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					                                      φ
                   Measurement of sin2φ1

   Stephen L.Olsen
        U. of Hawaii
                                                                    LP01
                                                                    Rome




               Representing the Belle Collaboration
July 23-28, 2001             LP01, Rome   The Belle Collaboration
               The Belle Collaboration




A World-Wide Activity Involving 50 Institutions

 July 23-28, 2001       LP01, Rome   The Belle Collaboration
              The Belle Collaboration




                   ~300 Authors

July 23-28, 2001       LP01, Rome   The Belle Collaboration
                       Outline

!      Introduction
!      KEKB/Belle performance
!                          φ
       Measurement of sin2φ1
!      Results & conclusions


    July 23-28, 2001      LP01, Rome   The Belle Collaboration
        CPV ala Kobayashi-Maskawa
CPV due to complex phases in the
Quark generation mixing matrix:

             d '  VudVusVub  d 
                               
             s '  = VcdVcsVcb  s 
             b'  V V V  b 
               td ts tb  
  Usually put in the Vtd and Vub corners
July 23-28, 2001        LP01, Rome   The Belle Collaboration
           sin2φ1 from B→fCP + B↔B→fCP interf.
               φ
Sanda, Bigi & Carter:
                            Vcb
                                            ψ
                                          J/ψ

   B0
                                             KS
                      +                                      ∝V*2
                                                               td

             V*       Vtb
                                            ψ
                                          J/ψ
              td

   B0                       B0
                Vtb   V*
                       td
                                              KS
   July 23-28, 2001          LP01, Rome   The Belle Collaboration
                    Mixing-induced CPV asymmetry
                                                            ±1
                                             ξf= ±1 for CP= ±




                   B0
                                                  PDG notation!
                              B0




                                         t
July 23-28, 2001            LP01, Rome       The Belle Collaboration
                     What do we measure?
                                 Flavor-tag decay
                                   (B0 or B0 ?)
                                                                        ψ
                                                                      J/ψ
            e+                                                                   fCP
 e−
                               t=0                                          KS
                                             ∆z
B-B
                                      more B’s
B+B                                                              t ≈ ∆z/c β γ
                    more B’s
                                               (1-2w)sin2φ1
                                             = = (1-2w)sin2φ
                                                                            1
 July 23-28, 2001               LP01, Rome        The Belle Collaboration
               Previous result (using 10.5 fb-1)
                               +0.32     +0.09
             φ
         sin2φ1 = 0.58         −0.34     −0.10



                                           Today:
                                        Results from
                                          29.1 fb-1
                                       4x more events


July 23-28, 2001          LP01, Rome   The Belle Collaboration
                    What’s needed?
• Lots of B mesons     (Br (B→fCP) ~ 10−3)
  – very high Luminosity      ⇒      KEKB
• Find CP eigenstate decays
                  4π
  – high quality ~4π detector ⇒ Belle
• Tag other B’s flavor
  – good particle id
• Measure decay-time difference
  – Asymmetric energies
  – good vertexing (@KEKB: γ β cτ≈200µm)
                                τ    µ

 July 23-28, 2001       LP01, Rome    The Belle Collaboration
                                 KEKB asymmetric e+e− collider
                       )



                                    TSUKUBA Area (Belle)
                      ER




                                                                                                   •Two separate rings




                                                                       Hi r Ele
                 (L




                                                                        fo
                                                                         gh c
                  g
               in




                                                                                                      e+ (LER) : 3.5 GeV




                                                                            En tron
       itr y R




                                       HER     LER




                                                                               er
     os erg




                                                                                  gy
          on




                                    Interaction Region
                                                                                                      e− (HER) : 8.0 GeV
  rP n




                                                                                     R
fo w E




                                                                                         in
                                                                                         g
  Lo




                                                                                          (H
                                                                                                   •ECM : 10.58 GeV at Υ(4S)




                                                                                              ER
                                                                                               )
                                                                                                   •Luminosity

                                                                               WIGGLER


                                                                                         RF
                      RF
      WIGGLER




                       NIKKO Area                                                        OHO Area
                                                                                                      •target:  1034 cm-2s-1
                                                                                         RF
                      RF




                                    (TRISTAN Accumulation Ring)
                                                                                                      •achieved:4x1033cm-2s-1
                           HE
                                                                                                   •±11 mrad crossing angle
                                                                      R
                                                           e
                                                              +

                                                                  LE




                             R   Electron
                                                             /e




                                                Positron
                                                                  -




                                                                                                   •Small beam sizes:
                                                                                                    σy ≈3 µm; σx ≈ 100 µm
                                                                      Li




                                               RF
                                                                       na




                                    RF FUJI Area
                                                                           c




                July 23-28, 2001                                                LP01, Rome             The Belle Collaboration
                     KEKB performance

                           225pb-1/day→
               Integrated luminosity/day


                                    32.8fb-1→
              Total accumulated luminosity




July 23-28, 2001             LP01, Rome    The Belle Collaboration
             Average luminosity during run


                     〉
                   〈L〉=3.5x1033/cm2s




                   All-time Lpeak = 4.5x1033/cm2s
July 23-28, 2001               LP01, Rome   The Belle Collaboration
             KEKB’s Special Features
• Small beam sizes ⇒ low beam currents
   – 4.5x1033 with less than 1 Amp in each ring
• ± 11 mrad beam crossing angle


                                        22mrad
      e+                                e-
   – No bending magnets near the IR
   – Fewer spent particles into Belle
   – Synchrotron X-rays easily expelled

 July 23-28, 2001          LP01, Rome      The Belle Collaboration
                 Detector Performance
" Silicon Vertex Detector
          µ
  " σ ~ 55µm for 1GeV/c @ 90o
" Central Drift Chamber
  "     σp/p ~ 0.35% @ 1GeV/c
  "                   %
        σπ (dE/dx) ~ 7%
" K± id up to plab=3.5 GeV/c
         σ ∼95
  " TOF (σ ∼ ps)
  " Aerogel (n = 1.01 ~ 1.03)
" γ, e± with CsI crystals
  " σE/Eγ ~ 1.8% @ 1GeV
" KL and µ± with KLM (RPCs)
  " µ± : effic. > 90% ; ~2% fakes
   July 23-28, 2001         LP01, Rome   The Belle Collaboration
                  KEKB/Belle summary
• World record luminosity
  – ~10 B mesons/sec
• Backgrounds are tolerable:
  – SVD occupancy < 4%
  – CDC inner layer occupancy < 10%
  – CsI pedestals endcap < 1MeV; barrel <500keV
• Headroom for improvement:
  – Plans: Lum ⇒ 1034 ;               rIPpipe 2.0 ⇒ 1.5 cm

   July 23-28, 2001      LP01, Rome       The Belle Collaboration
               B#CP Eigenstate Decays

Use ~all low-background ccK0 modes

             ψ
 BCP → J/ψ KS(→π+π− & π0π0)
                  →π
           ψ(2S)(→l+l− & J/ψπ+π−) KS
                 →         ψπ
    odd χc1(→J/ψγ KS
                                                              ξ f =-1
 P                ψγ)
               → ψγ
C
           ηc(→KSK+π−, K+K−π0) KS
              →
             ψ
         n J/ψ KL
      ve                                                      ξ f=+1
C P e      J/ψ K*0 (→KSπ0) (mostly)
             ψ      →

 July 23-28, 2001      LP01, Rome   The Belle Collaboration
                      Golden mode:          ψ
                                     B0 → J/ψ Ks(→π+π− )

                          ψ→µ
                        J/ψ→µ+µ−
                          ψ→
                                                                 Ks→π+π−

        σ~10MeV/c2                           σ~4MeV/c2                   Belle


                          ψ→e
                          ψ→
                        J/ψ→ +e−
        σ~11MeV/c2



Biggest contributor to the                   fcp event sample
   July 23-28, 2001             LP01, Rome     The Belle Collaboration
                           ψ
                    B0 → J/ψ KS(→π+π− ) (cont’d)
                                →π


 457 events
 ~3% bkgd

Energy difference:
∆E ≡ E J /ψ + EK S − ECM 2
Beam-constrained mass:
                            r        r 2
mbc = ( ECM          2) − ( p J /ψ + pK S )
                       2



 July 23-28, 2001                LP01, Rome   The Belle Collaboration
         For B→J/ψKS; use KS#π0π0
              → ψ            π




 Total events = 76
Bkgd ≈ 9 evts (12%)



                                   Mbc
 July 23-28, 2001     LP01, Rome   The Belle Collaboration
             Other charmonium modes



                             χc1
                                                1st observation
                                  χc2             of inclusive
                                                     B# χc2 X

                   M(l+l−γ) − M(l+l−)

July 23-28, 2001             LP01, Rome   The Belle Collaboration
                    All CP-1 modes

B0 → other modes                                         Belle
 290 candidates
 46 background
 (Purity = 84%)

B0 → J/ψ Ks(→π+π− )
       ψ
  457 candidates
  ~12 background
  (Purity = 97%)
 July 23-28, 2001     LP01, Rome   The Belle Collaboration
                              ψ
                       B0 → J/ψ KL

     ψ
1) J/ψ →l+l− + KL
2) Assume B#J/ψ KL:ψ
     compute PKL
3) Remove reconstructed
          ψ       ψ
   B → J/ψ K, J/ψ K*, …
4) Cut on a likelihood
   based on kinematical
   and shape quantities
5) Plot P* =|P J/ψ + PKL|
         B       ψ




    July 23-28, 2001        LP01, Rome   The Belle Collaboration
                            ψ
                     B0 → J/ψ KL signal yield

                                                                     Belle
                                          Nsig = 346 events
P* =| PJ/ψ + PKL|
 B
       *ψ     *


                                               Nbkg = 223 evts
       ψ
B0 → J/ψ KL
569 total events
  346 signal
(Purity = 61%)
                                                          PB(cms)

  July 23-28, 2001           LP01, Rome    The Belle Collaboration
          Flavor-tag the other B meson
 Use inclusive flavor-specific properties:
!Inclusive Leptons:
   !high-p l−       b# c l− ν
   !intermed-p l+         s l+ ν
!Inclusive Hadrons:
   !high-p π−       B0#D(*)+ π−, D(*)+ ρ−, etc.
   !intermed-p K−           K− X,        π−π0
   !low-p π+                 D0 π +

  Also need to consider correlations
  July 23-28, 2001    LP01, Rome   The Belle Collaboration
          2-level Multi-dimensional flavor tagging




                                              q = +1 ⇒ Btag
                                              q = −1 ⇒ Btag
                                               r=(1-2w)MC


July 23-28, 2001         LP01, Rome   The Belle Collaboration
         Determination of wrong tag fraction wl




get w from B⇔B⇔
mixing amplitude:
 (1-2wl)cos(∆md ∆t)
            ∆




 July 23-28, 2001     LP01, Rome   The Belle Collaboration
          Multi-dimensional Flavor Tagging

• Uses all events
  – Efficiency > 99%




                                      1-2wl
      ε effective = 27.0 ± 1.2%
• Includes correlations
• Use MC-r as a classifier
• Use data-w for CP fits                                          r

MC-determined r ≈ 1-2w measured from data

  July 23-28, 2001       LP01, Rome           The Belle Collaboration
               Vertex Reconstruction
                        ψ
• For CP-side, use J/ψ#l+l−
   – Reject poorly fit events.
     δzCP ≈ 75 µm (rms)
• For Tag-side
   – use well fit tracks
   – iterate: discard worst track
   – δztag ≈ 140 µm (rms)
• Require |zCP - ztag|<2mm (≈10τB)
                            ≈
  σ ∆t ≈ 1.5 ps
• Tails ≈ 3%; Effic. ≈ 85%
                  1137 evts used in the CP fit.
    July 23-28, 2001         LP01, Rome   The Belle Collaboration
                   Validation: B lifetimes
                   B#D*lν




         τB0 = 1.55 ± 0.02ps             τB+ = 1.64 ± 0.03ps
         PDG: 1.55 ± 0.03ps              PDG: 1.65 ± 0.03ps
July 23-28, 2001            LP01, Rome       The Belle Collaboration
                            Timeline
•   July 6:            end Y(4S) running
•   July 9:            finish data processing
•   July 11:           find wl’s
•   July 12:           Open the box!!
•   July 13:           PRL draft # Collab
•   July 18:           PRL submitted
•   July 23:           Announce results

    July 23-28, 2001           LP01, Rome   The Belle Collaboration
                       Combine q, ξf & ∆t

                   raw data




July 23-28, 2001              LP01, Rome   The Belle Collaboration
CP is violated in B decays!!
      •Large effect
      •Apparent in the raw data
      •Many σ
 July 23-28, 2001   LP01, Rome   The Belle Collaboration
          Event-by-event Likelihood




July 23-28, 2001    LP01, Rome   The Belle Collaboration
              Event-by-event Likelihood


                                                     resolution function
                                 From
background frac.                                     B-lifetime studies
                            Sidebands & MC
                                               b-flavor tag
                              PDG




                                  free              wrong-tag frac.
        ξf= ±1 for CP= ±1       parameter
    July 23-28, 2001           LP01, Rome    The Belle Collaboration
               sin2φ1 value that maximizes Πi Li
                   φ

        φ
    sin2φ1 = 0.99 ± 0.14 (stat) ±0.06(sys)
       B
   NB−NB
ξf N +N
    B




                                                      curve from
 weighted by
 CP sensitivity
                                                     unbinned fit
  July 23-28, 2001         LP01, Rome   The Belle Collaboration
          Do the fits & errors make sense?
         Use toy MC: run 1K similar expts
our                    φ
              with sin2φ1 (input)=0.99
        -0.14                                                      +0.14
fit:
                               low-side     high-side
                                 error        error




Toy MC                                              +0.116
                      -0.128
means:
   July 23-28, 2001                   LP01, Rome   The Belle Collaboration
                    Compare CP –1 and CP+1

                                         CP-1
                                                               φ
                                                           sin2φ1

                                                            ±
                                                        0.84±0.17
NB+NB
NB−NB




                                        CP+1             opposite!

                                                            ±
                                                        1.31±0.23

                                                          (statistical
                                                         errors only)

 July 23-28, 2001          LP01, Rome   The Belle Collaboration
      Control sample: B0→non-CP states

                                  ψ
use: B0#D(*)−π+, D*−ρ+, D*−l+ν, J/ψK*(K+π−)
            −      −      −



                                                     φ
                                                “sin2φ1”
                     ~17K events

                                                    ±
                                                0.05±0.04


                                                  (statistical
                                                  error only)

July 23-28, 2001    LP01, Rome   The Belle Collaboration
              φ
          sin2φ1 from various subsamples




  +
q=+1 560 evts
  −
q=−1 577 evts


                                                (statistical
                                                 errors only)
July 23-28, 2001     LP01, Rome   The Belle Collaboration
          CP fit : Systematic Error

                   Vertex algorithm          ±0.04
                   Flavor tagging            ±0.03
                   Resolution function       ±0.02
                   KL background fraction ±0.02
                   Background shapes         ±0.01
                   ∆md and τB0 errors        ±0.01
                   Total                     ±0.06


July 23-28, 2001                LP01, Rome   The Belle Collaboration
            Compare with CKM constraints
                                             σ
                                    Belle’s 1σ band
                                       (both sol’ns)




July 23-28, 2001       LP01, Rome    The Belle Collaboration
         Compare with constraints (cont’d)




                          e s al
                       lu t r
                   v a cen
                                        1σ


                      lle
                                                    95%

                   Be

      Ciuchini et al     1σ
                           95%




July 23-28, 2001           LP01, Rome        The Belle Collaboration
                    Conclusions
$CP is violated in B decay                             σ!!
                                                     >6σ!!

      φ
$sin 2φ1 is large:
0.99 ± 0.14 ± 0.06

  >0.7 @ 95%CL

 July 23-28, 2001        LP01, Rome   The Belle Collaboration
      Compare with other experiments




July 23-28, 2001   LP01, Rome   The Belle Collaboration
                   Variations on a theme
                                      ±
          Old data; old analysis: 0.58±0.33
                                      ±
          Old data; new analysis: 0.54±0.34
                                      ±
          New data; new analysis: 1.06±0.14

  Allow ∆md to float            φ
                            sin2φ1       ∆md (PDG:0.472)
                               ±          ±
                           1.00±0.14 0.478±0.057 ps-1

      Allow τB0 to float         φ
                             sin2φ1      τΒ0 (PDG:1.550
                               ±         ±
                           1.00±0.14 1.66±0.07 ps

July 23-28, 2001            LP01, Rome    The Belle Collaboration

				
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