L0 trigger and related detectors

1. L0 trigger and related detectors Alessia Satta Universita’ di Roma on behalf of the collaboration LHC2003 International Symposium Fermilab, 3 May 2003

2. Input figures at L0 • Bunch crossing frequency 40MHz • Non empty bunches 30MHz • ~80mb of non elastic interactions • ~60mb in the acceptance of the spectrometer sbb/sin ~ 6x10-3 • nominal luminosity 2*1032 cm-2s-1 • 8 (1.7) MHz of single (double) interactions • GOAL: L0 output rate 1MHz

3. PileUp Velo x-z view Strategy B decay signature: high PT (ET) particles mehgp0 L0 Pileupveto reduces rate to 9MHz. L0 CALO&MUON must provide reduction factor~9 => medium Pt cuts : ETh ~ 3.5 GeV, ETγ ~ 3 GeV, PTµ ~ 1.2 GeV

4. High Pt signature Pion transverse momentum (MeV/c)

5. Calorimeter detectors • SPD & PS : 15 mm scintillating detectors interspersed with 2.5X0 lead • Electromagnetic cal: shashlik 2mm lead + 4mm scintillator - 25Xo • Hadronic cal.: iron scintillating tiles - 5.6 lI

6. Calorimeter (II) • SPD/PS/ECAL: 3 zones • Cell • 40.4 /60.6 /121.2 mm • The smallest cell size ~Moliere radius - s(E)/E=10%/√E+ 1.5% • 5952 channels each • HCAL: 2 zones • Cell • 131.3 /262.6 mm - s(E)/E=80%/√E+ 10% • 1468 channels • SPD/PR/ECAL/HCAL fully projective - HCAL granularity doesn’t match the others

7. Calorimeter trigger principles • Goal: select the candidate of h, e, g, p0 with highest Et • shower has a 'small' size (~ contained in 2x2 cells) • search for a high energy releases in 2x2 tower in ECAL and HCAL • in each calo FE (4x8 cells) card the highest candidate is selected • process further only these candidates • Reduced complexity and cabling: ~200 candidates for ECAL and ~50 for HCAL starting from 6000 and 1500 cells. • e, g local candidates validation • Electromagnetic nature of ECAL maximum is validated using the PreShower , charge using the SPD

8. Calorimeter trigger principles cnt’d • Hadron local candidates validation • ideally add the energy lost in ECAL in front of the candidate • expensive : different granularity => complex connectivity • useful only if the ECAL contribution is important • look only at ECAL candidates ! • Manageable number of connections The Calorimeter gives also global information to the trigger : • total ET in HCAL gives interactions trigger (reject elastic, diffractive, m-halo) • hits multiplicity in SPD: potentially useable to reject too crowded events

9. Performance of L0Calo Assuming a trigger rate of ~600kHz for h, ~100kHz for e , ~25kHz for g L0Calo efficiency (%) for events selected by offline analyses All triggers important !!!

10. Muon system • 5 stations with calorimeter and iron shielding between them • Technology: MWPC with 4 ORed gas gaps (2 in M1) • 1380 chambers • Efficiency > 99% per station • Total absorber lI ~20 => minimum momentum ~ 8GeV

11. Muon system • 4 Regions, with different pad granularity • Y full projectivity • Pad dimension: • Min 6.3x31.3 mm2 • Max 25x31 cm2 • optimized for constant PT resolution • 55k pads combined in strips-> 26k channels to L0/DAQ

12. L0 Muon basic principle • Search tracks in M1-M5 • 192 projective towers in parallel • Required hits in all stations • Assuming origin = interaction point • Exploit B-kick to calculate PT (magnet PT kick ~ 1.2 GeV/c) • up to 8 m candidates • 2/quadrant with • highest pT

13. Performance • PT resolution ~20% • High efficiency • Very robust against high background level in the detector • Halo muon negligible in nominal conditions Neutron induced background Halo muon x10 =~0.1/x-ing * Normalized to events with m in Muon system

14. PileUp veto detector • 4 R-sensor half detectors upstream of interaction region • Coverage -4.2< η <-2.9 • Sensors active area: 8mm<R<42mm • Pitch 40µm to 103µm • 45o sections • OR of 4 neighbouring strips • 2048 channels towards L0 PileUp stations Half station

15. Pile Up veto motivation • LHCb designed for single interactions • Easiest to reconstruct and tag • More robust input for L1 and HLT • Multiple interactions fill bandwidth of L0 (~ 2x probability to pass L0).

16. 2 silicon R-stations B A RB RA ZPV ZA ZB Working principle of PU veto True combinations All combinations RB [cm] RA [cm] RA [cm] If hits are from the same track: ZPV [cm] build a ZPV histogram, search highest peak, to remove combinatorial background mask the hits in the peak , repeat the algo , find a second peak (signature of multiple interactions)

17. Performance B->pp Minimum bias Height of second peak If cut of second peak>3 retain >98% of single and reject ~60% of multiple Height of second peak possible to populate the 1 MHz with preferably single interactions

18. L0 hardware implementation • Custom electronics using commercial components • Synchronous system and pipelined • No dependence on occupancy and on history • Latency 4.0ms (~1.0ms for algorithms) • Part of L0Calo near the detector • Use SEU immune components • L0Muon &PU veto far from detector

19. Summary • L0 uses calorimeter – muon and dedicated silicon vertex detector • Reduces to 1MHz the input rate • Robust and flexible • Sends L0 candidates to L1 for further processing

20. Robustness The L0 efficiencies of various channels show a large region of very stable performance Decreasing the L0 bandwidth to 750KHz results in loss~15% PTm cut