Ashfaq Ahmad Institute of Physics Academia Sinica

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Collider Physics Mini-Workshop Taipei July 21 Ashfaq Ahmad ATLAS Experiment at the LHC Ashfaq Ahmad Institute of Physics Academia Sinica Introduction to ATLAS Physics motivation ATLAS Combined Test beam Commissioning Summary

Transcript of Ashfaq Ahmad Institute of Physics Academia Sinica

Collider Physics Mini-Workshop Taipei July 21 Ashfaq Ahmad

ATLAS Experiment at the LHC

Ashfaq AhmadInstitute of PhysicsAcademia Sinica

Introduction to ATLAS Physics motivationATLAS Combined Test beamCommissioningSummary

Ashfaq Ahmad

Diameter: 25 mBarrel toroid length: 26 mLength: 46 mOverall weight: 7000 Tons

ATLAS: A Toroidal Lhc ApparatuS

Multi purpose particle detector

(coverage up to |η|=5, L=1034 cm-2s-1)

Tracking (|η|<2.5, B=2T):Si pixels and stripsTransition Radiation Detector (e/π separation)

Calorimetry (|η|<4.9):LAr EM Calo: (|η|<3.2)HAD Calo: (|η|<4.9)scintillator-Tile (barrel), LAr (fwd)

Muon Spectrometer (|η|<2.7):Air-core toroids(B~0.5T) with muon chambers

p, 7TeVp, 7TeV

Collider Physics Mini-Workshop Taipei July 21 Ashfaq Ahmad

60 m92 m

ATLAS superimposed to the 5 floors of building 40

Atlas assembled 92 mbelow ground at CERN

Scale of ATLAS

Collider Physics Mini-Workshop Taipei July 21 Ashfaq Ahmad

Event rate

Reconstructed tracks with pt > 25 GeV

At high luminosity event rate ~ 1GHzSpace between two bunches is 25ns~7.5mOn average 23 minimum bias inelastic event low pT

events per bunch crossing of 25ns

Pile up: H →ZZ →4µ

Reconstructed tracks for pT >25GeV

Collider Physics Mini-Workshop Taipei July 21 Ashfaq Ahmad

Status(Atlas Cavern)

Installation of Barrel Toroidswill finish next month(Aug05)

LAr and Tile Barrel Calorimeters are in the pit

Collider Physics Mini-Workshop Taipei July 21 Ashfaq Ahmad

Basic Detector Components

Photons

muons

Π± , p

neutrons

Innermost Layer …Outermost Layer

Trackingdetector

Electromagneticcalorimeter

Hadroniccalorimeter

Muonchambers

Collider Physics Mini-Workshop Taipei July 21 Ashfaq Ahmad

Inner Detector (ID)The Inner Detector (ID) has three sub-systems:

Pixels (0.8 108 channels)

Silicon Tracker (SCT)(6 106 channels)

Transition Radiation Tracker (TRT)

(4 105 channels)

Radiation tracker : TRT

6m long, 1.1 m radius

Si strips tracker : SCTPixels

Precision Tracking: Pixel and SCTContinuous Tracking and e identification: TRTID inside 2 Tesla solenoid field

Collider Physics Mini-Workshop Taipei July 21 Ashfaq Ahmad

LAr and Tile CalorimetersTile barrel Tile extended barrel

LAr forward calorimeter (FCAL)

LAr hadronic end-cap (HEC)

LAr EM end-cap (EMEC)

LAr EM barrel

Collider Physics Mini-Workshop Taipei July 21 Ashfaq Ahmad

Muon Spectrometer

Precision chambers:- MDTs in the barrel and end-caps- CSCs at large rapidity for the

innermost end-cap stationsTrigger chambers:- RPCs in the barrel- TGCs in the end-caps

The Muon Spectrometer is instrumented with precision chambers and fast trigger chambers

Collider Physics Mini-Workshop Taipei July 21 Ashfaq Ahmad

Physics Motivation (i)

What gives particle mass?The missing piece of the SM is the Higgs (H)Breaks electroweak symmetryGenerates masses of particles

Higgs properties predicted-except its mass

From LEP direct search:MH > 114.4 GeV

From Electroweak fit of the SM:MH < 260 GeV

MH < 1.2 TeV else WW scattering violates unitarity

If SM is correct and there is Higgs then it can be observed at the LHC(ATLAS/CMS)

The LHC experiments have to coverFrom the LEP limit up to the TeV scale

Collider Physics Mini-Workshop Taipei July 21 Ashfaq Ahmad

Standard Model Higgs Production At LHCExcluded by LEP M. Spira, Fortsch. Phys. 46 (1998) 203.

Direct:Gluon Fusion

AssociatedProduction(tt or bb):Small σ

AssociatedProduction(W or Z):Small σ

Vector BosonFusion (VBF):Distinct FinalState

Collider Physics Mini-Workshop Taipei July 21 Ashfaq Ahmad

Standard Model Higgs Decay

Bra

nchi

ng R

atio

(Hig

gs)

Low mass range ~2 Mz

H →γγ : smallest BR but better resolution

H →bbar : good BR but poor resolution (15%)

Intermediate mass

H →WW*,ZZ*, useful at MH >125GeV

For MH >2 MZ

W decays to jets or lepton + neutrino

Search Channel depends on MH

Collider Physics Mini-Workshop Taipei July 21 Ashfaq Ahmad

Overall View of the SM Higgs

5σ observation is possible for 30 fb-1 (in first year(s) at low luminosity operation)

Observation of all channels important to extract convincing signal in first year

ATLAS30 fb-1

Collider Physics Mini-Workshop Taipei July 21 Ashfaq Ahmad

Physics Motivation (ii)

SUSY search at LHCunification matter-forces/fermions-bosons is beautifulallows incorporation of gravityallows unification of forces at GUT scaleprovides candidate for cold dark matternot ruled out by present datapredicts light Higgs as favored by data

Exotics: extra dimension, black holes production…

Collider Physics Mini-Workshop Taipei July 21 Ashfaq Ahmad

Testing the detector, Combined Test Beam (2004)

Collider Physics Mini-Workshop Taipei July 21 Ashfaq Ahmad

The ATLAS Combined Test BeamFull “vertical slice” of ATLAS tested on CERN H8 beam line May-November 2004

x

z

y

Geant4 simulated layout of the test-beam set-

up

For first time, all ATLAS sub-detectors integrated and run together with commonDAQ, “final” electronics, slow-control, etc. Gained lot of global operation experience during ~ 6 month run. Common ATLAS software used to analyze the data

Collider Physics Mini-Workshop Taipei July 21 Ashfaq Ahmad

TRT LAr

Tilecal

MDT-RPC

End-cap Muon chambers

~ 90 million events collected ~ 4.5 TB of data:e±, π ± 1 → 250 GeVµ ±, π ±, p up to 350 GeVγ ~ 30 GeV B-field = 0 → 1.4 T

Collider Physics Mini-Workshop Taipei July 21 Ashfaq Ahmad

Validating detector simulation at the CTBE = 100 GeV

σ = 16 µmSimulated data,

σ = 17 µm

Simulated data,σ = 23 µm

E = 180 GeVσ = 22 µm

Pixels

SCT

ATLAS preliminary

Collider Physics Mini-Workshop Taipei July 21 Ashfaq Ahmad

Detector calibration using CTB data

From the CTB data maps of dead/noisy straws are createdAlgorithms are in place to register maps in the databaseDuring the reconstruction straw status is read from the Condition databaseBad channels are masked, hence not used in reconstruction chain

180GeV electrons without magnetic field

Application of dead/noisy straws data

Collider Physics Mini-Workshop Taipei July 21 Ashfaq Ahmad

Nest Step: Atlas Commissioning

Collider Physics Mini-Workshop Taipei July 21 Ashfaq Ahmad

Step 1 : Cosmics run : end 2006-March 2007 commissioning at sub-detector level has startedhere “physics data” are cosmic muonsGood for the calibration and alignment of detectorAtlas has already started recording cosmic muons!

For now TileCalo, article in Nature on 14 July 2005:http://www.nature.com/nphys/journal/vaop/nprelaunch/full/nphys005.html

Step 2 : Only one beam in the machine : April-May 2007 ?here “physics data” are beam-halo muons and beam-gas events

Step 3 : First pp collisions : prepare the trigger and the detector

Step 4 : Commissioning of physics (e.g. understand backgrounds to discovery channels) can start ...

ATLAS Commissioning with “physics data”

Collider Physics Mini-Workshop Taipei July 21 Ashfaq Ahmad

ATLAS Commissioning~ 5 million cosmic ~ 5 million cosmic muonsmuons

enter the cavern in 15 minutesenter the cavern in 15 minutes First cosmic event in AtlasFirst cosmic event in Atlas

Tower energies:~2.5 GeV

Collider Physics Mini-Workshop Taipei July 21 Ashfaq Ahmad

Contribution from our groupHardware:

Provided opto links for Pixel, SCT, LAr and Tile (In fact we are giving “light” to Atlas!)

LMT for the SCTSoftware:

One of our colleague is Atlas software release coordinatorTaking care of smooth and useful release buildsProvided monitoring software for the TRT and global ID level inside Athena framework

Useful for debugging detector, spotting dead/noisy channels, studying correlations among sub-detectors…..

Grid:To deal with the enormous amount of data (Atlas ~ 1PB per year) produced by the LHC, Grid is essentialOur group is taking active part in the development, deployment and testing of the Grid (releases)Contributed actively to DC1 and DC2After all we are Tier1!! (the only one in Asia so far)You can access/process LHC data while sitting at home institute (Great chance for new people to join and take part in the LHC analysis)

Collider Physics Mini-Workshop Taipei July 21 Ashfaq Ahmad

SummaryATLAS offers a wealth of physicsATLAS sub-detectors have passed extensive period of construction, R&D, TestbeamATLAS commissioning has started on sub-detector levelThe whole ATLAS commissioning in 2006-2007We are looking forward to first p-p collision in summer 2007

Collider Physics Mini-Workshop Taipei July 21 Ashfaq Ahmad