The Belle II Experiment: Status and Prospects

Kodai Matsuoka (KMI, Nagoya Univ.) on behalf of the Belle II collaboration

ICHEP2020 July 30, 2020 2 Belle II at SuperKEKB

Plan to collect 50 ab–1 of collisions at and near Υ 4푆 Successor to Belle at KEKB (1.05 ab–1) Nano beam scheme ∗ 훾± 휎푦 푰±휉±푦 푅퐿 At Υ 4푆 , 퐸퐶푀 =10.58 GeV ℒ = 1 + − ∗ ∗ 7 GeV 풆 (HER; High Energy Ring) 2푒푟푒 휎푥 휷풚 푅푦 + 4 GeV 풆 (LER; Low Energy Ring) Belle II detector 5.9 → 0.3 mm KEKB SuperKEKB 풆− + 풆 Physics motivations ▪New physics search in 퐵, 퐵푠, 퐷, 휏 decays Belle II collaboration ▪Direct search for light new particles ▪Precise measurement ~1000 collaborators from of Standard Model 26 countries and regions ▪Hadron physics 3 Belle II detector Superconducting solenoid (1.5 T)

KL and m detector • Resistive plate chamber (outer barrel) Electromagnetic calorimeter • Scintillator + MPPC CsI(Tl), waveform sampling (inner 2 barrel layers, end-caps)

Particle ID detectors • TOP (Time-of-Propagation) counter (barrel) • RICH (forward end-cap) Tracking detector Drift chamber (He + C2H6) of small cell, longer lever arm with fast readout electronics

Silicon vertex detector Trigger and DAQ • 1→2 layers DEPFET (pixel) Max L1 rate: 0.5→30 kHz 4 outer layers DSSD • Pipeline readout Better performance even at GRID computing the higher trigger rate and beam background 4 Major detector issues in the operation ▪Detector lifetime (in particular TOP counter)

• To keep the MCP-PMT QE within an acceptable level (QE/QE0 > 80%) until 50 ab–1, the Touschek and beam gas backgrounds, which increase with (beam current)2, have to be kept constant by collimators, beam tuning, additional shielding, … → TOP PMT hit rate could limit the luminosity. ▪Permanent damage on PXD and SVD by accidental huge beam loss. ▪Synchrotron radiation from HER beam on PXD → Should be carefully monitored not to irradiate PXD unnecessarily. Projection of the QE degradation

QE degrades as (output charge)2

Assume luminosity background (MC) + 1.2 MHz/PMT Specific pattern of PXD hit distribution by SR 5 Operation status in 2020

▪SuperKEKB/Belle II was operated under Covid-19 pandemic

while minimizing risk of infection: Closed space • Minimize person-to-person contact and avoid 3C Crowded places Close-contact settings − Remote control room shifts and expert shifts − Travel restrictions (~40 Belle II colleagues on-site) − Online meetings • Hygiene (face mask, alcohol disinfection, ventilation, …)

KEK campus Beam background HV ctrl (SpeakApp) (RocketChat) Belle II Exp Hall Sub-system experts

Accelerator ctrl room Another bldg Ctrl room Safety shift Remote ctrl room shift

VPN

KCG (SuperKEKB CG) BCG (Belle II Commissioning Group) 6 Accelerator operation summary → Talk by Y. Ohnishi ∗ 훽푦 (mm) 3.0 2.0 1.0 0.8 2.4 x 1034 /cm2/s (WR) at ~half beam current of KEKB

HER crab waist

LER crab waist

Beam background was kept below the limit. TOP counter PMT TOPcounter

2019 2020 ∗ Try to squeeze 훽푦 down to 0.6 mm in this coming autumn run. 7 Integrated luminosity

Belle II data taking efficiency has been improved to 84%. ✓ Less DAQ errors and more prompt recovery from the errors by experts’ consistent effort 74 fb–1 ✓ Error analysis and monitor by –1 ELK (Elasticsearch Logstash Kibana) 1.3 fb /day ✓ More experienced shifters ✓ Controlled injection veto dead time (avg. 4.9%) as a result of injection background studies

Scheduled 10 fb–1 maintenance –1 Belle II trouble 6 fb Accelerator trouble Accelerator Physics tuning run 56.7% Run time fraction of ICHEP2020 dataset SuperKEKB operation in 2020 34.6(3.2) fb–1 on-(off-)resonance 8 Data analyses to be shown in ICHEP2020

Performance assessment for Dark sector with the data taken in 2018 the flavor physics program → Talk by E. Graziani • 퐵0 lifetime → Talk by C. Praz • 푍′ or LFV 푍′ to invisible + + • 퐵 flavor tagger → Talk by N. Rout 푒 푍′ 휇 푒 푍′ 푒 휈, 휒 휇 휈, 휒 • Reconstruction of (semi-)leptonic 퐵 휈, 휒 휈, 휒 − 훾 − 훾 decays with FEI → Talk by M. Milesi 푒 휇 푒 휇 0.276 fb–1; PRL 124 (2020) 141801 • Search for 퐵 → 퐾ℓℓ, 푋푠ℓℓ → Talk by Y. Sato 1st Belle II physics paper • 퐷0 lifetime, 퐷, 퐷 , Λ reconstructions 푠 푐 • Axion Like Particle → Talk by G. Casarosa 훾 푒+ 푎 ∗ 훾 Outset of flavor physics measurements − 훾 푒 훾 (Need more statistics for publication) 0 ∗+ − 0.445 fb–1; Being submitted to PRL • ℬ 퐵ത → 퐷 ℓ 휈ҧ , 푉푢푏 and 푉푐푏 → Talk by R. Cheaib; poster by S. Granderath 2nd Belle II physics paper • ℬ and 퐴퐶푃 of charmless B decays → Talk by E. Ganiev ∗ • 푓퐿 in 퐵 → 휙퐾 → Talk by N. Rout • 휏-lepton mass → Talk by K. Inami 9 Physics publication prospects in near future

▪140-240 fb–1 until Mar 2021 (depending on the operation budget)

Flavor physics Dark sector

2 Dark higgstrahlung • 푉푐푏 from hadronic 푞 moments • + + 푒 퐴′ 휇 • Inclusive 푉푢푏 from lepton endpoint 휇− 훾 퐴′∗ • Inclusive and FEI tagged 푏 → 푠훾 푒− ℎ′ • Inclusive 퐵+ → 퐾+휈휈 • Invisible dark photon 푒+ 훾 휒 • 퐵0 lifetime and mixing st 훾 퐴′ • 1 combined Belle + Belle II 푒− 휒ҧ analysis on BPGGSZ 휙3 • Visible dark photon 0 + • 퐷 , 퐷 , 퐷푠, Λ푐 lifetimes • 푍′ or LFV 푍′ to invisible update ′ • 퐵 → Λ푐 + invisible • 푍 → 휇휇 • 휏-lepton mass measurement • Inelastic dark matter • 휏 → ℓ + invisible(훼) search • Dark scalar → Talk by F. Tenchini • … ▪~1 ab–1 before long shutdown in 2022 to surpass BaBar and Belle → Belle II will join in with the hunting for New Physics in earnest. 10 Projection toward 50 ab–1 ▪Recently updated based on the past results.

∗ 훽푦 (mm) 1.0 0.6 0.5 0.3 11 Summary ▪Belle II plans to collect 50 ab–1 to extensively search for New Physics in the flavor and dark sectors as well as to provide better understanding of the Standard Model and hadron physics. ▪Accelerator and detector operation is in good shape: the world record of the peak luminosity 2.4 x 1034 /cm2/s (KEKB record: 2.1 x 1034 /cm2/s) was achieved with the acceptable beam background level. ▪Collected 74 fb–1, and 1st physics paper on dark sector was published, to be followed soon by other results on dark sector and flavor physics. ▪In a few years, Belle II will join in with the hunting for New Physics in earnest.