# Presentation: 736292

## 
Beate Heinemann
University of California, Berkeley and Lawrence Berkeley National Laboratory

AAPT, Baltimore, January 2008

**Beate Heinemann**
*University of California, Berkeley and Lawrence Berkeley National Laboratory*
*AAPT, Baltimore, January 2008*

- Exploring Nature’s Fundamental Forces and Particles with the Large Hadron Collider

## The Large Hadron Collider (LHC)

**The Large Hadron Collider (LHC)**

**√****s≈14 TeV**

***Circumference: 16.5 miles***

## The Challenge

**The Challenge**

- Measured hits in detector
- => use hits to reconstruct particle paths and energies
- => understand the underlying physics

## Particle Identification

- Detector designed to separate electrons, photons, muons, neutral and charged hadrons

## ATLAS and CMS Detectors

|  | Weight (tons) | Length (m) | Diameter (m) |
| --- | --- | --- | --- |
| ATLAS | 7,000 | 42 | 22 |
| CMS | 12,500 | 21 | 15 |

## Detector Size in Perspective

- CMS

- ATLAS

- five-storey building

## Detailed Layout

- About 100 million separate readout channels
- 3000 km of cables

## Silicon Tracking Detectors

**Silicon Tracking Detectors**

- Charged particle traverses silicon sensor (semi-conductor)
- Sets free charge carriers
- Drift to electrodes
- Measured charge gets collected at electrodes
- Thus we find out position of particle
- Resolution typically 15 m
- Detector placed inside magnetic field:
- Lorentz force: **F** = q **v** x **B**
- Hits along trajectory are fit to form a track
- deviation from straight line proportional to momentum (**p**=m**v**)
- Direction of curvature tells us the electric charge

- charged
- particle

- low p

- high p

- .

- B

## The ATLAS Pixel Detector

- Cylinder: L=1.4 m , R=12.25 cm
- 80,000,000 individual pixels arranged in modules:
- 16 chips per module, 2880 pixels per chip => 46080 pixels/module
- Distance between pixels: 50 m (“pitch”)
- Designed and built mostly in the United States (Berkeley)

**2 cm**

**6 cm**

**module**

## ATLAS Tracking Detectors

**ATLAS Tracking Detectors**

## Electromagnetic Calorimeter

- Sandwich structure:
- Absorber material: lead (Pb)
- Active material: Liquid Argon (LAr)
- Energy measurement:
- Electromagnetic shower produced through interactions with lead
- Photons collected in Liquid Argon
- N(photons) energy of particle
- Photomultiplier tube (“PMT”)
- Amplification of signal => readout
- Position measurement:
- High spatial granularity =>  position known

**e or ******

- Pb

- LAr

- PMT

## ATLAS Muon System and Calorimeters

**ATLAS Muon System and Calorimeters**

## CMS

## Cosmic Muon Data

**Experiments are currently preparing for LHC data taking**
**- analysis of cosmic muon data**

## 2000 Physicists from all over the World

** ****(including 400 PhD students)**
**+ many technician and engineers**

## Enormous Data Volumes

**Pushing the computing limits!**
- 1 second of LHC data: 1000 GigaBytes
**10,000 sets of the Encyclopedia Britannica**
- 1 year of of LHC data: 10,000,000 GB
**25 km tower of CD’s (~2 x earth diameter)**
- 10 years of LHC data:
**All the words spoken by humankind since its appearance on earth **
**Solution: the “Grid” **
- Global distribution of CPU power
- More than 100 CPU farms worldwide share computing power

## Three Example Analyses

**Finding **
**more Spatial Dimensions**

**Finding the Higgs Boson**
**with photons**
**with Z-bosons**

**Finding a Supersymmetric World**

## Finding the Higgs Boson (with photons)

**Finding the Higgs Boson (with photons)**

- Find 2 high energy  photons
- If M(H)<130 GeV/c2
- Separate signal from backgrounds
- Backgrounds can look exactly the same
- but for ’s from Higgs:

**M(H)=M(********)=√[(E****1****+E****2****)****2****-(p****1****+p****2****)****2****]**

**Background**

**M(********)**

**M(********)**

**Higgs signal**

**simulated event**

****

****

## Finding the Higgs Boson (with Z’s)

**Finding the Higgs Boson (with Z’s)**

- Find 4 high energy  muons or electrons
- If M(H)>130 GeV/c2
- Separate signal from backgrounds
- Again calculating the invariant mass
- Backgrounds much smaller than in diphoton case:
- Easier!

**Higgs signal**

**simulated event**

**Background**

- Z

- Z

- +

- -

- +

- -

****

****

****

****

**M(eeee)**

## Finding a Supersymmetric World

**Finding a Supersymmetric World**

**Supersymmetric particles decay into ordinary particles:**
- Measure decay products
- Dark matter particle (10) escapes detector unseen:
- Momentum balance tell us presence of dark matter particles (“missing ET”)
**Search strategy:**
- Search for many high energy particles plus large missing ET

- Might find the missing Dark Matter in the Universe

- ~

- ~

- ∑iETi+missing ET

- SUSY

- background

- ~

## Finding more Spatial Dimensions

**Finding more Spatial Dimensions**

- We live in a 4D world
- Gravity also lives in our world
- Gravity might also live in extra dimensions:
- Kaluza-Klein Gravitons can be produced at LHC and then escape into extra dimensions
- We cannot see the ED’s since they are tiny and curled up
- Escaping “graviton” causes momentum imbalance
- pp GKK+X (≈ “nothing” +X)
- Detect “nothing” experimentally: “missing energy”

- Momentum imbalance

- Backgrounds

- Extra Dim. signal

**graviton**

**matter**

## After a 20 year design and construction phase the LHC experiments are taking data!
Cosmic muons now
pp collisions later this year
2000 physicists collaborate on each experiment towards a common goal
Unraveling the physics of the fundamental building blocks of matter

- After a 20 year design and construction phase the LHC experiments are taking data!
- Cosmic muons now
- pp collisions later this year
- 2000 physicists collaborate on each experiment towards a common goal
- Unraveling the physics of the fundamental building blocks of matter

**Conclusions**

## After a 20 year design and construction phase the LHC experiments are taking data!
Cosmic muons now
pp collisions later this year
2000 physicists collaborate on each experiment towards a common goal
Unraveling the physics of the fundamental building blocks of matter

- After a 20 year design and construction phase the LHC experiments are taking data!
- Cosmic muons now
- pp collisions later this year
- 2000 physicists collaborate on each experiment towards a common goal
- Unraveling the physics of the fundamental building blocks of matter

**Conclusions**

**Will we find **
**those ?’s**

## Further Information

- CERN: _[http://public.web.cern.ch](http://public.web.cern.ch/)_
- Particle Physics: _[http://particleadventure.org](http://particleadventure.org/)_
- Experiments:
- ATLAS: _[http://www.atlas.](http://www.atlas.ch/)__[ch](http://www.atlas.ch/)_
- CMS: _[http://](http://cmsinfo.cern.ch/outreach/)__[cmsinfo](http://cmsinfo.cern.ch/outreach/)__[.](http://cmsinfo.cern.ch/outreach/)__[cern](http://cmsinfo.cern.ch/outreach/)__[.](http://cmsinfo.cern.ch/outreach/)__[ch](http://cmsinfo.cern.ch/outreach/)__[/outreach/](http://cmsinfo.cern.ch/outreach/)_
- (including many movies)
- And talks tomorrow in Session DHH:
- - Peter J. Limon: *the LHC Accelerator*
- Ayana T. Holloway Arce: *the ATLAS Experiment*