P780.02 Spring 2002 L19 Richard Kass

Intro to HEP/Nuclear ExperimentsWhat are the ingredients of a high energy or nuclear physics experiment?Consider three examples of different types of experiments:

FIXED TARGET (FOCUS, SELEX, E791)COLLIDING BEAM (CLEO, CDF, STAR)ACTIVE EXPERIMENT (Super K, SNO)

Some Common features:energy/momentum measurementparticle identificationtrigger systemdata acquisition and storage systemsoftwarehardworking, smart people…

Some Differences:experiment geometrydata ratesingle purpose Vs multi-purpose

P780.02 Spring 2002 L19 Richard Kass

Particle DetectionIn order to detect a particle it must interact with matter!The most important “detection” processes are electromagnetic. Energy loss due to ionization electrons particles heavier than electrons (e.g. , , k, p) Energy loss due to photon emission bremsstrahlung (mainly electrons) Interaction of photons with matter photoelectric effect Compton effect pair production ( e+e-) Coulomb scattering (multiple scattering) Other/combination of electromagnetic processes

cerenkov light scintillation light electromagnetic shower transition radiation

Calculation of above processes involve classical EM and QED

Hadrons (,k,p) interact with mattervia the strong interaction and create particles through inelastic collisions.These particles lose their energy via EM processes:0or ++e

P780.02 Spring 2002 L19 Richard KassFixed Target Experiment

Imagine an experiment designed to search for baryons with Strangeness=+1These particles would violate the quark model since baryons always have negative strangeness in the quark model.

A candidate reaction is: -pk-X+

Since this is a strong reaction we need to conserve:baryon number: X has B=+1strangeness: X has to have +1electric charge: X has to have Q=+1

General requirements of experiment: we need to know that only k- and one other particle produced in final stateTo achieve this we will have to:

get a beam of -’s with well defined momentum (we need an accelerator)get a target with lots of protons (e.g. liquid hydrogen)identify -’s and k-’s

eliminate background reaction: -p -p measure the momentum of the -’s and k-’s

eliminate background reactions: -pk-k+n or k-kop a way to record the data

P780.02 Spring 2002 L19 Richard Kass

Example of fixed target experiment: FOCUS

Real life view

Momentum: silicon+drift chambers+PWC’s+magnet

Energy: EM+hadronic calorimeters

Particle ID: Cerenkov Counters, muon filter calorimeter

P780.02 Spring 2002 L19 Richard Kass

Colliding Beam: CLEO III ExperimentGeneral purpose detector to study lots of different final statesproduced by e+e- annihilations at 10 GeV cm energy

Must have cylindrical geometry since beams pass through the detectorMust measure: momentum of charged particles energy of ’s and o’sMust identify particles: charged: e, , , k, p neutral: , 0, k0,

e+e-B+B-

B+

s

s

B-D

DDDK

P780.02 Spring 2002 L19 Richard Kass

CLEO III Charged Particle Tracking Detectors

Installation ofCLEO III silicondetector

hybrids:holds amps

Silicon wafers (layer 4) Drift chamber End Plates

Readout cables

Silicon detector has:1.25x105 stripsEach strip has its own: RC, preamp, ADC

Drift Chamberhas about 104 sense wires

P780.02 Spring 2002 L19 Richard KassCLEO III Drift Chamber

47 Layers of sense wires9796 sense wiresmeasures r- coordinate 100mGas is He:C3H8 (60:40)

x x xx o xx x x

drift chamber cellX=field wireO=sense wire

A drift chamber measuresposition by measuring thetime it takes for ions to drift toa wire: x=vt. (assume we know v)

P780.02 Spring 2002 L19 Richard Kass

Charged particle tracking and momentum resolution

We measure the momentum of a charged particle by determining its trajectory in a known magnetic field. Simplest case: constant magnetic field and pB trajectory is a circle with p=0.3Br

We measure the trajectory of the charged particle by measuring its coordinates (x, y, z or r, z, , or r, , ) at several points in space. Simplest case: determine radius of circle with 3 points

We measure coordinates in space using one or more of the following devices: Multiwire Proportional Chamber Drift Chamber Silicon detector

low spatial resolution (1-2 mm)moderate spatial resolution (50-250m) high spatial resolution (5-20 m) M

ost c

omm

on

Better momentum resolution better mass resolutionMany particles of interest are observed through their decay products: D0K-+D+K-+ +p-, K0+ +

By measuring the momentum of the decay products we measure the mass of the parent. m m1+m2 m2=(E1+E2)2-(p1+p2)2 = m1

2+ m22 +2[(m1

2+ p12 )1/2 (m2

2+ p22 )1/2 - p1p2 cos]

For fixed : pm pm// 2

2 1

2

Why do we need charged particle tracking in an experiment? Determine the number of charged particle produced in a reaction. Determine the identity of a charged particle (e.g. , K, p ID using dE/dx). Determine the momentum of a charged particle.

P780.02 Spring 2002 L19 Richard Kass

Momentum and Position Measurement

(0, y1) (L, y3)

(L/2, y2)

s=sagitta

Assume:we measure y at 3 equi-spaced measurements in (x, y) plane (z=0)each y measurement has precision y

have a constant B field in z direction so p=0.3BrThe sagitta is given by:

y

x

Trajectory of charged particle

p

BL

Bp

L

r

Lyyys

8

3.0

)3.0/(882

22231

2

Note: The exactexpression for s is:

4

22 L

rrs

The error on the sagitta, s, due to measurement error is found using propagation of errors to be: ys 2/3

Thus the momentum (toB) resolution due to position measurement error is:

z

)(6.323.0

2/38

)8/()3.0(

2/3222 TGeV/c,m,BL

p

BL

p

pBLspyyysp

P780.02 Spring 2002 L19 Richard KassMass Resolution and PhysicsDiscovery of the b-quark at Fermilab (1977). Used a double arm spectrometer to measureinvariant mass of -pairs. Had to do an elaborate fit to find 3 bb resonances:(1S), (2S), (3S)

Double arm spectrometer (E288)

1977

1986Upgraded doublearm spectrometer(E605) clearlyseparates the 3 states: improved mass resolution and particle ID (RICH)

PRL 39, 252 (1977)PRL 39, 1240 (1977)

pBeX

Better fit

P780.02 Spring 2002 L19 Richard Kass

Energy Measurement (Calorimetery)Why measure energy ?

I) Not always practical to measure momentum. An important contribution to momentum resolution is proportional to the momentum.Example: suppose we want to measure the momentum of a charged particlesuch that we can tell whether it is positively or negatively charged (to within 3). We demand: p/p < 0.33A more detailed analysis of momentum resolution gives:

Use CLEO or CDF-like parameters: B=1T, L=1m, n=100, =150m and find p:

)()3.0(4

7202 TGeV/c,m,

BL

p

npp

GeV/c24

22

105.2105.1

)1)(1)(3.0(

720

104)33.0(

)3.0(

720

4)33.0(

BLnp

Thus above 250 GeV/c we can’t reliably measure the charge of the particle! There are practical limits on the values of B, L, , n, etc.

II) Some interesting particles do not have electrical charge.Momentum measurement using B-field only works for charged particles.What about photons, 0’s and ’s (both decay to ), KL’s, neutrons, etc ?

P780.02 Spring 2002 L19 Richard KassCalorimetry

In addition to measuring energy calorimeter information can also be used to:identify particles (e.g. ’s, e’s)measure space coordinates of particles (no B-field necessary)form a “trigger” to signal an interesting eventeliminate background events (e.g. cosmic rays, beam spill)can be optimized to measure electromagnetic or hadronic energy

Calorimeter usually divided into active and passive parts:Active: responsible for generation of signal (e.g. ionization, light)Passive: responsible for creating the “shower”

Many choices for the “active” material in a calorimeter: inorganic crystals (CsI used by CLEO, BELLE, BABAR)organic crystals (ancthracene) {mainly used a reference for light output}plastic scintillatorliquid scintillator (used by miniBoone)Noble liquids (argon used by D0)gas (similar gases as used by wire proportional chambers)glass (leaded or doped with scintillator)

Many choices for the “passive” material in a calorimeter:high density stuff: marble, iron, steel, lead, depleted uranium lower(er) density stuff: sand, ice, water

P780.02 Spring 2002 L19 Richard KassParticle ID with Calorimeterselectron/positron: Charged particle undergoes EM shower in calorimeter,compare momentum (measured in drift chamber) with energy, require E/p1.Not efficient when electron has same energy as a minimum ionizing particle(both have E/p 1), also background from reactions: 0X.

photon: EM shower in calorimeter not matched to charged track in drift chamber.

muon: Charged track in drift chamber that does not shower in EM calorimeter orinteract in hadron calorimeter. Background from pions (and kaons) that decay in flight () and/or non-interacting /K.

neutrino: Compare visible energy (calorimeter) with measured momentum (drift chamber) and look for imbalance in event. Could be more than one neutrino missing!

neutron or KL: Hadronic shower in calorimeter that does not match to charged track in drift chamber. Need hadronic calorimeter.

0, : measure invariant mass of combinations.

P780.02 Spring 2002 L19 Richard Kass

A CLEO Event

A fully reconstructed event.Lots of ’s in event.

P780.02 Spring 2002 L19 Richard KassA CLEO Event

muon

CLEO event withmuons and electrons

P780.02 Spring 2002 L19 Richard Kass

Ring Imaging Cerenkov Counters (RICH)RICH counters use the cone of the Cerenkov light.The ½ angle () of the cone is given by:

np

pm

n

2211 cos

1cos

The radius of the cone is: r=Ltan, with L the distance to the where the ring is imaged.

L

r

For a particle with p=1GeV/c, L=1 m, and LiF as the medium (n=1.392) we find:

deg r(m) 43.5 0.95

K 36.7 0.75P 9.95 0.18Thus by measuring p and r we can identify what type of particle we have.

Problems with RICH: optics very complicated (projections are not usually circles) readout system very complicated (e.g. wire chamber readout, 105-106 channels) elaborate gas system photon yield usually small (10-20), only a few points on “circle”

Great /K/p separation!

P780.02 Spring 2002 L19 Richard Kass

CLEO’s Ring imaging Cerenkov CounterThe figures below show the CLEO III RICH structure. The radiator is LiF, 1 cm thick, followed by a 15.7 cm expansion volume and photon detector consisting of a wire chamber filled with a mixture of TEA and CH4 gas. TEA is photosensitive. The resulting photoelectrons are multiplied by the HV on the wires and the resulting signals are sensed by a rectangular array of pads coupled with highly sensitive electronics.

P780.02 Spring 2002 L19 Richard KassPerformance of CLEO’s RICH

Number of detectedphotons on 5 GeV electrons

A track in theRICH

D*’s without/withRICH information

Preliminary dataon /K separation

P780.02 Spring 2002 L19 Richard Kass

CLEO’s Ring imaging Cerenkov Counter

Lithium Floride (LiF) radiator

Assembled radiators. They are guarded by Ray Mountain. WithoutRay “living”at the factory that produced the LiF radiators we would stillbe waiting for the orderto be completed.

A photodetector:CaF2 window+cathode pads

Assembledphotodetectors

P780.02 Spring 2002 L19 Richard Kass

Example of active experiment: SuperKamiokande

Inside SuperK

Original purpose of experiment was to search for proton decay: pe+0 Baryon and lepton number violation predicted by many grand unified models (e.g. SU(5))

General Requirements for experimentNeed lots of protons (decay rate of 1032 years7x103 tons of H2O) Size: Cylinder of 41.4m (Height) x 39.3m (Diameter) Weight: 50,000 tons of pure water

Need to identify e-’s and 0’s Reject unwanted backgrounds (cosmic rays, natural radiation) 103m underground at the Mozumi mine of the Kamioka Mining&Smelting Co Kamioka-cho, Japan

P780.02 Spring 2002 L19 Richard Kass

SuperKamiokandeCloser look at experimental requirements: Identifying ’0s tricky since 0 thus must identify ’s Need to measure energy or momentum of e and 0

impractical to use magnetic field measure energy using amount of Cerenkov light detect cerenkov light using photomultiplier tubes 11,200 photomultiplier tubes, each 50cm in diameter , the biggest size in the world Energy Resolution: 2.5% @ 1 GeV and 16% (at 10 MeV) Energy Threshold: 5 MeV Need to measure direction of e and o to see if they come from common point cerenkov light is directional Need to measure timing of e and o to see if they were produced at common time cerenkov light is “quick”, can to timing to few nanoseconds

Nov. 13: Bottom of the SK detector covered with shattered PMT glass pieces and dynodes.

BUT DON’T FORGETCIVIL ENGINEERING!Nov 12: accident destroys 1/3 of phototubes

P780.02 Spring 2002 L19 Richard KassThe SNO Detector

Nucl. Inst. and Meth. A449, p172 (2000)

Located in a mine in Sudbury CanadaUses “Heavy” water (D2O)Detects Cerenkov light like SuperK

SNO=Sudbury Neutrino Observatory