CMS Desy by xeniawinifredzoe

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									Precision Tracking

    COLLID04
    Novosibirsk
     May 2004


   Joachim Mnich
                 Precision Tracking
                     at future colliders

LHC: Large Silicon Tracker    LC: A Novel Time Projection Chamber




  ATLAS                       Detector for TESLA
  CMS
The Large Hadron Collider (LHC) at CERN(Geneva)
pp-collisions at very high energy (2 7 TeV) and luminosity 1033-1034/cm2/s


          CMS




                         ATLAS

                                                         protons
                            protons
                    Tracking at the LHC
LHC physics programme                        Examples:
 Higgs                                       H  ZZ  4 
 SUSY and New Physics searches               H  
 Test of the Standard Model                             4 jets
                                              tt  bb + 2 jets + l
  + heavy ion                                            l l
                                               Atlas: bb + 22 min. bias events
Challenges for tracker
 LHC 25 ns bunch crossing rate
   fast detector response
  20 pp interactions  1000 tracks/bx
   high granularity
 Resistance to high radiation
 Tracking with silicon detectors
 Vertex: layers of pixel detectors
 Main tracker: large area silicon strip detectors
   + transition radiation detector (ATLAS) straw tubes & radiator
 Design Comparison
ATLAS:
• Hybrid pixel detectors
  3 layers
• Silicon strip detector (SCT)
  4 layers in barrel
  9 layers in endcap
    all layers 2 stereo detectors
• Transisiton Radiation Tracker
  straw tubes + radiator (36 points)
• All in a 2 Tesla solenoid                            Outer Barrel Pixel   Endcap
                                                           –TOB-            –TEC-
                                              Inner Barrel
                                                 –TIB-
CMS:                                       Inner Disks
• All silicon tracker              2,4 m     –TID-
• Hybrid pixel detectors
  3 layers
• Silicon strip detectors
  10 layers in barrel
   9 layers in endcap
• All in a 4 Tesla solenoid
                         Radiation Hardness
Expected radiation doses
• Pixel vertex detectors per year
   31014 n/cm2 (1 MeV equiv.)
   150 kGy charged particles
• Strip detectors in 10 years
    1.51014 n/cm2
    60 kGy
Effects on silicon sensors
• Creation of impurities
• Change of depletion voltage
    type inversion
• Increase of dark current
• Increase of oxide charges
   strip/pixel capacitance

Effects on readout chips
• Change of MOS structures
• Change of amplification
• Single event upset (bit flip)
                           Radiation Hardness
Radiation hard sensors:
                                                              10
• Operate at low temperature ( –10°C)
      increases time constant of                                 8




                                               Neff [1011cm-3]
       reverse annealing to many years                                   NA = ga eq                          N
      reduces dark current & avoids                              6                            reverse
       thermal runaway                                                                         annealing
                                                                  4
• Use <100> crystal orientation
  reduces charge trapping at Si/SiO2                              2    annealing                    gC eq
  boundaries
                                                                  0
                                                                   1        10         100   1000     10000
Radiation hard chips:                                annealing time at 60oC [min]
• Deep sub-micron technology
  0.25 m structures
      Small oxide structres  intrinsically radiation hard
      Industrial standard  cheap
 DMILL technology
  relies on high quality oxide
                       Vertex Detectors
Hybrid pixel detectors
• Active silicon sensor
• Bump-bonded to readout chip

 parallel readout & processing
  required for 40 MHz bunch
  crossing


General detector layout:

                                  CMS
             Vertex Detectors

        Comparison of parameters:

  Pixel detectors:    ATLAS          CMS
   # layer barrel        3            3
          endcap         4            2
        radii [cm]    5/10/12       4/7/10
   pixel size [m2] 50  300/400   100  150
        # channels     8107         7107
sensitive area [m2]      2            1.1


      area of LEP vertex detectors
                 Status of Pixel Detectors
• R&D finished
• Prototyping:
 ATLAS                      CMS readout chip




• Testbeam:
                                   CMS sensor in 25 ns beam at
                                   LHC hit rates of 80 MHz/cm2
       Silicon Strip Detectors                   ATLAS
                                                                       CMS


 At larger radius no
 pixel detector possible             Silicon strip det.:   ATLAS          CMS
 (# of readout channels)
                                       # layer barrel      4 stereo    10 (4 stereo)
   pixel  0.1  0.1    mm2
                                              endcap       9 stereo   9 (33% stereo)
  strip  0.1  100 mm2
                                            # modules 2  4088            15200
                                            # channels      6106         10106
                                     silicon area [m2]       61            206
         Silicon Area (m²)
1000
                             CMS
100                          GLAST
                             ATLAS
                                              Largest silicon
 10
                NOMAD                         detectors
                    DO
                    CDF                       ever build!
  1             AMS01
        CDF   LEP
 0.1
Silicon Strip Detectors
Example of modules:

                          CMS outer barrel




                          ATLAS endcap
          Production of Silicon Strip Detectors


• Mass production of modules
  has started
• Use robots to assemble thousands
  of modules to O(20 m) precision




                             CMS
Integration of Modules & Construction of Tracker
Support structure for the ATLAS   Part of the CMS barrel carbon
barrel tracker                    fiber support structure
          Expected Performance of LHC Trackers
Example CMS:
 pT resolution                 transverse impact parameter




For high momentum tracks:
 (pT)/pT  1.5 10-4 pT/GeV          (IPT)  10 m
 (=0)
Physics Performance of LHC Trackers

 Example: expected b-jet tagging with CMS
          ATLAS Transition Radiation Tracker
Bonus: electron/pion separation

   Two threshold analysis

5.5 keV
0.2 keV

                            ~1 TR hit
Bd0J/ψ Ks0
                                 ~7 TR hits
                             LHC Tracker
The back side of the medal:
                                     Example: CMS full silicon tracker
• Large scale silicon tracker
  à la CMS have large material                                   CMS
  budget
• Support, cooling, electronics,
  cables etc.
• Active silicon contributes
  only marginally
 Degradation of calorimeter
  performance
 Disadvantage compared to a
  gaseous trackers
  (TPC, jet chamber, ...)




                                   Active silicon
              Summary LHC Tracker
                (ATLAS & CMS)

• LHC enviroment requires fast, radiation hard detectors
  Choice of large silicon (pixel & detectors)
   (+ straw tubes at larger radii)

            Largest silicon detectors ever build

• Detectors under construction are adequate for the LHC
  physics programm
   - High resolution on momentum and secondary vertices
   - Can cope with hostile conditions at the LHC
     high muliplicity and extreme radiation doses
                      e+e– - Linear Collider
A Linear Collider with
• Energy in the TeV range
• High luminosity (> 1034/cm2/s)
is the next large international
HEP project

Concepts:
• Superconducting cavities: TESLA (Europe, DESY et al.)
• Warm cavities:            NLC (America) and GLC (Asia)
• Drive beams:              CLIC (CERN) route to multi-TeV energies
      Physics at a 1 TeV e+e– - Linear Collider
 Comparison of physics at LC and LHC
 • LHC discovery machine for Higgs & SUSY
 • LC precison measurements

 cf. discovery of W- and Z-bosons at hadron collider
 followed by precision tests at LEP & SLC

Example: Study of Higgs properties
e+ e–  H Z  H e+ e– (+ – )



                          1000 events/year



  Tag Higgs through leptonic Z decay (recoil mass)
  Study Higgs production independent of Higgs decay
            Higgs Physics at the Linear Collider
                                ideally: recoil mass resolution
                                only limited by Z width

                                 Momentum resolution (full tracker)
                                        (1/pt ) < 510-5 GeV-1




Determine Higgs branching ratios:
                                      Couplings to fermions:
                                           gf = mf /v
                                      Couplings to gauge bosons:
                                     gHWW = 2 mW2/v gHZZ = 2 mZ2/v

                                     Best possible vertex detector to
                                      distinguish b- and c-quarks
                   Tracking at the Linear Collider
Main difference for detector design between cold and warm
machines timing of bunches
                                        TESLA       GLC/NLC
                   bunch intervall      337 ns         1.4 ns
                   # bunches/train      2820            192
                     bunch length       950 s        0.27 s
                    repetition rate      5 Hz     100 – 150 Hz


                    199 ms                               7-10 ms

                                                                         time
                                 time            192 bunches
    2820 bunches                                                   GLC/NLC
                         TESLA                   t = 1.4 ns
    t = 337 ns


  • TESLA: higher readout speed to limit occupancy
           (several readout cycles per bunch train)
  • GLC/NLC: bunch separation is more difficult
                          Vertex Detector
Goal (TESLA TDR)
reconstruction of primary vertex to
d(PV) < 5 m  10 m / (p sin3/2 q)
cf: SLD 8 m  33 m / (p sin3/2 q)


 Multi-layer pixel detector
  • Stand alone tracking
  • Internal calibration
  • Small pixel (20 m  20 m)                                 TESLA       SLD
  • 800 million channel               Inner radius               15 mm    28 mm
                                      Single point resolution    < 5 m    8 m
                                      Material per layer (X0)    0.06%     0.4%
                                      Total material budget     < 1% X0
                         Vertex Detector
Three main issues:
I. Material budget
• Very thin detectors
   60 m (= 0.06% X0) of silicon
• No electronics in central part, i.e. no hybrid design
• Minimise support


II. Radiation hardness                                 TESLA          CMS
• High background from                              (ri = 1.5 cm) (ri = 4.3 cm)
  beam-strahlung and beam
  halo                             Dose (,e–,h)          10 kGy    1000 kGy
• Much less critical than LHC      Neutron flux           1010/cm2    1015/cm2
• But much more important
  than at LEP/SLC
                       Vertex Detector
III. Readout speed
Integration of background during                   CCD design
long bunch train

• Small pixel size (20 m  20 m)
  to keep occupancy low
• Read 10 times per train
  50 MHz clock (TESLA)


                                     CCD classic      CP CCD
 Use column parallel
  readout
                 Vertex Detector Technology
Several technologies under study
Examples:
 Charge Coupled Device:
• Classical technology
• Create signal in 20 m active layer
  etching of bulk  total thickness  60 m
• Coordinate precision 2-5 m
• Low power consumption

 DEPFET
   (DEPleted Field Effect Transistor)
• Fully depleted sensor with integrated
  pre-amplifier
• Low noise
   10 e– at room temperature!

                        Prototype (Bonn):
                        50 m × 50 m pixel
                        9 m resolution
               Vertex Detector Technology
 MAPS
 (CMOS Monolithic Active Pixel Detectors)

• Standard CMOS wafer integrating
  all functions
  i.e. no connections like bump bonds
• Very small pixel size achievable
• Radiation hardness proven
• Power consumption is an issue
  Pulse power?
                            Main Tracker
                                                 Simulation of one TESLA bunch train
                                                 background (beam strahlung) + 1 Higgs
Large Si-Tracker à la LHC experiments?
• Much lower particle rates at Linear Collider
• Keep material budget low

 Large Time Projection Chamber
• 1.7 m radius
• 3% X0 barrel (30% X0 endcap)
• High magnetic field (4 Tesla)


                                            Goals
                                            • (1/pt ) < 510-5 GeV-1
                                            • 200 points (3-dim.) per track
                                            • 100 m single point resolution
                                            • dE/dx 5% resolution
                                             10 times better single point
                                             resolution than at LEP
                   Time Projection Chamber
                                       Wires
New concept for gas amplification
at the end flanges:
Replace proportional wires with
Micro Pattern Gas Detectors

 GEM or Micromegas

- Finer dimensions                     GEM
- Two-dimensional symmetry
  (no E×B effects)
- Only fast electron signal
- Intrinsic ion feedback suppression
               Gas Electron Multiplier (GEM)     (F. Sauli 1996)
                                        140 m    Ø 75 m
• 50 m capton foil,
  double sided copper coated
• 75 m holes, 140 m pitch
• GEM voltages up to 500 V
  yield 104 gas amplification
For TPC use GEM towers for
safe operation, e.g. COMPASS
                             Micromegas   (Y. Giomataris 1996)
                                                      50 m pitch
• Asymmetric parallel plate chamber
  with micromesh
• Saturation of Townsend coefficient
  mild dependence of amplification
  on gap variations
• Ion feedback suppression
                   Micro Pattern Gas Detectors

Detection of electron signal
from MPGD:
no signal broadening by induction

 short & narrow signals


If signal collected on one pad
  No centre-of-gravity
 Possible Solutions
• Smaller pads
• Replace pads by bump bonds of
  pixel readout chips
• Capacitive or resistive coupling
  of adjacent pads
                R&D Work on TPC
Examples
             Aachen
                            DESY/Hamburg




                                           Karlsruhe
Triple GEM
structure

Carlton/Victoria            Orsay/Saclay
                 R&D Work on TPC
Examples of first results from triple GEM structures in high magnetic field
• Short & narrow pulses




• Low ion feedback 2 10-3            • Single point resolution O(100 m)

                                                            DESY
                  Summary & Conclusions

Tracking at the LHC:
• Large & precise tracking detectors mainly
  based on silicon technology under construction
• Hybrid pixel vertex detectors
• Start of data taking in 2007




Electron-Positron Linear Collider:
• Vertexing with ultrafine & fast silicon pixel detectors
• Tracking with high precision TPC exploiting
  micropattern gas detectors
• Worldwide R&D programs ongoing

								
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