ATLAS in the LHC collision era

ATLAS in the LHC collision era

M.BosmanIFAE - Barcelonaon behalf of the ATLAS CollaborationIMFP 2010 – La Palma

ATLAS, M.Bosman, IFAE 21/2/2010

Effort of the ATLAS Worldwide Scientific Community for > 20 years

~ 2900 scientists (~1000 students), 172 Institutions, 37

countries


ATLAS Detector

45 m

24 m

7000 T


Silicon pixels (Pixel): 0.8 108 channelsSilicon strips (SCT) : 6 106 channelsTransition Radiation Tracker (TRT) :

straw tubes (Xe), 4 105 channelse/ separation

/pT ~ 5x10-4 pT 0.01

Inner Detector

Tracking ||<2.5 B=2T


Calorimetry

Electromagnetic Calorimeterbarrel,endcap: Pb-LAr~10%/√E energy resolution e/γ180000 channels: longitudinal segmentation

Calorimetry ||<5

Hadron Calorimeterbarrel Iron-Tile EC/Fwd Cu/W-LAr (~20000 channels)/E ~ 50%/E 0.03 pion (10 )

Trigger for e/γ , jets, Missing ET


Muon System Stand-alone momentum resolution Δpt/pt < 10% up to 1 TeV

~1200 MDT precision chambers for track reconstruction (+ CSC)

~600 RPC and ~3600 TGC trigger chambers

2-6 Tm ||<1.3 4-8 Tm 1.6<||<2.7


People are happy again...

A key date for ATLAS in 2009


LHC went very quickly from circulating beams to collisions at √s = 900 GeV

Monday 23 November: first collisions at √s = 900

GeV ! ATLAS records ~ 200

events (first one observed at 14:22)

Friday 20 November: Circulating beams “Beam splashes”


Sunday 6 December: machine protection system commissioned

stable (safe) beams for first time full tracker at nominal voltage whole ATLAS operational


ATLAS, M.Bosman, IFAE 111/2/2010 Jet1: ET (EM scale)~ 16 GeV, η= -2.1Jet2: ET (EM scale) ~ 6 GeV, η= 1.4

8, 14, 16 December: collisions at √s = 2.36 TeV (few hours total)ATLAS records ~ 34000 events


■ 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

Detector is fully operational


Let’s go back in time..... Cosmic Muon Runs

216 Million Cosmics in Sep/Oct 2008 90 Million Cosmics in Jun/Jul 2009 266 Million Cosmics in Oct/Nov 2009


Cosmics-Muon-Runsuseful for initial detector calibration, operation experience, ...

some examples

Cosmic Muon Runs

alignment of SCT efficiency of MDT tubes

2008 Cosmics Data


Cosmics-Muon-Runsuseful for initial detector calibration, operation experience, ...

a couple of examples

Beam Splashes

Calorimeter energy calibrationET Level-1 trigger versus offline reconstruction

Muon Chambers Timing

Synchronize all chambers at a given z using the synchronous front of splash particles and the very large particle flux

Calorimeter Timing

After 2008 beam-splash data taking and analysis of many millions of cosmics events, timing good within a few ns


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 ~ 34k ≈ 1 μb-1

Average data-taking efficiency: ~ 90%

Recorded data samples


Max peak luminosity seen by ATLAS : ~ 7 x 1026 cm-2 s-1

Measuring luminosity

example: run with 4hours of stable beam scintillators in front of endcap

forward luminosity monitor (22 m / in front of quadrupole)

LAr endcaps

overall systematic uncertainty up to 30%.

ramping-up Silicon Detector

after stable-beam signal


Dataflow

EBHigh LevelTrigger

LVL2

ROS

LVL1Det.

R/O

Trigger

DAQ

2.5 s

~40 ms

Calo MuTrChOther detectors

L2P L2N

RoI

RoI data (~2%)

RoI requests

LVL2 accept (~3 kHz)

SFO

LVL1 accept (75 kHz)

40 MHz

EFEFP

~4 sec

EF accept (~0.2 kHz)

ROD ROD ROD

ROB ROB ROB

SFI

EBN

EFN

DFM

L2SVROIB500nodes

100nodes

150nodes

1800nodes

Infrastructure Control &Monitoring

Communication Databases

~100nodes

Trigger/DAQ Architecture

140M Channels


Scintillators (Z~± 3.5 m):rate up to ~ 30 Hz

Collision trigger (L1)

High-Level Trigger in rejectionmode (in addition, running > 150 chains in pass-through)

Spot size ~ 250 μm

Online determination of the primary vertex and beam spot using L2 trigger algorithms

Trigger


WLCG

MB/sper day Total data throughput through the Grid (Tier0, Tier-1s, Tier-2s)

Beam splashes

First collisions

Nov. Dec.

Cosmics

End of datataking

■ ~ 0.2 PB of data stored since 20th November■ ~ 8h between Data Acquisition at the pit and data arrival at Tier2 (including reconstruction at Tier0)■ increasing usage of the Grid for analysis

Worldwide data distribution and analysis


Collisions - Inner Detector


p

K

π

180k tracks

Inner Detector - PixelThe dE/dx is measured per track as the mean of the cluster charge properly weighted for the track length in silicon.

180k tracks (3 Pixel Hits)

10% of data

Track momentum X charge Q

Pixel cluster width as a function of the track incident angle in Rphi direction


Inner Detector - SCT

Lorentz angle extracted from the cluster-size vs angle compared to model prediction.

Silicon stripsIntrinsic module efficiency for tracks measured in the SCT Barrel (dead modules and chips are taken into account).


Inner Detector - TRTTransition Radiation Tracker

Transition radiation intensity is proportional to particle relativistic factor γ=E/mc2. Onset for γ ~ 1000

Foil

Anode wire

Xe

straw

HV - Energy of TR photons (proportional to 1-2): ~ 10-30 keV (X-rays) Many crossings of polypropylene foils (radiator) to increase TR photons Xenon as active gas for high X-ray absorption

electron from photon conversion reconstructed in ID with tight identification in calorimeter

all tracks


Reconstructing decays

pT (track) > 100 MeVMC signal and background normalized independently

-+0sK


Reconstructing decays+p ,p

K0S

Λ


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

e+e- conversions


Calorimeter – cell signalscell signal in randomly triggered events

LAr calorimeter

cell signal in collision events


Data and MC normalised

to the same area

Calorimeter – photons : π0 γγ

■ 2 photon candidates with ET (γ) > 300 MeV

■ ET (γγ) > 900 MeV

■ Shower shapes compatible with photons■ No corrections for upstream material applied

π0 γγ


Soft photons !Challenging because of material in front of EM calorimeter(cryostat, coil): ~ 2.5 X0 at η=0

Calorimeter – photons

Photon candidates: shower shape in the EM calorimeter


EM clusters ET > 2.5 GeV matched to a track 783 candidates in 330k minimum-bias eventsData and MC normalised to the same area

According to MC:■ Sample dominated by hadron fakes■ Most electrons from γ-conversions

E (cluster) / p (track)

Good data-MC agreement for (soft !)electrons and hadrons

ET spectrum

Transition radiation hits in the TRT(transition radiation from electrons producesmore high-threshold hits)

Calorimeter – Electron candidates


Good agreement in the (challenging) low-E region indicates good description of material and shower physics in Geant4 simulation

Years of test-beam, collaboration with Geant4 team

p(tracker)

ter)E(calorime

:hadrons Isolated

|η| < 0.8, 0.5 < pT < 10 GeV Cluster energy at EM scale

Monte Carlo and data normalized to same area

Calorimeter – Isolated hadron response


Calorimeter - Jets

Jets

√s=2.36 TeV √s=2.36 TeV

√s=900 GeV


Uncalibrated EM scale jets with pT>7 GeVMonte Carlo (Non Diffractive Minimim Bias)normalized to number of jets or events in data

Events with2 jets with pT> 7 GeV

Calorimeter - Jets


■ 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, ~ 200000 cells)

METy

METx / METy = x/y components of missing ET vector

METx

Calorimeter – Missing Transverse Energy


METx

Calorimeter – Missing Transverse Energy


Collisions: a physics Roadmap

time

Test beam, cosmic runs, pre-alignment

& calibration,

extensive simulations ...

Search for very striking new physics signature

Use SM processes as “standard candles”

Initial detector & trigger synchronisation, commissioning, calibration & alignment, material

Sensitivity to 1-1.5 TeV resonances → lepton pairs

Understand SUSY and Higgs background from SM

More accurate alignment & EM/Jet/ETmiss calibration

Higgs discovery sensitivity (MH=130~500 GeV)

Explore SUSY to m ~ TeV

Precision SM measurements

Inte

gra

ted L

um

inosi

ty (

a.u

.)

1

10

100


Example of first signals1 pb-13 days at 1031at 30% efficiency

ATLAS

J/

Y1S

After all cuts:~ 5000 (800) J/ (Y) / day @ L = 1031 cm-2 s-1

(for 30% machine x detector data taking efficiency) (at 7 TeV reduced by ~x2)

tracker momentum scale, trigger performance, detector efficiency, sanity checks, …

50 pb-1

After all cuts:~ 160 Z ee day at L = 1031 cm-2 s-1

energy/momentum scale of full detectorMuon Spectrometer alignment, lepton trigger and reconstruction efficiency, …

~25 k events for 50 pb-1 at 14 TeV

(at 7 TeV reduced by ~x2)

quickly dominated by systematic

Initial robust analysis

e10 trigger

loose identification

background extrapolated from side bands

14 TeV


W/Z ProductionW Trigger and offline efficiencies from tag-and-

probe (Z) Muon isolation in calo Missing ET > 25GeV

Ldt=50pb-1: 300k W, 20k bckgd events

Z Trigger and offline eff. from tag-and-probe Tracks in Muon Spectrometer

Ldt=50pb-1: 26k Z, 0.1k bckgd evt

ATLAS

14 TeV

at 7 TeV, about a factor 2 less signal events

ATLAS


ttbar pair production: semi leptonic decays

Top production

1 jet pT> 20 GeV

3 jets pT> 40 GeV +

PT(lep) > 20 GeV

Missing ET > 20 GeV

No b-tagging

for 200 pb-1

channel

1600 events Signal, 800 Bck

e channel:

1300 events Signal, 600 Bck

10 TeV

at 7 TeV, signal reduced by factor 2.5


■ 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.

Conclusionstaken from F.Gianotti, ATLAS Spokesperson Report to CERN Council Dec 09

Date post:	11-Jan-2016
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ATLAS in the LHC collision era

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