TrackinginLHCb's2020HLT · VertexLocator(VELO)...

Tracking in LHCb's 2020 HLTConnecting the Dots 2015

Tim Head, on behalf of LHCb

École Polytechnique Fédérale de Lausanne

9 February 2015

The LHCb Detector

250mrad

100mrad

• LHCb is a single-arm (2 < η < 5) spectrometer at the LHC

I Precision beauty and charm physics: CP violation, rare decays, heavy flavourproduction

• σbb and σcc are extremely large at the LHC

I 30 kHz bb̄ and 600 kHz cc̄ in LHCb acceptance!

Phys.Lett.B694(2010)209-216

Eur.Phys.J.C71

(2011)1645

Tim Head (EPFL) 9 February 2015 2

Heavy Flavour Signatures

Beauty hadrons

• B+ mass 5.28GeV, daughter pTO (1 GeV)

• lifetime ≈ 1.6ps ⇒ flight distance

≈ 1 cm

• common signature: detached µµ

Charmed hadrons

• D0 mass 1.86GeV, sizeable daughter pT

• lifetime ≈ 0.4ps ⇒ flight distance

≈ 4mm

• can be produced in B decays


Actual Signatures

SV

h

h

IP

Topo N-body

Inclusive dimuon

SVSV

p p

p pIP

IPp p

PV

hh

D∗ → πD(→hh)

p pπ±

Inclusive φµ+

µ−

B → hh

p p

h

h

K−K+

• Combining inclusive and

exclusive selections

• Main trigger is a Bonsai BDT

• What you really need is offline

like event reconstruction!

• Extremely powerful and

flexible software environment


LHCb at 40MHz

• In Run 2 LHCb will collect ≈ 8 fb−1 ⇒increase instantaneous luminosity

• At increased luminosity signals less well

separated in L0 ⇒ we need to read out

every event!

• Upgrade readout to 40MHz, full detector

readout of all visible pp interactions

• Replace hardware L0 by software Low Level

Trigger (LLT)

I Acts as temporary ``handbrake'' duringcommissioning, 1− 40MHz scaleableoutput rate


The Game has ChangedIn the upgrade area there are no ``boring'' events, it is about classifying signal events!

80GB/s of reconstructible D hadrons, 27 GB/s of reconstructible B hadrons. Compare to

10GB/s allowed to tape

Details: LHCb-PUB-2014-027


http://cds.cern.ch/record/1670985

The Game has ChangedIn the upgrade area there are no ``boring'' events, it is about classifying signal events!

80GB/s of reconstructible D hadrons, 27 GB/s of reconstructible B hadrons. Compare to

10GB/s allowed to tape

Details: LHCb-PUB-2014-027

83

Triggersin the future

Triggerstoday

Gligorov 2014Tim Head (EPFL) 9 February 2015 6


https://indico.cern.ch/event/323449/

Real Time Analysis


The LHCb Experiment in 2018

250mrad

100mrad

UT

SciFi

CER

N-L

HC

C-2

013-

021

/LH

CB-

TDR

-013

05/1

2/20

13

CER

N-L

HC

C-2

013-

022

/LH

CB-

TDR

-014

05/1

2/20

13

TDRUPGRADE

CERN/LHCC 2013-022

LHCb TDR 14

28 November 2013

LHCbLHCbParticle IdentificationParticle Identification

Technical Design Report

TDRUPGRADE

CERN/LHCC 2014-001

LHCb TDR 15

21 February 2014

LHCbTracker


Upstream Tracker

SciFi Tracker

LHCB-TDR-013

LHCB-TDR-014

LHCB-TDR-015


The LHCb Experiment in 2018

250mrad

100mrad

UT

SciFi

CER

N-L

HC

C-2

013-

021

/LH

CB-

TDR

-013

05/1

2/20

13

CER

N-L

HC

C-2

013-

022

/LH

CB-

TDR

-014

05/1

2/20

13

TDRUPGRADE

CERN/LHCC 2013-022

LHCb TDR 14

28 November 2013

LHCbLHCbParticle IdentificationParticle Identification


TDRUPGRADE

CERN/LHCC 2014-001

LHCb TDR 15

21 February 2014

LHCbTracker


Upstream Tracker

SciFi Tracker

CER

N-L

HC

C-2

014-

016

/LH

CB-

TD

R-0

1622

/05/

2014

TDRUPGRADE

CERN/LHCC 2014-016

LHCb TDR 16

21 May 2014

LHCbTrigger and Online


LHCB-TDR-013

LHCB-TDR-014

LHCB-TDR-015

LHCB-TDR-016


Vertex Locator (VELO)

• Hybrid pixel detectors, two moveable halves, active edge at 5.1mm from beam

• Basic building blocks are 14× 14mm2 pixel chips, three chips in a row share silicon

sensor

• Micro-channel CO2 cooling

UpgradeCurrent


Upstream Tracker

• Single-sided silicon strip detector

• Four layers (x, u, v, x) (5° stereo angles)

• Finer segmentation around beam-pipe

• 250µm thin sensors

• New read-out chip (SALT)

• Bi-phase CO2 cooling


Scintillating Fibre Tracker

• Scintillating fibres

I 250µm diameter, 2.5m long

• Three stations with four (x, u, v, x) layers each

• Read out by Silicon Photomultipliers

I inside light-tight read-out boxI cooled to −40 °C

• New ASIC for read-out (PACIFIC)

250µm


Tracking at 30MHz

VELO

Upstream Tracker

SciFi


Tracking at 30MHz

• Reconstruct all tracks

• Build doublets, extrapolate

to next module

• Extremely efficient and ghost

free

Velo


Tracking at 30MHz

from E. Bowen


Tracking at 30MHz

• Extrapolate tracks with

pT > 200MeV

• Measure track's curvature

• σp/p ≈ 15%

VeloUT


Tracking at 30MHz


Tracking at 30MHz

• Extrapolate tracks with

pT > 500MeV

• Use UT charge estimate to

cut search windows in half

• σp/p ≈ 0.5%

LongLong


Full Track Reconstruction on all Events

Velo tracking

Offline Tracking

Forward trackingpT > 70 MeV, δp/p ~ 0.5%

PV finding

Velo tracking

Online Tracking

Forward trackingpT > 500 MeV, δp/p ~ 0.5%

PV finding

Simplified Kalman fit

Particle Identification

Velo-UT trackingpT > 200 MeV, δp/p ~ 15%

Rate reducing cutsOutput < 1 MHz

Muon Identification

Full Kalman fit

Particle Identification

• Maximum flexibility and

robustness

• Details: LHCb-PUB-2014-028

• LHCb will be the first hadron

collider experiment to operate a

software only trigger at full event

rate!

Offline-quality tracking at 30MHz in software is possible!



Efficiency

• Compared to ``offline'' the HLT tracking

sequence is 98.7% efficient

• In addition tracks with pT < 0.5GeV/care available with lower momentum

resolution

Efficiency [%]

HLT relative

long, from B 72.8 80.3

long, pT > 0.5GeV/c 87.4 97.2

long, from B, pT > 0.5GeV/c 92.5 98.7

]-1c[GeVTp

0 5 10

Eff

icie

ncy

0.80

0.85

0.90

0.95

1.00

1.05LHCb simulation

Trigger

Offline

Ratio


Timing

• At nominal luminosity reconstruction

uses less than half the budget (13ms)

• CPU time does not ``explode'' at higher

luminosity

Algorithm CPU time [ms]

VELO 2.0

VELO-UT 1.3

Forward 1.9

PV finding 0.38

Total 5.4 3.8 7.6 11.4ν

0

1

2

3

4

5

6

7

CPU

tim

e [m

s]

LHCb simulation

VELO trackingVELO-UT trackingForward trackingPV finding

(ν =average number of interactions)


Conclusion

• The LHCb trigger has been very successful in 2011 and 2012

I using BDTs as the main trigger

• 2020 will see a truly upgraded trigger

• Tracking at 30MHz in software is possible

• Allows very diverse, efficient triggers that minimally bias the physics observables

I lifetime unbiased hadronic triggers

• Run 2 will be our ``test beam'', testing many techniques which will be needed for

2020:

I run-by-run calibration and alignmentI Turbo stream: analysis without offline reconstruction


One more thing ...

HLT1 Tracking Time

• Making the whole tracking sequence

faster is hard work

• Some competition is good as nobody

wants to be the slowest

• A dedicated group of people, working

together is needed

Jul 20

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Jan 20

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140

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4

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Trig

ger t

rack

ing

time

[ms]

LHCb simulation

Spillover was turned on

Total with GEC

VeloVeloUTForward


SciFi Track Reconstruction

• Forward track reconstruction algorithm efficiency and ghostrate

• Taken from LHCB-TDR-015


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