Hermeticity boost factor and other issues Koji Hara

Hermeticity, boost factor and other issues Koji Hara (Nagoya University) January 25, 2008 BNM 2008@Atami 1

Introduction Studies based on the physics cases are needed to validate and optimize the design of the detector performance and the accelerator. Boost factor and Hermeticity How the boost factor affect measurements using Dt and full reconstruction method. KL detection efficiency How important for the mode with missing energy. Test cases: B J/y. K 0, f. K 0 t. CPV measurement B n Br measurement Based on our results from Belle data. January 25, 2008 BNM 2008@Atami 2

Principle of t. CPV measurement (4 S) electron resonance (8 Ge. V) positron (3. 5 Ge. V) _ B 0 B 1 B 2 B 0 CP-side nm bg = 0. 425 (Belle) m+ J/y m KS/L p+ K - Dz ~ 200 mm (Belle) p m+ Flavor tag and vertex reconstruction 1. Fully reconstruct one B-meson which decays to CP eigenstate 2. Tag-side determines its flavor 3. January Proper time (Dt) is measured from decay-vertex difference 3(Dz) 25, 2008 BNM 2008@Atami

B n Analysis Concepts@Belle B decays with missing neutrinos lack the kinematic constraints which are used to separate signal events from backgrounds (Mbc and DE) e+ BB- X (4 S) n B+ More than 2 neutrinos appear in B decay ne n B+ + , + e+ e Reconstruct the decay of the non-signal B (tagging), then look for the signal decay in whatever is left over January 25, 2008 Tagging side : Fully reconstruct hadronic modes Signal side : Reconstruct particles from decay BNM 2008@Atami 4

B n Signal Selection Extra neutral energy in calorimeter EECL - Most powerful variable for separating signal and background -Total calorimeter(ECL) energy from the neutral clusters which are not associated with the tag B Background B n January 25, 2008 Signal BNM 2008@Atami 5

Hermeticity and boost factor Large boost factor better Dt resolution less acceptance in forward region Small boost factor worse Dt resolution more acceptance in forward region Baseline detector design study of adding super forward detector K. -F. Chen’s talk January 25, 2008 BNM 2008@Atami 6

Boost factor Dependence • Toy MC results considering Dt resolution and geometrical acceptance. • Geometrical acceptance is assumed to be same as the current Belle detector. - J/y. K 0 t. CPV - f. K 0 t. CPV - B n BR KEKB can operate worse better January 25, 2008 BNM 2008@Atami 7

KL Veto Efficiency for B n Main background in B n are B decays with KL. How KL detection efficiency affect the precision of Br(B n)? requirement for super KLM January 25, 2008 BNM 2008@Atami e+ D 0 B+ ne KL KL 8

KL Veto Efficiency Dependence Toy MC results for several KL veto efficiencies. Current is set to 35% worse guess by geant simulation + J/y. KL data Q: How can we improve KL detection efficiency of super KLM? January 25, 2008 better KL veto efficiency BNM 2008@Atami 9

Summary Boost factor and Hermeticity Considering both t. CPV and B n measurements, current KEKB energy (8 x 3. 5) seems the preferable point within the region KEKB can operate. KL veto efficiency for B n Higher KL veto efficiency is effective for B n measurement How can we improve KL detection efficiency of super KLM? Dependence of other detector performances (PID, tracking&vertexing) must be checked and optimized. Studies based on the fast simulator are being done. BNM 2008@Atami January 25, 2008 10