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Time Projection Chambers Antoni Aduszkiewicz University of Warsaw February 4-11, 2012 48th Karpacz Winter School of Theoretical Physics Antoni Aduszkiewicz (University of Warsaw) Time Projection Chambers February 4-11, 2012 1 / 13 Plan
Antoni Aduszkiewicz
University of Warsaw
February 4-11, 2012 48th Karpacz Winter School of Theoretical Physics
Antoni Aduszkiewicz (University of Warsaw) Time Projection Chambers February 4-11, 2012 1 / 13
Time Projection Chambers: What they are and how they work? What information we can obtain from them and how do we do it? TPCs in various experiments
Antoni Aduszkiewicz (University of Warsaw) Time Projection Chambers February 4-11, 2012 2 / 13
tracks reconstructed in the set of TPCs in NA61/SHINE
Charged particle 3-dimensional tracking detector Trajectory in the magnetic field → measurement of charge and momentum Energy loss in the gas in the chambers → mass identification
Antoni Aduszkiewicz (University of Warsaw) Time Projection Chambers February 4-11, 2012 3 / 13
R R R R R R R 1 . p r i m a r y p a r t i c l e i
i s e s t h e g a s electric field (drift) magnetic field field cage plate readout plane measured particle HV Voltage divider for the field cage
Charged particle detaches electrons from the atoms of the gas (ionisation) The electrons drift in the homogeneous electric field towards the readout plane Magnetic field (if any) should be parallel to the electric field, so it doesn’t affect the drift The position of the registered signal on the readout plane allows to reconstruct the track trajectory in two dimensions (perpendicular to the drift) The third coordinate (parallel to the drift) is calculated by multiplying the time of the signal by the drift velocity of the electrons
Antoni Aduszkiewicz (University of Warsaw) Time Projection Chambers February 4-11, 2012 4 / 13
At the end of drift the electrons reach thin ( ∼ 20µm) sense wires near the readout plane. The electric field is very high close to a thin wire: E(r) ∼ HV/r Electrons accelerate in the electric field and ionise atoms of the gas. The process repeats creating an avalanche of electrons. As the electrons get collected on the wire, they generate an electromagnetic pulse on the read-out pads, high enough to be registered by the electronics. The gas amplification effect is used in many other detector types: (multi-)wire chambers, Geiger counters, resistive plate chambers, GEM. . .
Antoni Aduszkiewicz (University of Warsaw) Time Projection Chambers February 4-11, 2012 5 / 13
Theoretical Landau distribution Experimental Landau distribution (measurement of a single particle!) Energy deposited in the primary ionisation given by the Landau distribution – very wide, asymmetric. Usually the long tail has to be truncated in order to obtain stable mean value
Antoni Aduszkiewicz (University of Warsaw) Time Projection Chambers February 4-11, 2012 6 / 13
source: PDG 2010
Average energy loss dependent on the particle velocity, given by the Bethe-Bloch formula (PDG 2010 27.3):
−
dx
A 1
β 2 ·
2 ln 2mec2β 2γ2Tmax I2
−β 2 − δ(βγ)
2
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0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 0.2 0.5 1 2 5 10 20 50 100
dE/dx plab [GeV/c]
e π K p
5 10 15 20 25 30 1 1.2 1.4 1.6
Entries dE/dx p K π
xF=0.05 pT=1.7 GeV/c plab=20 GeV/c
b)
Eur.Phys.J.C45:343-381,2006
The distributions are scattered due to large width of the Landau distribution Energy loss allows to extract particle yields, but not identify each particle ambiguously. Problems in the regions where curves are close to each other and cross Fits have to be done carefully
Antoni Aduszkiewicz (University of Warsaw) Time Projection Chambers February 4-11, 2012 8 / 13
~13 m MTPC-R MTPC-L VTPC-2 VTPC-1 Vertex magnets GAP TPC T arget Beam
B E
interior of one of the MTPCs (during construction)
5 cuboid TPCs 2 VTPCs and GAP TPC placed in superconducting magnets (up to 1.5 T). Tracks are curved allowing momentum reconstruction 2 big MTPCs measure long straight tracks for good energy loss (dE/dx) measurement Magnetic and electric fields perpendicular to the beam line.
Antoni Aduszkiewicz (University of Warsaw) Time Projection Chambers February 4-11, 2012 9 / 13
2 big TPC around the beam line Magnetic and electric fields parallel to the beam line.
arXiv:1001.1950v1 [physics.ins-det] Antoni Aduszkiewicz (University of Warsaw) Time Projection Chambers February 4-11, 2012 10 / 13
TPCs filled with about 600 tons of liquid argon which serves both as a working medium, as well as a target for the neutrinos TPC readout directly from 3 planes of wires, with no gas amplification Data aquisition triggered by measurement of argon scintillation
Antoni Aduszkiewicz (University of Warsaw) Time Projection Chambers February 4-11, 2012 11 / 13
The gas amplification process generates photons, which are detected using a CCD camera (single image) and a photomultiplier
Antoni Aduszkiewicz (University of Warsaw) Time Projection Chambers February 4-11, 2012 12 / 13
Time Projection Chambers: Charged particle 3-dimensional tracking detector Detection based on: ionisation, electron drift and gas amplification Measurement of momentum (with magnetic field) and mass identification Low mass (gas), large volume Spatial resolution ∼ 100µm Long time of collecting information (order of 50µs) due to relatively slow electron drift Many applications, the basic concept can be extended in many ways
Antoni Aduszkiewicz (University of Warsaw) Time Projection Chambers February 4-11, 2012 13 / 13