Transcript Document

Measurements of the unitarity
triangle parameters at Belle II
名古屋大学 堀井泰之
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 collider
Belle detector
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SuperKEKB collider
Belle II detector
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.
U(10860)
(8.0/3.5 GeV for KEKB.)
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.)
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SuperKEKB
SuperKEKB
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2020-2021年までに、KEKBの50倍のデータを取得したい。
Belle II detector
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。
ピクセル検出器導入による
崩壊点精度の向上（~20 mm）
シリコン検出器の外径拡大（140 mm）
によるKS (p+p-) acceptanceの向上
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。6
LHCbに比べ、中性粒子を終状態
に含むモードに強みを持つ。
Measurements of the CKM parameters
tension
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Search for new physics
from measurements
of angles and sides of UT.
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)K0
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Belle preliminary (Moriond 2011)
using full U(4S) data (0.71 ab-1).
Consistent results for the four modes.
B(cc)K0
sin2f1 (indirect CPV)
A (direct CPV)
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
Belle II, 5 ab-1
±0.016
±0.015
Belle II, 50 ab-1
±0.012
±0.013
Measured
Expected
O(0.01) precision at 50 ab-1.
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B(ss)K0
50 ab−1
J/K0
fK0
S(fK0)=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(Btn):
ICHEP 2010
~2.8s discrepancy


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.
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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 on
mH± 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).
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Note: BDtn at Belle II

Also sensitive to charged Higgs.
H-
Uncertainty in BD semi-leptonic form factor.
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Exclusion boundaries
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。
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Measurement of f3
L.Wolfenstein,
PRL 51, 1945 (1983)

Golden mode: B-DK- (and the conjugate)

Crucial parameters for extracting f3:
rB ~ 0.1 (CKM x color-supp).
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。
f3測定法は、f により分類できる。
①
B-D0K-

D0f
GLW法

B_
B-D0K-
f K-
f3
_
②
D0f
分岐比 ∝ |A(①) + A(②)|2
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
ADS法


f = CP固有状態（K+K-, p+p-, KSp0, …）。
f = K+p-, K+p-p0など。
Dalitz法

f = KSp+p-など。Dalitz解析。
GLW method
Relatively small contributions from CP-violating terms,
since rB is small (~0.1).
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Non-zero ACP+ obtained.
Useful for extracting f3.
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+ADS
is 15° at 1 ab-1 and 3° at 50 ab-1.
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Dalitz method

Previous measurement:
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Modeling of amplitudes on Dalitz plane.
(Especially strong phase for the D decays.)
Dalitz method
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ci and si are obtained by _
CLEO using (3770)D0D0.
Dalitz method
Belle preliminary (Moriond 2011).
Consistent with CKM fit
w/o direct measurement:
f3 = 67.2° ± 3.9°.
Precision of ci, si will be improved by BESIII measurements.
Expected precision for f3 at 50 ab-1 is 2°.
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_
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
50 ab-1
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Current contours
50 ab-1
Precision at 50 ab-1
Note: Kp puzzle
DCPV due to Vub.
If the only diagrams are a and b, we expect
a
b
However, significant difference is obtained.
BKp w/ 0.5 ab-1
Nature 452, 332 (2008)
Missing diagrams?
Large theoretical uncertainty…
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K-p+
K+p-
K-p0
K+p0
Note: DCPV for BKp at Belle II

We can compare to a model-independent sum rule:
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Current measurement
larger error for ACPK0p0
expected
expected
measured
measured
Can be represented as diagonal band
(slope precisely known from B and lifetimes):
50 ab-1
assuming current central value
Summary

SuperKEKB

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
Belle II

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
40 times higher luminosity of 8.0 x 1035 /cm2s.
Will reach 50 ab-1 by the end of 2021.
Conservatively designed to cope with high background.
Improvements in several aspects: vertex, KS acceptance, PID, …
Examples of physics at SuperKEKB/Belle II


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Measurement of f1(eff) from B0(cc)K0 and 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.)
Backup Slides
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SuperKEKB Collider
Approved in 2010.
Belle II
e-
Smaller asymmetry
8 / 3.5 GeV  7 / 4 GeV
e+
Larger crossing angle
2f = 22 mrad  83 mrad
for separated final-focus magnets.
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 to reduce the emittance.
TiN coated beam pipe
with antechambers
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L = 8 x1035 cm-2 s-1
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Belle II detector
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Dimensions for Belle II and Belle detectors
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Feb. 24th, 2011
H.Nakayama (KEK)
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Expected Performance for Belle II
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Vertex Detector
Improve decay-time precision
and acceptance (KS’s).
4lyr. Si strip  2lyr. pixel(DEPFET) + 4lyr. Si strip
Si strip
pixel
5th lyr.
4th lyr.
3rd lyr.
2nd lyr.
1st lyr.
Pixel:
r=14,22mm
Si strip:
r=38,80,115,140mm
Belle II
Belle
4th lyr.
2nd lyr.
1st lyr.
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6th lyr.
3rd lyr.
Particle Identification System at Belle II
Endcap PID: Aerogel RICH (ARICH)
Barrel PID: Time of Propagation Counter (TOP)
200mm
Quartz radiator
Focusing mirror
Hamamatsu MCP-PMT (measure t, x and y)
Aerogel radiator
n~1.05
Hamamatsu HAPD
+ new ASIC
TOP
n1 n2
Completely different from PID at Belle,
with better K/p separation, more
tolerance for BG, and less material.
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Multiple aerogel layers
with different indices
sq(1p.e.) = 14.4 mrad
Npe ~ 9.6
sq(track) = 4.8 mrad
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
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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.
Effective for the modes
including missing energy.
Missing
Also possible to partially reconstruct (semileptonically, …).
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A. Poluektov et al., PRD 81, 112002 (2010)
B-D(*)K-, DKSp+p- Dalitz

Amplitude of B±DK± process can be expressed as
Ratio of magnitudes
of interfering amplitudes.
Amplitude of DKSp+p- decay
determined 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.

Procedure of analysis:
1.
2.
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Background fractions are determined by 2-D UML fit for DE and Mbc.
Fit is performed to m± (Dalitz plane).
A. Poluektov et al., PRD 81, 112002 (2010)
B-D(*)K- Dalitz, Result


657 M BB
Using the background fractions, Dalitz plane is fitted
with the parameters x± = r±cos(±f3+d) and y± =
r±sin(±f3+d).
Combining the results for BD(*)K, we obtain
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Model-independent
analysis will be applied
for 772M BB.
Measuring si and ci for model-indep. Dalitz
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