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

2. 2 1. Introduction

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

4. SuperKEKB 4 Energy (e - /e + ) = 7.0/4.0 GeV Our design value is on the  (4S) resonance. Data for other  resonances will also be taken. Luminosity = 8.0 x 10 35 /cm 2 s 40 times higher than 2.1 x 10 34 /cm 2 s by KEKB. (Small beam size: x 20. Large beam current: x2.)  (10860) (8.0/3.5 GeV for KEKB.)

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

6. Belle II detector 6 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 ± (  ± ) を 95% の効率で選ぶ時、  ± (K ± ) は 1% の確率でしか残らな い。 シリコン検出器の外径拡大（ 140 mm ） による K S (   +  - ) 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  m ） 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。 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 7 Search for new physics from measurements of angles and sides of UT. tension

8. 8 2. Measurement of  1(eff) and related topics

9. Measurement of  1 9 B 0  (cc)K 0 B 0  (ss)K 0 Standard Model: Discrepancy in the results between B 0  (cc)K 0 and B 0  (ss)K 0 could be a signature of new physics.

10. B  (cc)K 0 10 Belle preliminary (Moriond 2011) using full  (4S) data (0.71 ab -1 ). Consistent results for the four modes.

11. B  (cc)K 0 11 sin2  1 (indirect CPV) A (direct CPV) Measured Belle, 0.49 ab -1 0.642±0.031±0.0170.018±0.021±0.014 Belle, 0.71 ab -1 0.668±0.023±0.0130.007±0.016±0.013 BaBar, 0.42 ab -1 0.687±0.028±0.012-0.024±0.020±0.016 Expected Belle II, 5 ab -1 ±0.016±0.015 Belle II, 50 ab -1 ±0.012±0.013 O(0.01) precision at 50 ab -1.

12. B  (ss)K 0 12 J/  K 0 K0K0 50 ab − 1 S(  K 0 )=0.39 is assumed. O(0.01) precision at 50 ab -1. Comparable to B  (cc)K 0.

13. Note: tension in the CKM fit 13  Tension between CKM fit and direct measurement of BR(B   ):  Tension will be slightly loosened when we include new result on  1, while it will be still larger than 2.5  …  Direct measurement of B   at Belle II will be important. ~2.8  discrepancy ICHEP 2010

14. Note: B   at Belle II 14  In Two-Higgs Doublet Model (THDM) Type II, the branching ratio of B   can be modified. 5 ab -1 assuming 5% errors for |V ub | and f B. 50 ab -1 assuming 2.5% errors for |V ub | and f B. Figures: constrains on m H± and tan  at Belle II. H-H- B   is helicity-suppressed, and we need 1.6 ab -1 (4.3 ab -1 ) for 3  evidence (5  discovery).

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

16. 16 3. Measurement of  3 and related topics

17. Measurement of  3 17  3 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  3  Golden mode: B -  DK - (and the conjugate)  Crucial parameters for extracting  3 : L. Wolfenstein, PRL 51, 1945 (1983) r B ~ 0.1 (CKM x color-supp).

19. Method of measuring  3 19 B-D0K-B-D0K- B-D0K-B-D0K- _ D0fD0f D0fD0f _ B-B- f K - 33 ① ② 分岐比 ∝ |A( ① ) + A( ② )| 2  3 測定法は、 f により分類できる。  GLW 法  f = CP 固有状態（ K + K -,  +  -, K S  0, … ）。  ADS 法  f = K +  -, K +  -  0 など。  Dalitz 法  f = K S  +  -  。 Dalitz 解析。 _  1,  2,  3 測定のためには、 | 振幅 | 2 が  1,  2,  3 の関数になる崩壊を用いる。  3 測定は、 D 0 と D 0 の同じ終状態 f への崩壊を利用し行われる。

20. GLW method 20 Relatively small contributions from CP-violating terms, since r B is small (~0.1). Non-zero A CP+ obtained. Useful for extracting  3.

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

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

23. Dalitz method 23 c i and s i are obtained by CLEO using  (3770)  D 0 D 0. _

24. Dalitz method 24 Belle preliminary (Moriond 2011). Precision of c i, s i will be improved by BESIII measurements. Expected precision for  3 at 50 ab -1 is 2°. Consistent with CKM fit w/o direct measurement:  3 = 67.2° ± 3.9°.

25. D 0 -D 0 mixing 25  D 0 -D 0 mixing is the largest theoretical uncertainty in the extraction of  3.  However, it can be safely neglected at the current precision:  3 ~10°.  The effect will be relatively larger at Belle II, while it can be explicitly included in the extraction of  3. _ _ J. P. Silva and A. Soffer, PRD61, 112001 (2000). Y. Grossman, A Soffer, and J. Zupan, PRD72, 031501(R). 50 ab -1 Current contours Precision at 50 ab -1

26. ab K-+K-+ K+-K+- K-0K-0 K+0K+0 Note: K  puzzle If the only diagrams are a and b, we expect However, significant difference is obtained. Missing diagrams? Large theoretical uncertainty… 26 B  K  w/ 0.5 ab -1 Nature 452, 332 (2008) DCPV due to V ub.

27. Note: DCPV for B  K  at Belle II  We can compare to a model-independent sum rule: Current measurement larger error for A CP K0  0 50 ab -1 assuming current central value Can be represented as diagonal band (slope precisely known from B and lifetimes): measured 27 expected

28. Summary 28  SuperKEKB  40 times higher luminosity of 8.0 x 10 35 /cm 2 s.  Will reach 50 ab -1 by the end of 2021.  Belle II  Conservatively designed to cope with high background.  Improvements in several aspects: vertex, K S acceptance, PID, …  Examples of physics at SuperKEKB/Belle II  Measurement of  1(eff) from B 0  (cc)K 0 and B 0  (ss)K 0. (Relation to the tension for B  . Note on B  D  )  Measurement of  3 from the tree B  DK (GLW, ADS, Dalitz). (Relation to D 0 -mixing and direct CPV in B  K .)

29. Backup Slides 29

30. SuperKEKB Collider 30 TiN coated beam pipe with antechambers Replace short dipoles with longer ones (LER). Redesign the lattices of HER & LER to reduce the emittance. e+e+ Smaller asymmetry 8 / 3.5 GeV  7 / 4 GeV e-e- Damping ring Belle II L = 8 x10 35 cm -2 s -1 L = 8 x10 35 cm -2 s -1  x ~10  m,  y ~60nm Larger crossing angle 2  = 22 mrad  83 mrad for separated final-focus magnets. Small beam sizes Approved in 2010. e - : 2.6 A e + : 3.6 A High currents

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32. Belle II detector 32

33. Feb. 24th, 2011 Dimensions for Belle II and Belle detectors H.Nakayama (KEK) 33

34. Expected Performance for Belle II 34

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

36. Aerogel radiator Hamamatsu HAPD + new ASIC Cherenkov photon 200mm n~1.05 Endcap PID: Aerogel RICH (ARICH)Barrel PID: Time of Propagation Counter (TOP) Quartz radiator Focusing mirror Hamamatsu MCP-PMT (measure t, x and y) TOP n1n2 Multiple aerogel layers with different indices   (1p.e.) = 14.4 mrad Npe ~ 9.6   (track) = 4.8 mrad Completely different from PID at Belle, with better K/  separation, more tolerance for BG, and less material. Completely different from PID at Belle, with better K/  separation, more tolerance for BG, and less material. Particle Identification System at Belle II 36

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

38. Physics at SuperKEKB/Belle II 38  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. One B meson (“tag” side) can be reconstructed in a common decay. Flavor, charge, and momentum of the other B can be determined. Also possible to partially reconstruct (semileptonically, …). Effective for the modes including missing energy. Missing

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40. B -  D (*) K -, D  K S  +  - Dalitz 40  Amplitude of B ±  DK ± process can be expressed as  Procedure of analysis: 1. Background fractions are determined by 2-D UML fit for  E and M bc. 2. Fit is performed to m ± (Dalitz plane). Amplitude of D  K S  +  - decay determined from Dalitz plot of large continuum data (Flavor is tagged by soft-pion charge in D *±  D  ± soft ). Isobar-model assumption with BW for resonances. Ratio of magnitudes of interfering amplitudes. A. Poluektov et al., PRD 81, 112002 (2010)

41. B -  D (*) K - Dalitz, Result 41  Using the background fractions, Dalitz plane is fitted with the parameters x ± = r ± cos(±  3 +  ) and y ± = r ± sin(±  3 +  ).  Combining the results for B  D (*) K, we obtain Model-independent analysis will be applied for 772M BB. A. Poluektov et al., PRD 81, 112002 (2010) 657 M BB

42. Measuring s i and c i for model-indep. Dalitz 42

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