Particle Identification @ ALICE - IRTG Heidelberg

Partcile Production from
Particle Identification @ ALICE,
SIS to the LHC
Techniques and physics interpretation
Helmut Oeschler
Darmstadt University of Technology
and
CERN
May 11 th , 20010

Melting Matter
smooth crossover

Size: 16 x 26 meters
Weight: 10,000 tons

Particle identification using three detectors:
Some steps in building the time projection chamber TPC
Calibration, cosmic rays, pp collisions
Time of Flight
Inner Tracker System
Results from the various detectors,
Final spectra and their understanding
Measuring particle yields and
what we can learn from it

October 2006

The ALICE Time Projection Chamber (TPC)
• main tracking and particle identification detector of Alice
• delivers almost complete picture of the collision:
tracking, particle momentum (pT = 0.3 B r), and particle ID
⋅ ⋅ 7
07.10.2009 | A.Kalweit@GSI.de
5 m

The time projection chamber (TPC)
largest ever
88 m3, l = 5 m, d = 5.6m
570 k channels
lightweight,
powerful FEE
Radius 2.5 m
Length: 5 m
Volume: 95 m 2
Gas: Ne CO 2 N 2

TPC

energy-loss formula
• energy loss per unit path length is described by the Bethe-
Bloch formula
(depends only on charge and rest mass for a fixed
momentum)
• parameterization is fitted to the data (Aleph-
Parameterization):
07.10.2009 | A.Kalweit@GSI.de

Particle identification via specific energy loss
• energy loss per unit path length is described by Bethe-Bloch formula:
• depends only on charge
and rest mass for a fixed
momentum
-> particle ID
• scaling variable:
βγ
= p/m
07.10.2009 | A.Kalweit@GSI.de
11
MC

TPC Krypton calibration
• Prerequisite for precise PID: Gain of 557568 pads has to be equalized
• Injection of radioactive Krypton: Rb -> Kr* -> Kr
A. Matyja, Cracow
07.10.2009 | A.Kalweit@GSI.de
41.6 keV
C side Gain Map

Field defining potential network

Calibration with laser beams

Calibration with cosmics
• ALICE TPC started cosmic data taking in February 2008, long run during 2009
• Almost all necessary calibrations were carried out with this data.
cosmic event
07.10.2009 | A.Kalweit@GSI.de
15
dE/dx spectrum
from 7 million
cosmic ray events

With magnetic field

First TPC pp event
6 Dec 2009

900 GeV pp data

Parametrize the dE/dx
for the various particles
Slices in pt
Difference between
measured value and
parametrized one
For charged particles:
pi, K and p

Secondary vertex studies:
+PId
Basis of topological identification
Weak decay of strange particles
displaced vertices (cτ ~cm)
charged decay daughters
K 0 s , Λ, Ξ- and Ω -
high branching ratio (>64%)
Reconstruction from charged tracks
tracking inward
secondary track selection
displaced vertex finder
Identification of secondary vertices
quality selection (ITS clusters…)
daughter PId (dE/dx, TOF, etc…)

Changes in the Reconstruction and the
ESD

Λ → πp
ALICE in full glory

Results from 900 GeV pp data
Λ → πp
PDG: 1115.7 MeV
Λ → πp
PDG: 1115.7 MeV
K 0 s
→ ππ
PDG: 497.6 MeV
φ → Κ + Κ −
PDG: 1019.5 MeV

Lambda analysis with and without PID
With PID:
PID cut at 3 sigma
Without PID:

Secondary vertex studies:
simulation
Multi-strange particle analysis ?
3 prong decays for Ξ and Ω
association of 3 tracks
High multiplicity environment
dNch /dy ~2000 (?)
2 units of rapidity
2 tracks: 2000 pos x 2000 neg
3 tracks: …
compromise efficiency / purity
Candidate quality evaluation
kinematical variables
distances of closest approach
χ 2 calculations

Ξ reconstruction

Kaon/pion ‘identification’ from their
weak decay inside ALICE TPC detector
24/05/10 28
ALICE Week, PWG2, MSS
K
K
K
K
K
→
μν
→ ππ
→ eπ
→
μπ
→ ππ
K- kinks
0
ν
0
0
0
ν
π
0
π- - kinks
π →
μ ν
63.
43%
21.
13%
4.
87%
3.
27%
1.
73%
99%

ALICE Data pp interactions at 900 GeV, KinkAngle VRS Mother Mom.
All Kinks
Blue:π Limit, Red:K Limit
24/05/10 29
ALICE Week, PWG2, MSS
Selected Kaon-kinks

ALICE MC (left) and Data(right) pp interactions at 900 GeV, K-kinks
MC
24/05/10 30
ALICE Week, PWG2, MSS
ALICE Data

ALICE Data pp interactions at 900 GeV, K-kinks Pt, Raw and corrrect
MC
24/05/10 31
ALICE Week, PWG2, MSS
Data, 3σ cut

ALICE MC pp interactions at 900 GeV, K-kinks correction factors
24/05/10 32
ALICE Week, PWG2, MSS
Blue->K+, Red->K-
Fraction of decaying
kaons in the given
volume
Probability of finding the
kink decays

ALICE Data pp interactions at 900 GeV, K-kinks Pt, Raw and corrrect
24/05/10 33
ALICE Week, PWG2, MSS

Time-of-flight Detector

Time difference between measured t TOF and
calculated (based on pass length)

TPC
SPD cone
SSD/SDD
IT
S
SPD barrel
SPD
Inner Tracking System
~ 10 m 2 Si detectors, 6 layers
Pixels, Drift, double sided Strips

Inner Tracking System (II)
• Design goals
– Optimal resolution for primary vertex and track
impact parameter
• Minimize distance of innermost layer from beam axis
(≈ 3.9 cm) and material budget
– Maximum occupancy (central PbPb) < few %
– 2D devices in all the layers
– dE/dx information in the 4 outermost layers for
particle ID in 1/β 2 region
Layer Det.
Type
Radius
(cm)
Length
(cm)
Resolution
(μ m)
PbPb dN/dy=6000
rφ Z Part./cm 2 Occupancy
(%)
1 SPD 3.9 28.2 12 100 35 2.1
2 SPD 7.6 28.2 12 100 12 0.6
37

ITS role in ALICE physics (II)
• Vertexing
– Reconstruction of primary (interaction) vertex
Resolution [μ m]
• From tracks: ITS crucial to obtain resolution better than 100 μm
• From SPD tracklets: done before tracking and used as a starting point (seed) in the
tracking phase. Allows for pileup tagging based on multiple vertices
– Identification of secondary vertices from decays of hyperons and open charm and
beauty hadrons
Primary vertex resolution vs.
multiplicity in p-p
Vertex from tracks
Interaction diamond:
σ x,y =50 μm
D + → K - π + π + decay vertex
resolution
38

SDD
Central
Cathode
at -HV
70.2 mm
Voltage divider
E drift
E drift
v d (e - )
v d (e - )
Modules mounted
on ladders
Anodes
HV supply
Front-end electronics (4 pairs of ASICs)
-> Amplifier, shaper, 10-bit ADC, 40 MHz
sampling
LV supply
Commands
Trigger
Data
Cooling (H 2 O) tubes
Cables to power
supplies and DAQ
Carbon fiber support
Layer # ladders Mod./ladde
r
SDD layers
into SSD
# modules
3 14 6 84
4 22 8 176
39

Pid via Energy loss

Same procedure as for TPC

Kaon analysis via the different methods

What do we learn from
the spectra?

Thermallyshaped
Soft
Production
Hard
Scattering
hep-ex/0305013 S.S. Adler et al.
RHIC
PHENIX
p+p->π 0 + X

a first glimpse of mini-
jets
ITS-TPC matching and tracking

a first glimpse of mini-
ALICE TPC Di-jet
jets
angular distribution of
particles in TPC relative to
a high p t trigger particle
(single event!)

Spectra from RHIC p+p and Au+Au
exponential low-energy
part with a pronounced
tails towards high
momenta
How to compare p+p with
Au+Au?
Volume?
Bulk, N part
Number of NN collisions?
Hard collisions, N coll

Deuterons and anti-deuterons selection
Natasha Sharma, PWG2 Meeting,
March 23rd, 2010
Thanks to Alexander
Kalweit
48

Anti deuteron
Natasha Sharma, PWG2 Meeting,
March 23rd, 2010
49

Outlook for 7 TeV

Statistical Model
Strangeness Suppression in pp
Resonance Suppression in HI
− In pp particle ratios are well described using canonical description
− In Au+Au only stable particle ratios are well described
Observed strangeness enhancement NOT signal for a QGP!

• Chemical decoupling
conditions extracted
from SIS up to RHIC
feature common
behavior
• parametrisation e.g.
T - μ B – systematics
Nucl. Phys. A 697 (2002)
902
J. Cleymans, HO, K. Redlich, S. Wheaton,
Phys. Rev. C 73 (2006) 034905

Chemical Freeze Out
Data points:
T μ B
Hadronization
Towards LHC!
T ≈ 170 MeV
μ B ≈ 1 MeV

Freeze-out parameters using the anti p/p ratio
pp 900 GeV
ALICE
pp 200 GeV
STAR
I. Kraus, et al., PRC 79 (2009) 014901

Predictions for pp and HI at LHC
Prediction for
heavy ions:
Grand can.
I. Kraus et al.,
PRC 74 (2007)
034903

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