LHC’s Second Run Hyunseok Lee 1. 2 ■ Discovery of the Higgs particle

1

LHC’s Second Run

Hyunseok Lee

2

■ Discovery of the Higgs par-ticle

3

• "for the theoretical discovery of a mechanism that contributes to our understanding of the origin of mass of subatomic particles, and which recently was confirmed through the discovery of the predicted fundamental particle, by the ATLAS and CMS experiments atCERN's Large Hadron Collider."

■ Who made the discovery possible

4

Oct 2008LHC

Official In-auguration

Mar 2010Proton colli-sion at 7TeV

Jul 2012Discovery of

the Higgs particle

Feb 2013Shutdown

Apr 2015Proton colli-

sion on 13TeV

■ Now is the Time!

We’re here!

LHC 2nd Run

■ Overview

Backgrounds

Particle Ac-celerator

The Standard Model

Upgrades

Beam

Magnet &Software

New Physics

Check of SM

Beyond SM

Dark Matter

• Backgrounds• Particle Accelerator• The Standard Model

• LHC upgrades• Beam• Magnet, Software

• New Physics• Check for SM• Beyond SM• Dark Matter

6

LHC 2nd Run

■ Why Particle Accelerator?

Backgrounds


The Standard Model

Upgrades

Beam

Magnet &Software

New Physics

Check of SM

Beyond SM

Dark Matter

p

p

p

7

• Einstein’s Special Relativity

enables chain of processes involving vari-ous particles in the regime of the allowed energy, restricted by certain rules such as conservation laws.

LHC 2nd Run

■ Particle is not Walnut

Backgrounds


The Standard Model

Upgrades

Beam

Magnet &Software

New Physics

Check of SM

Beyond SM

Dark Matter

8

LHC 2nd Run

■ Large Hadron Collider

Backgrounds


The Standard Model

Upgrades

Beam

Magnet &Software

New Physics

Check of SM

Beyond SM

Dark Matter

Lake Geneva

Large Hadron Col-lider

27 km circumference

CMS

ATLAS

LHCb

ALICE

9

• Accelerates in stages thenenters the beam ring

LHC 2nd Run

■ LHC Structure - Accelera-tor

Backgrounds


The Standard Model

Upgrades

Beam

Magnet &Software

New Physics

Check of SM

Beyond SM

Dark Matter

※Energy of proton mass ~ 1GeV

10

• Proton beams orbit along the beam ring guided by magnets(Lorentz force)• Collide at some fixed points

LHC 2nd Run

■ LHC Structure – Beam Ring

Backgrounds


The Standard Model

Upgrades

Beam

Magnet &Software

New Physics

Check of SM

Beyond SM

Dark Matter

11

• Detectors track down particles’ trajectory, momentum, energy, …to study the collisions byreconstruction of ‘events’

LHC 2nd Run

■ LHC Structure - Detector

Backgrounds


The Standard Model

Upgrades

Beam

Magnet &Software

New Physics

Check of SM

Beyond SM

Dark Matter

12

LHC 2nd Run

■ LHC Structure – Data Flow

Backgrounds


The Standard Model

Upgrades

Beam

Magnet &Software

New Physics

Check of SM

Beyond SM

Dark Matter

• Data• Type• Position• Momentum• Energy• Etc.

13

LHC 2nd Run

■ How does analysis work?

Backgrounds


The Standard Model

Upgrades

Beam

Magnet &Software

New Physics

Check of SM

Beyond SM

Dark Matter

Particle Accelerator + Detector

Simulate the collisionbased on theory

MC sampleData

Selection Cut

Selected Event

Analysis

Verification:Compare with theoryand preceding analysis

Apply Selection code toselect events and getdistribution of variables

p

p

p

p

14

LHC 2nd Run

■ Need Theory!

Backgrounds


The Standard Model

Upgrades

Beam

Magnet &Software

New Physics

Check of SM

Beyond SM

Dark Matter



MC sampleData

Selection Cut

Selected Event

Analysis



So, What is the Theory?

p

p

p

p

15

LHC 2nd Run

■ The Standard Model (SM)

Backgrounds


The Standard Model

Upgrades

Beam

Magnet &Software

New Physics

Check of SM

Beyond SM

Dark Matter

16

LHC 2nd Run


Backgrounds


The Standard Model

Upgrades

Beam

Magnet &Software

New Physics

Check of SM

Beyond SM

Dark Matter

17

• Quarks are held together to form Hadrons• Mesons: 2 quarks.

• ex) pion • Baryons: 3 quarks.

• ex) proton

LHC 2nd Run


Backgrounds


The Standard Model

Upgrades

Beam

Magnet &Software

New Physics

Check of SM

Beyond SM

Dark Matter

18

LHC 2nd Run


Backgrounds


The Standard Model

Upgrades

Beam

Magnet &Software

New Physics

Check of SM

Beyond SM

Dark Matter

19

LHC 2nd Run

■ SM limitation - Gravity

Backgrounds


The Standard Model

Upgrades

Beam

Magnet &Software

New Physics

Check of SM

Beyond SM

Dark Matter

Black holes, Dark mat-ter, …

20

• Fine-tuning• Matching between big and small numbers

• Does not necessarily mean that the theory is wrong, but some information must be missing.

• Why it has to be that way?• Beyond the Standard Model (BSM) Theories

LHC 2nd Run

■ SM limitation - Natural-ness

Backgrounds


The Standard Model

Upgrades

Beam

Magnet &Software

New Physics

Check of SM

Beyond SM

Dark Matter

− ¿

21

• In LHC, protons are accelerated to high energy and collide to provide data for par-ticle physics• Based on the successful theory of elemen-

tary particles, ‘the Standard Model,’ physi-cists analyze the data from LHC• The Standard Model has limitations, and

we’ll see how LHC can help breaking through the limitations.

LHC 2nd Run

■ Summary - Backgrounds

Backgrounds


The Standard Model

Upgrades

Beam

Magnet &Software

New Physics

Check of SM

Beyond SM

Dark Matter

22

• Upgraded during 2 years of shutdown• Hardware maintenance and repair is done• Using the acquired data of the first run,

optimized and strengthened experiments.• More stable and efficient data acquisition• Most importantly, the proton collision en-

ergy increased from 8 TeV to 13 TeV

LHC 2nd Run

■ Upgrades

Backgrounds


The Standard Model

Upgrades

Beam

Magnet &Software

New Physics

Check of SM

Beyond SM

Dark Matter

23

• Not just like crushing walnut harder!LHC 2nd Run

■ Higher energy beam

Backgrounds


The Standard Model

Upgrades

Beam

Magnet &Software

New Physics

Check of SM

Beyond SM

Dark Matter

24

• Totally new physics might be observed• Caveat: the particle’s mass is not necessar-

ily the limit for collision energy

LHC 2nd Run

■ Higher energy beam

Backgrounds


The Standard Model

Upgrades

Beam

Magnet &Software

New Physics

Check of SM

Beyond SM

Dark Matter

𝐸=𝑚𝑐2

-------------------8 TeV----------------

Higgs boson

Top quark

-------------------13 TeV--------------

New particle?New phenomena?

…

The first run

The second run

25

• Much more collision data!LHC 2nd Run

■ Narrower, Closer

Backgrounds


The Standard Model

Upgrades

Beam

Magnet &Software

New Physics

Check of SM

Beyond SM

Dark Matter

26

• Superconducting magnets are essential for guiding the proton beams

• Repaired magnets• Connection that provides alternative path

for current• Quench-protection system• Superior cryogenics

LHC 2nd Run

■ Resilient Magnet

Backgrounds


The Standard Model

Upgrades

Beam

Magnet &Software

New Physics

Check of SM

Beyond SM

Dark Matter

27

• 1 billion collision/s• Most of the collisions are uninteresting,

leaving perhaps few hundred collision/s• Needs fast filtering algorithm (‘trigger’) to

make search efficient and cope with real limitations of data storage

LHC 2nd Run

■ Improved Algorithm

Backgrounds


The Standard Model

Upgrades

Beam

Magnet &Software

New Physics

Check of SM

Beyond SM

Dark Matter

28

LHC 2nd Run

■ Summary - Upgrades

Backgrounds


The Standard Model

Upgrades

Beam

Magnet &Software

New Physics

Check of SM

Beyond SM

Dark Matter

• Beam• Higher energy(8 TeV -> 14 TeV)• Narrower beam• Closer proton packets

• Magnet, Software• Resilient magnet• Improved algorithm

• Search for new physics with stable and fast data acquisition!

29

• Now, we have numerous BSM theories • In the end, a theory should describe the

nature that we live in.• Experiments can tell what the nature is,

and thereby narrow down the BSM candi-dates that we would focus on further.

LHC 2nd Run

■ New Physics

Backgrounds


The Standard Model

Upgrades

Beam

Magnet &Software

New Physics

Check of SM

Beyond SM

Dark Matter

30

• Higgs boson has been discovered, but with limited statistics• Still unknown: Multiple Higgs particles,

rare decay channel, accurate properties,…

• Faster data acquisition, increased chance of creating Higgs bosons in collisions• Detect small, subtle differences between

the Higgs boson in experiment and the prediction of the Standard Model

LHC 2nd Run

■ Check of SM: Higgs boson

Backgrounds


The Standard Model

Upgrades

Beam

Magnet &Software

New Physics

Check of SM

Beyond SM

Dark Matter

31

• Each SM particle gets a superpartner• Provides natural mechanism to resolve

fine-tuning problem• Might be able to detect superpartner par-

ticle with higher energy beams• Study of the properties of new particle will

narrow down the supersymmetry models.

LHC 2nd Run

■ Beyond SM: Supersymme-try

Backgrounds


The Standard Model

Upgrades

Beam

Magnet &Software

New Physics

Check of SM

Beyond SM

Dark Matter

32

• Constitutes most of the mass of universe• Weakly interact with other SM matter• Inferred from gravity (motion of galaxy)• LHC cannot see it directly, but indirect de-

tection might be possible from missing energy and momentum

LHC 2nd Run

■ Dark Matter

Backgrounds


The Standard Model

Upgrades

Beam

Magnet &Software

New Physics

Check of SM

Beyond SM

Dark Matter

33

• LHC’s second run will give us new oppor-tunity to compare our existing theories with the nature• Improved data acquisition will help precise

study of the Standard Model• Higher collision energy might show new

particle predicted by some BSM theories• Search for the dark matter would benefit

the field of cosmology too

LHC 2nd Run

■ Summary – New Physics

Backgrounds


The Standard Model

Upgrades

Beam

Magnet &Software

New Physics

Check of SM

Beyond SM

Dark Matter

34

• LHC collides proton pairs to study elemen-tary particles described by Standard Model and to probe into the deeper na-ture• Upgrades enable the search for new

physics in a stable and fast manner• Physicists expect the new run to guide to-

ward new physics by precise study of SM, providing evidence for BSM, and searching for the dark matter• Now in calibration – stay tuned!

LHC 2nd Run

■ Conclusion

Backgrounds


The Standard Model

Upgrades

Beam

Magnet &Software

New Physics

Check of SM

Beyond SM

Dark Matter

35

LHC 2nd Run

■ Well, since I have more time…

Backgrounds


The Standard Model

Upgrades

Beam

Magnet &Software

New Physics

Check of SM

Beyond SM

Dark Matter

Backup Slides

An Example of Analy-sis:

Higgs Discovery

36

LHC 2nd Run

■ Starting Point

Backgrounds


The Standard Model

Upgrades

Beam

Magnet &Software

New Physics

Check of SM

Beyond SM

Dark Matter

• We want to know if the Higgs boson exists.• We know that if the Higgs boson exists,• Its mass should lie inside strict limits set by

previous searches• The collisions in which the Higgs boson is cre-

ated will involve one of the decay channels that results in the known final particles.Ex)

37

LHC 2nd Run

■ The Idea

Backgrounds


The Standard Model

Upgrades

Beam

Magnet &Software

New Physics

Check of SM

Beyond SM

Dark Matter

• Thus, we can try to reconstruct the Higgs boson from final particle candidates, while the reconstructed mass is allowed within the limits.• Problem:

We cannot say that the Higgs boson exists just because the final particles could make it – they could be from other process!• Answer:

Gather statistics, and compare rates of the Higgs events vs the other events!

38

LHC 2nd Run

■ Procedure

Backgrounds


The Standard Model

Upgrades

Beam

Magnet &Software

New Physics

Check of SM

Beyond SM

Dark Matter



MC sampleData

Selection Cut

Selected Event

Analysis



p

p

p

p

39

LHC 2nd Run

■ What do we analyze?

Backgrounds


The Standard Model

Upgrades

Beam

Magnet &Software

New Physics

Check of SM

Beyond SM

Dark Matter

• The rate of MC sample events with or without Higgs boson, and compare them with the real data

“Observation of a new particle in the search for the Standard Model Higgs boson with the ATLAS detec-tor at the LHC”,ATLAS Collabora-tion, Phys.Lett.B.(2012)

Documents

LHC’s Second Run Hyunseok Lee 1. 2 ■ Discovery of the Higgs particle