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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
HERA-B RICHHERA-B RICH
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
HERA-B RICHHERA-B RICH
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
HERA-B RICHHERA-B RICH
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
HERA-B RICHHERA-B RICH
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
HERA-B RICHHERA-B RICH
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
HERA-B RICHHERA-B RICH
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
HERA-B RICHHERA-B RICH
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
HERA-B RICHHERA-B RICH
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
HERA-B RICHHERA-B RICH
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
HERA-B RICHHERA-B RICH
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
HERA-B RICHHERA-B RICH
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
HERA-B RICHHERA-B RICH
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
HERA-B RICHHERA-B RICH
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
HERA-B RICHHERA-B RICH
Position Dependence of Residuals
1 mrad/box
16
HERA-B RICHHERA-B RICH
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
HERA-B RICHHERA-B RICH
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
HERA-B RICHHERA-B RICH
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
HERA-B RICHHERA-B RICH
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
HERA-B RICHHERA-B RICH
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
HERA-B RICHHERA-B RICH
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
HERA-B RICHHERA-B RICH
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!!!