1. ATLAS through first data
Fabiola Gianotti
(on behalf of the ATLAS Collaboration)

2. > 20 years of efforts of the worldwide ATLAS scientific community,
supported by Funding Agencies and Governments
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

3. Since 20 November: a fantastic escalation of events ….

4. Monday 23 November: first collisions at √s = 900 GeV !
ATLAS records ~ 200 events (first one observed at 14:22)

5. Sunday 6 December: machine
protection system commissioned
stable (safe) beams for first time
full tracker at nominal voltage
whole ATLAS operational

7. 8, 14, 16 December: collisions at √s = 2.36 TeV (few hours total)
ATLAS records ~ events at flat-top
Jet1: ET (EM scale)~ 16 GeV, η= -2.1
Jet2: ET (EM scale) ~ 6 GeV, η= 1.4

8. Detector is fully operational
Online detector
control panel
Pixels and Silicon strips (SCT) at nominal voltage only with stable beams
Solenoid and/or toroids off in some periods
Muon forward chambers (CSC) running in separate partition for rate tests

9. Average data-taking efficiency: ~ 90%
Max peak luminosity
seen by ATLAS :
~ 7 x 1026 cm-2 s-1
Recorded data samples Number of Integrated luminosity
events (< 30% uncertainty)
Total ~ 920k ~ 20 μb-1
With stable beams ( tracker fully on) ~ 540k ~ 12 μb-1
At √s=2.36 TeV (flat top) ~ 34k ≈ 1 μb-1
Average data-taking efficiency: ~ 90%

10. In the following: few examples from
large number of (preliminary)
detector performance results
obtained in only a few days ….

11. Trigger Online determination of the primary vertex and beam spot
High-Level Trigger in rejection
mode (in addition, running > 150
chains in pass-through)
Collision trigger (L1)
Scintillators
(Z~± 3.5 m):
rate up
to ~ 30 Hz
Online determination of the
primary vertex and beam spot
using L2 trigger algorithms
Spot size ~ 250 μm

12. Worldwide data distribution and analysis
5/6/2018
Worldwide data distribution and analysis
WLCG
MB/s
per day
Total data throughput through the Grid (Tier0, Tier-1s, Tier-2s)
Beam splashes
First collisions
Nov.
Dec.
Cosmics
End of data
taking
~ 0.2 PB of data stored since 20th November
~ 8h between Data Acquisition at the pit and data arrival at Tier2
(including reconstruction atTier0)
increasing usage of the Grid for analysis 12

13. Inner Detector Silicon strips Pixels Transition Radiation Trackerπ
180k tracks
Pixels
Transition Radiation Tracker
Transition radiation intensity is proportional
to particle relativistic factor γ=E/mc2.
Onset for γ ~ 1000

14. MC signal and background normalized independently
pT (track) > 100 MeV
MC signal and background normalized independently
K0S Λ

15. γ  e+e- conversions e- e+ γ conversion point
R ~ 30 cm (1st SCT layer)
pT (e+) = 1.75 GeV, 11 TRT high-threshold hits
pT (e-) = 0.79 GeV, 3 TRT high-threshold hits

16. π0  γγ 2 photon candidates with ET (γ) > 300 MeV
Shower shapes compatible with photons
No corrections for upstream material
Note: soft photons are
challenging because of
material in front of
EM calorimeter
(cryostat, coil):
~ 2.5 X0 at η=0
Data and MC normalised
to the same area

17. Jets
√s=2.36 TeV
√s=900 GeV

18. events with
2 jets pT> 7 GeV
Uncalibrated EM scale
Monte Carlo normalized to number of jets or events in data

19. Missing transverse energy
Sensitive to calorimeter performance (noise, coherent noise, dead cells, mis-calibrations,
cracks, etc.) and backgrounds from cosmics, beams, …
Measurement over full calorimeter coverage (3600 in φ, |η| < 5, ~ cells)
METx
METx
METx / METy indicate x/y
components of missing ET vector
METy

20. More comparisons data – simulation:
Photon candidates: shower shape
in the EM calorimeter
More comparisons data – simulation:
fundamental milestone for solid physics
measurements
Electron candidates: transition
radiation signal in TRT
Shower width in strip units (4.5mm)
Monte Carlo and data
normalized to same area
|η| < 0.8, 0.5 < pT < 10 GeV
Cluster energy at EM scale
Good agreement in the (challenging) low-E
region indicates good description of material
and shower physics in G4 simulation
(thanks also to years of test-beam …)

21. Conclusions ATLAS has successfully collected first LHC collision data.
The whole experiment operated efficiently and fast, from data taking
at the pit, to data transfer worldwide, to the production of first results
(on a very short time scale … few days).
First LHC data indicate that the performance of the detector, simulation
and reconstruction (including the understanding of material and control
of instrumental effects) is far better than expected at this (initial) stage
of the experiment and in an energy regime ATLAS was not optimized for.
Years of test beam activities, increasingly realistic simulations, and
commissioning with cosmics to understand and optimize the detector
performance and validate the software tools were fundamental to achieve
these results.
The enthusiasm and the team spirit in the Collaboration are extraordinary.
This is only the beginning of an exciting physics phase and a major achievement of the
worldwide ATLAS Collaboration after > 20 years of efforts to build a detector of
unprecedented technology, complexity and performance.

22. ATLAS cavern, October 2005

23. Many thanks to the accelerator team for the excellent
Hector Berlioz, “Les Troyens”, opera in five acts
Valencia, Palau de les Arts Reina Sofia, 31 October -12 November 2009
Many thanks to the accelerator team for the excellent
machine performance, for the impressive progress over a
few days of operation, and for the very pleasant and
constructive interactions with ATLAS

24. Back-up

25. Electron candidates EM clusters ET > 2.5 GeV matched to a track
 783 candidates in 330k minimum-bias events
Data and MC normalised to the same area
E (cluster) / p (track)
According to MC:
Sample dominated
by hadron fakes
Most electrons from
γ-conversions
ET spectrum
Transition radiation
hits in the TRT
(transition radiation from
electrons produces
more high-threshold hits)
Good data-MC
agreement for (soft !)
electrons and hadrons

26. Length : ~ 46 m Radius : ~ 12 m Weight : ~ 7000 tons
Muon Spectrometer (||<2.7) : air-core toroids with gas-based chambers
Muon trigger and measurement with momentum resolution < 10% up toE ~ TeV
Length : ~ 46 m
Radius : ~ 12 m
Weight : ~ 7000 tons
~108 electronic channels
3-level trigger
reducing the rate
from 40 MHz to
~200 Hz
Inner Detector (||<2.5, B=2T):
Si Pixels and strips (SCT) + Transition Radiation straws Precise tracking and vertexing,
e/ separation (TRT).
Momentum resolution:
/pT ~ 3.4x10-4 pT (GeV)  0.015
EM calorimeter: Pb-LAr Accordion
e/ trigger, identification and measurement
E-resolution: ~ 1% at 100 GeV, 0.5% at 1 TeV
HAD calorimetry (||<5): segmentation, hermeticity
Tilecal Fe/scintillator (central), Cu/W-LAr (fwd)
Trigger and measurement of jets and missing ET
E-resolution:/E ~ 50%/E  0.03 26

27. Zero Degree Calorimeter
Forward detectors
LUCID at 17 m
ALFA at 240 m
ZDC at 140 m
Luminosity Cerenkov
Integrating Detector
(Phase 1 operational since 2008)
Zero Degree Calorimeter
(Data taking in 2009)
ALFA: Absolute
Luminosity for ATLAS
(Installation in 2010)
LoI for Forward Proton detectors at 220 and 420 m (AFP):
ongoing ATLAS review 27 27 27

28. Jets √s=2.36 TeV √s=2.36 TeV √s=900 GeV Jet1: ET (EM scale)~ 15 GeV

29. Beam injection, record collision events. HLT algos off.
HLT active after LHC declares stable beam
Rejection factor of ~104 looking for space points in the Inner Detector at Level 2 trigger
~20
BPTX prescaled by x20 as input to L2

30. Architecture 150 500 nodes nodes 100 nodes 1800 nodes ~100 nodes 140M
5/6/2018
Trigger
DAQ
Calo MuTrCh
Other detectors
LVL1
40 MHz
2.5 ms
Det.
R/O
140M
Channels
LVL1 accept
(75 kHz)
ROD
RoI
High Level
Trigger
Dataflow
LVL2
~40 ms
150
nodes
500
nodes
ROS
RoI requests
ROB
ROIB
L2SV
RoI data (~2%)
L2P
L2N EB
100
nodes
EBN
DFM
LVL2 accept (~3 kHz)
SFI
1800
nodes
~4 sec
EFN EF
EFP
EF accept
(~0.2 kHz)
SFO
~100
nodes
Infrastructure
Control &
Monitoring
Communication
Databases

31. Foil The Transition Radiation detector (TRT) Xe straw
charged particles
Transition radiation is emitted whenever a relativistic
charged particle traverses the border between
two media with different dielectric constants.
TR intensity is proportional to the particle -factor
 for a given particle momentum p, electrons emit
more TR than pions  TR detectors used for
particle identification
Foil
Anode wire Xe
straw
HV -
Energy of TR photons
(proportional to 1-2):
~ keV (X-rays)
Many crossings of
polypropylene foils
(radiator) to increase
TR photons
Xenon as active gas
for high X-ray absorption
Radiator: Polypropylen foils (15 ) interleaved with straws