The LHCb RICH - CERN · 2018-10-12 · The LHCb RICH detectors Two RICH detectors RICH 1 (C4F10):...

The LHCb RICH

Silvia Gambetta,University of Edinburgh

on behalf of the LHCb RICH collaboration

July 30, 2018

Introduction

The LHCb experiment

General purpose single arm forward spectrometer(2 < η < 5, 4% of solid angle)

[J. Instrum. 3 (2008) S08005]

LHCb physics:

rare b- and c- hadrondecays

CP-violation in b sector

CKM parameters

indirect search for NP

spectroscopy

electroweak physics

Unprecedented collection of bottom and charm hadronsVery successful physics programme

3 / 27

The LHCb performance

LHCb designed to run at lower luminositythan ATLAS and CMS

mean number of interactions per bunchcrossing ∼ 1

pp beams displaced to reduce theinstantaneous luminosity:L ∼ 4× 1032cm−2s−1

twice the luminosity design value

Excellent performance in 2017!

∼ 3 fb−1 of pp collisions at 7-8 TeV in Run 1

∼ 5 fb−1 of pp collisions at 13 TeV in Run 2

expect to reach ∼9 fb−1 at the end of Run 2

4 / 27

The LHCb RICH detectorsTwo RICH detectors

RICH 1 (C4F10): upstream, 2 GeV/c - 60 GeV/c over 25 mrad - 300 mradRICH 2 (CF4): downstream, 30 GeV/c - 100 GeV/c over 15 mrad - 120 mrad

Charged particles produce Cherenkov radiation then focused on Hybrid PhotonDetectors (HPD) planeResponsible for charged hadrons particle identification (PID)

5 / 27

RICH 1

VELO exit

covers the low and intermediatemomentum region over the fullangular acceptance

detector close to the interactionpoint to limit its volume

two halves above and below thebeam pipe

gas enclosure sealed directly onVELO exit window to limit materialbudget

tilted spherical focusing primarymirrors (4 segments)

secondary flat mirrors to limitdetector length (16 segments)

The total material budget for RICH1 is only about 5% X0 within theexperimental acceptance

gas radiator: C4F10

6 / 27

RICH 1

7 / 27

RICH 2

7.2

m

spherical

mirrors

at

mirrors

magnetic

shieldsPhoton

Detectors

covers the high momentum region over the the angular range 15-120 mraddownstream detector since high momentum particles are less affected mymagnetic fieldtwo halves on the sides of the beam pipetilted spherical focusing primary mirrors (56 segments)secondary flat mirrors to limit detector length (40 segments)The total material budget for RICH 2 is about 15% X0 within the experimentalacceptancegas radiator: CF4

8 / 27

RICH 2

9 / 27

The Hybrid Photon Detectors

HPDs arranged incolumns with ancillaryfront-end electronics

LV and HV boards topower the column

Level-0 boards transmitdata to Level-1 boards(off detector) via opticallinks

Level-1 boards zerosuppress and transmitdata to the DAQ

photon detectors developed in collaboration withindustry for application in the LHCb RICH system:

quartz window with thin multialkaliphotocathode

cross focusing optics ⇒ photons focused onsilicon pixel array (granularity 2.5× 2.5mm2)

front-end chip encapsulated in the vacuumtube

magnetic shield installed around each HPD

active diameter 75 mm:

196 tubes in RICH 1288 tubes in RICH 2

10 / 27

RICH hitmaps

/RICH/Default Run 212325, started 2018-07-23 05:41:42, duration: 00:27:54

00 01 02 03 04 05 06 07 08 09 10 11 12 13

D0

D1

D2

D3

D4

D5

D6

0

50

100

150

200

250

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350

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310×HitMap for Rich1 bottom panel

13 12 11 10 09 08 07 06 05 04 03 02 01 00

U6

U5

U4

U3

U2

U1

U0

0

50

100

150

200

250

300

350

400

310×HitMap for Rich1 top panel

0 1000 2000 3000 4000 5000 6000 7000 8000 9000# hits / event

0

5000

10000

15000

20000

25000NHitInclusiveRich2Entries 543908Mean 1723Std Dev 873.6

Number of hits in Rich2

C0 C1

C2

C3

C4

C5

C6

C7

C8

15

14

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310×

HitMap for Rich2 CSide-right panel

0 1000 2000 3000 4000 5000 6000 7000 8000 9000# hits / event

0

5000

10000

15000

20000

25000

NHitInclusiveRich1Entries 543908Mean 1995Std Dev 1008

Number of hits in Rich1

A0 A1

A2

A3

A4

A5

A6

A7

A8

15

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310×

HitMap for Rich2 ASide-left panel

11 / 27

Alignment and Calibration

Intervention on RICH 1 Down box

Intervention performed during 2016-2017 winter shutdown: replacement of someHPDs, L0 and LV boards

13 / 27

Magnetic field correction (once per year)

HPD image distortion due to themagnetic field

distance from the measured lightspot to the test point before andafter correction

Dedicated setup illuminating the HPDs in RICH 1with pattern of light spots with magnet on

0 500 1000 1500 2000 2500 3000 35000

50

100

150

200

20

40

60

80

100

120

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RICH1 - down

D0

D1

D2

D3

D4

D5

D6

12

11

10

09

08

0706

05

04

03

02

01

1300

0 50 100 150 200 250 300 350 400 4500

0

0

0

0

0

0

0

0

0

0

✒ ✑

✓ ✏

✒ ✑

✓ ✏ ✒ ✑

✓ ✏

✒ ✑

✓ ✏

14 / 27

HPD image calibration (once per run ≃1h)

The position of the Photocathode image on the anode can change due to thermal andcharging effects degrading the reconstruction of the Cherenkov angle and affect thePID performance

image cleared from ionfeedback

edges detected applyingSobel filter

fit to determine the radiusand the centre position usedthen by reconstruction

0

1

2

3

4

5

6

7

8

9

10

HPD Image Shifts (x,y) | Run 212325

2− 1.5− 1− 0.5− 0 0.5 1 1.5 2

x / mm

2−

1.5−

1−

0.5−

0

0.5

1

1.5

2

y /

mm

Entries 444

Mean x 0.05336−

Mean y 0.05805

Std Dev x 0.3001

Std Dev y 0.3173

0

1

2

3

4

5

6

7

8

9

10

Entries 444

Mean x 0.05336−

Mean y 0.05805

Std Dev x 0.3001

Std Dev y 0.3173

HPD Image Shifts (x,y) | Run 212325

15 / 27

Refractive index calibration (once per run ≃1h)

The refractive index of the radiators can vary due to temperature, pressure andvariation in the gas mixture. Monitoring of these quantities not precise enough forphysics analysis ⇒ further correction needed

Very high momentum tracks, with well defined Cherenkov angle, are used to evaluatethe difference between the measured and the expected Cherenkov angles

1100

1200

1300

1400

1500

1600

310×

En

trie

s

Rich1Gas Rec-Exp Cktheta | All photonsEntries 1.993715e+08

Mean 0.0002482

Std Dev 0.004308

/ ndf2χ 898.4 / 90

Gaus Const 5.656e+05

Gaus Mean 0.0006317

Gaus Sigma 0.001666

Bkg Par 0 1.044e+06

Bkg Par 1 9.45e+06

Bkg Par 2 1.237e+09−

Bkg Par 3 1.609−

Entries 1.993715e+08

Mean 0.0002482

Std Dev 0.004308

/ ndf2χ 898.4 / 90


Gaus Mean 0.0006317

Gaus Sigma 0.001666

Bkg Par 0 1.044e+06

Bkg Par 1 9.45e+06

Bkg Par 2 1.237e+09−

Bkg Par 3 1.609−

0.008− 0.006− 0.004− 0.002− 0 0.002 0.004 0.006 0.008

delta(Cherenkov Theta) / rad

900

1000

1100

1200

1300

1400

1500

1600

310×

En

trie

s


Mean 0.0002482

Std Dev 0.004308

/ ndf2χ 898.4 / 90


Gaus Mean 0.0006317

Gaus Sigma 0.001666

Bkg Par 0 1.044e+06

Bkg Par 1 9.45e+06

Bkg Par 2 1.237e+09−

Bkg Par 3 1.609−

Run 212325SF 1.024069

Rich1Gas Rec-Exp Cktheta | All photonsRich1Gas Rec-Exp Cktheta | All photons

600

700

800

900

310×

En

trie

s


Mean 05−2.305e

Std Dev 0.002123

/ ndf2χ 864 / 88


Gaus Mean 0.0001728−

Gaus Sigma 0.0007202

Bkg Par 0 5.31e+05

Bkg Par 1 6.261e+06

Bkg Par 2 3.948e+09−

Bkg Par 3 0.7025−

Entries 1.044003e+08

Mean 05−2.305e

Std Dev 0.002123

/ ndf2χ 864 / 88




Bkg Par 0 5.31e+05

Bkg Par 1 6.261e+06

Bkg Par 2 3.948e+09−

Bkg Par 3 0.7025−

0.004− 0.003− 0.002− 0.001− 0 0.001 0.002 0.003 0.004

delta(Cherenkov Theta) / rad

500

600

700

800

900

310×

En

trie

s


Mean 05−2.305e

Std Dev 0.002123

/ ndf2χ 864 / 88




Bkg Par 0 5.31e+05

Bkg Par 1 6.261e+06

Bkg Par 2 3.948e+09−

Bkg Par 3 0.7025−

Run 212325SF 0.988728

Rich2Gas Rec-Exp Cktheta | All photonsRich2Gas Rec-Exp Cktheta | All photons

Correction factor extracted and used to compute the refractive index

16 / 27

Mirror alignment (once per fill ≃12h)

mirror misalignment can cause a displacement of thecentre of the ring with respect to the track

a dependence of the variation of the Cherenkov angleon the azimuthal angle is observed ⇒ sinusoidaldistributions

distribution fitted and misalignment corrected inreconstruction

Mirror alignment monitored during 2015 and 2016 ⇒ alignment tolerances determined

⇒ full automation implemented in 2017

17 / 27

Mirror tilts

alignment constants determined for each mirror

correlation of different mirror pairs taken into account

iterative procedure on a dedicated farm allows to extract mirror alignment to beapplied by the reconstruction for each fill

18 / 27

Mirror alignment stability in 2017 (RICH 1)

αy

αz

βy

βz

Alignment number [a.u.]0 50 100 150

Y V

aria

tion [

mra

d]

∆

0.1−

0.05−

0

0.05

0.1LHCb RICH 1

Preliminary

Primary Mirrors

2017/06/02 - 2017/11/29

primary mirror 0primary mirror 1primary mirror 2primary mirror 3


Z V

aria

tion [

mra

d]

∆

0.1−

0.05−

0

0.05

0.1LHCb RICH 1

Preliminary

Primary Mirrors

2017/06/02 - 2017/11/29

primary mirror 0primary mirror 1primary mirror 2primary mirror 3


Y V

aria

tion [

mra

d]

∆

1.5−

1−

0.5−

0

0.5

1

1.5 LHCb RICH 1Preliminary

M�� t� � ��

2017/06/02 - 2017/11/29

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19 / 27

Performance

Cherenkov resolution stability over time

Timestamp

RICH 1 resolution [mrad]

1.9

1.7

1.5

1.3

1.1

2016-04-30 2016-11-01 2017-05-05 2017-11-06 2018-05-11

Timestamp

RICH 2 resolution [mrad]0.99

0.89

0.79

0.69

0.59

0.49

0.39

0.29

Timestamp2016-04-30 2016-11-01 2017-05-05 2017-11-06 2018-05-11

Excellent stability!!!21 / 27

PID calibration sample

PID performance studied with pure samples: each particle species is selected withkinematical information only

pions performance studied using K0S→ π+π−

kaons performance studied using D∗ → D0(

K−π+)

π+

protons performance studied using Λ0 → pπ−

1.84 1.86 1.88 1.90

m(K−π+) GeV/c2

0

50000

00000

50000

200000

250000

Candidates/028

MeV/c2

LHCb

D;+→ D0π+

D0→ K−π+

1100 1110 1120 1130

m( π−) MeV/c2

0

0000

20000

0000

0000

50000

Candidates/00

MeV/c2

LHCb

Λ0→ π−

example of mass distribution for PID samples [PoS (ICHEP2016) 295]

22 / 27

RICH PID performance (2017)

Momentum (MeV/c)0 20 40 60 80 100

310×

Eff

icie

ncy

0

0.2

0.4

0.6

0.8

1

1.2

1.4) > 0πLL(K - ∆

) > 5πLL(K - ∆

K→K

K→π

= 13 TeV 2017 validationsLHCb

Momentum (MeV/c)0 20 40 60 80 100

310×

Eff

icie

ncy

0

0.2

0.4

0.6

0.8

1

1.2

1.4) > 0πLL<= >∆

) > 5πLL<= >∆

p→p

p→π

? @A BCD EF@G HIJKNIOKPQsLHCb

Momentum (MeV/c)0 20 40 60 80 100

310×

Eff

icie

ncy

0

0.2

0.4

0.6

0.8

1

1.2

1.4RRTU V WX Y Z∆

RRTU V WX Y [∆

p→p

p→\

] ^_ `ab cd^e fghijgkilmsLHCb

Excellent PID performance!!!23 / 27

Gas purity RICH 1

gas purity monitored during the year

RICH 1 filled with CO2 during wintershutdown and back with C4F10 beforethe beginning of the run

air contamination increases during theyear due to small leak

gas cleaning performed during technicalstops to ensure the stability of theperformance

Gas contamination affects refractive index, dispersion, photon yield....

24 / 27

Impact of gas purity

two periods in 2017 selected: gas clean and contamination above the limit forcleaning

both periods with the same magnet polarity (UP)

use calibration samples to compare PID performance in two time periods25 / 27

PID dependence on gas purity

0 20 40 60 80 100

310×

Track Momentum [MeV/c]

0

0.2

0.4

0.6

0.8

1

Eff

icie

ncy

K Clean Gas Sample→K K >1% Air Contamination→K

K Clean Gas Sample→ π K >1% Air Contamination→ π

0 20 40 60 80 100

310×


0

0.2

0.4

0.6

0.8

1

Eff

icie

ncy

p Clean Gas Sample→p p >1% Air Contamination→p

p Clean Gas Sample→ π p >1% Air Contamination→ π

0 20 40 60 80 100

310×


0

0.2

0.4

0.6

0.8

1

Eff

icie

ncy

p Clean Gas Sample→p p >1% Air Contamination→p

p Clean Gas Sample→K p >1% Air Contamination→K

PID performance stable in time

26 / 27

Conclusions

LHCb RICH detectors successfully and stably operating since 2010

Key ingredient to the successful physics program delivered by LHCb

]2c[GeV/−pKm

5.2 5.4 5.6 nop

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2 c

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0

200

400

600

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Comb. bkg.

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]2c[GeV/+Kpm

5.2 5.4 5.6 5.8

)2 c

Can

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ates

/ (

10

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0

200

400

600

800

1000 LHCb+Kp→b

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Comb. bkg.

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0

100

200

300

400

500

600

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200

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500

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Comb. bkg.

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“Search for CP violation in Λ0b→ pK− and Λ0

b→ pπ− decays”

[LHCb-PAPER-2018-025]

27 / 27

Thank you for your attention!

Extra slides

Timing scan

3 timing scans acquiredduring 3 bunch fill

RICH1 already well timed

corrections of timing appliedfor RICH2

further scan acquired toconfirm timing

Run 205938, after timingcorrection

RICH2 gas

RICH2 gas status monitored by gasgroup and plot available online

CO2 well contempt well controlled by gasgroup (very stable)

small air contamination observed thisyear

contamination is decreasing while newgas is pushed in

Mirror alignment stability in 2017 (RICH 2)

αy

αz

βy

βz


Y V

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tion [

mra

d]

∆

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0.1LHCb RICH 2

Preliminary

Primary Mirrors

2017/06/05 - 2017/11/29

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Preliminary

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The LHCb RICH - CERN · 2018-10-12 · The LHCb RICH detectors Two RICH detectors RICH 1 (C4F10):...

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