Calorimeters In Action!!

Calorimeters In Action!!

ILC Calorimeter SchoolCCAST & TUHEP, Tsinghua University

Apr. 22 – 26

Jae YuUniversity of Texas at

Arlington

Lecture Outline• Preparation of a HEP experiment

– Physics Goals– Accelerators and Detectors

• NuTeV Calorimeter– Physics Goals– Beam Characteristics– Detector and its performance

• DØ Calorimeter– Physics Goals– Beam Chracteristics– Detector and its performance

4/22/2009 ILC Calorimeter School, Tsinghua University J. Yu, Univ. of Texas at Arlington 2

Preparation of a HEP Experiment• Decide on physics topics and scientific goals to accomplish• Explore accelerators, existing, upgraded or new• Define the necessary detector performance requirements to

accomplish the measurements of the topics • Define the design parameters and look into available or new

technologies to fit the performance parameters• Perform Monte Carlo simulations to refine the requirements

and test technical feasibilities• Perform R&D for various detector technologies and construct

and test prototypes• Design an integrated detector and test them in the beam to

understand, improve and calibrate its performance• Construction, commissioning, data taking and analysis


Design Considerations – Scientific Goals• What are the critical physics questions to answer?

– Always changing, a moving target– Theoretical predictions based on previous theories and

the results of experimental tests– Previous experimental results

• Did we measure certain quantities to a satisfactory precision? – Sufficiently low statistical and systematic uncertainties?– What can be accomplished at the next level?– Are the sources of systematic uncertainties reducible?– Can the existing accelerator provide necessary statistical and

systematic precisions?– Do we need a new accelerator?



Standard Model Elementary Particle Table• SU3XSU(2)xU(1) gauge symmetry• Prescribes the following simple and elegant fundamental

structure:

• Total of 3 families of quarks and leptons with 12 force mediators form the entire universe

~0.1mp

Family

Discovered in 1995, ~170mp

Directly observed in 2000

Are we all happy with the current theory?• Standard Model has been extremely successful under

scrutiny EW sector tested very rigorously• Yet, there are outstanding issues lingering

– Neutrino masses Now proven that neutrinos oscillate– Electroweak symmetry breaking Origin of mass

• Search for the Higgs particle still on-going– CP violations kTeV and other experiments– Why are there so wide a range in constituents’ masses (hierarchy problem)?– At what energy does the unification of all forces occur?

• Is there any other model that describes nature better?– Will we find SUSY partner particles?

• To answer these questions we need – The accelerator– The detector



Current Status of Higgs Searches36 22680 GeV/cWM

39 22885 GeV/cHM

39 22885 GeV/cHM

Most optimal central value is below the experimental limit under the SM

Particle Accelerators• How can one obtain high energy particles?

– Cosmic ray Sometimes we observe 1000TeV cosmic rays• Low flux and cannot control energies or types of incident particles too well

• Need to look into small distances to probe the fundamental constituents with full control of particle types, energies and fluxes– Particle accelerators

• Accelerators need not only to accelerate particles but also to– Track them– Maneuver them– Constrain their motions better than 1m

• Why?– Must correct particle paths and momenta to increase fluxes and control

momenta


Role of Accelerators• Act as a probing tool

– The higher the energy The shorter the wavelength– Smaller distance to probe

• Take us back in time close to the creation of the universe• Two method of accelerator based experiments:

– Collider Experiments: pp, e+e-, ep• CMS Energy = 2sqrt(E1E2)

– Fixed Target Experiments: Particles on a target• CMS Energy = sqrt(2EMT)

– Each probes different kinematic phase space


Particle Accelerator Types• Depending on what the main goals of physics are, one can

use various kinds of accelerators• Fixed target experiments: Probe the nature of the nucleons

(Structure functions) and measure particle properties– Results also can be used for producing secondary particles for

further accelerations and beam particle selections• Colliders: Probes the interactions between fundamental

constituents– Hadron colliders: Wide kinematic ranges and high discovery

potential• Proton-anti-proton: TeVatron at Fermilab, SppS at CERN• Proton-Proton: Large Hadron Collider at CERN (to turn on late 2009)

– Lepton colliders: Very narrow kinematic reach and for precision measurements

• Electron-positron: LEP at CERN, Petra at DESY, PEP at SLAC, Tristan at KEK, ILC in the med-range future

• Muon-anti-muon: Conceptual accelerator in the far future– Lepton-hadron colliders: HERA at DESY


Collider Accelerators – Lepton Collider • Used primarily for precision measurements• Particles without the internal structures -

Point-like particles• Much lower total cross section than hadron

colliders – Much cleaner final states • CMS energy for each collision well

understood• Limited kimematic phase space• LEP, LEP-II, KEK, PEP-II, ILC4/22/2009 11ILC Calorimeter School, Tsinghua University

J. Yu, Univ. of Texas at Arlington

Collider Accelerators – Lepton-Hadron• Primarily used for internal nucleon structure

measurements• Point-like particle on a particle of structure

– Can extend the kinematic space of the structure functions to very low momentum fraction

– Needed for high energy experiments such as the LHC

• Very asymmetric final state• DESY in Germany (HERA)

4/22/2009 12ILC Calorimeter School, Tsinghua University J. Yu, Univ. of Texas at Arlington

Collider Accelerators – Hadron Collider• Primarily used as discovery machines• Collisions between structured particles• High total cross sections

– Large number of events– Messy final states– From spectator quarks– Multiple interactions per collisions

• Maximum kinematic reach for the given cost• Probes broad corners of kinematic phase space• CERN SppS(0.63TeV), Tevatron (2TeV), CERN LHC (14TeV)


Synchroton Accelerators• Synchrotons use magnets

arranged in a ring-like fashion.

• Multiple stages of accelerations are needed before reaching over GeV ranges of energies

• RF power stations are located through the ring to pump electric energies into the particles



Relativistic Variables• The invariant scalar, s, is defined as:

• Show that in the CMS frame • In the CMS frame

• Thus, represents the total available energy of the interaction in the CMS

22 21 2 1 2s E E P P c

r r

2 4 2 4 21 2 1 22m c m c E m c

2 4 2 4 21 2 1 22s m c m c E m c

22 21 2 1 2CM CM CM CME E P P c

r r

21 2CM CME E 2CMToTE

s

CMs E

Jog-your-memory Simple Exercise• Derive the formulae for the available center of

mass energy for– A fixed target experiment with incoming particle

four momentum P1 (E1, P1) (E1>> m1)and the target mass of MT

– A collider experiment with the two particle four momenta of P1 (E1, P1) and P2 (E2, P2)


12 Ts E M

1 22s E E

Particle Detectors• Subatomic particles cannot be seen with naked eyes but

can be detected through their interactions within matter• What do you think we need to know first to construct a

detector?– What kind of particles do we want to detect?

• Charged particles and neutral particles?• What kind of particles are they? EM, Hadrons, Jets, neutrinos?

– What do we want to measure?• Their momenta• Trajectories• Energies• Origin of interaction (interaction vertex)• Etc

– To what precision do we want to measure?• Depending on answers to the above questions we use

different detection techniques 4/22/2009 ILC Calorimeter School, Tsinghua University

J. Yu, Univ. of Texas at Arlington 17

Tracking Devices• Used to provide the traces of charged particles resulting

from interactions• Along with a magnet, provides the curvature of the charged

tracks (charge ID) and their momenta• Used to determine the location of the interactions called

vertices• Can provide secondary vertices resulting from the decay of

longer lived particles• Some devices can measure energy losses of particles via

radiations and provide additional particle ID information• Muon tracking system sits at the very outside for

momentum measurement and identification4/22/2009 ILC Calorimeter School, Tsinghua University


A Collider Experiment Tracking System (DØ)

• 800k channel Si vertex detector– Provides precise

location of the primary and secondary vertices

• High resolution scintillating fiber tracking system– Provide high resolution

position and momentum measurements


Calorimeters• Magnetic measurement of momentum is not sufficient,

why?– The precision for angular measurements gets worse as

particles’ momenta increases– Increasing magnetic field or increasing precision of the tracking

device will help but will be expensive– Cannot measure neutral particle momenta– Charge neutral particles do not leave traces in the tracker

• How do we solve this problem?– Use a device that measures kinetic energies of particles

• Calorimeter– A device that absorbs full kinetic energy of a particle– Provides the signal proportional to deposited energy– Can measure shower shapes with fine granularity– Must work as an integral part of the detector


Calorimeters• Large scale calorimeter were developed during

1960s– For energetic cosmic rays– For particles produced in accelerator experiments

• How do EM (photons and electrons) and Hadronic particles deposit their energies?– Electrons: via bremsstrahlung followed by a mixture of

photon pair production and electron bremsstrahlung– Photons: via electron-positron conversion, followed by

bremsstrahlung of electrons and positrons– These processes continue occurring in the secondary

particles causing an electromagnetic shower losing all of its energy


Interaction of Hadrons at High Energies• Hadronic collisions involve very small momentum transfers,

small production angles and interaction distance of order 1fm• Typical momentum transfer in hadronic collisions are of the

order q2 ~ 0.1 (GeV/c)2

• Mean number of particles produced in hadronic collisions grows logarithmically– ~3 at 5GeV– ~12 at 500GeV

• High energy hadrons interact with matter, they break apart nuclei, produce mesons and other hadrons– These secondaries interact through strong forces subsequently in

the matter and deposit energy4/22/2009 ILC Calorimeter School, Tsinghua University


Hadron Energy Deposit• Hadrons are massive thus their energy deposit via

bremsstrahlung is small• They lose their energies through multiple nuclear collisions• Incident hadron produces multiple pions and other secondary

hadrons in the first collision• The secondary hadrons then successively undergo nuclear

collisions• Mean free path for nuclear collisions is called nuclear

interaction lengths and is substantially larger than that of EM particles

• Hadronic shower processes are therefore more erratic than EM shower processes

• Slow neutron energy deposit also problematic


Sampling Calorimeters• High energy particles require large

calorimeters to absorb all of their energies and measure them fully in the device (called total absorption calorimeters)

• Since the number of shower particles is proportional to the energy of the incident particles

• One can deduce the total energy of the particle by measuring only fraction of their energies, as long as the fraction is known Called sampling calorimeters– Most the high energy experiments use

sampling calorimeters• Can measure E with much less

detector volume …4/22/2009 ILC Calorimeter School, Tsinghua University


How do particle showers look in detectors?

25ILC Calorimeter School, Tsinghua University J. Yu, Univ. of Texas at Arlington4/22/2009

EM

Hadron

Calorimeter Design Considerations• Full shower containment

– What are the expected energies of particles resulting from the interactions?

– How deep and wide does the calorimeter have to be to contain full shower?

• What is the necessary energy measurement precision? – What sensitive gap technology can allow to accomplish such

precision?– At what longitudinal frequency do we need to sample?– What is the necessary longitudinal and transverse granularity?

• What is the necessary position resolution?• What are the timing structure of the accelerator?• What are the particles to be identified in the detector?4/22/2009 ILC Calorimeter School, Tsinghua University


What are the most distinguishing characteristics of different particles?

• Electrons: Electromagnetic particle– Deposit virtually all of its energy in the electromagnetic

section of the calorimeter– Has an associated charged track pointing at the cluster

• Photons– Deposit virtually all of its energy in the electromagnetic

section of the calorimeter– No charged track associated with it


What are the most distinguishing characteristics of different particles?

• Hadronic particles, pions, Kaons, protons, neutrons, etc– Some have charge while some others don’t– Deposit energy throughout both EM and hadronic sections of the

calorimeter

• Hadroinc Jets induced from quarks and gluons• Multiple charged and neutral hadrons collimated like a jet

– Deposit energies throughout the entire calorimeter section– Leave long and wide hadronic showers in the calorimeter

• neutrinos: Does not interact in the calorimeter.. How do we measure its energy?– We measure its transverse energy using momentum imbalance



Particle Detection and Identification

InteractionPoint

electron

photon

jet

muonneutrino -- or any non-interacting particle missing transverse momentum

Ä B

Scintillating FiberSilicon Tracking

Charged Particle Tracks

Calorimeter (dense)

EM hadronic

Energy

Wire Chambers

Mag

net

Muon Tracks

We know x,y starting momenta is zero, butalong the z axis it is not, so many of our measurements are in the xy plane, or transverse

Monday, Jan. 26, 2009PHYS 1441-002, Spring 2009 Dr. Jaehoon Yu30

Computers put together a picture

Digital data

Data Reconstruction

pp

The NuTeV Detector• Physics goals• Beam characteristics• Detector requirements• NuTeV Calorimeter• NuTeV Calorimeter Performance



What are neutrinos?• Lepton species without electrical charge• Only affected by weak interactions, no EM• Have one helicity

– we have observed only left-handed neutrinos and right-handed anti-neutrinos

– This property led Yang & Lee to parity violation and eventually theory of weak interactions

• No mass prescription in the original SM Now some mass prescription corrections after the strong proof of neutrino oscillation

•Measurements show three species only

Z 2.92 0.05N


Physics With Neutrinos• Investigation of weak interaction regime

– Only interact via weak interaction This is why neutrinos are used to observe NC interactions

– Measurement of weak mixing angle• Measurement of coupling strength e=gsinW

• Test for new mediators, such as heavy neutral IVBs• Measurement of SM parameter• Indirect measurement of MW: sin2W=(1-MW

2/ MZ2)

• Measurement of proton structure functions• Measurement of neutrino oscillations


Neutrino Cross Sections

WEMweak QIcoupling 2)3( sin)3(weakIcoupling

2

3

21

22

22

,2

1

,22

,2

12

QxxFy

y

QxxFy

QxFE

Mxyy

MEG

dxdy

d F

GeVcm

GeVcm 2

2

/1035.0/

/1068.0/38

38

E

E

N

N

Charged Current

Neutral Current


Neutrino Experiments• Neutrino cross sections are small ~10-38 E• To increase statistics

– Increase number of neutrinos • Natural or reactor sources will not give you control of

beam intensity• Need man-made neutrino beams

– Increase neutrino energy– Increase thickness of material to interact with

neutrinos Detectors with dense material• Beam can be made so that it is enriched with a

specific flavors of neutrinos, such as s.– How does one do this?

The NuTeV Experiment• NuTeV (E815) was a fixed target Deep Inelastic

Scattering (DIS) experiment that used sign selected neutrino beams at Fermilab– Ran in the fixed target run at Fermilab 1996 – 1997

using 900 GeV protons hitting the target

• NuTeV used an improved version of the beam lines and the detector from its previous incarnation, the CCFR experiment in the same beam line

• NuTeV used a separate, dedicated beam line for constant in-situ detector calibration


NuTeV Scientific Goals • Measure sin2W with a greater precision

– Narrow down the Higgs mass range along with precise top quark mass measurements from other experiments

– Beam line modification required– Need to understand the detector at a greater precision

• Measure proton parton distribution functions to a greater precision– Provide precise knowledge on proton internal structure at high

momentum fraction (x) and determine the strong coupling constant with higher precision

– Good energy measurements– Good angle measurements



Proton Structure Function Measurements• A complete set of Lorentz scalars that parameterize the

unknown structure of the proton• Properties of the SF lead to parton model

– Nucleon is composed of point-like constituents, partons, that elastically scatter with neutrino

• Partons are identified as quarks and gluons of QCD• QCD does not provide parton distributions within proton• QCD analysis of SF provides a determination of

nucleon’s valence and sea quark and gluon distributions (PDF) along with the strong coupling constant, s


Factorization Concept

Non-perturbative, infra-red part

k k’

W+(W-)

p,

} EHadP

q=k-k’

q, (q)

xP

Partonic hard scatter

=f*p

f

p


How Are PDFs Determined?• Measure -N differential cross sections, correcting for target• Compare them with theoretical x-sec• Fit SF’s to measured x-sec• Extract PDF’s from the SF fits

– Different QCD models could generate different sets of PDF’s– CTEQ, MRST, GRV, etc

Fit to Data

for SF


sin2W and -N scattering• In the electroweak sector of the Standard Model, it is not known a priori what

the mixture of electrically neutral electomagnetic and weak mediator is This fractional mixture is given by the mixing angle

• Within the on-shell renormalization scheme, sin2W is:

20

22

1sinZ

WShellOn

w M

M

•Provides independent measurement of MW & information to pin down MHiggs via higher order loop corrections, in comparable uncertainty to direct measurements•Measures light quark couplings Sensitive to other types (anomalous) of couplings •In other words, sensitive to physics beyond SM New vector bosons, compositeness,-oscillations, etc


How is sin2W measured?

• Cross section ratios between NC and CC proportional to sin2W

• Llewellyn Smith Formula:

)(CC

)(CC

W4

W22

)(CC

)(NC)(

σ

σ1θsin

95

θsin21

ρσ

σR

WEMweak QIcoupling 2)3( sin)3(weakIcoupling

(or e)


Sources of Neutrinos:Atm and other• High energy cosmic-ray (He, p, n, etc) interactions in

the atmosphere– Cosmic ray interacts with air molecules– Secondary mesons decay– Muons decay again in 2.6s

• Neutrinos from Big Bang (relic neutrinos)• Neutrinos from star explosions• Neutrinos from natural background, resulting from

radioactive decays of nucleus• Neutrinos from nuclear reactors in power plants

K , pHe

e

ee

Beam Characteristics – NuTeV • Fermilab’s Fixed Target beam using 900GeV

protons hitting the target to generate neutrinos– How can we produce neutrino beams?



Conventional Neutrino Beam

• Use large number of protons on target to produce many secondary hadrons (, K, D, etc) and focus them well

• Let and K decay in-flight for beam– +K• What percentage of pions will decay in the 540 m decay region

when their mean energy are 150GeV?• Other flavors of neutrinos are harder to make• Let the beam go through shield and dirt to filter out and

remaining hadrons, except for – Dominated by

p

Good target

Good beam focusing

Long decay region

Sufficient dump


Improving Experimental Uncertainties• Electron neutrinos, e, in the beam fakes NC events from CC

interactions– If the production cross section is well known, the effect will be

smaller but since majority come from neutral K (KL) whose x-sec is known only to 20%, this is a source of large experimental uncertainty

• Need to come up with a beamline that separates neutrinos from anti-neutrinos


protons hitting the target to generate neutrinos– How can we produce neutrino beams?– How can we produce neutrino beams of specific signs (

or ?



How can we select sign of neutrinos?• Neutrinos are electrically neutral• Need to select the charge of the secondary hadrons from the proton interaction on target• NuTeV experiment at Fermilab used a string of magnets called SSQT (Sign Selected

Quadrupole Train)• Proton beam shot with a 7mr upward incident angle• Dipoles immediately behind the target bends the particles of right signs toward the detector• Wrong charge particles and the remaining protons are dumped


protons hitting the target to generate neutrinos– How can we produce neutrino beams?– How can we produce neutrino beams of specific signs (

or ?

• Two different beam lines used– Neutrino beam: Fermilab’s NC (Neutrino Center)

• 5 “pings” of widths 5 ms separated by 0.5 seconds

– Calibration Beam: NT (Neutrino Test) • A 18 second slow spill of continuous beam 1.8 seconds after

the last short pulsed neutrino beam



Charged Current Events

Neutral Current Events

How Can Events be Separated?

x-view

y-view

x-view

y-view

Nothing is coming in!!!

Nothing is coming in!!!

Nothing is going out!!!

Event Length


Experimental VariableDefine an Experimental Length variable Distinguishes CC from NC experimentally in statistical manner

to theoretical prediction of RCandidates CC

Candidates NC

Cut

Cut

Long

ShortExp N

N

LL

LL

N

NR

Compare experimentally measured ratio

Detector Requirements – NuTeV • Large mass in neutrino’s path to cause neutrino interactions

– Neutrino-nucleon cross section: – Anti-neutrino-nucleon cross section:

• High precision understanding of calorimeter energy resolution• High precision interaction position measurement • Ability to distinguish CC and NC interactions

– Tracks of leptons (e and ) from CC interactions for PID – Precise momentum measurement of muons– Precise measurement of hadronic shower energy up to ~150 GeV– Fine longitudinal segmentation– Cosmic-ray veto

• High efficiency, high rejection muon identification and momentum measurements

• Sensitivity to low energy interactions, such as MIP energy deposit4/22/2009 ILC Calorimeter School, Tsinghua University


38/ 0.68 10 /N E 2 cm GeV38/ 0.35 10 /

NE

2 cm GeV

NuTeV Calorimeter• Technology: Sampling Calorimeter• Passive (or absorber) material

– 5cm thick steel plates• What is the radiation length?

– What are the functionalities of these steel plates?

• Active material: 2.5cm thick Liquid Scintillation counters– What is the liquid scintillator material?

• Baby oil!!


NuTeV Calorimeter, cnt’d• Dimension of each unit: 3mx3m• Number of layers: 84 layers of liquid scintillator

sandwiched in between two steel plates interspersed with 42 drift chambers

• Readout technology: PMTs mounted in each of the four corners of the square

• Each layer read out independently, giving total of 64 longitudinal sections

• Can one distinguish different particles?– Electrons and hadroinc jets? Neutrinos? Muons?



• Calorimeter– 168 FE plates & 690tons– 84 Liquid Scintillator– 42 Drift chambers interspersed

The NuTeV Neutrino Detector

• Solid Iron Toroid• Measures Muon momentum p/p~10%

Continuous test beam for in-situ calibration


The NuTeV Detector

A picture from 1998. The detector has been dismantled to make room for other experiments, such as DØ

NuTeV Liquid Scintillation Counter


Particle incident position dependence

For structural support

For light transport

NuTeV Readout Electronics


3 different electronics gains to extend dynamic range

NuTeV Detector In-Situ Calibrations• In-Situ simultaneous calibration beam

which followed the neutrino pings by 1.4 s separation– 18 second long calibration beam spills


• Calibration beam line capable of providing wide range of momenta for various species of particles– Electrons, pions and muons– Particle selection done by the Cerenkov counter just upstream of

the detector– Beam momentum measured by an independent set of

spectrometer consisting of drift chambers and magnets

• Beam was directed to different locations on the detector through a rotating dipole

NuTeV Calibration Beam Line


Photon converter/ electron generator

focussing

Momentum selection

Electron Momentum selection

NuTeV Hadron Response and Resolution


Hadron Energy Resolution

Hadron Energy Response

NuTeV Calorimeter Performance• Hadron non-linearity 5.9 GeV – 190GeV: 3%• Hadron energy scale uncertainty: 0.43%• Hadron Energy Resolution: • Residual Position Dependence of EH: <0.5%• E/h response ratio: 1.08• Electron Energy Resolution:• Hadron MiP to GeV Conversion factor: 0.212


86% ( ) 2.2%E E GeV

50% ( ) 4.2%E E GeV

Ref: Nucl.Instrum.Meth.A447:377-415,2000

The DØ Detector• Physics goals• Beam characteristics• Detector requirements• NuTeV Calorimeter• NuTeV Calorimeter Performance


Scientific Goals – DØ • Top quark

– Discover the top quark– Measure its properties and production x-sec with high precision

• Electroweak Intermediate Vector Bosons– Measure W mass at a higher precision

• The Higgs Particle– Narrow down the mass range using Mt and MW measurements

– Search and discover the Higgs particle

• Super-Symmetry– Discover supersymmetric partner particles and measure properties

• QCD– Measure various jet cross sections with higher precision



Z and W Boson Decays• The weak vector bosons couples quarks and leptons

– Thus they decay to a pair of leptons or a pair of quarks• Since they are heavy, they decay instantly to the

following channels and their branching ratios– Z bosons: MZ=91GeV/c2 – – – – W bosons: MW=80GeV/c2

– –

0 69.9%Z qq

0 (20%)l lZ

0 (3.37% for each charged lepton species)Z l l

68%W qq (~10.6% for each charged lepton species)lW l


Precision Z/W Measurement Strategy• The weak vector bosons have masses of 91 GeV/c2 for Z

and 80 GeV/c2 for W• qqbar (2 jets of particles) the largest x-sec, the multi-jet

final states are also the most abundant in collisions– Background is too large to carry out a meaningful search

• The best channels are using leptonic decay channels of the bosons

– The final states containing electrons and muons are the cleanest• So what do we look for as signature of the bosons?

– For Z-bosons: Two isolated electrons or muons with large transverse momenta (PT)

– For W bosons: One isolated electron or muon with a large transverse momentum along with a signature of high PT neutrino (Large missing ET).


W and Z event kinematic properties

dots: Datadots: Datahistogram: histogram: MCMC

ET ETe

MT pTw

diEM Invariant mass (GeV)

Ze+e- cross-section


Cross Section: W(e) +X

• Transverse momentum distribution of electrons in W+X events


W Transverse Mass Distribution• Transverse mass is defined as 2 1 cosl

T T T lM E E


A W e+ Event


Z e+e-+2jets Event

Invariant Mass Distributions: Z(ee) +X

• Invariant mass distribution of electrons in Z+X events


How does the top quark final state look?• Top quarks produced in pairs with anti-top most of the time• The top decays through electro-weak process, coupled with

a W IVB and a b-quark, highest CKM coupling– and

• Depending on how W’s decay, many final state particle combinations possible– Both W’s decay leptonically 2 b-quark jets + 2 leptons + 2

neutrinos– One W decay leptonically and the other decay hadronically 2

b-quark jets + one lepton + one neutrino + 2 light quark jets– Both W’s decay hadronically resulting in 6 jets in the final state


t W b t W b

Simple Exercise• Draw Feynman diagrams of each of the following

tt final states and compute the branching ratios.– di-lepton– Lepton+jets– Six jets


'

'l l

tt ll bb

ltt l qqbb' " '" ""tt q q q q bb


The Higgs Mechanism• Recovery from a spontaneously broken electroweak

symmetry gives masses to gauge fields (W and Z) and produce a massive scalar boson– The gauge vector bosons become massive (W and Z) – The massive scalar boson produced through this

spontaneous EW symmetry breaking is the Higgs particle• In SM, the Higgs boson is a ramification of the

mechanism that gives masses to weak vector bosons, leptons and quarksThe

Higg

s

Mec

hanis

m


Higgs Production Processes at Hadron Colliders

Gluon fusion: Hgg

WW, ZZ Fusion: HZZWW ,

Higgs-strahlung off W,Z: HZWZWqq , , **

Higgs Bremsstrahlung off top: Httggqq ,


Hadron Collider SM Higgs Production

LHC

Tevatron

We use WHe+bb channel for search for Higgs


MH=130 GeV

For MH<130GeV• H bb• H WW• H gg or • H cc

• H WW/ZZ• H bb• H gg or • H cc

For MH>130GeV

Standard Model Higgs ChannelsmH < 130-140 GeV • WH l bb backgrounds Wbb, WZ, tt, single t

– factor ~ 1.3 improvement in S/B with neural network – possibility to exploit angular distributions (WH vs. Wbb) Parke and

Veseli, hep-ph/9903231

• WH qq bb overwhelmed by QCD background• ZH ll bb backgrounds Zbb, ZZ, tt• ZH bb backgrounds QCD, Zbb, ZZ, tt

– requires relatively soft missing ET trigger (35 GeV?)


Standard Model Higgs Channels

mH > 130-140 GeV• gg H WW* /ZZ* backgrounds Drell-Yan, WW, WZ, ZZ,

tt, tW, – signal:background ratio ~ 7 10-3 !

– Angular cuts to separate signal from “irreducible” WW background



How do we find a presence of a b-quark?• Use finite lifetime of mesons containing b-quarks

within a particle jets.

b vertex

SiliconDetectors

Beampipe

1”


What do we need to do all this?• Smaller Higgs x-sec Need higher rate• Increase CMS energy of the accelerator

– Increased x-sec– Increased kinematic reach for higher MH

• Increased instantaneous Luminosity– Increased Number of protons and anti-protons, especially

anti-protons– Increased duty factor/efficiency– Shorter fill time of anti-protons

Beam Characteristics – DØ • Fermilab’s Tevatron P – Pbar collider

– How is this different operationally from the LHC, a p-p collider?

• One of the two collider experiments on the Tevatron ring• Tevatron had the Main Ring booster accelerator circulating

beam right on top of the Tevatron beam– Accelerates protons up to 150GeV– Used to generate anti-proton beam and accumulate them– Now it is replaced by the Main Injector, a separate ring

• RF Frequency: 50MhZ• Bunch Spacing: 3.5 s (Run I)/396 ns (Run II)• Instantaneous luminosity:~1031/~1033



(tt) ~ 40% higher at 2 TeV MH ~ 40% per experiment • Increase in rates• Decrease in bunch spacing

Parameters Run I RunIIa/bLinst (cm-2 sec-1) ~1031 2x1032 ~1033

Bunch Spacing 3.5 sec 396 / 132 nsecECMS(TeV) 1.8 1.98

Lint ~110pb-1 2fb-1 / >6fb-1

Run II TeVatron Benchmarks


What do we need for the experiment to search for the top and the Higgs and measure IVB precisely?• We need to be able to identify isolated leptons

– Good electron and muon identification– Charged particle tracking

• We need to be able to measure transverse momentum well

– Good momentum and energy measurements• We need to be able to measure missing transverse

energy well– Good coverage of the energy measurement (hermeticity)

to measure transverse momentum imbalance well• Identify b-quark jets

Detector Requirements – DØ • High precision energy and momentum measurements• High efficiency and high rejection particle identification, in

particular the electrons and muons• High efficiency and high rejection neutrino identification and

high precision transverse energy measurements• High precision jet energy and position measurements• High efficiency and high rejection b-jet idenfication

– Capable of measuring vertex that are ~100m away from the primary vertex Precision vertex detector

– Tag and associate leptons with a jet



The DØ Detector

30’

30’

50’

• Conceived in 1983, construction completed in 1992

• Weighs 5000 tons• More than 100 million parts• Can inspect 1,700,000

collisions/second• Records 100 collisions/second• Records approximately 20

MB/second• Records 300TB data/year• Recorded over 4x109 events as

of Nov. 2008


Run II DØ Detector


• Ability to trigger on tracks for quick dicision• Measure momentum and identify charge• Upgrade tracking & Trigger systems

DØ Tracking System

Charged Particle Momentum ResolutionpT/pT ~ 5% @ pT = 10 GeV/c


DØ Silicon Microstrip Detector

Barrels F-Disks H-Disks

Channels 387072 258048 147456

Modules 432 144 96

I nner R 2.7 cm 2.6 cm 9.5 cm

Outer R 9.4 cm 10.5 cm 26 cm

234

98

11

1

67

5

1012

1

6

…...

1

2

3

4

•Covers immediate outside of beam pipe to just before the fiber tracker•Consists of Barrels and Disks•Total number of readout channels are 800k•Expected Position resolution 10~20m


DØ Detectormuon system

shielding

electronics


DØ Detector

Central Calorimeter

Solenoid

Fiber Tracker

Silicon

ILC Calorimeter School, Tsinghua University J. Yu, Univ. of Texas at Arlington Slide 93

The DØ Calorimeter• Three separate calorimeters:

– Central and Two End Caps for hermetic coverage– Concentric cylinders about the beam axis

4/22/2009

DØ Calorimeter• Technology: Sampling Calorimeter• Passive (or absorber) material

– 3mm (central) /4mm (end cap) thick depleted U238 plates in EM• What is the radiation length of each plate?• What is the depth in radiation length to contain over 98% of ET=45 GeV

electron energy?

– 10mm thick uranium-niobium alloy in fine hadronic section– 50mm thick copper plates in coarse hadronic section– Uranium used for compensation of e/pi responses

• Active material: 2.6mm Liquid Argon gap surrounding the resistive coated PCB readout board

• Used for energy measurements, p-ID and triggering


Unit Layer of the DØ Calorimeter


2.6m

m

HV

=+

2.5k

V

Grounded U238/U238 + Nb Alloy/Cu plates

Cell With Readout Electronics


Calorimeter Data Flow Diagram

4/22/2009 ILC Calorimeter School, Tsinghua University J. Yu, Univ. of Texas at Arlington 97Triggering system

calibration system

E sum for trigger

DØ Calorimeter Geometry• EM Section

– Preceded by 1 – 2 X0 of material

– 3mm Uranium (U238 – depleted) plates + LAr– Total of 21 gaps read out in four longitudinal sections

• 2+2+7+10 In which layer is the shower maximum for 40GeV electron?

– High granularity: x=0.1x0.1/0.05x0.05 at the shower maximum

• Hadronic Section: Iron/copper + LAr – Total of four longitudinal readout layers that cover the depth of 5 –

7 interaction lengths– Transverse granularity: x=0.1x0.1– Four independent longitudinal readout layers

• 460ns charge collection time4/22/2009 ILC Calorimeter School, Tsinghua University


Readout Geometry of the DØ Calorimeter


• Projective towers without obviously aligned cracks

• Angular coverage down to 5o from the beam pipe (||<4.2)

ILC Calorimeter School, Tsinghua University J. Yu, Univ. of Texas at Arlington Slide 100

The DØ Calorimeter• Uranium-Liquid Argon

– Total of 50,000 readout channels

– Compact, hermetic device Angular coverage to 5o from the beam line

– Uniform response – Stable calibration– ‘compensating’ – Fully absorbing with

relatively small diameter detector

– Where is Jae?4/22/2009

DØ CC in 1990

Hardware Calibration• Regular calibration runs for constant background

noise due to electronics thermal noise + beta rays from U plates

• Regular electronics gain calibration runs using pulse injection system

• Conversion between ADC counts and GeV obtained from test beams– Multiple loads of detector stacks exposed to electrons

and hadrons

• Refined using in-situ calibration points4/22/2009 ILC Calorimeter School, Tsinghua University


In-Situ Calibration• In-situ calibration helps to minimize remaining effects of detector

response variations and understand detector responses to unmeasurable quantities such as missing ET

• Electromagnetic energy scale: Use known mass resonances to correct for the scales (precision ~0.1%)– J/Y ee, Z ee– Correct for overall energy scale

• ~1.05

– Correct for azimuthal non-uniformities

• Jet energy scale corrections (precision varies 5 – 10%)– Utilized missing ET projection technique

– Assisted by simulations since jet composition is not known apriori– Out of cone corrections + underlying events


True measE E

In-Situ electron energy scale calibration


J/ e+e- Z e+e-

• Data

MC

DØ Calorimeter Performances• Single particle energy resolutions

– EM particles: – Hadrons

• Jet energy resolution:• Absolute EM energy scale precision: 0.1%• Response Linearity: Better than 0.5%• Average electron ID efficiency: ~85%• Jet reconstruction efficiency: >98% for PT>25GeV


15.5%(23%) ( ) 0.3%E E GeV

50% ( )E E GeV

80%(90%) ( )E E GeV

Epilogue• Calorimeters not only measure energies of various

particles but also plays a crucial role in particle identifications

• Depending on the physics goals, different requirements are applied on the calorimeter

• Previous calorimeters such as NuTeV, DØ, and others have performed marvelously and accomplished a great deal beyond their original goals

• Performance requirements on calorimeters for a Linear Collider is unprecedented A lot of work ahead

• Requires bright minds like yours to meet the challenge4/22/2009 ILC Calorimeter School, Tsinghua University


Reference Textbooks• R. Fernow, “Introduction to Experimental Particle

Physics,” ISBN 0-521037940-7, Cambridge University Press, 1986

• D. H. Perkins, “Introduction to High Energy Physics,” 4th Ed., ISBN 0-521-62196-8, Cambridge University Press, 2000

• D. Griffiths, “Introduction to Elementary Particles,” ISBN 978-0-471-60386-3, Wiley-VCH, 2004

• A. Bettini, “Introduction to Elementary Particle Physics,” ISBN 978-0-521-88021-3, Cambridge University Press, 2008


Detector Reference Papers• V. M. Abazov et al., DØ Collaboration, “The Upgraded DØ

detector,” Nucl. Instrum. Meth. A565, 463 (2006). • V.M.Abazov et al., DØ Collaboration, “Determination of the

absolute jet energy scale in the DØ calorimeters,” Nucl. Instrum. Meth. A424, 352 (1999).

• V.M.Abazov et al., DØ Collaboration,“The DØ upgrade,” Nucl. Instrum. Meth. A408, 103 (1998).

• S. Abachi et al., DØ Collaboration, “The DØ Detector,” Nucl. Instrum. Meth. A338, 185 (1994).

• S. Abachi et al., DØ Collaboration, “Beam tests of the DØ uranium liquid argon end calorimeters,” Nucl. Instrum. Meth. A324, 53 (1993).

• D.A. Harris and J. Yu et al., NuTeV Collaboration, “Precision Calibration of the NuTeV Calorimeter,” Nucl. Instrum. Meth. A447, 377 (2000).


Calorimeters In Action!!

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