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Transcript of States at CDF b First Observation of Bottom Baryon 2007-10-26¢  Outline 1...

  • First Observation of Bottom Baryon Σb States at CDF

    Igor Gorelov

    University of New Mexico

    On behalf of

    CDF Collaboration

    P-25 Seminar

    Los Alamos National Laboratory

    9 May 2007, Los Alamos, NM

    P-25 Seminars, May 9, 2007, Los Alamos National Laboratory I. Gorelov, First Observation of Bottom Baryon Σb ... Page 1

  • Outline

    1 – Outline

    • Introduction: Heavy Baryons with HQET.

    • Experimental Status.

    • Principle of an Analysis.

    • b-Physics at Tevatron with CDF II detector.

    • CDF II Triggers and Datasets involved. √

    Λ0b base signal.√ Reconstruction of Σb Candidates - Blind.

    √ Opened Box.

    √ Fits.

    √ Systematics.

    √ Significance.

    • Summary.

    P-25 Seminars, May 9, 2007, Los Alamos National Laboratory I. Gorelov, First Observation of Bottom Baryon Σb ... Page 2

  • Multiplets of Heavy Baryons

    2 – Multiplets of Heavy Baryons

    State Quarks JP (I, I3)

    Ground Bottom Baryon States

    Λ0b b[ud] (1/2) + (0, 0)

    Σ+b buu (1/2) + (1,+1)

    Σ0b b{ud} (1/2)+ (1, 0) Σ−b bdd (1/2)

    + (1,−1) Σ∗+b buu (3/2)

    + (1,+1)

    Σ∗0b b{ud} (3/2)+ (1, 0) Σ∗−b bdd (3/2)

    + (1,−1) Orbital P- wave Bottom Baryon States

    Λ∗0b b[ud] (1/2) − (0, 0)

    Λ∗0b b[ud] (3/2) − (0, 0)

    ⇒ Bottom baryon Λ- and Σ- states.

    • Heavy Baryon quark content: Qq1 q2

    • The [q1q2] denotes a pair antisymmetric in flavor and spin.

    • The {q1q2} denotes a pair symmetric in flavor and spin.

    P-25 Seminars, May 9, 2007, Los Alamos National Laboratory I. Gorelov, First Observation of Bottom Baryon Σb ... Page 3

  • Multiplets of Heavy Baryons

    ⇒ Baryons: Bottom Sector

    • Baryon: qf1 ,qf2 ,qf3 • Ordinary SUf (3) with fi ∈ u, d, s • Bottom SUf (5) with

    fi ∈ u, d, s, c, b • Y ≡ B + S− B

    3 , hypercharge.

    • B = −1, for b- quark. • SUf (3) “ground-state” (no orbital

    excitations!)

    • SUf (5) adds to “ground-states” additional floors along B−axis

    • do not consider here double “b-c” baryons like (qcb)

    • Up today established bottom ones: • ONLY Λ0b ≡ b [ud]

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    Q Q Q Q Q

    R R R R RR R R R R

    R R R R RR R R R R

    R R R R RR R R R R

    R R R R RR R R R R

    R R R R RR R R R R

    R R R R R

    S S S S SS S S S S

    S S S S SS S S S S

    S S S S SS S S S S

    S S S S SS S S S S

    S S S S SS S S S S

    S S S S SS S S S S

    S S S S SS S S S S

    S S S S SS S S S S

    S S S S SS S S S S

    S S S S SS S S S S

    T T T T TT T T T T

    T T T T TT T T T T

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    W WW W W WW W

    X XX X X XX X

    I

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    B

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    Σ

    Σ Σ

    dsb usb

    ssb

    udd

    dss

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    dsb

    uus

    dbb ubb sbb

    ddb uubudb

    Ξbb- Ξbb0

    Ω-bb Λ0b b0Σb Σ+b

    bΞ-

    -

    Ξb0 -Ωbn p

    uud

    uds

    Λ Σ0 0 uus

    uss dds- +

    -

    Ξ- Ξ0

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    usb

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    ddd udd uud uuu

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    bb *-Ω

    Σb*- Σ*+b Σb*0

    Ξ*-b Ξb*0

    Ωb*-∆ ∆ ∆- ++∆+0

    Σ- Σ+

    Ξ0Ξ-

    Ω0

    Σ0uds I

    Y

    3

    B

    3

    JP= - 12 +

    J P = - 2

    +3

    Picture courtesy: D. Litvintsev

    P-25 Seminars, May 9, 2007, Los Alamos National Laboratory I. Gorelov, First Observation of Bottom Baryon Σb ... Page 4

  • Motivation for an Experimental Search on Σb

    3 – Motivation for an Experimental Search on Σb

    • Well established charm baryon sector.

    • Wealth of experimental data on bottom B-mesons from e+e− and

    hadron beams.

    • Yet only one bottom baryon, the Λ0b , has been directly observed:

    • Λ0b → J/ψΛ0

    • Λ0b → Λ+c π−

    • Λ0b → Λ+c µ−νµ • World’s largest data sample of bottom

    baryons at CDF...

    • ∼ 3000, Λ0b → Λ+c π−

    • None of Σb states have been established so far.

    • Excellent track resolution of CDF tracker ...

    • precise vertex reconstruction by Si-Detector SVX II ...

    • provide fine mass resolution and ... • make possible to observe

    Σ (∗)± b → Λ0bπ±

    P-25 Seminars, May 9, 2007, Los Alamos National Laboratory I. Gorelov, First Observation of Bottom Baryon Σb ... Page 5

  • Spectroscopy with QCD

    4 – Spectroscopy with QCD

    ⇒ H.Q.E.T. Phenomenology: • QCD simplifies substantially in a presence of a heavy Q • mQ � ΛQCD � mqq, mQ ' 4.8GeV, Q ≡ b • mQ →∞: heavy quark spin decouples from light quark

    degrees of freedoms.

    • Heavy baryons’ properties are governed by the dynamics of the qq in a gluon field created by the Q acting as a static

    source of QCD field: Λ0b baryon as a “helium atom” of QCD.

    • Ground states, Lqq = 0 • Total qq spin sqq: 12

    + ⊗ 1 2

    + → 0+ ⊕ 1+

    • 0+ ⊗ 1 2

    + → 1 2

    + , ΛQ- like ground (i.e. Lqq = 0)

    states

    • 1+ ⊗ 1 2

    + → 1 2

    + ⊕ 3 2

    + , ΣQ- like ground states.

    ⇒ Heavy Q - Light (q1 q2) System: Orbital Angular Momenta.2q1Qq

    Q

    2q

    1q

    kl KL

    ⇒ jqq = sqq + Lqq ⇒ JQqq = sQ + jqq

    P-25 Seminars, May 9, 2007, Los Alamos National Laboratory I. Gorelov, First Observation of Bottom Baryon Σb ... Page 6

  • Spectroscopy with QCD

    ⇒ Low Lying Bottom Baryons ⇒ Theoretical Expectations:

    Σb property MeV/c 2

    m(Σb)−m(Λ0b) 180− 210 m(Σ∗b)−m(Σb) 10− 40 m(Σ−b )−m(Σ+b ) 5− 7 m(Λ0b), fixed 5619.7

    from CDF II ±1.2± 1.2 Γ(Σb),Γ(Σ

    ∗ b) ∼ 8,∼ 15

    see next slide...

    ⇒ HQET ⇒ Potential models ⇒ 1/Nc expansions ⇒ Lattice QCD calc.

    • In a physics reality mQ is finite. • Degeneration of a {Σb, Σ∗b} doublet is resolved by a

    hyperfine mass splitting.

    • Isospin mass splitting within isotriplets Σb and Σ∗b: • The size of the splitting is different

    (J. L. Rosner, hep-ph/0611207):

    (Σ∗+b − Σ∗−b )− (Σ+b − Σ−b ) = 0.40± 0.07MeV/c2.

    • Contribution to the systematic uncertainty.

    P-25 Seminars, May 9, 2007, Los Alamos National Laboratory I. Gorelov, First Observation of Bottom Baryon Σb ... Page 7

  • Spectroscopy with QCD

    ⇒ Pion Transitions into Λ0b Singlet.

    • H.Q.E.T.: pion transitions are governed by the light diquark.

    • Ground states (or S-wave) Σ

    (∗)± b → Λ0bπ±

    • single- π± in P -wave with qq(1+)→ qq(0+) + π±

    0−⊗1−

    • Orbital states (or P -wave) Λ∗0b → Λ0bπ+π− given sufficient phase space.

    • single- π± are forbidden: • I- spin conservation. • parity conservation (strong

    decays!) (for Λ∗0b ( 3 2

    − ) state)

    • 2- π± in P -wave with qq(1−)→ qq(0+) + (π+π−)1−

    antisymmb[qq] symmb{qq}

    2 G

    eV /c

    +1/2bΛ

    -1/2

    -3/2 + 1/2⊗-1*bΛ

    ππ p-wave

    π s-wave

    π d-wave

    π s-wave

    ππ p-wave

    + 1/2⊗+0

    bΣ2 +1

    * bΣ2

    +3

    π π p-waves

    + 1/2⊗+1

    I=0 I=1

    Pion Transitions

    P Q s⊗

    P qqnotation: j

    P-25 Seminars, May 9, 2007, Los Alamos National Laboratory I. Gorelov, First Observation of Bottom Baryon Σb ... Page 8

  • Natural Width of Σ (∗)± b Baryons

    5 – Natural Width of Σ (∗)± b

    Baryons

    • M(Σ(∗)b )(theor. pred.) ' M(Λ0b) + (180− 210)MeV/c2

    • Dominated by single P -wave πΣQ - transitions.

    ΓΣQ→ΛQπ ∼ |~pπ|2L+1 , L = 1

    ΓΣQ→ΛQπ = 1

    MΛQ MΣQ

    |fp|2 |~pπ|3

    fp ≡ gA/fπ; fπ = 92MeV; gA = 0.75; • depends from the