The Large Hadron ColliderMachine, Experiments, PhysicsIntroduction to the lecture

Johannes HallerThomas Schörner-Sadenius

Hamburg UniversitySummer Term 2009

JH/TSS UHH SS09: LHC 3

If NO objections: ENGLISH!– … good opportunity for practice …– … but only reasonable if nobody gets lost …– … and if we can make sure that everybody understands everything … Requires your active participation (questions, discussion, criticism).

If objections: – slides in english, – but german as working language.

A) WORKING LANGUAGE, STYLE

Style: informal!– The material will not always be presented in the theoretically most rigorous style but in a rather pedagogical way. – Many of the contents are difficult to understand – and it would be a pity if you got lost on the way. Please ask all questions! I hope I can answer most of them immediately; if not, I will think about them and come back with an answer in the next session.

Very often only your questions will bring out the full truth, in the sense that I am partially “betriebsblind” and will have problems to spot places where you might have problems. You help your fellow students, and you help me in improving the lecture.

Please bring typos, errors, etc. in thelecture / in the slides to my attention!

JH/TSS UHH SS09: LHC 4

JunProf. Dr. Johannes Haller

– Studies in Heidelberg– First HEP contact: DESY summer student (1997, H1 and HASYLAB)– Diploma in Heidelberg (OPAL experiment) – Dissertation Heidelberg: Search for supersymmetry at HERA (H1).– CERN fellow (2004-2006): Work on the ATLAS trigger; search for new physics.– UHH JunProfessor: Priorities are ATLAS (trigger and new physics) and ILC.

B) LECTURERS

Dr. Thomas Schörner-Sadenius

– First HEP contact: Internship at the Crystal Barrel Experiment (CERN, 1996)– Diploma at LMU Munich (1998): (“Search for Higgs bosons …”), OPAL ToF. – Dissertation MPI f. Physik München / LMU (2001): QCD studies at H1. – CERN fellow (2001-03): Work on ATLAS trigger and on EW physics at OPAL (LEP).– UHH WissAss (03-08): ZEUS calorimeter, run coordination, QCD, 6m Tagger, …-- DESY: Head of Analysis Centre (since 2009)

JH/TSS UHH SS09: LHC 5

– Purpose - Experimental lecture on all aspects of the Large Hadron Collider (LHC) project: Accelerator, detectors, physics. - We do NOT intend to provide the theo- retical basics for particle physics (field

theory, Standard Model, gauge principle, etc.) – these topics have been discussed in other lectures.

– Prerequisits: - at least “Nuclear and Particle Physics”

(Kern- und Teilchenphysik, P5) - better: “Advanced Particle Physics” (Teilchenphysik für Fortgeschrittene)

– Credits: - Active participation in the lecture - presentation in seminar on LHC and associated issues.

C) ORGANISATIONAL MATTERS

– Date: Wednesday, 14:00-15.30, HS III.

– Working language: English (if no strong protests).

- Web page: www.desy.de/~schorner/lehre/ss09/lhc.html - Outline - Slides - News - Seminar

– Contacts: johannes.haller@desy.de thomas.schoerner@desy.de

– Slides Hopefully on web evening before lecture .

User: lectures Password: sadenius

JH/TSS UHH SS09: LHC 6

(0) Introduction, organisation, overview (TSS)(1) Accelerators and the LHC (TSS)(2) Basics of pp physics: factorisation, PDFs,

minimum bias, QCD, underlying events (TSS)(3) Detectors 1: Trigger, DAQ, Lumi (TSS)(4) Detectors 2: Calorimetry (TSS)(5) SM physics 1: Electroweak, QCD (TSS)(6) SM physics 2: Top (TSS)(7) SM physics 3: Higgs (JH)(8) Detectors 3: Tracking (JH)(9) Beyond the SM (JH)(10) SUSY 1: Theory (JH)(11) SUSY 2: Experiment (JH)(12) SLHC, VLHC and LHeC (JH)(13) LHC at Hamburg University (JH)

For more details, dates etc. please refer to: http://www.desy.de/~schorner/lehre/ss09/lhc.html

D) OUTLINE

UHH SS09: LHC

JH/TSS UHH SS09: LHC 8

Status of the Standard Model– LEP and SLD Collaborations et al., “Precision Electroweak Measurements on the Z Resonance”, hep-ex/0509008, Phys. Rept. 427 (2006) 257.– LEP Collaborations and LEP EWWG, “A Combination of Preliminary Electroweak Measurements and Constraints on the Standard Model”, hep-ex/0511027.– Scripts for the following lectures: - Das Elektroschwache Standarmodell, http://www.desy.de/~schorner/lehre/ws0607/ew.html - Physik jenseits des Standard-Modells, http://www.desy.de/~haller/lehre/ss07/vorlesung/bsm.html - Teilchenphysik f. Fortgeschrittene, http://www.desy.de/~schorner/lehre/ss06/teilchen2.html

Higgs– LEP Higgs WG, “Search for the standard model Higgs boson at LEP”, Phys.Lett.B565 (2003) 61, hep-ex/0306033.– V. Büscher and K. Jakobs, “Higgs boson searches at hadron colliders”, hep-ph/0504099.

SUSY– S. Martin, “A Supersymmetry Primer”, hep-ph/9709356.– Haber and Kane, “The Search for Supersymmetry”, Phys. Rept. 117 (1985) 75.

Other new physics – R. N. Mohapatra, „Unification and Supersymmetry“, Springer, 1991– John Ellis, "Beyond the standard model for hill walkers", hep-ph/9812235. – Salavat Abdullin et al., "Tevatron-for-LHC Report: Preparations for Discoveries", hep-ph/0608322.

E) LITERATURE, FURTHER INFORMATION

JH/TSS UHH SS09: LHC 9

LEP experiments– http://opal.web.cern.ch/Opal/PPwelcome.html– http://aleph.web.cern.ch/aleph/– http://l3.web.cern.ch/l3– http://delphiwww.cern.ch/

Sources of literature, data bases etc. – http://www-library.desy.de/spires/hep– http://arxiv.org – http://pdg.lbl.gov

E) LITERATURE, FURTHER INFORMATION

LHC experiments– http://atlas.web.cern.ch/Atlas/index.html– http://cms.cern.ch

TEVATRON experiments– http://www-d0.fnal.gov– http://www-cdf.fnal.gov

HERA experiments– http://www-zeus.desy.de– http://www-h1.desy.de

Physics at the LHC: – ATLAS Collaboration: “Physics TDR” , CERN-LHCC-99-15, http://atlas.web.cern.ch/Atlas/index.html

Documentation Proposal & TDR-- ATLAS Collaboration: “Expected Performance of the ATLAS Experiment - Detector, Trigger and Physics”,

http://arxiv.org/abs/0901.0512– CMS Collaboration: “Physics TDR”, CERN-LHCC-06-001,

http://cmsdoc.cern.ch/cms/cpt/tdr/ptdr1_final_colour.pdf

JH/TSS UHH SS09: LHC 10

We want to organise a seminar (instead of “Übungen”). Exact date to be discussed / defined.

Middle / end of term? 1-2 days? Weekend? Continuously during term? Talks 25`

Possible topics (suggestions, need to be defined more strictly): Calorimetry Tracking Triggering Higgs physics Aspects of SUSY LHC and cosmology Beyond the LHC Forward and diffractive physics Jet finding at the LHC Limit-Setting The Monte Carlo method Electroweak fits

F) SEMINAR

Organisational Meeting for Seminar: Wednesday, April 29, 15:30

(after the lecture)

JH/TSS 11

When starting a lecture on the LHC there are 4 questions which have to be answered:

Why are we not satisfied with the current state of particle physics (i.e. the Standard Model)?

What kind of extensions of the SM could we think of?

What kind of machine do we need to increase our knowledgeand to go further than the SM?

How could we possibly find (=detect) ‘new’ physics?

In today’s quick overview I will briefly address these questions.

1.0 INTRODUCTION

You are not necessarily expected to understand all details of today’s lecture; having participated in former specializedHEP lectures might help. Otherwise you will (partially) be enlightened during the course of the lecture.

UHH SS09: LHC

JH/TSS 12

The Standard Model (SM)- Renormalisable (local) gauge field theory

with complex group structure: SU(3)C×SU(2)L×U(1)Y.

- Incorporates Glashow-Salam-Weinberg model (=QED + weak theory) and QCD.

- Complex Lagrangian (shown before EWSM)!

Particle content of the Standard Model- 6 quarks (plus their antiquarks) (spin ½)- 3 charged and 3 neutral leptons (spin ½)- Fermions organised in three families or

generations!- 8 gluons, W±, Z0, γ (spin 1) - … what about the Higgs boson?

Particle interactions in the SMMediated by the exchange of one of the

gaugebosons (g,W±,Z0,γ), depending on particle charges (EM, weak, color).

Calculable using perturbation methods (if hard energy scale present and couplings small), or (for QCD) on the lattice.

1.1 INTRODUCTION: THE STANDARD MODEL

AAflavours

babQCDaQCD

aa

L RRRLWLGSW

FFqmDiqL

BBWW

mDimDiL

,

,

0

4

14

1

4

1

UHH SS09: LHC

H(?)

JH/TSS 13

SM is invariant under local gauge transformations and renormalisable. Postulate of local gauge leads to existence of gauge bosons and fixes form of interactions.Using Euler-Lagrange equation on Lagrange density gives equations of motion (e.g. Dirac equation).

Remember: QED

– Gauge transformation (change of phase):

– in accordance to that: covariant derivative and gauge boson A with fixed behaviour under gauge transformation:

– Physics invariant! Noether theorem conserved quantity: electric charge!

1.1 INTERMEZZO: QED AND QCD

Remember: QCD – Gauge transformation: Rotation in color space:

– more complex structure of covariant derivative and of gluon fields under transformation (non-abelian theory with gluon self-interaction):

– Physics (Lagrange density) invariant under color transformations.

Remember: GSW Theory… next page

FFAqmiL4

1)(

)()(exp)()( xxiqxx

iqAD

)(2

exp)()(8

1

xg

i

b

g

r

x

b

g

r

xj

jjS

)()()()( xxAxAxA

jjS

lkjklSjjjj

Gg

iD

GfgGGG

2

/

k: rotation angles in color space, fjkl: structure constants j: rotation matrices (Gell-Mann, 33)

UHH SS09: LHC

JH/TSS 14

Glashow-Salam-Weinberg: SU(2)L×U(1)Y

– covariant derivative:

– The Wj are new vector fields (with their own

kinetic terms). It follows:

Invariant, if:

– To get also the photon, include further U(1) IA (masses neglected):

1.1 INTERMEZZO: GSW

– Go from W,B fields to W,Z,photon:

– Using …

… we arrive at:

jjWigTD

cbabcaaaa WgxWWW )(/

,4

1aaaa WWWTgmiL

BBWWDiDiL aaR

RRL

LL 4

1

4

1,0

BY

giD

BY

gWgTiWTWTigD

2 0

2

0

33

ZA

AZ

A

Z

B

W

WW

WW

WW

WW

sincos

sincos

cossin

sincos3

e,3

e,3

2sincos

2cossin

ZY

gTgii

AY

gTgiiL

WW

WWZ

2

2cossin

3

3

YeeT

YgTgeQ WW

WW gge cossin

QTeYgTg W

WWWW

2

33 sinsincos2sincos

ZQT

eeQAiiL W

WWZ

23 sin

sincos

UHH SS09: LHC

JH/TSS 15

– Especially combined fits to masses of t, W, H interesting (using variety of LEP/ TEVATRON data):

– LEP: There are exactly 3 interacting neutrinos (plus perfect description of Z boson line shape)!

Success of the SM:– No measurement to-date in contradiction to SM predictions!– SM does not only describe, but can predict – for example mass of top quark (in 1992!):

– Underlying effect: Virtual corrections – higher order terms in perturbative SM expansions!

Quadratic/logarithmic sensitivity to Mt, MH!

1.1 THE STANDARD MODEL: SUCCESSES

222 ln HtZ MBMAM

2GeV 9.170 cM t

Z Z Z ZHt

UHH SS09: LHC

JH/TSS 16

Even Higgs mass predicted:– MH ~ 76 GeV, MH < 144 GeV (Δχ2=2.7, CL=95%).

– But: Direct searches (yellow area) give higher limits:

… first hint towards a problem?

1.1 THE STANDARD MODEL: SUCCESSES

GeV 5.114HM

Going into a bit more detail: – Overall agreement of data with SM predictions is excellent:

UHH SS09: LHC

JH/TSS 17

More EW physics: Cross-section ee WW (LEP):– Requires calculation of many diagrams!

1.1 THE STANDARD MODEL: SUCCESSES

… and EW physics at HERA: – Electroweak unification established at HERA!– Neutral = charged current at high Q2!

Photon:

W boson:41~ Q

2

22

2

~

W

W

MQ

M

(MW)2

UHH SS09: LHC

JH/TSS 18

Average αS(MZ) : 1% uncertainty:

1.1 THE STANDARD MODEL: SUCCESSES

0010.01189.0 ZS M

)/ln()233(

12)(

22

QNQ

fS

Also strong interactions precisely measured and described: – For example the strong coupling constant αS:

– Or the proton structure from deep inelastic electron-proton scattering (HERA):

2222

22 ,,ln

,QxgPQxFP

Qd

QxdFgqSqgS

UHH SS09: LHC

JH/TSS 19

Testing– Coupling αS;

– PDFs fi;– Factorisation– PDF universality– QCD dynamics– …

Jet cross-sections at HERA and Tevatron:

1.1 THE STANDARD MODEL: SUCCESSES

n jijiFR

nijjFpjiFpijiR

nSTev

n i BjFR

niFpiR

nS

nipi

n

nSHERA

xxxfxfdxdx

x

xxdxff

,

)(//

)(/

)(/

,,,,,

,,,

UHH SS09: LHC

JH/TSS 20

1.2 PROBLEMS OF THE SM

– large number of free (a-priori unknown) parameters: – Particle masses, mixing angles, couplings, … – Explanation for values in fundamental theory?

– Gauge structure? – Why exactly three (?) generations? – Connection fermions – bosons? – Connection leptons – quarks (charge!)? Connection SU(2)L, U(1)Y and SU(3)C?

– Without Higgs: SM diverges at 1 TeV! – Development of SM: story of avoiding singularities! – Only scalar boson can avoid divergencies. – Nature of EW symmetry breaking?

– SM decoupled from gravitation!

– In SM, no unification of couplings, masses etc. – Hoping for more fundamental theory to unify these parameters?

– Hierarchy and fine-tuning problems?

– Question of dark matter? – No SM candidate!

UHH SS09: LHC

JH/TSS 21

1.3 POSSIBLE EXTENSIONS OF THE SM

Many proposals on the market, some quite esoteric. Hottest candidates for discoveries at the LHC:

– (one or more) Higgs bosons (note that “only” the SM Higgs boson would not solve too many of the above mentioned problems!).

– Supersymmetry: - Symmetry between fermions and bosons proposed by Wess and Zumino in 1973.- introduce SUSY partner for all SM particles.- SUSY must be broken symmetry!

Arguments for SUSY:– Why not? - compatible with all

experimental data! – Last extension of Poincare group of SRT

(after translation, rotation, Lorentz trafo, C,P,T).

– Explanation of spin?– removes fermion-boson asymmetry! – Leads to unification of interactions

(GUT). – Solves hierarchy problem. – Introduces dark matter candidate

(LSP). – Predicts MH < 130 GeV.

– Allows introduction of gravity – is limit of string theories at low energies.

Discovery of SUSY similarly fundamental like discovery of antimatter!

Leptonen (e, Leptonen (e, ee, …), …)Quarks (u, d, …)Quarks (u, d, …)

GluonenGluonenWW

ZZ00

Photon (Photon ())

HiggsHiggs

GravitonGraviton

1/21/2

11

00

22

SpinSpin SM particlesSM particles SpinSpin

00

1/21/2

1/21/2

3/23/2

Sleptonen (e, Sleptonen (e, ee, …), …)Squarks (u, d, …)Squarks (u, d, …)

SUSY partnersSUSY partners

GluinosGluinosWinoWinoZinoZinoPhotino ( Photino ( ))

HiggsinoHiggsino

GravitinoGravitino

~~

~~ ~~~~ ~~

UHH SS09: LHC

JH/TSS 22

– Unification of gauge couplings in SUSY models!

– Solution to hierarchy problem via SUSY corrections to Higgs diagrams!

1.3 POSSIBLE EXTENSIONS OF THE SM – SUSY

– Unification of masses!

UHH SS09: LHC

JH/TSS 23

1.3 POSSIBLE SM EXTENSIONS: SUSY

¶ SM Fits – precise measurement of Mt, MW allows exclusion SM and confirmation of SUSY?

¶ currently: … heavy SUSY prefered!

UHH SS09: LHC

JH/TSS 24

1.3 POSSIBLE SM EXTENSIONS: SUSY If gravitation ~ 1/r2 expect rotational curves v(r) ~ 1/sqrt(r) (Kepler)

New form of invisible matter:Dark Matter = SUSY particles ?

Solar system Galaxy NGC6503

UHH SS09: LHC

JH/TSS 25

1.4 MOTIVATION FOR THE LHC

History of particle physics: Discoveries mostly done at hadron machines (cf. Livingston plot):

– ISR: hard interactions QCD!– SppS: W and Z!– Tevatron: top Quark

UHH SS09: LHC

JH/TSS 26

Higgs, SUSY, ED, CI, …… all propose “new” physics at high energy scales and high particle masses

Other view: We are interested in the smallest possible structures of matter

need high energy

Problem in ring accelerators: synchrotron radiation! Loss per turn

proportional to inverse of ring radius, to fourth power of energy and to fourth inverse power of particle mass:

Choose the heaviest reasonable particles in the largest possible radius!

… Large Hadron Collider !

1.4 MOTIVATION FOR THE LHC

History of particle physics: Discoveries mostly done at hadron machines (cf. Livingston plot):

– ISR: hard interactions QCD!– SppS: W and Z!– Tevatron: top Quark

2mcE ~px

41

m

E

RE

UHH SS09: LHC

JH/TSS 27

Other BSM models:– Contact interactions– Extra dimensions– Technicolor– Extra Z bosons– …

Forward and diffractive physics:– Total cross-section measurements– Understand diffraction– Saturation phenomena– Low-x physics

Heavy ions:– Quark-gluon plasma– …

… you name it …

1.5 LHC PHYSICS PROGRAM OVERVIEW

Standard Model physics:– Top: all quantum numbers– W,Z (and possibly PDFs from that?)– QCD studies (jets, prompt photons, strong

coupling αS, …) important as background to all BSM studies!

– Heavy flavours (b physics)All SM topics also have relevance for physics

beyond the SM – either as backgrounds or because BSM physics could reveal itself in SM signatures …

Higgs physics:– SM Higgs: Quantum numbers? – Higgs in SM extensions? – Little Higgs

Supersymmetry:– Discover!– Understand: Which model? – What can we tell about physics at the

highest scales (unification?).UHH SS09: LHC

JH/TSS 28

1.6 THE LHC AND ITS EXPERIMENTS

UHH SS09: LHC

JH/TSS 29

1.6 THE LARGE HADRON COLLIDER

– proton-proton collider, √s = 14 TeV = 14·1012 eV– frequeny: 40 MHz (25 ns, +overlays) – max. luminosity: 1034 cm-2s-1, 100fb-1/a. – Start: Delayed until autumn 2009– Experiments ATLAS, CMS (LHCb, ALICE)

UHH SS09: LHC

JH/TSS 30

1.6 THE ATLAS EXPERIMENT- Length ~40 m- Diameter ~25 m- Weight ~7000 t- 108 channels (2MB/event)- ‘Inner Detector’ (tracking)

- Numerous calorimeters- Large muon system

- central: solenoid around ID, Toroids in muon system- End caps: Toroidal fields

~40 Nations~150 Institutes~2000 physicists

UHH SS09: LHC

JH/TSS 31

1.6 ATLAS: CAVERN

UHH SS09: LHC

JH/TSS 32

1.6 ATLAS: STATUS (~MÄRZ 2007)

Requirements: – 5% pT resolution for muons (1 TeV)– 20 μm spatial resolution– EM energy scale to 0.1% – uniformity: 1%

UHH SS09: LHC

JH/TSS 33

1.6 ATLAS: ‘INNER DETECTOR’: TRACKING

Pixel detector:

- 3 barrel layers - 2•4 end discs - 140•106 channels- R=12m,z,R=~70m- || <2.5

Silicon Tracker:

- 4 barrel layers, || <1.4 - 2•9 end discs, 1.4 < < 2.5- area 60 m2

- 6.2•106 channels- R=16m, z,R=580m

‘Transition Radiation Tracker (TRT)’

- 0.42•106 channels- =170m pro tube- || <2.5

UHH SS09: LHC

JH/TSS 34

1.6 ATLAS: CALORIMETERS ‘Hadronic Tile’

- 463000 scintillating ‘tiles’- 10000 PMTs- granularity 0.1•0.1 - : <1.0, (0.8-1.7)- L=11.4 m, Rout=4.2 m

‘Hadronic LArEndcaps’

- Steel aboserber - 4400 channels- 0.1•0.1 / 0.2•0.2- 1-5

‘EM LAr Accordeon’

- Lead absorber - 174000 channels- 0.025•0.025- : <2.5, <3.2

‘Forward LAr’

- 30000 ‘rods’, each 1mm- Cell size 2-5cm2 (4 rods)- : <3.1, <4.9- copper / tungsten

‘LAr Pre-Sampler’

Compensates energy loss in front of calorimeters

UHH SS09: LHC

JH/TSS 35

1.6 ATLAS: MUON SYSTEM

‘Monitored Drift Tubes’

- 3 cylinders at R=7, 7.5, 10m- 3 layers at z=7, 10, 14 m- 372000 tubes, 70-630 cm- space=80m, t=300ps (24-bit FADCs)

‘Cathode Strip Chambers’

- 67000 wires- space=60m, t=7ns

‘Thin Gap Chambers’

- 440000 channels- ~MWPCs

‘Resistive Plate Chambers’

- 354000 channels- space=1cm- Trigger signals in 1ns

UHH SS09: LHC

JH/TSS 36

Task of the trigger (and DAQ):– Identify, select and read-out interesting

events and reject the others in short time:

ATLAS: 3-layer system:

1.6 ATLAS: TRIGGER AND DAQ

Cross-sections at the LHC:– Factors 109 between bread-and-butter

physics and interesting processes like Higgs, SUSY …

– In addition, extremely high rate (25 MHz) with large event sizes (2 MB) need fast and efficient rejection of uninteresting events UHH SS09: LHC

JH/TSS 37UHH SS09: LHC

JH/TSS 38

Transverse slice through CMS detectorClick on a particle type to visualise that particle in CMS

Press “escape” to exit

UHH SS09: LHC

¶ Almost complete coverage of full solid angle … with “individual” detection capabilities for all particle types.

JH/TSS 39

1.6 PARTICLES IN CMS

¶ Almost complete coverage of full solid angle … with “individual” detection capabilities for all particle types.

UHH SS09: LHC

JH/TSS 40

1.6 SUSY EVENT IN CMS

Squark produktion ET,miss = 360 GeV

ET,jet = 330, 140, 60 GeV

φ η

UHH SS09: LHC