TCPV. David Heffernan Yamanaka Taku Lab 2008/12/22

Transcription

1 B χc1ks TCPV David Heffernan Yamanaka Taku Lab 2008/12/22

2 Contents 1) Introduction to TCPV 2) B χc1ks Analysis Motivation Belle Experiment Event Selection Criteria Relevant Background ΔE fit Background Δt fit Lifetime fit...

3 What is CP Violation? What is CP Violation?

4 Two types of CP Violation There are two main types of CP Violation Direct CP Violation Differences in partial decay widths, branching fractions, partial lifetimes τ A B τ Ā B B(A B) B(Ā B) Indirect CP Violation CP differences rising from mixing effects in Hamiltonion.

5 B 0 B 0 -bar mixing B 0 B 0 -bar mixing is caused by a transition between a particles that was originally B 0 into a B 0 -bar, and vice-versa. Mixing occurs through the following diagram: t b d { B 0 } W W B 0 d t b

6 Time dependent CP violation Because of (time dependent) B 0 B 0 -bar mixing, decays to a flavour neutral final state contain direct decays as well as decays through mixing. This gives interference which causes CPV. This is referred to as time-dependent CP violation (TCPV).

7 Time dependent CP violation Because of (time dependent) B 0 B 0 -bar mixing, decays to a flavour neutral final state contain direct decays as well as decays through mixing. This gives interference which causes CPV. This is referred to as time-dependent CP violation (TCPV). B 0 d b Direct Decay Final State

8 Time dependent CP violation Because of (time dependent) B 0 B 0 -bar mixing, decays to a flavour neutral final state contain direct decays as well as decays through mixing. This gives interference which causes CPV. This is referred to as time-dependent CP violation (TCPV). B 0 d b Direct Decay Final State Mixing Decay d b B 0

9 Time dependent CP violation Because of (time dependent) B 0 B 0 -bar mixing, decays to a flavour neutral final state contain direct decays as well as decays through mixing. This gives interference which causes CPV. This is referred to as time-dependent CP violation (TCPV). B 0 d b Direct Decay Interference Final State Mixing Decay d b B 0

10 Time dependent CP violation 2 Time dependent behaviour A CP ( t) Γ B0( t) Γ B 0( t) Γ B0( t) + Γ B 0( t) = S sin( m t)

11 Measuring sin2φ1 Size of time dependent CP violation depends on complex phase of mixing and decay diagrams. t b d { B 0 } W W B 0 d b t { b B 0 s } d d c c } J/ψ K 0 e i2φ 1 e iφ cs e i0 S = sin 2φ 1

12 Experimental measurement Time dependent behaviour A CP ( t) Γ B0( t) Γ B 0( t) Γ B0( t) + Γ B 0( t) = S sin( m t) With asymmetry S = sin 2φ 1 Can be measured experimentally, and used to derive the SM parameter sin2φ1 This is the main goal of the Belle Experiment

13 B χc1ks TCPV analysis B χc1ks TCPV analysis

14 Motivation for using B χc1ks decays B χc1ks is a CP eigenstate (flavour neutral : possible decay for both B 0 and B 0-bar ) { B 0 b d CP violation parameter is partially known in the standard model from B J/ψKS : [φ1 22 o ] (Comparatively) large effective efficiency Interesting possibility to observe new physics which only couples to vector bosons. c b c }χ c c1 B 0 { c }χ c1 s } K 0 s } d S KS 0 d d

15 Motivation 2 TCPV measurement using χc1ks. Previous results from Belle with 140 /fb found 101 events, with purity 0.92 ± 0.01 ( PRD 71, (2005) hep-ex/ ). Measurement was sin2φ1 = 1.54 ± BaBar result from 2008 (arxiv: ) with (465 ± 5)M BB pairs found 385 events with 88% purity: sin2φ1 = ± ± Plan to update with ~4x data.

16 CP Violation The Belle Experiment

17 International Collaboration: Belle BINP Chiba U. U. of Cincinnati Ewha Womans U. Fu-Jen Catholic U. U. of Giessen Gyeongsang Natʼl U. Hanyang U. U. of Hawaii Hiroshima Tech. IHEP, Beijing IHEP, Moscow IHEP, Vienna ITEP Kanagawa U. KEK Korea U. Krakow Inst. of Nucl. Phys. Kyoto U. Kyungpook Natʼl U. EPF Lausanne Jozef Stefan Inst. / U. of Ljubljana / U. of Maribor U. of Melbourne Nagoya U. Nara Womenʼs U. National Central U. National Taiwan U. National United U. Nihon Dental College Niigata U. Nova Gorica Osaka U. Osaka City U. Panjab U. Peking U. Princeton U. Riken Saga U. USTC Seoul National U. Shinshu U. Sungkyunkwan U. U. of Sydney Tata Institute Toho U. Tohoku U. Tohuku Gakuin U. U. of Tokyo Tokyo Inst. of Tech. Tokyo Metropolitan U. Tokyo U. of Agri. and Tech. INFN Torino Toyama Natʼl College VPI Yonsei U. 14 countries, 55 institutes, ~400 collaborators

18 KEKB

19 KEKB

20 KEKB

21 KEKB

22 KEKB

23 Belle Detector

24 B χc1ks decay event topology To search for B χc1ks events, I use the decays χc1 J/ψγ, J/ψ µ + µ - or J/ψ e + e -, and KS π + π -. The final state particles (γ, µ ±, e ±, π ± ) can all be measured in the Belle detector. π + π γ µ + B 0 K S χ c1 J/Ψ Signal side of the event is fully reconstructed. Υ(4S) B 0 µ D + z = βγc t βγ = Detected Invisible µ Tag side uses lepton for vertex and flavour tag. ν µ

25 Selection Criteria 1 : J/ψ Cut using J/ψ mass: x Raw J/Psi mass 8000 Events (/0.005 GeV) Raw J/Psi Mass (GeV) J/ψ mass

26 Selection Criteria 2 : χc1 Cut using (χc1 - J/ψ) mass difference: GeV < Δm < GeV 225 Scaled Chic1 - J/Psi mass difference distribution (SB) Events (/0.002 GeV) Scaled - J/Psi Mass Difference (GeV) χc1 - J/ψ mass difference

27 Selection Criteria 3 : KS Cut using Ks mass: MINUIT! 2 Fit to Plot 19!0 K_S mass File"./index/chic1ks_skim2-39-psiskim-chic1ks-byyyymmdd_hhmm newtigh 19-MAR "40 Plot Area Total/Fit E+05 / E+05 Fit Status 3 Func Area Total/Fit E+05 / E+05 E.D.M E-05! 2 = 87.4 for 64-7 d.o.f., C.L.=0.598 # Errors Parabolic Minos Function 1" Polynomial of Order 1 NORM E+06 $ E E E+04 POLY E+06 $ E E E+06 " OFFSET $ Function 2" Two Gaussians (sigma) AREA $ MEAN $ E E E-06 SIGMA E-03 $ E E E-05 AR2/AREA $ E E E-02 " DELM $ SIG2/SIG $ E E E KS invariant mass

28 Background Predominant background in SB comes from J/ψ inclusive modes, including B 0 J/ψ K *0 B + J/ψ K *+ Studied using Charmonium group J/ψ inclusive mixed and charged MC. Used experiments (33~41)x100, corresponding to a total of ~20/ab.

29 Background determination We use two kinematic variables to distinguish signal from BG : E = E B 0 E beam m bc = E 2 beam p2 B 0

30 Background 1 : ΔE (signal, J/ψ µ + µ - ) Delta E distribution (Signal Box) Delta E distribution (Signal Box) χc1 signal component removed Events (/0.008 GeV) Events (/0.008 GeV) Delta E (GeV) Green : Signal Blue : J/ψ K *+ Yellow : J/ψ K * Delta E (GeV) Magenta : ψ(2s) KS Cyan : χc1 K *0,± Black : All other

31 Background 2 : Mbc (signal, J/ψ µ + µ - ) Mbc distribution (Signal Box) χc1 signal component removed Mbc distribution (Signal Box) Events (/0.001 GeV) Mbc (GeV) Green : Signal Blue : J/ψ K *+ Yellow : J/ψ K *0 Events (/0.001 GeV) Mbc (GeV) Magenta : ψ(2s) KS Cyan : χc1 K *0,± Black : All other

32 Signal sample χc1ks (J/ψ µ + µ - ) AREA = 2764 ± 61 SIGMA1 = 5.64 ± 0.1 [MeV] AR2/AREA = 9.9% SIG2/SIG1 = 2.60 ± 0.49 AREA = 326 ± 19 SIGMA1 = 6.58 [MeV] AR2/AREA = 9.9% SIG2/SIG1 = ΔE [GeV] J/ψ inclusive MC ΔE [GeV] Exp. 7~55 Data

33 Yield from data μ + μ - e + e - l + l - BG Signal Total Purity 91.9% 90.0% 88.9% Fit integrated in SB : -30 MeV < ΔE < 30 MeV Total yield from fit to ΔE agrees roughly with predictions based on MC.

34 Lifetime fit Preliminary lifetime fit with BG

35 Lifetime fit procedure Have checked lifetime fitter on experiment 39 J/ψ inclusive MC sample. (47.1 ± 0.7) *10E6 * 100 BB pairs. For the fit PDF I use PDF = fsig(pdfsignal) + (1-fsig) PDFbg

36 Lifetime fit for signal sample TAU_B = (1.547 ± 0.028) [ps] Generated value : TAU_B = [ps] !t (ps)

37 Lifetime fit for control sample TAU_B = (1.650 ± 0.012) [ps] Generated value : TAU_B = [ps] !t (ps)

38 Summary Update of B 0 χc1 KS with ~4x data sample. Event selection is finalised. Based on fit to ΔE distribution we find ~650 events with about 90% purity. Lifetime fit shows consistent results. Studies underway for CP fit.

39 B Backup Slides 1