Slides - Alice
Download
Report
Transcript Slides - Alice
Sez. di Bari
The ALICE Inner Tracking System:
present and future
Vito Manzari – INFN Bari
([email protected])
on behalf of the ITS Collaboration in the ALICE Experiment at LHC
Outline
Sez. di Bari
ALICE
Inner Tracking System
experiment
Detector overview and Performance
ITS Upgrade:
Physics motivations
Upgrade strategy
R&D activities
Timeline
Conclusions
V. Manzari - INFN Bari
HSTD8 – December7th, 2011
2
A Large Ion Collider Experiment
Sez. di Bari
ALICE is the dedicated heavy ion experiment at LHC
Study of the behavior of strongly interacting matter under extreme conditions of
compression and heat in heavy-ion collisions up to Pb-Pb collisions at 5.5 TeV
Proton-proton collisions:
•
Reference data for heavy-ion program
•
Genuine physics (momentum cut-off < 100 MeV/c, excellent PID)
V. Manzari - INFN Bari
HSTD8 – December7th, 2011
3
The ALICE detector
Sez. di Bari
Central Barrel
2 p tracking & PID
Dh ≈ ± 1
Detector:
Size: 16 x 26 meters
Weight: 10,000 tons
V. Manzari - INFN Bari
HSTD8 – December7th, 2011
4
Central Barrel
Sez. di Bari
Tracking
Pseudo-rapidity coverage |η| < 0.9
Robust tracking for heavy ion environment
• up to 150 points along the tracks
Wide transverse momentum range (100 MeV/c –
100 GeV/c)
• Low material budget (13% X0 for ITS+TPC)
PID over a wide momentum range
Combined PID based on several techniques: dE/dx,
TOF, transition and Cherenkov radiation
Inner Tracking System (ITS)
Rate capabilities
Interaction rates: Pb-Pb < 8kHz, p-p < 200 kHz (~30
events in the TPC)
Multiplicities: central Pb-Pb events ~2000, Pb-Pb
MB ~ 600
V. Manzari - INFN Bari
HSTD8 – December7th, 2011
5
The Inner Tracking System (ITS)
Sez. di Bari
The ITS plays a key role for the study of yields and spectra of particles
containing heavy quarks
The ITS tasks:
Secondary vertex reconstruction (c, b
decays) with high resolution
•
Good track impact parameter resolution
< 60 µm (rφ) for pt > 1 GeV/c in Pb-Pb
Improve primary vertex reconstruction,
track momentum and angle resolution
Tracking and PID of low pt particles, also
in stand-alone
Prompt L0 trigger capability (FAST OR)
with a latency <800 ns (SPD)
V. Manzari - INFN Bari
HSTD8 – December7th, 2011
6
The “current” Inner Tracking System
Sez. di Bari
ITS requirements
Good spatial precision
High efficiency
High granularity (≈ few % occupancy)
Minimize distance of innermost layer
from beam axis (mean radius ≈ 3.9 cm)
Limited material budget
Analogue information in 4 layers for
particle identification via dE/dx
The ITS (Inner tracking System) consists of 6 concentric barrels of silicon detectors
based on 3 different technologies
•
2 layers of Silicon Pixel Detector (SPD)
•
2 layers of Silicon Drift Detector (SDD)
•
2 layers of Silicon double-sided microStrip Detector (SSD)
V. Manzari - INFN Bari
HSTD8 – December7th, 2011
7
The Inner Tracking System in numbers
Sez. di Bari
Radial distance defined by beam-pipe
(inwards) and requirements for track
matching with TPC (outwards)
Inner layers: high multiplicity environment
(~100 tracks/cm2) 2 layers of pixel
detectors
Layer
Det.
1
Radius
(cm)
3.9
Length
(cm)
3
5
7.6
28.2
15.0
44.4
23.9
59.4
38.0
86.2
V. Manzari - INFN Bari
12
100
barrel
end-cap
9.8M
50x425
1.35k
30
133K
35
25
202x294
1.14
1.13
1.06k
1.75k
1.0
1.26
4.0
2.6M
20
830
95x40000
97.8
HSTD8 – December7th, 2011
0.83
850
3.3
Material
budget
(% X/X0)
1.14
2.5
5.0
43.0
z
Power dissipation
(W)
0.6
1.31
SSD
6
rf
Max
occupancy
central PbPb
(%)
2.1
0.21
SDD
4
Ch.
Cell
(μm2)
28.2
SPD
2
Surface
(m2)
Spatial
precision
(mm)
1.15k
0.86
8
PbPb event @ 2.76 A TeV
Sez. di Bari
V. Manzari - INFN Bari
HSTD8 – December7th, 2011
9
Online SPD Vertex
Sez. di Bari
SPD Vertex built out of tracklets
Same algorithm in pp and PbPb
with different configuration
parameters
• e.g.: cut on # clusters on SPD
Vertex diamond information
delivered to LHC
SPD vertex used as input for
offline reconstruction
V. Manzari - INFN Bari
HSTD8 – December7th, 2011
10
Track impact parameter
Sez. di Bari
The transverse impact parameter in the bending
plane d0(rφ) is the reference variable to look for
secondary tracks from strange, charm and beauty
decay vertices
Few hundred micron
Impact parameter resolution is crucial to reconstruct
secondary vertices : below 60 µm for pt > 1 GeV/c
Good agreement data-MC (~10%)
The material budget mainly affect the
performance at low pt (multiple
scattering)
The point resolution of each layers
drives the asymptotic performance
Pb-Pb
ITS standalone enables the tracking for
very low momentum particles (80-100
MeV/c pions)
V. Manzari - INFN Bari
HSTD8 – December7th, 2011
11
Particle IDentification
Sez. di Bari
dE/dx measurement
• Analogue read-out of charge deposited in 4 ITS
layers (SDD & SSD)
• Charge samples corrected for the path length
• Truncated mean method applied to account for the
long tails in the Landau distribution
PID performance
• PID combined with stand-alone tracking allows to
identify charged particles below 100 MeV/c
• p-K separation up to 1 GeV/c
• K-p separation up to 450 MeV/c
• A resolution of about 10-15% is achieved
p-p
Pb-Pb
p-p
V. Manzari - INFN Bari
HSTD8 – December7th, 2011
12
Intermediate Summary
Sez. di Bari
The ITS performance are well in agreement with the design values
ALICE has collected p-p and PbPb data at the various energies and the data analysis is
progressing very well
Many papers are being published containing very relevant results
Then …..
Why do we want to upgrade the ITS?
V. Manzari - INFN Bari
HSTD8 – December7th, 2011
13
ITS Upgrade Motivations
Sez. di Bari
Extend ALICE capability to study heavy quarks as probes of the QGP in
heavy-ion collisions
Main Physics Topics and Measurements of interest
Study the quark mass dependence of the energy loss
• Measure the Nuclear Modification factor RAA vs pT, down to
low pT, of D and B mesons
Study the thermalization process of heavy quarks in the hot and
dense medium formed by heavy ion collisions
• Measure the baryon over meson ratio (Λc / D or Λb / B)
• Measure elliptic flow of charged mesons
Exploit the LHC luminosity increase improving the readout capabilities,
now limited to ≈1 kHz
V. Manzari - INFN Bari
HSTD8 – December7th, 2011
14
Upgrade Strategy
Sez. di Bari
Improve the impact parameter resolution by a factor 2÷3
How:
Reduce of the radial distance of the innermost layer (closest to the IP)
Reduce of the material budget
Reduce of the pixel size
Physics reach:
Low pT heavy-flavour mesons
v2 of charmed hadrons
Heavy flavour baryons (Λc, Λb, …)
Better identification of secondary vertices from decaying charm and
beauty and increase statistical accuracy of channels already measured by
ALICE (e.g. displaced D0, J/Ψ, etc.)
V. Manzari - INFN Bari
HSTD8 – December7th, 2011
15
Upgrade Strategy
Sez. di Bari
Improve trigger capabilities
How:
Improve standalone tracking efficiency and pT resolution
Selection of event topologies with displaced vertices at Level 2 (~100 μs)
Physics reach:
Strong enhancement of relevant signals
Exploit luminosity increase
How:
Improve readout time and standalone tracking capability
Physics reach:
Strong enhancement of relevant signals
V. Manzari - INFN Bari
HSTD8 – December7th, 2011
16
Improve the impact parameter resolution
Sez. di Bari
Get closer to the IP
Radius of innermost Pixel layer is defined by central beam pipe radius
•
•
Present beam pipe: ROUT = 29.8 mm, ΔR = 0.8 mm
New Reduced beam pipe: ROUT = 19 mm, ΔR = 0.5 mm
Reduce material budget (especially innermost layers)
reduce mass of silicon, electrical bus (power and signals), cooling,
mechanics
•
•
Present ITS Pixel layers: X/X0 ~1.14% per layer
Target value for new ITS: X/X0 ~0.3 – 0.5% per layer
Reduce pixel size
Reduce size of interconnect bumps, monolithic Pixels
•
currently 50μm x 425μm
V. Manzari - INFN Bari
HSTD8 – December7th, 2011
17
Improve tracking, triggering and pT resolution
Sez. di Bari
Higher standalone tracking efficiency
Increase granularity
Increase number of layers in the outer region (seeding) and inner region
(occupancy)
Extended trigger capabilities
High standalone tracking efficiency
Low readout time < 50μs for Pb-Pb, ~μs for p-p (current ITS ~1ms in both cases)
Increase momentum resolution
increase track length
increase spatial resolution
reduce material budget
V. Manzari - INFN Bari
HSTD8 – December7th, 2011
18
Upgrade Scenario
Sez. di Bari
7 silicon layers (r = 2.2 ÷ 45 cm) or more to cover the region from IP to TPC
3 innermost layers made of pixels, 3 outer layers either pixels or double sided strips
Pixel size ~ 20-30 µm (rφ), rφ resolution ~ 4 ÷ 6 µm
Material budget 0.3 ÷ 0.5% X0 per layer
Power consumption 250-300 mW/cm2
Innermost pixel layer: ultra-light high-resolution high-granularity as-close-as-possible
to IP (r ≈ 2.2 cm)
• Hit density ~ 100 tracks/cm2 in HI collisions
• Radiation tolerant design (innermost layer) compatible with 2 Mrad / 2 x1013 neq
over 10 years (safety factor ~2 included)
V. Manzari - INFN Bari
HSTD8 – December7th, 2011
19
Upgrade Scenario
Sez. di Bari
The new ITS will be based on Pixel and Strip detectors
• The innermost layers should be mounted on an insertable mechanics and should
be served from one side only for a fast replacement in case of reduced
efficiency
Current
Upgrade
V. Manzari - INFN Bari
HSTD8 – December7th, 2011
20
Impact parameter resolution
Sez. di Bari
An additional innermost pixel layer would achieve already a substantial
improvement of the pointing resolution (factor 3 at 200 MeV/c)
ITS standalone tracking
However, a completely new ITS is mandatory to improve the standalone
tracking efficiency at low pT and cope with the increased LHC luminosity
• New detector technologies for a faster readout
V. Manzari - INFN Bari
HSTD8 – December7th, 2011
21
Standalone Tracking Efficiency
Sez. di Bari
A factor 2 gain in tracking efficiency at 200 MeV is achieved with the
configuration under study
Tracking efficiency and an improved d0 resolution allow to detect
charmed and beauty hadrons below 2 GeV/c
V. Manzari - INFN Bari
HSTD8 – December7th, 2011
22
Sez. di Bari
Physics signal benchmark
D0 Kπ
Increase of the statistical significance
reduction the statistical uncertainty!
pT range not accessible with the current ITS
V. Manzari - INFN Bari
HSTD8 – December7th, 2011
23
Sez. di Bari
Physics signal benchmark
Λc
New measurement!
Important physics reach:
barion over meson ratio in heavy-quark sector
V. Manzari - INFN Bari
HSTD8 – December7th, 2011
24
R&D activities
Sez. di Bari
Pixel detectors
• Hybrid pixels with reduced material budget and small pitch
• Monolithic pixels rad-tolerant
Double-sided strip detectors (outer layers)
• Shorter strips and new readout electronics
Electrical bus for power and signal distribution
• Low material budget
Cooling system options
• air cooling, carbon foam, polyimide and silicon micro-channels structure,
liquid vs evaporative
• low material budget
V. Manzari - INFN Bari
HSTD8 – December7th, 2011
25
Monolithic Pixel R&D
Sez. di Bari
State-of-the-art architecture (MIMOSA family) uses rolling-shutter readout
Pixel size ~20 µm possible
Target for material budget < 0.3 % X0 (50 µm thick chip)
•
STAR HFT Monolithic: 0.37% X0
Ongoing developments:
• Evaluation of properties of a quadruple well 0.18 CMOS
•
radiation tests structures
• study characteristics of process using the MIMOSA architecture as reference
• design of new circuit dedicated to ALICE (MISTRAL)
• investigation of in-pixel signal processing using the quadruple-well approach
• Novel high resistivity base material for depleted operation (LePix)
V. Manzari - INFN Bari
HSTD8 – December7th, 2011
26
Hybrid Pixel R&D
Sez. di Bari
Pixel size limit due to flip chip bonding technology (~30 µm)
Target for overall material budget < 0.5 % X0, about 1/3 of silicon
(100 µm sensor, 50 µm front-end chip)
•
Present SPD 1.14% X0, silicon 0.38% X0
(200 µm sensor, 150 µm front-end chip)
Edgeless sensors to reduce insensitive overlap regions
High S/N ratio, ~ 8000 e-h pairs/MIP
Power/Speed optimization
Proven radiation hardness
Ongoing developments:
•
Thin and Edgless detectors (FBK, VTT, IZM)
Low cost bump bonding, Lower power FEE
V. Manzari - INFN Bari
HSTD8 – December7th, 2011
27
Double-sided Micro-strip R&D
Sez. di Bari
Sensor layout
• Strip detector technologies are rather mature
• Optimize the design to cope the expected higher multiplicity at smaller
radius and nominal LHC energy
•
Optimize stereo angle to limit ambiguities in track reconstruction
•
Smaller “virtual” cell to reduce occupancy
Front-end electronics
• Low-momentum PID requires a wide dynamic range
• Data digitization directly on front-end chip
Ongoing developments
•
Sensor layout
•
Fully differential front-end chip
•
ADC or ToT for the digitization of the analogue information
V. Manzari - INFN Bari
HSTD8 – December7th, 2011
28
ITS Upgrade Timeline
Sez. di Bari
The upgrade should target the 2017-18 shutdown (Phase I)
• Decisions on the upgrade plans in terms of physics strategy, detector
feasibility and funding availability will be taken in 2012
• The global upgrade may require a two-stage approach with a Phase II in
2020 and beyond.
end 2011: Preparation of a Conceptual Design Report
2011-2014: R&D for Phase I
2014-2016: Production and pre-commissioning for Phase I
2017-2018: Installation and commissioning for Phase I
V. Manzari - INFN Bari
HSTD8 – December7th, 2011
29
Conclusions
Sez. di Bari
The current Inner Tracking System performance is well in agreement with the
design requirements and expectations
•
The achieved impact parameter resolution allows to reconstruct the secondary
vertices of charm decays
•
Standalone capability allows to track and identify charged particles with momenta
down to 100 MeV/c
An upgraded ITS will extend the ALICE physics capabilities:
•
Strong increase of the statistical accuracy in the measurements of yields and spectra
of charmed mesons and baryons already possible with the present detector
•
A significant extension of the present physics programme with new measurements
that at present are not possible
Several options for the detector technology implementation are being investigated
and developed
V. Manzari - INFN Bari
HSTD8 – December7th, 2011
30
Sez. di Bari
Back-up slides
V. Manzari - INFN Bari
HSTD8 – December7th, 2011
31
“Russian Doll” Installation
Sez. di Bari
SDD barrel
SSD barrel
Inserting the SDD barrel inside
the SSD barrel
V. Manzari - INFN Bari
HSTD8 – December7th, 2011
32
“Russian Doll” Installation
Sez. di Bari
SPD half-barrels
mounted face to face
around the beam pipe
Moving of the SDD+SSD barrel
over the SPD
V. Manzari - INFN Bari
HSTD8 – December7th, 2011
33
“Russian Doll” Installation
Sez. di Bari
Moving the TPC over the ITS barrel, i.e. SPD+SDD+SSD
V. Manzari - INFN Bari
HSTD8 – December7th, 2011
34
SPD L0 trigger
Sez. di Bari
The SPD is made of 120
modules, called half-staves
SPD Half Stave
Pixel chip prompt Fast-OR
• Active if at least one pixel hit in
the chip matrix
1
• 10 signals in each half-stave
(1200 signals in total)
• Transmitted every 100 ns
Pixel chips
Overall latency constrain 800 ns (Central Trigger Processor)
Key timing processes are data deserialization and Fast-OR extraction
• Algorithm processing time < 25 ns
10 Algorithms provided in parallel
• Detectors commissioning, p-p and PbPb physics
• Cosmic, minimum bias and multiplicity algorithms
V. Manzari - INFN Bari
HSTD8 – December7th, 2011
35
Tracking strategies
Sez. di Bari
“Global”
1.
2.
3.
4.
Seeds in outer part of TPC (lower track density)
Inward tracking from the outer to the inner TPC radius
Matching the outer SSD layer and tracking in the ITS
Outward tracking from ITS to outer detectors PID
ok
5. Inward refitting to ITS Track parameters OK
“ITS stand-alone”
Recovers not-used hits in the ITS
layers
Aim: track and identify particles
missed by TPC due to pt cut-off,
dead zones between sectors, decays
• pt resolution ≤ 6% for a pion in
pt range 200-800 MeV/c
• pt acceptance extended down to
80-100 MeV/c (for p)
TPC-ITS track matching
pt resolution
V. Manzari - INFN Bari
HSTD8 – December7th, 2011
36
Vertexing
Sez. di Bari
Primary vertex reconstructed with tracklets
Tracks reconstruction starts from outside (TPC) towards ITS using the vertex as seed
TPC reconstructed tracks are matched with SSD outer layer
Once the reconstruction reaches the first SPD layer it is back-propagated
Re-fit from outside and the vertex is recalculated using the tracks
V. Manzari - INFN Bari
HSTD8 – December7th, 2011
37
Upgrade Simulation Tools
Sez. di Bari
3 independent simulation tools have been developed
Fast Estimation Tool: “Toy-Model” originally developed by the STAR HFT
collaboration which allows to build a simple detector model. The model featured
the calculation of the covariance matrix at each step of a measurement (e.g. layer
with radius r) including the multiple scattering.
Fast MC Tool: Extension of the FET that allows to disentangle the performance of
the layout from the efficiency of the specic track finding algorithm.
Full MC: Transport code (geant3) designed to be flexible : the detector
segmentation, the number of layers, their radii and material budgets can be set as
external parameters of the simulation.
V. Manzari - INFN Bari
HSTD8 – December7th, 2011
38
Upgrade Simulation Validation
Sez. di Bari
Fast Estimation Tool (pions)
Full MC
Fast MC shows the same perfomance as the FET
The 3 simulation tools reproduce the current ITS performance
V. Manzari - INFN Bari
HSTD8 – December7th, 2011
39
Pointing Resolution
Sez. di Bari
Effects of the innermost layer L0
• No vertex resolution
Radial
Distance
Material
Budget
V. Manzari - INFN Bari
HSTD8 – December7th, 2011
40
Pointing Resolution
Sez. di Bari
Spatial
Resolution
Configuration design for better pointing resolution performances:
Improvement at low pT:
• Smallest radial distance to the beam line
• Smallest material budget
Improvement at high pT:
• Smallest cell size
V. Manzari - INFN Bari
HSTD8 – December7th, 2011
41
Particle Identification
Sez. di Bari
Different configurations are being studied
V. Manzari - INFN Bari
HSTD8 – December7th, 2011
Red : proton/Kaon
separation
Black : kaon / pion
separation
42
Hybrid pixel material budget
Sez. di Bari
Each urrent SPD layer
• Carbon fiber support: 200 μm
• Cooling tube (Phynox): 40 μm wall thickness
• Grounding foil (Al-Kapton): 75 μm
• Pixel chip (Silicon): 150 μm 0.16%
• Bump bonds (Pb-Sn): diameter ~15-20 μm
• Silicon sensor: 200 μm 0.22%
• Pixel bus (Al+Kapton): 280 μm 0.48%
• SMD components
• Glue (Eccobond 45) and thermal grease
Two main contributors: silicon and interconnect structure (bus)
V. Manzari - INFN Bari
HSTD8 – December7th, 2011
43
How material budget can be reduced
Sez. di Bari
How can the material budget be reduced?
Reduce silicon chip thickness
Reduce silicon sensor thickness
Thin monolithic structures
Reduce bus contribution (reduce power)
Reduce edge regions on sensor
Review also other components (but average contribution 0.1-0.2%)
What can be a reasonable target
Hybrid pixels: ~0.5% X0
•
silicon: 0.16% X0 (present SPD 0.38%)
•
bus: 0.24% X0 (present SPD 0.48%)
•
others: 0.12% X0 (present SPD 0.24%)
Monolithic pixels: 0.37% X0 (as for STAR HFT)
V. Manzari - INFN Bari
HSTD8 – December7th, 2011
44