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CHARGED-PARTICLE DETECTORS kinematics complete incomplete momentum

VIEWS: 15 PAGES: 23

									               CHARGED-PARTICLE DETECTORS

       kinematics                            complete
                                             incomplete

       momentum                              tracking

       particle identification               time-of-flight
                                             energy loss
                                             Cerenkov radiation
                                             transition radiation

       energy                                "calorimeter"


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                             (not only) HISTORY I

                                                           inelastic      pion absorption
emulsions (discovery of charged π and K)                   pion-nucleus   ⇒  nuclear fragments (star)
                                                           scattering
today biophysical research




TeV cosmic ray particles                                Tau physics: DONUT collaboration




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                          (not only) HISTORY II

(Wilson) cloud chamber
typical Open Day presentations

saturated alcohol vapor


⇓                                α-particle emitting nuclide

overheated LH2,
                                                               BEBC @ CERN 73 until 80ies
bubble chamber (D. Glaser noble prize 1960)
                                                               3.7 T, 35 m3 LH2
+
magnetic field

"beer" inspired !!!




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                TRACKING DEVICES


MWPC             multi-wire proportional chambers
                 NOBEL PRIZE Charpak
                 many times "Geiger-Müller" counter


STRAW TUBES      "Geiger-Müller" counter

SILICON STRIP    position-sensitive semiconductor detectors

RICH             ring-imaging Cerenkov hodoscope

TPC              time projection chamber



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                       KINEMATICS EXAMPLE
3-particle decay of particle A in its rest frame (without polarisation)          A →1+ 2 + 3
                                                          r       r   r
final state           9 degrees of freedom                p1 , p 2 , p 3 ,

                    - 4 energy-momentum conservation
                    - 2 isotropy in space of e.g. particle 1 (2 angles)
                    - 1 isotropy of azimuthal angle φ12

                                                if masses are known = particles identified
                                                experiment kinematically complete
                                                by measuring
                                                at rest - 2 independent variables
                                                e.g. T1,T2
                                                      T1,Θ12
                                                in flight - 5 independent variables
                                                e.g. T1, T2, Θ1, Θ2, Θ13
                                                      r       r
                                                      p1 , p 2        already onefold overdetermined


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                      PARTICLE IDENTIFICATION I



                                                particle identification by time-of-flight (TOF)

                                                                   m 2              m
                                                              T=     v   ⇒   ∆t ∝
                                                                   2                T




range telescope




        T3: time "zero"

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                   PARTICLE IDENTIFICATION II

                                                             particle identification by dE/dx

                                                                      dE    1  m m2
                                                                         ∝    ∝ ∝
                                                                      dx   v2  T  p2




                         1




                                                   focus
                                              16



ANKE - COSY                                                       counter number
FOCAL PLANE SPECTROMETER
for positively charged particles


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                           PAIR SPECTROMETER
DIRAC-experiment CERN – PS212                    (
                                                Γ(π+π− → ποπο)           πο → γγ in 10-16 s

p (24 GeV/c) + A(Z,N) → p + (π+π-)bound + a lot more ...

p → | π+ + π- number of dissociated atoms

                                     ⋅
life time 1 µm corresponds to about 3⋅10-15 s

                                                     detection of dissociated
                                                      π
                                                     (π+π−)atoms in a double arm
                                                     magnetic spectrometer

                                                     as a function of the target thickness

                                                     targets: titanium foils of several µm




   WS 2009/2010               D. Gotta Tools in Hadron Physics                        8
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                                     WIRE CHAMBERS I

                                 electron multiplication
                                 around anode (fast)

                                 drift of ions (slow)

                                 typical ion drift velocity:
                                                 ⋅
                                  1 - 10 cm/(µs⋅kV)
                                 Ar CH4

multiplication → avalanche
gain 105 - 106




 to control avalanche
 quench gases, e.g. CO2, CH4, C2H6                                      wire chambers tutorial:
                                                                        F. Sauli
                                                                        CERN yellow report 99-07
    WS 2009/2010                     D. Gotta Tools in Hadron Physics                         9
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               WIRE CHAMBERS II

                                   tracking: cut on fiducial target volume

                                       example: π-3He → pnn or dn

                                                                    3He   vesssel


                                                                pn coincidences

                        beam defining counters
                        mainly π carbon reactions




                                                                dn coincidences




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                             DRIFT CHAMBERS I
time ⇔ position              trick: choose field configuration,
external time reference,     which keeps the nonlinearity of
e.g., plastic scintillator   time-to-position relation small      position resolution




 WS 2009/2010                D. Gotta Tools in Hadron Physics                     11
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                              DRIFT CHAMBERS II

improved position resolution by nearest 3 wires method
                                                                     inclined wires

                                               The wires are arranged in layers that
                                               pass through the cylinder at three
                                               different angles. The set of wires that
                                               give a signal can be used to allow
                                               computer reconstruction of the paths (or
                                               tracks) of all the charged particles
                                               through the chamber.


The "drift" in the name of this chamber refers to the time it takes electrons to drift to the
nearest sense wire from the place where the high-energy particle ionized an atom. Any three
sense wires are only nearby in one place so a set of "hits" on these three fix a particle track in
this region. By measuring the drift time, the location of the original track can be determined
much more precisely than the actual spacing between the wires.



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                        ATLAS - LHC
                     inflation in the number of channels




                                                           coils




               toroidal magnet configuration



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                                            STRAW TUBES
"simple" mechanics                   individual counters, timing 20 ns
10 MHz rate                          HV: coat, ground: sense wire (~ kV)
inside magnetic field                typical size: length 1 - 2 m, φ mm - cm

                                             Type-2 module (520 ‘straws’)
                              gas filling
                            e.g., Ar/C2H6
                                                                          ATLAS at the LHC
                                                                                             Monte Carlo
                                                                                              simulation

    Ileft      Iright
  resistive read out
     ∆z < 1 mm
                        z




                                                                      ZEUS - DESY wedge
   wall: aluminised mylar foils
   anode wire: φ ≈ 20 µm

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                                                   Track Cluster
Pixel Tracker
• Pixel Size
• Occupancy
• Charge Sharing
• S/N                                                                  Single Track
• ExB Drift
• Radiation Damage
  LHC - 1014 /cm2/yr

  & Trigger



                                charge center of gravity           Charge Sharing
                                             ⇓
                                high position resolution


Vertex Resolution
(20-30)µm IP
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           Pixel Tracking Detectors

•compact
•redundent
•fast readout
•reliable
•radiation hard

                                       b physics project Fermilab (CP violation)



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                SILICON MICRO - STRIP DETECTORS I

             principle        typical x-y (front-back)       miniaturisation
                                   arrangements
             pn diode                                               Readout Chip
                                   200 µm strips
     as almost all            layer thickness 300 µm                 Sensor
semiconductor detectors

charged
 particle

                                                             arrays of soldering dots



      + −



       − +




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              SILICON MICRO - STRIP DETECTORS II
                                                                             silicon µ-strip module
CMS - LHC scheme


 •inner tracker




ANKE - COSY



 •vertex detection
 •recoils
 •polarisation (left-right asymmetry)

                                                                    semiconductor telescope
                                                                    65/300/300/5500 µm thick
                                                                    double-sided Si-strip detectors

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               RICH - ring imaging Cerenkov hodoscope
        LHCb

                       Schematic of the mirror monitoring system

                                                                   transport




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                     TPC - time projection chamber                    David Nygren, 1974


idea:     avoid pile-up many MWPC planes (typical gas thickness of 1 cm)

principle: electrons produced follow the constant electric field lines to a single MPWC plane
           located at one end of the volume ( x-y coordinates on this plane)
          Third coordinate, z, from the drift time of the electrons to the anode plane

                                                                    STAR TPC - RHIC, Brookhaven




properties:
•full 3-dimensional detector
•constant drift velocity due to the collisions
 in the gas mixture (typical a few cm/µs).
•low occupancy even for high background (high rates)
•large dE/dx due to large gas thickness (particle identification)

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               ALICE - LHC




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                BABAR - SLAC/PEP → PANDA - FAIR ( pp)
                final example




 e + e − → DD + ...

D mesons contain a b quark

DD oscillations
measure
strength of
CP violation
(like K K )




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Todays detectors comprise ...
•Silicon Vertex Tracker (SVT) - provides precise position information on
charged tracks, and is also the sole tracking device for very low-energy
particles.
•Drift Chamber (DCH) - provides the main momentum measurements for
charged particles and helps in particle identification through dE/dx
measurements.
•Detector of Internally Refected Cerenkov radiation (DIRC or DRC) -
provides charged hadron identification.
•Electromagnetic Calorimeter (EMC) - provides particle identification for
electrons, neutral electromagnetic particles, and hadrons.
•Solenoid (not a subdetector) - provides the 1.5 T magnetic field for needed
for charge and momentum measurements.
•Instrumented Flux Return (IFR) - provides muon and neutral hadron
identification.
• ...
               ... and more

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