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13.8.12
Mitg
lied
der H
elm
holtz-G
em
ein
schaft
Data Acquisitionat a particle physics experiments
Sergey Mikirtytchiants, IKP FZJ
GGSWBS'12, Batumi Aug. 13-17
13.8.12 Slide 2
Outline.
How to study interaction of an elementary particles?
Particle identification and detectors.
Digitizing of detector signals.
Data acquisition system.
Trigger.
Example: Strange particle production in p-p collision.
Summary.
13.8.12 Slide 3
How to study interaction of an elementary particles?
p 1 ,m1
incident
targetpT ,mT
interaction ejectilesp 1 ,m1
p 2 , m 2
p21 ,m2
1
p n , m n
p22 ,m2
2?
Kinematics(conservation law)
Reconstruct ejectiles,unobservable directly(missing mass)
Example:
Strange particle production in proton-proton collisionpp → K + p Λ , Λ→π + p , BR=0.639
pp → K + p Σ 0 , Σ 0→γ Λ , BR=1.00
pp →K + n Σ + , Σ + → p π 0 , BR=0.516→π + n , BR=0.483
total
~ b
13.8.12 Slide 4
What is needed to carry out such study?
Accelerator
Target
Setup to detect and identify ejectiles
Incident particle beam
Particle: p; Energy: 2 GeV; Intencity: nb = 1012 1/s
Particle: p; Dencity (thikness): nt = 1014 1/cm2
Luminosity: L = nt n
b f
b= 1014 x 1012 x 106 = 1032 cm-2 s-1
Event rate: R = total
L = 10-29 cm-2 x 1032 cm-2 s-1 = 103s-1
13.8.12 Slide 5
Particle identification.
Energy losses in matter
Cherenkov radiation
Bending of trajectory in magnetic field B
Time of flight
Means the type of the particle (mass) and its momentum (P)Charged particles
(π + , π − , K + , K− , ... , p , n , ...)
E/x [ MeV/cm ]
(velocity)
R=P/eBR=P/eB → P=f(x,y)
tof = (t1-t
0)/L [ ns/m ]
13.8.12 Slide 6
Detectors.
Temporal resolution TOF Spatial resolution Tracking Energy resolution E, E Dead time
MW ChambersProp.
DriftScintillators Organic Inorganic Silicon
StripPixel
2 ns 2 ns 0.1 ns 10 ns 1 ns ------
0.1mm 0.1mm DG DG 10 m 1 m
------ ------ 1 MeV 0.1MeV 0.1MeV 0.1MeV
0.2 s 0.1 s 10 ns 1 s 10 s 100 s
DG - Detector Geometry
13.8.12 Slide 7
Digitizing (1).
TDC — Time Digital Converters
ADC — Analog Digital Converters
Resolution - [ns/bin]Range (full scale) – n-bits Nonlinearity - = f(bin)Conversion time ~ s
Resolution - [AV / bin]Range (full scale) – n-bitsNonlinearity - = f(bin) Conversion time ~ s
Amplitude A N i=k A⋅Ai
Flash ADC aj
N ij=k A⋅ai
j
0 m T
clk
0 < j < m
Charge Q N i=kQ⋅∫0
t
I (t)dt
t
t0
start t
0
stop t
1 t
stop_m t
n t
j
N i = k T ⋅(t 1−t0)N ij=k T ⋅(t j−t 0)Multihit TDC: m times
m times
13.8.12 Slide 8
Digitizing (2).
Registers
Scalers
Coordinate detector (MWPC)
Each input signal increments the counter content by ONE Data = Data + 1
Double pulse resolution ~ 5...10 ns Max. speed ~ 20...200 MHz Capacity – 24...32 bits
0/1
0/10/10/1
1 0 1 1
Latch
Data MSB n MSB n 0 LSB 2 1
13.8.12 Slide 9
Data acquisition.
Common hardware structure
DATA stucture
Detectors Front endelectronics
Digitizers Digitizers Interface Computer
CAMACVME
LVDS BusPCI Bus
…..
ADCTDCREGSCL ….
PreAmpAmplifier
Discriminator ….
D1...Dn
HV, LVGas,
Cooling ….
TriggerLevel 1
…..
DATAstorage.
Header (Run number, comment) {Event number; Time stamp; Source ID (ADC_1); {Data_ADC_1}; Source ID (TDC_1); {Data_TDC_1}; …........ End of event}; // event size {Next Event};
Amount of DATA = <event size> x Accepted Trigger rate upto 100 MB/s !!!
→ Zero data suppression → Selective Trigger
13.8.12 Slide 10
Data acquisition.
Common hardware structure
Dead time: After each accepted event DAQ is insensitive during a period (DT)
Detectors Front endelectronics
Digitizers Digitizers Interface Computer
….. …. t
0 , gate
….
Trigger
…..
DATAstorage.
D1...Dn
DT ninp
nacc
ninp
Full Dead time: Full Live time:
nacc⋅1−nacc⋅
For a unit of time:
Efficienty of Data taking:
naccninp
= 11+ninp⋅
= ninp⋅(1− ninp⋅ )
nacc
Average DT: <> = 100
s<n
inp>
103 1/s 0.91
104 1/s 0.50
105 1/s 0.09
106 1/s 0.01
Efficiency increasing by
→ Clusters ( less DT ) → Selective Trigger (less n
inp )
DT
DT BUSY
nacc
13.8.12 Slide 11
Data acquisition.
Cluster structure
Advantages: a) Flexibility; b) High performance …
Detectors Front endelectronics
Digitizers Interface Computer
….. …. …..
DATAstorage.
D1
nacc
cluster_1
Triggern
inp
DT DAQBUSY
nacc
…. t
0 , gate
…. Dn cluster_n
clustersynchro
clusterevent builder
13.8.12 Slide 12
Trigger.
Level 1: very fast, but pure rejection
Level 2: stronger rejection, but slower ; needs data buffering
Higher trigger levels: more selective and slower
Aim: digitize and store data only in case of the certain conditions.
Goal: reduce data losses and amount of stored data by ignoring of undesirable background events.
Hardware logic based on Timing (restricted time window for TOF)E,E (cut π by setting of high threshold Spatial selection by coincidence of certain SC's
Dedicated digital signal processing based on special algoriythm (rough track reconstruction)
Software based, can be applied ofline.
13.8.12 Slide 13
Example.Strange particle production in p-p collision near to threshold T
p 1.8 – 2.2 GeV
pp → K + p Λ , Λ→π + p , BR=0.639
pp → K + p Σ 0 , Σ 0→γ Λ , BR=1.00
pp →K + n Σ + , Σ + → p π 0 , BR=0.516→π + n , BR=0.483
total
Searching for pair: (K+p), (K+π+)
Триггер: K+
Aim of experiment:
13.8.12 Slide 14
COoler SYnchrotron COSY.
p, d (un)polarized momentum 0.3...3.7 GeV/c intencity upto 1010 1/s
Cooling electron: ~0.3 GeV/c stochastic: >1.5 GeV/c
13.8.12 Slide 15
Spectrometer ANKE.
STT
Target
1 m
ND (SC, MWPC)
H2,D
2
cluster jet
FD (SC, MWPC, MWDC)
PD (SC, MWPC) K+,π
p, d
13.8.12 Slide 16
Frontend electronics of Scintillator Detectors.
Y= 0
Front endelectronics
Sc
PMT_up
PMT_dn
HV_up
PS
HV_dn
FanOut
CFD
Meantimer
FanOut
CFD
PdSo14_Tup → TDC, Scaler
PdSo14_MT → TDC, Scaler , Trigger
PdSo14_Tdn → TDC, Scaler
PdSo14_Tdn → QDC
PdSo14_Tup → QDC
Y= L
L=1m =7 ns/mt = 2L = 14 ns
13.8.12 Slide 17
Raw spectra.
Source: TDC'sTOF spectra between So13 and Sa1...23
Source: QDC'sEnergy loss spectra So13 and Sa1...23
criterion efficiency of registration K+ BGValid Sa 1.0 0.25
13.8.12 Slide 18
Time of flight (TOF).
TOF spectrum of So13 (& Sa1...23)
criterion efficiency of registration K+ BGTOF onl 1.0 0.11TOF ofl 0.99 0.29
online
offline
Energy loss spectrum of So13
13.8.12 Slide 19
'Delayed Veto'.
criterion efficiency of registration K+ BGDel_Ve onl ~0.2 ~ 5x10 -3
Del_Ve ofl 0.2 < 10 -3
offline online
Delayed Veto spectrum of Tel13
&
t-So
&del_1
&del_2
&del_n
Valid Sa
TOF triggerunit
So
t-Ve
del_Ve Trigger
Ve
K+→+ν ; (BR=0.63)
K+=12.4 ns
13.8.12 Slide 20
Vertical angle.
criterion efficiency of registration K+ BGVertical angle 0.99 0.11
Vertical angles after K+-cuts in SC of Tel.13
13.8.12 Slide 21
Summary of Criteria
criterion efficiency of registration K+ BGValid Sa 1.0 0.25TOF 1.0 0.11Del_Ve ~0.2 ~ 5x10 -3
TOF 0.99 0.29Del_Ve 0.2 < 10 -3
Vertical angle 0.99 0.11
All 0.2 < 3.5x10 -6
Trigger ratesuppresion
10 — 30 times
50 — 200 times
Right Criteria allows to study rare processes !
13.8.12 Slide 22
Result: total cross section
Σ nKpp
PLB 652, 245-249 (2007)
)( Σ
Tp =2.16 GeV
13.8.12 Slide 23
Summary.
Data Acquisition : Small dead time Cluster stucture Flexibility
Trigger: Compromise of a criteria Cut Background Do not cut effect
Online Data Handling: To control trigger criteria setting and thus be sure in quality of taken data
For effictiveness data taking it is needed:
13.8.12 Slide 24
Questions.
Detectors: 1. Which types of detectors can be used for tracking? 2. Which detectors have fast time response?
Digitizers: 1. Types and main characteristics of a digitizers?
Data Acquisition : 1. What is important for effictiveness data taking? 2. Ways how to increase the efficiency of data taking?
Trigger: 1. What is aim of trigger? 2. Which criteria could be used on the first level of trigger?
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