Particle Identification in ALICE Detector · • If time of flight (tof) is known for a particle...
Transcript of Particle Identification in ALICE Detector · • If time of flight (tof) is known for a particle...
Particle Identification in ALICE Detector
Zafar Yasin
PINSTECH (PAEC)
Outline
• Introduction to ALICE detector
• Introduction to ALICE Physics
• Determenation of time resolution
• Time resolution in ALICE TOF detector
• Particle Identification in ALICE detector
• The Large Hadron Collider (LHC) accelerates protons in a 27 km long tunnel.
• The LHC will also accelerate lead ions to make them collide at the highest energy ever.
• The acceleration process starts in LINAC 2 for protons and in LINAC 3 for lead ions.
• The protons accelerated in LINAC2, are injected to a Proton Synchrotron Booster with an energy of 50 MeV.
• In the Synchrotron, protons reach an energy of 1.4 GeV .• The SPS takes 26 GeV protons from the PS and brings them
to an energy of 450 GeV before extraction.• The LINAC 3 produces 4.2 MeV/u lead ions.
The Large Hadron Collider
The Large Hadron Collider• The Low Energy Injector Ring (LEIR) is used as a storage
and cooler unit.
• It provides ions to the Proton Synchrotron with an energy of 72 MeV/nucleon.
• Ions will be further accelerated by the Proton Synchrotron and the Super Proton Synchrotron before they are injected into the LHC where they reach an energy of 2.76 TeV/nucleon.
• The LHC consists of 1232 superconducting dipole magnets with double aperture that operate at up to 9 Tesla magnetic field.
• The accelerator also includes more than 500 quadrupole magnets and more than 4000 corrector magnets of many types.
Introduction to ALICE Physics
• ALICE is one of the big experiments at the LHC, which focuses on QCD, the strong-interaction sector of the Standard Model.
• It focuses on the study of heavy ion collisions at ultra-relativistic energies
• Its main goal is to observe a transition of ordinary matter into a plasma of quarks and gluons
• Nucleus–nucleus and proton–proton collisions will also be studied
• The ALICE detector has been built by a collaboration including currently over 1000 physicists and engineers from 105 Institutes in 30 countries.
Two major caregories of Detectors
Introduction to ALICE-Detector
• The ALICE detector has been built by a collaboration including currently over 1000 physicists and engineers from 105 Institutes in 30 countries.
• Its overall dimensions are 16 × 16 × 26 m 3 with a total weight of approximately 10 000 t.
• The experiment consists of 18 different detector systems each with its own specific technology
• The different subsystems were optimized to provide high-momentum resolution as well as excellent Particle Identification (PID) over a broad range in momentum.
• This will allow for comprehensive studies of hadrons, electrons, muons, and photons produced in the collision of heavy nuclei
LHC Experiments
ATLAS
CMS
Designed for high pTphysics in p-p
collisions
ALICE
Dedicated LHC HI experiment~ 9 km
CERN
LHC
The ALICE Detector
TRDTOFHMPID
PMD
PHOS TPC
Muon Arm
ITS
ALICE Set-up
Six Layers of silicon detectors for precision tracking in |η|< 0.9
3-D reconstruction (< 100mm) of the Primary Vertex
Tracking+Standalone reconstruction of very low momentum tracks
Particle identification via dE/dx for momenta < 1 GeV
SPD - Silicon Pixel
SDD - Silicon Drift
SSD - Silicon Strip
Secondary vertex Finding (Hyperons, D and B mesons)
Three tecnhnologies:
ALICE Inner Tracking System – ITS
• Can separate pions and protons up to 0.8 GeV/c
Efficient (>90%) tracking in η < 0.9
s(p)/p < 2.5% up to 10 GeV/c
Conventional TPC optimized for extreme track densities
ALICE Time Projection Chamber (TPC)
Two-track resolution < 10 MeV/c
PID with dE/dx resolution < 10%
Space-Point resolution 0.8 (1.2) mm in xy,(z), occupancy from 40% to 15%
Tranisition Radiation Detector
Surrounds ALICE TPC• radial position 2.9 < r < 3.7 m• maximal length 7 m• full azimuthal coverage• |η| < 0.9• 540 detector modules arranged in:•ϕ: 18 super modules• r : 6 layers• z: 5 stacks• 694 m2 active area• 28 m3 detector gas of Xe/CO2• 30 tons• 10 M Euro and 250 person years
ALICE Time Of Flight – TOF
Large array at R ~ 3.7 m, covering | η| < 0.9 and full φ
Extensive R&D, from TB data:
Intrinsic Resolution ~ 40 psEfficiency > 99%Can separate π/K and K/p up to 2.5 GeV/c
Readout pads3.5x2.5 cm2
122 c
m
TOF basic element:double-stack Multigap RPC strip
Occupancy < 15% (O(105) readout channels)
2x5 gas gapsof 250mm
(fully installed & commissioned)ITS, TPC, TOF, HMPIDMUON, PMD, V0, T0FMD, ZDC, ACORDEPartially completed:● TRD (7/18)● PHOS (3/5)● EMCAL (4/11)ALICE capabilities for first physics:• 100% for hadron physics• partial for electron and photon physics
Current Status of the ALICE-Detector
Tracking Efficiency / Fraction of Fake Tracks for dN/dy = 2000, 4000, 6000, 8000
For dN/dy = 2000 ÷ 4000,efficiency > 90%,fake track probability < 5%!!!
For dN/dy = 2000 ÷ 4000,efficiency > 90%,fake track probability < 5%!!!
Full chain, ITS + TPC + TRD
ALICE Tracking Performance
ALICE PID
efficiency
contamination
p dependence of:
Central Pb + Pb HIJING events – kaon case
ITSstand-alone TPC
stand-alone
TOFstand-alone
Combining the PID information from different detectors allows a weaker momentum dependence of the efficiency (contamination) which stays higher (lower) or at least equal
than with stand-alone detectors!!!
Combining the PID information from different detectors allows a weaker momentum dependence of the efficiency (contamination) which stays higher (lower) or at least equal
than with stand-alone detectors!!!
ITS & TPC & TOFcombined!!combined!!!!
• TOF detector in ALICE is dedicated to charged particle identification over a large part of the phase space
• The basic Physics of ALICE detector demands a TOF detector with outstanding characteristics
• The detector should cover the momentum range from 0.5 GeV/c to 2.5 GeV/c
• The intrinsic time resolution must be well below 100 ps and over all time resolution 160 ps
• Since a large area has to be covered (~160 sq. meter), a gaseous detector is the only choice
• Multiplate Resistive Parallel Plate chambers are selected
TOF detector in ALICE
• Electric field should be high and uniform across the plates• Ionisation produced by a through-going particle will start
an avalanche
Basic idea of time of flight
• This method is used to obtain energy spectrum to identify the particles.
• It relies on accurate and fast time measurements• If time of flight (tof) is known for a particle that traverses a
given flight path (tp), the energy of the particle Ep, is given by
• Ep = E0 (1/(1-β2)1/2 -1)where,β = fp/tof. 1/c, c is the velocity of light.E0 = Particle rest massTo measure TOF, there is need a pulse to start a TDC (time
to digitical convertor) and a second pulse to stop the TDC. Both pulses are provided by the detectors.
• The energy resolution will be a function of the timing characteristics of the electronics and of the flight path.
• The longer the flight path the better the resolution.
Advantages of MRPC• It operates at atmospheric pressure; • The construction requires commercially available glass; • The signal is the analogue sum of signals from many gaps,
so there is no late tail and the charge spectrum is not of an exponential shape, it has a peak well separated from zero;
• The resistive plates quench the streamers so there are no sparks, thus high gain operation becomes possible;
• Both an array of single cells and a multicell strip design produce good uniformity: for the second option, the geometric arrangement is far simpler and it explains the choice of this design.
d
.Primaryelectron
N ~ exp (α . d)
Cathode
Anode
2)()exp(
dd
CemV
αα
=
N (d) = N0 exp (α. d)
Priciple and Operation of MRPCThe number of secondary electrons are
given by:
N0 = number of primary electrons
α = first Towsend coefficient
d = drift path
The voltage pulse generated by a fragment:
m = total number of primary electrons
C = the detector capacitance
Determination of Time Resolution
Experimental setup for determination of time resolution
Schematic overview of the electronic setup used to calculate time resolution.
CFD
ADC2
PPAD2
PPAD1
Attenuator
Pre-amplifier
Cf252
CFD
OR/AND ADC1
LATCH
OR
TDC
Scaler2 Scaler1
Gate generator
Fan out
VETO
Four fold logic unit
Computer
Stop
Start
Stop2 Stop1
Start
NIM
ADC
Gate
Fanout
Interrupt
Delay
Electronic Setup
400 440 480 520 560 600 640 680 720 760 800
500100015002000250030003500400045005000550060006500
Cou
nts/s
Voltage (V)
Pressure = 10 Torr
520 560 600 640 680 720 760 800
500100015002000250030003500400045005000550060006500
Cou
nts/s
Voltage (V)
Pressure = 15 Torr
520 560 600 640 680 720 760 800
500100015002000250030003500400045005000550060006500
Cou
nts/s
Voltage (V)
Pressure = 18 Torr
Count rate as a function of voltage and pressure using a PPAD for a
252Cf .
Testing of Detectors
14 15 16 17 18 19 20100
150
200
250
300
350
400
450
500
Cou
nts/s
P ressu re (T orr)
V oltage = 570 V
Effect of pressure on count rate at constant voltage.
Offline analysis is performed using the computer code ROOT.
The ROOT software is an object-oriented (C++) data analysis package developed at CERN.
It was developed keeping in mind the high energy physics experiments and several laboratories around the world use ROOT for the analysis of data.
Data analysis
Data analysis
A pulse height spectrum from a PPAD A time spectrum
A time spectrumA time spectrum
Data analysis
A coincidence time spectrum A time spectrum
A pulse height spectrum A pulse height spectrum
If the intrinsic time resolutions of the start and stop detectors are equal, then we can write,
Δt2exp = Δt2
kin + Δt2geom + 2 Δt2
intr
In the present geometry the value of the Δtkin comes out to be 0.6 ns and Δtexp 1.25 ns. If we assume the Δtgeom to be 0.17 ns, then the intrinsic time resolution is 0.76 ns.
Time resolution
400 420 440 460 480 500100
200
300
400
500
600
700
FWH
M (p
s)
Voltage (V)
0 2 4 6 8 10
0
2
4
6
8
10
8 12 16 20 24
1.05
1.20
1.35
1.50
1.65
1.80
1.95
Tim
e re
solu
tion
(FW
HM
)
Pressure (Torr)
0 5 10 15 20 250.25
0.50
0.75
1.00
1.25
1.50
1.75
Effe
ctiv
e tim
e re
solu
tion
(ns)
Pressure (torr)
0 20 40 60 80
100
200
300
400
5000 20 40 60 80
100
200
300
400
500
5.5 MeV alpha particles 8.1 MeV protons 2.3 MeV protonsTi
me
reso
lutio
n(FW
HM
)
Gas pressure(torr)
Effect of voltage and presssure and pressure on time resolution
Time Resolution
TOF time resolution as a function of applied voltage
Time Resolution
Efficiency and time resolution versus high voltage
Random coincidences
True coincidences
Time
Counts
Data analysis
A schematic TDC spectrum
Focal plane sum spectrum
Focal plane sum spectrum after ADC and TDC cut
Data analysis
Particle identification capabilitiesof the detectors
ALICE TOF Particle Identification
Reconstructed mass with the TOF detector in the momentum range 0.5 GeVfc<p<2.5 GeV/c for 50 HIJING Pb-Pb events at B=0.4 T.Individual mass distributions of the true π, K, p are also shown as hatched area.
ALICE TOF Particle Identification
Mass separation as a function of momentum with the Time of Flight detector in Pb-Pb collision
Likelihood can be based on:• total deposited charge (LQ)• deposited charge/position (LQX)• Exceed design goal of factor 100 pion rejection for isolated tracks
Test beam measurement at CERN PS with electron and pion beam
Electron Identification in TRD
ALICE is Ready for Data
`̀Take some more tea,Take some more tea,’’ the March Hare said to Alice, very the March Hare said to Alice, very earnestly. earnestly. `I've had nothing yet,' Alice replied in an offended tone, `I've had nothing yet,' Alice replied in an offended tone, `so I can't take more.`so I can't take more.’’`You mean you can't take LESS,' said the Hatter: `it's very `You mean you can't take LESS,' said the Hatter: `it's very easy to take MORE than nothing.easy to take MORE than nothing.’’
L. Carroll, Alice in WonderlandL. Carroll, Alice in Wonderland