# Presentation: 034857

## Physics Opportunities at the Large Hadron Collider 

**Albert De Roeck **
**CERN and University of Antwerp**
**PANIC05  Santa Fe October’05**

## Contents

- The LHC Status
- The LHC Experiments
- The hunt for the Higgs
- Beyond the Standard Model signals: Supersymmetry, extra dimensions...
- QCD, forward physics, heavy ions, b-physics etc.
- Summary

## The LHC Machine and Experiments

- pp collisions at 14 TeV

- 25 ns bunch spacing  2835 bunches  with 10**11** p/bunch
- First years lumi
- ~2.10**33**cm**-2**s**-1**  20 fb**-1**/year
- Design Luminosity:
- 10**34**cm**-2**s**-1** 100 fb**-1**/year
- Stored energy/beam: 350 MJ
-      The LHC will be a very
-        challenging machine

**(LHCf)**

**totem**

## The LHC is Coming!

**The LHC is Coming!**

## The LHC Progress & Schedule

- Can follow progress on the LHC dashboard
- http://lhc-new-homepage.web.cern.ch/lhc-new-homepage/

**The LHC Progress & Schedule**

- More than 100 dipoles
- installed by now
- Next: 20 dipoles/week

-           The LHC Schedule(*)
-  LHC will be closed and set up for
-   beam on 1 July 2007
-  First beam in machine: August 2007
- LHC commissioning will take time!
-  First collisions expected in
-   October/November 2007
- Followed by a short pilot run
- 0.01-0.1 fb**-1 **?
-  First physics run in 2008
-       one to a few fb**-1**?
-  Physics run in 2009 +...
-    10-20 fb-1/year 100 fb**-1**/year

- (*) eg. M. Lamont et al, April 2005.
- Achtung! Lumi estimates are mine, not
- from the machine
- Also: sad accident on 25/10...

## ATLAS

- Tilecal

- Barrel LAr ECAL

- TRT end-cap wheel

- Muon end-cap chamber

- Length  : ~40 m
- Radius  : ~10 m
- Weight : ~ 7000 tons

- Solenoid

- Barrel coil cryostat

## CMS

- Length  : ~20 m
- Radius  :  ~7 m
- Weight : ~ 13000 tons

- ECAL crystals

-  Barrel HCAL

-  Endcap Muon Chambers

- Silicon tracker

-  Coil + inner vacuum tank

## A few numbers...

-  Energy of pp is about 7 times higher than that of the Tevatron at FNAL
-  Weight of the CMS experiment: ~ 13000 tons (30% more than the Tour Eiffel)
-  Amount of cables  used in ATLAS : ~ 3000 km
-  Data volume recorded at the front-end in CMS  is 1 TB/second which
-   corresponds to 10,000 Encyclopedia Britannica
-  Data recorded during the 10-20 years of LHC life will be equivalent to all the
-   words spoken by mankind since its appearance on earth
-  Machine temperature : 1.9 K  (largest cryogenic system in the world)
-  Total cost of machine + experiments : ~ 5000 MCHF
-  Total number of involved physicists : ~ 5000
- ....

**A few numbers...**

## Physics at the LHC: pp @ 14 TeV

- Higgs!

- Supersymmetry?

- Extra Dimensions?

- Black Holes???

- Precision
- measurements
- e.g top!

- QGP?

- CP triangle!

- The LHC will be the new collider energy frontier

- LHC will explore directly the highly-motivated TeV-scale and say the final word
-  about the SM Higgs mechanism and many TeV-scale New Physics predictions
- Also LHC will be a great machine for: QCD, B-physics, Heavy Ions, EW precision..

## Event Rates for pp at s=14 TeV

- Huge event rates:
-     (1033cm-2 s-1)
- The LHC will be
- a W-factory, a
- Z-factory, a top
- factory, a Higgs
- factory etc..

- Precision EW physics
- measurements will be
- limited by systematics

##  Higgs Physics

-  What is the origin of Electro-weak Symmetry Breaking?
-  If Higgs field at least one new scalar particle should exist: The Higgs
-     One of the main missions of LHC: discover the Higgs for m**H**< 1 TeV

## Higgs Searches

- Low M**H** < 140 GeV/c**2**

- Medium 130<M**H**<500 GeV/c**2**

- High M**H** > ~500 GeV/c**2**

## SM Higgs Search Channels

|         Production
DECAY | Inclusive | VBF | WH/ZH | ttH |
| --- | --- | --- | --- | --- |
| H → γγ | YES | YES | YES | YES |
| H → bb |  |  | YES | YES |
| H → ττ |  | YES |  |  |
| H → WW* | YES | YES | YES |  |
| H → ZZ*, Z l+l-, l=e,μ | YES |  |  |  |
| H → Zγ, Z →  l+l-, l=e,μ | very low σ |  |  |  |

- Low mass MH **≲ **200 GeV

- H **→ **γγ and H **→ **ZZ* **→** 4l are the only channels with a very good mass resolution ~1%

- Intermediate mass
- (200 GeV **≲ **MH **≲**700 GeV)

- High mass (MH **≳ **700 GeV)

- inclusive H **→** WW
- inclusive H **→** ZZ

- VBF qqH **→** ZZ **→** llνν
- VBF qqH **→** WW **→** lνjj

- M. pieri

## Higgs Reach

-     _final word  about SM Higgs mechanism  by 2009 or so_
-  However: it will take time to understand and calibrate ATLAS and CMS ...
-  In most difficult region mH < 130 GeV  3 different channels observable  robustness

- Important test for theories requiring a light Higgs (SUSY, Baryogenesis)

**Higgs Reach**

## Heavy MSSM Higgs Search

- At low tan , we may exploit
- the sparticle decay modes:

-  A, H   20 20   4*l**  **+ E**T**miss*
-  A, H in cascade decays of sparticles

- MSSM 5 Higgses: h,H,A,H****

- Contours for 5  discovery
- M**H****MAX** scenario
- New: includes VBF channels

-  A/H  
-  A/H  
-  A/H  bb/  in bb H/A

-  H  
-  H  tb

## Discovery/ Mass measurement

**MSSM Higgs****                        ********m/m**** (%)      300 fb****-1**
**h, A, H ********                                     ****0.1********0.4**
**H ******** 4 ********                                            ****0.1********0.4**
**H/A ******** ********0.1-1.5**
**h ******** bb                                                ****1********2**
****** ****hh ******** bb ********1-2**
****** ****Zh ******** bb ********                                ****1********2**
**H/A ******** ********1-10**

- 0.1-1%

- Different channels

## What can the LHC do?

- LHC will discover the SM Higgs in the full region up to 1 TeV or exclude its existence. If no Higgs, other new phenomena in the WW should be observed around 1 TeV
- The LHC will measure with full luminosity (100 fb**-1**)
- The Higgs mass with 0.1-1% precision
- The Higgs width, for m**H**> 200 GeV, with ~5-8% precision
- Cross sections x branching ratios with 5-20% precision
- Ratios of couplings with 10-30% precision
- Absolute couplings only with additional assumptions
- Spin information in the ZZ channel for m**H**>200 GeV

**What can the LHC NOT do?**

- See next talk...

##  Beyond the Standard Model

- Supersymmetry

- Extra dimensions

- New physics expected around the TeV scale 
- Stabelize Higgs mass, Hierarchy problem, Unification of gauge couplings, CDM,...

- +...

- + a lot of other ideas...
- Split SUSY, Little Higgs models,  new gauge
- bosons, technicolor, compositness,..

## Example of New Physics: Di-lepton Resonance

- If we are lucky:
- a signal could be
- seen very early on

## Examples of Dilepton Resonance Signatures

- Separate models with
- forward-backward
- asymmetries

- Reach masses up to 4-5.7 TeV depending on the model

- Z’ gauge bosons

- Z**h** bosons in Little Higgs Models

- Arkani-Hamed et al.
- Han et al.

## Curved Space: RS Extra Dimensions

- Study the channel ppGraviton e+e-

- sensitivity

- phenomenology

- signal+
- Drell-Yan
- backgr.

## Supersymmetry 

- SUSY could be at the
- rendez-vous very early on!

- Main signal: lots of activity (jets, leptons, taus, missing E**T**)
- Needs however good understanding of the detector & SM processes!!

- 10fb**-1**

- Therefore:
- SUSY one of the
- priorities of the
- “search” program

## Reach versus Integrated Luminosity

- If low energy Supersymmetry exists, LHC will almost certainly  observe it
- Squarks and Gluinos detectable up to 2.5-3 TeV mass with 300 fb**-1**
- Masses up to 1 TeV already detectable with 1 fb**-1**

- Usually minimal Supergravity (mSUGRA)
- taken for  studies 5 parameters
- m**1/2**: universal gaugino mass at GUT scale
- m**0**:    universal scalar mass at GUT scale
- tan: vev ratio for 2 Higgs doublets
- sign(): sign of Higgs mixing parameter
- A**0**:    trilinear coupling

## Sparticle Detection & Reconstruction

**Sparticle Detection & Reconstruction**

- Mass precision for a favorable benchmark point at the LHC
-                            LCC1~ SPS1a~ point B’

- Lightest neutralino  Dark Matter?
- Fit SUSY  model parameters to the
- measured SUSY particle masses to
- extract ****h**2**** **  O(10%) for LCC1

- hep-ph/0508198

**GeV**

- m**0**=100 GeV
- m**1/2**= 250 GeV
- A**0**=-100
- tan = 10
- sign()=+

## Is it SUSY?

- Look for variables sensitive to the particle spin eg. lepton charge asymmetries
- in squark/KKquark decay chains  Barr hep-ph/0405052; Smillie & Webber hep-ph/0507170

- KK like
- spectrum
- (small mass
- splitting)

- SPS1a benchmark
- type spectrum

- Method works better or worse depending on (s)particles spectrum

-                            Example: Universal Extra Dimensions
- Phenomenology: a Kaluza Klein tower pattern like a SUSY mass spectrum:
-                                       Can the LHC distinguish?

- e.g. Cheng, Matchev, Schmaltz hep-ph/0205314

## Recent Studies: New Signatures

-                Split Supersymmetry
- Assumes nature is fine tuned and SUSY is broken at some high scale
- The only light particles are the Higgs and the gauginos
-     - Gluino can live long: sec, min, years!
-     - R-hadron formation: slow, heavy particles containing a heavy gluino.
-      Unusual interactions with material
-       Gravitino Dark Matter and GMSB
- In some models/phase space the gravitino is the LSP
- Then the NLSP (neutralino, stau lepton) can live ‘long’

- Challenge to the experiments!

- Sparticles stopped in the detector or
- walls around of the cavern.
- They  decay after hours---months...

- Arkani-Hamed, Dimopoulos hep-th/0405159

- Eg. hep-ph/0508198

## But Also: QCD Studies @ LHC

- E.g. Jet Physics

- Huge cross sections:
- Eg for 1 fb**-1**  ~ 10000 events with E**T**> 1 TeV
-                              100 events with E**T**> 2 TeV

-  PDFs
-  Jet shape
-  Underlying event
-  **s**
-  Diffraction
-  BFKL studies
-  low-x
-  New physics?
- ...

- Understanding QCD at 14 TeV
- will be one of the first topics
- at LHC

- ...and a whole b-physics program

## LHCb:  b-physics at the LHC

- Sensitive to
- new physics
- complementary
- to ATLAS/CMS

- Examples

- CKM
- triangle

## Heavy Ion Physics at the LHC

**Heavy Ion Physics at the LHC**

**

*J/**ψ*

- Heavy ions part of the LHC physics program
- with ALICE, but also CMS and ATLAS

- LHC ready for heavy ions in 2008?

- High P**T**
- particle and
- jet production
- Jet-quenching

-  melt down

- Event shapes

- Size: 16 x 26 meters
- Weight: 10,000 tons

## Forward Coverage: TOTEM/LHCf

- LHCf:   measurement of
- photons and neutral pions
- in the very forward region
- of LHC
- Add a EM calorimeter at
- 140 m from the Interaction
- Point (of ATLAS)

- TOTEM: measuring the total, elastic and
- diffractive cross sections
- Add Roman pots (and inelastic telescope)
- to CMS interaction regions.
- Common runs with CMS planned

- Connection with
- cosmic rays

## Forward Detectors in CMS/ATLAS

- TOTEM: T1  3.1<  <4.7
- TOTEM T2  5.3< <6.7
- CMS Castor 5.25< <6.5

- CMS/.TOTEM: Extend the reach in  from ||<5 to || <6.7
- + neutral energy at zero degrees (ZDC)

**Forward Detectors in CMS/ATLAS**

- ATLAS: Roman Pots at 240 m
- Cerenkov Counter (LUCID)
- 5.4 << 6.1
- + neutral energy at zero degrees

- IP5

- IP1

- CMS+TOTEM: first full acceptance detector?

## What’s Next? Preparing for the Start-up

- Detectors, including LHCb and Alice
- will be fairly complete at start-up

-  Complete detector instalation  and prepare for detector
- commissioning with cosmics, single beams etc.

## Cosmic muons

- observed by
- ATLAS in the pit
- (recorded by hadron
- Tilecal calorimeter)

- Cosmic muons observed
- by CMS at IP5
- (recorded by hadron
- barrel calorimeter)

## Summary

- The LHC and its experiments are on track for first collisions in 2007 and physics runs starting from 2008 onwards
- Challenge: commissioning of machine and detectors of unprecedented complexity, technology and performance
- The LHC should be decisive in revealing the Electro Weak Symmetry Breaking mechanism in the SM (Higgs/no Higgs)
- The LHC will break new ground in exploring the TeV scale, hunting for new physics
- Will it be easy or shall we have to sweat through years of data  taking and hard work before we can claim a discovery ?
- But the LHC will also explore QCD in new domains, is a B-factory and a heavy ion collider
- PANIC08 should be very interesting.