Commissioning and Performance of the ATLAS Transition Radiation Tracker with High Energy Collisions at LHC

Transcription

1 Commissioning and Performance of the ATLAS Transition Radiation Tracker with High Energy Collisions at LHC 1 A L E J A N D R O A L O N S O L U N D U N I V E R S I T Y O N B E H A L F O F T H E A T L A S C O L L A B O R A T I O N 1 2 T O P I C A L S E M I N A R O N I N N O V A T I V E P A R T I C L E A N D R A D I A T I O N D E T E C T O R S ( I P R D 1 0 ) J U N E S I E N A, I T A L Y

2 ATLAS Inner Detector TRT Timeline How the TRT works Tracking Particle Identification Summary Outline 2

3 ATLAS InnerDetector 3 2T Solenoid Field TRT goals: Momentum resolution: σ(p T )/p T = 0.05%p T 1% Charged track above 0.5 GeV/c, η <2 Electron identification : η <2 p > 1 GeV/c

4 Transition Radiation Tracker 4 TRT Barrel: 3 layers * 32 ϕ modules 1.44m long straws parallel to beam axis Wires electrically split in the middle to reduce occupancy (1.5cm dead region) Each straw has an independent readout on both ends readout channels 2 TRT end-caps, each with: 20 wheels with 8 layers of straws each 39cm long radial straws readout channels

5 TRT Design Accurate pt measurement: Long arm needed Many hits ~30 TRT hits per track Effect measured in Cosmics Provide Electron Identification Very high occupancy: up to 30% Very high counting rate: up to 20 MHz/straw Time between bunch crossings: 25 ns Minimal amount of material (in radiation lengths) Radiation environment: ~10MRad, ~10 14 n/cm 2 year Fast and chemically passive straw gas: Ageing Chemically resistant straw materials Extremely precise and robust mechanical structure Tolerances < 30 µm Temperature stability: cooling 5

6 Timeline 1989: R&D for the TRT begins (1990: RD6) : LHC machine approved. First full-size TRT prototype completed ( channels for end-cap wheel) : Major Technical Design Reports for ATLAS construction approved 2000: Assembly of barrel modules and end-cap wheels start. Front-end electronics specified and vendor chosen. 2006: First cosmic tracks recorded 2006: Installation of barrel ID in ATLAS 2007: Installation of ID end-caps in ATLAS 2008: TRT routinely operated Various Milestones Cosmics runs September 10 th 08: First LHC beam seen (beam splashes) 2009: Stable Operation Spring/Summer Cosmic Combined runs October ATLAS 24/7 Operation First proton collision at 900 GeV!!!!!!!!!!! 2010: Stable 24/7 Operation First high energy proton collision (7TeV)!!!!!!!!!!!!!!

7 Timeline 1989: R&D for the TRT begins (1990: RD6) : LHC machine approved. First full-size TRT prototype completed ( channels for end-cap wheel) : Major Technical Design Reports for ATLAS construction approved Beam Splash: ~100 events per straw Used for timing the whole TRT 2000: at once Assembly of barrel modules and end-cap wheels start. Front-end electronics specified and vendor chosen. 2006: First cosmic tracks recorded 2006: Installation of barrel ID in ATLAS 2007: Installation of ID end-caps in ATLAS 2008: TRT routinely operated Various Milestones Cosmic runs September 10 th 08: First LHC beam seen (beam splashes) 2009: Stable Operation Spring/Summer Cosmic Combined runs October ATLAS 24/7 Operation First proton collision at 900 GeV!!!!!!!!!!! 2010: Stable 24/7 Operation First high energy proton collision (7TeV)!!!!!!!!!!!!!!

8 Timeline 1989: R&D for the TRT begins (1990: RD6) : LHC machine approved. First full-size TRT prototype completed ( channels for end-cap wheel) : Major Technical Design Reports for ATLAS construction Fast-OR approved TRT Level 1 trigger developed: Ready November 2008 Number of cosmic tracks 2000: Assembly of barrel modules and end-cap wheels start. doubled in 1 week Front-end electronics specified and vendor chosen. 2006: First cosmic tracks recorded 2006: Installation of barrel ID in ATLAS 2007: Installation of ID end-caps in ATLAS 2008: TRT routinely operated Various Milestones Cosmic runs September 10 th 08: First LHC beam seen (beam splashes) 2009: Stable Operation Spring/Summer Cosmic Combined runs October ATLAS 24/7 Operation First proton collision at 900 GeV!!!!!!!!!!! 2010: Stable 24/7 Operation First high energy proton collision (7TeV)!!!!!!!!!!!!!!

9 Timeline 1989: R&D for the TRT begins (1990: RD6) : LHC machine approved. First full-size TRT prototype completed ( channels for end-cap wheel) : Major Technical Design Reports for ATLAS construction approved 2000: Assembly of barrel modules and end-cap wheels start. Front-end electronics specified and vendor chosen. 2006: First cosmic tracks recorded 2006: Installation of barrel ID in ATLAS 2007: Installation of ID end-caps in ATLAS 2008: TRT routinely operated September 09-September 08: Various Milestones Cosmic runs September 10 th 08: First LHC beam seen (beam splashes) 2009: Stable Operation Spring/Summer Cosmic Combined runs October ATLAS 24/7 Operation First proton collision at 900 GeV!!!!!!!!!!! 2010: Stable 24/7 Operation First high energy proton collision (7TeV)!!!!!!!!!!!!!!

10 Timeline 1989: R&D for the TRT begins (1990: RD6) : LHC machine approved. First full-size TRT prototype completed ( channels for end-cap wheel) : Major Technical Design Reports for ATLAS construction approved 2000: Assembly of barrel modules and end-cap wheels start. Front-end electronics specified and vendor chosen. 2006: First cosmic tracks recorded 2006: Installation JiveXML_152166_ link.png of barrel ID in ATLAS 2007: Installation of ID end-caps in ATLAS 2008: TRT routinely operated September 07- September 08: Various Milestones Cosmics runs September 10 th 08: First LHC beam seen (beam splashes) 2009: Stable Operation Spring/Summer Cosmic Combined runs October ATLAS 24/7 Operation First proton collisions recorded (900GeV)!!! 2010: Stable 24/7 Operation First high energy proton collisions (7TeV)

11 How the TRT works 11 4 mm 30 µm Pulse height Ç Particle Arrival T 0 T Drift High Threshold (HT) at 6keV Ç Low Threshold Ç (LT) at 300eV Time Measured Time Over Threshold Ç Ç 4 mm straws with drift time (T drift ) measurement for increased spatial resolution T 0 depends on ToF, cable lengths, electronic delay Different for each straw May change from run to run: Calibrated every 24h

12 TRT Event phase 12 4 mm TRT event phase: Measure of the time of the interaction Including readout window offset and time of flight effects 30 µm

13 TRT R-T dependency 13 4 mm 30 µm Convert T Drift to drift radius used in tracking Gas composition, gas conditions and magnetic field dependent Can change with time and straw to straw Calibrated every 24h Very stable Same performance 900GeV/7TeV

14 TRT Performance (Resolution) TRT unbiased spatial residuals During cosmic runs a good understanding of the barrel was achieved Cosmic rays studies did not allow to study end-caps in detail, further commissioning is required to achieve similar performance as barrel 5 microns improvement 900GeV/7TeV Track selection: p T > 1GeV d 0 <5mm; Silicon hits >= 7 hits; TRT hits>= 14 hits 14 1$2#)34)25'67#)8)-9)µ+) 1$2#)34)25'67#)8)-9)µ+) < ;... : >... =... < ;... D'2')9.-. EF1G89/:0A-;9)µ+ G342")H'5(3 EF1G89/:0A-;:)µ+ ATLAS)=5"($+$4'5>?!?)@'55"( #)A)B)?"C!-!./0../0 -!"#$%&'()*++, E'2')9.-. FG1H89/:0C-<-) µ+ H342")I'5(3 FG1H89/:0C-:0)µ+ ATLAS)?5"($+$4'5@ A!A)"4%!6'B# #)C)=)A"D : !-!./0../0 -!"#$%&'()*++,

15 TRT Performance (Efficiency) 15 Number of straws with a hit on track divided by the number of straws crossed by the track. The 2% of known non- functioning straws are excluded from this study Same performance 900GeV/7TeV The tracks selection: Pixel hit >=1 SCT hits >=6 TRT hits >=15 pt > 0.5 GeV d0 < 10 mm z0 < 300 mm

16 Particle Identification 16 Transition Radiation: Photon emitted by a charged particle when traversing the boundary between material with different dielectical constants (ε 1, ε 2 ) Intensity: I ~ γ=e/m, θ ~ 1/γ Emitted photos per transitions ~O(α em γ) Many transitions needed Oriented fibers for barrel Regular foils for endcaps Emitted Energy: ~(ε 1 - ε 2 ) TRT: Gas and light plastic, Photon Energies: 10-30keV Pulse height Ç Time Over Threshold Ç High Threshold (HT) at 6keV Ç Low Threshold Ç (LT) at 300eV Time Bit Ç (3.15ns) Gas with great photon absorption required: Xe(70%) CO 2 (27%) O 2 (3%) High Threshold, requires calibration Rejection power optimal in a short range of threshold values depend on TR energy, gas properties.

17 TR onset curve Probability of TRT HT hit as a function of γ = E/m, Above γ=1000, pure sample of electrons obtained from conversions Low values of gamma: all selected tracks in the event are used (assumed pion mass) TRT to separate electrons from pions over a momentum range between 1 GeV and 150 GeV Track is identified as an electron when %HT hits >12 Endcaps: -More conversions and higher momentum because more amount of material and boost in the forward direction Saturation of the TR production steeper in the endcap than for the barrel because different materials used 17 e - region e - region

18 Particle Identification (2) 18 Time Over Threshold (TOT) TOT corrected for z effects on the straws and divided by transverse length in the straws Pion candidates: SCT hits >3 TRT hits >20 Tracks from conversions are rejected Electron candidates: Part of a double track conversion Selection performance in MC: Pion selection: 80.5% pions 11.3% kaons 6.9% are protons 1.3% are other particles. Electron selection: 99.6% electrons.

19 TRT PID: Z ee Candidate 19

20 Summary 20 Very successful commissioning process have been accomplish in the last years Good understanding of the detector achieved with Cosmic Rays (barrel) and Collisions TRT is operating smoothly on a 24/7 basis since September 2009 thanks to the great and devoted TRT Team!!! Many studies ongoing to improve TRT performance Many analyses of first data already make use of the excellent TRT performance Ready to collect data for at least next 10 years!!!!!!!

21 BACKUP 21

22 Importance of TRT, Pt resolution 22 p x!(q/p) Split tracks Data, full ID Data, Si only Simulation, full ID ATLAS Preliminary Cosmic p T [GeV]

23 W eν Candidate 23