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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