the alice inner tracking system: present and future vito manzari – infn bari
DESCRIPTION
The ALICE Inner Tracking System: present and future Vito Manzari – INFN Bari ( [email protected] ) o n behalf of the ITS Collaboration in the ALICE Experiment at LHC. Outline. ALICE experiment Inner Tracking System Detector overview and Performance ITS Upgrade: - PowerPoint PPT PresentationTRANSCRIPT
Sez. di Bari
The ALICE Inner Tracking System:
present and futureVito Manzari – INFN Bari
on behalf of the ITS Collaboration in the ALICE Experiment at LHC
Sez. di Bari
ALICE experiment Inner Tracking System
Detector overview and Performance
ITS Upgrade: Physics motivations Upgrade strategy R&D activities Timeline
Conclusions
Outline
V. Manzari - INFN Bari HSTD8 – December7th, 2011 2
Sez. di Bari
V. Manzari - INFN Bari HSTD8 – December7th, 2011 3
A Large Ion Collider Experiment
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)
Sez. di Bari
Detector:Size: 16 x 26 metersWeight: 10,000 tons
Central Barrel2 p tracking & PID
Dh ≈ ± 1
The ALICE detector
V. Manzari - INFN Bari HSTD8 – December7th, 2011 4
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
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
Inner Tracking System (ITS)
Central Barrel
Sez. di Bari
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)
The ITS plays a key role for the study of yields and spectra of particles containing heavy quarks
The Inner Tracking System (ITS)
V. Manzari - INFN Bari HSTD8 – December7th, 2011 6
Sez. di Bari
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)
The “current” Inner Tracking System
V. Manzari - INFN Bari HSTD8 – December7th, 2011 7
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
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
The Inner Tracking System in numbers
V. Manzari - INFN Bari HSTD8 – December7th, 2011 8
Layer Det. Radius
(cm)Length
(cm)Surface
(m2)Ch.
Spatial precision
(mm)Cell
(μm2)
Max occupancy
central PbPb (%)
Power dissipation(W) Material
budget(% X/X0)
rf z barrel end-cap
1SPD
3.9 28.20.21 9.8M 12 100 50x425
2.11.35k 30
1.14
2 7.6 28.2 0.6 1.14
3SDD
15.0 44.41.31 133K 35 25 202x294
2.51.06k 1.75k
1.13
4 23.9 59.4 1.0 1.26
5SSD
38.0 86.25.0 2.6M 20 830 95x40000
4.0850 1.15k
0.83
6 43.0 97.8 3.3 0.86
Sez. di Bari
PbPb event @ 2.76 A TeV
V. Manzari - INFN Bari HSTD8 – December7th, 2011 9
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
Online SPD Vertex
V. Manzari - INFN Bari HSTD8 – December7th, 2011 10
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
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
ITS standalone enables the tracking for very low momentum particles (80-100 MeV/c pions)
Track impact parameter
V. Manzari - INFN Bari HSTD8 – December7th, 2011 11
Pb-Pb
Few hundred micron
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- separation up to 450 MeV/c• A resolution of about 10-15% is achieved
p-p
p-p
Pb-Pb
Particle IDentification
V. Manzari - INFN Bari HSTD8 – December7th, 2011 12
Sez. di Bari
Intermediate Summary
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
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
ITS Upgrade Motivations
V. Manzari - INFN Bari HSTD8 – December7th, 2011 14
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.)
Upgrade Strategy
V. Manzari - INFN Bari HSTD8 – December7th, 2011 15
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
Upgrade Strategy
V. Manzari - INFN Bari HSTD8 – December7th, 2011 16
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
Improve the impact parameter resolution
V. Manzari - INFN Bari HSTD8 – December7th, 2011 17
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
Improve tracking, triggering and pT resolution
V. Manzari - INFN Bari HSTD8 – December7th, 2011 18
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)
Upgrade Scenario
V. Manzari - INFN Bari HSTD8 – December7th, 2011 19
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
Upgrade Scenario
Upgrade
Current
V. Manzari - INFN Bari HSTD8 – December7th, 2011 20
Sez. di Bari
Impact parameter resolution
V. Manzari - INFN Bari HSTD8 – December7th, 2011 21
ITS standalone tracking
An additional innermost pixel layer would achieve already a substantial
improvement of the pointing resolution (factor 3 at 200 MeV/c)
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
Sez. di Bari
Standalone Tracking Efficiency
V. Manzari - INFN Bari HSTD8 – December7th, 2011 22
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
Sez. di Bari
HSTD8 – December7th, 2011 23V. Manzari - INFN Bari
Physics signal benchmarkD0 Kπ
Increase of the statistical significance
reduction the statistical uncertainty!
pT range not accessible with the current ITS
Sez. di Bari
HSTD8 – December7th, 2011 24V. Manzari - INFN Bari
Physics signal benchmarkΛc
New measurement!
Important physics reach: barion over meson ratio in heavy-quark sector
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
R&D activities
V. Manzari - INFN Bari HSTD8 – December7th, 2011 25
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)
Monolithic Pixel R&D
V. Manzari - INFN Bari HSTD8 – December7th, 2011 26
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
Hybrid Pixel R&D
V. Manzari - INFN Bari HSTD8 – December7th, 2011 27
Sez. di Bari
HSTD8 – December7th, 2011 28V. Manzari - INFN 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
Double-sided Micro-strip R&D
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
ITS Upgrade Timeline
V. Manzari - INFN Bari HSTD8 – December7th, 2011 29
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
Conclusions
V. Manzari - INFN Bari HSTD8 – December7th, 2011 30
Sez. di Bari
HSTD8 – December7th, 2011 31V. Manzari - INFN Bari
Back-up slides
Sez. di Bari
HSTD8 – December7th, 2011 32V. Manzari - INFN Bari
“Russian Doll” Installation
SSD barrel
SDD barrel
Inserting the SDD barrel inside the SSD barrel
Sez. di Bari
“Russian Doll” Installation
Moving of the SDD+SSD barrel over the SPD
SPD half-barrels mounted face to face
around the beam pipe
V. Manzari - INFN Bari HSTD8 – December7th, 2011 33
Sez. di Bari
HSTD8 – December7th, 2011 34V. Manzari - INFN Bari
Moving the TPC over the ITS barrel, i.e. SPD+SDD+SSD
“Russian Doll” Installation
Sez. di Bari
The SPD is made of 120 modules, called half-staves
Pixel chip prompt Fast-OR• Active if at least one pixel hit in
the chip matrix
• 10 signals in each half-stave (1200 signals in total)
• Transmitted every 100 ns
SPD L0 trigger
SPD Half Stave
Half stave
Sensor
Pixel chips
Readout MCM
Sensor141 mm
1
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
Sez. di Bari
“Global”1. Seeds in outer part of TPC (lower track density)
2. Inward tracking from the outer to the inner TPC radius
3. Matching the outer SSD layer and tracking in the ITS
4. 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 )
pt resolution
TPC-ITS track matching
Tracking strategies
V. Manzari - INFN Bari HSTD8 – December7th, 2011 36
Sez. di Bari
HSTD8 – December7th, 2011 37V. Manzari - INFN 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
Vertexing
Sez. di Bari
HSTD8 – December7th, 2011 38V. Manzari - INFN Bari
Upgrade Simulation Tools
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.
Sez. di Bari
HSTD8 – December7th, 2011 39V. Manzari - INFN Bari
Upgrade Simulation Validation
Fast MC shows the same perfomance as the FET
The 3 simulation tools reproduce the current ITS performance
Fast Estimation Tool (pions) Full MC
Sez. di Bari
HSTD8 – December7th, 2011 40V. Manzari - INFN Bari
Pointing Resolution
Effects of the innermost layer L0• No vertex resolution
Radial Distance
Material Budget
Sez. di Bari
HSTD8 – December7th, 2011 41V. Manzari - INFN Bari
Pointing Resolution
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
Sez. di Bari
HSTD8 – December7th, 2011 42V. Manzari - INFN Bari
Red : proton/Kaon separationBlack : kaon / pion separation
Particle Identification
Different configurations are being studied
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)
Hybrid pixel material budget
V. Manzari - INFN Bari HSTD8 – December7th, 2011 43
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)
How material budget can be reduced
V. Manzari - INFN Bari HSTD8 – December7th, 2011 44