Detection Methods and Detectors

Energy Loss

TOF detectors

Gas Detectors

Cherenkov Detectors

Tracking

Dilepton Reconstruction

Range of charged particles

(E. Segrè, Nuclei and particles)

Particle through themedium:

1) Looses energy

2) is deflected

Alpha-particles in air (discovery of the proton)

(E. Segrè, Die großen Physiker...)

( )

2 4 2

2

2 2

0

2ln

4 21

e

e

ee mdE

dx

n

m

z v

v I=Bethe – Bloch formula:

Energy loss of charged particles due to ionisation

Range of charged particles

(aus: C. Grupen, Teilchendetektoren)

Muons in rock: Electrons in various

materials:

Energy loss of various charged particles in air

(C. Grupen, Teilchendetektoren)

Bragg curves

(E. Segrè, Nuclei and particles)

Energy loss of minimum ionising particles

-1 -1 2

min min

-3

Absorber MeVcm MeVg cm( )

Water 2.03 2.03

Xenon (gaseous) 7.3 10

dE dE

dx d x

1.24

Iron 11.7 1.48

Lead 12.8 1.13

Hy -4drogen (gaseous) 3.7 10 4.12

RAW Data

Beam: (1.17GeV/c) Beam: + + p

Counts

Counts

Charge [ADC chan.]

380 keV470 keV

Contributions to the energy loss of muons in iron (C. Grupen, Teilchendetektoren)

Multiple scattering of electrons

(W.R. Leo, Techniques...)

Beam broadening:

Backscattering:

High Acceptance Di-Electron Spectrometer

T. Eberl, TUM –E12

RICH in detail

pad plane

tank

window

mirror

tank shell

target

radiator gas

detector gas

beam

field plane

photon detector

Status 10/01Status 10/01PreShower

Magnet

CoilsRICH

ToF

Heavy-ion collisions atrelativistic energies (1÷2 AGeV)

p

n++

K

p

T 0, B 0

Physics Motivations

Light vector mesons

Probes for nuclear matter

2.9·10-4K+K-441019

7.1·10-5 + - 023783

4.5·10-5 1.3769

Branching

ratio e+e-

Main

decay

Mean life

[fm/c]

Mass

[MeV/c2]Mesons

e+

e-

LEPTONS

NO strong final interaction

Very low probability

Hadron properties inside the

nuclear matter M,

Organic Scintillator

(Leo, Techniques...)

Very rapid fluorescence signal (a few ns) timing

Production of light requires 100 eV per photon (NaI: 25 eV)

< 10 ps

ns

Scintillator – light guide – photomultiplier

(Leo, Techniques...)

Measurement of time-of-flight

(Grupen, Teilchendetektoren)

e.g. also as a veto detector

Photomultiplier tube

(Grupen, Teilchendetektoren)

Quantum efficiency of the photocathode: 10 – 30 %

Amplification: up to 107

The TOF Detector

• 6 x 64 Scintillators

tof : 90-140 ps

• In beam start detector

Diamond, d = 120μm,

t = 66ps

TDCt1 t2

Start-Detektor

Catania (INFN - LNS)

Milano (INFN, Univ.)

Rez (CAS, NPI)

Bratislava (SAS, PI)

2 radiation lengths Pb converter

Field

Sense

wires

Pads

Post1-conv Post2-conv.Pre-conv

Pre-Shower detector side view

TOFINO

Pre-Shower

target

3 pad chambers (20000 pads)

em. showers in Pb converters

beam

tof

measurement

t 0.35 ns

Pre-Shower/TOF system <450

esingle 80%

C+C 1.5 AGeVOne event: detector response

Pre-converter Post1-converter Post2-Converter

Shower

candidate

Pre-Conv

Post1-Conv

Pre-Conv

Post1-Conv

p beam e- beam

Ionisation chamber

(Grupen, Teilchendetektoren)

1 electron – ion pair per w 30eV

: 2.35 , 0.2Fw

Energy resolution R FE

= <

Yield of ions in a gas detector

(Leo, Techniques...)

Multiwire chamber (Charpak)

position sensitivity

Track Reconstruction:

1. Search for Wire Hit

2. Targetprojection

3. Straight-line-fit

Track Reconstruction in the Drift Chamber

Particle ID with the tracking chambers

t2 ~ dE/dx * Corr.

Correct time-above-threshold for track topology.

• Simulation (Garfield)• Use tracking information

Will be exploited for:

• Track matching• Close pair rejection

Momentum Calculation

1. Kickplane-Algorithm

„Impuls-Kick“ on one virtual

( parametrized via Simulations)

2. Numerical Integrations of the

equation of motion.

(„Runge-Kutta: Method“)

Anfangsbed.:

Momentum Reconstruction

0rr

MDC1

MDC2

MDC3

MDC4

( )= )(2

2

lrBdl

rd

p

kq

dl

rd rrrr

0

,,,,

rrdl

dy

dl

dxyxp

rr=

Momentum* charge [MeV/c]

Ve

loc

ity

[c

]

Relative Momentum Resolution with

All tracking Chambers: ~ 3% for p < 800 MeV

tan( ) ~ 1/p

Cherenkov - Effect

> thr =1

n= 1

1

thr

2

cos C =1

n

1

1

n

p = m0v = m

0c

1 m

0c

thr =18

for e : pthr = 0.511MeV /c 18 = 9MeV /c

for pions : pthr =135MeV /c 18 = 2.43GeV /c

Cherenkov-radiators

Material 1 -min -min

solid Sodium 3.22 0.24 1.029

Diamond 2.91 0.26

n

1.034

Flintglas 0.92 0.52 1.17

Water 0.33 0.75 1.52

Aerogel 0.025

-3

-4

- 0.075 0.93 - 0.976 4.5 - 2.7

Pentane 1.7 10 0.9983 17.2

Air 2.93 10 0.9997 41.1

Helium 5 3.3 10 0.99997 123

The HADES RICH Detector

Photon Detector :

• CH4 MWPC

• CsI cathode

• 28.600 pads

• 10 μs readout

CaF2 window

VUV mirror

The RICH Detector

Photon Detector :

• CH4 MWPC

• CsI cathode

• 28.600 pads

• 10 μs readout

Photon Detector

Single events in the RICH

Lepton identification: C+C @ 2 AGeV

tof [ns]tof [ns]

q*

mom

ent

um

q*m

oment

um

Log z!

= 18o - 50o = 50o - 85o

RICHon

RICHoff

T. Eberl, TUM –E12

Online Lepton ID

• Fast readout of all PID -detectors (10μs)

• Real time processing with

– Calibration

– Pattern recognition

– Position calculation

• Transfer to Matching Unit

• Decision and second leveltrigger distribution

Matching UnitSecond

Level

Trigger

TOFShowerRICH

Efficiency calibration(OEM)

beam

Photons produced by 600 AMeV 12C

beam particles passing two different

solid radiatorspad plane

tank

window

mirror

tank shell

target

radiator gas

detector gas

beam

field plane

photon detector

1

0.8

0.6

0.4

0.2

0.0120 140 160 180 200 220

SiO2

MgF2T

ransm

issio

n

[nm]

OEM Radiator

2cm

beam

beam line

beam pipe shadow

Nph ~ N0 * Z2

500 evt accumulated

MgF2

SiO2

Detector Response to VUV Photons

1 evt

C12 ions, E = 600 AMeV

Pulse Height Analysis

Class 1 Class 2 Class 3

Pad X Coordinate

Primary and feedback photons

Feedback

Primary

Pa

d Y

Co

ord

ina

te

1 Event

Puls

e H

eig

ht

1 primary

photon?

Pulse Height Distribution

• Pulse Height AnalysisQ Mean = 5 * 10 4 e-

SE ~ 90%

Anode Voltage = 2450 V

CH4 atmos. press.

Coupling to Neighbouring Pads

Along the wire

photon impact

resolution ~ 0.5 mm

Perpendicular to wire

Only Class 1 clusters are used!!

Charge Distribution of Single Photons

Simulation

Experiment

single photon response

well understood

Analysis of Photon Yield

Experimental Data Simulation Input ((HGeantHGeant))

– Optical parameters (all independently measured)

– Simulation of single photon response

– Electronic noise

N0=102100 Events

Beam pipe

shadow

N0 Calculation

20

0

20

2

1

2

1

)()(.

102

)(.

=

=

=

i

Sim

i

Exp

Sim

i

Sim

i

Sim

RconstN

N

constN

98/

130

88/

100

102102

78/

88

102

80/

99

102

96/

110

94/

106

92/

106

78 /

88

102102102102

Sector 6

MgF2 SiO2

Sector 3

MgF2 SiO2

Sector 2

MgF2 SiO2

Sector 1

MgF2 SiO2

NSim0

NExp0

e+/e- from different Sources!

Same-event like-sign (LS) CB

• Correlations under Mee = 150MeV/c2

• Low Statistic above Mee~ 450 MeV/c2

Event-Mixing (EM) CB

• Good statistics

• The correlation is not described

e+e+

e-e-

e+e+

e-e-

++=eeeeCB

N*N*2N

Mee < 150 MeV/c2 - Like-sign CB

Mee > 150 MeV/c2 - Event mixing CB

Mee [MeV/c2]1/N

0 d

N/d

M [

Me

V/c

2]-

1

Same Event

Mixed Event

Hybrid

Hybrid Method

Normalization of the EM-CB on top of the

LS-CB [150 MeV/c2 < Mee < 550 MeV/c2]

Combinatorial Background

Dilepton Spectroscopy

Comb. Backgr.

Suppression

Close pair

recognition !!!!

&

rejection

2 close rings

in RICH

2 close tracks

in MDC0 200 400 600 800 1000

10-1

1

10

102

103

104

dalitzη

dalitzΔ

pn bremstr.combin. back.

ρ

dalitzω

ω

dalitz0π

φ

C + C�E = 2*A GeV

]2 [MeV/c-e+eM

/ 10

col

l.2

coun

ts /

20 M

eV/c

9

HADES : Study of in-medium hadron properties via low mass e+e- pairs from , p, A + A collisions

full scale HGEANT simulation

Example:

Data vs. PLUTO cocktail: C+C@2AGeV

Cocktail A: 0 + +

= “long-lived” components only

Cocktail B: Cocktail A + +

Large excess yield!

Efficiency corrected spectra!

SSystematic errors:ystematic errors:

15% efficiency correction10% combinatorial background11% 0 normalization

21% TotalAgakishiev et al., Phys. Rev. Lett. 98, 052302 (2007)