The RICH system of LHCbThe RICH system of LHCb

Roger Forty (CERN)on behalf of the LHCb collaboration

1. RICH detector layout

2. Photon detectors

3 Performance and first data3. Performance and first data

1st International Conference on Technology and Instrumentation in Particle PhysicsTIPP09, Tsukuba, 13 March 2009

The LHCb experimentp• Dedicated B physics experiment at the LHC

searching for new physics in complementary way to ATLAS & CMS through precision measurement of CP violation and rare decays

• B hadrons are predominantly produced in the forward directionsingle arm spectrometer (working in pp collider mode)→ single-arm spectrometer (working in pp collider mode)including two RICH detectors for charged hadron identification

10 – 300 mradRICH1RICH2

p p

Roger Forty The RICH system of LHCb 2

From design… to reality!

RICH2 RICH1

RICH2RICH1

Roger Forty The RICH system of LHCb 3The experiment it fully installed and commissioned, ready for first collisions

Requirementsq• Momentum range ~ 1 < p < 100 GeV

to match spectrum of B decay products

Without RICH

to match spectrum of B decay products

• Hadron identification is crucial for some modes (eg B → hh)

With RICH

Roger Forty The RICH system of LHCb 4

Radiators• Correlation between polar angle of tracks and p → two RICH detectors used

eθC max

250

200

Aerogel

eμ

p

K

π

242 mradC max

RICH1

θ C (

mra

d) 150

100

pRICH1

100

50

C4F10 gas

CF gas

53 mrad

32 mrad

RICH2

01 10 100

Momentum (GeV/c)

CF4 gasKπ

Momentum (GeV/c)

• RICH1 for low and intermediate momenta (before spectrometer magnet) combines use of two radiators: C4F10 gas (n = 1.0014) and aerogel (n = 1.03)RICH2 f hi h t i CF di t ( 1 0005)

Roger Forty The RICH system of LHCb 5

• RICH2 for high momentum, using CF4 gas as radiator (n = 1.0005)

RICH1 layouty

Magnetic

Cross section (side view) 3D model

Photon Detectors

Magneticshielding Vertex detector

vacuum tank

250 mrad

Beam pipe

Aerogel SphericalMirror

C4F10

Track

Beam pipe

VELO exit window

C4F10

PlaneMirror

0 100 200 z (cm)Photon detectors

Roger Forty The RICH system of LHCb 6

0 100 200 z (cm)

RICH1 construction• Challenge: to minimize material budget (since within tracking volume)

– “No entrance window” — attached directly to vertex detector tank– Inner acceptance defined by conical beryllium beam pipe– Carbon-fibre composite construction of spherical mirror (~ 1% X0)

Spherical mirror

Aerogel

Pl iRoger Forty The RICH system of LHCb 7

Plane mirror

RICH2 layouty• Much larger structure

High precision required ~ 0.7 mradInternal view

Glass mirror substrate, segmentedFlat mirrors

Spherical MirrorsSpherical Mirrors

Support Structure

7.2 m

Photon Detectors + Shielding

Central Tube

m

Roger Forty The RICH system of LHCb 8

Photon Detectors + Shielding

RICH2 installation• RICH2 constructed on surface, including alignment of optical elements

Delicate transport (~ 1 kph) to the LHCb cavern, 100 m underground

Roger Forty The RICH system of LHCb 9

Photon detectors• Hybrid Photon Detectors (HPD) developed in collaboration with industry

Principal partner: DEP-Photonis for encapsulation of pixel anode in tube

(−18 kV)

8192-channel pixel chip 8× OR → 1024 pixels ( )( ) (500 × 500 μm square)→ Presentation by K. Wyllie

(cm)

5× demagnification from electron optics → 2 5 mm at photocathode as requiredRoger Forty The RICH system of LHCb 10

5× demagnification from electron optics → 2.5 mm at photocathode, as required

HPD productionp• 484 HPDs required in LHCb (196 in RICH1, 288 in RICH2)

550 produced including spares over 18 months up to July 2007

• Multialkali (S20) photocathode, quantum efficiency improved during production, significantly better than the specification

Average & running average/batch

Window cutoff Sensitivity in visible range for aerogel

33

35

37<QE> per batchrunning <QE> (batch 0-25)

Average & running average/batch

25

27

29

31

QE

[%]

19

21

23

0 2 4 6 8 10 12 14 16 18 20 22 24batch no.

Batch number

Roger Forty The RICH system of LHCb 11

Batch number

HPD installation• HPDs mounted in columns, to cover detector plane

M l i hi ld b d h HPDMumetal magnetic shield tube around each HPDServices for HV, LV, and readout electronicsmounted in frame

Roger Forty The RICH system of LHCb 12

Fully equipped planey q pp p

Roger Forty The RICH system of LHCb 13

Test patternp• Regular array of light spots projected

over HPD plane in situ in RICH2

0 100 200 300 4000

500

1000

1500

2000

2500

3000

3500

4000

Pixel Hit Map - All Hits

over HPD plane in situ in RICH2 (similar results achieved in RICH1 using motorized stage with LEDs)

0 100 200 300 4000

500

1000

1500

2000

2500

3000

3500

4000

Pixel Hit Map - All Hits

• Nicely uniform response and very low noise for almost all the HPDsA few show noisy behaviour, peaking

0 100 200 300 4000

500

1000

1500

2000

2500

3000

3500

4000

Pixel Hit Map - All Hits

around the central axis of the tube

• Due to degraded vacuum quality in th t b

0 100 200 300 4000

500

1000

1500

2000

2500

3000

3500

4000

Pixel Hit Map - All Hits

those tubes

• Photoelectrons ionize residual gas Ions then accelerated back to the

0 100 200 300 4000

500

1000

1500

2000

2500

3000

3500

4000

Pixel Hit Map - All Hits

photocathode producing further p.e. → ion feedback 0 100 200 300 4000

500

1000

1500

2000

2500

3000

3500

4000

Pixel Hit Map - All Hits

Hits/pixel

Roger Forty The RICH system of LHCb 14

Ion feedback• Ion feedback rate determined using fraction of large clusters (≥ 5 hits)

Rate measured regularly for all HPDs over the last 18 months

• Most show a linear increase of ion feedback with time, with low gradientThe noisy tubes have a higher gradientThe noisy tubes have a higher gradient

• The bad tubes eventually start to glow, but only after ion feedback rate > 5%

Glow light

Roger Forty The RICH system of LHCb 15

HPD repairp• 24 HPDs in the RICH detectors

that started to glow have been l d i hreplaced with spares

• Failure of tubes can be accurately predicted from theaccurately predicted from the ion feedback measurements

~ 11 HPDs / year predicted to require replacement over the lifetime of the experiment(i.e. 2% / year)( y )

• Removed tubes are successfully repaired by DEP-Photonis O d l d h h dOpened, cleaned, photocathode reapplied: ion feedback gradient is low after repair

Roger Forty The RICH system of LHCb 16Age (days)

Beam test• Before final installation in the

RICH detectors, production HPDsRICH detectors, production HPDs used in a beam test with 25 ns bunch structure and C4F10 radiator

• Clean reconstructed ring spread over a number of HPDs →exercised alignment procedure

Number of detected photoelectrons

X (mm)

Number of detected photoelectronsmatches expectation from the GEANT-based full simulation

N b f hit i l

Roger Forty The RICH system of LHCb 17

Number of hit pixels

Magnetic distortionsg• Minor distortions to HPD image expected from fringe field of magnet

Test pattern: B = 0 B axial (30 G) B transverse (50 G)

• Calibration of distortion from LHCb spectrometer dipole made in situ, using light spot pattern, g g p p

• Raw data superimposed from runs taken with (B = 0, B +ve, B –ve)di l d i lldisplayed sequentially

• Distortion can be parameterizedwith a few constants per HPD

Roger Forty The RICH system of LHCb 18

with a few constants per HPD

Alignment & calibrationg• After all corrections, reconstructed

light spot positions match precisely

-300 -200 -100 0 100 200 300

-600

-400

-200

0

200

400

600

HPD array

with regular ~ 10 mm grid pattern

• Residual contribution to resolution σ 0 6 mm << pi el si e (2 5 mm)

-300 -200 -100 0 100 200 300

-600

-400

-200

0

200

400

600

HPD array

σ ~ 0.6 mm << pixel size (2.5 mm)→ correction of magnetic distortion and misalignment is under control

-300 -200 -100 0 100 200 300

-600

-400

-200

0

200

400

600

HPD arraym

m)

-300 -200 -100 0 100 200 300

-600

-400

-200

0

200

400

600

HPD arrayy

(m

xResEntries 3400

Mean 0.03103

RMS 0.7814

Constant 5.9± 240.9

Mean 0.01234± 0.06125 Sigma 0.0108± 0.6329

-6 -4 -2 0 2 4 60

50

100

150

200

250

300

xResEntries 3400

Mean 0.03103

RMS 0.7814

Constant 5.9± 240.9

Mean 0.01234± 0.06125 Sigma 0.0108± 0.6329

xRes yResEntries 3400

Mean -0.01304

RMS 0.7214

Constant 6.4± 257.6

Mean 0.010556± 0.007389

Sigma 0.0105± 0.5977

-6 -4 -2 0 2 4 60

50

100

150

200

250

300

350

yResEntries 3400

Mean -0.01304

RMS 0.7214

Constant 6.4± 257.6

Mean 0.010556± 0.007389

Sigma 0.0105± 0.5977

yResResiduals in both dimensions

-300 -200 -100 0 100 200 300

-600

-400

-200

0

200

400

600

HPD array

xResEntries 3400

Mean 0.03103

RMS 0.7814

Constant 5.9± 240.9

Mean 0.01234± 0.06125 Sigma 0.0108± 0.6329

-6 -4 -2 0 2 4 60

50

100

150

200

250

300

xResEntries 3400

Mean 0.03103

RMS 0.7814

Constant 5.9± 240.9

Mean 0.01234± 0.06125 Sigma 0.0108± 0.6329

xRes yResEntries 3400

Mean -0.01304

RMS 0.7214

Constant 6.4± 257.6

Mean 0.010556± 0.007389

Sigma 0.0105± 0.5977

-6 -4 -2 0 2 4 60

50

100

150

200

250

300

350

yResEntries 3400

Mean -0.01304

RMS 0.7214

Constant 6.4± 257.6

Mean 0.010556± 0.007389

Sigma 0.0105± 0.5977

yRes

-300 -200 -100 0 100 200 300

-600

-400

-200

0

200

400

600

HPD array

xResEntries 3400

Mean 0.03103

RMS 0.7814

Constant 5.9± 240.9

Mean 0.01234± 0.06125 Sigma 0.0108± 0.6329

-6 -4 -2 0 2 4 60

50

100

150

200

250

300

xResEntries 3400

Mean 0.03103

RMS 0.7814

Constant 5.9± 240.9

Mean 0.01234± 0.06125 Sigma 0.0108± 0.6329

xRes yResEntries 3400

Mean -0.01304

RMS 0.7214

Constant 6.4± 257.6

Mean 0.010556± 0.007389

Sigma 0.0105± 0.5977

-6 -4 -2 0 2 4 60

50

100

150

200

250

300

350

yResEntries 3400

Mean -0.01304

RMS 0.7214

Constant 6.4± 257.6

Mean 0.010556± 0.007389

Sigma 0.0105± 0.5977

yRes

Δx (mm) Δy (mm)

Roger Forty The RICH system of LHCb 19

-300 -200 -100 0 100 200 300

-600

-400

-200

0

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HPD array

x (mm)Δx (mm) Δy (mm)

Pattern recognitiong• Simulated event from 14 TeV collision: high multiplicity, overlapping rings

60 60 RICH 2Radiator (Npe/saturated track)

40

60 RICH 1

40

60 RICH 2Aerogel (6)( pe )

0

20

y (c

m)

0

20

y (c

m)C4F10 gas (24)

-40

-20

y

-40

-20

y

CF gas (18)

-60

-60 -40 -20 0 20 40 60

x (cm)

-60

-60 -40 -20 0 20 40 60

x (cm)

CF4 gas (18)

• Pattern recognition based on reconstructed tracks: θC of each p.e. from each track calculated under (e, μ, π , K, p) hypotheses Vary chosen hypotheses of tracks to maximize the global event likelihood

x (cm)

Roger Forty The RICH system of LHCb 20

Vary chosen hypotheses of tracks to maximize the global event likelihood

Expected performancep p• Determined using bb events

from PYTHIA passed through the full simulation

• Efficiency to identify kaons and misidentification rate of

K → K ⟨ε⟩ = 96 %and misidentification rate of pions plotted vs momentum

• Performance fed into the physics studies recently undertaken for six of the key measurements of LHCb:

π → K ⟨ε⟩ = 4 %

measurements of LHCb:

B (Bs → μμ), AFB (B0 → K*μμ) ACP (Bs → φγ), ACP (Bs → J/ψφ) Momentum (GeV/c)CP ( s φγ), CP ( s ψφ)ACP (B → DK), ACP (B → hh)

• Particle ID performance matches well the requirements from the physics

( )

Roger Forty The RICH system of LHCb 21

First LHC data• No collisions yet, but data from injection

tests last September:HPD data from RICH2

tests last September:

Particle flux (plan view)

Beamstop

LHCb

• Unfortunately tracks passed through LHCb in “wrong” direction, high density ~ 10/cm2

→ Cherenkov light in the HPD windows→ Cherenkov light in the HPD windows

• Sufficient to measure relative timingReady for collisions!

Roger Forty The RICH system of LHCb 22

Ready for collisions!

Upgrade planspg p• Upgrade of LHCb under discussion to follow first data-taking phase

Expected at ~ 2015, but need to consider now to launch any R&D required

• Plan to increase B rate by running at higher luminosity (~ 1033 cm-2s-1)and read out full experiment at 40 MHz (instead of 1 MHz at present)→ upgraded HPD or a different photon detector will be required→ upgraded HPD or a different photon detector will be required

• Detector concept also under study to use of time-of-flight for p < 10 GeVQuartz plate with focusing system (PANDA-style) to correct for photon time-of-propagation in plate: p p p g p

Roger Forty The RICH system of LHCb 23σ(t) ~ 100 ps / photon required

ConclusionsConclusions• The LHCb RICH system is fully installed and commissioned

• The HPD photon detectors have been thoroughly tested in beam tests and with the first LHC beams, and most perform excellently

A f ff f i d t d d d lit d b iA few suffer from noise due to degraded vacuum quality and are being replaced as necessary (predict 2% of the HPDs / year)

• Alignment and calibration of magnetic distortions has been performedAlignment and calibration of magnetic distortions has been performed using light spot data, and will be refined with data from collisions

Particle ID performance determined from simulation matches the requirements of the LHCb physics programme

• First ideas for an upgrade are being considered, to be ready in case the (new) physics from the first phase of LHC running demands itthe (new) physics from the first phase of LHC running demands it

• We are ready for the first LHC collisions expected later this year

Roger Forty The RICH system of LHCb 24