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