Search for B + l + X 0 with hadronic tagging method at Belle

Transcription

1 YongPyong-High1 015 Joint Winter Conference on Particle Physics, String and Cosmology Search for + l + X 0 with hadronic tagging method at elle Chanseok Park (Yonsei Univ.) pcs437@yonsei.ac.kr High cspark Yonsei, YHEP 1

2 Contents elle Experiment Motivation X 0 candidate Analysis procedure Hadronic tagging method Preliminary result Summary High cspark Yonsei, YHEP

3 elle Experiment High cspark Yonsei, YHEP 3

4 elle Experiment High cspark Yonsei, YHEP 4

5 Motivation At elle, there are searches that have invisible particle in the final states. eg) + l ν, 0 ν ν, K ν ν, D(*) τ ν Neutrino is not detected at elle detector, from this we have interesting assumption What if massive particle can substitute neutrino? From now, we call it X 0 Possible mass range that X 0 can have 0 m(x 0 ) m( + ) m(l + ) High cspark Yonsei, YHEP 5

6 Why + l + X 0? + D 0 l + X 0 * We don t consider 3body decay ( moment is not clear ) + τ + X 0 * additional neutrino produced Hard to search We consider + l + X 0 ( l = e, μ ) For m(x 0 ) : GeV/c High cspark Yonsei, YHEP 6

7 High cspark Yonsei, YHEP 7 X 0 candidate : LSP (RPV) ~ ~ ~ ) ( 8 ~ X l b u l b u l i i M M M M M M m m p m f g l i R L i When we assuming r-parity violation, one lightest neutralino can be produced from meson decay via slepton or squark. We can give bounds for unknown parameters PRD 65,

8 X 0 candidate : Large Extra Dimension PL 489, * RH-neutrino in large extra dimension might candidate of X 0. * When there are δ additional dimensions, decay width via H or W. (Γ W >> Γ H ) * Decay width is proportional to R δ. M Pl : 4D Planck scale M * : (4+δ)D fundamental Planck scale R : size of additional dimension High cspark Yonsei, YHEP 8

9 + l + X 0 Sample for analysis mode Mass of X Amount + e + X 0.1, 0., 1.8 GeV,000,000 events for each mass of X + μ + X 0.1, 0., 1.8 GeV,000,000 events for each mass of X ackground MC Separately generated! Signal MC We have 18 kinds of X for different mass Mode Process Amount Generic MC, qq 5 streams Rare b s, d 50 streams Ulnu X u lν 0 streams eνγ + eνγ 1000 streams μνγ + μνγ 1000 streams π + K 0 + π + K streams π 0 eν + π 0 eν 300 streams π 0 μν + π 0 μν 300 streams High cspark Yonsei, YHEP 9

10 Hadronic tagging method Signal lepton Tagged Signal D K Y(4S) Ex) D + (K - π + π + ) π - π - Invisible >96% of Y(4S) with nothing else produced one -meson is completely reconstructed from known b c decays without ν * channels are used for reconstruction. * Low efficiency, high purity Good way to reconstruct modes with invisible particle High cspark Yonsei, YHEP 10

11 + l + X 0 - event selection Particle Identity L e > 0.9 L μ > 0.9 Track quality Dz < cm Dr < 0.5 cm Continuum suppression cosθ thrust < 0.9 for + e + X cosθ thrust < 0.8 for + μ + X E ECL Quality of tagged- meson ΔE < 0.05 GeV M bc > 5.7 GeV/c O N > e p l sideband E ECL Sideband linded Region p l (GeV/c) E ECL : Remaining energy of ECL calorimeter (tagged- & signal lepton) p l : signal lepton s momentum in the signal rest frame High cspark Yonsei, YHEP 11

12 + l + X 0 PDF modeling Fitting Signal Fitting ackground p l peak changes by mass of X p l cut should be optimized for each mass of X Fitting Peaking ackground High cspark Yonsei, YHEP 1

13 + l + X 0 obtain U.L. of.f.. F. N obs sig G est N( ) *.F. is obtained by Feldman-Cousins method * Signal region is optimized. N obs : Number of Data in the signal region (counting) G est : expected background in the signal region, decided by background PDF, data distribution in the p l sideband ε sig : decided by signal PDF. High cspark Yonsei, YHEP 13

14 + l + X 0 - preliminary result e mode μ mode Sideband Signal region + e + X M(X) : 1.8 GeV Sideband Signal region + μ + X M(X) : 1.8 GeV High cspark Yonsei, YHEP 14

15 + l + X 0 E ECL sideband calibration + e + X + μ + X There are some disagreement between Data and MC, about p l >. GeV/c for E ECL sideband region(0.5 < E ECL < 1.0 GeV). Get Calibration Factor!! High cspark Yonsei, YHEP 15

16 High cspark Yonsei, YHEP 16 + l + X 0 ounds for parameters ~ ~ ~ ) ( 8 ~ R L i b u l b u l i i M M M m m p m f g l ) ( ).(. ) ( ~ ~ ~ 13 0 X l l i b u b u l i m m m p m f g X l U L m m M M M i i R L i This is parameter we give bounds!

17 Summary * We search for + l + + X 0, where X 0 have 0.1 ~ 1.8 GeV mass range * Hadronic tagging method enables effective background suppression * + l + X 0 has preliminary results, and analysis enters the final steps * e + e - -factory experiments has an advantage for this study. High cspark Yonsei, YHEP 17

18 ACKUP High cspark Yonsei, YHEP 18

19 + l + X 0 - skim procedure S KIM PATH Hadronic Tagging LX_SKIM ANALYSIS_CODE L X _ S K I M 1 charged particle not used in Full_recon call it c (Charge of c) x (Charge of tagged ) = -1 Momentum of c(la frame) >1.0 GeV High cspark Yonsei, YHEP 19

20 e mode dz, dr, deltae -log(nboutput) distributions High cspark Yonsei, YHEP 0

21 e mode Mbc, Eecl, cos(thrust), pl distributions with basic cut High cspark Yonsei, YHEP 1

22 μ mode dz, dr, deltae -log(nboutput) distributions High cspark Yonsei, YHEP

23 μ mode Mbc, Eecl, cos(thrust), pl distributions with basic cut High cspark Yonsei, YHEP 3

24 Fitting to obtain PDFs (MC samples) - 1D ML fit for p l was done (1.8~3.0 GeV/c) - Cuts for all remaining variables are same - Using simple function as much as possible Some modes in Ulnu are scaled High cspark Yonsei, YHEP 4

25 e-mode signal region(e ecl <0.5 GeV) All Other cuts are applied to signal region : Gaussian Ulnu :.G. Rare : Exp eνγ :.G. π0eν : G +.G. High cspark Yonsei, YHEP 5

26 μ-mode signal region(e ecl <0.5 GeV) All Other cuts are applied to signal region : Gaussian Ulnu : Gaussian μνγ :.G. Rare : Exp + Argus πk0 : G + G π0μν : G +.G. High cspark Yonsei, YHEP 6

27 Signal (left : e mode, right : μ mode) For E ecl <0.5 & 1.8< p l <3.0 Signal is fitted with Gauss+Gauss+.G M X : 0.1 GeV M X : 1.0 GeV M X : 1.8 GeV High cspark Yonsei, YHEP 7

28 Expectation of ranching Fraction Statistical uncertainty PDG uncertainty PDF uncertainty Data in sideband MC(signal)/MC(side) Estimated # of G Signal efficiency and uncertainty Estimate.F.(or upper limit) for observed events when open box. High cspark Yonsei, YHEP 8

29 Expected Upper Limit. F. U. L.( Yield ) N( ) sig 1. Relative uncertainty of ε sig. Estimated G and uncertainty 3. # of observed events POLE U.L. Uncertainty from PDG(F), PDF, systematic, etc High cspark Yonsei, YHEP 9

30 Optimization Study using the criterion of est Upper Limit Mean of U.L. 6 n0 6 Yield n0 U. L. ( G est Poisson( G ; n) Poisson( G est est ; n;1000) N( ) ; n;1000) sig - n : # of observed events in signal region. - Yield_{U.L.} : U.L. of Yields using POLE program - Poisson : # of values of 1,000 events have Poisson dist High cspark Yonsei, YHEP 30

31 + l + X 0 - Optimization G : Fit p l sideband extrapolate PDF G est Data side S( MC) S( MC) sig side Feldman-Cousins method 1. Relative uncertainty of ε sig. Estimated G and uncertainty 3. # of observed events POLE U.L. Uncertainty from PDG(F), PDF, systematic, etc High cspark Yonsei, YHEP 31

32 + l + X 0 - Optimization Mean of upper limit of branching fraction based on MC for each p l criteria + e + X M(X) : 1.8 GeV/c + μ + X M(X) : 1.8 GeV/c High cspark Yonsei, YHEP 3

33 Summary Table (e-mode) M(X) pl cut G_est Efficiency( ) Observed event U.L. (10^{-6}) 0.1 (GeV).5 < pl < ± ± < pl < ± ± < pl < ± ± < pl < ± ± < pl < ± ± < pl < ± ± < pl < ± ± < pl < ± ± < pl < ± ± < pl < ± ± < pl < ± ± < pl < ± ± < pl < ± ± < pl < ± ± < pl < ± ± < pl < ± ± < pl < ± ± High < pl < ±0.455 cspark 0.90±0.11 Yonsei, YHEP

34 Summary Table (μ-mode) M(X) pl cut G_est Efficiency( ) Observed event U.L. (10^{-6}) 0.1 (GeV).58 < pl < ± ± < pl < ± ± < pl < ± ± < pl < ± ± < pl < ± ± < pl < ± ± < pl < ± ± < pl < ± ± < pl < ± ± < pl < ± ± < pl < ± ± < pl < ± ± < pl < ± ± < pl < ± ± < pl < ± ± < pl < ± ± < pl < ± ± High < pl < ±0.40 cspark 1.1±0.14 Yonsei, YHEP

35 + l + X 0 E ECL sideband calibration 1.8 < p l < < p l < < p l <.3 E ECL cut : 0.5 < E ECL <.0 GeV (ecause we want more statistics) Data/MC ratio is fitted to linear function Ratio function : R(p l ) = p 0 + p 1 ( p l ) when p 0 and p 1 is parameter To fit well, we apply error to bins where no events (but MC exist) High cspark Yonsei, YHEP 35

36 + l + X 0 E ECL sideband calibration Originally we use Data & MC ratio in p l sideband region to scale expectation of G So we use this ratio fitting function to scale G expectation. Calibration factor R* is used for scaling. We use ratio fitting function when fitting range 1.8 < p l <.65 GeV/c Old : G est Data side S( MC) S( MC) sig side New : G est R* Data side S( MC) S( MC) sig side High cspark Yonsei, YHEP 36