hera-b rich university of texas at austin university of barcelona university of coimbra, portugal...

HERA-B RICHHERA-B RICH

HERA-B RICH

University of Texas at Austin

University of Barcelona

University of Coimbra, Portugal

DESY, Hamburg

University of Houston

Northwestern University

J. Stefan Institute and University of Ljubljana, Slovenia

Fall ’99:Status and Prospects

2


Detector

PhotonDetectors

SphericalMirrors

PlanarMirrors

M16 PMTHamamatsu 16-anode multiplier

Base BoardSocket, voltage divider, output circuitry for 4

multianode PMT’s

Plastic Molding

Lens System2:1 image reduction

Super Module

Crate made from plastic molded

iron sheets; magnetic shield and mounting

structure

Readout Cards16 ch, using two ASD08

(amplifier, shaper, discriminator) chip

each

C4F10 radiator

PhotonDetectors

1488 M16’s 752 M4’s

3


Photon Detectors

• ASD Summary– 4-8 single hot channels

(faulty boards)

– 3 full boards, 2 half-boards faulty

– 90 dead channels (broken lines in cables)

• PMT Summary– 6 missing

– 11 dead (mostly in unpopulated regions)

– 13 faulty (?)

4


The Bottom Line

• 98% of channels installed and working• Photon yield and resolution agree with

design report expectations• Hardware issues:

– Two fallen mirrors replaced/remounted• Traced to poor adhesive batch• Safety wires improved• System appears stable

– Radiator gas leaks fixed• Improvements to re-circulation-

purification system implemented• Present C4F10 concentration ~ 50% • Complete filling later this Fall

• Present efforts concentrating on “fine-tuning” performance

5


Ongoing Activities

• Studies to refine alignment– Correlations with tracking systems to “fine-tune” alignment of

individual detector modules/mirrors

• Refine ring-finding/particle-ID routines– Likelihood analyses– Speed-up (?) stand-alone ring-finding

• Monitoring performance/database updates– Run-by-run ring-radius determination – Hot/dead channels

• Hardware– Gas system: review/refill C4F10 by end of year– PMTs: exchange faulty channels

6


Expected Performance

• Cherenkov relations:

• Widths of bands

• Critical RICH parameters: which depend on:– relative photon yield path length/detection efficiency

– angle error/photon dispersion/optical quality/cell size

2

220

2C

1cos

p

m

n C

12 / 20

200photons nNN C

2/12

/1

4222)(

pmp

00 /22 N (independent of C and p!)

p

p

pp

2/1

22 (usually smaller than term)

N p

hot

on

s

1 /p2

2 N 0

C2

pK

e

( )p

200 /N

7


Detected Photon Yields

• Basic Cherenkov relation: independent ofradiator composition

– Design value: (corresponds to 47L(cm)<c>2 in PDG

notation)

• Actual limiting angle does depend on radiator:

• Biases in measurement of yield– Efficiency in ring-finding

– Nearby conversion pairs

– Shadowing by beam-shroud

– Acceptance

2photons CN

222

21041041041 NFCFCFCC ff mrad 8.23 mrad 9.52

2104 NFC

Relative biases willChange with radius

000,13/ 2 CN

8


Uncorrected Data

• Yield in pure N2

• Scan rings with mixed C4F10

ring radius (rad)0.02 0.022 0.024 0.026 0.028 0.030

10

20

30

40

50

60

70

80

90htemp

Nent = 994

Mean = 0.02392

RMS = 0.001034

htemp

Nent = 994

Mean = 0.02392

RMS = 0.001034

E ECAL>8GeV

photons per ring0 10 20 30 40 50 60 70 80

0

2000

4000

6000

8000

10000

12000ring_photonsNent = 70552 Mean = 7.988RMS = 2.564

ring_photonsNent = 70552 Mean = 7.988RMS = 2.564

000,142

photons C

N

1000000,122

photons C

N

C eren k o v an g le (m rad )

num

ber

of p

hoto

ns

0

10

20

30

40

50

60

0 10 20 30 40 50 60

9


Issues in Alignment and Resolution

• RICH measures angles: xhit/R, yhit/R

• Dispersion and granularity set scale– gas = 0.4 mrad

– cell = 1.6/12 mrad

– Nphoton = 5 - 6

• Spherical aberrations important– Scale as (projection of ray from origin)3

– Distort ring shape and displace center

– Analytic expressions for distortions and shifts exist at required accuracy

0.6 mradV,H 0.15 mrad

D h C

T ra c kd ire c tio n

h

v

Dv C

ta n -1 (2 v h /( v - h ) )/2A D DOverall goal: V,H 0.3 mrad

10


Compare with ECAL

• Upper/Lower half-planes have systematic offset ~ 0.5 mrad

• Within a half-plane, V, H ~ 0.7 mrad

-0.004-0.003-0.002-0.001 0 0.0010.0020.0030.0040

20

40

60

80

100

120

140

160

180

200

220

240

htemp

Nent = 5434

Mean = 0.0002475

RMS = 0.001415

ty_rich-ty_ecal {ty_rich>0&&pho>20&&esum >5} htemp

Nent = 5434

Mean = 0.0002475

RMS = 0.001415

-0.004-0.003-0.002-0.001 0 0.0010.0020.0030.0040

50

100

150

200

250

htemp

Nent = 6497

Mean = 0.0003307

RMS = 0.001421

ty_rich-ty_ecal {ty_rich<0&&pho>20&&esum >5} htemp

Nent = 6497

Mean = 0.0003307

RMS = 0.001421

U p p er L o w er

RICH/ECAL vertical residuals (radians)

11


Self-consistent Test of Alignment

• Examine Upper/Lower detector yields vs position– Symmetry of detector placement w.r.t.

mid-plane of mirrors

– Signal/background

• Define Up/Down photon asymmetry:

• Expect:

U p p er

L o w er

LU

LU

NN

NNf

f

o ffse t

SB /1

1

CL

T

2

12


Asymmetry Data

• Photon detectors are close to symmetric (within ~ 0.2 mrad) in their nominal geometric positions

• Vertical spot size OK (2.8/11.4)40 mrad

• Background photons ~25%– Implies occupancy ~1%, consistent

with observed occupancies

– Background is subtracted in usual stand-alone ring-finding algorithm

(rad)-0.015 -0.01 -0.005 0 0.005 0.01 0.015

f

-1

-0.8

-0.6

-0.4

-0.2

-0

0.2

0.4

0.6

0.8

1

f vs.

-0.015 -0.01 -0.005 0 0.005 0.01 0.015

-1

-0.5

0

0.5

1

m yf

N ent = 10825

M ean x = -0 .0004687

M ean y = -0 .05691

R M S x = 0.008558

R M S y = 0.5514

m yf

N ent = 10825

M ean x = -0 .0004687

M ean y = -0 .05691

R M S x = 0.008558

R M S y = 0.5514

f vs Nominal

UpperShifted4 mm

1 mrad shift

Conclusions:

13


How to Reconcile RICH – ECAL ?

• Most sensitive geometrical parameter in RICH is placement of photon detectors within respective focal planes.– d/dx = 0.16 mrad/mm (in focal plane)

• ECAL and U/L asymmetry data suggest a symmetric displacement of each set of supermodules by 2 mm – At limit of estimated survey errors

– Not unique

• New set of geometrical constants generated with this shift

14


Results with Shifted Photon Detectors

(rad)-0.004-0.003-0.002-0.001 0 0.0010.0020.0030.004

0

200

400

600

800

1000

1200

1400

upper plane

RICH-ECAL

(rad)-0.004-0.003-0.002-0.001 0 0.0010.0020.0030.004

0

200

400

600

800

1000

1200

1400

1600

lower plane

(rad)-0.004-0.003-0.002-0.001 0 0.0010.0020.0030.004

0

200

400

600

800

1000

1200

1400

RICH-ECAL

upper plane

(rad)-0.004-0.003-0.002-0.001 0 0.0010.0020.0030.004

0

200

400

600

800

1000

1200

1400

1600

lower plane

• Mean offsets< 0.2 mrad

• Overall RMS~ 0.7 mrad

15


Position Dependence of Residuals

1 mrad/box

16


Comments on aligning using ECAL

• Advantages– Only system available on regular basis

– Matches RICH acceptance

• Disadvantages– Not a tracking system—must make assumptions about track

directions

– Efficiencies differ for different particle types

– Response not uniform/constant

– Biases apparent at boundaries of active regions

– Biases due to photon/track overlap

– Resolution at limit needed for RICH alignment

17


Match RICH rings with OTR tracks

• TDC information not used

• Horizontal offset ~0.5 mrad

• RMS horizontalmatch < 1 mrad

• Vertical RMS broadened by OTR stereo

horizontal angle (rad)

-0.02 -0.015 -0.01 -0.005 0 0.005 0.01 0.015 0.020

200

400

600

800

1000

vertica l angle (rad)-0.02 -0.015 -0.01 -0.005 0 0.005 0.01 0.015 0.020

50

100

150

200

250

18


Preliminary Conclusions on Alignment

• Small adjustments to nominal detector positions are indicated by the data

• System is at the design level of accuracy with only this correction

• The ultimate accuracy of the RICH will be better than the design specification

• Comparisons will be performed with other tracking systems to understand potential optical errors– Adjustments to individual detector supermodules and mirrors– Ultimate accuracy in track direction of ~0.3 mrad/ plane seems

feasible

• Initial matching with OTR promising

19


Critical RICH Parameters

• Measure N/2 and directly from fits to rings that match with ECAL

• No corrections for partial rings

0 0 .2 0 .4 0 .6 0 .8 1 .0 1 .2 1 .4 1 .60

2 0 0 0

4 0 0 0

6 0 0 0

8 0 0 0

1 0 0 0 0

(m rad )0 1 0 0 0 0 2 0 0 0 0 3 0 0 0 0 4 0 0 0 0 5 0 0 0 0 6 0 0 0 0

0

2 0 0 0

4 0 0 0

6 0 0 0

8 0 0 0

1 0 0 0 0

1 2 0 0 0

N / 2

20


Spring ’99 Data

• Critical RICH parameters already at or near design specs:

Design Measured

– 13,000 10,000

– 1 mrad 0.7 – 1.0 mrad syst. err.

~0.5 mrad

• Particle ID in ECAL/RICH mode differs from design mainly because of poor p/p

200 /N

0.0 0

N p

hoto

ns

1000 1/p2

2

10

00

C

2

1 0

2 0

3 0

4 0

0

0.50

1.00

1.50

2.00

2.50

3.00

0.00 2.00 4.00 6.00 8.00 10.00

e

pi

K

p

0.0 0

N p

hoto

ns

1000 1/p2

2

10

00

C

2

1 0

2 0

3 0

4 0

0

0.50

1.00

1.50

2.00

2.50

3.00

0.00 2.00 4.00 6.00 8.00 10.00

e

pi

K

p

p (GeV )

8 0 3 0 2 0 1 5 1 0

21


Consequences for Particle ID

E le c tro n-P io n S e p aratio n(2 -s ig m a)

p (G e V /c )

100

0 C

2

2.10

2.20

2.30

2.40

2.50

2.60

2.70

10 15 20 25 30

Today’s ECAL/RICH “tracking”

With Design Tracking:Electrons:15 17.5 GeV/c

— K:46 58 GeV/c

22


Summary

• RICH working at design performance level– Photon yields and resolution at or near specifications

– Occupancies as expected (magnet on)

– Stand-alone ring finding gives post-magnet tracks to ~0.5 mrad

• Ongoing effort to “institutionalize” performance monitoring– Automatic database updating of critical parameters

– Continuing alignment studies should reduce optical errors to below design specifications

• We encourage the use of RICH information by everyone– Global alignment studies

– Physics!!!

hera-b rich university of texas at austin university of barcelona university of coimbra, portugal...

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