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B 0  +  -  0 from the Calorimeter Software point of view

B 0  +  -  0 from the Calorimeter Software point of view. J. Lefrançois F. Machefert P. Robbe M-H Schune. Dalitz Plot Technical framework Some results. 2 regions in the Dalitz Plot : Fast  0 + fast  + + slow  - Slow  0 + fast  + + fast  -. M 2 (  -  0 ).

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B 0  +  -  0 from the Calorimeter Software point of view

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  1. B0+-0 from the Calorimeter Software point of view J. Lefrançois F. Machefert P. Robbe M-H Schune • Dalitz Plot • Technical framework • Some results B00 calorimeter Software Marie-Hélène Schune, LHCb Software week March 2003 1

  2. 2 regions in the Dalitz Plot : Fast 0 + fast + + slow - Slow 0 + fast + + fast - M2(- 0) + or - is at rest in the B center of mass frame M2(+ 0) 0 at rest in the B center of mass frame B00 calorimeter Software Marie-Hélène Schune, LHCb Software week March 2003 2

  3. At truth level on B0+-0 events: B00 calorimeter Software Marie-Hélène Schune, LHCb Software week March 2003 3

  4. Truth level lower zone of the Dalitz plot: about 82% of the p0have separated clusters. merged p0 For comparison : upper zone of the Dalitz plot: pT(p0) about 35% of the p0have separated clusters B00 calorimeter Software Marie-Hélène Schune, LHCb Software week March 2003 4

  5. Framework • DaVinci v7r3 : • 103.5k signal events • 870.3k bb events • Use the event with only one Primary Vertex (PrimVtxFinder) • p0  g g (no merged p0 yet) • ET(g) > 200 MeV • use both converted and non converted g TDR production B00 calorimeter Software Marie-Hélène Schune, LHCb Software week March 2003 5

  6. Preselection cuts • Use the event with only one Primary Vertex (VtxFinder) • p0  g g (no merged p0 yet) • ET(g) > 200 MeV • use both converted and non converted g • p : pT > 150 MeV . 2(vtx) < 5 (zVtx –zPV)> 500 mm • ImpP(p )/sImpP > 2 • Combine the  with the p0 (4-vector addition) slowest p fastest p B00 calorimeter Software Marie-Hélène Schune, LHCb Software week March 2003 6

  7. p0 mass M=140 0.3 MeV =11.8 0.4 MeV DaVinci v7r3 DaVinci v6r2 same g selection : both converted and non converted B00 calorimeter Software Marie-Hélène Schune, LHCb Software week March 2003 7

  8. p0 efficiency all p0in ECAL p0in ECAL with p< 20 GeV zoom B00 calorimeter Software Marie-Hélène Schune, LHCb Software week March 2003 8

  9. Cuts optimized for this region M(p+ p-) < 1200 MeV or M(p+p0) < 1200 MeV or M(p-p0) < 1200 MeV 2 regions M(p+p0)2 + M(p-p0) 2 < 10 GeV2 M(p+p0)2 + M(p-p0) 2 > 10 GeV2 B00 calorimeter Software Marie-Hélène Schune, LHCb Software week March 2003 9

  10. D [p] : defined by the p momentum and the first pointOnTrack D [B] : defined by the B momentum and the PV Use of the B0 direction Rec. B pmax d(D[pmax], D[B]) d(D[pmin], D[B]) pmin B line of flight p0 PV q q angle between the B momentum and the B line of flight B00 calorimeter Software Marie-Hélène Schune, LHCb Software week March 2003 10

  11. q : angle between the B momentum and the B line of flight signal bb all plots normalized to the same area B00 calorimeter Software Marie-Hélène Schune, LHCb Software week March 2003 11

  12. ImpP(p )/sImpP slowest p dmax fastest p bb signal overflow a lot of bckgd for the slowest track, use only the detached ones the fastest track is well measured, d should be close to 0 B00 calorimeter Software Marie-Hélène Schune, LHCb Software week March 2003 12

  13. pT(B0) cos(q)p0 signal bb bb B00 calorimeter Software Marie-Hélène Schune, LHCb Software week March 2003 13

  14. Double counting : - 1 double counting on generic bb (2 entries) - on signal : 242 entries : 171 after choice always due to the p0  choose the best p0 according to the p0 mass B00 calorimeter Software Marie-Hélène Schune, LHCb Software week March 2003 14

  15. s=267 MeV m=52904 MeV the « signal cross-feed » background bb  200 MeV region is too wide B00 calorimeter Software Marie-Hélène Schune, LHCb Software week March 2003 15

  16. Numbers for the lower region of the Dalitz plot Several cand./event Not always selecting the right one Soft neutral matching ? (75% cut on cluster E) B00 calorimeter Software Marie-Hélène Schune, LHCb Software week March 2003 16

  17. Conclusions • p0mass shifted by about 5 MeV • In the lower zone of the Dalitz plot M(p+p0)2 + M(p-p0) 2 < 10 GeV2 : better S/B .5 10-2  15. 10-2 • Define the signal region within 100 MeV region S/B * 2 • Use of the self cross-feed background • Specific background to be studied : • B0+- , K*g … • Merged p0 : still to be tried B00 calorimeter Software Marie-Hélène Schune, LHCb Software week March 2003 17

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