testing the mu-e universality with kl2 decays · e – energy deposition in lkr p – momentum from...
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Testing the m-e universality with K±→l±n decays
Venelin KozhuharovUniversity of Sofia “St. Kl. Ohridski” / JINR Dubna
Neutrino Oscilation Workshop 2006
on behalf of the NA48/2 collaboration
Cambridge, CERN, Chicago, Dubna, Edinburgh, Ferrara, Firenze, Mainz,
Northwestern, Perugia, Pisa, Saclay, Siegen, Torino, Vienna
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• Physics motivation• Experimental setup• Data analysis• Preliminary result for 2003 data• Conclusions
OverviewOverviewOverviewOverview
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MotivationMotivation
where dRM arises from the radiative corrections, M=p±,K±
For K±: dRK= -(3.78±0.04)%, leading to
RRKK= (2.472 = (2.472 ± ± 0.001) * 100.001) * 10-5-5
Within the Standard Model:
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M. Finkemeier: Phys.Lett.B387:391-394,1996
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MotivationMotivation
where dRM arises from the radiative corrections, M=p±,K±
For K±: dRK= -(3.78±0.04)%, leading to
RRKK= (2.472 = (2.472 ± ± 0.001) * 100.001) * 10-5-5
• The value of RK could be different in case of SUSY and LFV
models – the correction could be as high as 3% in both directions
• Measurement of RK tests the m-e universality and provides a
sensible test of the SM
Within the Standard Model:
HH++
LFVLFV
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M. Finkemeier: Phys.Lett.B387:391-394,1996
A. Masiero et al. Phys.Rev. D74 (2006) 011701
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MeasurementsMeasurements
• Experimental error on RK: two orders of magnitude
larger than the theoretical
Standard Model Standard Model
RRKK=(2.472=(2.472±±0.001)*100.001)*10-5-5
Experiments with stopped kaons
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Phys. Rev. Lett 29 (1972), 1274
Phys. Lett. 55B (1975), 327
Phys. Lett. 60B (1976), 302
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Beam setupBeam setup
PK: spectra603 GeV/c
54 60 66
Width ~ 5mm
K+/K- ~ 1mm
K+
K
K+
K
beam pipebeam pipeBe target
400 GeV400 GeVprotonsprotons
Beam Beam spectrometerspectrometer
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Detector setupDetector setup
Beam direction
• Magnetic spectrometer4 drift chambersp
┴
kick = 121 MeV/c
DDp/p = 1% p/p = 1% 0.044*p [GeV/c] 0.044*p [GeV/c]
• Hodoscopes(s(t) = 150 pst) = 150 ps
• Liquid Krypton CalorimeterDDE/E E/E 3.2%/√E 3.2%/√E 9%/E 9%/E 0.42% 0.42%
• Hadron Calorimeter, Muon counters, Anticounters, Kaon Beam Spectrometer
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Experiment primarily designed for the Experiment primarily designed for the measurement of the charge asymmetry in measurement of the charge asymmetry in
KK pp pp+ + pp and and KK pp00 pp0 0 pp decaysdecays
2003 2003 run:run: ~ 50 days nominal conditions~ 50 days nominal conditions~ 12 hour special run~ 12 hour special run
2004 2004 run: ~ 60 days nominal conditionsrun: ~ 60 days nominal conditions~ 56 hour special run~ 56 hour special run
~ ~ 200 TB of data recorded200 TB of data recorded
The huge statistics ( ~4The huge statistics ( ~4∙10∙109 9 KK p p++pppp ) allows to) allows tostudy rare kaon decays with high precisionstudy rare kaon decays with high precision
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2003 data: Trigger2003 data: Trigger• Km2 events: signal from the charged hodosopesignal from the charged hodosope
• Ke2 events
– L1 trigger:L1 trigger: – hodoscope signal + Energy deposition in the EM calorimeter > 10GeV
– L2 trigger:L2 trigger: – online kinematics reconstruction
MMFakeFake
2 2 = M = MKK
2 2 + M+ Mpp2 2 - S- S
S=(pK-p
p)2, p
K=(0,0,60) GeV/c
KK±±→→pp±±pp00 events: M events: MFakeFake
peaks at 495 MeV peaks at 495 MeV
L2 trigger efficiency
(85.6 (85.6 ±± 0.5(stat) 0.5(stat) ±± 0.2(syst))% 0.2(syst))%
online cutonline cut
L2 efficiency using Ke3 events
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• The similarity between the decays allows to exploit systematics cancellation
– Charged track with momentum 15 GeV<P<55 GeV
– No extra clusters with Ecl > 1.5 GeV, no hits in the anticounters, no in
time tracks.
– Vertex reconstructed within 2000 cm < Zvtx < 8500cm
• Km2 selection:
– Muon hypothesis
– |Mmiss
2| < 0.02 (GeV/c2)2
E – energy deposition in LKRP – momentum from the spectrometer
• Ke2 selection:
– PID: E/Pc>0.95
– Electron hypothesis
– |Mmiss
2| < 0.02 (GeV/c2)2
Found 5329 Ke2 candicatesFound 5329 Ke2 candicates
Ke2 events
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2003 data: Event Selection2003 data: Event Selection
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2003 data: MC simulation2003 data: MC simulation
• Full Geant3 based simulation of the detector response
• Radiative corrections
Difference in acceptance:Difference in acceptance: DD(R(RKK)=1.116 )=1.116 ±± 0.002(stat) 0.002(stat) ±± 0.006(syst) 0.006(syst)
Eg (CM) – SDEg (CM) – IB
DD(R(RKK)=1.063 )=1.063 ±± 0.005 0.005
Logarithmic scale
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2003 data: Background in Ke22003 data: Background in Ke2
KKmm22
Ke2Ke2
Missing mass vs track momenum
Dominant background is Km2
Background events: 659 ± 26
Signal events: 4670 4670 ± 77(stat)± 77(stat)+29+29
-8-8(syst)(syst)
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2004 data2004 data• Dedicated data taking period:
– 60 GeV kaon beam with diminished intensity
– No Level-2 trigger – using only minimum bias triggers
• Simpler selection – better control of the systematics
• Analysis performed in momentum bins– Better background subtraction
• Sample with similar statistics as in 2003
Efficiency: ~100%Efficiency: ~100%
Deposited energy(Gev/c2)2 GeV
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ResultsResults
NA48 measurement is already two timestwo times more precise than the world average
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SM prediction
Standard Model (theory)PDGNA48: 2003 dataNA48: 2004 data in progress
( 2.472 ± 0.001) * 10-5
( 2.45 ± 0.11 ) * 10-5
( 2.416 ± 0.043 ± 0.024) * 10-5
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ConclusionConclusion
• K±→l±n decays provide a very challenging opportunity to search for physics beyond the Standard Model
• Preliminary result for RK based on 2003 data sample
presented
• 2004 data analysis very advanced
• A sub-percent precision measurement of RK will allow to
probe for New Physics or rule out regions in the parameters space in different models
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