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

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

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

The hot spots in the Muon spectrometer (it was always known…) cool region, shielded by the barrel calorimeter Simulation results from ATL-GEN-2005-001 hot region due to proximity to the beam pipe Sept., 28th, 2011 Tracking and triggering in the Muon Spectrometer TWEPP2011, Vienna Robert Richter

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

 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

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

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

Latency calculation for the TGC L1 trigger latency from particle passage to the Sector Logic in USA15 Example: TGC Available: 1075 ns TGC max: 920 ns „Safety“: 155 ns G. Mikenberg, N. Lupu, L. Levinson, Weizmann and Technion Sept., 28th, 2011 Tracking and triggering in the Muon Spectrometer TWEPP2011, Vienna Robert Richter

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

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

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

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 2017- 2018 Sept., 28th, 2011 Tracking and triggering in the Muon Spectrometer TWEPP2011, Vienna Robert Richter 30

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

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

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

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

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