Status and prospects of the Belle II experiment . Sam Cunliffe Birmingham, 05.12.2018
Status ● The project ● The apparatus ● Where we are in data-taking ● First results and prospects ● dark sector ● b → sℓℓ | Status and prospects of the Belle II experiment | S Cunliffe 05.12.2018 Page 2
Status
● 700+ physicists Belle II at SuperKEKB ● 100+ institutes ● 23 countries The project | Dark sector physics with photons at Belle II | S Cunliffe 25.09.2018 Page 4
Belle II at SuperKEKB The project ● Located at KEK, Tsukuba. (Japanese national HEP laboratory) ● つくば布市 ● �エネルギー加速器研究機槌加速器研究機構 | Status and prospects of the Belle II experiment | S Cunliffe 05.12.2018 Page 5
Belle II at SuperKEKB The project ● Located at KEK, Tsukuba. (Japanese national HEP laboratory) ● つくば布市 ● �エネルギー加速器研究機槌加速器研究機構 | Status and prospects of the Belle II experiment | S Cunliffe 05.12.2018 Page 6
Belle II at SuperKEKB The project ● Located at KEK, Tsukuba. (Japanese national HEP laboratory) ● つくば布市 ● �エネルギー加速器研究機槌加速器研究機構 | Status and prospects of the Belle II experiment | S Cunliffe 05.12.2018 Page 7
SuperKEKB ● Reason for the second iteration of the project: upgraded accelerator . ● A factor 40 increase in instantaneous luminosity ×2 from upgraded ring (higher beam current) – ×20 β* from final focus magnets. – y (µm) ) m µ positron damping ring ( x z (mm) y (µm) ) m µ ( z (mm) x | Status and prospects of the Belle II experiment | S Cunliffe 05.12.2018 Page 8
First collisions • 2018 年 4 月 26 日 ► Probably e + e - → qq • 500 pb -1 calibration data recorded this year. | Status and prospects of the Belle II experiment | S Cunliffe 05.12.2018 Page 9
Data? Integrated luminosity (ab -1 ) Target dataset: 50 ab -1 Commissioning collisions Full physics Cosmics Belle dataset: ~1 ab -1 Peak luminosity (cm -2 s -1 ) Year | Status and prospects of the Belle II experiment | S Cunliffe 05.12.2018 Page 10
Data? Integrated luminosity (ab -1 ) “Phase 2” “Phase 3” Target dataset: 50 ab -1 Commissioning collisions ~500pb -1 Full physics Cosmics Belle dataset: ~1 ab -1 Peak luminosity (cm -2 s -1 ) Year | Status and prospects of the Belle II experiment | S Cunliffe 05.12.2018 Page 11
Belle II The detector | Status and prospects of the Belle II experiment | S Cunliffe 05.12.2018 Page 12
Belle II The detector 30° 17° Direction of boost Direction of electron beam “Forward” | Status and prospects of the Belle II experiment | S Cunliffe 05.12.2018 Page 13
Belle II The detector | Status and prospects of the Belle II experiment | S Cunliffe 05.12.2018 Page 14
Belle II Running without The detector high-level trigger In phase 2 1/8 vertex detector (for beam background and commissioning) new (larger) Drift chamber tracking wires in 50:50 He:C 2 H 6 | Status and prospects of the Belle II experiment | S Cunliffe 05.12.2018 Page 15
Belle II The detector new Two layers of DEPFET high granularity pixel detector new (larger) Silicon vertex detector double sided Si microstrips new (larger) Drift chamber tracking wires in 50:50 He:C 2 H 6 | Status and prospects of the Belle II experiment | S Cunliffe 05.12.2018 Page 16
Recent news @belle2collab | Status and prospects of the Belle II experiment | S Cunliffe 05.12.2018 Page 17
Recent news Photo: L. Zani | Status and prospects of the Belle II experiment | S Cunliffe 05.12.2018 Page 18
Recent news | Status and prospects of the Belle II experiment | S Cunliffe 05.12.2018 Page 19
Belle II The detector early phase 3 new 1.25 layer of DEPFET high granularity pixel detector new (larger) Silicon vertex detector double sided Si microstrips new (larger) Drift chamber tracking wires in 50:50 He:C 2 H 6 | Status and prospects of the Belle II experiment | S Cunliffe 05.12.2018 Page 20
Belle II The detector magnet 1.5T new Barrel particle ID quartz bars totally internally reflect Cherenkov photons Electromagnetic calorimeter CsI(Tl) crystals… new readout new Endcap PID: Aerogel K L and muon detectors Ring Imaging Resistive plate chambers + Cherenkov (new) scintillator w/ iron flux return | Status and prospects of the Belle II experiment | S Cunliffe 05.12.2018 Page 21
Calorimeter details 90° small gap Endcap gaps | Status and prospects of the Belle II experiment | S Cunliffe 05.12.2018 Page 22
New tracking and clustering work well Radiative dimuon events in first data | Status and prospects of the Belle II experiment | S Cunliffe 05.12.2018 Page 23
Rediscoveries! π 0 , φ 0 , Λ 0 , τ, J/ωψ M KK [GeV/c²] Λ 0 → pπ φ 0 → K + K − | Status and prospects of the Belle II experiment | S Cunliffe 05.12.2018 Page 24
Rediscoveries! B mesons B ± B 0 | Status and prospects of the Belle II experiment | S Cunliffe 05.12.2018 Page 25
Prospects dark sector b → sℓℓ
Perhaps dark matter doesn’t interact directly. | Status and prospects of the Belle II experiment | S Cunliffe 05.12.2018 Page 27
Dark sector ? ? ? ? ? ? ? ? Standard model ? ? ? | Status and prospects of the Belle II experiment | S Cunliffe 05.12.2018 Page 28
Dark sector physics in a nutshell • Dark sector can contain one or more dark matter particles. • Interact with SM via coupling/mixing with a portal particle. • Many theory possibilities. • Categorise theories by the portal particle. ► Axion-like particle: generic scalar ► Dark photon: vector ► Z’: vector, maybe LFV ► Higgs: scalar w/ mass coupling ► Neutrinoes. • Add terms to SM Lagrangian… see what happens. | Status and prospects of the Belle II experiment | S Cunliffe 05.12.2018 Page 29
Axion-like particle Theory ● Axion-like particle a. ● Couples to EW sector post EWSB: JHEP 1712 (2017) 094 ALP-strahlung Photon fusion | Status and prospects of the Belle II experiment | S Cunliffe 05.12.2018 Page 30
Axion-like particle Analysis ● Experimentally easier: ALP-strahlung. ► Do this first. ● Three photons that add up to the beam energy + bump on diphoton mass. Nothing else in event. ● The SM background: ee → γγ(γ). JHEP 1712 (2017) 094 | Status and prospects of the Belle II experiment | S Cunliffe 05.12.2018 Page 31
Axion-like particle Analysis ● Experimentally easier: ALP-strahlung. ► Do this first. ● Three photons that add up to the beam energy + bump on diphoton mass. Nothing else in event. ● The SM background: ee → γγ(γ). ● Also search for “invisible” (more on that later). JHEP 1712 (2017) 094 | Status and prospects of the Belle II experiment | S Cunliffe 05.12.2018 Page 32
Axion-like particle JHEP 1712 (2017) 094 Physics reach LEP BaBar SN 1987A | Status and prospects of the Belle II experiment | S Cunliffe 05.12.2018 Page 33
Axion-like particle JHEP 1712 (2017) 094 Physics reach Belle II simulation Belle II 3 γ 500pb -1 | Status and prospects of the Belle II experiment | S Cunliffe 05.12.2018 Page 34
Dark photon Theory ● Massive vector particle A’, mixes with the SM photon: ● Depending on dark photon/dark matter ratio: Can decay directly to dark matter final state. ► Experimentally invisible A’ → χ 1 χ 2 Can decay to two leptons A’ → l + l - ► ● Experimentalist’s trick: require ISR photon. PhysRevD.80.015003 | Status and prospects of the Belle II experiment | S Cunliffe 05.12.2018 Page 35
Dark photon Analysis Belle II simulation ● First analysis: ee → γA’ → γ( χ 1 χ 2 ) ● Generic strategy: nothing in the event except one photon. (no tracks, other good photon clusters) Bump search in recoil mass – spectrum. ● Backgrounds ee → eeγ(γ) and ee → γγ(γ) | Status and prospects of the Belle II experiment | S Cunliffe 05.12.2018 Page 36
Dark photon ee → γγ, endcap gaps Analysis Belle II simulation ● First analysis: ee → γA’ → γ( χ 1 χ 2 ) ● Generic strategy: nothing in the event e e → except one photon. (no tracks, other good γ γ photon clusters) , 9 0 ° Bump search in recoil mass – g a p spectrum. s ● Backgrounds ee → eeγ(γ) and ee → γγ(γ) ee → eeγ, leptons ee → 3γ, endcap gaps out of acceptance | Status and prospects of the Belle II experiment | S Cunliffe 05.12.2018 Page 37
Dark photon Physics reach The Belle II Phyiscs book arXiv:1808.10567 BaBar’s analysis PRL.119.131804 | Status and prospects of the Belle II experiment | S Cunliffe 05.12.2018 Page 38
Prospects dark sector b → sℓℓ
B physics from 2019+ Dramatis personae | Status and prospects of the Belle II experiment | S Cunliffe 05.12.2018 Page 40
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