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Status of Belle II

Status of Belle II. Introduction E miss measurements (with comments on the upgrade) Inclusive decays (with comments on the upgrade) Neutral final states (with comments on the upgrade) Summary. Boštjan Golob University of Ljubljana/ Jožef Stefan Institute Belle/Belle II Collaboration.

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Status of Belle II

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  1. Status of Belle II Introduction Emiss measurements (with comments on the upgrade) Inclusive decays (with comments on the upgrade) Neutral final states (with comments on the upgrade) Summary BoštjanGolob University of Ljubljana/Jožef StefanInstitute Belle/Belle II Collaboration University of Ljubljana “Jožef Stefan” Institute

  2. Introduction Belle II is an intensity frontier experiment being built at Super-KEKB in Tsukuba, Japan successor of extremely successfull B factories (Belle & BaBar) 2001 2012 With current accuracy deviations from SM still possible at O(10%) Intensity frontier

  3. Introduction Quest for NP..... ...continues Intensity frontier B Factories (BF) → Super B Factory (SBF) Illustrative reach of NP searches • s1/N  O(102) higher luminosity • complementarity to other intensity frontiers • experiments (LHCb, BES III, ....); • accurate theoretical predictions to compare to NP reach in terms of mass Terra Incognita NP flavor violating couplings( 1 in MFV)

  4. Introduction SuperKEKB sx~10mm,sy~60nm sx~100mm,sy~2mm Nano beams design (P. Raimondi) e- e+ ∫L dt [ab-1] b*: beta-function (trajectories envelope) at IP xy: beam-beam parameter ∫L dt=50 ab-1(2022-2023) small by* large xy (by*/ey)  small ey hourglass effect  small bx* increase I ∫L dt=10 ab-1(2018) current B factories L [s-1cm-2] design L=8·1035 s-1cm-2 magnet installation for SuperKEKB; Being built on schedule

  5. Introduction SuperKEKB Belle II e+ New IR New superconducting /permanent final focusing quads near theIP New beam pipe & bellows Replace short dipoles with longer ones (LER) e- Add / modify RF systems for higher beam current Low emittance positrons to inject Redesign the lattices of HER & LER to squeeze the emittance Positron source Damping ring Low emittance gun Low emittance electrons to inject New positron target / capture section TiN-coated beam pipe with antechambers

  6. Introduction Installation of 100 new long LER bending magnets done Installation of HER wiggler chambers in Oho straight section is done. Damping ring tunnel: built!

  7. Introduction Methods and processes where (S)BF can provide important insight into NP complementary to other experiments: Emiss: B(B→tn), B(B → Xctn), B(B → hnn),... Inclusive: B(B → sg), ACP(B → sg), B(B → sll ), ... Neutrals: S(B → KSp0g), S(B → h’ KS), S(B → KSKSKS), B(t→ mg), B(Bs→ gg), ... Detailed description of physics program at SBF in: B. O’Leary et al., arXiv: 1008.1541 A.G. Akeroyd et al., arXiv: 1002.5012

  8. Introduction KL and muon detector: Resistive Plate Counter (barrel outer layers) Scintillator + WLSF + MPPC (end-caps , inner 2 barrel layers) EM Calorimeter: CsI(Tl), waveform sampling (barrel) Pure CsI + waveform sampling (end-caps) Particle Identification Time-of-Propagation counter (barrel) Prox. focusing Aerogel RICH (fwd) electrons (7GeV) Beryllium beam pipe 2cm diameter Vertex Detector 2 layers DEPFET + 4 layers DSSD positrons (4GeV) Central Drift Chamber He(50%):C2H6(50%), small cells, long lever arm, fast electronics

  9. Missing energy Btn, hnn, ... fully (partially) reconstruct Btag; reconstruct h from Bsig→hnnor Bsig→ t(→ hn)n; no additional energy in EM calorim.; signal at EECL~0; Btag full reconstruction: NeuroBayes; TOP detector; ECL, increased background; Missing E (n) Btag Bsig Bsig → tn candidate event approx. expected precision @ 50 ab-1

  10. Missing energy Belle preliminary, arXiv:1303.3719, 711 fb-1 Btn, hnn, ... B(B+ K(*)+nn) can be measured to ±30% with 50 ab-1; limits on right-handed currents -- signal -- background approx. expected precision @ 50 ab-1 SM W. Altmannshofer et al., arXiv:0902.0160

  11. Calorimeter new electronics with 2MHz wave form sampling 2x improved s at 20x bkg. Better suppression of background Belle II full simulation: B0D0p0, D0 p0p0, p0gg DE= EB* - Ebeam fine tuning detector response default g energy after rough calibr. after calibr. and D0 mass fit endcap: pure CsI crystals; (may be staged)

  12. KLM KLandmdetector • Endcaps: • scintillators, two orthogonal • directions in one super-layer • avalanche photo-diode in • Geiger mode (GAPD) • 2 inner barrel layers: • upgrade to scintilators • main backround from KL‘s, better KL efficiency • better background rejection

  13. Inclusive decays • B → sg • direct CPV • Semi-inclusive, sum of many • exclusive states: • all flavor specific final states; • 0.6 GeV Ms 2.8 GeV, Eg  1.9 GeV; • topological continuum event suppression; • explicit p0, h veto; • <D>: average dilution due to • flavour mistag, 1 • DD: difference between • flavour mistag for • b and b, << 1 • Adet: detector induced • asymmetry BaBar, PRL101, 171804(2008),350 fb-1 b → sg b → sg HFAG, ICHEP’10

  14. Inclusive decays B → sg direct CPV Expectations Adet = - 0.007 ± 0.005 Adet: careful study of K/p asymmetries in (p,qlab) using D decays or inclusive tracks from fragmentation; BB, cross-feed background: comparison data control samples/MC; JETSET fragment. from meas.; lots of work, few 10-3 exp. sensitivity LHCb, 5 fb-1 : s(S(yf)) ~0.02 super B fact. sensitivity LHCb sensitivity 5 fb-1 example of overlap region A. Soni et al., PRD82, 033009 (2010) Mt’ 400 GeV 600 GeV SM LHCb, arXiv:0912.4179 (Mt‘ >550 GeV from LHC) extrap. from 337 pb-1: ±0.05 (syst. @ 337 pb-1 ± 0.07)

  15. PID Belle II / Inclusive b →s(+d)g barrel: TOP detector partial Cerenkov ring reconstruction from x, y and t of propagation y x endcap: Proximity focusing Aerogel RICH 200mm Cherenkov photon Belle/Belle II full simulation: B0K*(Kp)g, B0r(pp)g, DE= EB* - Ebeam prototype quartz bar Aerogel radiator n~1.05 Improved PID performance Hamamatsu HAPD

  16. Neutrals t-dependent decays rate of B → fCP; S and A: CP violating parameters B → K* (→KSp0)g t-dependent CPV SM: SCPK*g -(2ms/mb)sin2f1  -0.04 Left-Right Symmetric Models: SCPK*g 0.67 cos2f1  0.5 SCPKsp0g = -0.15 ±0.20 ACPKsp0g = -0.07 ±0.12 HFAG Summer 2012 D. Atwood et al., PRL79, 185 (1997) B. Grinstein et al., PRD71, 011504 (2005) 5 ab-1 HFAG, Summer’12 s(SCPKsp0g)= 0.09 @ 5 ab-1 0.03 @ 50 ab-1 50 ab-1 (~SM prediction)

  17. Vertex detector SVD+PXD PXD+SVD Belle II r [cm] DSSD’s SVD Belle pixels z [cm] z [cm] sBelle Design Group, KEK Report 2008-7 Improved vertex determination accuracy; Improved Ks→p+p-(with phits in PXD+SVD) reconstruction efficiency

  18. Requirements for SBF Requirements • O(102) higher luminosity • complementarity to other intensity • frontiersexperiments (LHCb, • BES III, ....); • accurate theoretical predictions to • compare to Super B factory LHCb K experiments theory uncertainty matches the expected exp. precision B(B →Xsg) 6% Super-B B(B →Xdg) 20% Super-B S(B →rg) 0.15 Super-B B(t→mg) 3 ·10-9 Super-B (90% U.L.) B(B+→Dtn) 3% Super-B B(Bs→gg) 0.25 ·10-6 Super-B (5 ab-1) sin2qW @ U(4S) 3 ·10-4 Super-B theory uncertainty will match the expected exp. precision with expected progress in LQCD Adopted from G. Isidori et al., Ann.Rev.Nucl.Part.Sci. 60, 355 (2010)

  19. Additional material

  20. Introduction Accelerator “B-Factory”,KEKB @ KEK accelerator institute KEKB: e- (HER): 8.0 GeV e+ (LER): 3.5 GeV crossing angle: 22 mrad ECMS=M(U(4S))c2 dNf/dt = s(e+e-→f) L Tokyo (40 mins by Tsukuba Exps) LER e- HER Belle 2010 e+ Ldt = 1020 fb-1 (1.02 ab-1) 1999

  21. Accelerator Accelerator BF,KEKB @ KEK / PEPII @ SLAC b b b Belle Ldt 1020 fb-1 BaBar Ldt550 fb-1 u,d Bd0, B- b Bd0, B+ energ. threshold for BB production U(4S) s(e+e-→hadrons) [nb] “on resonance” production e+e-→ U(4S) → Bd0Bd0, B+B- s(e+e-→ BB)  1.1 nb (~109 BB pairs Belle) u,d f g* f ”continuum” production, qq, ll, tt e- s(e+e-→ c c) 1.3 nb(~1.3x109XcYcpairs Belle) running at Y(nS), e.g. Y(5S) (BsBs) (hadrons) e+ (hadrons)

  22. Accelerator high-current: large I Luminosity: nano-beam: small by* large xy (by*/ey)  small ey hourglass effect  small bx* b*: beta-function (trajectories envelope) at IP small by*[mm]:5.9(LER)/5.9(HER)→ 0.27/0.30 small bx*[mm]:1200(LER)/1200(HER)→ 32/25 small ey: keep current xy 0.101(LER)/0.096(HER) → 0.09/0.09 increase I [A]:1.8(LER)/1.45(HER) → 3.6/2.1 sx~100mm,sy~2mm small e LER: longer bends; HER: more arc cells small b*: separate quadrupoles closer to IP small e, b*: small dynamic aperture, larger Touschek background and smaller tbeam sx~10mm,sy~60nm dynamic aperture: phase space volume of acceptable trajectories; Touschek effect: Coulomb scattering causing transfer of transverse to longitud. momentum between particles in a bunch; if transfer is too large particles are lost

  23. Accelerator Hourglass effect Sx,y*: (sx,y1*2+sx,y2*2) horiz., vertical bunch size @ IP naive luminosity formula: valid if sz << b*x,y; if not  sx,y depending on b*x,y reduction of luminosity; effect: more involved formula b(s) function focusing quad defocusing quad to avoid large hourglass effect (reducing L): sx L sz 2f by*  sz by*  L= sx/f  bx*/f crossing-angle: head-on:

  24. Accelerator Touschek effect In Coulomb scattering between particles in a bunch transverse momentum is transfered to longitudinal one (multiplied by g); if the longitudinal momentum transfer exceeds accelerator momentum acceptance particles are lost; beam current decreases exponentially: Nbunch/sxsysz: particle density in bunch (Dp/p0)acc: momentum acceptance rC: orbit radius for large t: increase (Dp/p0)acc; this also reduces sxsysz but the overall effect on t is positive H. Wiedemann, Particle Accelerator Physics, Springer effect more important for LER

  25. Accelerator dynamic aperture: • high current option: • high operation costs • too low beam-beam parameter • CSR prevents squeezing the beam • difficult to find solution for IR with • low enough b* increasing (bx*,by*) increasing tbeam sx 0 (Dp/p0)acc

  26. Inclusive b →sg Inclusive b →s(+d)g FCNC process; sensitive to NP in loop; experimental challenge: huge background only g reconstructed on signal side g Bsig Xs Btag l±1.26 GeV < E < 2.20 GeV Eg continuum p0 gg h gg b  sg continuum p0 gg h gg b  sg on off b →dgsubtracted Belle, PRL103, 241801, (2008), 605 fb-1 Eg

  27. Inclusive on off Inclusive b →s(+d)g subtract scaled Eg from off-resonance; Belle, PRL103, 241801, (2008), 605 fb-1 main syst. uncertainties: continuum subtraction, g’s from sources other than p0, h s(B)·10-4 0.3 0.2 0.1 b →dgsubtracted expected accuracy on B(B→sg)at Belle II un-tagged (assuming 10% of data at off) Eg s(B)~0.10·10-4 syst. dominated measurement! hadronic tag 5 10 15 20 25 30 35 40 45 50 L[ab-1]

  28. sin2f1 sin2f1 Belle, 710 fb-1, arXiv:1201.4643 f1from B0 → cc K0 Improved tracking, more data (50% more statistics than last result with 480 fb-1); cc = J/y, y(2S), cc1 for KL only cluster (direction) in ECL, KLM; missing info from kinematic constraints; detector effects: wrong tagging, finite Dt resolution, determined using control data samples cc KS cc KL

  29. sin2f1 sin2f1 Belle, 710 fb-1, arXiv:1201.4643 S= 0.667 ± 0.023 ± 0.012 A= 0.006 ± 0.016 ± 0.012 main systematic uncertainties: vertexing, Dt resolution, tag side interf. “bread&butter” of BF; not the main motivation of SBF, but still extremely important s(S) 0.02 0.015 0.01 0.005 “Irreducible” systematic uncertainty decreased by 50% compared to previous estimate s(S)~0.008 expected accuracy on sin2f1 at Belle II 5 10 15 20 25 30 35 40 45 50 L[ab-1]

  30. Btn Nsig=69 ± 21 Btn main syst. is reducible: bkg. ECL shape, e Btag); B(B+→t+n)=(1.80 ± 0.56± 0.26) ∙10-4 BaBar, arXiv: 1008.0104, 350fb-1 B(B+→t+n)=(1.65 ± 0.38± 0.36) ∙10-4 Belle,PRD82, 071101 (2010), 605fb-1 hadronic tag 0.4 0.3 0.2 0.1 s(B)·10-4 Nsig=154 ± 36 expected accuracy on B(B+→t+n) at Belle II, semileptonic tag semilept. tag 5 10 15 20 25 30 35 40 45 50 L[ab-1] including hadronic tag,s(B)~0.06·10-4

  31. t → m g simplified (1D) toy MC UL90% B(t → m g) [10-8] 4 2 1 0.4 0.2 Search for t → m g  1/L w/o polarization: UL90%(B(t → m g))  3x10-9 @ 50 ab-1 w/polarization: factor ~(2-3)x better sensitivity decays t→ 3l, l h0 background free UL90%(B(t → m g))   1/ L to ~10ab-1 B(t → m g)<4.4 ·10-8 Updated expected sensitivities  1/√L 0.2 1 10 L[ab-1] t → m g t → mmm t → mh Belle, PLB66, 16 (2008), 535 fb-1 K. Inami, PANIC 2011

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