Impact of the Belle II Pixel Detector on CP-Violation Measurements

Transcription

1 Impact of the Belle II Pixel Detector on CP-Violation Measurements Fernando Abudinén September 6, SuperKEKB and Belle II 2 CP-Violation Measurements 3 Belle II Pixel Vertex Detector 4 B-Meson Vertex Resolution 5 Summary and Outlook

2 KEKB/SuperKEKB Collider Upgrade: KEKB SuperKEKB Belle Belle II 3km e+ e Colliding bunches 1 KEK = kō enerugī kasokuki kenkyū kikō high energy collider research organization At: Tsukuba, Ibaraki Prefecture, Japan

3 Belle/Belle II Experiment 2 KEKB/Belle SuperKEKB/Belle II operation Inst. Lumi. L cm 2 s cm 2 s 1 e /e + beam E 8/3.5 GeV 7/4 GeV Boost βγ e /e + beam I 1.2/1.6 A 2.6/3.6 A

4 Nano Beam Scheme Lorentz factor L = γ ± 2er e beam size σ x,y = ε x,y β x,y ( emittance SuperKEKB 1 + σ ) ( y I ± ξ ± σ x β y 6 beam-beam parameters ) ( ) RL present KEKB R ξy Geometric factors 3

5 Time of Propagation counter with 2 mm quartz bars MCP-PMT readout K L /µ Detector (outside) RPC Plates and plastic scintillators with SiPM readout Superconducting Magnet homogeneous field of 1.5 T Electromagnetic Calorimeter 8 CsI Crystals, 16 X PMT/APD readout Pixel Vertex Detector 2 layer pixel detector (8MP) technology Silicon Vertex Detector 4 layer double sided strips 2 5 ns shaping time Central Drift Chamber proportional wire drift chamber 15 sense wires in 58 layers Aerogel RICH Proximity focusing RICH with silica aerogel

6 CP-Violation in the SM η excluded area has CL >.95 CP-V. in the SM Weak Interaction V CKM d s = V ud V us V ub V cd V cs V cb d s b V td V ts V tb b Params: 3 Real, 1 Im.: λ= sin θ C.2, A, ρ, η Unitarity: k V ki V kj = V ud Vub + V cdvcb + V tdvtb = O(λ 3 ) O(λ 3 ) O(λ 3 ) Largest CP-V. within the SM in the B-system. sin 2β LHCb sin 2β WA ε K γ m d & m s m d α ε K CKM f i t t e r La Thuile 215 sol. w/ cos 2β < (excl. at CL >.95) α 5 V ub.1 α γ β ρ

7 σ(e + e Hadrons) [nb] Υ(1S) Υ(2S) Υ(3S) Time-dep. CP-Analysis at B-Factories Υ(4S) continuum background e + e Center-of-Mass Energy [GeV] e Υ(4S) B tag e + B CP Υ(4S) above BB prod. threshold Υ(4S) BB > 96 % Γ(B + B ) Γ(B B ) 1.6 B-Factory l J/ψ K S K z Belle 2 µm z Belle II 13 µm π + 6 t = Boost P Sig ( t, q) = z µ +µ z βγ c since B B at rest in Υ(4S) frame e t /τ B 4τ B π q B,B = 1, 1 [1 + q (A CP cos( m t) + S CP sin( m t))]

8 Time-dependent CP-Asymmetry a CP = N ( B, t ) N ( B, t ) N (B, t) + N ( B, t ) = A CP cos( m t) + S CP sin( m t) A CP : Direct CP Violation: A = f B f B = Ā S CP : Mixing-induced CP Violation: J/ψ K S A CP = S CP = sin(2β) 7 B B B B A CP f f B B S CP f CP

9 Pixel Vertex Detector Ac or tiv ep ec t i x e l Det active area gaten clearn 76 8 px 25 px m gaten m clearn+1 ( 12.5 mm pixel center) SwitcherB (32 channels gate/clear) DCD-B (analog readout) DHP (digital processing) power 75 μm active area thickness ground 8 Background Closest to IP Occupancy ( r 2 ) mounting hole flexible interconnect (polyimide/copper) Inst. Lumi.: LBelle II 4 LBelle conductive layers (Al/Al/Cu) hβγibelle II < hβγibelle 2 mm / 42 μm rigid frame differential data transmission ( 1.6 Gb/s) S. talk on Sept 5 by C. Koffmane smaller z Pixel Detector needed! Technology most suited DEPleted Field Effect Transistor

10 9 Active Pi xel Detector The Impact Parameter Particle track parametrization t(d, φ, Ω = q p t, z, tan(λ)) d (z ): distance between point of closest approach and IP. σ d σ z Improvement by factor 2

11 Pixel Vertex Detector Material (scattering) Point Resolution Distance to IP σ d Mult. Scattering: φ X X Low material budget required! 1 p/ GeV/c

12 11 Active Pi xel Detector B CP Vertex B CP J/ψ KS π+ π, π π : Decay outside of PXD. K S J/ψ µ + µ : Both muons have at least on PXD hit. Kinematic Vertex Fit B CP Belle II Bias = 2. μm Resolution = 26 μm Belle Bias =.2 μm Resolution = 63 μm Result fitted with 3 Gaussians

13 12 Active Pi xel Detector B tag Vertex Resolution Algorithm: Adaptive Vertex Fit (AVF) CMS NOTE 28/33 Access: RAVE (Reconstruction in a Abstract, Versatile Environment) Track weighting according to proximity to other tracks and spatial constraint. 6µm on K S Tracks. Belle II Bias = 6 μm Res. = 53 μm B tag t = t BCP t Btag Belle Bias = 29 μm Res. = 89 μm Belle II Bias = -. Res. =.77 Belle Bias =.2 Res. =.9

14 t Distribution MC Analysis B CP J/ψK S a) q MC truth, ε Eff = 1 % b) q tagged, ε Eff = 35.5 % B tag B tag Impact on P( t, q, r): P Obs ( t, q) = e t τ B 4τ B [1 + q r (A CP cos( m t) + S CP sin( m t))] 13 ε Eff (Belle) = 29 %

15 14 Active Pi xel Detector Time-dependent CP-Analysis For B ππ: tree and penguin diags. contribute! i: A CP = S CP = sin(2α) i+ f: A CP S CP = 1 A CP sin(2α eff ) α eff = α α Extr. of α through isospin S π π. I α γ CKM-Triangle β R S π π needs z 13µm of B π π where π γγ Challenge!

16 15 Active Pi xel Detector Extraction of α angle from B ππ p value 1 - CL w/out S π π 8 fold ambiguity on α CKM f i t t e r WINTER 12 B ππ (BABAR) B ππ (Belle) B ππ (WA) α (deg) CKM fit 1 - CL Extrapolated to L Belle II = 5ab α ( ) arxiv:hep-ex/7329 with S π π 2 fold ambiguity on α Converted γ e + e and π e + e γ req. for z Possible with L Belle II = 5 L Belle and Belle II PXD? α ( )

17 B CP Vertex Reconstruction y / cm 3 2 γ e + e Pipe PXD 1 PXD 2 τ π.9 as =.1 nm x γ x / cm e π Vertex ˆ= B Vertex. Kinematic Vertex Fit with spatial constraint centered at the Beam Spot. x π e + e γ e γ 16 BS B γ γ e + z BS B e + γ γ z

18 B z-vertex Resolution B π π γ γ e + e Events / (.6 cm ) Entries 112 Mean -4.9 µm Std Dev µm Events / (.6 cm ) Entries 556 Mean.2 µm Std Dev 88.5 µm B_Z - Gen. B_Z / cm No PXD Hit required B_Z - Gen. B_Z / cm At least one track (e + or e ) has one PXD Hit

19 t Resolution Events / (.1 ps ) t = t B CP t B tag B CP π π Entries 1316 Mean.6 ps Std Dev 3.42 ps t - Gen. t / ps No PXD Hit required Events / (.1 ps ) γ γ e + e Entries 5861 Mean -.17 ps Std Dev 2.22 ps t - Gen. t / ps At least one track (e + or e ) has one PXD Hit

20 19 Active Pi xel Detector t Resolution B CP π π e + e γ t = t B CP t B tag Events / (.6 cm ) Entries Mean 3.3 µm Std Dev 69.3 µm B_Z - Gen. B_Z / cm Events / (.1 ps ) 4 Entries Mean -.14 ps Std Dev 1.76 ps t - Gen. t / ps

21 2 Active Pi xel Detector Summary and Outlook Upgrade of KEK to SuperKEKB: Boost reduction, Background increase, required maintenance of vertex resolution. New Pixel Vertex Detector (PXD) for Belle II. PXD is crucial for the Belle II physics programm. Impact of the PXD is studied with Monte Carlo Simulations: Belle II t resolution is higher although βγ has been decreased! Machine commissioning started! Begin of data taking planned for 218!

22 Vertex of γ-conversions in B π π y / cm 3 γ e + e Pipe 2 PXD 1 PXD x / cm Υ(4S) B 1 B 2 B 1 generic B 2 π π π γγ (B = 98.82%) π e + e γ (B = 1.17%) N Belle II = L Belle II B(Υ(4S) B B ) 2 B(B π π ) 5ab 1 1.1nb k events. Accept.: θ [17, 15] ECL: θ [12.4, 155.1]

23 Events with γ-conversions % a) If there is an event with γ-conversions How Many? % b) How many Events have at least one γ-conversion? Vertex in Events % Beam Pipe 2. % 1st. PXD Layer.6 % 2nd. PXD Layer.5 % Total inside PXD 3.1 % %.8%.1% Number of γ-conversions c)... and at least one γ-conversion or one π e + e γ decay? π e + e γ 2. % Total π γ 5.5 % 22 Requirement: All converted γ in accept. and not converted in ECL

24 t t t Active Pi xel Detector e +, e e +, e Track Reconstruction / cm σ d.25.2 Fit / GeV/c p MC p / GeV/c t MC p / GeV/c t / cm σ z p / GeV/c MC t MC / p Fit p p / GeV/c MC t