Study of )me- dependent CP viola)on in Ks eta gamma decays at Belle. Hiroshi Nakano. 20th- Feb Tohoku University

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1 Study of )me- dependent CP viola)on in Ks eta gamma decays at Belle Tohoku University Hiroshi Nakano th- Feb- 1 This work is supported by JSPS KAKENHI No

2 Study of )me- dependent CP viola)on in Ks eta gamma decays at Belle Tohoku University Hiroshi Nakano th- Feb- 1 [ Index ] 1. What is TDCPV?. Why it is interes)ng? 3. How we can detect? (experimental setup). The result of the study. This work is supported by JSPS KAKENHI No

3 What is Gme dependent CP violagon? Time dependent CPV is caused by quantum interference (like double slit experiment). Double slit experiment [ POINT ] Two paths can interfere both construcgve and destrucgve. source slit screen Quantum interference on the screen. Time dependent CPV B B B IniGal state virtual states f CP final state [ POINT ] B can change to B, and vice- versa (B- Bbar oscillagon). decay Gme Both B and B can decay to CP eigenstate, f CP. Quantum interference ( This IllustraGon is on decay )me distribu)on. drawn with an exaggeragon.) ExponenGal distribugon is changed by interference. Difference btw. B and B- bar à

4 Combine equagons using q. q = +1 : B at t =. q = 1 : at t =. Formula of TDCPV Formulas of decay Gme distribugon of B and B are shown here. Γ B (t) e t/τ B [1 + {A CP cos( mt)+s CP sin( mt)}] Γ B (t) e t/τ B [1 {A CP cos( mt)+s CP sin( mt)}] B A cos + S sin e t/τ B [1 + q{a CP cos( mt)+s CP sin( mt)}].gif animagon t There are two CPV parameters in the formula. A CP Coefficient of cosine term. Caused by CP asymmetry in B f CP amplitude. S CP Coefficient of sine term. Caused by CP phase in B- Bbar oscillagon. τ B = ±.7 [ps] Life Gme of B meson. t : Decay Gme. m =.57 ±. [ps 1 ] Frequency of B- Bbar oscillagon. TDCPV of b to s γ à

5 Why TDCPV of b sγ mode is interesgng? In the SM, (and ) process is strongly suppressed. Because γ L and γ R are different, TDCPV cannot be seen. On the other hand, some new physics permit process. Table of b sγ process The SM expectagon b s γ R diagram amplitude B B B b s γl Interference is suppressed. No TDCPV is expected. (the SM) (the SM) (new phys.) W b L s R b R s L W t L t L If there is new physics B B B If we observe TDCPV, this is the sign of new physics! γ L (b d) Xs CP γ R ( b d) Xs CP b s γ R b sγ L b sγ R b sγ R m b G F V tb V ts X CP s γ L γ R m s G F V tb V ts b L??? γ R s R Interference could be occur. TDCPV can be seen!? X CP s X CP s * is CP eigenstate which contain s quark. In this study, it is Ks eta. γ L γ R

6 Why TDCPV of b sγ mode is interesgng? In the SM, (and ) process is strongly suppressed. Because γ L and γ R are different, TDCPV cannot be seen. On the other hand, some new physics permit process. Table of b sγ process Example b s γ R diagram amplitude b s γl (the SM) (the SM) (new phys.) γ L b s γ R b sγ L b sγ R b sγ R W b L s R b R s L W t L t L m b G F V tb V ts Lei Right Symmetric Model predicts large S cp. W ± can couple to ψ R as well as ψ L Diagram of LRSM γ R m t G F V tb,l Vts,R Back up P1-19 b L t L t R s R S cp γ R m s G F V tb V ts b L SM??? ( mixing angle of two W ) γ R s R

7 How can we know q and t? e How to measure TDCPV experimentally Υ(S)(= b b) Γ(t) e t/τ B [1 + q{a cos( mt)+s sin( mt)}] boost e another B Y(S), b b- bar resonance, is produced by e+ e- collision. B mesons are produced by decay of Y(S). signal B

8 How can we know q and t? e How to measure TDCPV experimentally Υ(S)(= b b) Γ(t) e t/τ B [1 + q{a cos( mt)+s sin( mt)}] boost e another B q (B B- bar idengficagon) can be measured by using pargcle type and momentum from another B. signal B Type of signal B at this Gme can be measured. b b W + + c B typical decay ( ) W s K + (high ) (low ), Λ p p

9 How can we know q and t? e How to measure TDCPV experimentally Υ(S)(= b b) Γ(t) e t/τ B [1 + q{a cos( mt)+s sin( mt)}] boost e another B q (B B- bar idengficagon) can be measured by using pargcle type and momentum from another B. Δz = Δt c β γ typical b decay ( B ) + W + b c signal B W s K + (high ) (low ) t corresponds to decay Gme difference Δt. O(1 μm) flight length by asymmetric energy collision and Be[er accuracy of vertex reconstrucgon than flight length enables us to measure Δt by Δz (decay posigon) measurement., Λ p p z- axis

10 KEKB accelerator KEKB accelerator / Belle detector Belle detector Asymmetric energy collision ( vs. 3.5 GeV) for large Δz. Average Δz is ~ μm. 1.5 GeV center of mass energy at Y(S) resonance; It is suitable for BB producgon. 77 x 1 BB pair! 1) ~75 μm resolugon of vertex detector for Δz measurement. ) Drii chamber measures pargcle s momentum. 3) CsI (Tl) calorimeter for γ and e ±. ) Other sub detectors disgnguish pargcle s kind (e ±, μ ±, π ±,K) for selecgon and B idengficagon. (1) () (3) () () inside 1.5 T Super ConducGng Solenoid () outside

11 Signal qq BG B π + π π Signal and backgrounds η γ Light quark jets (u, d, s, c). Random miss- reconstrucgon makes fake signal candidate. BB BG K S π + π π γγ Other B decay modes. Difficult to disgnguish from signal. Some decay mode have known CPV. RejecGon Use decay shape difference! Signal : spherical decay. qq BG : jet- like decay. Neural network is used for mul) variable analysis. RejecGon (example) Find mass peak! J/ψ Ks has peak at 3.1 GeV on M(γη) B J/ψ K S 3. ηγ SelecGon and BG rejecgon is done to maximize significance (except for known CPV BGs rejecgon) reject.9 M()[GeV] M

12 A RooPlot of " E [GeV]" Events / (.5 ) D fit for signal yield Aier reconstrucgon and BG rejecgon, 3 dimensional fit (ΔE, M bc, NN ) is done. Fit on ΔE, M bc and NN distribugon. Free parameters are N sig and N qq. FuncGon shapes and N BB are fixed. ProjecGons on each parameter Red: signal Blue: qq BG Green: BB BG E [GeV] E E B E beam A RooPlot of "M [GeV]" Events / (.5 ) bc [GeV] M bc Mass of B candidate from beam energy and B s momentum. A RooPlot of "NB " Events / (.5 ) ΔE [GeV] M bc [GeV] NN M bc Ebeam p B Energy difference btw. beam energy and B candidate. NB Modified distribugon of Neural network output used for qq BG rejecgon. Yield is N η γ = , they will be used for Δt distribugon fit. How to N η 3π = +7 fit Δt à

13 The way of Δt analysis Δt distribugon is fi ed by the following funcgon. P ( t) =f sig P sig ( t)+f BG P BG ( t) qr# qr# IllustraGon of Δt distribugon when (S,A) = (+.5, ). qr#1 Event- by- event fracgons of { signal/bg } funcgon are obtained by 3D fit (last page). RooPlot of " E [GeV]" E [GeV] e t /τ B [1 + q{a CP cos( m t)+s CP sin( m t)}] with wrong B- Bbar idengficagon probability detector resolugon of Δz Graph consideragon. smeared qr# qr# qr# qr#3 qr#5 Total B signal Background B- bar signal Δt BG distribugon is fixed by BG data fit (for qq) and MC simulagon (for BB) 5 Δt Fit on Δt distribugon. Free parameters are S CP and A CP. Other parameters are fixed. result à

14 The result of Δt analysis P ( t) =f sig P sig ( t)+f BG P BG ( t) e t /τ B [1 + q{a CP cos( m t)+s CP sin( m t)}] events / [ps] Preliminary B rec =B : 3 B rec =B : 5 Δt distribugon for the events which have good quality in B- Bbar idengficagon. Events which do not have Δt informagon are also used. raw asymmetry t [ps] Preliminary S CP = 1.3 ±.77(stat.) ±.3(syst.) A CP =. ±.1(stat.) ±.7(syst.) We obtained the result. No significant deviagon from (,). StaGsGcal error is dominant.

15 Current status of TDCPV in b sγ Golden mode for this study is B Ks pi gamma. However, measurements of other decay mode are also important. This study is first Ks eta gamma measurement of Belle experiment data. HFAG 1 h p:// A New 1.3 ±.77 ±.3. ±.1 ±.7

16 Conclusion Time dependent CP violagon is one of probe of new physics which predict b sγ R process. B Ks η γ mode is studied with using data of Belle experiment. The result obtained is S CP = 1.3 ±.77(stat.) ±.3(syst.) A CP =. ±.1(stat.) ±.7(syst.) Preliminary We couldn t see significant deviagon from the SM expectagon. The result can be used for constraint on new physics model. Backups Example of new physics (P1, 19) Upgrade of B factory (P)

17 Back up

18 Related new physics model (LRSM) [1/] Let s consider Lei Right Symmetric Model W ± can couple to ψ R as well as ψ L. amplitude of b sγ L amplitude of b sγ R [LRSM] Phys. Rev. D 1, 5 () There are some parameter sets which permit S cp have large value. ζ is mixing angle of W L and W R. Such kind of model can be constrained by this type of study. b R b L Diagram of LRSM W Although precise BR(b sγ) measurement is consistent to the SM expectagon, and a NP can be large if they sagsfy A SM + A NP + a NP = A SM > σ S (of the study) BR(b sγ) cp A NP A SM + A NP m t G F V tb,r V ts,l a SM + a NP suppressed m t G F V tb,l Vts,R γ L s L γ R s R SM γ R/L b L/R t L/R t R/L s R/L

19 Related new physics model (LRSM) [/] However, the model with simple parameter set are excluded by direct search. h ps://twiki.cern.ch/twiki/bin/view/atlaspublic/exogcspublicresults ( mass of W ) > 1. TeV (ATLAS) ζ M 1 M < (M 1 = GeV, see eq.(3) of [LRSM] ) S cp direct search SM Right upper figure is based on an assumpgon V CKM, L = V CKM, R Assuming that V ts, R >> V ts, L (~.), S CP can take large value while ζ is small. Unexplored area is s)ll remaining, and the area can be searched by b sγ TDCPV! Although, simple parameter region is excluded by direct search already, TDCPV measurement of b sγ can search unexplored area.

20 Future prospect Upgrade to Belle II experiment is in progress. Improvement of vertexing resolugon 5 Gmes integrated luminosity Extension of silicon tracker volume (= Larger Ks acceptance). Error of S cp is expected to be 1 order smaller. Related douments h p://arxiv.org/abs/1.51 Physics at Super B Factory SecGon 3., h p://xxx.lanl.gov/abs/ Belle II Technical Design Report

21 Wrong B B- bar idengficagon probability Probability of wrong idengficagon must be considered. e t /τ B [1 + q{a cos( m t)+s sin( m t)}] e t /τ B [(1 q w)+q(1 w){a cos( m t)+s sin( m t)}] w : Probability of wrong idengficagon. In order to avoid bias from MC data, distribugon is divided into 7 bins. Δw : Difference of w btw. B and B- bar. Considering efficiency of Λ, Λ- bar. O(1%) at most. Bad quality L Good quality J # #1 # #3 # #5 # signal qq BG Not used DistribuGon of 1 w

22 ResoluGon fucngon, R(Δt) is convoluted to theoregcal funcgon. qr# ResoluGon funcgon e t /τ B [(1 q w)+q(1 w){a cos( m t)+s sin( m t)}] qr# ResoluGon funcgon consist from 3 parts as described below. Detector resolu)on : R det Gaussian for vertex resolugon. qr# Basically, parameters are decided by real data. Vertex shij by Non- Primary par)cle (like D meson) : R np ExponenGal for D meson flight. qr# Basically, parameters are decided by MC data. 9 Graph 7 Δt 5 Kinema)cs from Y(S) decay : R k Small contribugon and no systemagcs Δt [ps]

23 BG Δt distribugon Δt distribugon data contains background. We have to know about Δt distribugon of them. B signal B- bar signal qq BG δ funcgon (= light pargcle from collision) and exponengal funcgon (= D meson) are convoluted to double Gaussian. FuncGon shape is fixed by real data. ( qq BG dominant region are used for fixing.) BB BG delta Δt [ps] ExponenGal funcgon is convoluted to resolugon funcgon. FuncGon shape is fixed by MC data Outlier P qq ( t) P BB ( t) P ol ( t) Background Δt Δt [ps] Describe long tail component aier ResoluGon funcgon consideragon. FracGon is an order of O(1 ), Gaussian which has ~3- [ps] width.