Belle II status
K. Matsuoka (KEK)Aug. 27, 2021

Belle II operation strategy• Data taking with a high efficiency (≥ 90%)
・・・ Mission of the luminosity frontier experiment– Establish sustainable operation system (labor-saving, automation, …)– Along with the luminosity increase, in a step-by-step manner, solve issuesof the detectors, trigger, computing, etc. which arise from the highluminosity and beam background.

• Mitigate the beam background without interfering theaccelerator performance.
– Suppress the detector degradation by the radiation and performancedegradation by the huge beam background within the acceptable level
until accumulating 50 ab–1.
・・・ Necessary for high precision measurements• Safe operation without damaging the detectors– Occasional huge beam losses damaged the innermost PXD.

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Belle II operation shifts under COVID-19
Limited number of people (~50) in KEK staying for several months or longer.
• Keep minimizing person-to-person contact, avoiding 3C, and taking hygiene.
Operation by people traveling to KEK in turns → mainly by remote people.
• Control room shift: 2 local → 2 remote + 1 local shifters… Remote shifters are actively working, and load on local people has been reduced.

• BCG shift: accelerator control room → another bldg.

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Tireless efforts for a higher data taking efficiency
Understand the existing situation
Iteration• Monitors (ELK; Elasticsearch, Logstash, Kibana)– We can easily know how well we are doing.

Find what should be improved• Lesson of errors– Review of every major downtime longer than 30 min

Work on the issues• Fix the cause of the error• Speed up the recovery procedure from the error• Documentation, instructions, trainings for subsystem experts

Quality of operation shifters• Documentation, instructions, trainings for shifters• Experienced local shifters (special situation under Covid-19)

Feb 16 - Jul 5, 2021

Data taking efficiency in 2021ab

5

Accelerator tuning, Belle IIaccess Belle II study
trouble, etc.
Physics run
0%
30.7%
66.7%
0.6%
Scheduled
Whole run time
maintenancefraction
2.1%
SALS
Running
2.4% HV trip
93.8%
Physics run timeor error
fraction
0.2%
Belle II trouble or calibration HV rampInjection veto2.8%4.0%
up/down
DAQ dead time
0.7%
4.6% in total
fraction

Fraction (%)

0%100908070605040302010010% 20% 30% 40% 50% 60% 70% 80% 90% 100%

Overall data taking
efficiency = 89.5%(Target 90%)

Physics run / whole run time
DAQ running / physics run(DAQ running - dead time) / physics run
2019c

2020ab2020c

2021ab

Toward 90% data taking efficiency• Data taking efficiency has been improved slightly in 2021ab
in spite of more frequent DAQ stops due to a higher beam
background, thanks to✓ More automation, recovery tools✓ Improved documentation, training✓ Experienced local CR shifters• To achieve 90% eff, we should continue improving our system:[Short term]– Reduce recovery time (e.g. recovery GUI) and time for SALS (e.g. auto-mode)(Reduction by 1 min will increase the efficiency by 0.7%.)[Long term]– Make our system robust against the beam background.
– Mitigate the neutron background by adding shields andmachine/collimator tuning.

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Recorded/delivered luminosity
245 fb–1 (delivered)
213 fb–1 (recorded)7

Mitigation of the beam background• If the beam background level reaches Belle II limit, the beam
current cannot be increased any more. So far, the beam
background did not limit the beam current.
• Strategy for the beam background mitigation– Understand the beam background– Close and add collimators• Better injection performance will allow tighter collimator settings.

→ Need to open collimators to relax TMCI
• but cannot open them now to avoid frequent beam aborts by bad injections.

– Optimize collimators– Introduce a non-linear collimator– Add shield around the QCS bellows– (QCS modification)

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Most stringent limit on the beam background by TOP
due to degradation of MCP-PMT photocathode caused by background photon detection

Storage background (Touschek and beam gas) will
Reduction mainly by LER vacuum scrubbing
2
increase with 𝐼beam
unless any improvements areand by adding/closing collimators
anticipated.

Original run plan in 2020c• Accelerator tuning (squeeze 𝛽𝑦∗ from 1.0 to 0.8, 0.7 and 0.6 mm).
–Target luminosity: 4 x 1034 /cm2/s with 750-1000 mA.

However, many troubles prevented the progress.

Lambertson

Vacuum leak

10/19
3.5 weeks

Good condition of making progress
only in these 3 days

To protect D2V110Beam background (TOP) in 2020c
HER by*= 1 mm
Collimator tuning
HERD02V1 damagedb *= 2 mm
y11

LER by*= 1 mm
HER bx*= 60 mm CW40%
LER optics on 11/13
LER adjusted phase
The width of this band
represents the amountof injection background.

2020b (𝛽𝑦∗ = 1.0 mm)
without LER rotatable sextupoleGood condition

LER steering tuning

Phase matched optics• The LER steering tuning increased the injection background a lot.
That was why the collimators had to be closed for stable operation.
• The phase matched optics was tried to protect D02V1 by D03V1,
which eventually increased TMCI.
PMT hit rate normalized by the expectation based on the measurement on May 9:
1.1𝐸 −2𝐼2𝐼2+ 1.9𝐸 −4 𝐼 + 1.8𝐸 −7 𝐼 2+ 3.0𝐸 −2+ 2.4𝐸 −4 𝐼 + 9.1𝐸 −7 𝐼 2+ 7.85𝐸 −2 ℒ 1034 /𝑐𝑚2 /𝑠
𝜎𝑦 𝑛𝑏
𝜎𝑛𝑦 𝑏𝐻𝐸𝑅𝐿𝐸𝑅Strategy in 2021

12• Collect as much data as possible to produce as many physics
results of publication quality as possible during LS1.
– In 2021, we should exceed at least 424 fb–1 = BaBar at Y(4S).

Mar.
➢ Restore the same luminosity performance as June 2020,2.4 x 1034 /cm2/s at LER 712 mA, HER 607 mA, 978 buncheswith the same optics and collimator settings. (→ ~1.4 fb–1/day incl. eff.)

Apr.
➢ Change 978 → 1565 bunches and increase the total beam currents.
→ Target: 3.8 x 1034 /cm2/s (~2.1 fb–1/day incl. eff.)• We put priority on the luminosity rather than the beam background
reduction in terms of the accelerator tuning/operation.
– Limits: L1 rate < 13-14 kHz for DAQ, TOP PMT hit rate < 3 MHz + luminosity

during physics run

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𝐼𝐻𝐸𝑅 𝐼𝐿𝐸𝑅
10/fb/week challenge
HER beam aborts with huge beam loss
LER huge beam loss Infection
June 2020
Frequent HER beam loss

D2V1
damage

CLAWS abort
enabled
Aggressive baking run Nb 1174 -> 1272
Push to increase beam
LER 860 -> 1000 mA LER 840 -> 910 mAcurrents more aggressively HER 840 -> 920 mA
HER 680 -> 730 mA

D01V1
replacement

Poor HERinjection

D02V1
replacement

Increasing the beam current is a tough challenge.
• PXD, diamond readout and collimators were damaged by the huge beamloss on May 10.
• It is yet unresolved what is the cause of huge beam losses.

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Trigger rate and beam background in 2021ab• L1 NN track trigger since 3/20
• HLT filtering since 3/24 (exp17)• Prescale of L1 Bhabha trigger since 4/7 (exp18)• L1 rate was kept below the DAQ limit without applying
prescales to the main trigger bits.

L1 rate (Hz)10kTOP rate (MHz)NN track

3.2

D2V1 damage
Bhabha prescale

Openedcollimators

5k

Accepted a higher beam background, which did not reach the limit.

1.60exp.run number

Stable operation is a key• To integrate the luminosity, to make progress in theaccelerator tuning, to reduce risk of damaging the detectors
and machine components.

– Represent operation stability at a high luminosity– Assumption in the MEXT 2020 load map: 70% operation efficiency

Fraction (%)•

Delivered luminosity
Operation efficiency =‫ ׬‬ℒmax (𝑡)⋅d𝑡80
706050403020100Physics run / whole run time
Operation efficiency
2019c2020ab2020c

2021ab15

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Baking run• When the beam current is increased above the max current in each run
period, Belle II HV is kept at STANDBY for safety (to avoid risk of detector
damage by dust event or beam instability) until the accelerator is stabilized.
– Baking run for 30 min at the new high current above 300 mA.

• The step size of the current increase in the baking run is determined by theaccelerator experts. The current should not be far from the one during physics run.
• Baking run should be done in the same collision condition as physics run.

– Start physics run at a lower beam current by 20 mA or less than the max ofthe baking run. Gradually increase the current up to the max of the baking
run. Meanwhile accelerator tuning is necessary at a constant current.
• The beam current at physics run is determined by Belle II in consultation with KCG.
Beam current

300 mA

Baking runs

by* = 2 mm

The first threshold (300 mA) should be revisited.

by* = 1 mmdayPhysics results

17Only publications are shown here.

World-leading/competitive results with the data up to last summer.
Search for 𝑒 + 𝑒 − → 𝛾𝑎, 𝑎 → 𝛾𝛾
PRL 125, 161806 (2020)

PRL 124, 141801 (2020)

Search for 𝑒 + 𝑒 − → 𝜇+ 𝜇− 𝑍 ′ , 𝑍 ′ → invisible

Measurement of 𝐷0 and 𝐷 + lifetime

submitted to PRL

submitted to PRL18

Need more data

• Before the long shutdown in 2022, we need data comparable to711 fb–1 = Belle at Y(4S) or more to be fully back in the game.
– Data in a timely manner is essential to compete with LHCb.

• Short runs in 2021c around 10.75 GeV, which is almost
unexplored and promising for O(10) publications.
at each black point

B. Fulsom

Plan of the above-Y(4S) runs in 2021c

Swing Day

Owl

Swing DayOwl

Swing DayOwl

Day 1 Wed

Maintenance

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Integrated luminosity projection at each energy

2 Thu

3 Fri

4 Sat

5 Sun

6 Mon

7 Tue

(0.2/fb)(1.5/fb)(0.5/fb)(2.0/fb)(3.5/fb)(0.5/fb)(0.5/fb)

10.706 GeV(1.0/fb)(2.5/fb)

10.751 GeV(1.0/fb)

10.657 GeV(1.0/fb)(0.2/fb)(1.5/fb)(3.0/fb)(0.2/fb)(1.5/fb)

8 Wed

9 Thu

10 Fri11 Sat12 Sun13 Mon14 Tue(2.0/fb)(3.5/fb)(5.0/fb)(6.5/fb)(8.0/fb)(9.5/fb)(0.5/fb)

10.810 GeV(1.0/fb)(2.5/fb)(4.0/fb)(5.5/fb)(7.0/fb)(8.5/fb)(3.0/fb)(4.5/fb)(6.0/fb)(7.5/fb)(9.0/fb)(0.2/fb)(1.5/fb)

15 Wed16 Thu17 Fri18 Sat19 Sun20 Mon21 Tue(2.0/fb)
MaintenanceY(4S)Contingency

Y(4S)Summary• Belle II has improved the operation system and89.5% of the data taking efficiency was achieved in 2021ab.
– Even 1 min loss concerns us now.
– We will continue efforts to improve it.

• Compromise on the beam background mitigation by opening
the collimators will be necessary to achieve a higher luminosity.
– Belle II can still accept a higher beam background until it hits the limit.
– Once the injection quality gets better, the collimators can be opened.

• Increasing the beam current while keeping the stable condition
is challenging.
– Need to understand the cause of huge beam losses and prevent it.
→ Nakayama-san’s talk for more detail• Belle II needs more data to produce physics results, which are
the driving force of this project.

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