1 / 22

Chiara Casella University of Geneva - PSI

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) ,

reece
Télécharger la présentation

Chiara Casella University of Geneva - PSI

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. 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

  2. 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

  3. 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

  4. 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) …

  5. … near future: • Dominant contribution from: • FAST • mLAN

  6. 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

  7. 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+?

  8. 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 !

  9. - 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

  10. 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

  11. 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

  12. 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 ]

  13. 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)

  14. 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)

  15. 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)

  16. 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

  17. 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

  18. TB2003: online event display (typical event)

  19. 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

  20. 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

  21. 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 ! ! !

  22. 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

More Related