BS Mixing Results at Tevatron Donatella Lucchesi CDF

BS Mixing Results at Tevatron Donatella Lucchesi CDF Padova

Outline n Introduction n Bs mixing in the Standard Model n Ingredients to perform a measurement n CDF measurement n D 0 analysis and result n New Standard Model constraints 1/13/2022 2

Introduction § Decay channels selection using Tier 1 and data stored at CNAF Casarsa (TS), Da Ronco, Pagan, Delli Paoli, Lucchesi § Event by event Primary Vertex determination Casarsa (TS), Da Ronco, Lucchesi § Bs lifetime measurement in hadronic decays: trigger efficiency determination used in mixing analysis 1/13/2022 Da Ronco, Ph. D thesis 3

Bs Mixing in The Standard Model Eigenstates are: 1/13/2022 4

Bs Mixing in The Standard Model cont’d In the ratio uncertainties cancels: From lattice-QCD, big uncertanties |Vtd| determined at 15% +0. 035 2 = 1. 21+0. 02 -0. 014 Applying unitarity… 1/13/2022 5

Bs Mixing constraints the Standard Model Winter 2006 ms>16. 6 at 95% C. L. Lower limit on ms Upper limit on ms = 0. 217± 0. 032 = 0. 344± 0. 021 D 0 results: 17< ms<21 90% C. L. CDF effect in about one hour… 1/13/2022 6

Measurement Principle in a Perfect World Bs vs Bd oscillation Rather than fit for frequency perform a ‘fourier transform’ A B lifetime 1/13/2022 ms [ps-1] 7

Road Map to ms Measurement Opposite Side fragmentation particle: , K… , K 3. Tag B flavor at production time 1. Final state reconstruction 2. High resolution on proper decay length measure efficiency and dilution D: D 2 gives the “effective” number of events 1/13/2022 8

Detector for the measurement Trigger: displaced tracks (SVT) Tagging Power: TOF & d. E/d. X (COT) Proper time Resolution: SVX and L 00 Padova project! 1/13/2022 9

Adding all the realistic effects Flavor tagging power 1/13/2022 Proper time resolution 10

Road Map to ms Measurement Opposite Side fragmentation particle: , K… , K 3. Tag B flavor at production time 1. Final state reconstruction 2. High resolution on proper decay length measure efficiency and dilution D: D 2 gives the “effective” number of events 1/13/2022 11

Tevatron Luminosity 1 fb-1 Used in this analysis 1/13/2022 12

Trigger on displaced tracks: SVT B L De ca y Le ng th Secondary Vertex ØTwo tracks: § Pt>2 Ge. V/c § 120 m<|d|<1 mm § minimum separation Ø precision tracking in SVX ~ 48 m includes 33 m of beam spot Primary Vertex d = impact parameter 1/13/2022 13

Bs Data sample Signal Bs Ds Ds KK Ds K*0 K K*0 K Ds 3 Partially Bs Ds 3 reconstructed Ds B mesons Ds K*0 K B 0 D- 1/13/2022 Combinatorial background 14

Hadronic Bs yields summary Decay channel Yield Bs Ds Ds 1570± 43 Bs Ds Ds K*0 K 857± 32 Bs Ds Ds 3 612± 37 Bs Ds 3 Ds 493± 37 Bs Ds 3 Ds K*0 K 204± 26 Total 3736± 79 B+ D 0 ~ 26, 000 B 0 D- ~ 22, 000 1/13/2022 15

Semileptonic samples Bs Dsl. X Ds KK Ds K*0 K K*0 K Ds 3 1/13/2022 Dsl ~ 53, 000 16

Road Map to ms Measurement Opposite Side fragmentation particle: , K… , K 3. Tag B flavor at production time 1/13/2022 1. Final state reconstruction 2. High resolution on proper decay length 17

B Lifetime measurement Lifetime Measurement: hadronic and semileptonic B decays Hadronic decays: well measured ct = Lxy/ t t = Pt(B)/M(B) SVT trigger bias: P(t) = e-t’/ R(t’, t) (t) 1/13/2022 Semileptonic decays: missing X need correction factor 18

B Lifetime measurement c (Bs)=1. 60± 0. 10(stat)± 0. 02(sys) ps High precision measurement to be done!! 1/13/2022 c (Bs)=1. 538± 0. 040(stat) ps 19

Proper time resolution, t § Lifetime measurement not very sensitive § In the ms fit each event weighted by its resolution § Dedicated calibration need Prompt Charm + track sample 1/13/2022 20

Proper time resolution, t Layer 00 is a layer of silicon placed directly on beam pipe Additional impact parameter resolution, radiation hardness 1/13/2022 21

Road Map to ms Measurement Opposite Side fragmentation particle: , K… , K 3. Tag B flavor at production time 1. Final state reconstruction 2. High resolution on proper decay length measure efficiency and dilution D: D 2 gives the “effective” number of events 1/13/2022 22

Flavor tagger calibration: OST Dilution Nright-Nwrong = 2 Pright-1 D= Nright+Nwrong Opposite Side Tagger (OST): § Use data to calibrate the tagger and to evaluate D § Fit semileptonic and hadronic Bd sample to measure: D, md Hadronic: md = 0. 535± 0. 028(stat)± 0. 006(sys) ps-1 Semileptonic: md = 0. 509± 0. 010(stat)± 0. 016(sys) ps-1 W. A. : md = 0. 506± 0. 005 ps-1 1/13/2022 23

Flavor Tagger calibration: SSTK B 0/B± likely to have nearby B 0 s likely to have K Use TOF and d. E/d. X to separate pion from kaon Tune Monte Carlo to reproduce B 0, B- distributions then apply to Bs 1/13/2022 24

Flavor Tagger performances § Exclusive combination of tags in OST § SSTK-OST combination assumes independent tagging information 1/13/2022 25

Amplitude Scan § A is introduced: § A=1 when msmeasured = mstrue 0 mixing in hadronic decay B § Points: A± (A) from Likelihood fit for different m § Yellow band: A± 1. 645 (A) § m where A± 1. 645 (A)<1 excluded at 95% C. L. § Dashed line: 1. 645 (A) vs m § Measured sensitivity: 1. 645 (A)=1 1/13/2022 26

Choice of Procedure § Amplitude scan helpful to set m limit and combine results § How does an evidence of a signal look like? § What procedure if aiming at measurement? § These questions must be asked before performing the Analysis! Otherwise lack of coverage is the punishment! § Before un-blinding: p-value: probability that observed effect is due background fluctuation. No search window. yes make double sided confidence interval from (ln(L)), measure ms 1/13/2022 p-value<1%? no set 95% C. L. based on Amplitude Scan 27

p-value Estimation (ln(L))= ln[L(A=1)/ ln. L(A=0)] Probability of random tag fluctuation estimated on data (randomized tags) and checked with toy Monte Carlo 1/13/2022 28

Systematic Uncertanties in Amplitude Scan Related to absolute value of A important when setting a limit Cancel out in A/ A Very small compared to statistical error 1/13/2022 29

Amplitude Scan: Semileptonic decays 1/13/2022 30

Amplitude Scan: Hadronic decays 1/13/2022 31

Amplitude Scan: Combined Sensitivity better than the W. A. 20. 1 ps-1 Rare case!! 1/13/2022 32

Combined Amplitude Scan: an other view 1/13/2022 33

Likelihood Profile How often random tags produce a likelihood deep this dip? 1/13/2022 34

Likelihood significance § Find maximum (ln(L)) in data randomizing 50, 000 times tags § In 228 experiments found (ln(L))>6. 06 Probability of fake, p-value=0. 5% Measure ms !!! 1/13/2022 35

Systematic Uncertanties on ms Fit Model: negligible Relevant only lifetime scale 1/13/2022 36

Measurement of ms 0. 42 ms =17. 33+-0. 21 ± 0. 07 ps-1 17. 00 < ms <17. 91 ps-1 at 90% C. L. 1/13/2022 16. 94 < ms <17. 97 ps-1 at 95% C. L. 37

|Vtd|/|Vts| Determination Used as inputs: § m. Bs/m. Bd = 0. 9830 PDG 2006 +0. 47 § 2 = 1. 210 -0. 35 (M. Okamoto, hep-lat/0510113) § md = 0. 507± 0. 005 PDG 2006 +0. 008 |Vtd|/|Vts|=0. 208 -0. 007 (stat. +syst. ) Latest Belle result b s (hep-ex/050679): |Vtd|/|Vts| = 0. 199 1/13/2022 +0. 026 -0. 025 (stat) +0. 018 -0. 015 (syst) 38

D 0 Analysis Trigger: single muon pt>2 Ge. V/c Decay channel: Bs +Ds-X Ds- - and K+K- NBs = 26, 710 ± 556(stat) Cuts selected maximize + D - 1/13/2022 + D s - 39

D 0 Analysis N = 5601 ± 102 (stat) Opposite Side Tagging: -lepton (electron or muon) - Secondary Vertex - Event Charge + D - 1/13/2022 + D s - Tags combined: d>0 b tag d<0 b tag 40

D 0 Procedure Correction factor due to missing neutrino Several effects taken into account: § Resolution scale factor for detector mismodeling § Reconstruction efficiency as function of decay length § Physical and combinatorial background contributions 1/13/2022 41

D 0 Results “favored value’’ = 19 ps-1 17< ms<21 ps-1 at the 90% C. L. 1/13/2022 m 19 ps-1 : A/ A=2. 5 and A-1/ A=1. 6 Sensitivity = 14. 1 ps-1 ms>14. 8 at the 90% C. L. 42

Unitarity Triangle fit with ms Old: Upper limit on ms Lower limit on ms = 0. 217± 0. 032 = 0. 344± 0. 021 New: = 0. 193± 0. 029 = 0. 355± 0. 019 1/13/2022 43

New Physics Limit UTfit Model independent approach | F|=2 Hamiltonian CBs = ms. SM+NP / ms. SM = 1. 01 0. 33 [0. 33, 2. 04] @ 95% C. L. 1/13/2022 44

Conclusions Ø CDF has an experimental signature for Bs-Bs oscillations Ø Probability of random fluctuation is 0. 5% First direct measurement of: 0. 42 ms =17. 33+-0. 21 ± 0. 07 ps-1 +0. 008 |Vtd|/|Vts|=0. 208 -0. 007 (stat. +syst. ) 1/13/2022 45

BACKUP 1/13/2022 46

The Accelerator 1/13/2022 47

Detectors • Upgraded muon coverage • New Tracking System • New Silicon Micro-vertex • New Solenoid • New Pre-showers 1/13/2022 48

Detectors 1/13/2022 49

Introduction Designed by Padova group and detectors tests done in Padova 1/13/2022 50

Flavor tagger calibration Reconstructed decay “S Fragmentation a me product “O pp Si d os ite e” B meson Si de ” lepton Secondary Vertex Jet Charge 1/13/2022 51