BEAST results on SuperKEKB beam background: focus on the PLUME pixelated system Jerome Baudot on behalf of the BEAST/Belle II collaboration ➙ Beam induced background at SuperKEKB & Belle II: BEAST ➙ The double-sided PLUME device ➙ Single Beam background estimates ➙ Outputs with 2-sided measurements
Belle II physics goals The intensity frontier SuperKEKB • Built up on B factories success e+e- coll. at (4s) - integrated luminosity x 50 - early phase 3 • Flavour studies New source of CP violations - Phase 2 Lepton non-universality - Charged lepton flavour violation - Left-Right symmetry contribution - Dark sector - Complementary / LHCb • Vertex Detector (VXD) Requirements • Track impact parameters • Innermost layer - Goal s( high p ) ~ 15 m m - Hit rate >0.4 hits/ m m 2 /s • B, D, decay vertices - TID: 20 kGy/year - Goal s ~ 60 m m • 30 kHz trigger rate See F. Luetticke’s talk from Monday 10 th 2 BEAST results on beam Background at SuperKEKB: PLUME focus - J. Baudot - PIXEL 2018
SuperKEKB collider HER: e - 7GeV Large currents e + 4GeV :LER HER I beam = 3.6 A Higher e+ energy LER I beam = 2.6 A to mitigate Touschek bkg New final focusing magnets Nominal L peak = 8x10 35 cm -2 .s -1 Add / modify RF systems for higher beam current New LER pipe Nanobeam scheme e + Vertical beam size 60 nm Crossing (Piwinski) angle =83 mrad to mitigate beamstrahlung e - Positron source Damping ring = 𝐽 ± ±𝑧 for low emittance e+ 𝑀 ∝ 𝑂 − 𝑂 + 𝑔 revol low emittance e- gun ∗ 𝜏 𝑦 𝜏 𝑦 𝜒𝜏 𝑨 𝛾 𝑧 3 BEAST results on beam Background at SuperKEKB: PLUME focus - J. Baudot - PIXEL 2018
The Belle II detector An upgrade of Belle 4 BEAST results on beam Background at SuperKEKB: PLUME focus - J. Baudot - PIXEL 2018
Beam induced backgrounds Single beam effects s y << s z • Touschek intra-beam scattering 2 2 𝐽 𝑐𝑣𝑜𝑑ℎ 𝑂 𝑐𝑣𝑜𝑑ℎ 𝐽 𝑐𝑓𝑏𝑛 - rate ∝ = 3 3 𝜏 𝑦 𝜏 𝑧 𝐹 𝑐𝑓𝑏𝑛 𝜏 𝑦 𝜏 𝑧 𝐹 𝑐𝑓𝑏𝑛 𝑂 𝑐𝑣𝑜𝑑ℎ • Beam gas vacuum residues - rate ∝ 𝐽bunch × 𝑂bunch × 𝑄 𝐽 Dynamic pressure 𝑄 𝐽 = 𝑞 0 + 𝑞 1 𝐽 𝑐𝑓𝑏𝑛 - • Synchrotron radiation magnet bending - rate ∝ 𝐽 beam Beam-beam effects (QED) e + e + • rate ∝ Luminosity e - e - Radiative Bhabha 2-photon interaction scattering 5 BEAST results on beam Background at SuperKEKB: PLUME focus - J. Baudot - PIXEL 2018
Beam induced backgrounds Single beam effects Expectations • Touschek intra-beam scattering • Dominates beam lifetime • Higher relative impact 2 2 𝐽 𝑐𝑣𝑜𝑑ℎ 𝑂 𝑐𝑣𝑜𝑑ℎ 𝐽 𝑐𝑓𝑏𝑛 - rate ∝ = at large radii (CDC, TOP) 3 3 𝜏 𝑦 𝜏 𝑧 𝐹 𝑐𝑓𝑏𝑛 𝜏 𝑦 𝜏 𝑧 𝐹 𝑐𝑓𝑏𝑛 𝑂 𝑐𝑣𝑜𝑑ℎ • Beam gas vacuum residues • Sub-dominant - rate ∝ 𝐽 𝑐𝑣𝑜𝑑ℎ × 𝑂 𝑐𝑣𝑜𝑑ℎ × 𝑄 𝐽 Dynamic pressure 𝑄 𝐽 = 𝑞 0 + 𝑞 1 𝐽 𝑐𝑓𝑏𝑛 - • Synchrotron radiation magnet bending • Issue for innermost PXD - rate ∝ 𝐽beam (mostly horizontal plane ) Beam-beam effects (QED) • Dominant at L nominal • rate ∝ Luminosity • Saturate VXD occupancy 6 BEAST results on beam Background at SuperKEKB: PLUME focus - J. Baudot - PIXEL 2018
Belle II in Phase 2 BEAST goals • Safe background conditions for VXD insertion / phase 3 Real-time background monitoring • during SuperKEKB tuning • Understand individual background components BEAST setup No final VXD During Phase 1 (no collisions): Initial measurements with another BEAST setup 7 BEAST results on beam Background at SuperKEKB: PLUME focus - J. Baudot - PIXEL 2018
The BEAST setup: complementarity Sensor Measurement DEPFET B-II PXD 2 ladders In-situ occupancy tracking & vertexing DSSD B-I SVD 4 ladders Diamond Ionizing dose in VXD 8 sensors Hybrid pix Charged particle & X-ray FANGS (ATLAS) synchroton rates 3 ladders Scint.tile SiPM Rates with ns precision / CLAWS (ILC) injection 2 ladders 2sided MAPS Final VXD BEAST PLUME Rates & two-sided track. (ILC) 2 ladders ~3.5 % X 0 ~4.0 % X 0 MicroTPC Fast neutron rate 8 units He3 tube Thermal neutron rate 4 units Material budget Rad.Film Radiation level Many PinDiode 80 units Radiation at focus.magnet 8 BEAST results on beam Background at SuperKEKB: PLUME focus - J. Baudot - PIXEL 2018
PLUME double-sided layer Concept • Double-sided layer of pixel sensors • Designed driven by ILC-VXD • Air cooled • Collab: Bristol, DESY, IPHC PLUME-2 • 2x6 MIMOSA-26 sensors - Pitch 18.4 m m - Binary output - Thinned to 50 m m • 8 Mpixels • integration time 115 m s • 2 mm thick Si-carbide foam Material budget 0.4% X0 • • 4 ladders produced Side view 9 BEAST results on beam Background at SuperKEKB: PLUME focus - J. Baudot - PIXEL 2018
PLUME geometry in BEAST 2 complementary angles 135 0 & 225 o • • Opposite to VXD sector (0 o ) Radius covered • SVD range 10 BEAST results on beam Background at SuperKEKB: PLUME focus - J. Baudot - PIXEL 2018
Phase 2 data taking SuperKEKB • Started March Ended July 2018 • Collimator adjustment and tuning ∗ decreased from 8 to 3 mm ( s * y ~ 400 nm) • 𝛾 𝑧 • Beam current up to ~800 mA Best peak lumi: 5.4x10 33 cm -2 .s -1 BEAST • Permanent online monitoring during tuning • dedicated study with varied: collimator, current, beam size, injection PLUME CLAWS BEAM size 11 BEAST results on beam Background at SuperKEKB: PLUME focus - J. Baudot - PIXEL 2018
Radiation levels From radiochromic films • Decrease with radius in inner volume: ~1 kGy few 100’s Gy • Clear contribution from low penetrating radiations PLUME specific • 99% up time during all Phase 2 period • No significant sign of TID crosschecked by radio.films (~200 Gy) 12 BEAST results on beam Background at SuperKEKB: PLUME focus - J. Baudot - PIXEL 2018
Single-Beam background estimates Separate contributions through their dependence to current and beam-size 2 𝐽 𝑐𝑓𝑏𝑛 2 𝑆𝑏𝑢𝑓 𝐽, 𝜏 𝑧 = 𝑈 𝜏 𝑧 𝑂 𝑐𝑣𝑜𝑑ℎ + B 𝑞 1 𝐽 𝑐𝑓𝑏𝑛 +𝑞 0 𝐽 𝑐𝑓𝑏𝑛 • 2 absolute contributions to rate: T (Touschek), B (Beam-gas) T, B specific to each detector - PLUME fit examples Rate (particle/cm 2 /s) LER I beam (mA) 13 BEAST results on beam Background at SuperKEKB: PLUME focus - J. Baudot - PIXEL 2018
Single-Beam background estimates Unknown additional contribution for HER For large beam size, rate rise again! • • Data favour a Touschek-like contribution 2 2 𝐽 𝑐𝑓𝑏𝑛 𝐽 𝑐𝑓𝑏𝑛 +𝑞 0 𝐽 𝑐𝑓𝑏𝑛 + X 2 𝑆𝑏𝑢𝑓 𝐽, 𝜏 𝑧 = 𝑈 𝜏 𝑧 𝑂 𝑐𝑣𝑜𝑑ℎ + B 𝑞 1 𝐽 𝑐𝑓𝑏𝑛 3 𝑂 𝑐𝑣𝑜𝑑ℎ 𝜏 𝑧 • Unclear origin Rate (particle/cm 2 /s) - Large beam tails PLUME to account for it HER I beam (mA) 14 BEAST results on beam Background at SuperKEKB: PLUME focus - J. Baudot - PIXEL 2018
Single-Beam background findings • PLUME data shown so far, but of course similar plots for all BEAST/Belle II Rates in inner volume during Phase 2 • Of course O (10 2 ) smaller than expectation for phase 3 • Dominated by LER wrt HER Additional collimators for phase-3 • Beam Gas Touschek for PXD radii • Beam Gas < Touschek for SVD radii Synchrotron radiation 1 st observation (PXD, SVD, FANGS) • X-rays in 8-15 keV range - • Not well reproduced in simulation • Not seen in PLUME 15 BEAST results on beam Background at SuperKEKB: PLUME focus - J. Baudot - PIXEL 2018
Sinlge-Beam background findings PLUME preliminary Comparison to simulation Touschek DATA/MC • Dedicated beam simulation (SAD) + GEANT 4 • Relative rates (r, f ) OK • LER rates reproduced within a factor 5-20 • HER rates not reproduced reasonably Under investigation Beam Gas DATA/MC 16 BEAST results on beam Background at SuperKEKB: PLUME focus - J. Baudot - PIXEL 2018
Luminosity background ? Luminosity background Mostly e from interaction point (IP) at low momentum (< 50 MeV) • • p T > 15 MeV to reach PLUME (5 cm radius) “Tracking” with PLUME double -sided feature • Associate nearest hits on both sides pointing to IP • Bending & low p => dR< few mm & f ~ p /2 associated rejected dR Projected view 2 mm dR Outer side f PLUME Beam axis Inner side 17 BEAST results on beam Background at SuperKEKB: PLUME focus - J. Baudot - PIXEL 2018
Luminosity background in MC dR f 200 ms of Two Photon simulation Projected view f (Rad) Combinatorial • Ultra-dominant in real data Selections • Sensors nearest IP along beam axis • -2.0 < f < 1.4 Rad • dR < 2 mm Efficiency on total # particles from luminosity background = (5 1) 10 -3 18 BEAST results on beam Background at SuperKEKB: PLUME focus - J. Baudot - PIXEL 2018
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