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L0 trigger and related detectors
Alessia SattaUniversita’ di Roma
on behalf of the collaboration
LHC2003 International SymposiumFermilab, 3 May 2003
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Input figures at L0
• Bunch crossing frequency 40MHz• Non empty bunches 30MHz• ~80mb of non elastic interactions• ~60mb in the acceptance of the
spectrometerbb/in ~ 6x10-3
• nominal luminosity 2*1032 cm-2s-1
• 8 (1.7) MHz of single (double) interactions• GOAL: L0 output rate 1MHz
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Strategy
Velo x-z view
Pile
Up
B decay signature: high PT (ET) particles e h 0
L0 Pileupveto reduces rate to 9MHz.
L0 CALO&MUON must provide reduction factor~9 => medium Pt cuts : ET
h ~ 3.5 GeV, ETγ ~ 3 GeV,
PTµ ~ 1.2 GeV
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High Pt signature
Pion transverse momentum (MeV/c)
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Calorimeter detectors
• SPD & PS : 15 mm scintillating detectors interspersed with2.5X0 lead
• Electromagnetic cal: shashlik 2mm lead + 4mm scintillator - 25Xo
• Hadronic cal.: iron scintillating tiles - 5.6
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Calorimeter (II)
• SPD/PS/ECAL: 3 zones– Cell
• 40.4 / 60.6 / 121.2 mm• The smallest cell size
~Moliere radius
(E)/E=10%/√E 1.5%– 5952 channels each
• HCAL: 2 zones– Cell
• 131.3 / 262.6 mm
(E)/E=80%/√E 10%– 1468 channels
• SPD/PR/ECAL/HCAL fully projective - HCAL granularity doesn’t match the others
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•Goal: select the candidate of h, e, , 0 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, local candidates validation –Electromagnetic nature of ECAL maximum is validated using the PreShower , charge using the SPD
Calorimeter trigger principles
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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, -halo)
– hits multiplicity in SPD: potentially useable to reject too crowded events
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Performance of L0Calo
e h
B-> 9 3 55
Bs->Ds K 5 2 37
Bs->J/Ψ(ee) 36 4 24
Bs->K* 28 47 30
Assuming a trigger rate of ~600kHz for h, ~100kHz for e , ~25kHz for
L0Calo efficiency (%)for events selected byoffline analyses
All triggers important !!!
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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 I ~20
=> minimum momentum ~ 8GeV
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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
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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 candidates • 2/quadrant with highest pT
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Performance
• PT resolution ~20%
• High efficiency • Very robust against
high background level in the detector
• Halo muon negligible in nominal conditions
Nominal bkg Max bkg (nominalx5)
Max bkg+Max halo muon
B->X (*) 46% 41% 36%
B->J/()Ks 90% 83% 79%
Neutron induced background
* Normalized to events with in Muon system
Halo muon x10=~0.1/x-ing
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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
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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).
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Working principle of PU veto
RB [
cm]
RA [cm]RA [cm]
True combinations All combinations
ZPV [cm]
ZB ZA
RB
RA
ZPV
2 silicon R-stations B A
kZZZZ
RR
PVA
PVB
A
B
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)
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Performance
possible to populate the 1 MHz with preferably single interactions
If cut of second peak>3retain >98% of single and reject ~60% of multiple
B-> Minimum bias
Height of second peak
Height of second peak
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L0 hardware implementation
• Custom electronics using commercial components
• Synchronous system and pipelined– No dependence on occupancy and on
history• Latency 4.0s (~1.0s for algorithms)• Part of L0Calo near the detector
– Use SEU immune components• L0Muon &PU veto far from detector
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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
L0 efficiency (%)
e h all
B-> 7 9 3 55 61
Bs->DsK 8 5 2 37 44
Bs->J/(ee) 7 36 4 24 52
Bs->J/() 90 5 3 30 93
Bs->K* 6 28 47 30 82
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Robustness
The L0 efficiencies of various channels show a large region of very stable performance
Decreasing the L0 bandwidth to 750KHzresults in loss~15%
PT cut