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High Energy ExperimentDetector

2010. 5. 18

Kihyeon Cho

HEP

Global Sketch of HEP Experiment

Determine Physics GoalDetermine Physics Goal

Simulation StudySimulation Study

Decide subdetectorsDecide subdetectors

Subdetector R&DSubdetector R&DElectronics R&DElectronics R&D Software R&DSoftware R&D

System IntegrationSystem Integration

System CalibrationSystem Calibration

Data TakingData Taking

Data AnalysisData Analysis

Publish ResultsPublish Results

ReadoutTrigger(hardware)

Simulation codeTrigger(software)

Rawdata recordingData reconstruction

Skimming/MDSTAnalysis tools

DatabaseCaliibrationMonitoring

Beam/Detector

Beam test

Cosmic raysBeam commissioning

System debugging

Momentum/Energy/MassPID/Lifetime/BF

Resolution/Efficiency/backgroundSystematic study

Particle Accelerator

Particle Accelerator

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Experiments related to CKM parameters

Talk by Elisabetta Barberio

e+e- B Factories

Major experiments ongoing, some ended

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전자 - 양전자 충돌 가속기 실험

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Belle II (2014~)

http://www.kek.jp

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양성자 - 반양성자 충돌 가속기 실험(Tevatron)

Heavier B => Full Service of B factory

)kHz! 15(~ TeV 2at 150)( bbbpp 0Zat 7)( nbbbee

(4S)at 1)( nbBBee

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양성자 - 양성자 충돌 가속기 실험 (Large Hadron Collider)

CMSCMS ALICEALICE

ATLASATLASLHCbLHCb CERNCERN

LHC at CERN

High Energy Experiment

Fixed target vs Colliding beams

(total energy)2-(total momentum)2 = invariant in all frames of reference

Assume that 800GeV(Ebeam) proton collides in a fixed target(proton).

Center of mom. frame Laboraroty frame

Total energy: ECM Ebeam+mp2

Total momentum: 0 Pbeam

Invariant: ECM2 (Ebeam+mp

2)2-Pbeam2

E = [ 2(mp2+Ebeammp) ]1/2 = 38.8GeV

We are enough to 19.4GeV+19.4GeV proton beams in collider !!!

Question: What’s the advantage of a fixed target experiment?

Introduction to particle detectorIntroduction to particle detector

• In order to research about fundamental particles, physicists create collisions between high-energy particles

• After new particles have been produced in collisions, it is necessary to track and identify them.

• A particle detector is device (or system of device) used to monitor the process occurring in collision and to determine the particle created in collisions.

Identification of a particle

To describe an event, one must/need to know: The time when the event occurred The direction of particles Momentum or Energy or Velocity of particles Identification of particles:

– Electric charge– Mass– Spin orientation

Secondary decays within the detector volume.

Goal of Particle Detector

• Interactions of particles and radiation with matter• Ionization and track measurements• Time measurement• Particle identification• Energy measurement• Momentum measurement

Particle Detectors, C.Grupen, Cambridge Univ. Press, 1996

Experimental techniques in HEP, T.Ferbel, World Scientific, 1991

http://www.cern.ch/Physics/ParticleDetector/BriefBook

Type of Detectors

1. Tracking Detector => momentum, charge

2. Particle ID => mass

3. Calorimeter => Energy

4. Muon Detector => Muon

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입자 검출기의 구성요소

Muons (Muons ())

Hadrons (h)Hadrons (h) ee±±, ,

Charged Charged TracksTracks

ee±±, , ±, ±, hh±±

Heavy absorber,(e.g., Fe)Heavy absorber,(e.g., Fe)Zone where Zone where and and remain remain

High Z materials, e.g., High Z materials, e.g., lead tungstate lead tungstate

crystalscrystals

Heavy material, Heavy material, Iron+active materialIron+active material

TrackerTrackerE.M.E.M.Cal.Cal.

HADHADCal.Cal.

ee±±

±±

±±,, ppnn

MuonMuonCham.Cham.

LightweigLightweightht

Particle detector

Principal types of particle detectorsPrincipal types of particle detectors

There are many particle detectors invented and developed.It is possible to divide them into two categories:

– Tracking detectors: Monitor the trajectory of particle in collision

• Cloud chambers• Emulsions• Bubble chambers• Wire chambers

– Calorimeters (Shower detectors): Measure of particle’s energy, particle’s coordinates across calorimeter surface

• Electromagnetic calorimeters• Hadronic calorimeters

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• Multipurpose detector :

– A variety of detectors

– 4 pi hermetic detectors

– Large cost and long time development and construction

– High end technology involved -> applied to industry (so many examples)

High Energy Experiments Detector

How can detectors determine particles• Time when the event takes place: determined by a detector with fast

response on passage of a particle (Scintillator and Photo-Multiplying tubes)

• Direction of particles:

– Charged particle: measure the ionization track left behind

– Neutral particle: measure center of gravity of a electromagnetic /hadronic shower

• Momentum of charge particle: from track curvature in magnetic field

• Energy of particle: from electromagnetic or hadron shower size

• Velocity of particle: from Time of Flight (TOF), Cerenkov light angle

• Energy-momentum: from the energy-momentum conservation laws

• Electric charge: from density of ionization (dE/dx)

• Mass of particle: from momentum vs velocity.• Secondary decays within detector volume investigated by reconstructing an

explicitly secondary vertex.

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High Energy Experiments Detector• Particles are detected via their

interaction with matter

– Different physical processes

– For charged particles predominantly excitation and ionization

• The common methods for particle identification are:

– Vertexing and Tracking particles through a magnetic field.

– Thin (low Z) material– Gas, liquid, solid

– Energy loss measurement– Calorimeter– High-Z material

(absorber)– ID of particles like Cerenkov– Others like Time of flight See http://public.web.cern.ch/public/

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HEP detector

Structure of a typical particle detector

Vertex detector: gives the most accurate information on the position of the tracks.

Drift chamber: detects the positions and momentum of charged particle.Cerenkov detector: measures particle velocity

Calorimeter, stops most of the particles and measures their energy. This is the first layer that records neutral particlesThe large magnet coil separates the calorimeter and the next layer.

Typical experimental setup

1. Tracking Chamber

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Heavy charged particle interactions w/ atoms

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Tracking Particle through a Magnetic Field

• Gas detectors: MWPC, TPC, Drift Chamber, GEM, …• Solid State (Silicon) detectors: PIN diode, CMOS, CCD, … (Pixel, Strip, ..)

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• Momenta of charged particles can be measured in a relatively straightforward fashion using magnetic spectrometer.

• In certain situations, however, magnetic measurement may not be viable. For example, precise magnetic measurements becomes difficult and expensive at very high energies because they require either large magnetic fields in extended regions of space, or very long lever arms for measuring small changes in the angular trajectories of particles passing through magnets, or both.

• In addition, magnets can not be used for measuring energies of neutral particles.

• Calorimeters are then used to measure the total energy deposition in a medium.

Tracking Detector: Cloud chambers• Invented by Charles Thomson Rees Wilson (Nobel Prize in

1927)• Used from the beginning of the 20th century till mid-1950s

• Principle of operation: – In over-saturated vapor, primary ionization cluster

left behind a charge particle. This particle will become center of condensation. Droplets will follow the track of particle. Their number per unit of length is proportional to the density of ionization. A picture of droplets is taken and chamber is compressed again.

• Characteristics: – Moderate spatial resolution (mm to sub mm)– Momentum (P) calculated from curvature in

magnetic field– Velocity (v) determined from dE/dx (density of

ionization)

Wilson chamber (cloud chamber)

Cloud-chamber photograph, showing track of positively

charged particle (C. D. Anderson - 1932)

Tracking Detector: Emulsions

• Used since mid-1940s and are still in use• Developed by F. Powell (Nobel Prize in 1950)

• Principle of operation:– Emulsion films consist from crystal of AgBr and AgCl

suspended in a body of gel. An charged particle passing through the emulsion film breaks up AgBr/AgCl molecules and releases metallic Ag grains. With the help of a microscope, these grains can be observed as black dots.

• Characteristics: – Very high spatial resolution (0.2 m)– Momentum can be estimated from the scale of multiple

scattering

Emulsion images

A K meson stops at P, decaying into a muon and neutrals. The muon decays at Q to a electron and neutrals. The muon track is shown in two long sections.

Tracking Detector: Bubble chambers

• Invented by Donald Glaser (from Berkeley, Nobel Prize in 1960) in 1952 and used from mid 1950s till the 1970s.

• Principle of operationPrinciple of operation:

– The bubble chamber consists of a tank of unstable transparent liquid. When a charged particle forces its way through the liquid, the energy deposited initiates boiling along the path, leaving a trail of tiny bubbles. Pictures from different angles are taken and the pressure is restored.

• Characteristics:Characteristics:– Good spatial resolution (100 um)– Velocity determined from density of grains (dE/dx)– Momentum investigated from bending in magnetic field.– Quite appropriate for neutrino physics

Bubble chamber images

A 7-foot chamber at Brookhaven

The bubble chamber picture of the first omega-minus

An incoming K- meson interacts with a proton in the liquid hydrogen of the bubble chamber and produces an -, a K° and a K+ meson which all decay into other particles. Neutral particles which produce no tracks in the chamber are shown by dashed lines. The presence and properties of the neutral particles are established by analysis of the tracks of their charged decay products and application of the laws of conservation of mass and energy.

Tracking Detector: Wire ChambersHere are some types of wire chamber: Proportional counters Multi-wire proportional chambers Drift chamber

Tracking detector

(+)

(-)

Wire Chamber: Proportional Counters

A charged particle passing through a Geiger counter causes ionization. The ionization electrons drift to the wire creating further ionization, so producing a large signal.

Principle of operation:

Wire Chamber: Drift chambers

- To achieve a high spatial solution over large area, an enormous number of wires is required --> high cost

- A great reduction in cost can be achieved by using drift chambers (planar or cylindrical proportional chambers)

Drift chamber

The wires are arranged in layers that pass through the cylinder at three different angles. The set of wires that give a signal can be used to allow computer reconstruction of the paths of all the charged particles through the chamber

Some 35,000 fine wires are strung the length of the cylinder between precisely placed holes in the aluminum ends. When the chamber is filled with a gas mixture and high voltage is applied to groups of wires it becomes a giant set of Geiger counter

2. Particle ID

1) dE/dx

2) TOF

3) Cerenkov detector

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Particle Identification

1) Energy Loss (dE/dx)

• dE/dx Counter– A counter telescope consists of two or more detectors through which a

charged particle passes in sequence, usually stopping in the last one. The fraction of energy dE it loses in the passing detectors is a measure of the stopping power. The stopping power (given by Bethe-Bloch formula to be discussed in a few weeks) varies approximately as z2/v2 or mz2/E, where v is the speed of the particle of mass m and charge ze. The energy E is obtained by summing the signals from all the detectors, and the product E x dE is roughly proportional to mz2. A graph of DE versus E gives a family of hyperbolae, each corresponding to a different values of mz2. For light ions with sufficient energy, this often is enough to identify the ion uniquely. However, this method is limited by the finite energy resolution of the passing detector.

Stopping power

)ionization (includingenergy excitationmean : I

material stopping theofdensity mass:

particleheavy theofvelocity :

number sAvogadro' :n

:material target ofnumber mass :A

material target ofnumber atomic : Z

particle ionizing theof charges ofnumber : z

)1(

2ln

4

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2

22

22

22

0

2

c

I

cm

A

Z

cm

nze

dx

dE e

e

Heavy charged particles interact with matter mainly thru electrostatic

forces during collisions with orbiting electrons. (excitation, ionization)

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Global 5-parameter fit for phmp_nml vs

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13ln2

1p

pp

ppp

dx

dE

binning with nearly the same statistics at each point to reduce the error

Using garbage events in order to fastly calibrate this curve for BESIII in future

A uniform formula to avoid discrete expression for density effect

The curve fit the BESII data OK

Beam-gas proton

Cosmic rays

Radiative bb

BESII data

p

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2) Time of Flight

• Time of flight (TOF) measurements have important applications in providing discrimination between particles of similar momentum but different mass that may be produced from a reaction.

For two particles of massm1 and m2, the time differencewill be given as:

For p1 = p2 = p,

Time measurement

The scintillation counter is capable of measuring a precise passing time of a particle because the scintillation is a fast phenomenum and the conversion of a light burst into a voltage signal inside PMT is also a very fast process.

3) Cherenkov counter

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Detection of Cherenkov light

v > c/n in medium (refraction index n) β = c/v

cosφ=1/nβ

Introduction: Gas Cherenkov DetectorsIntroduction: Gas Cherenkov Detectors

HBD Violet – Ultraviolet (VUV) light detection

Reference: http://encyclopedia.thefreedictionary.com/Cherenkov%20effect

Georgia Karagiorgi, FAS 2005

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Cherenkov Detector

• When a charged particle moves with uniform velocity in vacuum, it does not emit radiation. However, if it travels in a dielectric medium of index of refraction n>1, and with a speed greater than the speed of light in that medium (I.e. v > c/n), then it emits what is known as Cherenkov radiation (after Pavel Cherenkov, who first observed the effect in 1934). The direction of the emitted light can be calculated classically using Huygen’s wave construction, and can be attributed to the emission of coherent radiation from the excitation of atoms and molecules in the path of the charged particle. The effect is completely analogous to the “shock” front produced by a supersonic aircraft.

• The emitted light has a spectrum of frequencies, with the most interesting component being in the blue and ultraviolet band of wavelengths. The blue light can be detected with relatively standard photomultiplier tubes, while the ultraviolet light can be converted to electrons using photosensitive molecules that are mixed in with the operating gas in some ionization chamber. The angle of emission for Cherenkov light is given by:

Registration by Cherenkov detector

Water

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• The intensity of the produced radiation per unit length of radiator is

proportional to sin2θc. Consequently, if βn>1, light will be emitted, and if β n<1, no light can be observed.

• Cherenkov Detector Types– Threshold Cherenkov counter: Based on the choice of the

index of refraction of a given radiator– Differential Cherenkov counter: Based on the light cone

angles for different particles for the same n

RICH

RICH detector

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Calorimeters

• Electromagnetic Calorimeter

• Hadron Calorimeter

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Types of Calorimeters

For electrons/photons: electromagnetic

cascade is measured in a dedicated relatively

fine segmented (Electromagnetic Calorimeters:

ECAL)

Pion/Kaon/proton: hadronic cascade is

measured in much bulkier Hadron calorimeter:

HCAL

Jets of hadrons often produced in high energy

collision: HCAL

Energy measurement

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Calorimeters

A calorimeter is a device that absorbs the full kinetic energy of a particle, and provides a signal that is proportional to that deposited energy.

• Gas detectors: MWPC, GEM, …• Solid State (Silicon) detectors: PIN diode, CMOS, CCD, … (Pixel, Strip, ..)• Scintillation detectors: Crystal, Plastic, …

EM particles(EM Cal.)

Hadrons(Hadron Cal.)

Electromagnetic calorimeters (ECAL)

The Electromagnetic Calorimeter absorbs the energies of all electrons, positrons and photons traversing it (this constitutes the "electromagnetic energy"), and produces signals proportional to those energies. It is finely subdivided so that it can measure the directional dependence of the electromagnetic energy. An electromagnetic

Calorimeter

Principle of operation:

e interactions w/ atoms

Hadron Calorimeters: HCAL The hadronic calorimeter allows to measure energy and position of charged hadrons. By measuring the energy and direction of jets, this calorimeter plays an essential role in the identification of quarks and gluons

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Neutron Detector

• A neutron detector does not record the presence of a neutron directly but responds to secondary radiation (generally fast charged particles) which is emitted when the neutron undergoes a nuclear reaction in the detector medium.

• For slow and thermal neutrons, the (n,p), (n,alpha) or (n, fission) reactions on light nuclei are among those most commonly used in detectors. Many of these reactions exhibit a 1/v dependence at low energy, giving high cross sections for thermal neutrons.

• For fast neutrons of several MeV, scattering off a light target can give enough energy to a recoiling nucleus for detection.

Muon Detector

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Why Muons and Electrons? Leptons

● rare in pp (<1% of the tracks), often related to very interesting physics processes

● taus special case (m = 1.777 GeV, cτ = 87.11 μm)● decay well before they reach the silicon detector, lifetime more then a factor

of five smaller then for B mesons● can also produce hadrons in decay, more difficult to identify● always involve neutrino in decay (incomplete reconstruction)

● muons have very characteristic signature● penetrate the calorimetry, are detected in the muon chambers● leave minimally ionizing signature

● electrons have very characteristic signature● maximal ionization in tracking system● get absorbed completely in ECAL no signature in the HCAL● shower shape in ECAL is short and broad

Psedorapidity

η= -ln (tan 2/θ )

→ z 방향 Beam 방향 Longitude 방향

Transverse 방향

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CDF Muon Detection System Muon detection starts at the muon chambers

CMU● on HCAL● |η| < 0.6

CMUP● add steel● |η| < 0.6

CMX● 0.6<|η|

<1.0 IMU

● 1.0<|η|<1.5

● no trigger

C.Paus, LHC Physics: Detectors: Electron/Muon and Particle Id

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CDF Muon Detection System

C.Paus, LHC Physics: Detectors: Electron/Muon and Particle Id

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CDF Muon Detection System

C.Paus, LHC Physics: Detectors: Electron/Muon and Particle Id

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CDF Muon Detection System

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CDF Muon Detection System

More details on CMU(P)/CMX:● up to 8 drift chamber planes ● 1-2 scintillator layers● incorporated in the trigger (low+high momentum muons)

More details on IMU

● 4 planes of drift chambers

● 2 scintillator layers● high backgrounds

prevent triggering on those counters

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CDF Muon Detection System

taken from the design report for the CDF II detector

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CDF Muon Triggers

Trigger at hadron colliders

ex. Tevatron, LHC● collision rate 3-40 MHz● writing rate: order 100 Hz● trigger absolutely crucial to

see muons● muons are ideal candidate for

trigger● muons often connected to

interesting physics● muon trigger in CDF already

at level 1 needs tracker information

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Muons for the Analysis How do I get a clean and unbiased muon?

● no way for single muon● irreducible background

● decays (kaons, pions)● punch though, sail through

● clean muon?● use clean muon based signal

● J/ψ → μμ, many, O(10M)● Upsilon → μμ, higher momenta

● apply sideband subtraction● subtract irreducible background

● unbiased muon? (trigger)● use single muon trigger● use independent trigger

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Example for Sideband Subtraction Determine primary distribution (mostly masses)

● select signal, sideband areas● make histograms for both areas● scale sideband and subtract from

signal area plot

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Muon Signatures in Muon Detector

Colors: muon, pion, kaon, proton

Distance of muon stub fromextrapolated position

Tracker is needed

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Signature in Non-Muon Detectors

Colors: muon, pion, kaon, proton

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CMS – Compact Muon Solenoid

compact does not mean smallvolume smaller than Atlas by ~5.6, butweights 30% more than the Eiffel towereye catcher: brilliant design in separately removable slices

12,500 ton weight, 15 m diameter, 22 m long

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CMS Muon Systems Drift Tubes, DT, barrel only Cathode Strip Chambers, CSC, endcap only Resistive Plate Chambers, RPC, barrel and endcaps

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CMS Muon Detector

C.Paus, LHC Physics: Detectors: Electron/Muon and Particle Id

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CMS Muon Detector

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CMS Muon Detector

Watch the muon● curving left initially● curving right outside● hmm ....

Magnetic field● inside: homogeneous

solenoidal field● outside: iron yoke

arranges for reflux so opposite direction field in the yoke material

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CMS Muon Detector: Distortions

Distortion due to forces: detailed online detector position monitor needed

C.Paus, LHC Physics: Detectors: Electron/Muon and Particle Id

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CMS Drift Tubes

Drift tube design ● layers for effective

production● again geometry and

wire position crucial

C.Paus, LHC Physics: Detectors: Electron/Muon and Particle Id

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Cathode Strip Chambers Advantages● good spacial resol. (50μm)● fast (close wire spacing)● readout: strips and wires● two dimensional position● strips can align such that

azimuthal angle measured● loose conditions for gas

system● intrinsic alignment very

precise

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RPC Principle

The signal is induced on the read-out electrodes

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RPC Principle

Mode to operate gas detector● usually: streamer mode

● high field● intense enough to initiate spark

breakdown

● CMS runs in avalanche mode● lower field but multiplication● multiplication proportional

Performance● timing resolution 1-2 ns space resolution ≈ cm

rate capability good (avalanche mode)low cost design and arbitrary shapes possible

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Summary of muon detector

Muons in hadron colliders● provide a very clean signature

● muons pass in minimal ionizing fashion through dense material● leave signal in chambers outside of calorimeters● leave characteristic signal in calorimeters

● essential for reducing general rate of events: trigger● fundamental tool to trigger on interesting physics● very clean reconstruction and excellent resolutions up

to very high momenta

References[1] Gordon Kane, Modern Elementary Particle Physics, Updated Edition, Addison-Wesley Pub., 1993

[2] Donald H. Perkins, Introduction to High Energy Physics, 4th edition, Cambridge University Press, 2000

[3] Introduction to Elementary Particle Physics, Lecture D12-13 (http://www.phys.ufl.edu/~korytov/phz5354/lecture_D12.pdf)

[4] Different websites, such as:

http://www2.slac.stanford.edu/vvc/detectors.html

http://www.shef.ac.uk/physics/teaching/phy311/

http://www.lbl.gov/abc/wallchart/chapters/12/2.html

…

[5] C.Paus, LHC Physics: Detectors: Electron/Muon and Particle Id

Thank you.