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FAST: A precision measurement (1ppm) of. muon lifetime t m and G F. Chiara Casella University of Geneva - PSI. FAST COLLABORATION: A.Barczyk (1) , J. Berdugo (2) , J. Casaus (2) , C. Casella (3,4) , K. Deiters (4) , P. Dick (4) , A. Dijksman (4) ,

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Chiara Casella University of Geneva - PSI

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Chiara casella university of geneva psi

FAST:

A precision measurement (1ppm) of

muon lifetimetmandGF

Chiara Casella

University of Geneva - PSI

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


Outline

Outline

  • Whydo we want to measure tm?

  • Howdo we want to measure tm?

    • detection principle

    • beam

    • target

    • readout chain

    • DAQ and trigger

  • Test beam (Sept 2003 – Dec 2003)

  • Future plans and conclusions


Motivations of fast

Motivations of FAST:

Standard Model becomes predictive only when the free parameters of its Lagrangian are fixed by experimental inputs.

SM of electroweak interactions3 free parameters in the bosonic sector:

a=1/(137.035990 ± 0.000006)0.045 ppm

MZ= 91.1876 ± 0.0021 GeV23 ppm

GF= 1.16639 ± 0.00001 x 10–5GeV-2 9 ppm

  • GF is a fundamental parameter of SM

  • it can be derived from muon lifetime:

_

nm

_

nm

m+

W+

m+

e+

e+

Dq include higher order

QED and QCD corrections

ne

ne


Uncertainties on g f where do they come from

Uncertainties on GF:where do they come from?

PDG 2002

Ritbergen and Stuart - PLB 437 (1998) 201

PDG 2002 (from direct measurement)

Dominant contribution from:

Balandin et al. (1974)

Bardin et al. (1984)

Giovanetti et al. (1984)


Chiara casella university of geneva psi

… near future:

  • Dominant contribution from:

  • FAST

  • mLAN


How do we want to measure t m

to photomultiplier, preamplifier, dicriminator, TDC

19.2 cm

  • active high granularity (~ 1500 pixels) scintillator target

  • each pixel seen by the readout and DAQ chain

12.8 cm

20cm

beam degrader to horizontally spread the stopping p+position

  • DC pion beam

  • p = 170 MeV/c

  • atPSI - pM1area

p+

QUITE SIMPLE DETECTION PRINCIPLE

MAIN CHALLENGE : 1 ppm REQUIREMENT

How do we want to measure tm ?

p+m+e+

tp = 26.03 ns PDG2002

tm = 2.197 ms PDG2002


1 ppm precision measurement

1012 x 9tm / 0.5 ~ 1.5 y

PARALLELISATION NEEDED !!!

morep+ m+  e+at the same time in the target

~ 20 ms

estimated

efficiency

  • reasonable data taking period

  • (2 months ca.)

  • technical challenge: DEAL WITH A HUGE

  • AMOUNT OF DATA

  • ability to disentangle overlapping events

high beam rate

(1 MHz beam rate)

high data rate~ 80 MB/sec

+ ONLINE ANALYSIS

tracking capabilities, high

granularity of the target

1 ppm precision measurement:

  • Large data sample of 1012 events (=>1ppm statistical uncertainty)

  • Suppress Systematics effects

Remove time dependent effects (to the ppm level) that, together with asymmetries in the target,

could compromise the measurement.

 As an example, mSR EFFECTS( why p+ m+  e+?


M sr effects

Sm

B

mSR effects

local magnetic field at

the detector (Earth)

Positrons are preferably emitted along Sm

Precession movement of Sm around B

e+ direction emission

IF: polarised muon source AND asymmetries in positron detection

time dependent detection efficiency

Solution : ISOTROPIC m SOURCE

p+ m+

To suppress RESIDUAL mSR effects :

force the muons to precess on a time scale known and detectable

Magnetic field + proper fit procedure  mSReffects under control (0.2 ppm)

BEarth ~ 0.5 G nm ~6.8 KHz  T ~ 150ms

B ~ 80 G nm ~1.1 MHz  T ~ 0.9ms

PERMANENT MAGNETIC FIELD (80G) IN THE TARGET REGION !


Beam p m1 area at psi

  • - pM1 at PSI

  • momentum

  • - RF frequency

  • - size

  • - intensity

  • - purity

:p+DC beam

: 170 MeV/c (±3%)

: 50.633 MHz ( T=19.75 ns )

: variable

: variable (~ MHz)

: ~ 50%

 4 m

sc2

( sc3 )

p+

sc1

Beam : pM1 area at PSI

  • separation of the beam components:

  • positrons  for calibration purposes

  • pions  for normal running

LEVEL 1 trigger

  • RF signal of the machine in coincidence with 3 beam counters

  • Possibility to use narrow (selective) or wide trigger


Target

Scintillating FIBERS replaced by scintillator BARS

NOW:

“baguette” +

2 wave lengh shifter fibers

painted with white reflective paint

1 pixel =

4mm

4mm

Bicron

BC 400

BCF

BC 620

Scintillator

WLSF

Paint

16 pixels grouped (4x4) to fit in one photomultiplier

  • active scintillator target

  • high granularity

Target

ORIGINAL IDEA:

Fiber Active Scintillator Target

testbeam 1998 - 1/10 target

1 pixel = bunch of 64 fibers


Target1

Target

preamplifier

photomultiplier

12.8 x 19.2 x 20.0 cm3

32 x 48 pixels = 1536 pixels

8 x 12 = 96 groups of 16 bars

LED mask at the bottom of the target (1 LED for 1 pixel) to check the mapping

beam counter


Readout chain

x 16

TDC

Preamp

Discri

x 16

LL - data

PSPM

x 96

LV2 board

x 96

x 96

x 96

HL - data

Readout chain

  • 4 x 4 channels PHOTOMULTIPLIERS ( Hamamatsu H6568-10 ) rise time < 2 ns

  • 16 channels custom made PREAMPLIFIERS ( PSI )

  • gain ~ 10

  • 16 channels custom made DISCRIMINATORS ( PSI )

  • double threshold discriminators (remote controlled):

  • - low threshold (MIPS)  to TDCs

  • - high threshold (stopping p / m)  to LV2 trigger

  • 128 channels continuous mode TDC’s ( CAEN V767 )

    • dead-time free

    • read out window : -10 ms < ttrig < +20 ms

    • - driven by 2 external Rb clocks [stability = 10-10: ~ 1sec / 300y ]


Daq system from tdc s to pc s

DAQ system: from TDC’s to PC’s

  • challenging task: despite the small dimensions of the detector, the DAQ system must sustain a very high event rate

  • baseline DAQ architecture design:

  • DAQ goal in the present design (4 nodes) = 80 MB/sec

PVIC solution = PCI to VME intercrate connection (CPU-less solution for the VME)

  • 4 VME crates ;

  • 4 TDCs for each VME ;

  • 2 parallel PVIC buses

  • (nominally: 20 MB/sec for each node)

  • DAQ PC:

  • - from raw data from TDCs to time and position data

  • event builder

  • analysis “farm”: ONLINE analyses the data and stores

  • the histograms (2003 run: 1 single PC)


Date rate lv2 trigger

Raw data rate: ~ 2300 MB/sec

(from simulations)

DAQ sustainable data rate :

80 MB/sec

if :

  • 1 MHz beam rate

  • Entire target (16 TDC’s always read)

DATA REDUCTION NEEDED ! ! !

LEVEL 2 TRIGGER

  • LV2 trigger idea:

    • all the relevant time informations are contained in the “superpixel” (5x5 pixels) centered on the stopping p

    • 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

p

m

Date rate & LV2 trigger

  • What LV2 trigger does:

    • define (x,y) for stopping pion

    • look for the muon in a neighbouring pixel

    • send trigger only to the TDC’s containing the superpixel (4 at max)


Lv2 trigger

t0+15ns

t0+100ns

p

m

1. Calculate p stopping point coordinates:

- HL hits of the incoming pion track accumulated by rows

in the beam direction

- projection of the track in the 2 axes

2. Look for the muon

3. If muon is found, send LV2 signal to the interested TDC’s

Flag events overlapping in time and space (very important when the trigger rate increases)

LV2 trigger

TDC time window

t0

-10ms

+20ms

LV1

3 stages for LV2 operation:

HL-hits data

LV2

LV2 signals (x16) – one for each TDC

pstopping point coordinates, muon flag

LV1 trigger

pion overlapping flag

RF (50MHz)


Lv2 trigger architecture ciemat madrid

LV2 trigger architecture (CIEMAT Madrid)

  • 17 FPGA based VME boards

  • (FPGA XILINX 2S 200):

  • 16 BOX PROCESSORS:

  • each one processing data from 1 TDC

  • in charge of stages 1 and 2

  • MAIN CONTROLLER:

  • sends the triggers

  • manages the list of overlapped events

  • accomodated in a single VME crate, and interconnected via a backplane designed ‘ad hoc’

  • LV2 schedule:

    • testbeam 2003 : single board prototype test

    • June 2004 : prototype (1/4) test

    • End 2004 : final commissioning


2003 testbeam sept dec 2003

discriminators

2003 testbeam (Sept-Dec 2003)

preamps

phomultipliers

  • completed target (1536 pixels)

  • 80/96 PSPM’s available

  • 20 from 2000 commissioning + 60 commissioned in 2003

  • new tubes are MUCH BETTER tubes !!!

  • complete readout chain

  • DAQ matches the requirements (75 MB/sec)

  • no LV2 trigger (single board prototype test performed)

  • trigger (LV1) rate: from 35 to 100 KHz max

  • TB2003 mainly devoted to target understanding and tuning


Tb2003 online event display typical event

TB2003: online event display (typical event)


Tb2003 muon lifetime plot

TB2003: muon lifetime plot

  • ‘Long’ run (few days run)

  • Total statistics : 7.4 107 events from online analysis

  • (10% written to disk for offline studies)

  • RUN CONDITIONS:

  • narrow p trigger

  • no LV2 trigger ( all 16 TDC’s)

  • low LV1 trigger rate

  • Good exponential fit,

  • in agreement with PDG value

  • PDG st~ 40 ps

  • TB2003 st~ 350 ps

  • Good background suppression

It will be a blind experiment in the future !!!

1 tick = 1.041667 ns

= 1/30(*) x 32(**)(*) = TDC clock (MHz)

(**) = TDC bits


Tb2003 pion lifetime plot

TB2003: pion lifetime plot

Unexpected result from HL run

  • pion lifetime: not primary FAST goal

  • veryshort run with:

  • - narrow LV1 p trigger,

  • - threshold = 400 mV

  • (not sensitive to electrons,

  • only pions and muons)

  • Good (PRELIMINARY!) exponential fit,

  • in agreement with PDG value

  • PDG st~ 0.005 ns

  • TB2003  st~ 0.024 ns

1 tick = 1.041667 ns


Conclusions

Conclusions

  • FAST will measure the Fermi coupling constant GF with a precision 10 times better than the present world average.

  • FAST major challenges:

    • HIGH DATA RATE : from a 0.005 m3 detector, a LHC detector equivalent throughput has to be handled

    • SYSTEMATICS

  • Feasibility of the experiment checked, NOT ONLY from simulations, BUT ALSO from real data (2003 testbeam)

  • Many expectations from 2004 run ! ! !


Acknowledgments

Acknowledgments:

We wish to thank the following people who have contributed to early phases of the FAST experiment:

F. Cavallo (Bologna), P. de Jong (NIKHEF), P. Kamel (Berkeley), A. Konig (Nijmegen), R. Nahnhauer (DESY), F. Navarria (Bologna), G Passaleva (Florence), A. Perrotta (Bologna), W.Schoeps (PSI), R.Stuart (Michigan), G. Valenti (Bologna), D. Vitè (CERN), D. Della Volpe (Naples), S. Waldmeier-Wicky


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