[PPT] - The Belle and BelleII Experiments in Japan The Belle Experiment is PowerPoint Presentation

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ATLAS style lectures series presents

The Belle and BelleII Experiments in Japan

The Belle Experiment is an asymmetric e+e- collider situated in KEK Japan and its primary purpose is to study the CP-Violation and indirectly look for new physics

running on the Upsilon(4S) center of mass = 10.58GeV

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ATLAS style lectures series presents

The Belle and BelleII Experiments in Japan

The Belle Experiment is an asymmetric e+e- collider situated in KEK Japan and its primary purpose is to study the CP-Violation and indirectly look for new physics

running on the Upsilon(4S) center of mass = 10.58GeV

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Measurement of CP Violation

Objective: Measure time dependent decay asymmetry of B and B going to the same final state aCP(t) = Γ (B0 → fCP; t) − Γ (B0 → fCP; t) Γ (B0 → fCP; t) + Γ (B0 → fCP; t)

3 possible contributions

▸ CP-Violation in decay (direct) ▸ CP-Violation in mixing (indirect) ▸ CP-Violation by interference of

mixing and decay (mixing induced)

s

c d d W+ b c B0 K0

S

J/ψ

+

d d c b W− u, c, t W+ d u, c, t b c W− s B0 K0

S

J/ψ

2

≠

d

c d c b W− s B0 K0

S

J/ψ

+

b s c u, c, t d d d W+ u, c, t W− b W+ c B0 K0

S

J/ψ

2

▸ For B mesons, contributions from indirect CP-Violation are negligible ▸ For many decays, loop diagrams contribute to the amplitudes

possibility to indirectly detect new physics

Martin Ritter The Belle II Experiment

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Measurement of CP-Violation

Experimental challenging task:

▸ lifetime of B mesons is 1.5 ps ▸ flavour of B meson has to be known

Solution

▸ Υ(4S): coherent B-meson pair production ▸ one B to determine flavour (tag side),

ther B for CP measurement (CP side)

▸ boost system using asymmetric beam energies

t → ∆t =

∆z ⟨βγ⟩c

t (ps) ∆

6
4
2

2 4 6 Entries / 0.5 ps 50 100 150 200 250 300 350 ∆z Υ(4S) e− e+ B0

CP

B0

tag

J/ψ µ+ µ− ℓ− K− π− π+ K0

S

Boost ⟨∆z⟩ ∼ 200 ţm

Martin Ritter The Belle II Experiment

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Experimental requirements

9.46

σ(e+e− → Hadrons) [nb] Υ(1S) e+e− Center-of-Mass Energy [GeV] Υ(2S) Υ(3S) Υ(4S)

continuum background 9.44 10.0010.02 10.34 10.37 10.54 10.58 10.62 5 10 15 20 25

Best place to produce BB in a clean environment is at the Υ(4S):

▸ lowest energy with free B mesons ▸ 1/3 of all events are BB ▸ possibility to “turn off” B production by

lowering center of mass energy by 50 MeV

Differences to LHC

Energy is factor O(1000) smaller than for LHC:

▸ there are no real “jets”: we see single particles ▸ mean momentum of charged particles is around 500 MeV

Electron Collider:

▸ full knowledge about the center of mass frame ▸ no underlying events ▸ but: low cross section (more than factor 100)

Martin Ritter The Belle II Experiment

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Belle/Belle II Experiment

Asymmetric e+e− experiment mainly at the Υ(4S) resonance (10.58 GeV) KEKB/Belle SuperKEKB/Belle II

peration

1999 – 2010 2014 – peak luminosity 2.11 × 1034 cm−2s−1 8 × 1035 cm−2s−1 integrated luminosity 1023 fb−1 (772 million BB pairs) 50 ab−1

Martin Ritter The Belle II Experiment

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8

Electromagnetic Calorimeter

▸ no hadronic calorimeter needed due to low energy ▸ around 8000 CsI crystals: pure CsI in the endcaps,

CsI(Tl) in the barrel

▸ crystals are expensive and will be reused from Belle ▸ good pointing and energy resolution

Earthquake

▸ During the earthquake, the Belle detector

(1500 t) moved by 6 cm

▸ but most probably it moved 20 cm in one

direction and then came back

▸ inner detector was already disassembled but

crystals were still in so far tests show that crystals are still working

Martin Ritter The Belle II Experiment

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Electromagnetic Calorimeter

▸ no hadronic calorimeter needed due to low energy ▸ around 8000 CsI crystals: pure CsI in the endcaps,

CsI(Tl) in the barrel

▸ crystals are expensive and will be reused from Belle ▸ good pointing and energy resolution

Earthquake

▸ During the earthquake, the Belle detector

(1500 t) moved by 6 cm

▸ but most probably it moved 20 cm in one

direction and then came back

▸ inner detector was already disassembled but

crystals were still in so far tests show that crystals are still working

Martin Ritter The Belle II Experiment

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Particle Identification System

Good separation between Kaons and Pions is very important

▸ Momentum and dE/dx will be measured in the tracking system ▸ Use of Cherenkov detectors to measure speed of the particle ▸ Cherenkov light is the optical analogy

to the sonic boom

▸ particles that are faster than the speed

f light in a given medium emit

cherenkov light

▸ direction of the light is dependent on

β

Martin Ritter The Belle II Experiment

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Time of Propagation Counter

DIRC = Detecton of internaly reflected Cherenkov light

▸ array of rectangular quartz bars ▸ cherenkov light is reflected internally ▸ MCP-PMT array at the end will detect

position and time

▸ 40 ps time resolution, 3 σ K/π

separation

Martin Ritter The Belle II Experiment

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Endcap A-RICH

RICH = Ring Imaging Cherenkov Detector

▸ silica aergoel radiators used to create

Cherenkov light

▸ light will form in circle screen ▸ two layers of different refractive materials

used to produced focussed ring

▸ 4 σ K/π separation

Silica Aerogel

▸ produced by drying silica gel in a specific

way

▸ low density (world record at 1.9 mg/cm3) ▸ low refractive index

Martin Ritter The Belle II Experiment

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Central Drif Chamber

▸ wire chamber with ∼ 15000 sense

wires

▸ drif time ∝ distance to wire ▸ position resolution of O(100 ţm) ▸ stereo wires to get θ-information ▸ determination of particle

momentum

Martin Ritter The Belle II Experiment

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Contribution to PID

Drif chamber also contributes to particle identification due to different energy losses for different kind of particles

Muon momentum 1 10 100 Stopping power [MeV cm2/g] Lindhard- Scharff Bethe Radiative Radiative effects reach 1%

µ+ on Cu

Without δ Radiative losses βγ 0.001 0.01 0.1 1 10 100 1000 104 105 106 [MeV/c] [GeV/c] 100 10 1 0.1 100 10 1 100 10 1 [TeV/c] Anderson- Ziegler Nuclear losses Minimum ionization Eµc

µ− µ π K p

e

D

e Energy deposit per unit length (keV/cm) Momentum (GeV/c) 8 12 16 20 24 28 32 0.1 1 10

Particle Identification uses the combined information of all sub detectors the particle traversed

Martin Ritter The Belle II Experiment

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Strip Vertex Detector

n bulk strip

+

n strip

+

p

electron hole

stop p-

▸ 4 layer double sided strip detector ▸ pitch of 50 ţm resp. 160 ţm ▸ shaping time of 20 − 50 ns

Martin Ritter The Belle II Experiment

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SVD Material Budget

To reduce the material budget, the readout chips will be thinned down and put directly

n the sensor

Martin Ritter The Belle II Experiment

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SVD Material Budget

To reduce the material budget, the readout chips will be thinned down and put directly

n the sensor

they call it the “Batman-shape”

Martin Ritter The Belle II Experiment

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Pixel Vertex Detector

▸ innermost part of the detector ▸ 2 layer pixel detector (8M pixels) ▸ readout time of 20 ms ▸ data rate of 240 Gb/s = 30 GB/s ▸ pixel size of 50 × 50 ţm and 50 × 75 ţm ▸ single track vertex resolution

O(15 − 30 ţm)

VON EINEM AUTODESK-SCHULUNGSPRODUKT ERSTELLT

14.00 22.00 136.00 90.00 124.00 170.00 23.00 23.00 23.00 23.00

Martin Ritter The Belle II Experiment

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Material budget

PXD different design compared with existing Silicon detectors

▸ silicon sensors self supporting ▸ sensitive area will be thinned down to 75 ţm ▸ almost no additional material inside of the

acceptance total material budget of 0.28% X0 But: Silicon is very brittle: Once there is a small crack, this crack can grow very easily

Martin Ritter The Belle II Experiment

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Material budget

PXD different design compared with existing Silicon detectors

▸ silicon sensors self supporting ▸ sensitive area will be thinned down to 75 ţm ▸ almost no additional material inside of the

acceptance total material budget of 0.28% X0 But: Silicon is very brittle: Once there is a small crack, this crack can grow very easily

Martin Ritter The Belle II Experiment

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Martin Ritter The Belle II Experiment

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Martin Ritter The Belle II Experiment

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Conclusions

Belle/Belle II is a precision measurement focusing on the production of B mesons

▸ Center of Mass energy of 10.58 GeV ▸ boosted system to transform lifetime difference between the two B mesons into

vertex difference

▸ very good vertex detector ▸ good identification of final state particles (K,π)

Belle II will increase the data sample of BB Events by a factor of 50

▸ opens possibilities to examine very rare decays ▸ will push sensitivity of CP measurements to a level to really challenge SM

Martin Ritter The Belle II Experiment

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Tank you for your attention

Martin Ritter The Belle II Experiment

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Unitarity Triangle

▸ unitarity of CKM matrix leads to column constraints ∑k VikV ∗ jk = 0 ▸ triangles in complex space ▸ almost degenerate in Kaon system, large angles in B meson system

VudV ∗

ub O(λ3)

+ VcdV ∗

cb O(λ3)

+ VtdV ∗

tb O(λ3)

= 0

3

φ

2

φ

2

φ

d

m ∆

K

ε

K

ε

s

m ∆ &

d

m ∆

ub

V

1

φ sin 2

(excl. at CL > 0.95) < 0

1

φ

sol. w/ cos 2

2

φ

1

φ

3

φ

ρ

−0.4 −0.2 0.0 0.2 0.4 0.6 0.8 1.0

η

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

excluded area has CL > 0.95 Moriond 09

CKM

f i t t e r

ρ = (1 − λ2 2 ) ρ η = (1 − λ2 2 ) η ϕ1 = arg ⎛ ⎝− Vcd V∗

cb

Vtd V∗

tb

⎞ ⎠ ϕ2 = arg ⎛ ⎝− Vtd V∗

tb

Vud V∗

ub

⎞ ⎠ ϕ3 = arg ⎛ ⎝− Vud V∗

ub

Vcd V∗

cb

⎞ ⎠

Martin Ritter The Belle II Experiment

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Standard Silicon Detector

for example ATLAS

▸ multiple sensitive modules are glued on support ribs which provide mechanical

stability

▸ support, cooling and cables inside acceptance region (between 5% and 30% X0)

too much material for Belle II (10 GeV CM energy)

Martin Ritter The Belle II Experiment