View
40
Download
0
Category
Preview:
DESCRIPTION
Measurement of DE and INT in K ± → ± 0 g with NA48/2. Mauro Raggi FlaviaNet Workshop on K decays Frascati 18/05/2007. LKr EM calorimeter. Spectrometer - 4 Drift Chambers (DCH) - Magnet. NA48/2 beam and detector. IB. DE. DE. IB. IB. INT. DE. Gamma production mechanism. - PowerPoint PPT Presentation
Citation preview
Measurement of DE and INTin K0g with NA48/2Mauro RaggiFlaviaNet Workshop on K decaysFrascati 18/05/2007
NA48/2 beam and detector
Kpp0g amplitudesTwo type of contributions:Electric (J=l1) dipole (E1)Magnetic (J=l) dipole (M1) Electric contributions are dominated by Inner Bremsstrahlung (EIB)Thanks to Lows theorem IB contribution can be related to the non radiative decay pp0 using QED corrections.DE shows up only at order O(p4) in CHPTIs generated by both E and M contributions:Magnetic contributions are dominated by chiral anomalyElectric contributions come from L4 CHPT lagrangian and loops L2Present experimental results suggest a M dominated DE
General expression for decay rateP*K=4-momentum of the K P*p=4-momentum of the p P*g=4-momentum of the radiated g
Experimental status for DE and INTAll the measurements have been performed in the T*p region 55-90 MeV to avoid pp0p0 BGAll of them are assuming the Interference term to be = 0INT estimates [20][21]:DE measurements
E787 2000 measurement20K K+ eventsFit in 8 bins 0.1-0.9Fit function:
with b set to 0 (INT=0).
Kpp0g selection cutsTrack Selection# tracks = 1.Pp+ > 10 GeVE over P < 0.85No muon veto hits0 MeV < T*p+ < 80 MeVGamma selectionNg = 3. (well separated in time LKr clusters)Minimum g energy > 3 GeV (>5 for the fit)Gamma tagging optimizationCHA and NEU vertex compatibilityOnly one compatible NEU vertexBG rejection cutsCOG < 2 cmOverlapping g cuts|MK-MKPDG| < 10 MeV
Reconstruction strategy We can get two independent determination of the K decay vertex: - The charged ZV(CHA) using the K and p flight directions (spectrom.) - The neutral ZV(NEU) choosing g pair with the best p0 mass (LKr) Once the neutral vertex has been chosen we also know which is the radiated g.
Main BG sourcesPhysical BG rejection:For pp0 we can relay on the cut in T*p< 80 MeV, MK and COG, cutsFor pp0p0 we have released the T*p cut, but we can anyway reach the rejection needed (MK COG (missing g) and overlapping g cut (fused g)) Accidental BG rejection (pp0, Ke3(p0 en), Km3(p0 mn)) Clean beam, very good time, space, and mass resolutions.
DecayBRBackground mechanismKpp0(21.130.14)%+1 accidental or hadronic extra clusterKpp0p0(1.760.04)%-1 missing or 2 overlapped gammasKp0 en(4.870.06)%+1 accidental g and e misidentified as a pKp0 mn(3.270.06)%+1 accidental g and m misidentified as a pKp0 en(g)(2.660.2)104e misidentified as a pKp0 mn(g)(2.40.85)105m misidentified as a p
The miss tagged g events: a self BGThe miss tagged gamma events behave like BG because they can induce fake shapes in the W distribution. In fact due to the slope of IB W distribution they tend to populate the region of high W simulating DE events. The mistagging probability has been evaluated in MC as a function of the mistagging cut to be 1.2 at 400 cmThe identification of radiative gamma has 2 steps: 1. Compatibility of charged and neutral vertices (2.5% mistagging)2. Distance between best and second best neutral vertices>xx cm
Data MC comparisonThe IB dominated part of W spectrum is well reproduced by MCThe radiated g energy (IB part of the spectrum) is well reproduced
Fitting algorithm To get the fractions of IB(a), DE(b), INT(g), from data we use an extended maximum likelihood approach:The fit has been performed in 14 bins, between 0.2-0.9, with a minimum g energy of 5 GeV, using a data sample of 124K events.To get the fractions of DE and INT the raw parameter are corrected for different acceptances
Systematic uncertaintiesSystematic effects dominated by LVL1 and LVL2 triggers!Learning from experience both LVL1 and LV2 triggers have been modified in 2004. We are confident that both systematics will be smaller in 2004 data set.
EffectSyst. DESyst. INTEnergy scale+0.09-0.21Fitting procedure0.020.19LVL1 trigger0.170.43g Mistagging_0.2LVL2 Trigger0.170.52Resolutions difference
Effect of the DE form factorCould the negative INT be faked by DE ff? NoDE(no ff)-DE(ff)Only INT>0 could be fakedDE could be underestimated
Could IB+DE(ff) be enough to improve MC agreement with data spectrum? NoCould the DE ff change the results for DE and INT? Yes (results moving on the correlation line)
Backup slides
L1 trigger NT-PEAKY viewX OR Y > 2 view
MBX1TR-P LVL2 triggerAim to reject Kpp0 and get pp0p0. Its based on the online computation of Mfake:
Recommended