Measurements of the unitarity triangle parameters at Belle II

名古屋大学　堀井泰之

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B ファクトリー物理勉強会 第 6 回ミーティング (2011.6.11)

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1. Introduction

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Introduction

KEKB colliderBelle detector

SuperKEKB colliderBelle II detector

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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.)

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SuperKEKB2020-2021 年までに、 KEKB の 50 倍のデータを取得したい。

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Belle II detector

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。

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。

LHCb に比べ、中性粒子を終状態に含むモードに強みを持つ。

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Measurements of the CKM parameters

Search for new physicsfrom measurementsof angles and sides of UT.

tension

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2. Measurement of f1(eff)

and related topics

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Measurement of f1

B0(cc)K0 B0(ss)K0

Standard Model:

Discrepancy in the results between B0(cc)K0 and B0(ss)K0

could be a signature of new physics.

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B(cc)K0Belle preliminary (Moriond 2011)using full U(4S) data (0.71 ab-1).

Consistent results for the four modes.

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B(cc)K0

sin2f1 (indirect CPV)

A (direct CPV)

Measured

Belle, 0.49 ab-1 0.642±0.031±0.017 0.018±0.021±0.014

Belle, 0.71 ab-1 0.668±0.023±0.013 0.007±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.

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B(ss)K0

J/K0

fK0

50 ab−1

S(K0)=0.39 is assumed.

O(0.01) precision at 50 ab-1.Comparable to B(cc)K0.

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Note: tension in the CKM fit Tension between CKM fit and direct measurement of

BR(Btn):

Tension will be slightly loosened when we include new result on f1,while it will be still larger than 2.5s…

Direct measurement of Btn at Belle II will be important.

~2.8s discrepancy

ICHEP 2010

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Note: Btn at Belle II In Two-Higgs Doublet Model (THDM) Type II,

the branching ratio of Btn can be modified.

5 ab-1

assuming 5% errorsfor |Vub| and fB.

50 ab-1

assuming 2.5% errorsfor |Vub| and fB.

Figures: constrains onmH± and tanb at Belle II.

H-

Bmn is helicity-suppressed, and we need 1.6 ab-1 (4.3 ab-1) for 3s evidence (5s discovery).

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Note: BDtn at Belle II Also sensitive to charged Higgs.

H-

Exclusion boundaries

Uncertainty in BD semi-leptonic form factor.

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3. Measurement of f3

and related topics

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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。

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).

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Method of measuring f3

B-D0K-

B-D0K-_

D0f

D0f_

B- f K-f3

①

②

分岐比 ∝ |A(①) + A(②)|2

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。

_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。

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GLW method

Relatively small contributions from CP-violating terms,since rB is small (~0.1). Non-zero ACP+ obtained.

Useful for extracting f3.

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ADS method

Well-balanced |amplitudes|.

First evidence of the signal obtained.(At rB=0.1, RADS is in 0.002-0.025.)

Sensitivity for f3 via GLW+ADSis 15° at 1 ab-1 and 3° at 50 ab-1.

f = K+p-

f = K+p-

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Dalitz method

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

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Dalitz method

ci and si are obtained byCLEO using y(3770)D0D0.

_

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Dalitz method Belle preliminary (Moriond 2011).

Precision of ci, si will be improved by BESIII measurements.

Expected precision for f3 at 50 ab-1 is 2°.

Consistent with CKM fitw/o direct measurement:f3 = 67.2° ± 3.9°.

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D0-D0 mixing 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.

_

_

J. P. Silva and A. Soffer, PRD61, 112001 (2000).Y. Grossman, A Soffer, and J. Zupan, PRD72, 031501(R).

50 ab-1 50 ab-1

Current contours Current contoursPrecision at 50 ab-1

a b

K-p+ K+p-

K-p0 K+p0

Note: Kp puzzleIf the only diagrams are a and b, we expect

However, significant difference is obtained.

Missing diagrams?Large theoretical uncertainty…

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BKp w/ 0.5 ab-1

Nature 452, 332 (2008)

DCPV due to Vub.

Note: DCPV for BKp at Belle II We can compare to a model-independent sum

rule:

Current measurement larger error for ACP

K0p050 ab-1

assuming current central value

Can be represented as diagonal band(slope precisely known from B and lifetimes):

measu

red

measu

red

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ed

expect

ed

sum

rule

sum

rule

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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)K0 and B0(ss)K0.(Relation to the tension for Btn. Note on BDtn.)

Measurement of f3 from the tree BDK (GLW, ADS, Dalitz).(Relation to D0-mixing and direct CPV in BKp.)

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Backup Slides

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SuperKEKB Collider

TiN coated beam pipewith antechambers

Replace short dipoles with longer ones (LER).

Redesign the lattices of HER & LER to reduce the emittance.

e+Smaller asymmetry 8 / 3.5 GeV 7 / 4 GeV

e-

Damping ring

Belle II

L = 8 x1035 cm-2 s-1

sx~10mm, sy~60nm

Larger crossing angle 2f = 22 mrad 83 mradfor separated final-focus magnets.

Small beam sizes

Approved in 2010.

e-: 2.6 Ae+: 3.6 A

High currents

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Belle II detector

Feb. 24th, 2011

Dimensions for Belle II and Belle detectors

H.Nakayama (KEK) 3333

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Expected Performance for Belle II

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=14,22mmSi strip:r=38,80,115,140mm

Si strippix

el

Improve decay-time precisionand acceptance (KS’s).

Belle II

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Aerogel radiator

Hamamatsu HAPD+ new ASIC

Cherenkov photon200mm

n~1.05

Endcap PID: Aerogel RICH (ARICH)

Barrel PID: Time of Propagation Counter (TOP)

Quartz radiatorFocusing mirror

Hamamatsu MCP-PMT (measure t, x and y)

TOP

n1 n2

Multiple aerogel layerswith different indices

sq(1p.e.) = 14.4 mradNpe ~ 9.6sq(track) = 4.8 mrad

Completely different from PID at Belle,with better K/p separation, more tolerance for BG, and less material.

Particle Identification System at Belle II

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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 ns50 ns)

KL/Muon detector RPCScintillator+MPPC

Better performance against neutron BG

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Physics at SuperKEKB/Belle II

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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.

Also possible to partially reconstruct (semileptonically, …).

Effective for the modesincluding missing energy.Missing

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B-D(*)K-, DKSp+p- Dalitz Amplitude of B±DK± process can be expressed as

Procedure of analysis:1. Background fractions are determined by 2-D UML fit for

DE and Mbc.

2. Fit is performed to m± (Dalitz plane).

Amplitude of DKSp+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.

Ratio of magnitudesof interfering amplitudes.

A. Poluektov et al., PRD 81, 112002 (2010)

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B-D(*)K- Dalitz, Result 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 BD(*)K, we obtain

Model-independent

analysis will be applied for 772M

BB.

A. Poluektov et al., PRD 81, 112002 (2010)

657 M BB

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Measuring si and ci for model-indep. Dalitz

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