Measurements of the unitarity triangle parameters at Belle II

1. Measurements of the unitarity triangle parameters at Belle II Bファクトリー物理勉強会 第6回ミーティング (2011.6.11) 名古屋大学　堀井泰之

2. 1. Introduction

3. Introduction KEKB collider Belle detector SuperKEKB collider Belle II detector

4. SuperKEKB SuperKEKB Energy (e-/e+) = 7.0/4.0 GeV Our design value is on the U(4S) resonance. Data for other U resonances will also be taken. Luminosity = 8.0 x 1035 /cm2s 40 times higher than 2.1 x 1034 /cm2s by KEKB. (Small beam size: x 20. Large beam current: x2.) U(10860) (8.0/3.5 GeV for KEKB.)

5. SuperKEKB 2020-2021年までに、KEKBの50倍のデータを取得したい。

6. Belle II detector シリコン検出器の外径拡大（140 mm） によるKS (p+p-) acceptanceの向上 ピクセル検出器導入による 崩壊点精度の向上（~20 mm） 高いバックグラウンド環境に耐えられるように設計。それに加え、種々の性能向上。 electron(7 GeV) positron (4 GeV) チェレンコフイメージ検出器による粒子識別性能の向上 K± (p±)を95%の効率で選ぶ時、p± (K±)は1%の確率でしか残らない。 LHCbに比べ、中性粒子を終状態 に含むモードに強みを持つ。

7. Measurements of the CKM parameters tension Search for new physicsfrom measurements of angles and sides of UT.

8. 2. Measurement of f1(eff) and related topics

9. Measurement of f1 B0(cc)K0 B0(ss)K0 Standard Model: Discrepancy in the results between B0(cc)K0 and B0(ss)K0could be a signature of new physics.

10. B(cc)K0 Belle preliminary (Moriond 2011) using full U(4S) data (0.71 ab-1). Consistent results for the four modes.

11. B(cc)K0 O(0.01) precision at 50 ab-1.

12. B(ss)K0 50 ab−1 J/K0 fK0 S(K0)=0.39 is assumed. O(0.01) precision at 50 ab-1. Comparable to B(cc)K0.

13. Note: tension in the CKM fit • Tension between CKM fit and direct measurement of BR(Btn): • Tension will be slightly loosened when we include new result on f1,while it will be still larger than 2.5s… • Direct measurement of Btn at Belle II will be important. ICHEP 2010 ~2.8s discrepancy

14. Note: Btn at Belle II • In Two-Higgs Doublet Model (THDM) Type II,the branching ratio of Btn can be modified. H- Figures: constrains onmH± and tanb at Belle II. 5 ab-1 assuming 5% errors for |Vub| and fB. 50 ab-1 assuming 2.5% errors for |Vub| and fB. Bmn is helicity-suppressed, and we need 1.6 ab-1 (4.3 ab-1) for 3s evidence (5s discovery).

15. Note: BDtn at Belle II • Also sensitive to charged Higgs. Exclusion boundaries H- Uncertainty in BD semi-leptonic form factor.

16. 3. Measurement of f3 and related topics

17. Measurement of f3 f3測定はLHCbが有利とされている。しかし、実際にはとてもチャレンジング。 予想よりも多いBX当たりの反応。

18. Measurement of f3 • Golden mode: B-DK- (and the conjugate) • Crucial parameters for extracting f3: L. Wolfenstein, PRL 51, 1945 (1983) rB ~ 0.1 (CKM x color-supp).

19. Method of measuring f3 f1, f2, f3測定のためには、|振幅|2がf1, f2, f3の関数になる崩壊を用いる。 • f3測定は、D0とD0の同じ終状態fへの崩壊を利用し行われる。 _ ① B-D0K- D0f • f3測定法は、fにより分類できる。 • GLW法 • f = CP固有状態（K+K-, p+p-, KSp0, …）。 • ADS法 • f = K+p-, K+p-p0など。 • Dalitz法 • f = KSp+p-など。Dalitz解析。 B- f K- f3 _ _ B-D0K- D0f ② 分岐比 ∝ |A(①) + A(②)|2

20. GLW method Relatively small contributions from CP-violating terms, since rB is small (~0.1). Non-zero ACP+ obtained. Useful for extracting f3.

21. ADS method First evidence of the signal obtained.(At rB=0.1, RADS is in 0.002-0.025.) f = K+p- Well-balanced |amplitudes|. f = K+p- Sensitivity for f3 via GLW+ADSis 15° at 1 ab-1 and 3° at 50 ab-1.

22. Dalitz method • Previous measurement: Modeling of amplitudes on Dalitz plane. (Especially strong phase for the D decays.)

23. Dalitz method ci andsi are obtained byCLEOusing y(3770)D0D0. _

24. Dalitz method Belle preliminary (Moriond 2011). Consistent with CKM fitw/o direct measurement:f3 = 67.2° ± 3.9°. Precision of ci, siwill be improved by BESIII measurements. Expected precision for f3 at 50 ab-1 is 2°.

25. D0-D0 mixing _ J. P. Silva and A. Soffer, PRD61, 112001 (2000). Y. Grossman, A Soffer, and J. Zupan, PRD72, 031501(R). _ • D0-D0 mixing is the largest theoretical uncertainty in the extraction of f3. • However, it can be safely neglected at the current precision: df3~10°. • The effect will be relatively larger at Belle II, while it can be explicitly included in the extraction of f3. Current contours Current contours Precision at 50 ab-1 50 ab-1 50 ab-1

26. Note: Kp puzzle DCPV due to Vub. If the only diagrams are a and b, we expect However, significant difference is obtained. Missing diagrams?Large theoretical uncertainty… a b K-p+ K+p- BKpw/ 0.5 ab-1 Nature 452, 332 (2008) K-p0 K+p0

27. Note: DCPV for BKpat Belle II • We can compare to a model-independent sum rule: Can be represented as diagonal band (slope precisely known from B and lifetimes): sum rule sum rule measured measured expected Current measurement larger error for ACPK0p0 50 ab-1assuming current central value expected

28. Summary • SuperKEKB • 40 times higher luminosity of 8.0 x 1035 /cm2s. • Will reach 50 ab-1 by the end of 2021. • Belle II • Conservatively designed to cope with high background. • Improvements in several aspects: vertex, KS acceptance, PID, … • Examples of physics at SuperKEKB/Belle II • Measurement of f1(eff) from B0(cc)K0and B0(ss)K0.(Relation to the tension for Btn. Note on BDtn.) • Measurement of f3 from the tree BDK (GLW, ADS, Dalitz).(Relation to D0-mixing and direct CPV in BKp.)

29. Backup Slides

30. SuperKEKB Collider Approved in 2010. Belle II Larger crossing angle 2f = 22 mrad  83 mrad for separated final-focus magnets. e- Smaller asymmetry 8/ 3.5 GeV  7 /4 GeV e+ High currents e-: 2.6 A e+: 3.6 A Replace short dipoles with longer ones (LER). Small beam sizes sx~10mm, sy~60nm Damping ring Redesign the lattices of HER & LER toreducethe emittance. TiN coated beam pipewith antechambers L = 8 x1035 cm-2 s-1

32. Belle II detector

33. Dimensions for Belle II and Belle detectors 33 H.Nakayama (KEK)

34. Expected Performance for Belle II

35. Vertex Detector Improve decay-time precision and acceptance (KS’s). 4lyr. Si strip  2lyr. pixel(DEPFET) + 4lyr. Si strip 6th lyr. Si strip 5th lyr. 4th lyr. 3rd lyr. 2nd lyr. pixel 1st lyr. Pixel: r=14,22mm Si strip: r=38,80,115,140mm Belle II Belle 4th lyr. 3rd lyr. 2nd lyr. 1st lyr.

36. Endcap PID: Aerogel RICH (ARICH) Particle Identification System at Belle II Barrel PID: Time of Propagation Counter (TOP) Quartz radiator TOP Focusing mirror Hamamatsu MCP-PMT (measure t, x and y) 200mm Cherenkov photon sq(1p.e.) = 14.4 mrad Npe ~ 9.6 sq(track) = 4.8 mrad n1 n2 Aerogel radiator n~1.05 Completely different from PID at Belle, with better K/p separation, more tolerance for BG, and less material. Hamamatsu HAPD + new ASIC Multiple aerogel layers with different indices

37. Other Upgrades for Belle II Silicon vertex detector: new readout chip (APV25) shorter integration time (800 ns50 ns) Drift chamber: smaller cells Belle Belle II Calorimeter: new readout system with waveform sampling (x1/7 BG reduction) KL/Muon detector RPCScintillator+MPPC Better performance against neutron BG

38. Physics at SuperKEKB/Belle II • A benefit to use One B meson (“tag” side) can be reconstructed in a common decay. Flavor, charge, and momentum of the other B can be determined. Effectivefor the modesincluding missing energy. Missing Also possible to partially reconstruct (semileptonically, …).

40. A. Poluektov et al., PRD 81, 112002 (2010) B-D(*)K-, DKSp+p-Dalitz • Amplitude of B±DK± process can be expressed as • Procedure of analysis: • Background fractions are determined by 2-D UML fit for DE and Mbc. • Fit is performed to m± (Dalitz plane). Ratio of magnitudesofinterfering amplitudes. Amplitude of DKSp+p- decaydetermined from Dalitz plot of large continuum data(Flavor is tagged by soft-pion charge in D*±Dp±soft). Isobar-model assumption with BW for resonances.

41. A. Poluektov et al., PRD 81, 112002 (2010) B-D(*)K-Dalitz, Result 657 M BB • Using the background fractions, Dalitz plane is fittedwith the parameters x± = r±cos(±f3+d) and y± = r±sin(±f3+d). • Combining the results for BD(*)K, we obtain Model-independent analysis will be applied for 772M BB.

42. Measuring si and ci for model-indep. Dalitz