1 Translation from Near to Far at K2K T.Kobayashi IPNS, KEK for K2K beam monitor group (K.Nishikawa, T.Hasegawa, T.Inagaki, T.Maruyama, T.Nakaya,....) Especially for T.Maruyama(KEK  Chicago) who played major role in PIMON construction/measurement/analysis July 4, 2002 College London

2 Strategy of K2K Pion monitor (PIMON) MUMONFD ++  Target+Horn 200m decay pipe ＳＫ 100m~250km    measure w/ FD measured by PIMON （ＭＣ） w/o osc. w/ osc? Extrapolate by multiplying ratio(≠0) arb. unit

3 What’s new in the treatment of far/near extrapolation Before –Observable for osc. analysis: total # of events –added syst. error from each energy bins linearly (= 100% positive correlation) to be safe. New –Observables for osc. analysis total # of events, E rec spec. shape for 1-ring  -like events –Correlation for far/near ratio btw energy bins are taken into account

4 Far/Near ratio in oscillation analysis (method1) systematics parameters spec nQE/QE Far/near  SK (efficiency) SK Enegry scale Overall Norm Error For Jun99 and Nov99- Maximum Likelihood Method

5 Normalization term i : energy bin index j : processes (=QE, nQE) Spectrum meas. in FD( f  i ) cancels first order but far/near ratio f F/N does not.

6 E rec spectrum shape term for FC 1R  P: reconstructed E distribution for 1R  (gen’ed by using MC) Total 29 events for Nov99~ data Detector response from MC

7 Systematic constraint term M FD, M , M SK : error matrix of syst. errors.  n6 : overall norm. err. for Jun99  evts)  n11 :overall norm. err. for Nov99~ (=5.34%)  Esk : SK Enery scale error (3%) Far/near ratio

8 Qeustions Central values of far/near ratio (relative to MC prediction) f F/Ni Correlation of far/near ratio btw. energy bins (error matrix) M 

9 A tool:Pion Monitor (PIMON) N(p ,   )  Neutrino flux  (E ) at any distance using only decay kinematics R(E )≡  SK (E )/  FD (E ) as a result of pion monitor Gas Cherenkov detector to avoid signal from 12GeV protons  insensitive to p  <2GeV (E <1GeV) PMT array

10 Strategy to obtain f F/N, error matrix Above 1GeV  PIMON Below 1GeV  Beam MC(Sanford-Wang parameterization fitted to previous data) validated by PIMON measurement at >1GeV Error matrix 0 0 MC PIMON 1GeV (4x4) (2x2) MC part: Fit previous pion production data below ~2GeV/c move paraemters within error  get error matrix No correlation w/ PIMON part

11 Pion Monitor Results pp  w1w1 w2w2 w3w3 w4w4 ….. : : : :

12 Pion Monitor Result(relative weight) beam axis ++ 

13 Pion distribution to far/near ratio (incl. error matrix) Relative weight W i ( i =1~50) 50x50 error matrix on weight From PIMON fitting (4x4) (4x50) (50x50) (50x4) E Contribution to flux from each p -  bin (by MC. To 1 st order, depend only on decay kinematics &geometry FD,SK flux Ratio as func. of weights Dependence of R on W (50x4 matrix) Error matrix transformation from  weight  far/near ratio

14 Other systematic errros treated in matrix form as described 1.move syst. parameter within error 2.Check correlation btw energy bins Ri Rj

15  spectra from Pion Monitor Measurement Agree with MC very well.

16 PIMON result for F/N ratio Good Agreement!

17 Far/Near Error Matrix “sqrt” of error matrix (%) Beam MC PIMON

18 Summary of systematic errors on total # of events w/o osc. Center: 80.1evts (%) Jun99 (4.55evts) Total +1.0%  0.9% Nov99~ (75.5evts) Spectrum +0.6%  0.6% nQE/QE +0.5%  1.1% Far/Near +4.9%  5.0% Norm5.0% Total +7.7%  6.7%

19 Summary K2K uses pion distribution measured in- situ(>1GeV) and beam MC(<1GeV) for spectrum extrapolation The beam MC is validated by the PIMON measurements Correlation of far/near ratio btw energy bins is taken into account (instead of linear sum = 100% positive correlation Still far/near ratio is major source of systematic error Expect precise data from HARP (measurement in Aug.26~). Many many thanks to HARP collaborators

20 Syst. error: far/near spectrum diff. Typical OA beam(80mDV) 280m 295km K2K case (MC) FD(300m) (xL SK 2 /L FD 2 ) SK Important not only for  disappearance, but also for sig/BG estimation for e search Large(~x2) effect around peak!!

 POT for Analysis 200kA 250kA POT PIMON meas.

22 Stability of  Energy Spectrum Muon Energy of MRD events Muon Energy in KT on ’01, ‘00 Every months

23 Exp’ed E rec spectrum for 1R  estimated by FD measurements

24 PIMON in target station

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26 K2K osc. analysis overview  production near/far extrapolation oscillation probability neutrino interaction in water detector responce(1kt, scifi)detector responce(SK) FD observation  1KT  Scifi SK observation  total # of events  E rec spectrum shape(1ring  -like events) PIMON p  -   dist Want to know this!! Near Far (1R  )