introduction to particle collider experimentshome.kias.re.kr/mkg/upload/collider/suyong_choi.pdf ·...

Introduction to

Particle Collider

Experiments Suyong Choi

Korea University

1

Contents

• http://goo.gl/VlBhfq

• Preliminaries

• Particle Colliders

• Cross Section and Luminosities

• Particle detectors for Particle Colliders

2

http://goo.gl/VlBhfq

http://goo.gl/VlBhfq

PRELIMINARIES

3

Natural Units

• ℏ = 1, 𝑐 = 1

• 𝐸2 = 𝑚2 + 𝑝 2

• Δ𝑝Δ𝑥 ≥1

2

• Recover correct dimensions later by multiplying suitable

combinations of

• ℏ𝑐 = 197 𝑀𝑒𝑉 ⋅ 𝑓𝑚

• 𝑐 = 3 × 108 𝑚/𝑠

4

Four Vector

• Four vector: 𝐸, 𝑝𝑥, 𝑝𝑦, 𝑝𝑧 = 𝑝

• Sum of two four vectors:

• 𝐸1, 𝑝1𝑥, 𝑝1𝑦, 𝑝1𝑧 + 𝐸2, 𝑝2𝑥 , 𝑝2𝑦, 𝑝2𝑧 =

𝐸1 + 𝐸2, 𝑝1𝑥 + 𝑝2𝑥 , 𝑝1𝑦 + 𝑝2𝑦, 𝑝1𝑧 + 𝑝2𝑧

• Lorentz Invariant: 𝐸2 − 𝑝 2 = 𝑝2

• In case of a real particle, this is its mass

5

Definitions and Relations

• 𝛽 =𝑣

𝑐= 𝑣

• 𝛾 =1

1−𝛽2

• 𝑝 =𝑚𝛽

1−𝛽2= 𝑚𝛽𝛾

• 𝐸 = 𝑚𝛾

• For 𝛽 → 1, 𝐸 ≈ 𝑝

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PARTICLE COLLIDERS

7

LHC

8

LHC 가속기 및 실험

지하 100m, 둘레 27km

ATLAS, CMS, ALICE, LHCb, TOTEM, LHCf

CERN 연구소

1954년 설립, 유럽 20 개의 회원국 참가

핵 및 입자 물리 관련 순수 과학 연구

연간 약 1.3 조원 독립 예산 (스페인 1200억 분담)

다수 특허 보유 – World Wide Web의 발상지

CERN Accelerator

Complex

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Particle Colliders

• Center of mass energy

• 𝑠 = 2𝐸𝑏𝑒𝑎𝑚

• 𝑝𝑝 or 𝑝𝑝 Collider

• 𝑠: 7,8,13,14 TeV for LHC

• Described well by quarks/gluons collisions

• they carry 1/3 of proton momentum on average

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c

쿼크

발견

b

쿼크발견

t

쿼크발견

W,Z

발견

힉스발견

Accelerator Technologies

• New accelerator

technologies needed

to reach factor of

10~100 in Energy

1/22/2015 Winter School on Collider Physics

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LHC Dipole Magnet

• 1232 15 meter dipole

magnets in LHC

tunnel

• 11000 ampere current

max

• 8.5 T max. B field

• 1.9K operating

temperature


12

Charged Particle Motion

in Constant B Field

• Motion of charged particle perpendicular to 𝐵

𝛾𝑚𝑣2

𝑟= 𝑞𝑣𝐵 ⇒ 𝛾𝑚𝑣 = 𝑝𝑇 = 𝑞𝐵𝑟

• Practical equation: 𝑝𝑇𝐺𝑒𝑉

𝑐= 0.3 × 𝐵 𝑇 × 𝑟[𝑚]


13

Storage Rings

• Storage ring • Probability of interaction

is low at high energies

• Only a small fraction of particles interact

• Need to recycle the beams

• LHC has two vacuum rings that cross at collision points


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Fixed Target vs Collider

• Colliding beam experiment

• First proposed in 1956 by Kerst

• Oppositely directed beam with same energy

• Center of mass energy is 2𝐸 whereas in fixed target it is

2𝑚𝑡𝑎𝑟𝑔𝑒𝑡𝐸

• 1 TeV=1000 GeV energy beam, in a fixed target can only

produce 44 GeV of useful energy

• In collider, it is 2000 GeV


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𝑒+𝑒− and Hadron Colliders

• Electron collider

• Clean

• Precision measurement

• Due to synchrotron radiation, difficult to get to high energies (radiated power ~ 𝛾4/𝑟2)

• Hadron collider

• Easier to accelerate to high energies

• Proton breakup produces many particles

• Better for search for heavy particles – continuous range of E


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CROSS SECTION

AND LUMINOSITIES


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• Cross section for inelastic collision is ~0.1 barn at 10 TeV CM Energy (1 barn=10-24 cm2)

• If two protons are separated by distance less than b, then they collide and break up the proton

• cross section: 𝜎 = 𝜋𝑏2

Cross Section 1/22/2015 Winter School on Collider Physics

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b

Naïve Cross Section

• If beam energy is the only scale in the system, then

𝜎 ∝1

𝐸2

• From dimensional analysis

• If other scale present, then this is not valid


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Cross Section

and Luminosity

• If a certain process has 1 fb=10-15 barn, then probability

for this process to occur is 10-14 times smaller than that to

break up the proton

• In accelerators, you have a “bunch” of particles colliding

• N particles in transverse beam radius of r


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r

Luminosity

• Probability for interaction?

• Assume particles are uniformly distributed: 𝑁1𝜎

𝜋𝑟2

• By making the beam size r smaller, one can increase probability for interaction


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r

𝑁1

Luminosity

• Probability of interaction when two bunches collide

𝑃 =𝑁1𝜎

𝜋𝑟2𝑁2


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N1 N2

Instantaneous

Luminosity

• Rate of interaction and Instantaneous Luminosity

• In an accelerator bunches cross at a fixed frequency

𝑅 = 𝑓𝑁1𝑁2𝜎

𝜋𝑟2= ℒ𝜎

• Unit of instantaneous luminosity is usually in 𝑐𝑚−2𝑠−1

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May 13 2008

24 Collisions at the LHC

Bunch Crossing 4 10 7 Hz

7x10 12 eV Beam Energy 10 34 cm -2 s -1

Luminosity 2835 Bunches/Beam 10 11

Protons/Bunch

7/8/13/14 TeV Proton Proton colliding beams

Proton Collisions 10 9 Hz

Parton Collisions

New Particle Production 10 -5 Hz

(Higgs, SUSY, ....)

p p H

µ +

µ -

µ +

µ -

Z

Z p p

e - n

e

m +

m -

q

q

q

q

c 1

-

g ~

~

c 2 0 ~

q ~

c 1 0 ~

Selection of 1 event in 10,000,000,000,000

7.5 m (25 ns)

Cross Sections

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Integrated Luminosity

• 𝐿 = ℒ𝑑𝑡

• Unit of integrated luminosity: cm-2

• 𝜎 ℒ𝑑𝑡 : Expected number of events for certain process


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1 b-1 1024 cm-2

1 mb-1 = 103 b-1 1027 cm-2

1 mb-1 = 103 mb-1 1030 cm-2

1 nb-1 = 103 mb-1 1033 cm-2

1 pb-1 ?

1 fb-1 ?

“inverse

picobarn”

𝐻 → 𝑍𝑍 → 4ℓ 27

PARTICLE DETECTION IN

COLLIDER EXPERIMENTS

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Particle Detectors at

Coliders

• Symmetric, Layered, Hermetic

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Particle Detectors at

Colliders

• Most collider detectors are “general purpose” detectors

• Sensitive to all kinds of physics processes

• Detect variety of particles

• Large acceptance: from low to high 𝑝𝑇, low to high angle

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Particle Detection

• Energy loss of particles in medium

light, temperature change, ionization

detectable signal


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Particle

Principle of Particle

Detection

• To detect a particle

• The particle must reach the detector → particle must be long-lived

• AND interact with detector material

→ Ionize the material → light signal or electron signal

→ measurable signal above noise

• To distinguish particle types

• Different types interact differently

• Goal: measure particle type and momentum (or energy)

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General Particle Detector

Concept

• Different particles interact differently with material

• Electron and gamma interact early

• Hadronic particles undergo nuclear interactions with material

• Muons pass through


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EM Interactions

of Particles in Material


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Energy Loss by Charged

Particles Through Ionization

• Minimum ionizing

particle when 𝛽𝛾~3

−𝑑𝐸

𝑑𝑥∼ 2(𝑀𝑒𝑉 ⋅ 𝑐𝑚2/𝑔)

× 𝜌(𝑔

𝑐𝑚3)

• Relativistic rise ~ log 𝛽𝛾


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Radiative Energy Loss of

Relativistic Electrons

• Bremsstrahlung

• Depends on particle mass 1

𝑚2

• Much more important for 𝑒±

• Loss of energy

−𝑑𝐸

𝑑𝑥∝ 𝐸

• Radiation length 𝑋0 length scale where energy reduces to 1/e • Value depends on material


36

Electromagnetic Shower

• Ultrarelativistic electron/positron or high-energy 𝛾

• Bremsstrahlung pair production Bremsstrahlung

• Shower of electrons and photons are produced

• Process continues until electron energies are below the

critical energy for Bremsstrahlung


37

Hadronic Shower

• Pion, Kaon, proton, neutrons can interact with nucleus

• Nuclear cross sections are much smaller than EM interaction cross sections • Longer and wider showers

• Interaction length (𝜆) • scale of interaction

• Depends on material

• 𝜆 = 18𝑐𝑚 , 𝑋0 = 0.6𝑐𝑚 for lead


38

The depths not

drawn to scale

Hadronic Jets

CMS Detector 39

+z

CMS Quarter View 40

+z

𝜂 = − ln tan𝜃

2

CMS Slice 41

Measuring 𝑝𝑇 of Charged

Particles

• Radius of curvature R 𝑝𝑇 = 0.3𝑞𝐵𝑅

• Momentum resolution depends

• position resolution of each layer

• # of layers and distance between layers


42

d

R

Measuring Energy using

Calorimeters

• Energy in calorimeter ~ # of showered particles

• Fluctuations of showering determines energy resolution

• Example) Electromagnetic Calorimeter

• # of visible photons ~ Energy of stopped electron/gamma

• Fluctuation in # of photons → Energy resolution

43

Electromagnetic shower

in CMS PbWO4 crystal

Dilepton Resonances

• Muon momentum

• Tracker + muon detectors

• Detector alignment

• Electron energy

• Electromagnetic

calorimeter + tracker

• Effects of resolution

and event selection seen

44

EVENT RECONSTRUCTION AND

ANALYSIS

45

The Data Problem

• Cannot save all collision data

• Inelastic collision cross section is very large

• Trigger

• Select interesting events only

• High-pT objects


46

Event Reconstruction

• From electronic signals to particles (physics objects)

• Complex algorithms to reject noise

• Track reconstruction

• Jets

47

Hit Positions Track

segments Tracks

Calorimeter Energies

Clustering Jets

Data Analysis

• Preselection • Background rich sample

• Compare with known SM backgrounds (usually simulation)

• Test understanding of the detector and reconstruction algorithms

• Event selection • Signal rich sample

• Compare with signal+bkgd prediction

48

Collected

Data Signal

Region

Collected Data

Background

Preselection

Event Selection

Cross Section

Measurement

• Cross section formula: 𝜎 =𝑁 𝑜𝑓 𝐸𝑣𝑒𝑛𝑡𝑠−𝐵𝑘𝑔𝑑.𝐸𝑣𝑒𝑛𝑡𝑠

𝐴×𝜖× ℒ𝑑𝑡

• Acceptance (𝐴) – fraction of signal events that can be detected

• Kinematic – Certain momentum needed to reach detector

• Geometric – finite coverage, cracks

• Efficiency (𝜖) – fraction of accepted signal events that pass event selection

• Acceptance and efficiency measured from Simulated Events assuming theory correctly reproduces kinematics of the event

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Parameter Extraction

• For a given theory with {𝜃𝑖} parameters, predict expected

number of signal events

𝑆 = 𝐴({𝜃𝑖}) × 𝜖({𝜃𝑖}) × 𝜎({𝜃𝑖}) ℒ𝑑𝑡

• And compare with number from experiment: 𝑁 − 𝐵

• Uncertainty of 𝑁 − 𝐵 is 𝑁 𝛿𝐵 = 𝑁 + 𝛿𝐵 2

50

SELECT CMS RESULTS

51

Running 𝛼𝑠

52

Cross Sections Measured

at CMS

53

Particle Searches

54

LHC Long Term Schedule

• Operation up to 2035

55

7,8 TeV LS 1 Run 2

13,14 TeV LS 2

Run 3

14 TeV LS 3

~2035

Run 4,…

14 TeV

2013 2010 2015 2018 2020 2023 2025

25 fb-1 100 fb-1 300 fb-1 3000 fb-1

HANDS ON WITH REAL CMS

EVENT

56

CMS Event Display

• http://www.i2u2.org/elab/cms/event-display/

• Click “folder” → Select “collections” to look for various selected real data events

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http://www.i2u2.org/elab/cms/event-display/




한국-CMS 실험 사업

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한국 CMS 참여

• 1998-2011년까지 한국은 CMS검출기 제작에 총 20억원을

현금/현물로 지원 초전도자석의 테이블 (한국 중공업)

• 전방 뮤온 검출기 중 RPC 제작

• DAQ시스템 건설에 공헌

• 2007년부터 한-CERN 사업 안에서 진행

• 2014년 현황

• 8개 대학, 교수 14인, 17인 postdoc 포함 총 80 명

• 예산: 14.5억 (체재비, 인건비) + 6.7억 (검출기 R&D) = 21.2억

59

1998-2006 : 자석 회전 장치 60

1998-2006: 전방 뮤온

RPC 검출기 61

전방 저항판 (RPC) 검출기 RE4

제작 (2013-2014)

• KCMS RPC gap 660장 전량 공급

63

BACKUP

65

Cyclotron

• 1932 Lawrence and Livingston at Berkeley

• Accelerate with fixed RF frequency and constant B-field


66

60 Inch Cyclotron (1939)

67

220 ton magnet

16 MeV

184 inch Cyclotron (1942)

68

4000 ton magnet

200 MeV

Linear Accelerator

• In a uniform wave guide, 𝑣𝑝ℎ𝑎𝑠𝑒 > 𝑐, RF field quickly

becomes out of phase with particles

• We need a disk-loaded wave guide


69

time

Accelerator Structure

• Focusing


70

Synchrotron Accelerator

• Particle accelerates in closed path

• RF accelerating field should be synchronized with beam

• B field should be increased as E increases


71

Bending Charged

Particles

• Dipole magnetic field is used to bend


72

Mandelstam Variables

• Assume process

• In scattering between two particles, one can define 3 variables

𝑠 = 𝑝𝐴 + 𝑝𝐵2 = 𝑝𝐶 + 𝑝𝐷

2

𝑡 = 𝑝𝐶 − 𝑝𝐴2 = 𝑝𝐵 − 𝑝𝐷

2

𝑢 = 𝑝𝐴 − 𝑝𝐷2 = 𝑝𝐶 − 𝑝𝐵

2


73

pD

pC

pB pA

𝑝𝐴 + 𝑝𝐵 = 𝑝𝐶 + 𝑝𝐷

KEKB


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• 1998.12 ~ 2010. 6

• Asymmetric collider

𝐸𝑒− = 8 𝐺𝑒𝑉 𝐸𝑒+ = 3.5 𝐺𝑒𝑉

• Total integrated luminosity: 1052 fb-1

• CKM Matrix and b-quark sector probed to unprecedented degree

Tevatron

• Proton on antiproton at 1.96 TeV

• Discovered top quark in 1995

• 20 years of running (1989-2009)


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introduction to particle collider experimentshome.kias.re.kr/mkg/upload/collider/suyong_choi.pdf ·...

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