# Presentation: 506768

## Muon Reconstruction in ATLAS

**Georgios Stavropoulos****U.C. Berkeley**
- LBNL
- 20 May 2005

## Contents

- The knows and the whys in H.E.P.
- LHC and ATLAS description
- The ATLAS Muon Spectrometer
- Muon Reconstruction and Identification
- ATLAS potential to discover the SM Higgs.

- G. Stavropoulos

## Elementary Particles

| “Ordinary” matter consists of → | Leptons |  | Quarks |  |
| --- | --- | --- | --- | --- |
|  | Electron
Mass = 0.00051
Charge = -1 | El. neutrino
Mass ≈ 0 ;
Charge = 0 | up
Mass ≈ 0.005
Charge = +2/3 | down
Mass ≈ 0.007
Charge = -1/3 |
| Found in cosmic rays and accelerators | Muon
Mass ≈ 0.106 
Charge = -1 | Μυ. neutrino
Mass ≈ 0 ;
Charge = 0 | charm
Mass ≈ 1.4
Charge = +2/3 | strange
Mass ≈ 0.150 
Charge = -1/3 |
|  | Tau
Mass ≈ 1,777
Charge = -1 | Tau neutrino
Mass ≈ 0 ;
Charge = 0 | top
Mass ≈ 175
Charge = +2/3 | bottom
Mass ≈ 4.5
Charge = -1/3 |
| Anti-matter |  |  |  |  |

- Fermions: Spin 1⁄2.

- G. Stavropoulos

## The Forces in Nature

|  | Intensity | Field Quantum |
| --- | --- | --- |
| Strong Nuclear | ~ 1 | 8 Gluons (Massless, Charge 0) |
| Electromagnetic | ~ 10-3 | Photon (Massless , Charge 0) |
| Weak Nuclear | ~ 10-5 | Z0 (Mass ≈ 91 GeV)
W± (Mass ≈ 80 GeV) |
| Gravity | ~ 10-38 | (Graviton; Massless; Charge 0;) |

- Bosons: Spin 0, 1, 2.

- G. Stavropoulos

## Open Questions

-  Are really elementary the “elementary” particles?
-  Why do they have these mass and charge values?
-  Why so many forces?
-  The Graviton exists?
-  Are they other undiscovered particles in Nature?
-  Why 3 generations?
-  Why ...... ?

- G. Stavropoulos

## The Standard Model and Beyond

-  Today, the most successful theoretical model, explaining lots of experimental data.   Predicted the existence of the W±, Z0 particles.
-  Predicts the existence of one more neutral particle, the Higgs. Experimental   measurements confirm that Higgs should have, if it exists, mass > 114 GeV
-  But, leaves a lot open questions
-  Why these particles masses?
-  Gravity?
-  If neutron have mass;
-  Beyond the Standard Model
-  GUTs
-  Supersymmetry
-  Strings
-  ..........

- G. Stavropoulos

## Physics studies with LHC

**All theories agree, that the systematic study of the physics phenomena in the**
**energy range between ****100 ****– ****1000 ****GeV will answer many of our questions**

- Standard Model Physics - Higgs search
- B-physics
- Heavy quarks and leptons
- QCD
- Supersymmetry
- Exotics
- .........

- G. Stavropoulos

## Large Hadron Collider

-  ~27 km circumference
-  pp colisions.   7 TeV beam energy (c – 10 km/h)
-  Bunch spacing 25 ns
-  Designed Luminosity 1034 cm-2s-1
-     109 interactions/s

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## SM Higgs Production @ LHC

- Gluon Fusion
- - dominant process

- Vector Boson Fusion
- - 20% of gg @ 120GeV

- Associated Production
- - W or Z (1-10% of gg)

- Associated Production
- - tt or bb (1-5% of gg)

- 4 production mechanism     key to measure H-boson parameters

- -

- -

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## Main Discovery Channels

**Main Discovery Channels**

**_**

- _m(H) > 2 m__Z__ :_
- H  ZZ   4
- qqH  ZZ    * qqH  ZZ   jj *
- qqH  WW jj  *            * for mH > 300 GeV forward jet tag

- _Low mass region: m(H) < 2 m__Z__ :_
- H   : small BR, but best resolution
- H  bb : good BR, poor resolution  ttH, WH
- H   : via VBF
- H  ZZ*  4
- H  WW*   or jj : via VBF

- Dominant BR for mH<2mZ:
-   (H  bb)  20 pb;
-   (bb)          500 b
- for m(H) = 120 GeV
-  no hope to trigger
-     or extract fully
-     had. final states
-  look for final
-     states with , 
-     ( = e, )

- -

- -

- -

- -

- G. Stavropoulos

## The LHC detectors

*Η → ΖΖ → 4μ*

-   1 GHz interaction rate
-   23 minimum bias interactions per bunch crossing (pile-up)

- _Extreme demands on detectors:_
- high granularity
- high data-taking rate
- high radiation environment

- G. Stavropoulos

## The ATLAS Detector

- For com- parison

**Muon Detectors**
**Fast response for trigger**
**Good *****p***** resolution (e.g., A/H ******** ********)**

**Electromagnetic Calorimeters**
**excellent electron/photon identification**
**Good *****E***** resolution (e.g., H******

**Inner Detector**
**High efficiency tracking**
**Good impact parameter res.**
**(e.g., H ******** bb)**

**Hadron Calorimeters**
**Good jet and E****T**** miss performance**
**(e.g., H ************)**

**Length: ~40m**
**Radius: ~10m**
**Weight: ~ 7000 t**
**El. Channels: ~10****8**
**Cables: ~3000 km **

- G. Stavropoulos

**Notes:**
Quite some stringent requirements on the performance of the different detectors come from the different Higgs searches

## The ATLAS Detector (cont.)

- Data Acquisition System

- Trigger System

- Αnalog
- Signals (10 PB/s)

- Decisions

- Detector & Trigger Simulation

- Raw data

- Reconstruction &
- Αnalysis

- Design feedback

- Trigger and DAQ

- Mass Storage

- Physics Results

- G. Stavropoulos

## Measurement of Charged Tracks

- To measure a pT = 1 TeV track with 10% resolution in a magnetic field of L = 5 m and ∫Bdl = 3 Tm we should aim for a σ(χ) < 50μm detector resolution.A pT = 20 GeV is measured with
- 0.2% accuracy in the same detector.

**B**

**s**

**θ**

**ρ**

**L**

- Multiple scattering contributes to themeasurement error. In a 3-layer aluminum detector, with 1 cm thicklayers, these error is calculated tobe ~0.8%.

- G. Stavropoulos

## The ATLAS Muon Spectrometer

- Three toroidal magnets create a magnetic field with:
-  **Barrel:** ∫Bdl = 2 – 6 Tm
-  **Endcaps:** ∫Bdl = 4 – 8 Tm

-  **RPC ****και ****TGC: **Trigger the detector and measure the muons in the xy and Rz planes with an accuracy of several mm.
-  **CSC: **Measure the muons in Rz with ~80 μm accuracy and in xy with several mm. Cover 2<|η|<2.7
-  **MDT: **Measure the muons in Rz with ~80 μm accuracy . Cover |η|<2

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## The MDT Chambers

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## An Event

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## Muon Reconstruction with MOORE

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## Muon Identification with MuID

**Muon Identification with MuID**

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## Results 

- P**T** /GeV

- Efficiency vs pT

**Results **

**Michela Biglietti**

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## Resolution

- 1/pΤ pull =
- (1/pΤrec - 1/pΤgen)/Error(1/pT)

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## Experimental verification of the detectors’ design characteristics

- A significant and very important part of the construction phase of a detector, is the experimentalverification of its design and construction characteristics.
- Several measurements have already been performed (or they currently happen) in cosmic andtest-beam setups, which confirm that the detector under construction will be able to deliver thequality measurements as it is requested by the ATLAS Physics program.
- The design characteristics that have already been experimentally verified:
-  Track reconstruction efficiency.
-  Spatial resolution
-  Efficiency and timing of the trigger chambers
-  Detector performance in high event rates.
-  Alignment system.

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## Experimental verification of the detectors’ design characteristics

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## Spatial Resolution

- drift distance [cm]

- Hit Residuals:

**Spatial Resolution**

**Katharina Mair**

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## Alignment

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## And finally the Higgs....

**And finally**** ****the Higgs....**

- Invariant Massof the 4 muons in GeV

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## Overall Higgs Significance

- VBF channels at low mass not yet included in the plot!  Low mass will improve!

**LEP2 Limit**

- 114 GeV < mH < 190 GeV:
- several complementary channels

- 190 GeV < mH < 700 GeV:
- easy with H  ZZ  4

- 700 GeV < mH < 1 TeV:
- need H  ZZ  , jj
-          H  WW  jj

**5******

-  L dt = 100 fb-1

- G. Stavropoulos

## Status of MDT Production

**Status of MDT Production**

- Over 95% of the MDT chambers have been produced.
- Over 85% are equipped with gas manifold and Faraday cages.
- 52% of the MDT’s already at CERN.
- 40% fully tested with cosmics (partly at the home institutions) as individual chambers.
- 10% of the RPC/MDT stations have past the qualification tests.

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## Installation

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