RICH status report
Transversity Meeting A March 05 -Jlab
• Detector Performances
• Possible upgrade
The PID Challenge
Very forward angle ---> high background of p and p
-TOF and 2 aerogel in not sufficient for unambiguous K identification !
Kaon Identification through Aerogels:
p kp
All events
p
k
p
AERO1
n=1.015
AERO2
n=1.055
KAONS = AERO1•AERO2
Hypernuclei -> smaller scattering angle
-> higher background --> something else is needed
KAON Id Requirements
Signal Vs. Background
Process
Rates
signal
(e,e’K)
10-4 – 10-2
accidentals
(e,e’)(e,p)
(e,e’)(e,p)
(e,e’)(e,k)
100
100
0.1
bound state
Very forward angle  high
background of p and p
 TOF and 2 threshold
Cherenkov aerogel are NOT
sufficient for unambiguous K
identification
 RICH DETECTOR
JLAB RICH detector, similar to the ALICE and STAR RICH
Ch
“MIP”
Separation power Cherenkov
angle
NP.E. N. of detected photons 2  1  n s s 
resolution p.e.
c
s
AND sq angular uncertainty
s c  
N p .e .
Relevant quantities:
JLAB Hall A RICH MonteCarlo Simulations
N. of detected photoelectrons
N p.e.  370 L sin 2 c   i E  20  50
i
Separation power
2  1  n s s 
c
p, K Separated by
qp – qK = 30 mrad
s C  4.4 mr
p, K Separated by  6.8 s
JLAB Hall A RICH: some components
Rich MWPC performance at lower HV
HV = 2100 V
HV = 1900 V
JLAB Hall A RICH OPERATING conditions
Gas: Pure Methane (Minimize Photon Feedback, High Q.E.)
High Voltage: ~ 2100 Volts for a gain of 8x104
Grid Voltage: 250 - 450 Volts
Optimal trigger to read-out delay: ~ 400 ns (peaking time of gassiplex response)
MIP charge and hit size
cluster charge and hit size
RICH Performances – key parameters
p Cherenkov angle reconstruction
Npe for p and P
Nclusters
Cherenkov average angle (rad)
Npe p/p ratio :
P
N clus
1   P2 n 2

 0.66
p
2 2
N clus 1  p n
Angular resolution :
s   5 mrad
c
RICH Performances – PID
p/K population ratio
 100
Aero Selected p
Aero Selected K (!)
Angular resolution
s   5 mrad
Aero Selected P
c
Separation power
p   K  6s c
Aero Selected K
on a large sample
of filtered data
Kaon selection:
K  3s 
c
This would accept ~ 10-4 pions
x p/K ratio
1/100 pion contamination
…. But NON GAUSSIAN
TAILS GIVE AN
IMPORTANT
CONTRIBUTION !
Rich – PID – Kaon selection results :
Time of coincidence for Aerogel Selected Kaons w/o and w/ rich :
AERO K
AERO K && RICH K
p
P
K
RICH – PID – Pion rejection factor :
Time of coincidence for Aerogel Selected Pions: effect of Rich Kaon selection
AERO p && RICH K
AERO p
p
p
N.Evts in the peak
Backgnd subtr. =
64656
N.Evts in the peak
Backgnd subtr. =
63
Pion rejection
~ 1000
JLAB Hall A exp e94-107 Preliminary Results on 12C Target
Missing Energy Spectra:
Aerogel Kaon
selection
12C(e,e’K)12B
RICH Kaon
selection
Missing energy (MeV)
L
250 ps
p
p
K
Pion rejection
~ 1000
K
Possible improvements
-
MWPC stability for high rates
For single rates ≤ 60 KHz HV=2100 V is OK
In the range 60 KHz – 100 KHz HV=2075 V is OK
Above 100 KHz HV must be reduced further
(running at reduced gain with moderately good
performance seems to be feasable)
- p/K separation for p>2.5 GeV/c
Doable “just” replacing the radiator
DAQ rate bottleneck (~1 KHz) can be ovecome replacing
part of the readout
RICH electronics upgrade:The HMPID ALICE RICH DAQ scheme
fbD[27..0]
fbD[31..0]
LOC_ADD[11..0]
LOC_CS
LOC_ADD[3..0]
Segment
Controlle
r
LOC_CS
LOC_R/Wn
Column
Controller
(1 to 8)
LOC_R/Wn
RCB BOARD
Front end
digitization/
multiplexing
On board
48 multiplexed
channels
(instead of 240)
Clock rate up
to 10 MHz
SEGMENT
DILO 5
Boards
(ADC and
DILOGIC)
GASSIPLEX
VME
to
Local Bus
Interface
HV = 2100 V
HV = 1900 V
PC40 scan
60
no. of pads /ring
50
2150 V
40
2100 V
30
2050 V
2000 V
20
1950 V
10
1900 V
0
0
20000
40000
60000
chamber gain [e-]
80000
MIP IN 19,25
MIP IN 30,25
MIP IN 41,25
MIP IN 55,25
MIP IN 18,32
MIP IN 27,32
MIP IN 41,32
MIP IN 53,32
100000
120000
Rich p/K separation for p > 2.5 GeV/c
Radiator C6F14 n=1.29
sCh ~ 5mr
4
s separation at ~ 2.5 GeV/c
Radiator C5F12 n=1.24
sCh ~ 5mr
4
s separation at ~ 3.0 GeV/c
FOCUSING FOUR-LAYERED AEROGEL TILE
Danilyuk, Novosibirsk, RICH2004
aerogel
photodetector
particles
L = 4.4 cm at 400 nm
Layer
1
2
3
4
t
n
mm desired
6.0 1.030
6.3 1.027
6.7 1.024
7.0 1.022
Produced in May 2004
n
measured
1.0297
1.0268
1.0234
1.0213
RICH SOFTWARE PRESENT STATUS
1.
PID algorithm is based on:
recognition of the “Clusters” (that is continue spots of
fired pads) on the cathode planes.
2. Identification of the baricenters of the clusters with the
Čerenkov photon hits on the cathode planes
3. Calculation of the Cherenkov photon emission angle
through Čerenkov photon hits on the cathode planes.
4. Calculation of the average of the Cherenkov photon angle
distribution and check of the value obtained with the
expected emission angle (three checks, one for each
hypothesis on the particle to be identified: Pion, Kaon
and Proton).
5. Three c2 tests (one for each hypothesis on the kind of
the particle) to check the obtained Čerenkov photon
angle distribution with the expected one.
6. A procedure to cross out the signals from noise. This
procedure is based on the c2 test values and is
performed when none of the hypothesis on the particle
hitting the Rich seems statistically significant.
- The p rejection factor obtained with the algorithm
described above is ~ 999/1000
To be done
-A better method to determine the Cherenkov
photon hits on the pad plane (so far identified
with the baricenters of the clusters) will be
used. This method will employ an algorithm
(Mathieuson formula) that takes in account more
accurately of the charge distribution in the
pads.
-The systematic errors in the particle entrance
angles in the RICH will be lowered using a new
algorithm. The particle entrance angles will be
assumed as those that make the Cherenkov
photon angle distribution variance minimum (so
far particle entrance angles in the RICH are
given by the tracking chambers).
-An accurate check on RICH parameters (above
all the radiator refraction index) will be
performed.
-The RICH analysis code is still slow. Some
improvements has to be done to make it faster.
- Correction for temperature variation (n(L))
Conclusions
RICH detector : excellent Kaon Identification and clean Kaon
signal over a large p and p background for p=2 GeV/c (5 s)
limited speed (~ 1KHz) --> electronic upgrade (~ 2KHz) ongoing
separation @2.4 GeV/c : 3.9 sigma (extrapolated)
possible improvement(s):
Changing radiator and proximity gap
~ 5sigma @2.4 geV/c
~3 Sigma at 3 GeV/c
Dual radiator for further improvement ??