# Presentation: 268679

## 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

- Bunch crossing frequency 40MHz
- Non empty bunches          30MHz
- ~80mb of non elastic interactions
- ~60mb in the acceptance of the spectrometer
- bb/in ~ 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
-  e h  0

- 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

## High Pt signature

- Pion transverse momentum (MeV/c)

## 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 

## 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

## 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

- 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

## 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

## 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 by
- offline analyses

- All triggers important  !!!

## 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

## 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

## 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

## 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

## 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**

## 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

- 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 peak>3
- retain >98% of single
- and reject ~60% of multiple

- B->

- Minimum bias

- Height of second peak

- Height of second peak

## L0 hardware implementation

- Custom electronics using commercial components
- Synchronous system and pipelined
- No dependence on occupancy and on history
- Latency 4.0s (~1.0s for algorithms)
- Part of L0Calo near the detector
- Use SEU immune components
- L0Muon &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

|                                 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 |

## 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  cut