Commissioning with cosmic rays of the Muon Spectrometer

Commissioning with cosmic rays of the Muon Spectrometer of the ATLAS Experiment at LHC Luca Spogli Università Roma Tre & INFN Roma Tre LNF Frascati Spring School 2007

Outline o o o The ATLAS experiment at LHC Muon Spectrometer Commisioning Status Test with cosmic rays Summary 2

ATLAS detector Electromagnetic Calorimeter Muon Spectrometer Solenoid Barrel Toroid Inner Detector Forward Calorimeter Endcap Toroid Hadronic Calorimeter Radiation Shielding 3

MDT (Monitored Drift Tubes) o good space resolution (~100 μm per point) n pt/pt 2 -3% @ pt<200 Ge. V/c n pt/pt 10% @ pt 1 Te. V/c ~1200 chambers / ~7000 m 2 Tubes per layer Layer per multilayer Chamber lenght (mm) Chamber heigth (mm) h=1. 4 h=1 MDT RPC TGC ECT CSC 4

MDT Calibration: r(t) o o Drift time measurement Determination of space-time rt-relation with a typical accuracy of 10µm relationship r(t) via autocalibration Time measurement 5

Muon Reconstruction In a single multilayer Track segments MDT mutilayer Momentum measurement from sagitta determination p=0. 3 Br 6

Installation and commissioning o o Installation in the pit started in Summer 2005 First tests with cosmic muons during Summer 2006 First curved muon (magnetic field on) in November 2006 MDT chamber installation completed in the barrel region 7

Installation o It is not an easy task. . . 8

Cosmics o o o 19 -20 November data Sector 13 with RPC timing informations Magnetic field on-off ~1 Mevents 9 chambers Many tests on MDT’s n n n o Drift behavior Calibration Efficiency Noise Dead channels Preliminary alignment Some results in this talk Sector 13 Side A 9

Event Display BIL chamber 10

Fired tubes per event. . . after noise reduction cuts Accidental trigger coincidences 4 multilayers 2 multilayers 6 multilayers Number of Fired Tubes / event 11

Impact of magnetic field on r(t) B field expected to change drift-toradius relationship by Lorentz angle o o B field parallel to the wire Electrons do not travel straight forward radially They travel under an angle ψ Drift time t for a certain radius r increases τ: mean time between collisions 12

Measured muon spectra µµ+ Z coordinate Momentum (Ge. V) Ratio of µ+ / µ- = 1. 48± 0. 27 v. According to P. D. G Charge ratio of cosmic ray muons is between 1. 1 - 1. 4 from 1 to 100 Ge. V v Effects of geometrical acceptance have to be taken into account Small shaft Big shaft 13

Muons coming from the shafts, are deviated in the upper part of Muon Spectrometer before ending in sector 13; due to the magnetic field µ+, µ- result in different angles. Small shaft ~12 m Big shaft ~18 m Surface-Pit ~100 m SIDE A SIDE C Sector 13 Side A 14

Conclusions o o Barrel installations is completed Test with cosmic muons: complete analysis of sector 13 data Systematic study of the MDT performance over the all barrel sectors (magnetic field off) Further tests with cosmics in June with B field on. 15

Backup slides. . . 16

Higgs @ 114. 1 Ge. V < m. H < 1 Te. V Energy per Proton 7 Te. V Bunch spacing 25 ns Bunch size 15 m 12 cm Protons per bunch 1011 Bunches per ring 2835 Beam mean life Project Luminosity Circumference Collisions per bunch 10 hours 1034 cm-2 s-1 27 Km 25 Detection of Higgs decay final states: H ZZ 4µ “Golden Channel” 17

MDT (Monitored Drift Tubes) o o o o two multilayers of 3 (in Middle and Outer rings) or 4 (in the Inner ring) layers of staggered drift tubes each. thin wall (400 μm thick) 3 cm diameter aluminum tubes. low longitudinal diffusion gas mixture, 93%Ar− 7%CO 2, absolute pressure of 3 bar. Gold-plated W-Re anode wire, 50 μm diameter is tensioned at 350 g crimped in copper pins. low gas gain of 2× 104 (3080 V andode voltage) to avoid ageing effects. good space resolution (~100 μm per point) robust and reliable operation for many years (no ageing problems). ~1200 chambers / ~5500 m 2 Tubes per layer Layer per multilayer Chamber lenght (mm) Chamber heigth (mm) 18 From F. Petrucci

Impact of resolution Space resolution ~100 micron From TDR Transverse momentum resolution Z mass resolution (combined with Inner Detector tracking) Z->µµ Invariant Mass (Ge. V) 19

ATLAS Installation Schedule 9. 1 20

Setup o 13 Muon stations read-out BIL 3 BIL 2 BIL 1 Side A BML h=0 BOL 3 BOL BOF BML 3 BOF 1 21 From R. Nikolaidou

ADC counts TDC vs ADC spectrum Signal “double hits” When a tube has a second hit in the same event. Noise Background TDC counts 22 From C. Bini

Magnetic field map Magnetic field strongly inhomogeneous, in particular in BILs! 23 From C. Bini

Angle of tracks µ+ Muons coming from the small shaft Big shaft µAngle of tracks with respect to vertical axis. Shift in spectrum for different signs (run with magnetic field on) degrees µµ+ Angle of tracks: superposition of run with and without magnetic field • µ- µ+ run with magnetic field on • µ run with no magnetic field 24 From R. Nikolaidou