The ATLAS ExperimentLHC C Gemme F Parodi LHC

The ATLAS Experiment@LHC C. Gemme, F. Parodi LHC ATLAS detector: overview and performance Physics objetcs

LHC physics ü – test the Standard Model, hopefully find “physics beyond SM” ü – find clues to the EWK symmetry breaking - Higgs(ses)? ü Standard Model is a gauge theory based on the following “internal” symmetries: SU(3)c × SU(2)I × U(1)Y ü The SU(3) is an unbroken symmetry, it gives Quantum Chromo-Dynamics (QCD), a quantum theory of strong interactions, whose carriers (gluons) are massless, couple to color (strong force charge) ü SU(2) × U(1) (quantum theory of electroweak interactions) is spontaneously broken by the Brout-Englert-Higgs mechanism; which gives mass to electroweak bosons (massive W+, W-, Zo and a massless photon) and all fermions ü In the Minimal Standard Model, the Higgs sector is the simplest possible: contains one weak isospin doublet of complex Higgs fields, which after giving masses to W+, W-, Zo leaves a single neutral scalar Higgs particle which should be observed 28/5/2013 C. Gemme - F. Parodi - Atlas results 2

LHC physics ü Matter is build of fermions - quarks and leptons, three families of each, with corresponding antiparticles; quarks come in three colors, leptons are color singlets, do not couple to gluons. ü Bosons are carriers of interactions: 8 massless gluons, 3 heavy weak bosons (W, Z) and 1 massless photon. ü A neutral scalar Higgs field permeates the Universe and is (in some way) responsible for masses of other particles (they originate from couplings to Higgs field). ü SINGLE NEUTRAL HIGGS SCALAR - THE ONLY PARTICLE MISSING IN MSM 28/5/2013 C. Gemme - F. Parodi - Atlas results 3

7 anni di costruzione nel tunnel gia‘ utilizzato da LEP: 1989 -2000 LHC Tunnel LHC: 27 km di circonferenza CMS LHCb ALICE 28/5/2013 C. Gemme - F. Parodi - Atlas results 4 Leonardo Rossi ATLAS 4

LHC • The key parameters of an accelerator are the c. m. s. energy (√s) and the number of collisions that can be generated (L). • Higher energy means possibility to generate particles with higher mass and with larger cross-section. • High luminosity gives the opportunity to generate a significant amount of events in a reasonable time. • • N x = ∫ x L (t) dt LHC pp collider, designed for √s = 14 Te. V and Maximum design luminosity at 14 Te. V Lmax = 1034 cm 2 s-1 ü Run at √s = 7 Te. V in 2010 and 2011, and at √s = 8 Te. V in 2012 • 28/5/2013 Upgrading at √s = 13 Te. V in 2015 C. Gemme - F. Parodi - Atlas results 5

A collider particle detector ü Tracking systems (based on silicons+TRT) to reconstruct trajectories and momenta of charged particles ü EM/hadronic calorimeters to measure energy of particles and missing energy ü Muon Spectrometers to precisely measure muon momenta ü Efficient Trigger system to reduce the huge collision rate 28/5/2013 C. Gemme - F. Parodi - Atlas results 6

http: //www. atlas. ch/multimedia/atlas-built-1 -minute. html 28/5/2013 C. Gemme - F. Parodi - Atlas results 7

Trigger 28/5/2013 ü The interesting events are only few hundreds every second out of the 20 MHz of interactions frequency. ü Rather than useless, It would even be impossible to transfer out of the detector such a huge amount of data (each event is ~ few MB) ü The trigger system is designed to select the interesting events, based on their signatures, in a short time. ü The ATLAS trigger system has a 3 -levels structure: ü Each level analysis only events accepted by the previous step, the algorithms being more and more complex, requiring more information and more time to take a decision. C. Gemme - F. Parodi - Atlas results 8

ATLAS Data Taking ü % detector non operativa (typ~0. 5%, max 4%) ü e(data taking)~94% ü % di dati di buona qualita’ (=ok x analisi) ~94% 28/5/2013 C. Gemme - F. Parodi - Atlas results 9

Typical run conditions. . . 28/5/2013 C. Gemme - F. Parodi - Atlas results 10

Typical run conditions. . . 28/5/2013 C. Gemme - F. Parodi - Atlas results 11

The Challenge in 2012: Pileup ü Running with 50 ns bunch spacing (rather than 25 ns) results in 2 x larger pile-up for the same luminosity • On average ~20 interactions per bunch-crossing • Up to 40 interactions at peak luminosity ü Huge effort to minimize physics impact • Biggest impact for computing and trigger rates 28/5/2013 C. Gemme - F. Parodi - Atlas results 12

The Challenge in 2012: Pileup Z → μμ event in ATLAS with 25 reconstructed vertices: Display with track p. T threshold of 0. 4 Ge. V and all tracks are required to have at least 3 Pixel and 6 SCT hits 28/5/2013 C. Gemme - F. Parodi - Atlas results 13

What happens now? 28/5/2013 C. Gemme - F. Parodi - Atlas results 14

Elettroni/fotoni ü bb 28/5/2013 C. Gemme - F. Parodi - Atlas results 15

Muons reconstruction ü Several algorithms to identify muons, exploiting all the detectors to get the maximum coverage. ü Main algorithm combines ID and MS. ü Muon reconstruction efficiency is studied with the tag-and-probe method: ü Z → μμ (high pt) and J/ → μμ (low pt) decays selected with one CB muon as tag. ü Muons required to be isolated to suppress background in many analyses 28/5/2013 C. Gemme - F. Parodi - Atlas results 16

Muon energy resolution 28/5/2013 C. Gemme - F. Parodi - Atlas results 17

Jet 28/5/2013 C. Gemme - F. Parodi - Atlas results 18

Energia mancante 28/5/2013 C. Gemme - F. Parodi - Atlas results 19

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Trigger vs Pile up ü Tecniche di trigger ottimizzate per gestire gli effetti del pile-up e della cresciuta luminosita’ tenendo il + basso possibile le soglie sulle osservabili critiche. ü Chiave di volta: “object isolation” (e peso del vertice con piu’ energia trasversa). ü Tenere le soglie per gli oggetti di base piu’ basse possibili. L 1: ~ 65 k. Hz L 2: ~ 5 k. Hz EF: ~ 400 Hz 28/5/2013 C. Gemme - F. Parodi - Atlas results 21

Spares 28/5/2013 C. Gemme - F. Parodi - Atlas results 22

PHASE 0 Upgrades 2013– 2014 Running 2014 -2018 Insertable B-Layer: Layout 23 ü The Insertable B-Layer (IBL) will be built around a new beam pipe and slipped inside the present detector in situ or, if the pixel package is removed to replace the services, this operation can be carried out on the surface. ü IBL will have • <rsens> = 33 mm vs present 50. 5 mm smaller beam pipe radius (29 25 mm). Pixel +IBL Existing B-Layer 27/3/2012 C. Gemme, ATLAS Upgrades

PHASE 0 Upgrades 2013– 2014 Running 2014 -2018 Insertable B-Layer: Layout 24 ü The Insertable B-Layer (IBL) will be built around a new beam pipe and slipped inside the present detector in situ or, if the pixel package is removed to replace the services, this operation can be carried out on the surface. ü IBL will have • <rsens> = 33 mm vs present 50. 5 mm smaller beam pipe radius (29 25 mm) • Coverage: z = 60 cm, |h| <2. 5 • 14 staves with f overlap • No h overlap possible due to clearance • minimize modules edge: Mixed scenario with 3 D and slim edge planar IBL envelope 9 mm in R! 27/3/2012 C. Gemme, ATLAS Upgrades

Tracking: Inner Detector ü Three different technologies detectors in a 2 T Solenoid Magnet ü ~ 6 m long, 1. 1 m radius ü Pixels: 50 x 400 μm 2 cell ü Silicon Strips (SCT): 80 μm pitch, 40 mrad stereo strips ü Transition Radiation Tracker (TRT): straw tubes providing up to 36 hits/track with e/p separation Challenge: ~1 k tracks /25 ns 36 precision points per track in TRT 7 precision Si points/track each rf and z Required Resolution on momentum: p. T /p. T = 0. 05% p. T ⊕ 1%, | h |<2. 5 MC

Calorimeters ü Calorimeters cover the range |h| < 4. 9, using different techniques. Electromagnetic calo • Accordion, Pb/LAr, |h|<3. 2 Hadronic calo • Tile: Fe/scintillator, |h|<1. 7 • LAr HEC: Cu/LAr, two longitudinal wheels, 1. 5<|h|<3. 2 • LAr FCal: Cu/W/LAr, 3. 1<|h|<4. 9 Required Energy Resolution: EM: E/E= 10%/√E ⊕ 0. 7%, | h |<3. 2 Hadro: E/E = 50%/√E ⊕ 3% , | h |<3. 2 ü Provide Trigger for e/γ, jets, missing ET

Muon spectrometer ü High momentum resolution with 3 layers of high precision tracking • MDT: Monitored Drift Tubes • CSC: Cathode Strip Chambers ü Trigger chambers make part of the LVL 1 trigger in ATLAS • RPC : Resistive Plate Chambers • TGC: Thin Gap Chambers ü The air core system generates a strong bending power in a large volume (minimization of multiple-scattering effects). Required Standalone Momentum resolution: /p. T < 10% up to 1 Te. V Acceptance: |h| <2. 7

Muon spectrometer ü High momentum resolution with 3 layers of high precision tracking End-Cap Toroid: 8 coils in a common cryostat • MDT: Monitored Drift Tubes • CSC: Cathode Strip Chambers ü Trigger chambers make part of the LVL 1 trigger in ATLAS • RPC : Resistive Plate Chambers • TGC: Thin Gap Chambers ü The air core system generates a strong bending power in a large volume (minimization of multiple-scattering effects). Barrel Toroid: 8 separate coils Required Standalone Momentum resolution: /p. T < 10% up to 1 Te. V Acceptance: |h| <2. 7

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Trigger 28/5/2013 ü The interesting events are only few hundreds every second out of the 20 MHz of interactions frequency. ü Rather than useless, It would even be impossible to transfer out of the detector such a huge amount of data (each event is ~ few MB) ü The trigger system is designed to select the interesting events, based on their signatures, in a short time. ü The ATLAS trigger system has a 3 -levels structure: ü Each level analysis only events accepted by the previous step, the algorithms being more and more complex, requiring more information and more time to take a decision. C. Gemme - F. Parodi - Atlas results 30