Download A poor man`sVHMPID for ~ identification until 16GeV/c

Aerogel Cherenkov Counters
for the ALICE Detector
G. Paić
Instituto de Ciencias Nucleares
UNAM
For the ALICE VHMPID group
Layout
• PID in ALICE in the current design
• Physics needs
• Current studies
– Simulations of the Belle design
– Simulations of the integrating box design
(Phenix)
– Preliminary test beam results for the WLS
readout of aerogel type (Novosibirsk)
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ALICE LAYOUT: PID
HMPID: High Momentum Particle
Identification (, K, p)
• RICH
• Hard Probes
TOF
PID (K,p,)
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ALICE hadron PID today
• , K, p identified in large acceptance (2 * 1.8 units ) via a combination of
dE/dx in Si and TPC and TOF from ~100 MeV to 2 (p/K) - 3.5 (K/p) GeV/c
•In small acceptance HMPID extends PID to ~5 GeV
/K
TPC + ITS
(dE/dx)
K/p
?
e /
/K
e /
TOF
K/p
/K
HMPID
K/p
(RICH)
0
1
2
3
4
5 p (GeV/c)
The new results from RHIC point out for a serious need to
extend the PID range especially for protons
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Reasons to increase the momentum
range of the PID
• The present situations @ RHIC has strongly
increased the need for PID @large momenta
• The jet quenching has not resulted in an adequate
increase of the low momentum multiplicities
• The interesting range for protons is well above
5 GeV/c
• At LHC one may estimate that the interesting
range will up to 10-12 GeV for protons
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The baryon puzzle at RHIC
• where does the large proton over
pion ratio at high pt come from?
• why do protons not exhibit the
same suppression as pions?
 fragmentation yields Np/Nπ<<1
 fragmentation starts with a single
fast parton: energy loss affects pions
and protons in the same way!
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Jet-Quenching: Primer
What is a jet?
leading
particle
What happens if partons traverse a
high energy density colored
leading
medium?
particle
suppressed
hadrons
hadrons
q
q
q
q
hadrons
hadrons
leading
particle
suppressed
leading
particle
fragmentation of hard • partons can lose energy and/or
scattered partons into fragment differently than in the
vacuum
collimated “jets” of
hadrons
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The case for aerogel threshold
detectors
• Due to the space constraints in ALICE the
only conceivable extension of the PID is
the use of threshold Cherenkov detectors
with aerogel.
• Currently studying three basic designs
– The “Belle” design
– The integrating box design
– The WLS
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Belle type
– Collect scattered photons
• Non-directional lights
• Area of photocathode/cell
size
http://utkhii.px.tsukuba.ac.jp/~highpt/
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Simulation of the “Belle” design
• Ingredients of the
simulation:
– Treatment of the
Raileigh scattering
– 98% reflection from
the walls
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One photon
Full event
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Number of photoelectrons in function
of impact for the Belle configuration
Good agreement with exp results at n=1.017
With 2 PMT we can reach ~15 p.e/event
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integrating box design
Advantage – possibility to
use only one PM – not
dependent on the
coordinate of the impact
Integration Sphere
Aerogel
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Results for the integrating box
design
N=1.008
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Summary I
• The Belle type with two PMTs gives ~ 50% light
more compared to the integrating box
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Study of the aerogel thickness &
variation with n
With one PMT operation at 1.005 still possible
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Alternative design
A. Onuchin, A. Shamov, Yu. Skovpen and A. VorobiovA. Danilyuk, T.
Gorodetskaya and V. Kuznetsov NIM 315, 1992, 517
Test made in October 2004 at the CERN PS
WLS readout of the
aerogel
• Al container with sizes of 56 x 56 x 310 mm,
• total volume of Aerogel ~ 0.5 liters
•multi-layer Tetratex PTFE UV-film reflector,
• WLS - Plexiglas plates ( 3 x 10 x 250 mm ) doped with
BBQ
• plastic light-guide
• micro-channel plates (MCP) PMT with multi-alkali
photocathode of 18 mm dia
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Preliminary results
• 7 GeV negative beam at CERN PS
• Possibility to trigger out of the WLS
•
•
•
Efficiency
n = 1.008 -- 65-70%
n= 1.05 -- 99
• Number of photoelectrons
n= 1.008 --<N>= 1-2 photoelectrons = 1.008
n= 1.008 --<N>= 1-2 photoelectrons
Comparison with the simulations of the integrating box. The
number of photoelctrons is much smaller but:
Smaller photo detector by a factor 4
To be investigated the contribution to contamination by WLS.
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Summary II
• Possibilities of light output increase.
–
•
•
•
•
•
•
The ratio of signals from 1.05 and 1.008 are in agreement with the
ratio of intensities of Cherenkov light from radiators of given indices.
– the KEDR detector use the same aerogel (n=1.05) as was tested in our
experiment.
–
Having the same quality of WLS and better MCP PMTs we could
increase light output from proposed counters by a factor of
203/69=2.94.
The length of WLS used in our prototype is 250 mm, KEDR
ASHIPH counter – 500 mm.
We expect the light attenuation in our shifters could be smaller by
a factor of 1.3-1.4.
The design of our counter gives the possibility to increase
thickness of aerogel from 200 mm to 250 mm and more (additional
factor of 1.25)
Using the existing technology the light output could be increased
by a factor of 5.
The further possibilities are:
PMT with AsGa photocathode of 30-40 % quantum efficiency (MCP
PMTs we use have multialcali photocathode with mean QE=22%)
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Where to place the VHMPID
ALICE HMPID
Charged particles
multiplicity: ~ 80 m-2
Interaction rate: 104 (3%
central events)
PID:
1 < p < 3 GeV/c p K
2 < p < 5 GeV/c p
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