Поликарпов Сергей, 12 апреля 2012, ИТЭФ

Статья принята в Physics Letters B 1 марта 2011

Outline• LHCb detector• Decay trees• Data analysis, simulation• Results

ф modef0 moderatio f0 to ф

• Conclusions

Детектор LHCb

Decay trees

Data analysis33 1/pb data collected with LHCb detector in 2010J /ψ →μ+ μ− :

opposite sign tracks

pT > 500 MeV/c,

identified as muons,

vertex χ2/ndof < 11,

tz = dZ(J/psi)/{Pjp/Mjp} > 0.5 ps

| M(μ+ μ− ) – 3096.9 | < 48 MeV for further analysis

549 , 000 ± 1100 J /ψ signal events in the entire mass range

J/psi -> μ+ μ−

Crystal Ball function

χ2( IP[ pi (or K) ] == 0) > 9 (pi and K tracks do not come from PV), Perfect pi/K separation with RICH, Opposite-sign di-pion candidates -> sum pT > 900 MeV Opposite-sign di-kaon candidates ->

o sum pT > 1000 MeV, o|M(K+ K-) – M(φ) | <20 MeV

B0s : two pions(+ and -) (or kaons) form vertex with a χ2< 10, with the J /ψ they form the B0s vertex: χ2/ndof< 5, Angle between P(this B0s candidate ) and direction to the PV

<0.68◦

Data analysis(2)

Simulations to find out efficiencyThe efficiencies of having all four decay tracks in the geometric acceptance and satisfying the trigger, track reconstruction and data selection requirements are:

(1.471 ± 0.024)% for J/ψ f0,requiring the π+ π− invariant mass be within ±500 MeV of 980 MeV,

and (1.454 ± 0.021 )%for J /ψ φ ,having the K+ K− invariant mass be within ±20 MeV of the φ mass.

[Monte Carlo events generated using PYTHIA [..], and LHCb detector simulation based on GEANT4 [..]. ]The uncertainties of the efficiencies are statistical only.

RESULTS

Mass (J /ψ K+ K−) (in φ-> K+ K− mode)

Gaus + pol1 B0s mass =5366.7 ± 0.4 MeV, width = 7.4 MeV

635± 26 events

Mass (J/psi pi+ pi-)

signal(gaus)

B+→J /ψ K+ (π+)

23 ± 9 B→J /ψ π+π− events

B0s →J /ψη + B0s → J /ψφ

111± 14 signal events within ±30 MeV of the B0s mass

Mass(pi+ pi-) = ( 980±90) MeV

Polarization in f0 mode

S(B0s) = 0 S(J/ψ ) = 1

S(f0) = 0

J /ψ rest frame

B0sf0

f0 rest frame

μ+

μ-

θJ/ψ

θJ/ψ should be distributed as [1− (cos θJ/ψ)^2)]

B0s J/ψ

π-

θf0

θf0 should be distributed uniformly (~const)

π+

Angular distributions of events within ± 30 MeV of the B0s mass and± 90 MeV of the f0 mass after like-sign background

subtraction.

because of efficiency&background effects [1− a*(cos θJ/ψ)^2)];a= 0.81± 0.21 (fit result)

χ2/ndof = 10.3 / 8

χ2/ndof = 15.9/9,

Spin(J /ψ) perpendicular to its momentum and a spin-0 f0 meson.

Mass(π+ π−) | Mass(J /ψ π+ π−) = Mass(B0s) ± 30 MeV

265 ± 26 events, including 169(+31−21) f0 (980) events

635 +- 26 φ events

taking into account efficiencises

Model-independent result {M(pi pi) = (980±90) MeV , here are 111 ± 14 events.}

ConclusionsThe first observation of a new CP-odd eigenstate decay mode of the B0s meson into J /ψ f0(980) has been made Using a fit including two interfering resonances, the f0(980 ) and f0(1370) ,the ratio to J /ψ φ production is measured as

By selecting events within ±90 MeV of 980 MeV the ratio becomes R’ = 0.162 ± 0.022 ± 0.016.The events around the f0(980) mass are large enough inRate and have small enough backgrounds that they could be used to measure βs without angular analysis.

BACKUP SLIDES

Crystal Ball

Systematic uncertaintaes