# Presentation: 951400

## An Introduction to theLHCand ATLAS

- M. Garcia-Sciveres
- Lawrence Berkeley National Laboratory

- M. Garcia-Sciveres  --- LHC and ALTAS -- Introduction

- June 2004

## Outline

- Introduction (motivation, history, LHC, ...)
- Chapter 1: The ATLAS detector
- Chapter 2: Silicon detectors, Pixel detector.

- M. Garcia-Sciveres  --- LHC and ALTAS -- Introduction

- June 2004

## Physics Motivation

- Electrons account for everything we experience- almost
- We know a lot about electrons
- There’s one thing we can “feel” that has nothing to do with electrons- **mass**
- We know very little about mass at a fundamental level
- The purpose of ATLAS is to discover fundamental things about mass. What is is really?

- M. Garcia-Sciveres  --- LHC and ALTAS -- Introduction

- June 2004

## Standard Model

- M. Garcia-Sciveres  --- LHC and ALTAS -- Introduction

- June 2004

## Proton Accelerators

- o

- Lawrence’s
- First Cyclotron
- 5in. diameter
- 0.8 MeV

- Bevatron
- ~150ft dia.
- 6,000 MeV

- Fermilab Tevatron
- (present highest energy)
- ~1 mile diameter
- 1,000,000 MeV on
- 1,000,000 MeV

- Large Hadron Collider
- (under Construction)
- ~5 mile diameter
- 7,000,000 MeV  on
- 7,000,000 MeV

- M. Garcia-Sciveres  --- LHC and ALTAS -- Introduction

- June 2004

## Aerial View of the LHC Site

- Circumference of 27 km

- Main CERN Site

- M. Garcia-Sciveres  --- LHC and ALTAS -- Introduction

- June 2004

## Underground

- LEP tunnel before LHC installation

- M. Garcia-Sciveres  --- LHC and ALTAS -- Introduction

- June 2004

## The LEP Tunnel

- Getting around

- Tunnel excavation completed in 1988 using boring machines like this one

- LEP tunnel crew

- M. Garcia-Sciveres  --- LHC and ALTAS -- Introduction

- June 2004

## Why 27Km?

- Tunnel was designed to house LEP, an electron-positron collider.
- Beam energy had to be 1⁄2 Z mass with regular RF cavities, and 2xW mass with superconducting cavities.
- RF cavities put energy into the beam, synchrotron radiation (due to bending) takes it out.
- Beam energy is when max RF power = synchrotron loss
- Synchrotron loss ~ 4 R-1 .
-   (LEP-II) = 2x105,  (LHC) = 7x10
- So if synchrotron loss is irrelevant why not even higher E?
- Large proton momentum makes them very hard to bend. Need powerful magnets. 7TeV beam energy is set by most powerful bending magnets possible, 8.33T

- M. Garcia-Sciveres  --- LHC and ALTAS -- Introduction

- June 2004

## LHC Segments

- Beam pipe, magnets, and cooling are integrated into a single 15m long segment that looks like a big pipe.
- The color of the pipe tells you what’s inside.
- Most pipes are blue dipole bending magnets.

- Clockwise beam pipe

- Counter-clockwise beam pipe

- Non-magnetic collars

- Iron yoke

- Channels for superconducting  wire

- M. Garcia-Sciveres  --- LHC and ALTAS -- Introduction

- June 2004

## LHC Magnets

- Magnets are cooled by superfluid Helium at 1.9oK to achieve the highest possible magnetic field with the “standard” superconductor used.

- Dipole in tunnel

- M. Garcia-Sciveres  --- LHC and ALTAS -- Introduction

- June 2004

## LHC operation

- LHC collides protons against protons.
- The protons are accelerated in bunches spaced by 25ns (25feet)
- Each bunch has ~10 protons (1 cc of hydrogen has ~1019 protons)
- Each bunch is 7.5cm long (Z), and gets squeezed down to 15x15m in X,Y at an interaction point, where collisions take place.

- ATLAS IP beam profiles

- Z (m)

- X,y (m)

- Naive calculation suggests each proton occupies a volume of 15x15x75000 / 1011 ~ 10-4 m3 (that’s much bigger than an atom!) so a collision is still rare.
- But with 1011 p/bunch we will do OK (a few interactions every crossing)

- M. Garcia-Sciveres  --- LHC and ALTAS -- Introduction

- June 2004

## LHC Experimental Environment

- A proton Microscope
- Each proton can(crudely) be thought of as a collection of constituents/virtual particles.
- The interactions will happen between gluons in one proton and gluons in the other. There are no quark-antiquark pairs to annihilate (like at Fermilab).
- The “hard”, high energy(actually transverse momentum) collisions of these constituents are of interest to probe the smallest distances and to produce the highest mass new particles
- The “soft” debris is background to the interesting, hard collisions.

- M. Garcia-Sciveres  --- LHC and ALTAS -- Introduction

- June 2004

## What Comes out of a Collision?

- Hadronic Jets(pions, kaons etc.)
- More photons
- Heavy Quark hadrons
- Electrons
- Muons
- Taus
- Neutrinos

- Gluons
- Light Quarks
- Heavy Quarks (c, b)
- Photons
- Neutrinos
- Electrons
- Muons
- Taus

**Depends what you mean by “out”**

- 1 nuclear diameter away

- Thickness of a hair away

- Photon, pion, kaon, nucleon jets
- Photon, pion, kaon nucleon “heavy quark” jets
- Photons
- Electrons
- Muons
- Neutrinos

- 1m Away

- M. Garcia-Sciveres  --- LHC and ALTAS -- Introduction

- June 2004

## What Is Detected?

- Detect
- Electrons
- Muons
- Photons
- Jets(will explain)
- Heavy quark jets
- Neutrinos or other non-interacting particles

- How?
- Electromagnetic calorimetry/tracking
- Absorber/tracking
- Electromagnetic calorimetry/tracking
- Calorimeter/tracking
- Secondary vertices/tracking
- Logical inference

- A “detector” combines different types of single-purpose subdetectors, just like your head has eye, ear, nose, etc. subdetectors.

- Like your brain, the Data Acquisition System combines input from all subdetectors to paint a physical picture.

- M. Garcia-Sciveres  --- LHC and ALTAS -- Introduction

- June 2004

## CDF

- You’ve seen one Collider detector you’ve seen them all conceptually

- (but the devil is in the detials- not shown)

**Installation of CDF Silicon Tracking**
** ****2001**

- M. Garcia-Sciveres  --- LHC and ALTAS -- Introduction

- June 2004

## CDF Photon Conversions

- r-view (data)

- r vs. zview (data)

- Conversion radius (cm)

- Simulation

- Data

- Photon

- electron

- positron

- matter

- M. Garcia-Sciveres  --- LHC and ALTAS -- Introduction

- June 2004

## Heavy Quark Jets

**Silicon Detectors are used to detect heavy quark jets by reconstructing “DISPLACED VERTICES”**

- Actual Top Quark Decay Recorded by CDF

- M. Garcia-Sciveres  --- LHC and ALTAS -- Introduction

- June 2004