José Ocariz

(1)

José Ocariz

LPNHE –Université Paris Diderot et IN2P3

Les enjeux du LHC

(2)

José Ocariz

Les enjeux du LHC

(3)

Vers l’infiniment petit: la structure de la matière

(4)

Les constituants fondamentaux: leptons et quarks

(5)

Les quatre interactions fondamentales

(6)

Les quatre interactions fondamentales

(7)

Trois familles de leptons et de quarks

Particules et antiparticules

(8)

Les assemblages de quarks: hadrons

(9)

The Standard Model (SM) of fundamental interactions

(10)

The Standard Model (SM) of fundamental interactions

(11)

For the last 35 years, the SM has been successfully tested in experiments, with varying levels of accuracy, in many independent sectors :

Cross sections of lepton and hadron (pair) production up to M ~ TeV Electroweak unification (relations between masses and couplings) “Asymptotic freedom” property of QCD coupling at % level

“Universality” of weak interaction at 0.3% level V–A structure of charged weak current

Matter-antimatter symmetry (CP) violation through CKM mechanism Absence of electric dipole moments (and CP-V) at particle level

QED via e and µµµµ anomalous magnetic moments at ppm level … many more tests

The Standard Model (SM) of fundamental interactions

(12)

The Standard Model (SM) of fundamental interactions

For the last 35 years, the SM has been successfully tested in experiments, with varying

levels of accuracy, in many independent sectors :

(13)

The Standard Model (SM) of fundamental interactions

For the last 35 years, the SM has been successfully tested in experiments, with varying

levels of accuracy, in many independent sectors :

(14)

The Standard Model (SM) of fundamental interactions

For the last 35 years, the SM has been successfully tested in experiments, with varying

levels of accuracy, in many independent sectors :

(15)

The Standard Model (SM) of fundamental interactions

For the last 35 years, the SM has been successfully tested in experiments, with varying

levels of accuracy, in many independent sectors :

(16)

The Standard Model (SM) of fundamental interactions

For the last 35 years, the SM has been successfully tested in experiments, with varying

levels of accuracy, in many independent sectors :

(17)

The Standard Model (SM) of fundamental interactions

For the last 35 years, the SM has been successfully tested in experiments, with varying

levels of accuracy, in many independent sectors :

(18)

The Standard Model (SM) of fundamental interactions

Constraints on the Electroweak sector : Compare many

direct measurements and theoretical preds.

Up to ~10ppm precision measurements :

For the last 35 years, the SM has been successfully tested in experiments, with varying

levels of accuracy, in many independent sectors :

(19)

The Standard Model (SM) of fundamental interactions

For the last 35 years, the SM has been successfully tested in experiments, with varying levels of accuracy, in many independent sectors :

Constraints on the “quark mixing” (flavour) sector : Compare many direct

measurements and theoretical preds.

All measurements compatible With CKM mixing mechanism : Another impressive

SM success !

(20)

Unsolved issues within the SM

The Higgs is not yet discovered !

The Higgs is the only fundamental scalar ( )

What is the origin of the huge mass hierarchy between matter particles ?

. . . a n d :

Dark matter (and, perhaps, “dark energy”)

Baryogenesis and Leptogenesis (Matter-Antimatter asymmetry) Grand Unification of the gauge couplings

The gauge hierarchy Problem

The strong CP Problem (why is θ ~ 0 ?)

Neutrino masses

(21)

Most of these problems are related to the earliest moments of our Universe

Unsolved issues within the SM

(22)

What’s the matter with the matter ?

65%

30%

0.5% 4%

0.03%

Dark energy Dark matter Free H and He Stars

Neutrinos

Heavy elements

74%

22%

arXiv:astro-ph/0603451

Cosmology data : the universe contains lots of unknown matter and energy !

Moreover: the universe is “almost” empty (in terms of ordinary, baryonic matter)

and is mainly made of matter ; where did all the antimatter go ?

( )

baryon

baryon 10

~ 10

n n

n O

n

_γ

n

_γ

−

∆ =

Sakharov conditions (1967) for Baryogenesis

(23)

What’s needed : a three-fold approach …

(24)

What’s needed : a three-fold approach …

•Experimental tests of the SM, both in the gauge and flavour sectors :

… large-spectrum successes …

… but the SM leaves still many unanswered questions …

• Most envisaged SM extensions have in common that they introduce new particles at the TeV scale.

• To find these, a new collider, providing hard parton collisions with centre-of- mass energy well above 1 TeV is needed :

a Large Hadron Collider !

(25)

Motivation for the LHC

Mont Blanc (4810 m)

(26)

LHC CERN

Meyrin site

LHC : a pipeline of accelerators, 4 large experiments

(27)

ATLAS

CMS

ALICE LHCb

ma x: 1 50 m

LHC : a pipeline of accelerators, 4 large experiments

LIN- AC2 BOO- STER PS SPS LHC

50 MeV 1.4 GeV 26 GeV 450 GeV

7 TeV

PROTONS

20 minutes are required to accelerate a proton in the LHC from 450 GeV to 7 TeV

(28)

The LHC surpasses existing accelerators in 2 main aspects:

7 TeV beam energy in 26.7 km (LEP) tunnel (Tevatron: 0.98 TeV in 6.3 km)

LHC dipole field strength: 8.3 T HERA / Tevatron: ~ 4 T

Unprecedented peak luminosity for hadron machine

(note: no. of events = luminosity × cross section)

LHC (pp): ~ 10

³⁴

cm

^–2

s

^–1

[requires: many bunches + many protons + small beam size]

Tevatron/SppbarS: 2.5 × 10

³²

/ 6 × 10

³⁰

cm

^–2

s

^–1

The combination of very high field magnets and very high beam intensities required to reach luminosity targets makes LHC operation a great challenge

LHC : the Large Hadron Collider

(29)

LHC: Some Technical Challenges

Circumference (km) 26.7

100-150m underground

Number of superconducting twin-bore dipoles

1232

Cable Nb-Ti, cold mass 37million kg

Length of Dipole (m) 14.3

Dipole Field Strength (Tesla) 8.4

Results from the high beam energy needed

Operating Temperature (K) (cryogenics system)

1.9

Superconducting magnets needed for the high magnetic field

Super-fluid helium

Current in dipole sc coils (A) 13000

Results from the high magnetic field 1ppm resolution

Beam Intensity (A) 0.5

^2.2.10^-6loss causes quench

Beam Stored Energy (MJoules) 362

Results from high beam energy and high beam current 1MJ melts 1.5kg Cu

Magnet Stored Energy (MJoules)/octant 1100

Results from the high magnetic field

(30)

2808 bunches filled with 10 ¹¹ protons à 7 TeV per bunch 360 MJ stored energy per proton beam

Equivalent to Colliding 2 ×××× 120 Elephants

120 elephants with 40 km/h 120 elephants with 40 km/h

Energy of a single 7 TeV proton equivalent to flying

Eye of a needle: 0.3 mm diameter Proton beams at interaction point are

High energy collisions ? a concept in perspective

(31)

2808 bunches filled with 10 ¹¹ protons à 7 TeV per bunch 360 MJ stored energy per proton beam

Equivalent to Colliding 2 ×××× 120 Elephants

120 elephants with 40 km/h 120 elephants with 40 km/h

Energy of a single 7 TeV proton equivalent to flying mosquito (1 µJ)

Eye of a needle: 0.3 mm diameter Proton beams at interaction point are 20 x smaller: 16 µµµµ m diameter

High energy collisions ? a concept in perspective

(32)

The four large LHC experiments

(33)

The four large LHC experiments

I will concentrate on high-p _T physics and on ATLAS

(34)

The ATLAS detector at the LHC

(35)

The ATLAS detector at the LHC

(36)

ATLAS : Air Toroidal Lhc Apparatus System

(37)

the ATLAS collaboration

(38)

~3000 scientists from 174 Institutions and 38 Countries

(39)

~3000 scientists from 174 Institutions and 38 Countries

Annecy-LAPP

Clermont-LPC

Grenoble-LPSC

Marseille-CPPM

Orsay-LAL

Paris-LPNHE

Saclay-IRFU

(40)

ATLAS Detector Layers

Particles are detected through their interaction with active detector materials

(41)

ATLAS Detector Layers

Particles are detected through their interaction with active detector materials

Photo effect

Compton scattering Pair creation

Photons

Strong interaction creates showers with charged particles photons

neutral hadrons

Hadrons

Excitation Ionisation

Bremsstrahlung Cherenkov radiation Transition radiation

Charged particles

(42)

Charged Particle Interaction with Matter

Particles are detected through their interaction with the active detector materials

Energy loss by ionisation

Primary ionisation can generate secondary ionisation

Primary ionization

Primary + secondary ionization Typically:

Total ionization = 3 x primary ionization ~ 90 electrons/cm in gas at 1 bar

dE/dx described by Bethe-Bloch formula dE/dx described by Bethe-Bloch formula

MIP

Relativistic rise

(43)

Charged Particle Interaction with Matter

Particles are detected through their interaction with the active detector materials

Bremsstrahlung Energy loss by ionisation

Due to interaction with coulomb field of nucleus

Dominant energy loss mechanism for

electrons down to low momenta (~10 MeV) Initiates EM cascades (showers)

(more later)

(44)

Charged Particle Interaction with Matter

Particles are detected through their interaction with the active detector materials

Energy loss by ionisation Bremsstrahlung Multiple scattering

(45)

Charged Particle Interaction with Matter

Particles are detected through their interaction with the active detector materials

Energy loss by ionisation Bremsstrahlung Multiple scattering

(46)

The ATLAS inner Tracker

(47)

The ATLAS Semiconductor Tracker (SCT)

(48)

The ATLAS Pixel Detector

2 ×××× 3 Endcap disks, each with 8 sectors and 48 modules

Length: 1.3 m, weight: ~4.4 kg, ∅ ∅ ∅ ∅ : 34.4 cm

(49)

Combining Tracking with PID: the ATLAS TRT

Barrel TRT Module

e/ π separation via transition radiation: polymer ^(PP) fibres/foils interleaved with DTs

Charged particle Anode

wire (HV+)

Cathode (HV–)

Nobel Gas

Fibres or foils

Radiator

Straws

Total: 370k straws Barrel (| η | < 0.7): 36 r- φ measurements / track Resolution ~130 µ m / straw 18 Endcap wheels (| η | <

2.5): 35 or less z- φ ^points

51 cm 144 cm

Electrons radiate more higher signal;

TR

increases signal

Transition radiation

(50)

ATLAS Liquid Argon EM Calorimeter

ATLAS: LAr Sampling Calorimeter

Passive, heavy absorber (Pb, 1.1–1.5 mm thick [barrel] ) inter-leaved with active

detector material (liquid argon) Granularity (Barrel: ∆ η × ∆ φ = 0.0252 rad)

Longitudinally segmented (3 layers +

preshower)

(51)

Electromagnetic Cascades

A high-energy electron or photon incident on absorber initiates EM cascade

Bremsstrahlung and pair production generate lower energy electrons and photons Shower profile strongly depends on the absorber’s X

₀

Longitudinal shower profile Transverse shower profile Width given by Molière radius :

0 Pb

21 MeV 600

, 7

M c

1.2

c

R X E

E Z

= ≈ ≈

+ Governed by high-energy part of cascade

[for E<E

_c

cascade exhausts by ionisation, Compton, …]

~ 22 X

₀

~ 2 X

₀

Calorimeters aim at large X/X

₀

(20 – 30)

And wish transparent material in front

(52)

Energy Resolution

Number of particles in shower ∝ ∝ ∝ ∝ energy of initial particle: N _part ~ E / E _c

Error in energy measurement due to statistical fluctuation in N

_part

: σ (E) ~ √ N

_part

( ) E 1

E E

σ _∝

Phenomenological resolution formula:

“Stochastic term”

Shower fluctuations and containment

“Constant term”

Non-uniformities in calo response due to inhomogeinities, non-linearities

“Noise term”

Electronics noise

(pile-up also contributes)

( )

(GeV) (GeV)

E a c

E E b E

σ ₌ _⊕ _⊕

Sampling calorimeter: absorber material does not contribute to energy measurement

( ) E d 1 3

σ

≈ 1

(53)

The ATLAS Muon Spectrometer

Outer layer of LHC detectors, only reached by WI(M)Ps ( ν , χ ) or EM MIPs ( µ )

Good containment of jets requires ~11 λ before muon systems

ATLAS opted for good standalone tracking (for HLT) if too high-backgrounds in ID

Huge magnetic volume

ATLAS has 8 (barrel) 3 T

_max

and 2 × 8 (endcap) 6 T

_max

superconducting toroid magnets

Huge mechanical structure

Challenging tolerances for mechanical stability, positioning and alignment (optical sensors)

Huge active detectors area

Open structure minimises multiple scattering

Dedicated trigger chambers

(54)

The ATLAS Muon Spectrometer

Outer layer of LHC detectors, only reached by WI(M)Ps ( ν , χ ) or EM MIPs ( µ )

Good containment of jets requires ~11 λ before muon systems

ATLAS opted for good standalone tracking (for HLT) if too high-backgrounds in ID

Huge magnetic volume

ATLAS has 8 (barrel) 3 T

_max

and 2 × 8 (endcap) 6 T

_max

superconducting toroid magnets

Huge mechanical structure Huge active detectors area

Open structure minimises multiple scattering Dedicated trigger chambers

Y (m ) B (T)

(55)

Calorimeter Trigger

Muon Trigger CTP

Latency <2.5 µµµµ s

ROD ROD ROD

Calo & Muon

trigger boards Other detectors 1 PB/s

200 Hz 40 MHz

RoI data (~ 2%) 75 kHz

L1 Accept

Event Builder

EB

4 GB/s ROS

ROB ROB ROB

120 GB/s

300 MB/s, 1.5 MB / event 3.5 kHz

L2 Accept RoI’s

EF Accept RoI requests

Trigger & Data Flow

EFN

L2

L2P

L2SV

L2P L2N L2P ROIB

Latency <10ms

Level-1

[hardware]

High- Level Trigger

[software] L3

EFP EFP

EFP

Latency <1 s

Event data

Storage Trigger streams

Tier-0 _{~48 hours}

Recon-

In cavern On surface In cavern

On surface

(56)

Each LHC experiment will produce 10 000 TB of data each year Data analysis requires 100 000 of the fastest PC processors

ATLAS collaboration spread all over the world need distributed computing

Transfer of data from CERN at 10 Gbits/s rate to 11 world-wide computing centres These centres send and receive data to 200 smaller centres within “clouds”

User analysis philosophy: “Avoid copying data: run the program where the data is”

(57)

A physics programme for the LHC

1. Mass

― Search for the Higgs Boson

2. Electroweak unification

― Precision measurements (M _W , m _top ) & tests of the Standard Model

4. Flavour

― B mixing, rare decays and CP violation as tests of the Standard Model

3. Hierarchy in the TeV domain

― Search for Supersymmetry, Extra dimensions, Higgs composites, …

(58)

Collider Luminosity

The event rate

The event rate R R that we measure that we measure in a collider is proportional to the interaction in a collider is proportional to the interaction cross section

cross section σ σ _i _i and the factor of proportionality is called the luminosity and the factor of proportionality is called the luminosity

If two bunches containing

If two bunches containing n n ₁ ₁ and n and n ₂ ₂ particles collide with frequency f particles collide with frequency f, the , the luminosity is

luminosity is

The The integrated luminosity integrated luminosity is just is just

(59)

Simulation of a Higgs event in ATLAS

Higgs boson decaying into 2 Z bosons, with:

A Higgs decaying into 4 leptons

(60)

A Higgs decaying into 4 leptons

(61)

Higgs boson decaying into 2 Z bosons, with:

Higgs mass over background Higgs mass over background

A Higgs decaying into 4 leptons

(62)

Compare with the Higgs decaying into 2 photons

(63)

September 2008 : 1 ^st attempt at starting the LHC

(64)

September 2008 : 1 ^st attempt at starting the LHC

(65)

September 2008 : 1 ^st attempt at starting the LHC

(66)

(too much? ) world-wide buzz …

(67)

On Sept 10 ^th commissioning of the magnets to 5 TeV was not finished…

Completed between Sept 14

^th

and Sept 19

^th

(cryogenic problems…).

Last commissioning step of the main dipole circuit in sector 34 :

>> ramp to 9.3kA (5.5 TeV).

At 8.7kA an electrical fault developed in the dipole bus bar located in the interconnection between quadrupole Q24.R3 and the neighboring dipole.

Later correlated to a local resistance of ~220 n Ω – nominal value < 1 n Ω.

An electrical arc developed which punctured the helium enclosure.

Secondary arcs developed along the arc.

Around 400 MJ from a total of 600 MJ stored in the circuit were dissipated in the cold-mass and in electrical arcs.

Large amounts of Helium were released into the insulating vacuum.

In total 6 tons of He were released.

Event sequence to Sept. 19th, 2008

(68)

Event sequence to Sept. 19th, 2008

Dipole busbar

Vac. chamber

(69)

Event sequence to Sept. 19th, 2008

QV PT

QV QV SV SV QV QV

Cold-mass Vacuum vessel Line E

Cold support post Warm Jack

Compensator/Bellows Vacuum barrier

Q D D D Q D D D Q D D D Q D D D Q

Pressure wave propagates along the magnets inside the insulating vacuum enclosure.

Rapid pressure rise :

– Self actuating relief valves could not handle the pressure.

designed for 2 kg He/s, incident ~ 20 kg/s.

– Large forces exerted on the vacuum barriers (every 2 cells).

designed for a pressure of 1.5 bar, incident ~ 8 bar.

– Several quadrupoles displaced by up to ~50 cm.

– Connections to the cryogenic line damaged in some places.

– Beam vacuum to atmospheric pressure.

(70)

Event sequence to Sept. 19th, 2008

Dipole bus bar

(71)

Event sequence to Sept. 19th, 2008

Main damage area ~ 700 metres.

39 out of 154 dipoles,

14 out of 47 quadrupole short straight sections (SSS)

from S34 had to be moved to the surface

for repair (16) or replacement (37).

(72)

2009 : a high-intensity time

(73)

2009 : powering tests schedule

86 days - 10398 test done

162 days – 11637 tests done

2009

2008

(74)

2009 : powering tests schedule

1n Ω !!

(75)

Friday, november 20 ^th 2009 : beams are back!

18:30 Beam 1

– 19.00 beam through CMS (23, 34, 45)

• beam1 through to IP6 19.55 Starting again injection of Beam1

• corrected beam to IP6, 7, 8, 1

– 20.40 Beam 1 makes 2 turns

• Working on tune measurement, orbit, dump and RF

• Beam makes several hundred turns (not captured)

– Integers 64 59, fractional around .3 (Qv trimmed up .1)

– 20.50 Beam 1 on beam dump at point 6 – 21.50 Beam 1 captured

22:15 Beam2

– 23.10 Start threading Beam2

• Round to 7 6 5 2 1

– 23.40 First Turn Beam2

• Working on tune measurement, orbit, dump and RF

• Beam makes several hundred turns (not captured)

– Integers 64 59, fractional around .3 (Qv trimmed up .05)

(76)

Monday, november 23 ^th 2009 : collisions !

– Both beams circulating in LHC. Hands off by OP for half an hour.

– Transverse Steering into collision using BPMs through 1 and 5.

– Hands off by OP for half an hour

• Recorded collision events in ATLAS and CMS

• From 16:00

– Two beams in LHC at buckets 1 and 8911 – Quiet beams for ALICE

– Then 2 beams in LHC at buckets 1 and 26701 – Quiet beams for LHCb

• Recorded collision events in ALICE and LHCb

• From 19.00

(77)

ATLAS ATLAS

Beams and first collisions

(78)

Nov 20 – 23: beam history from ATLAS perspective

Friday, November 20:

~ 20:30h: beam-1 threading 6 beam splashes to ATLAS

~ 22:30h: beam-2 threading 7 beam splashes to ATLAS

Saturday, 21 November:

~ 1h: beam-2 splashes to ATLAS 27 events (side C)

~ 4h: beam-1 splashes to ATLAS 26 events (side A)

Sunday, 22 November:

~ 6h: 15 splash events to test beam abort by BCM successful

Monday 23 November:

~ 6:30: last series of splashes to ATLAS 25 events (side C)

~ 13:30: two beams injected for collisions at IP1 and IP5

~ 14:22: first ATLAS collision event seen

(79)

Beam-splash events

Avalanche of scattered particles from beam-on-collimator hits Detectors fully lit, typically

• 300,000 SCT hits

• 350,000 TRT hits

(~all passing high-threshold)

• 3000 TeV calo energy sum

• 490,000 MDT hits

• 320,000 RPC hits

• 65,000 TGC hits

(80)

• Triggering on splashes: ATLAS received and triggered on 106 splashes

Thank you LHC –

we’ve taken them all ! Thank you LHC –

we’ve taken them all !

(81)

Timing studies with beam-splash events (Inner Detector)

• Inner tracking systems:

– SCT already well timed-in from cosmics and known cable lengths (better than 2 ns)

– TRT boards timed-in to better than 2 ns

TRT Barrel: plot made with collision timing

sensitive to ToF effect on Inner Boards ! Beam-1 arriving from A-side: timing as

collisions for C-side, but wrong for A-side

C-side A-side

1 5 n s

ATLAS preliminary

(82)

(83)

Single beam, two beams, two synchronised beams,

colliding beams, collisions ?

(84)

Shorty after colliding beams were announced,

at 14:22 an interesting

(85)