1. Super flat IR beam pipe Super B Factory WS in Hawaii Jan. 22, 2004 Hidekazu Kakuno (TIT) Hitoshi Ozaki & Nobu Katayama (KEK)

2. Jan. 22, 2004 H.Kakuno, H. Ozaki & N. Katayama 2 Outline Motivation Super flat geometry Simulation method Simulation results –Vertexing and B/D separation –B s – B s mixing parameter measurement –B  D  branching fraction measurement Issues and conclusions

3. Jan. 22, 2004 H.Kakuno, H. Ozaki & N. Katayama 3 Single B samples It’s been discussed that many interesting measurements require “single B event” samples –B  K –B  ,  B s   –B  D  –b  ul and other inclusive measurements –…

4. Jan. 22, 2004 H.Kakuno, H. Ozaki & N. Katayama 4 B reconstruction at  (4S) At B factories we can identify (reconstruct) only much less than 1% of the actual B decays. This is because –B has many decay modes, and D has many decay modes –Average multiplicity of the B decay is 5~6 charged, 3 neutral  Lots of combinatorial backgrounds  Combinatorial background can be reduced using topological information on tracks (combinations) –Continuum backgrounds as well (ccbar for B  D and uds for non-charm decays)

5. Jan. 22, 2004 H.Kakuno, H. Ozaki & N. Katayama 5 Standard Vertex Resolution Thickness of the material before the first measurement  ~1mm (Au/Ag + Be + Si + …) Distance between the vertices and the first measurements  minimum 2~3 cm Resolution of the first measurement  7~30  m   X,  Z : 80~100  m (  Y:20  m  IP profile + B flight length) Solid angle coverage of the first measurements  ~92%

6. Jan. 22, 2004 H.Kakuno, H. Ozaki & N. Katayama 6 Super Vertexing If the error in the vertex measurement,  z were less than 10  m, it helps in doing –B reconstruction We can separate B, Bbar, D and Dbar vertices, we can greatly reduce the combinatorial and continuum background and identify many B decays –Continuum separation –Measurements of some decays such as B  D  Reconstruct momentum vector using two vertices –B s – B s mixing measurements; even for X>15

7. Jan. 22, 2004 H.Kakuno, H. Ozaki & N. Katayama 7 B  D  reconstruction IP profile + D direction  B vertex B vertex +  vertex (helix ext.) +  mass   momentum (and the entire  kinematics): 0c-fit Make missing mass of the  from B Lots of combinatorial backgrounds but measure Br. without full B reconstruction tag D  B IP profile

8. Jan. 22, 2004 H.Kakuno, H. Ozaki & N. Katayama 8 Much more difficult as we cannot measure the B decay vertex IP profile + 2  vertex (helix ext.) + 2  mass  B vertex (and the entire  kinematics): 0c-fit –Or + vertex of the other B to get V x : 1c-fit  B IP profile  B s   reconstructions

9. Jan. 22, 2004 H.Kakuno, H. Ozaki & N. Katayama 9 Super flat geometry Make first measurements as close to IP as possible –Follow the flat beam profile (times >100 sigmas) –Flat because silicon wafer is flat (without thinning) Sort of ideal geometry for physics –Machine issues not seriously considered Keep hermeticity similar to what we have now (90% of 4  ) Geometry is not optimized (yet)

10. Jan. 22, 2004 H.Kakuno, H. Ozaki & N. Katayama 10 IP profile B factories have proven  * y ~ 5 mm and bunch length of 5mm are possible For Super B factories, the parameters have been aggressively pushed to: 3mm and 3mm giving IP beam size of  y < 2  m –  y is said to be limited by beam-beam effects –Due to X-Y coupling,  y is also affected by  * x IR beam pipe can be as small (and short) as the size of beams (times clearance, say, 100 sigmas)

11. Jan. 22, 2004 H.Kakuno, H. Ozaki & N. Katayama 11 Super KEKB beam parameters Assuming XY coupling of 5%  z ~ 3 mm @IP@±5cm xx 60  m63  m yy 1.9  m32  m xx 15 cm17cm yy 3 mm84 cm Maybe parameters are somewhat old

12. Jan. 22, 2004 H.Kakuno, H. Ozaki & N. Katayama 12 Cross section of the S-F beam pipe y x 1 mm 10 mm Ｖａｃｕｕｍ Beryllium ｂｅａｍ ｐｉｐｅ (500  m) Ｓｉｌｉｃｏｎ ｖｅｒｔｅｘ ｄｅｔｅｃｔｏｒ （３００  m thick) Cooling

13. Jan. 22, 2004 H.Kakuno, H. Ozaki & N. Katayama 13 Top view of the S-F beam pipe Z (boost) 1.4cm ±2.5 cm is Enough! Detector length 1cm Cone for 17° Cone for 30° Pixel Detector 1.6 cm Sensitive region is 1.4cm wide

14. Jan. 22, 2004 H.Kakuno, H. Ozaki & N. Katayama 14 Side view of S-F beam pipe Ｖａｃｕｕｍ or accelerator components (nano beta??) Ｓｉｌｉｃｏｎ ｖｅｒｔｅｘ ｄｅｔｅｃｔｏｒ （３００  m thick) Beryllium beam pipe (500  m) 1.6 cm

15. Jan. 22, 2004 H.Kakuno, H. Ozaki & N. Katayama 15 Study of the S-F beam pipe Using Geant4 we defined the S-F geometry; vacuum and beam pipe @IP and the silicon vertex detector In BelleG4, the event generator information written in Belle format is read in. After propagating the tracks in the above geometry, momentum and position of the tracks at r=2cm as well as hits on the silicon vertex detector are written out The silicon hits are smeared using DSSD intrinsic resolution –sigma = 5 + 10.65*alpha (alpha in rad) for both Z and  We then process the tracks (track by track trackerr) using the Belle SVD 1.x + old CDC geometry (100% effic) Explicit Kalman filter is applied to the inner silicon hits and multiple scattering in the silicln and beam pipe materials The tracks have been extrapolated at the vertex using IP constraint (y=0) r  inner/outer layer Z (inner/outer layer) Outer SVD resolution used in simulation

16. Jan. 22, 2004 H.Kakuno, H. Ozaki & N. Katayama 16 B  D*l + Bbar  D 

17. Jan. 22, 2004 H.Kakuno, H. Ozaki & N. Katayama 17 Inefficiency (no SVD hit) due to the above flat geometry is about 10% (1.4cm sensitive Region) for single track

18. Jan. 22, 2004 H.Kakuno, H. Ozaki & N. Katayama 18 1 mm

19. Jan. 22, 2004 H.Kakuno, H. Ozaki & N. Katayama 19 dr and dZ resolution at the vertex  (dr)  (dZ)  (deg)  (deg)  <10  m <20  m <10  m <20  m <30  m p=1GeV/c muon

20. Jan. 22, 2004 H.Kakuno, H. Ozaki & N. Katayama 20 Background reduction By requiring a good vertex (prob.<1%), backgrounds become 1/3 with 1% signal reduction – first Si hit for both tracks – no. of CDC hits >20 for both tracks – 17 < theta < 150 deg. for both tracks – pt > 50 MeV/c for both tracks – IP info is not used in vertexing With primary, B and D/  vertices separated cleanly, combinatorial and continuum backgrounds can greatly be reduced D  k  w/wo vertex fit (no PID)

21. Jan. 22, 2004 H.Kakuno, H. Ozaki & N. Katayama 21 One B  D , D  K 

22. Jan. 22, 2004 H.Kakuno, H. Ozaki & N. Katayama 22 B   D     , D   K     , resolution study (1) D  vertexing efficiency and resolution –All three (K      ) tracks are to have CDC hits > 20 17 50 MeV/c –If all three tracks hit the first SVD, use them for vertexing, if one misses, use the other two tracks vertexing efficiency = 96.9  0.2% resolution ~10  m

23. Jan. 22, 2004 H.Kakuno, H. Ozaki & N. Katayama 23 B   D     , D   K     , resolution study (2) B  vertexing efficiency –Both (     ) tracks are to have CDC hits > 20 17 50 MeV/c –If both tracks hit the first SVD, use them for vertexing, if one misses, use the other track and IP profile vertexing efficiency: 98.6  0.2% resolution ~10  m

24. Jan. 22, 2004 H.Kakuno, H. Ozaki & N. Katayama 24 D flight distance from B decay Generated (  m) Measured (  m) Mean 310  m No degradation!!

25. Jan. 22, 2004 H.Kakuno, H. Ozaki & N. Katayama 25 S-F geometry vs current geom. Error on flight distance (  m) See difference in scale

26. Jan. 22, 2004 H.Kakuno, H. Ozaki & N. Katayama 26 Separating B and D with L/  L Using a flight length cut (L/dL) we can separate B and D vertecies With S-F beam pipe, the separation is 4~5 times better Significance (L/  L) S-F geometry Current geometry Better Cut

27. Jan. 22, 2004 H.Kakuno, H. Ozaki & N. Katayama 27 B s – B s mixing With S-F geometry, resolution is good enough to observe B s – B s mixing We have generated events with X=15 for about 30 fb  of  (5S) running  Z distribution using generator information

28. Jan. 22, 2004 H.Kakuno, H. Ozaki & N. Katayama 28 Analysis using dileptons two same sign leptons (opposite sign events not used) p(lepton) > 1 GeV/c (for clean lepton ID) both lepton hit SVD 1st layer 30<theta<150 deg to reject bad z resolution region p*(lepton) > 1.2 GeV/c to reject 2nd lepton from charm

29. Jan. 22, 2004 H.Kakuno, H. Ozaki & N. Katayama 29  Z resolution and  Z distributions with  Z cuts Gen Meas/no cut 50  m 40  m 30  m20  m FWHM/2.36 ~27  m Expected  Z distribution 30  m Residual(Measured – generated)

30. Jan. 22, 2004 H.Kakuno, H. Ozaki & N. Katayama 30 Results and comments  (  (5S)) ~ 0.27 nb Fraction of B s : 0.263(B s *B s *), 0.022(B s *B s ), 0.046(B s B s ) (L=odd dominant, an estimation) We have not done fits but, It seems we can easily observe mixing if X=15 with a few tens of fb -1 @ 5S with the super flat beam pipe. Considering the vertex resolution, we can go up to X=20 Note that we have not added other same sign dilepton backgrounds

31. Jan. 22, 2004 H.Kakuno, H. Ozaki & N. Katayama 31 Analysis using D*l  + B  anything D*  D   K  /K3  vertexing with nominal D mass and D* - D mass difference cuts Signal side B vertex using D, l, and IP Standard Belle tagging + vertrxing for the tag side For now generator information is used to select combinations We generated 10 5 B d - B d events with X=15 We generated assuming  y =15  m. In super B design it is 2  m. Although smearing due to B flight length dominates (20  m) results will be slightly worse than it could be in the following analyses

32. Jan. 22, 2004 H.Kakuno, H. Ozaki & N. Katayama 32 Vertex resolutions  =13  m  =28  m, Offset:14  m

33. Jan. 22, 2004 H.Kakuno, H. Ozaki & N. Katayama 33 Results We can clearly see oscillation as well 10 5 events is ~6fb -1 at  (5S)

34. Jan. 22, 2004 H.Kakuno, H. Ozaki & N. Katayama 34 B  D  analysis Reconstruct D  K  and   3 , extrapolate D momentum vector from D vertex, make B vertex using IP, use the B vertex and  vertex to calculate  direction, calculate  momentum using  mass constraint Problem:   3  has lots of combinatorial background even in signal (with the other B decaying generically) Monte Carlo sample We use tight cuts for vertexing and flight length cuts requiring separation of vertices

35. Jan. 22, 2004 H.Kakuno, H. Ozaki & N. Katayama 35 B, B tag and  vertex separation True D  Wrong D  The best candidate in a event is selected using sum of  2 for the vertex fits

36. Jan. 22, 2004 H.Kakuno, H. Ozaki & N. Katayama 36 B  D  missing mass C = 2×p* D  ×p* B cos  = MM 2 /C Solid: this method Dotted: with generated  direction

37. Jan. 22, 2004 H.Kakuno, H. Ozaki & N. Katayama 37 P  and m  reconstruction after MM 2 cut Solid: this method Dotted: generated  momentum Using the rest of event

38. Jan. 22, 2004 H.Kakuno, H. Ozaki & N. Katayama 38 Efficiencies (cumulative) D mass, D vertex & vertex quality cut20%  momentum reconstruction 19% vertex position cuts ( |V z (sig)-V z (tag)| and |V z (  )-V z (tag)| ) 6% cos_theta_tau_nu > -0.5, M 3  > 1GeV4.5% abs(MM 2 ) < C2.5%

39. Jan. 22, 2004 H.Kakuno, H. Ozaki & N. Katayama 39 Results S/N = 2427/264 ~ 10 where N is combinatorial background in signal MC Need to estimate background from generic B decays Using D*l +generic (D*l +D*l ) sample, treating l as , we see 8(7) events in 100,000 samples As we know all kinematical info for  3  we can compute  polarization as well

40. Jan. 22, 2004 H.Kakuno, H. Ozaki & N. Katayama 40 Prospects Br(B  D  ) 1% Br(D  final) ~10% (averaging D 0 and D + ) (D 0  K , K3  D +  K2 ...) Br(   3  ) 10% Efficiency: 2% Number of reconstructed signals = 0.01 × 0.1 × 0.1 × 0.02 × 2 × 10 6 / fb  = 4 events / fb  = 4k events / ab  (<200 / ab   for full recon. tag method) We can observe B  D  and measure polarization “without full reconstruction”!

41. Jan. 22, 2004 H.Kakuno, H. Ozaki & N. Katayama 41 Difficulties/Further studies Beam clearance Accidental damage Image current: assume r = 0.5mm round bp (Yamamoto) –r = 0.5mm, l = 2cm, I beam = 10amp.(LER) –bunch spacing = 0.6m, bunch-length(  z ) = 3mm. –total Wattage = 1.0 KW(LER) + 0.25KW(HER) HOM Noise Backgrounds …

42. Jan. 22, 2004 H.Kakuno, H. Ozaki & N. Katayama 42 Conclusions A simulation-reconstruction-analysis chain has established using new (?) tools –The S-F beam pipe geometry has been implemented in a simulation program using Geant4 and Belle data format –A track-by-track version of trackerr has been implemented in Belle framework –A Kalman filter has been implemented for the S-F beam pipe geometry If we can separate (most of) B and D (and other) vertices in an event, the B reconstruction and flavor tagging techniques will dramatically be improved –Need more studies B s -B s bar mixing possible @  (5S) New way of reconstruction technique is possible –Use two vertices to obtain direction of momentum vector

43. Jan. 22, 2004 H.Kakuno, H. Ozaki & N. Katayama 43 Conclusions We need to investigate feasibility of the S-F beam pipe with the accelerator group –The round beam pipe design may have limitation in making the first measurements as close as possible for the current flat beam profile. We can either go to round beams or flat beam pipe –If the bunch length can be shorter, the flat beam pipe can be shorter L = 2~3*  z +60*  y +3 mm The shorter the beam pipe the smaller heating will be SF beam pipe is very cheap, compared with the machine upgrade to get high luminosity to achieve the same “luminosity×efficiency” for many analyses

44. Jan. 22, 2004 H.Kakuno, H. Ozaki & N. Katayama 44 History of beam pipe radius 1mm@ 2010!