavern BG at the sLHC:
What do we know about rates in phase I & II ?
Need reliable simulation predictions to set a scale for upgrade
Hottest regions in the muon spectrometer
New chamber technology for precision tracking
Concept for how to keep the L1 rate below 20 kHz
Summary
Sept., 28th, 2011
Tracking and triggering in the Muon Spectrometer TWEPP2011, Vienna Robert Richter

3. LHC upgrade drives Detector upgrades
Possible upgrade timeline
Have to live with ~2,6 ms L1 trigger latency
transition period
7 TeV
→14 TeV
→ 5x1034cm-2s-1
luminosity leveling
∫ L dt
Limit of nomin. LHC operation
1x1034 →
~2x1034cm-2s-1
3000 fb-1
phase-2
→ 1x1034cm-2s-1
~300 fb-1
1027 →
2x1033cm-2s-1
phase-1
L1 trigger latency of ~ 6,4 ms will be available
~50 fb-1
phase-0
~10 fb-1
2013/14
2018
~2022
Year
T. Kawamoto
Sept., 28th, 2011
Tracking and triggering in the Muon Spectrometer TWEPP2011, Vienna Robert Richter

4. The hot spots in the Muon spectrometer (it was always known…)
cool region, shielded by the barrel calorimeter
Simulation results from ATL-GEN
hot region due to proximity to the beam pipe
Sept., 28th, 2011
Tracking and triggering in the Muon Spectrometer TWEPP2011, Vienna Robert Richter

5. Experimental verification of cavern BG predictions in the Muon spectrometer
Up to ~ 2010 the only source for cavern background was simulation, done in 2004
Uncertainties were globally compounded by a „safety factor 5“ on background rates
Now measurements are available of background hits in the MDT tubes and are compared to simulation
Result: 2004-predictions for barrel were quite correct, endcap was underestimated
Simulation is improved and adapted to changes in the shielding geometry
Sept., 28th, 2011
Tracking and triggering in the Muon Spectrometer TWEPP2011, Vienna Robert Richter

6. Measured hit rates in the MDT tubes
Hot. region:
marginal at phase I
fails in in phase II
Intermed. region:
OK for factor 2
in phase I
Cold region:
OK for factor 5
increase in phase II
CSC region even much hotter!
L. Jeanty et al., Harvard
Sept., 28th, 2011
Tracking and triggering in the Muon Spectrometer TWEPP2011, Vienna Robert Richter

7. 2010/2011 measurements vs. 2011 simulation
New simulation reproduces cavern BG inside a factor 2
This provides a sufficiently good basis for detector design in phase I and II
Sept., 28th, 2011
Tracking and triggering in the Muon Spectrometer TWEPP2011, Vienna Robert Richter

8. Measured R-dependence in the Small Wheel
The g-rates seem to increase exponentially with decreasing distance from the beam, doubling about every 80 cm.
This allows an extra-polation for MDTs down to R~100 cm:
Expect ~ 14 kHz/cm^2
@ 5 * 10^34
Sept., 28th, 2011
Tracking and triggering in the Muon Spectrometer TWEPP2011, Vienna Robert Richter

9. Summary of cavern BG considerations at sLHC
 The cool region (barrel, Big Wh and Outer Wh) is about OK for sLHC
The hot region (Small Wheel) will already be close to the design limit at the nominal luminosity
little margin for going to higher luminosity
 need to build a new tracker with higher BG tolerance
Sept., 28th, 2011
Tracking and triggering in the Muon Spectrometer TWEPP2011, Vienna Robert Richter

10. Performance limitations of the Small Wh. w.r.t. sLHC
4 layers of CSC: - too few layers
- insuff. angular resol.
- no L1-trigger capability
4+4 layers MDT: - rate capabilities not sufficient for cavern BG at sLHC
2 layers of TGC (not visible, behind MDTs): - insufficient spatial resolution - insufficient angular resol. due to small lever arm
V. Polychronakos, BNL
Sept., 28th, 2011
Tracking and triggering in the Muon Spectrometer TWEPP2011, Vienna Robert Richter

11. Proposed new tracking devices
Small MDT tubes: diameter 15 mm instead of 30 mm. Gives rate improvement of factor 7
rugged construction, easy to build, limited number of elx channels, lots of experience, triggering to be done by RPCs or TGCs
Micromega chambers with 0.5 mm strip pitch:
excellent rate capability, time resolution
many channels, production of large area chambers difficult, triggering a challenge
Sept., 28th, 2011
Tracking and triggering in the Muon Spectrometer TWEPP2011, Vienna Robert Richter

12. Performance of Small tube MDTs w.r.t. BG
Measurements at the GIF facility, CERN (2010)
segment reconstr. eff. for 6 tube layers
single tube eff. at the max. rate
Tracking quality in 30 and 15 mm drift tubes at high g/n BG (schematic). Occupancies from BG hits (red dots) are 50% in the 30 mm but only 7% in the 15 mm tubes due to shorter drift time and smaller area.
Sept., 28th, 2011
Tracking and triggering in the Muon Spectrometer TWEPP2011, Vienna Robert Richter

13. Track must point to the IP vertex to be accepted for L1
Possible contribution of the precision tracking chambers to L1 selectivity
Track must point to the IP vertex to be accepted for L1 IP
O. Sasaki, KEK
In the present system the MDT have much better spatial resolution than the trigger chambers!
However, new trigger chamber types will largely improve spatial resolution.
Sept., 28th, 2011
Tracking and triggering in the Muon Spectrometer TWEPP2011, Vienna Robert Richter

14. L1 triggering in the Endcap
Max. L1 trigger rate will be 100 kHz, even at phase II
The muon trigger can only use ~ 20 kHz
The present muon trigger might already run up to 100 kHz in phase I !
90 % of all Muon triggers are generated in the Endcap
What‘s wrong with the muon trigger in the EC?
Sept., 28th, 2011
Tracking and triggering in the Muon Spectrometer TWEPP2011, Vienna Robert Richter

15. Limitations of the L1 trigger in the present muon endcap
Fake triggers in the EC (schematic)
Future L1 trigger: slope and position of the muon will also be measured in the EI wheel.
Fake triggers type C and B will be discarded.
slope diff. before and behind magnet defines momentum
The slope has to be measured with < 1 mrad accuracy. EO EM
New trigger chambers to measure slope in EI (Small Wheel)
T. Kawamoto EO EM
Present L1 trigger: slope and position of the muon are only measured in the EM wheel. Tracks are assumed to come from the IP (A).
However, there are many fake triggers from muons from decays and scattering, not coming from the vertex (C).
Coiling tracks from the EC-magnet also create fakes (B).
magnet b
Sept., 28th, 2011
Tracking and triggering in the Muon Spectrometer TWEPP2011, Vienna Robert Richter

16. Limited pT resolution of the muon L1 trigger
pT = 20 GeV
Fake triggers
the L1 trigger is suffering from fake tracks from p/K-decays + multiple scattering in the calorimeter, pair production etc.
The limited pT resolution combined with the steep slope of the pT spectrum allows for many triggers from low pT tracks.
Sept., 28th, 2011
Tracking and triggering in the Muon Spectrometer TWEPP2011, Vienna Robert Richter

17. But finer strip granularity is not enough…!
Better position resolution requires finer strip segmentation in trigger chambers
New type of TGCs with pick-up strips of 3 mm pitch to measure the bending coordinate (h) (present TGCs have ganged wires of 11 to 56 mm)
New type of RPCs with 2 mm pitch strips (present RPCs have a strip width of ~ 30 mm)
Micromega chambers are proposed as tracking device AND trigger chambers. Strip pitch 0,5 mm
But finer strip granularity is not enough…!
The available lever arm in the Small Wheel is only ~ 250 mm, so 1 mrad requires < 0,25 mm spatial resolution!
Sept., 28th, 2011
Tracking and triggering in the Muon Spectrometer TWEPP2011, Vienna Robert Richter

18. Precision coord. for L1 from charge interpolation
Charge distribution on RPC strips, schematic
G. Aielli, R. Santonico, R. Cardarelli, Rome II
Classical method:
- select strips above threshold
- look for strip with max. PH
- get precise location of avalanche from convolution with PH of adjacent strips
Brings improvement of factor 10 – 50 compared to only recording hit/non-hit strips
ToT is preferred option for PH determination
threshold
Sept., 28th, 2011
Tracking and triggering in the Muon Spectrometer TWEPP2011, Vienna Robert Richter

19. The RPC in the endcap
Schematic layout of an RPC package with 3 gas gaps, giving 3 pos. measurements in h and F, respectively
Sept., 28th, 2011
Tracking and triggering in the Muon Spectrometer TWEPP2011, Vienna Robert Richter

20. Typical R/O scheme for L1 trigger with centroid finding
Narrow 2-out-of-3 coincidences (2 ns)
G. Aielli, R. Santonico, R. Cardarelli, Rome II
Sept., 28th, 2011
Tracking and triggering in the Muon Spectrometer TWEPP2011, Vienna Robert Richter

21. RPCs allow rejection of late tracks by time of flight
The excellent time resolution of the RPC (s < 1ns) allows to reject tracks coming „backwards“ from the toridal magnet or tracks with large scattering angle in the calorimeter due to their late arrival. Can be used at the L1 trigger level (1 m = 3 ns).
Mean-Time from 3 Positions along an RPC pickup strip
Reading signals on both sides of a strip and using a Mean-Timer-Circuit the travel time along the strip can be corrected for.
Proposal by J. Chapman, Univ. of Michigan
Sept., 28th, 2011
Tracking and triggering in the Muon Spectrometer TWEPP2011, Vienna Robert Richter

22. E.g.: the MDT + TGC hybrid system for the New Small Wheel
4 planes of trig. ch.
4 planes of trig. ch.
~280 cm
lever arm
To achieve 1 mrad ang. res. with a lever arm of 280 cm at L1:
- need at least 0,2 mm position resol. for the trigger chamber package  ~0,3 mm per plain
- need to compute the result inside the latency
Present trigger ch. spatial resolution is ~ 1-2 cm!
What to do?
Proposed:
RPC with ~2 mm strips or TGC with ~3 mm
MicroMegas w. 0.5 mm
 get precision through centroid finding.
~200 cm l.a.
2 x 6 layers of MDT small tube ch.
Sept., 28th, 2011
Tracking and triggering in the Muon Spectrometer TWEPP2011, Vienna Robert Richter

23.  Need detailed latency estimate!
During phase I (2018 – 2022) the trigger scheme has to work under the tight constraints of 2,55 ms L1 latency.
 Need detailed latency estimate!
Sept., 28th, 2011
Tracking and triggering in the Muon Spectrometer TWEPP2011, Vienna Robert Richter

24. Available latency in phase I
1075 ns = 43 BCs available for L1 Muon trigger (incl. ~500 ns = 20 BC for 90 m fiber to SL)
V. Polychronakos, BNL
Sept., 28th, 2011
Tracking and triggering in the Muon Spectrometer TWEPP2011, Vienna Robert Richter

25. Planned demonstrator for fast TGC R/O
This trigger demonstrator built from FPGAs is to test the „real“ latency of the proposed L1 scheme.
A numerical estimate for the expected latency is given in the next slide.
Sept., 28th, 2011
Tracking and triggering in the Muon Spectrometer TWEPP2011, Vienna Robert Richter

26. Latency calculation for the TGC
L1 trigger latency from particle passage to the Sector Logic in USA15
Example: TGC
Available: 1075 ns
TGC max: ns
„Safety“: ns
G. Mikenberg, N. Lupu, L. Levinson, Weizmann and Technion
Sept., 28th, 2011
Tracking and triggering in the Muon Spectrometer TWEPP2011, Vienna Robert Richter

27. Summary of L1 trigger upgrade
3 technologies available for trigger chamber upgrade of the Small Wheel
all 3 rely on fine strip segmentation + centroid finding  achieve s < 0,2 mm position accuracy
challenging task for fast centroid finding and slope determination inside the ~ 1,1 ms latency
chamber technology mostly proven, but R/O electronics needs demonstrators w.r.t. latency
new rad-hard ASICs required  development must start soon
Sept., 28th, 2011
Tracking and triggering in the Muon Spectrometer TWEPP2011, Vienna Robert Richter

28. 3D view of the New Small Wheel
Support structure
Schematic layout trigger ch‘s + MDT
Sept., 28th, 2011
Tracking and triggering in the Muon Spectrometer TWEPP2011, Vienna Robert Richter

29. Some details of chamber integration
The high position measurement accuracy of the New Trigger Chambers must be matched by precision alignment chamber-to-chamber and to the global optical alignment system
Sept., 28th, 2011
Tracking and triggering in the Muon Spectrometer TWEPP2011, Vienna Robert Richter

30. Summary
1 mrad ang. precision on slope in Small Wheel yields considerable improvement against fake triggers and allows to improve momentum resolution (reject low pT muons)
1 mrad ang. res. requires an order of magnitude better position res. in trigger chambers 
use much finer strip pitch
use centroid finding to get to ~ 1/10 th to 1/50th strip pitch resol.
Use custom electronics for fast position and subsequent slope determination from PH distribution on adjacent strips
Precision tracking: use Small tube MDTs or Micromega detectors to gain immunity against cavern background, maintaining high tracking efficiency
Muon community is preparing Technical Proposal
Decision needed soon to match installation schedule in
Sept., 28th, 2011
Tracking and triggering in the Muon Spectrometer TWEPP2011, Vienna Robert Richter 30

31. Spares
Sept., 28th, 2011
Tracking and triggering in the Muon Spectrometer TWEPP2011, Vienna Robert Richter 31

32. Overview of L1 muon upgrade, phase-1& phase-2
Outer part of BW (h=1- 2): sees moderate rates. Preserve MDTs + TGCs. L1 upgrade in phase-2
Barrel (h=0-1): sees low-moderate rates. Preserve MDTs and RPCs. L1 upgrade in phase-2
This region is improved by the
new small wheel
Track angle behind EC toroid at EM
existing TGC trigger : pT determination
Track angle before EC toroid needed  build new Sm. Whl.
Tip of BW (h=2- 2.4/2.6): sees the highest rates. Present TGCs to be replaced for phase-2
T.Kawamoto
Sept., 28th, 2011
Tracking and triggering in the Muon Spectrometer TWEPP2011, Vienna Robert Richter 32

33. Complex B-field distribution in the „transition region“
ATLAS muon spectrometer integrated B strength vs. |h|
Difficulties to measure pT over the full h-range:
B field not homogeneous vs. h
Region around h = 1,5 has òBdl ~ 0! (This region can be masked off in L1).
We measure momentum p but want to select pT  requires much higher pos. resol. in the endcap than in the barrel  (p = pT / sin(q)
Sept., 28th, 2011
Tracking and triggering in the Muon Spectrometer TWEPP2011, Vienna Robert Richter

34. Possible reason of high BG in the Small Wheel
L. Jeanty et al., Harvard
IA point
Sept., 28th, 2011
Tracking and triggering in the Muon Spectrometer TWEPP2011, Vienna Robert Richter

35. Detector reasons for high pT trigger problem
TGC trigger ch‘s
RPC trigger
ch‘s b
MDT Outer Whl.
MDT Big Whl.
MDT Small Whl.
Particular difficulties in the End-cap:
High rate of tracks, increasing with h
Particles emerging from the EC toroid may fake high-pT trigger
The combination of the Barrel and the Endcap toroidal magnet yields a complex B-field distribution
Sept., 28th, 2011
Tracking and triggering in the Muon Spectrometer TWEPP2011, Vienna Robert Richter