Peter Križan, Ljubljana Oct. 18, 2006Seminar, SLAC Peter Križan University of Ljubljana and J. Stefan Institute Rare decays at Belle

Peter Križan, Ljubljana Oct. 18, 2006Seminar, SLAC KEK-B in Tsukuba ~diameter 1 km Tsukuba-san KEKB Belle

Peter Križan, Ljubljana Oct. 18, 2006Seminar, SLAC Belle spectrometer at KEK-B Aerogel Cherenkov Counter (n= ) Electromag. Cal. (CsI crystals, 16X 0 ) ToF counter 1.5T SC solenoid Silicon Vertex Detector (4 layers DSSD)  and K L detection system (14/15 layers RPC+Fe) Central Drift Chamber (small cells, He/C 2 H 6 ) 8 GeV e GeV e + Accumulated data sample >600 M BB-pairs

Peter Križan, Ljubljana Oct. 18, 2006Seminar, SLAC Contents FCNC b  s decays b  s  : CP violation Measurement of A fb vs q 2 in B  K * l + l - decays Decays with >1 neutrino Purely leptonic decay: B -      B  K (*)  Upgrade plans PID in the forward region

Peter Križan, Ljubljana Oct. 18, 2006Seminar, SLAC Why FCNC decays? Flavour changing neutral current (FCNC) processes (like b  s, b  d) are fobidden at the tree level in the Standard Model. Proceed only at low rate via higher-order loop diagrams. Ideal place to search for new physics.

Peter Križan, Ljubljana Oct. 18, 2006Seminar, SLAC B  X s  CP Asymmetry Sensitive to NP – right handed currents Theoretically clean. Standard Model “~Zero”. –  is polarized, and the final state is almost flavor specific. –Helicity flip of  suppressed by ~m s /m b  S ~ 0.02 –QCD corrections  S remains small (Grinstein, Pirjol, PRD ; Matsumori, Sanda, PRD ) Time dependent CPV requires vertex reconstruction with K S   +  - C7C7 mbmb mbmb msms msms     IP profile B vertex   Vertex recon. eff. at Belle 51% (SVD2), 40% (SVD1)  K S trajectory

Peter Križan, Ljubljana Oct. 18, 2006Seminar, SLAC B 0  K S  0  time dependent CPV M(K S  0 ) < 1.8GeV/c 2 –NP effect is independent of the resonance structure. Belle: data sample 535MBB Three M(K S  0 ) regions(MR1: GeV/c2, MR2: , MR3: rest with M<1.8GeV/c 2 ) , , events in MR1,2,3. Atwood, Gershon, Hazumi, Soni, PRD71, (2005) All events: S= -0.10±0.31±0.07 A= -0.20±0.20±0.06 Good tag (0.5<r<1.0)

Peter Križan, Ljubljana Oct. 18, 2006Seminar, SLAC B 0  K S  0  time dependent CPV A cp mix (B  K* , K*  K S  0 ) 50ab -1 5ab -1 Results: Belle (275M BB) hep-ex/ S(B  K* , K*  K S  0 )=-0.01 ± 0.52 ± 0.11 S(B  K S  0  )=0.08 ± 0.41 ± 0.10 BaBar (232M BB) PRD 71 (2005) S(B  K* , K*  K S  0 )=-0.21±0.40 ±0.05 Belle (535M BB) hep-ex/ S(B  K* , K*  K S  0 )= ± 0.05 S(B  K S  0  )=-0.10 ± 0.31 ± 0.07 Prospects: Add more modes: B  K S  (with angular analysis), higher K resonances, B  K S  (recent observation by BaBar), A cp dir (B  X s  )

Peter Križan, Ljubljana Oct. 18, 2006Seminar, SLAC A cp (B  X s  ) vs SUSY models mSUGRA tan  =30 U(2) tan  =30 SU(5)+ R tan  =30 degenerate SU(5)+ R tan  =30 non-degenerate mSUGRA tan  =30 U(2) tan  =30 SU(5)+ R tan  =30 degenerate SU(5)+ R tan  =30 non-degenerate Mixing CPV Direct CPV A cp dir A cp mix 50ab -1 T. Goto, Y.Okada, Y.Shimizu,T.Shindou, M.Tanaka hep-ph/ , also in SuperKEKB LoI 5ab -1

Peter Križan, Ljubljana Oct. 18, 2006Seminar, SLAC B  K * l + l - Important for further searches for the physics beyond SM C i : Wilson coefficients

Peter Križan, Ljubljana Oct. 18, 2006Seminar, SLAC Particularly sensitive: forward-backward asymmetry in K * l + l B K*K* ll ll  Forward event B K*K* ll ll  Backward event [γ* and Z* contributions in B  K * l l interfere and give rise to forward-backward asymmetries c.f. e + e -   +  - ]

Peter Križan, Ljubljana Oct. 18, 2006Seminar, SLAC Sample used for A FB (B  K*ll)(q 2 ) Sample for B  K* l l: 113±13 events Treat q 2, cos(θ) dependence of bkgs. PRL 96, (2006) Unbinned fit to the variables q 2 (di-lepton invariant mass) and cos(θ) for the B  K * l l data. Fit parameters A 9 /A 7 and A 10 /A 7 (A i = leading term in C i )

Peter Križan, Ljubljana Oct. 18, 2006Seminar, SLAC Control sample B  Kll B  K l l control sample: 96±12 events Consistent with 0 Integrated asymmetry:

Peter Križan, Ljubljana Oct. 18, 2006Seminar, SLAC Constraints on Wilson coefficients from A FB (B  K * l l)(q 2 ) Observed integrated A FB rules out some radical New Physics Models with incorrect signs/magnitudes of C 9 and C 10 (red and pink curves) Projections of the full fit to q 2, cos(θ) Integrated FB asymmetry  J/  ’ BaBar: A FB > % CL)

Peter Križan, Ljubljana Oct. 18, 2006Seminar, SLAC Best fit SM A 9 /A 7 A 10 /A 7 Results of the unbinned fit to q 2 and cos(θ) distributions for ratios of Wilson coefficients ＳＭ A 9 /A 7 A 10 /A 7 at 95% C.L. |A 7 | constrained from b  s  to be close to SM

Peter Križan, Ljubljana Oct. 18, 2006Seminar, SLAC A FB (B  K* l + l - )[q 2 ] at Super B Factory  A FB zero-crossing q 0 2 will be determined with 5% error with 50ab -1 Precision with 5ab -1  C 9 ~ 11%  C 10 ~14%  q 0 2 /q 0 2 ~11% q02q02

Peter Križan, Ljubljana Oct. 18, 2006Seminar, SLAC Purely leptonic decay B   Challenge: B decay with at least two neutrinos Proceed via W annihilation in the SM. Branching fraction Provide information of f B |V ub | –|V ub | from B  X u l f B cf) Lattice –Br(B   )/  m d |V ub | / |V td | Expected branching fraction |V ub | = (4.39 ± 0.33)×10 -3 (HFAG) f B = (216 ± 22) MeV (lattice) BF(B    ) = (1.59 ± 0.40)×10 -4

Peter Križan, Ljubljana Oct. 18, 2006Seminar, SLAC Charged Higgs contribution to B   H/WH/W  Br(SM) ~ 1.59 x  0 = SUSY corrections to b Yukawa coupling ~

Peter Križan, Ljubljana Oct. 18, 2006Seminar, SLAC Full Reconstruction Method Fully reconstruct one of the B’s to –Tag B flavor/charge –Determine B momentum –Exclude decay products of one B from further analysis Υ(4S) e  (8GeV) e+(3.5GeV) B B  full reconstruction B  D  etc. (0.1~0.3%) Offline B meson beam! Decays of interest B  X u l, B  K  B  D ,  Powerful tool for B decays with neutrinos

Peter Križan, Ljubljana Oct. 18, 2006Seminar, SLAC Fully reconstructed sample Belle (447M BB)  4.12x10 5 B 0 B x10 5 B + B -  SLAC seminar by Ilija Bizjak, Nov 2005

Peter Križan, Ljubljana Oct. 18, 2006Seminar, SLAC Event candidate B -     

Peter Križan, Ljubljana Oct. 18, 2006Seminar, SLAC B    decay modes –Cover 81% of  decays –Efficiency 15.8% Event selection –Main discriminant: extra neutral ECL energy Submitted to PRL, hep-ex/ Fit to E residual  signal events.  3.5 σ significance including systematics -4.7 Obtained E ECL

Peter Križan, Ljubljana Oct. 18, 2006Seminar, SLAC Consistency Check with B  D * l Extra neutral energy E ECL validation with double-tagged sample (control sample): –B tag is fully reconstructed –B sig is a semileptonic decay B +  D (*)0 X + (full reconstruction) B -  D *0 B -  D *0 l - D 0  D 0  0 K -  + K -  + K -  +  -  + K -  +  -  + B+B-B+B- 494  18 B0B0B0B0 7.9  2.2 Total 502  18 Data458 Purity ~ 90% Extra energy in the calorimeter Calibration data

Peter Križan, Ljubljana Oct. 18, 2006Seminar, SLAC B   yields broken down by  decay mode For all modes, the background is fitted with a 2 nd order polynomial plus a small Gaussian peaking component. (stat sign. only) MC studies: small peaking bkg in the    0 and    0 modes.

Peter Križan, Ljubljana Oct. 18, 2006Seminar, SLAC B     Product of B meson decay constant f B and CKM matrix element |V ub | Using |V ub | = (4.39 ± 0.33)×10 -3 from HFAG First measurement of f B ! f B = (216 ± 22) MeV (an unquenched lattice calc.) [HPQCD, Phys. Rev. Lett. 95, (2005) ] 15%15% = 13%(exp.) + 8%(V ub )

Peter Križan, Ljubljana Oct. 18, 2006Seminar, SLAC Impact of B -      Use BF(B    ) with  m d  constraint in the  plane

Peter Križan, Ljubljana Oct. 18, 2006Seminar, SLAC Charged Higgs limits from B -      If the theoretical prediction is taken for f B  limit on charged Higgs mass vs. tan  r H =1.13  0.51

Peter Križan, Ljubljana Oct. 18, 2006Seminar, SLAC B   prospects Expected precision at Super-B –13% at 5 ab -1 –7% at 50 ab -1 Search with D (*) l tag will help.  BaBar 232M BB PRD 73 (2006) –Tag eff ~ 1.75 x –Signal selection eff. ~31% –Similar S/N to Belle (full recon. sample)

Peter Križan, Ljubljana Oct. 18, 2006 Future Prospects: B   95.5%C.L. exclusion boundaries rHrH 50ab -1 If  |V ub | = 0 &  f B = 0 (for BF obs = BF SM )

Peter Križan, Ljubljana Oct. 18, 2006Seminar, SLAC B  K (*) B  K (*) is a particularly interesting and challenging mode (with B  τν as a small background), theoretically clean Experimental signature: B  K + nothing The “nothing” can also be light dark matter with mass of order 1 GeV. Direct dark-matter searches cannot see the M<10 GeV region. SM prediction for B +  K + : ( ) x B  τν analysis is a proof that such a one prong decay can be studied at a B factory Present limits: BaBar (89M BB): BF(B +  K + νν ) < 52 x PRL 94 (2005) Belle (277M BB): BF(B +  K + νν ) < 36 x hep-ex/

Peter Križan, Ljubljana Oct. 18, 2006Seminar, SLAC SM: BF(B  K * ) ~1.3 x (Buchalla, Hiller, Isidori) BSM: New particles in the loop PRD 63, Other weakly coupled particles: light dark matter Motivation for B  K * (b  s with 2 ’s)

Peter Križan, Ljubljana Oct. 18, 2006Seminar, SLAC The experimental signature is B  K + Nothing The “nothing” can also be light dark matter (mass of order (1 GeV)) DAMA NaI 3  Region CDMS 04 CDMS 05 Direct dark-matter searches cannot see M<10 GeV region C. Bird et al PRL Motivation for B  K * - 2

Peter Križan, Ljubljana Oct. 18, 2006Seminar, SLAC Search for B  K * (at 90% C.L) Extra Calorimeter Energy (GeV) (1.7σ stat. significance) Sideband = 19 MC expectation = 18.7  3.3 SM (Buchalla, Hiller, Isidori) 1.3 x BELLE-CONF x 10 6 B Bbar pairs

Peter Križan, Ljubljana Oct. 18, 2006Seminar, SLAC π+π+ K- γ Tag Side B  D + a 1 - D +  K - π + π + a 1 -  ρ 0 π -, ρ 0  π + π - Event display for a B  K * candidate due to an identified background (B  K * γ) (Hard photon is lost in the barrel-endcap calorimeter gap) Missing mass ~ 0 MC: Expected bkg from this source ~0.3 evts.

Peter Križan, Ljubljana Oct. 18, 2006Seminar, SLAC B -  K -  prospects MC extrapolation to 50 ab -1 Observation of B ±  K ±  55 Fig. from SuperKEKB LoI Extra EM calorimeter energy SM prediction: G.Buchalla, G.Hiller, G.Isidori (PRD )

Peter Križan, Ljubljana Oct. 18, 2006Seminar, SLAC Summary Radiative, electroweak and tauonic B decays are of great importance to probe new physics. We are starting to measure B  , K, D , A FB (K*ll), A CP (K    ) etc. at the current B factories.  Hot topics in the coming years ! For precise measurements, we need a Super-B factory!  Observe K (*), zero crossing in A FB, D (*)   Expected precision (5ab -1  50ab -1 ); –Br(  ):13%  7% –Br(D (*)  ):7.9%  2.5% –q 0 2 of A FB (K*ll):11%  5% –A CP (K    ) tCPV:0.14  0.04  Substaintial upgrade of the detector is mandatory

Peter Križan, Ljubljana Oct. 18, 2006Seminar, SLAC Belle Upgrade for Super-B SC solenoid 1.5T New readout and computing systems CsI(Tl) 16X 0  pure CsI (endcap) Aerogel Cherenkov counter + TOF counter  “TOP” or DIRC + Aerogel RICH Si vtx. det. 4 lyr. DSSD  2 pixel/striplet lyrs. + 4 lyr. DSSD Tracking + dE/dx small cell + He/C 2 H 5  remove inner lyrs. fast gas+Si r<20 cm  / K L detection 14/15 lyr. RPC+Fe  tile scintillator

Peter Križan, Ljubljana Oct. 18, 2006Seminar, SLAC Belle upgrade – side view Two new particle ID devices, both RICHes: Barrel: TOP or focusing DIRC Endcap: proximity focusing RICH

Peter Križan, Ljubljana Oct. 18, 2006Seminar, SLAC PID upgrade in the endcap improve K/  separation in the forward (high mom.) region for few-body decays of B mesons good K/  separation for b -> d , b -> s  improve purity in fully reconstructed B decays low momentum ( Kll) keep high the efficiency for tagging kaons

Peter Križan, Ljubljana Oct. 18, 2006Seminar, SLAC Proximity focusing RICH in the forward region K/  separation at 4 GeV/c  c (  ) ~ 308 mrad ( n = 1.05 )  c (  )–  c (K) ~ 23 mrad d  c (meas.) =   ~ 13 mrad With 20mm thick aerogel and 6mm PMT pad size  6  separation with N pe ~10

Peter Križan, Ljubljana Oct. 18, 2006Seminar, SLAC Beam test: Cherenkov angle resolution and number of photons Beam test results with 2cm thick aerogel tiles: excellent, >4  K/  separation but: Number of photons has to be increased.  NIM A553 (2005) 58

Peter Križan, Ljubljana Oct. 18, 2006Seminar, SLAC How to increase the number of photons? What is the optimal radiator thickness? Use beam test data on  0 and N pe Minimize the error per track: Optimum is close to 2 cm 00 N pe

Peter Križan, Ljubljana Oct. 18, 2006Seminar, SLAC measure overlaping rings  “focusing” configuration How to increase the number of photons without degrading the resolution? normal Radiator with multiple refractive indices

Peter Križan, Ljubljana Oct. 18, 2006Seminar, SLAC Beam tests Clear rings, little background Photon detector: array of 16 H8500 PMTs

Peter Križan, Ljubljana Oct. 18, 2006Seminar, SLAC 4cm aerogel single index 2+2cm aerogel Focusing configuration NIM A565 (2006) 457

Peter Križan, Ljubljana Oct. 18, 2006Seminar, SLAC ● upstream aerogel: d=11mm, n=1.045 ● downstream aerogel layer: vary refractive index ● measured resolution in good agreement with prediction ● wide minimum allows some tolerance in aerogel production Single photon resolution refractive index difference NIM A565 (2006) 457 Focusing configuration – n 2 -n 1 variation

Peter Križan, Ljubljana Oct. 18, 2006Seminar, SLAC Resolution per track Single photon resolution Number of detected photons Multilayer extensions  N pe Multiple layer radiators combined from 5mm and 10mm tiles Cherenkov angle resolution per track: around 4.3 mrad → p/ K separation at 4 GeV better than 5 s

Peter Križan, Ljubljana Oct. 18, 2006Seminar, SLAC BURLE MCP-PMT: ● multi-anode PMT with two MCP steps ● 25  m pores ● bialkali photocathode ● gain ~ 0.6 x 10 6 ● collection efficiency ~ 60% ● box dimensions ~ 71mm square ● 64(8x8) anode pads ● pitch ~ 6.45mm, gap ~ 0.5mm ● active area fraction ~ 52% ●  ~13 mrad (single cluster) ● number of clusters per track N ~ 4.5 ●  ~ 6 mrad (per track) ● -> ~ 4  /K separation at 4 GeV/c MCP-PMT multi-anode PMTs ● Tested in combination with multi-anode PMTs ● 10  m pores required for 1.5T ● collection eff. and active area fraction should be improved ● aging study should be carried out Photon detector candidate: MCP-PMT

Peter Križan, Ljubljana Oct. 18, 2006Seminar, SLAC With the use of a fast photon detector, a proximity focusing RICH counter can be used also as a time-of-flight counter. Cherenkov photons from two sources can be used: ● photons emitted in the aerogel radiator ● photons emitted in the PMT window Cherenkov photons from PMT window Cherenkov photons from aerogel MCP-PMT aerogel track START STOP 2GeV/c p /K: D t ~ 180ps 4GeV/c p /K: D t ~ 45ps Beam tests: study timing properties of such a configuration.  TOF capability

Peter Križan, Ljubljana Oct. 18, 2006Seminar, SLAC Time resolution for Cherenkov photons from the aerogel radiator: 50ps  agrees well with the value from the bench tests Resolution for full ring (~10 photons) would be around 20 ps Distribution of hits on the MCP- PMT (13 channels were instrumented) - left Corrected distribution using the tracking information - left TOF capability: photons from the ring

Peter Križan, Ljubljana Oct. 18, 2006Seminar, SLAC TOF test with pions and protons at 2 GeV/c Distance between start counter and MCP-PMT is 65cm Expected number of detected Cherenkov photons emitted in the PMT window (2mm) is ~15 Expected resolution ~35 ps  TOF capability: window photons

Peter Križan, Ljubljana Oct. 18, 2006Seminar, SLAC Time-of-flight with photons from the PMT window Cherenkov angle aerogel, n=1.05 Aerogel: kaons (protons) have no signal below 1.6 GeV (3.1 GeV): identification in the veto mode. Benefits: Čerenkov threshold in glass (or quartz) is much lower than in aerogel. Window: threshold for kaons (protons) is at ~0.5 GeV (~0.9 GeV):  positive identification possible. Threshold in the window:  K p