Search for the decay BcBs

Masato Aoki

September 13, 2006

1. BsJ/ channel1. Pion reconstruction efficiency2. Cut variables and optimization

2. First check BsDs,Ds data

Pion(from Bc) reconstruction& vertexing efficiency

• BcBs, BsJ/ Monte Carlo :10,000,000 events generated– Reconstruct only Bs meson

• 54487 events

– Reconstruct pion as well • VtxFit Prob(2

r-)>0.1%, Si+COT hits

• 31819 events

58 % (just reconstructed : 39613 events : 73%)

Pre-selection• dataset : xpmm0d, 0h and 0i with v13 goodrun list (1.1fb-1)

• pT > 0.35 GeV for all tracks

• Number of Silicon r- hit layers >= 3 for all tracks

• Number of COT axial hit layers (with minimum 5 hits) >=3 for and tracks

• Muons– pT > 1.5 GeV, 2

stub < 9 for CMU muons

– pT > 2 GeV, 2stub < 9 for CMX muons

– () < 120degree

• Mass window– mass window : 10 MeV around PDG mass

– J/ mass window : 50 MeV around PDG J/ mass (mass constraint)

– Bs mass window : 30 MeV around 6.33601 GeV (mass constraint)

• Vertex– Prob(2

r-) > 0.1 % for the Bs and Bc vertex fitting

Variables to be optimized• pT(Bc), pT(Bs), pT(J/), pT(), pT()• Impact parameter of Bc : dxy

• R(Bs,)

• ct(Bc), ct(BsBc), ct(BsPV)

• Signal : Monte Carlo (pre-selection : 11 events expected)• Background : data (sideband events)• Maximize S / (1.5 + Sqrt(B))• N-1 iteration method• Cleanup 30 MeV Bs mass window (corresponding to 3)

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Optimized cut variables• pT(Bc) > 4.15 GeV• pT(Bs) > 0 GeV, pT(J/) > 0 GeV• pT() > 1.49 GeV• pT() > 1.25 GeV• |dxy(Bc)| < 77 m•

R(Bs,) < 0.801• 50 m < ct(Bc) < 1740 m• -550 m < ct(BsBc) < 4060 m• 200 m < ct(BsPV) < 3620 m

• Expected events in 30 MeV Bs mass window expected S/N = 2.37 / 1.17

Blind Box : 6.2765 ± 3[0.005(uncertainty)+0.005(resolution)]

BsDs, Ds• stripped dataset : chdl07, skbh01 (no one uses those datasets)

• Obtained ~1000 Bs, this should be ~1500(mixing analysis)

• What’s wrong? Bug? Trigger? Selection? Goodrun? Fit modeling?

Summary

• Cut optimization was performed– Expected events : S/N = 2.37 / 1.17 – Are there much better variables?– Likelihood? Neural Network?

• Looked at BsDs,Ds stripped dataset

– A large disagreement was observed