Bs d m m At CDF ChengJu Lin

Bs, d + m m At CDF Cheng-Ju Lin and Matt Herndon For the CDF Collaboration Mini Workshop on "Interdisciplinary" Approach to Constraint Low-Energy SUSY Models Fermilab 18 May 2006 1

TEVATRON Projection D es ig n Tevatron Integrated Luminosity Projection We are here s Ba e n eli • Tevatron is expected to deliver 8 fb-1/exp for Run II • Most of the data is still ahead of us!! 2

CDF Detector Monte Carlo CDF: • Excellent silicon vertex detector • Good particle identification (K, p) • Good momentum and track impact parameter resolutions M(Bs)-M(Bd)~90 Me. V • CDF can distinguish Bs and Bd decays 3

B Triggers at CDF • • Trigger is the lifeline of B physics in a hadron environment !!! Rare B “Di-Muon” triggers: • Low single muon thresholds • Require Sum p. T or outer muon chambers • Di-muon trigger is the primary trigger CDF for the CDF Bs + - search • SVT “Hadronic” triggers using silicon vertex detectors: • exploit long lifetime of heavy quarks • Two-track trigger (CDF) – • Two oppositely charged tracks with large impact parameters 4

Keeping Rare B Trigger Alive CDF L 2 Rare B Trigger Rate CDF Rare B Trigger • Rare B trigger is highly prescaled for Linst > 1. 2 E 32 • Currently small amount of integrated luminosity with Linst > 1. 2 E 32 • At Linst order 3 E 32, could use hybrid di-muon/SVT to keep the rate down Goal: Keep rare B trigger alive (without significantly raising p. T threshold or prescale) for the entire Run II period 5

Rare B Dataset • CDF: – 780 pb-1 di-muon triggered data – Two separate search channels • Central/central muons (CMU-CMU) • Central/forward muons (CMU-CMX) – Search for Bs and Bd separately Potential sources of background: • continuum Drell-Yan • sequential semi-leptonic b c s decays • double semi-leptonic bb X • b/c x+fake • fake + fake Search region Effective background rejection is the key to this analysis!! 6

Analysis Overview Motto: reduce background and keep signal eff high Step 1: pre-selection cuts to reject obvious background Step 2: optimization (need to know signal efficiency and expected background) Step 3: reconstruct B+ J/y K+ normalization mode Step 4: open the box compute branching ratio or set limit 9. 8 X 107 B+ events 7

CDF Pre-selection • Pre-Selection cuts: – 4. 669 < m < 5. 969 Ge. V/c 2 – p. T( )>2. 0 (2. 2) Ge. V/c CMU (CMX) – p. T(Bs cand. )>4. 0 Ge. V/c – Track, muon and vertex quality cuts – 3 D displacement L 3 D between primary and secondary vertex Bkg substantially reduced but still sizeable at this stage 8

B m+m- Signal vs Bkg Discrimination Using 3 D variables for additional discrimination + L 3 D – + - mass PT( ) - di-muon vertex – Isolation (Iso): primary vertex + LT PT( ) - LT – B vertex displacement: di-muon vertex primary vertex (fraction of p. T from B within DR=(Dh 2+Df 2)1/2 cone of 1) – “pointing (Da)”: 9 (angle between Bs momentum and decay axis)

CDF Optimization • CDF constructs a likelihood ratio using discriminating variables l, Da, Iso • Optimize expected upper limit • LR(optimized)>0. 99 10

Background Estimate • Assume linear background shape extrapolate # of background events sidebands to signal region ± 60 Me. V signal window • CDF signal region is also contaminated by B h+h- (e. g. B K+K-, K+p-, p+p-) - K, p muon fake rates measured from data Decay B hh Background Combinatoric Background Total Background Bs 0. 19± 0. 06 1. 08± 0. 36 1. 27± 0. 36 Bd 1. 37± 0. 16 1. 08± 0. 36 2. 45± 0. 39 LR > 0. 99 11

Now Look in the Bs and Bd Signal Windows LR > 0. 99 Bs Limits (combine both channels): Br(Bs )<8. 0× 10 -8 @ 90%CL Br(Bs )<1. 0× 10 -7 @ 95%CL Bd Limits (combine both channels): Br(Bd )<2. 3× 10 -8 @ 90%CL Br(Bd )<3. 0× 10 -8 @ 95%CL CMU-CMU Channel: Expect Observed Bs 0. 88± 0. 30 1 Bd 1. 86± 0. 34 2 Prob 67% 63% CMU-CMX Channel: Expect Observed Bs 0. 39± 0. 21 0 Bd 0. 59± 0. 21 0 Prob 68% 12 55%

Branching Ratio Limits • Evolution of limits (in 95%CL): CDF Bs->mm 176 pb-1 7. 5× 10 -7 Published DØ Bs->mm 240 pb-1 5. 1× 10 -7 Published DØ Bs->mm 300 pb-1 4. 0× 10 -7 Prelim. <2. 3× 10 -7> Prelim. Sensitivity pb-1 DØ <Bs->mm 700 CDF Bs->mm 364 pb-1 2. 0× 10 -7 Published CDF Bs->mm 780 pb-1 1. 0× 10 -7 Prelim. World’s best limits 90% CL Babar Bd->mm 111 fb-1 8. 3× 10 -8 Published CDF Bd->mm 364 pb-1 4. 9× 10 -8 Published CDF Bd->mm 780 pb-1 3. 0× 10 -8 Prelim. 13

CDF Projection Conservative projection based on our current (780 pb-1) performance Summer improvements sensitivity enhanced ~15 -20% Factor of 4 improvement at 8 fb-1? 14

Previous TEVATRON Projection This projection was made about 1 year ago 15

Updated TEVATRON Reach on Bs mm Conservative projection based on our current performance Old 90% CL exclusion curve is now our 95% CL exclusion Overall limit improves by ~15 -20% combining CDF+D 0 results 16

Summary • CDF and D 0 have analyzed first ~800 pb-1. • No signal is seen in the CDF data. • D 0 has not opened the box for the later data. • A full Tevatron Bs analysis update for 1 fb-1 is planned for this summer. Expected sensitivity is ~7× 10 -8 level • Tevatron can reach low 10 -8 level. LHC needed for observation of SM level. 17