27 th June 2008Johannes Albrecht, BEACH 2008 Johannes Albrecht Physikalisches Institut Universität...

27th June 2008 Johannes Albrecht, BEACH 2008

Johannes Albrecht

Physikalisches Institut Universität Heidelberg

on behalf of the LHCb Collaboration

The LHCb Trigger System

27th June 2008 Johannes Albrecht, BEACH 2008 2 / 19

LHCb Environment

• B-physics at LHC:– pp collisions at 14 TeV

= 0.5 mb for b-bbar– bunch crossing rate: 40 MHz– L=2*1032 cm-2s-1 @ LHCb

12 MHz visible interaction rate

• Visible B decays: 15kHz 1011 fully contained B’s / 2 fb-1

• Interesting B decays: BR~ 10-4-10-9

102-107 events / 2 fb-1 ( per channel)

Interactions / bunch crossing


B Event in LHCb

• Signature of B-decays: – pt ( B-daughter) > pt ( inelastic pp)

trigger: need high bandwidth

– decay length L ~7 mm trigger: CPU intense to calculate IP

• 15 kHz of B-decays save only relevant decays

primary vertex (PV)(PV)~40-60m

+

-

K-

K+

Bs0

J/

L

b-hadron D+

+


B Event in LHCb

B decay & underlying event

1 cmsecondary vertex


The LHCb Experiment

Magnet

OT

RICH-1

TTIT

Tracker

PSSPD

VELO

Muon StationsM2-M5

CalorimetersRICH-2

M1

HCalECal


Trigger Overview

• Hardware Trigger (L0)– “high pt” calorimeter & muon objects– rejects busy events

• Software Trigger (High Level Trigger)– HLT first level:

• trigger on B decay products– HLT second level:

• trigger fully reconstructed B decays on tape2 kHz

L0

HLT

visible collisions12 MHz

detector readout1 MHz


• Muons:– with constraint to (0,0,0):

p/p ~ 20%– single- (pt >1.3 GeV) – di-muon (pt > 1.5 GeV)

• Calorimeter: – “high Et” hadrons, e±, and 0

(threshold: 2.3 - 4.5 GeV)– particle identification from

• ECal / HCal energy• PS and SPD information

– reject busy events

Hardware Trigger Strategy

Scintillating Pad Detector (SPD)

Pre-Shower Detector (PS)

ECalECal HCal

(0,0,0) M1 M2 M3

B


Hardware Trigger Performance

thresholdpt / Et (GeV)

rate / kHz

3.5

700

h

1.3

200

> 1.5

2.6

200

e±

2.3

4-4.5

0 combined

1 MHz

Bandwidth share:

B Ds 45% 5% 10% 50%

B J/ 20% 90% 5% 90%

B K* 30% 10% 60% 70%

L0 trigger performance:

efficiencies corrected for acceptance and selection


Trigger & DAQ System

• Front-end– detector read out– performs zero suppression

• Readout network– gigabit Ethernet– total throughput: ~50 GB/s

• Event Filter Farm– 1000 – 2000 nodes

(~16.000 CPU cores)– organized in ~50 sub farms

Front-endVelo Calo Muon

L0 Trigger

Trigger and Fast control

Readout network

Event Filter Farm1000-2000 nodes

CPU CPU CPU

RICHTrackers

trigger datafast controlfull data

Y/N Y/N


HLT: Software Trigger I

• HLT first level (HLT1):– confirm L0 decision using tracking system– reconstruction in region of interest– trigger on simple signatures (pt, IP, ..)

increase fraction of bbar

• HLT second level (HLT2):– exclusive signal selections

• full B analysis (relaxed offline cuts) – inclusive streams

• trigger on clear signatures• gives unbiased B sample

selection of interesting B-decaysexclusive200 Hz

HLT 2

detector data:1 MHz

full event reconstruction:

~30 kHz

inclusive1800 Hz

HLT 1


HLT: Software Trigger II

• Independent alleys: follow L0 triggered candidate– hadron, muon, ECal

• Confirmation: via Tracker or via Velo– important to reduce rate fast– example: hadron alley via main tracker

L0 HLT 1st level HLT 2nd level

hadron

muon

ECal


HLT1: Confirmation with Tracker

HCaltracker

two charge assumptions two R.o.I.


HLT1: Confirmation with Tracker

HCaltracker

• In RoI: ~160 hits (~4000 in total) CPU time: ~1.5ms / event (~1.3 L0 candidates)

• Track finding efficiency: 98%(normalized to offline tracks)

• pt/pt ~3%

Pt resolution (hadrons)

L0:Et/Et~30%

online track: pt/pt ~3%

pt / Et resolution

even

ts /

a.u.


HLT1 Example: Hadron Alley

Retention from pt and IP cut

• Confirmation:– first confirm with tracker, then

match Velo track

– require high pt and IP

rate 700kHz 30 kHz

• Additional signature trigger:– make two track vertex

• HLT1 hadron trigger:– single: pt>5 GeV, IP>100 m

– di-h: IP>100m, pt1>2.5GeV, pt2 > 1GeV, vertex pointing to PV

rate ~11 kHz

• Overall signal efficiency: ~70-85%

signal (BdK)inelastic pp

IP>0

, pt >

0

IP>1

00m

,

pt >

2.5

GeV

IP>5

0m

, pt

> 1

.5 G

eV

IP>7

5m

, pt

> 2

GeV


HLT1: Trigger on Simple Signatures

700 kHz

30 kHz

hadron

L0

Confirmation

11 kHzadditional signature

trigger

ECal

200 kHz

80kHz

muon

17 kHz

• Combination of all Hlt first level steps 30-40 kHz

• Rate allows full event reconstruction

work in progress

200 kHz

Pre

limin

ary

num

bers

!


HLT2: Exclusive Selections

• HLT second level: ~30 kHz fully reconstructed events– select interesting signals exclusively– select inclusive channels for calibration, physics

• Exclusive selections:– ~100 core physics channels

(control channels included) – full reconstruction and analysis

200 Hz

offline Bd

= 15 MeV = 32 MeV

B mass / MeV/c2B mass / MeV/c2

sig

nal

MC

online Bd


HLT2: Inclusive Streams

charm physics, PID calibration

partly -unbiased B decays,lifetime calibration

trigger-unbiased B, calibration of tagging

physics

D*

Di-(J/)

Generic B(single )

Line

300 Hz

900 Hz

600 Hz

• The generic B sample:– 900 Hz of B X, 550 Hz true– from the accompanying B meson:

~ 1.5109 fully contained, decay-unbiased B mesons / 2fb-1

unbiased BPV

trigger

rate


Trigger Performance

muonic

hadronic

radiative

Type

90%

50%

70%

L0

80%

80%

60%

Hlt

Total efficiency:

70%

40%

40%

totalefficiency

efficiencies corrected for acceptance and selection

Bs J/

B hh

B K*

Example

• Timing:– profiling run of Event Filter Farm end 2007 full HLT1 + HLT2: ~1600 events /s / box (16 single CPU cores) we can run the HLT at 1 MHz


Summary

• L0 (hardware):– high pt calorimeter & muon– efficiency: hadron: 50%

muon: 90%

• HLT (software):– confirmation step– full B-candidate reconstruction

and analysis in Trigger• exclusive selections of B

decays (200 Hz)• inclusive streams (1800 Hz)

– efficiency: 50-80%permanent storage:

2 kHz

L0:• high pt particles

(calorimeter & Muon)

HLT:• confirmation step• selection step

visible collisions:12 MHz

full detector readout:1 MHz


Backup slides


L0 Pile-Up System

• Detector components:– 2 silicon planes upstream of nominal

IP, part of the Velo

• Strategy: Identify multi PV events – calculate z of vertices for all

combinations of A and B– find highest peak in histogram of z– remove hits that contribute to that

peak– find second highest peak

• two interactions / bunch crossing identified with ~60% efficiency and 95% purity

Vertex Locator (Velo)

Vertex z Position


Confirmation With Vertex Detector

For trigger, VELO R-sensors allow for a fast search of high IP tracks in 2-D:

R

z

IP ~ 14m ± 35 m/pT

offline !


Detailed HLT Performance

L0HLTL0HLT


Trigger Monitoring

• General monitoring approach:

– TOS: Trigger on Signal

– TIS: Trigger independent of Signal

– Efficiency: (TIS ∩ TOS ) / TIS

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27 th June 2008Johannes Albrecht, BEACH 2008 Johannes Albrecht Physikalisches Institut Universität...

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