Status and First Results of Atlas at LHC
Outline• Atlas Collaboration• Atlas Experiment Physics Goals• Atlas Detector
• LNF Contribution to the Atlas Detector• Analysis Activity of the Atlas LNF Group
• Detector Status• Detector Commissioning with Cosmic Rays
• LHC runs • First results with LHC data
• Conclusions
Bellisario Esposito
LNF , 2 February 2010 1
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Albany, Alberta, NIKHEF Amsterdam, Ankara, LAPP Annecy, Argonne NL, Arizona, UT Arlington, Athens, NTU Athens, Baku, IFAE Barcelona, Belgrade, Bergen, Berkeley LBL and UC, HU Berlin, Bern, Birmingham, UAN Bogota, Bologna, Bonn, Boston, Brandeis, Brasil Cluster, Bratislava/SAS Kosice, Brookhaven NL, Buenos Aires, Bucharest, Cambridge, Carleton, CERN, Chinese Cluster, Chicago, Chile, Clermont-Ferrand, Columbia, NBI Copenhagen, Cosenza, AGH UST Cracow, IFJ PAN Cracow, SMU Dallas, UT Dallas, DESY, Dortmund, TU Dresden, JINR Dubna, Duke, Edinburgh, Frascati, Freiburg, Geneva, Genoa, Giessen, Glasgow, Göttingen, LPSC Grenoble, Technion Haifa, Hampton, Harvard, Heidelberg, Hiroshima IT, Indiana, Innsbruck, Iowa SU, Iowa, UC Irvine, Istanbul Bogazici, KEK, Kobe, Kyoto, Kyoto UE, Lancaster, UN La Plata, Lecce, Lisbon LIP, Liverpool, Ljubljana, QMW London, RHBNC London, UC London, Lund, UA Madrid, Mainz, Manchester, CPPM Marseille, Massachusetts, MIT, Melbourne, Michigan, Michigan SU, Milano, Minsk NAS, Minsk NCPHEP, Montreal, McGill Montreal, RUPHE Morocco, FIAN Moscow, ITEP Moscow, MEPhI Moscow, MSU Moscow, Munich LMU, MPI Munich, Nagasaki IAS, Nagoya, Naples, New Mexico, New York, Nijmegen, BINP Novosibirsk, Ohio SU, Okayama, Oklahoma, Oklahoma SU, Olomouc, Oregon, LAL Orsay, Osaka, Oslo, Oxford, Paris VI and VII, Pavia, Pennsylvania, Pisa, Pittsburgh, CAS Prague, CU Prague, TU Prague, IHEP Protvino, Regina, Rome I, Rome II, Rome III, Rutherford Appleton Laboratory, DAPNIA Saclay, Santa Cruz UC, Sheffield, Shinshu, Siegen, Simon Fraser Burnaby, SLAC, NPI Petersburg, Stockholm, KTH Stockholm, Stony Brook, Sydney, Sussex, AS Taipei, Tbilisi, Tel Aviv, Thessaloniki, Tokyo ICEPP, Tokyo MU, Tokyo Tech, Toronto, TRIUMF, Tsukuba, Tufts, Udine/ICTP, Uppsala, UI Urbana, Valencia, UBC Vancouver, Victoria, Waseda, Washington, Weizmann Rehovot, FH Wiener Neustadt, Wisconsin, Wuppertal, Würzburg, Yale, Yerevan
~ 2900 scientists (~1000 students), 172 Institutions, 37 countries
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1989 : Detector R&D starts 1992 : Letter of Intent 1994 : Technical Proposal 1996 : ATLAS approved by CERN DG and Research Board 1997 : Construction starts 2003 : Installation in the underground cavern starts 2008 : Installation completed cosmics runs with full detector operational September 2008 : LHC single-beam events recorded
20 years of efforts of the worldwide
ATLAS scientific community
Nov. 2009 : first LHC collisions recorded
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Since 20 November: a fantastic escalation of events ….
Atlas Physics goals
• Search and discover of: – the Higgs Boson for masses ~ 0.1-1 TeV– Supersymmetry – New Physics foreseen by other models beyond SM
• Precision measurements of SM processes
• To detect and measure unexpected effects due to unforeseen scenarios
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General purpose large complex detector
To exploit the full physics potential of LHC
ATLAS Detector
EM Calorimeters/E 10%/E(GeV) 0.5% Inner Detector: /pT 3.410-4 pT (GeV) 0.015 Impact parameter resolution
(d0)= ) 10 140/ pT (GeV) m
Stand-alone Muon Spectrometer,
/pT 10% at 1 TeV/c
Hadron Calorimeters, /E 50% / E(GeV) 3%
Magnets: solenoid (Inner Detector) 2T, 3 air-core toroids (Muon Spectrometer) ~0.5T
Tracking (||<2.5) Si Pixel and strips (SCT) Transition radiation tracker (TRT) Calorimetry (||<5) EM : Pb-Lar HAD : Fe/scintillator (central) , Cu/W-LAr (fwd)Muon Spectrometer (||<2.7) MDT CSC for tracking RPC TGC for triggering
To observe new heavy resonance X as “narrow” peak
L~5m
B~0.5T
zy
L~5m
B~0.5T
zy
zy
/p<10% for E~ 1 TeV
/p /p ~10% ~50 m alignment accuracy to ~30m
ATLAS Muon Spectrometer:E ~ 1 TeV sagitta ~500 m
Momentum measurement in the Muon Spectrometer
Stringent specification on the mechanical precision of the muon chambers σwire position < 20 μm
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Barrel Muon Spectrometer 700 precision chambers (MDT) 600 trigger chambers (RPC)
The MDT precision tracking chambersand the LNF contribution
LNF contribution: Conceptual design , R&D, final design of the assembly Design and construction of the facilities for the series production and QA/QC
Construction and of the the BML (Barrel Middle Large) chambers:94 BML area=600 m2 6 layers of tubes 28000 tubes
Installation and commissioning of the chambers in the Atlas detector
The MDT chambers are large area assembly of high pressure drift tubes with wire positioning specification: < 20 um rms
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The high level work of the LNF technical staff has been fully recognised by the Atlas Collaboration and the contribution of our Group technicians, the SPAS mechanical design service, the SSCR mechanical design service, workshop, metrology service and the Automation service has to be duly aknowledged.
3.6 m
1.7 m
Automated Tube Wiring Machine Chamber Assembly Table
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MDT Chamber mechanical precision checked with the Cern X-ray tomograph
Wire position fluctuation with respect to the nominal grid
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LNF analysis activity
H4l Higgs boson search h/A0 Supersimmetric Higgs boson search Z’ New Z Bosons search (Thesis)Lepton Flavour violation search (PhD Thesis)Z ,W measurement of Z , W production
Muon chamber and Muon Spectrometer performances from test beam and cosmics data analysis MDT tube calibration, Sagitta resolution
Development of methods for in-situ calibration of the Muon Spectrometer using events Z->µµ , J/ψ-> µµ Determination of the Muon spectrometer performance, Muon track reconstruction efficiency, Trigger efficiency, Momentum scale, Missing Et performance and corrections
Physics processes
Detector aspects
Developed analysis algorithms for : Signal/Background separation, data driven background subtraction, trigger, selection and reconstruction efficiency correction, expected signal significance estimation for given integrated luminosity
(In collaboration with other Atlas groups within the Atlas working groups Documented in Notes and papers)
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H ZZ* 4l
MH = 130 GeV MH = 150 GeV
MH = 180 GeV MH = 300 GeV
The ATLAS discovery potential for MSSM neutral Higgs bosons decaying to a mu+mu- pair in the mass range up to 130 GeV.
Eur. Phys. J. C 52, 229-245 (2007)
Previsione: bb A/h/H ==> bb +-
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Measurement of Z and W cross section
Z selection1. One triggering muon with pT> 20 GeV2. A second muon with pT> 15 GeV3. Cut on muon isolation4. M> 30 GeV
W selection1. One triggering muon with pT> 20 GeV2. Missing ET far from Jet3. Cut on muon isolation4. MT above 10 GeV
Goal: Get ready for first “good” 15 pb-1. Status: Most of the analysis code completed and running on grid.
Developing algorithms for signal selection and for the evaluation from the data of the efficiency and background
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Ongoing study of track and cluster efficiency track to cluster association criteria, calorimeter energy subtraction, fakes ...Already very promising results
Missing ET using Energy Flow
Z PT(MeV)
<ME
TL >
(MeV
)
Standard reconstruction Energy flow
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Detector status fully operational
Commissioning with cosmics
Simulation of 10 ms of cosmics through ATLAS
Started in 2005:• Understand/Fix the hardware while
installing.
Large number (>500M) of Cosmics collected in 2008 and in 2009.
• Understand the initial calibrations and alignment.
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Pixels alignment with cosmics
residualsbefore alignment
residualsafteralignment
MC (perfect detector)
SCT alignement with cosmics
MDT alignment with cosmics
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Momentum resolution determination from cosmics
Inner Detector Muon Spectrometer standalone
Resolution on the parameters of tracks is obtained from cosmics comparing up and bottom track segments
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LHC data
2009 LHC run
2008 LHC start upSep 2008: single beam splash
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Beam bunches stopped by (closed) collimators upstream of experiments “splash” events in the detectorsTiming studies with beam-splash events
First ATLAS beam splash event, recorded 10 Sep 08
tertiarycollimators
140 mBeam pick-ups (BPTX) (175 m)
Beam splash
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Monday 23 November: first collisions at √s = 900 GeV ! ATLAS records ~ 200 events (first one observed at 14:22)
Two beams in the machine, how to detect a collision event? • Trigger synchronized with beam pickup signals (suppresses
cosmics)• Separation of beam-related backgrounds and collisions via
timing measurements on A and C sides of ATLAS (ToF)– Use minimum bias scintillators (MBTS) in forward regions
(use also multiplicity)– Use precise Liquid-argon endcap calorimeter timing
MBTS: t(A – C) LAr calorimeter: t(A – C)
Mean: 1.1 ± 0.1 nsSigma: 1.5 ± 0.1 nstwo beams
z ~ 7m
ns
z ~ 9m
ATLAS preliminary
ATLAS preliminary
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Detector in READY with STABLE BEAM
Sunday 6 December: machine protection system commissioned stable (safe) beams for first time full tracker at nominal voltage whole ATLAS operational
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8, 14, 16 December: collisions at √s = 2.36 TeV (few hours total)ATLAS records ~ 34000 events at flat-top
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Spot size ~ 250 μm
Trigger
Scintillators (Z~± 3.5 m):rate up to ~ 30 Hz
Collision trigger (L1)
Online determination of the primary vertex and beam spot using L2 trigger algorithms
High-Level Trigger in rejectionmode (in addition, running > 150 chains in pass-through)
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Recorded data samples Number of Integrated luminosity events (< 30% uncertainty)
Total ~ 920k ~ 20 μb-1
With stable beams ~ 540k ~ 12 μb-1
At √s=2.36 TeV ~ 34k ≈ 1 μb-1
Average data-taking efficiency: ~ 90%
Max peak luminosity seen by ATLAS : ~ 7 x 1026 cm-2 s-1
Collected LHC Collision Data
Inner Detector alignment in the Barrel
Inner Detector
p
K
π
180k tracks
Pixels Transition Radiation Tracker
Transition radiation intensity is proportional to particle relativistic factor γ=E/mc2. Onset for γ ~ 1000
Particle separation by dE/dx in Pixels
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γ e+e- conversions
e+
e- γ conversion pointR ~ 30 cm (1st SCT layer)
pT (e+) = 1.75 GeV, 11 TRT high-threshold hitspT (e-) = 0.79 GeV, 3 TRT high-threshold hits
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γ e+e- conversion point
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pT (track) > 100 MeVMC signal and background normalized independently 32
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π0 γγ
■ 2 photon candidates with ET (γ) > 300 MeV■ ET (γγ) > 900 MeV■ Shower shapes compatible with photons■ No corrections for upstream material
Data and MC normalised to the same area
Note: soft photons are challenging because of material in front of EM calorimeter(cryostat, coil): ~ 2.5 X0 at η=0
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Jets
√s=2.36 TeV √s=2.36 TeV
√s=900 GeV
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Uncalibrated EM scaleMonte Carlo normalized to number of jets or events in data
events with2 jets pT> 7 GeV
Jets
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Good agreement in the (challenging) low-Eregion indicates good description of material and shower physics in G4 simulation(thanks also to years of test-beam …)
Shower width in strip units (4.5mm)
Photon candidates: shower shape in the EM calorimeter
Isolated hadrons : E(calorimeter)p(tracker)
|η| < 0.8, 0.5 < pT < 10 GeV Cluster energy at EM scale
Electron candidates: transition radiation signal in TRT
More comparisons data – simulation:fundamental milestone for solid physics measurements
Monte Carlo and data normalized to same area
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ConclusionsAfter 20 year work for designing, building, installing and commissioning the detector the Atlas experiment has started to collect data at LHC.
The detector is fully operational and performs as expected.
The analysis of the first collected data is on-going.
The Atlas Collaboration eagerly look forward to integrating larger luminosity.
