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FAST: A precision measurement of muon lifetime. Chiara Casella FAST collaboration: A.Barczyk (1) , J. Berdugo (2) , J. Casaus (2) , C. Casella (3,4) , K. Deiters (4) , P. Dick (4) , - PowerPoint PPT Presentation
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2 July 2004 Journée DPNC 2004
FAST: A precision measurement of muon lifetime.
Chiara Casella
FAST collaboration:
A.Barczyk (1) , J. Berdugo (2) , J. Casaus (2) , C. Casella (3,4) , K. Deiters (4), P. Dick (4), A. Dijksman (4), J. Kirkby (1), L. Malgeri (1), C. Mana (2), J. Marin (2), G. Martinez (2),
C. Petitjean (4), M. Pohl (3,5), E. Sanchez (2), C. Willmott (2)
CERN 1 , CIEMAT 2 , UNIGE 3 , PSI 4 , NIJMEGEN 5
2 July 2004 Journée DPNC 2004
Goal of the experiment
• Balandin et al. (1974)• Bardin et al. (1984)• Giovanetti et al. (1984)
ppm18
• the uncertainty on is the dominant contribution to the uncertainty on GF:
2
2
42
1
2
5
m
mth
m
m
G
G
F
F qmGF 1192 3
521
• FAST goal: ppm1
0.07 ppm (PDG 2002) 0.5 ppm
(Van Ritbergen and Stuart - 1998)
≤12 ppm (PDG 2002)
ppmG
G
F
F 5.0
9 ppm
2 July 2004 Journée DPNC 2004
Description of the experiment
1 pixel = 0.4 x 0.4 x 20 cm3
12.8 x 19.2 x 20.0 cm3
32 x 48 pixels = 1536 pixels 8 x 12 = 96 groups of 16 bars
DC pion beamp = 170 MeV/cat PSI - pM1 area
+
~ 26 ns ee~ 2.2 s
PS
PM
x 96
x 96
Target and optoelectronics readout
Pream
pD
iscri
x 96x 96
An
alo
gu
e e
lectro
nics
LV
2 board
TD
C
LL
- data
HL
- data
x 16
x 16
Digital electronics
Dual threshold discriminators:- low thr : mip’s- high thr : stopping pcls
2 July 2004 Journée DPNC 2004
1ppm requirement
Ability to disentangle overlapping events
Tracking capabilities and high granularity of the target
Very high data rate Constraints on the DAQ
FAST DAQ design 80 MB/sec +
ONLINE ANALYSIS !!!
High beam rate, because PARALLELISATION is needed!
~ 1 MHz (2-3 months data taking)
Sample of 1012 events
needed (+ + e+)
Suppression of systematic effects at
the ppm level
Remove time dependent effects that, together with asymmetries in the target, could compromise
the measurement
DC beam
Isotropic muon source (by the identification of
+ + decay) SR effects suppression
2 July 2004 Journée DPNC 2004
Level 2 trigger (i.e. data reduction)Max data rate sustainable by DAQ 80 MB/sec(Simulated) Raw data rate from the target 2300 MB/sec
Trigger system (level 2 trigger) to reduce data bandwidth:
LV2 trigger idea:
• all the relevant time informations are contained in the “superpixel” (5x5 pixels) centered on the stopping
• no need to read 16 TDC’s always at the same time – but only the TDC’s containing at least one pixel of the superpixel DATA REDUCTION
LV2 trigger task:
• find the stopping coordinates• search for the subsequent • trigger only the interested TDC’s
• flag the event if another is found in the superpixel
(LV2 trigger input = HL data from discriminators)
beam
2 July 2004 Journée DPNC 2004
Level 2 trigger
• Level 2 trigger : the only hardware missing element
• CIEMAT – Madrid in charge of it
• Prototype tests performed:– Single board (1/16) prototype tested - Dec 2003– Prototype (1/4) tested - June 2004– Prototype (1/4) test ? - July 2004 (?)
• Final level 2 commissioning: end 2004
2 July 2004 Journée DPNC 2004
2003 Activities:• Target completed + assembling at PSI
80/96 tubes available Complete readout and DAQ chain No LV2 trigger available
• DAQ chain tested 75 MB/sec
• Fine tuning of the detector and beam(High Voltages, Thresholds, Ranges, Timing properties)
Some problems found Some improvements needed
• Few days of data taking, LV2 trigger prototype tested
Beam time: Sept – Dec 2003
2 July 2004 Journée DPNC 2004
2003 beam test : fine tuningHV efficiency curves for each tube
range of beam (and ) in the target with variable thickness absorber
Preliminary beam tuning ( stopping points distribution)
beam
Blind in the vertical (z) direction
beam profile! ! !
x
y
2 July 2004 Journée DPNC 2004
20 tubes, 2000 commissioning
60 tubes,2002 commissioning
2003 beam test : timing propertiesTime resolution monitored using straight tracks t ~ 1 ns stable with time
reflection @ 50 nsmismatch prempl/discr
Afterpulses structurein old commissioned tubes
replaced 20 old tubes
impedance mismatch cured: - preamp modified- replaced preamp / dicrim cables
2 July 2004 Journée DPNC 2004
2003 beam test: Muon lifetime
• few days run (‘long run’)• total statistics : 7.4 107 events
from online analysis • (10% written to disk for offline
studies)
• Run conditions: - narrow trigger- no LV2 trigger ( all 16 TDC’s)- low LV1 (beam) trigger rate
• Good background suppression• Good exponential fit:
- in agreement with PDG value, within a bigger error:
PDG ~ 40 ps;
2003 ~ 350 ps
2 July 2004 Journée DPNC 2004
2003 beam test: Pion lifetime
Unexpected result from HL run
• Pion lifetime: not primary FAST goal
• Short dedicated high threshold run
• Good exponential fit, in agreement with PDG value
PDG = 0.005 ns 2003 = 0.024 ns
• Preliminary result… but feasible measurement !!!
2 July 2004 Journée DPNC 2004
What’s going on now
• 20 old tubes replaced, 16 new tubes in place• Preamplifiers modified, impedance mismatch cured
Re-tuning of the target
• New DAQ version (faster!)
• Improvements in the target:– Magnetic field– Z-counter
2 July 2004 Journée DPNC 2004
Near future improvementsPermanent magnet~ 80 G
to suppress residual SR effects:
B = 80 G forces ‘s to precess on a known time scale ( ~ 1 s)
1. Suppress beam ’s2. Measure vertical beam profile3. Measure as a function of the
z position in the target Hodoscope Z-counter
z
yx
2 July 2004 Journée DPNC 2004
Conclusions and future plans:
• FAST is a small dimension experiment!
• 2003 testbeam: successful test
- Understanding of the detector
- Readout and DAQ chain performances
- Preliminary (and encouraging) results!
• 2004 beam time ( 6 August) – magnet– Z-counter
• End 2004: – Level 2 trigger First FAST data taking run