A new MDT-based L1 trigger for ATLAS Sebastian Nowak - - PowerPoint PPT Presentation

A new MDT-based L1 trigger for ATLAS

Sebastian Nowak

nowak@mpp.mpg.de

Max-Planck-Institut für Physik, Munich

Young Scientist Workshop, Ringberg Castle July 23, 2013

The ATLAS Muon Spectrometer

designed for LHC nominal luminosity: L = 1034 cm−2s−1

Precision tracking chambers

1150 Monitored Drift Tube Chambers (MDT) 32 Cathode Strip Chambers (CSC)

Trigger chambers

606 Resistive Plate Chambers (RPC) 3588 Thin Gap Chambers (TGC)

2 / 21

The ATLAS MDT chambers

3 or 4 drift tube layers

• 0.05 mm

W−Re wire

r

30 mm Al tube wall RO HV

length: 1−6 m width: 1 −2 m

Gas mixture: Ar/CO2 (93/7) 3 bar absolute pressure

• Max. drift time: ≈ 700 ns

Single tube resolution: 80 µm Wire positioning accuracy: ≈ 20 µm Chamber tracking resolution: ≈ 40 µm

Support Frame 3 / 21

Muon tracks for different momenta

pT = 10 GeV pT = 20 GeV pT = 40 GeV RPC 2 RPC 1 RPC 3

schematic, not to scale

RPC strip width ~30mm Example: Muon barrel The sagitta in the barrel is ~ 24 mm for pT = 20 GeV

RPC: Resistive Plate Chamber → Trigger chamber

4 / 21

LHC Long Term Schedule

5 / 21

Rates in the ATLAS Muon Spectrometer

Neutrons, γs and charged hadrons from secondary reactions in detector components and shielding cause high background rates Background rate increases proportional with the luminosity ⇒ Rate capability in the Big Wheels exceeded

2 4 6 8 10 12 14 16 18 20 2 4 6 8 10 12 m

BIL BML BOL EEL EML EOL EIL CSC 1 2 3 4 5 6 1 2 3 4 5 6 EIL4 1 2 3 4 5 6 1 2 3 4 5 6 1 2 3 4 5 1 2

3

End-cap magnet y z 1 2 10% 10%

Expected cavern background occupancy

10% 7% 5% 3% 3% 8% 4% 6% 5% 3%

(L = 7 * 1034 cm-2 s-1)

6 / 21

MDT read-out chain (now)

RPC 3

The trigger logic identifies high-pT candidates readout Search path for MDT hits

Middle

CSM

Inner

CSM

Outer

CSM RPC 2 RPC 1 Trigger tower (schematic)

Sector Logic Reference point for the search path

example barrel

CSM: Chamber Service Modul RPC: Resistive Plate Chamber

MDT

Use of more precise MDT information for triggering.

7 / 21

MDT read-out chain (proposed)

RPC 3

The trigger logic identifies high-pT candidates The existing readout structure will be preserved Search path for MDT hits

Middle

CSM

Inner

CSM

Outer

CSM RPC 2 RPC 1 Trigger tower (schematic)

Sector Logic The existing L1 trigger path is preserved Reference point for the search path Additional fast read-out

example barrel

CSM: Chamber Service Modul RPC: Resistive Plate Chamber

Use of more precise MDT information for triggering.

8 / 21

ATLAS Muon Trigger and DAQ System

RPC 3 The trigger logic identifies high-pT candidates readout Search path for MDT hits Middle CSM Inner CSM Outer CSM RPC 2 RPC 1 Trigger tower (schematic) Sector Logic Reference point for the search path

example barrel

CSM: Chamber Service Modul RPC: Resistive Plate Chamber

MDT

Level 1: Trigger chamber → MDT read-out Level 2: First track reconstruction New concept (Upgrade Phase 2): Level 0: Trigger chambers → MDT fast read-out Level 1: MDT chambers fast read-out → MDT read-out Level 2: First track reconstruction

9 / 21

ATLAS Muon Trigger and DAQ System

RPC 3 The trigger logic identifies high-pT candidates The existing readout structure will be preserved Search path for MDT hits Middle CSM Inner CSM Outer CSM RPC 2 RPC 1 Trigger tower (schematic) Sector Logic

The existing L1 trigger path is preserved Reference point for the search path Additional fast read-out

example barrel

CSM: Chamber Service Modul RPC: Resistive Plate Chamber

Level 1: Trigger chamber → MDT read-out Level 2: First track reconstruction New concept (Upgrade Phase 2): Level 0: Trigger chambers → MDT fast read-out Level 1: MDT chambers fast read-out → MDT read-out Level 2: Track reconstruction

10 / 21

Performance of the existing L1 pT trigger

Total muon production cross section

pT = 20 GeV Fake triggers

cross section for pT > 10 GeV: ∼400 nb cross section for pT > 20 GeV: ∼47 nb

The interesting physics is mainly at pT above ∼ 20 GeV (see W,Z cross section) The slope of the inclusive pT spectrum is rising very steeply with decreasing pT − → threshold definition of the L1 trigger must be sharp to avoid high trigger rates from low pT muons

ATLAS Level-1 muon trigger efficiency 11 / 21

Histogram based track finding algorithm

for an additional MDT fast read-out

preceding bunch crossing t = −1 correct bunch crossing t = 0 following bunch crossing t = +1 Bunch crossing: Time of muon production

12 / 21

Simulation framework

Stand-alone Monte Carlo simulation Adjustable parameters: Drift tube chamber geometry Angle of incidence of the muon and spread of the angle Rate of non-correlated background Effect of δ-rays Inefficient regions (tube walls, glue gaps) are included Real r-t relation (implemented as look-up table) Performance studied as a function of the background rate with and without spread of the incident muon angle

13 / 21

Parameters used for all simulation

Drift time resolution 25 ns (∼ 0.5 mm) Algorithm bin width 2 mm Angle of incidence (EML1) 0.123 < α < 0.238 [rad] Worst case scenario: EML1

2 4 6 8 10 12 14 16 18 20 2 4 6 8 10 12 m

BIL BML BOL EEL EML EOL EIL CSC 1 2 3 4 5 6 1 2 3 4 5 6 EIL4 1 2 3 4 5 6 1 2 3 4 5 6 1 2 3 4 5 1 2

3

End-cap magnet y z 1 2

α

Chamber for simulation 10% 10%

Expected cavern background occupancy

10% 7% 5% 3% 3% 8% 4% 6% 5% 3%

(L = 7 * 1034 cm-2 s-1)

14 / 21

Definitions for simulation results

Efficiency: Calculated track is within 2 mm region (bin width) of real track Fake probability without ROI (Region Of Interest): Calculated track is outside 2 mm region of real track The track fitting is not based on trigger chambers information Fake probability with ROI: Calculated track is within 3 cm ROI and outside 2 mm region of real track The track fitting is based on trigger chambers information

15 / 21

MDT Level-1 muon trigger simulation for EML1

No incidence angle spread With δ-rays Background occupancy

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

Efficiency

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Minimum number of hits: 3 Minimum number of hits: 4 Trigger (within 2mm region of real track) Fake probability (within 3cm ROI) Fake probability 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Trigger efficiency (hits > 3) Trigger efficiency (hits > 4)

Fake probability 10% Occupancy (3 hits required): Efficiency: 98.5% Fake probability with ROI: 0.2% Fake probability without ROI: 0.5%

16 / 21

Incidence angle spread

Angle: α = 0.123 rad

Angle spread [mrad]

2 4 6 8 10 12 14 16 18 20

Efficiency

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Minimum number of hits: 4 Efficiency: Within 2 mm region of real track

• rays

δ No

Expected incidence angle spread for EML (pT = 32 GeV): Trigger chamber information not available 20 mrad algorithm inefficient Trigger chamber information available 3 mrad minor degradation

17 / 21

Test of new read-out hardware (planned)

CERN Gamma Irradiation Facility (GIF)

Goal: Measurement of efficiency and resolution of additional fast read-out

Filters Source

Scintillator Layer

Lead Lead Lead

Scintillator Layer

µ

Cs

137

150 GBq

No muon beam in the GIF → use (low energy) cosmic muons Fast read-out and normal read-out are triggered by scintillators ⇒ Trigger chambers information is calculated out of muon tracks

18 / 21

Summary and Outlook

HL-LHC luminosities lead to ATLAS muon spectrometer trigger rate problem → Proposal of an MDT-based additional trigger Simulation results for most difficult region (occupancy 10%):

Efficiency: 98.5% Fake probability: 0.5%

Hardware test setup in development First test planned in autumn 2013

19 / 21

New trigger implementation based on MDT

Angular resolution of trigger chambers: 3.0 mrad Necessary angular resolution: 1.0 mrad Fast MDT read-out resolution: 25 ns / 12.5 ns → 0.5 / 0.26 [mm] → 1.7 / 0.9 [mrad]

2 4 6 8 10 12 14 16 18 20 2 4 6 8 10 12 m

BIL BML BOL EEL EML EOL EIL CSC 1 2 3 4 5 6 1 2 3 4 5 6 EIL4 1 2 3 4 5 6 1 2 3 4 5 6 TGCs 1 2 3 4 5 1 2

3

End-cap magnet RPCs y z 1 2

20 / 21

Hardware implementation

MDT_FPGA_R2 Test Setup Board Actel FPGA Actel FPGA Serial configuration of ASDs L0 Trigger Decoding L0 Counters L0 Counter Serial Encoding Serial TDC data decoding ENC (L1, ECR, EBR, GR) Data transfer to MC L0 Trigger Encoding L0 Serial Decoding ASD ASD ASD HPTDC

Hit[23:0] Serial Interface

MC USB Windows-PC Software Test Setup Adaption Analysis Extension 3 phys. trigger inputs

USB 40-pin flat cable

MDT chamber Scintillator module

MDT L0-Trigger Prototype Scheme

Unit / Board Chip / Circuit Ready To be done 21 / 21