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L0 trigger and related detectors: 

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

Input figures at L0: 

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


Strategy B decay signature: high PT (ET) particles m e h g p0 L0 Pileupveto reduces rate to 9MHz. L0 CALOandamp;MUON must provide reduction factor~9 =andgt; medium Pt cuts : ETh ~ 3.5 GeV, ETγ ~ 3 GeV, PTµ ~ 1.2 GeV

High Pt signature: 

High Pt signature Pion transverse momentum (MeV/c)

Calorimeter detectors: 

Calorimeter detectors SPD andamp; 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

Calorimeter (II): 

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

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 Calorimeter trigger principles

Calorimeter trigger principles cnt’d: 

Calorimeter trigger principles cnt’d Hadron local candidates validation ideally add the energy lost in ECAL in front of the candidate expensive : different granularity =andgt; 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

Performance of L0Calo: 

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 !!!

Muon system: 

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

Muon system: 

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-andgt; 26k channels to L0/DAQ

L0 Muon basic principle: 

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


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

PileUp veto detector: 

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

Pile Up veto motivation: 

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).

Working principle of PU veto: 

Working principle of PU veto RB [cm] RA [cm] RA [cm] True combinations All combinations ZPV [cm] If hits are from the same track: 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)


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

L0 hardware implementation: 

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 andamp;PU veto far from detector


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


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% PT m cut