ATLAS b0 Baryon Studies...Introduction 0 b reconstructionLifetime measurementHelicity study 0 b!...

ATLAS Λ0b Baryon Studies

Dongliang Zhang (University of Michigan)

on behalf of ATLAS Collaboration

Hadron2015, Jefferson LabSeptember 13-18, 2015

Introduction Λ0b reconstruction Lifetime measurement Helicity study Λ0

b → ψ(2S)Λ0 Summary 1/18Λ0b baryon

q Λ0b is the lightest b-baryon

q m ∼ 5620 MeVq Beyond the reach of B-factoriesq Was less studied

q Lifetimeq Polarizationq Decay properties

q Included in this talk:

q Mass and lifetime measurement [Phys. Rev. D 87 (2013) 032002]q Λ0

b → J/ψΛ0 decay asymmetry parameter and helicity amplitude measurement [Phys.

Rev. D 89 (2014) 092009]q Observation of Λ0

b → ψ(2S)Λ0 decay and Γ(Λ0b → ψ(2S)Λ0)/Γ(Λ0

b → J/ψΛ0)measurement [arXiv:1507.08202 [hep-ex], submitted to Phys. Lett. B.]

Dongliang Zhang [UM] Hadron2015 14/09/2015

http://journals.aps.org/prd/abstract/10.1103/PhysRevD.87.032002



http://arxiv.org/pdf/1507.08202v1.pdf


b → ψ(2S)Λ0 Summary 2/18ATLAS detector



b → ψ(2S)Λ0 Summary 3/18J/ψ and Λ0 candidates

q J/ψ candidates

q Two combined muons, |η| < 2.5q Sufficient Inner Detector hitsq In J/ψ or ψ(2S) mass window

(MeV)µµm

2800 2900 3000 3100 3200 3300 3400

Candid

ate

s / 1

5 M

eV

0

10000

20000

30000

40000

50000

ATLAS

1 = 77 pbL

= 7 TeVs

q Λ0 candidates

q Two good ID tracks, pT > 400 MeVq pπ− and pπ+ combination, in Λ0

mass window

(MeV)πpm

1080 1090 1100 1110 1120 1130 1140 1150

Candid

ate

s / 3

.25 M

eV

0

20

40

60

80

100

120

140

1603

10×

ATLAS

1 = 77 pbL

= 7 TeVs



b → ψ(2S)Λ0 Summary 4/18Λ0b reconstruction

q Λ0b fit

q mµ+µ− and mpπ− (mpπ+ ) fixed to J/ψ and Λ0 mass valuesq Dihadron vertex point to dimuon vertexq χ2/Ndof < 3

q Also fitted to B0d → J/ψ(µ+µ−)K 0

S (π+π−) hypothesis for B0d background

rejection cuts

q In lifetime measurementq Refitted Λ0

q pT > 3.5 GeVq Lxy > 10 mm

q PΛ0b− PB0

d> 0.05


(MeV)0Λ ψJ/

M

5400 5500 5600 5700 5800 5900

Ca

nd

ida

tes /

17

Me

V0

50

100

150

200

250

300

350

400

450 candidates0

bΛ

candidates0

bΛ

ATLAS

1 = 4.9 fbL

= 7 TeVs

4074 Λ0b

4081 Λ0b


b → ψ(2S)Λ0 Summary 5/18Λ0b lifetime measurement

q Proper decay time

τ =Lxym

PDG

pT

q Mass-lifetime unbinned likelihood fit

L =N∏i=1

[fsigMs(mi |δmi )Ts(τi |δτ i )ws(δmi , δτ i ) + (1− fsig)Mb(mi |δmi )Tb(τi |δτ i )wb(δmi , δτ i )]

q Mass

q Ms(mi |δmi ): Gaussianq Mb(mi |δmi ): 1st order polynomial

q Proper decay time

q Ts(τi |δτ i ): exponential with efficiency correctionq Tb(τi |δτ i ):

– prompt: Dirac delta + symmetric exponential– non-prompt: two exponential

q ws,b(δmi , δτ i ) is the PDF for δmi and δτ i , from data and same for signal andbackground



b → ψ(2S)Λ0 Summary 6/18Λ0b mass and lifetime

(MeV)0Λ ψJ/

m

5400 5500 5600 5700 5800 5900

Candid

ate

s / 1

7 M

eV

0

100

200

300

400

500

600

700

800 0.7 MeV± = 5619.7 bΛm

0.03± = 1.18 M

S

0.8 MeV± = 31.1 M

σ

57± = 2184 sigN

160± = 5970 bkg N

= 1.09dofN/2χ

= 7 TeVs1 = 4.9 fbL

Data

Fitted model

Signal

Background

ATLAS

(ps)τ

2 0 2 4 6 8 10 12

Candid

ate

s / 0

.46 p

s

10

210

310

0.036 ps± = 1.449 b

Λτ

0.02± = 1.05 τS

0.003 ps± = 0.117 τσ

= 1.09dofN/2χ

= 7 TeVs1 = 4.9 fbL

Data

Fitted model

Signal

Background

ATLAS

mΛ0b

= 5619.7± 0.7(stat)± 1.1(syst) MeV

τΛ0b

= 1.449± 0.036(stat)± 0.017(syst) ps

q Consistent with results from other experiments and theoretical predictions

q Main systematic uncertainty from muon trigger efficiency and Λ0 reconstructionbias


Phys. Rev. D 87 (2013) 032002



b → ψ(2S)Λ0 Summary 7/18Λ0b → J/ψ(µ+µ−)Λ0(pπ−) decay

q Asymmetric decay

dN

d cos θ=

1

2(1 + P · αb cos θ)

q In subsequent decay:

q 4 helicity combination

Amplitude λΛ λJ/ψa+ = |a+|e iω+ 1/2 0a− = |a−|e iω− -1/2 0b+ = |b+|e iρ+ -1/2 -1b− = |b−|e iρ− 1/2 1

q Full PDF of Ω = (cos θ, φ, cos θ1, φ1, cos θ2, φ2):

w(Ω) =1

(4π)3

19∑i=0

f1i (~A)f2i (P, αΛ)Fi (Ω)

q 7 free parameters: P, 6 helicity parameters in ~A



b → ψ(2S)Λ0 Summary 8/18Parametrization

q For αb measurement, using P = 0, reduced to 6 terms (i = 0, 2, 4, 6, 18, and 19)

q Parameters ~A

q αb = |a+|2 − |a−|2 + |b+|2 − |b−|2

q k+ = |a+|√|a+|2+|b+|2

q k− = |b−|√|a−|2+|b−|2

q ∆+ = ω+ − ρ+

q ∆− = ω− − ρ−

i f1i Fi

0 1 12 (k2

+ + k2− − 1) + αb(k2

+ − k2−) cos θ1

4 14

[(3k2− − 3k2

+ − 1) + 3αb(1− k2− − k2

+)] 0.5(3 cos2 θ2 − 1)

6 − 14

[(k2+ + k2

− − 1) + αb(3 + k2+ − k2

−)] 0.5(3 cos2 θ2 − 1) cos θ1

18 3√2

[ 1−αb2

√k2−(1− k2

−) cos(−∆−)− 1+αb2

√k2

+(1− k2+) cos(∆+)] sin θ1 sin θ2 cos θ2 cos(φ1 + φ2)

19 − 3√2

[ 1−αb2

√k2−(1− k2

−) sin(−∆−)− 1+αb2

√k2

+(1− k2+) sin(∆+)] sin θ1 sin θ2 cos θ2 sin(φ1 + φ2)



b → ψ(2S)Λ0 Summary 9/18Method of moments

q Least square fit

χ2 =∑i

∑j

(〈Fi 〉expected − 〈Fi 〉)V−1ij (〈Fj〉expected − 〈Fj〉)

q 〈Fj〉 measured from dataq Vij is the covariance matrix

q 〈Fi 〉expected depends on the parameters ~A

〈Fi 〉expected(~A) =

∫Fi (Ω′)

∫T (Ω′,Ω)w(~A,Ω) dΩdΩ′

=∑j

1

(4π)3

∫∫f1j(~A)f2j(αΛ)Fi (Ω′)T (Ω′,Ω)Fj(Ω) dΩ′dΩ

=∑j

f1j(~A)f2j(αΛ)Cij

q The effects of detector are in Cij

q T (Ω′,Ω) is the resolution and efficiency function



b → ψ(2S)Λ0 Summary 10/18Efficiency correction from MC

Cij=1

(4π)3

∫∫Fi (Ω′)Fj(Ω)T (Ω′,Ω) dΩ′dΩ

≈ εTNmc

Nmc∑n=1

Fi (Ω′n)Fj(Ωn)

1θcos

1 0.5 0 0.5 1

Fra

ctio

n /

0.1

0

0.02

0.04

0.06

0.08

0.1

Flat PDF

=1b

α

=0.3b

α

=1b

α

ATLAS

Simulation

2θcos

1 0.5 0 0.5 1

Fra

ctio

n /

0.1

0

0.02

0.04

0.06

0.08

0.1

Flat PDF

=1b

α

=0.3b

α

=1b

α

ATLAS

Simulation



b → ψ(2S)Λ0 Summary 11/18Event selection & Background

q 2011 7 TeV data

q Λ0b selection

q Exclude tracks from primary vertexq τ > 0.35 psq Loose B0

d veto: PΛ0b> PB0

d

q 5560 < m < 5680 MeV

q Combinatorial background

q Estimated from sidebands (SB)

q Peaking background

q B0d → J/ψ(µ+µ−)K 0

S (π+π−)q Yield from the mass fitq 〈Fi 〉 from Mont Carlo

Parameter [5340, 5900] MeV [5560, 5680] MeVNsig 1400± 50 1240± 40NComb 1090± 80 234± 16NB0

d210± 90 73± 30


[MeV])

0Λ(0ΛψJ/

m

5400 5500 5600 5700 5800 5900

Eve

nts

/ 1

0 M

eV

0

50

100

150

200

250

300

Data 2011

Fitted modelSignal

bkgd0

BComb. bkg 50± = 1400 sigN

90± = 210 d

0B

N

80± = 1090 Comb.N

) = 0.892χProb(

ATLAS 1

L dt = 4.6 fb∫ = 7 TeV, s0

bΛ+0bΛ

Left SB Right SB

2F

1 0.5 0 0.5 1

Events

/ 0

.1

0

50

100

150

200

[5560, 5680] MeV

[5400, 5520] MeV

[5720, 5840] MeV

ATLAS

1 L dt = 4.6 fb∫ = 7 TeV, s

cos θ1


b → ψ(2S)Λ0 Summary 12/18Results

Fit resultsαb= 0.30± 0.16(stat)± 0.06(syst)

k+ = 0.21+0.14−0.21(stat)± 0.13(syst)

k− = 0.13+0.20−0.13(stat)± 0.15(syst)

corresponding to

|A( 1/2, 0)| = 0.17+0.12−0.17 ± 0.09

|A(−1/2,−1)| = 0.59+0.06−0.07 ± 0.03

|A(−1/2, 0)| = 0.79+0.04−0.05 ± 0.02

|A( 1/2, 1)| = 0.08+0.13−0.08 ± 0.06

Main systematic uncertaintiesq MC statistics

q Background shape modeling

bα

1 0.5 0 0.5 1

valu

em

in

2 χ

0

10

20

30

40

50

60bΛ + bΛ

=0.30bestbα

)=3.15bestbα(

min

2χ

ATLAS

1 L dt = 4.6 fb∫ = 7 TeV, s

2σ

3σ

pQCD: −(0.14 ∼ 0.17)

HQET: 0.78

LHCb 0.05± 0.17± 0.07

q Between two theory predictions

q Consistent with LHCb results


Correlation

Parameter αb k+ k−αb 1 0.41 −0.19k+ 1 0.20k− 1

Phys. Rev. D 89 (2014) 092009

Ref: LHCb [Phys. Lett. B 724 (2013) 27]; pQCD [Phys. Rev. D 65 (2002) 074030]; HEQT [Phys. Lett. B 614 (2005) 165173];


http://www.sciencedirect.com/science


http://www.sciencedirect.com/science/article/pii/S0370269305004910


b → ψ(2S)Λ0 Summary 13/18Λ0b → ψ(2S)Λ0 selection

q Fiducial rangeq pT(Λ0

b) > 10 GeV, |η(Λ0b)| < 2.1 (Kinematic range)

q pT(µ±) > 4 GeV, |η(µ±)| < 2.3q pT(Λ0) > 2.5 GeV

q Other selectionc cutsq pT(π−) > 0.45 GeVq τ > 0.35 ps, P(Λ0

b) > P(B0d )

)) [MeV]0

Λ(0

Λ ψm(J/

5400 5500 5600 5700 5800 5900

Events

/ 1

0 M

eV

0

200

400

600

800

1000

1200

1400 ATLAS1 = 8 TeV, 20.6 fbs

0

bΛ + 0bΛ

130± = 6940 sigN

Data

Fitted model

signal0bΛ

reflection0

B

) [MeV]0

S Kψm(J/

5100 5200 5300 5400 5500

Events

/ 1

0 M

eV

0

100

200

300

400

500 ATLAS1 = 8 TeV, 20.6 fbs

84± = 854 sigN

Data

Fitted model

signal0

B

reflection0bΛ


Λ0b → J/ψΛ0 B0

d → J/ψK 0S


b → ψ(2S)Λ0 Summary 14/18Λ0b → ψ(2S)Λ0 selection

)) [MeV]0

Λ(0

Λ(2S) ψm(

5400 5500 5600 5700 5800

Events

/ 1

5 M

eV

0

50

100

150

200

250

300ATLAS

1 = 8 TeV, 20.6 fbs0

bΛ + 0bΛ

38± = 603 sigN

Data

Fitted model

signal0bΛ

reflection0

B

) [MeV]0

S(2S) Kψm(

5100 5200 5300 5400 5500

Events

/ 1

5 M

eV

0

20

40

60

80

100

ATLAS1 = 8 TeV, 20.6 fbs

28± = 124 sigN

Data

Fitted model

signal0

B

reflection0bΛ

q Simultaneous Λ0b and B0

d mass fit

q Signal: modified Gaussian p(x) = exp[−0.5 · x1+1/(1+0.5·x)], x = |(m −m0)/σ|q B0

d and Λ0b reflection using MC templates

q Non-resonant background: exponential functions


Λ0b → ψ(2S)Λ0 B0

d → ψ(2S)K 0S


b → ψ(2S)Λ0 Summary 15/18

) [MeV]

µ+µm(

2700 2800 2900 3000 3100 3200 3300 3400

Events

/ 2

0 M

eV

0

500

1000

1500

2000

2500ATLAS

1 = 8 TeV, 20.6 fbs0

bΛ + 0bΛ

120± = 9770 sigN

Data

Fitted model

signalψJ/

Background

) [MeV]

µ+µm(

3400 3500 3600 3700 3800 3900 4000 4100 4200

Events

/ 2

0 M

eV

0

20

40

60

80

100

120

140

160

180ATLAS

1 = 8 TeV, 20.6 fbs0

bΛ + 0bΛ

45± = 724 sigN

Data

Fitted model

(2S) signalψ

Background

) [MeV]

πm(p

1060 1080 1100 1120 1140 1160 1180

Events

/ 2

MeV

0

500

1000

1500

2000

2500 ATLAS1 = 8 TeV, 20.6 fbs

0Λ ψ J/→

0bΛ

120± = 7710 sigN

Data

Fitted model

signal0

Λ

Background

) [MeV]

πm(p

1060 1080 1100 1120 1140 1160 1180

Events

/ 2

MeV

0

50

100

150

200

250

ATLAS1 = 8 TeV, 20.6 fbs

0Λ(2S) ψ →

0bΛ

38± = 702 sigN

Data

Fitted model

signal0

Λ

Background



b → ψ(2S)Λ0 Summary 16/18Branching ratio

q Yields from fits

Λ0b → J/ψΛ0 B0 → J/ψK0

S Λ0b → ψ(2S)Λ0 B0 → ψ(2S)K0

S

Nsig 6940± 130 854± 84 603± 38 124± 28

msig [MeV] 5620.4± 0.4 5274.7± 2.3 5618.2± 1.2 5272.4± 4.9

σsig [MeV] 19.7± 0.5 19.2± 2.2 14.3± 1.1 16.7± 4.1

q Acceptance correction Ncor = Nsig/Aq Efficiency (Aeff) and acceptance (Akin) in fiducial range

pT(Λ0b) > 10 GeV, |η(Λ0

b)| < 2.1

pT(µ±) > 4 GeV, |η(µ±)| < 2.3

pT(Λ0) > 2.5 GeV

Channel Aeff [%] Akin [%]

Λ0b → J/ψΛ0 4.16± 0.02 7.57± 0.06

Λ0b → ψ(2S)Λ0 4.30± 0.03 9.61± 0.07



b → ψ(2S)Λ0 Summary 17/18Branching ratio

In kinematic range pT(Λ0b) > 10 GeV, |η(Λ0

b)| < 2.1:

Γ(Λ0b → ψ(2S)Λ0)

Γ(Λ0b → J/ψΛ0)

=Ncor(Λ0

b → ψ(µ+µ−)Λ0)

Ncor(Λ0b → J/ψ(µ+µ−)Λ0)

· B(J/ψ → `+`−)

B(ψ(2S)→ `+`−)

= 0.501± 0.033(stat)± 0.016(syst)± 0.011(B)

q B(J/ψ → µ+µ−) = 0.05961± 0.00033 [PDG]

q B(ψ(2S)→ µ+µ−) = B(ψ(2S)→ e+e−) = 0.00789± 0.00017 [PDG]

q Systematic uncertainties

q Signal extraction fits (2.8%)q MC statistics (1.3%)q Λ0

b polarization model (1.1%)

q In the range 0.5–0.8 for B meson decays; smaller than calculation 0.8± 0.1 [Phys.

Rev. D 88 (2013) 114018]


arXiv:1507.08202 [hep-ex]



http://arxiv.org/pdf/1507.08202v1.pdf


b → ψ(2S)Λ0 Summary 18/18Summary

q Studying Λ0b production and decay using ATLAS data

q Lifetime measurement

mΛ0b

= 5619.7± 0.7(stat)± 1.1(syst) MeV

τΛ0b

= 1.449± 0.036(stat)± 0.017(syst) ps

q αb measurement

αb = 0.30± 0.16(stat)± 0.06(syst)

|a+| = 0.17+0.12−0.17(stat)± 0.09(syst)

|a−| = 0.59+0.06−0.07(stat)± 0.03(syst)

|b+| = 0.79+0.04−0.05(stat)± 0.02(syst)

|b−| = 0.08+0.13−0.08(stat)± 0.06(syst)

q Observation of Λ0b → ψ(2S)Λ0 and the measured branching ratio

Γ(Λ0b → ψ(2S)Λ0)

Γ(Λ0b → J/ψΛ0)

= 0.501± 0.033(stat)± 0.016(syst)± 0.011(B)


Backup 19/18Backup: Efficiency correction of lifetime measurement

’ (ps)τ

0 1 2 3 4 5 6

Effic

iency

0.018

0.02

0.022

0.024

0.026

0.028

56 ps± = 113 bΛ

c

ATLAS

Simulation

= 7 TeVs

bΛ

c

’τ

e’) ~ τ(ε

(ps)trueτ

0 1 2 3 4 5 6

Effic

iency

0.03

0.035

0.04

0.045

0.05

43 ps± = 94 dB

c

ATLAS

Simulation

= 7 TeVs

dB

c

’τ

e’) ~ τ(ε


Backup 20/18Backup: B0

d lifetime measurement

(MeV)S

KψJ/M

5100 5150 5200 5250 5300 5350 5400 5450 5500

Candid

ate

s / 1

3 M

eV

0

500

1000

1500

2000

2500

3000

3500

4000 0.2 MeV± = 5279.6 dBM

0.01± = 1.11 M

S

0.2 MeV± = 27.8 M

σ

110± = 17530 sigN

65± = 10069 bkg N

= 1.03dofN/2χ

= 7 TeVs1 = 4.9 fbL

Data

Fitted model

Signal

Background

ATLAS

(ps)τ

2 0 2 4 6 8 10 12 14

Candid

ate

s / 0

.46 p

s

10

210

310

410 0.012 ps± = 1.509

dBτ

0.02± = 1.06 τS

0.003 ps± = 0.107 τσ

= 1.03dofN/2χ

= 7 TeVs1 = 4.9 fbL

Data

Fitted model

Signal

Background

ATLAS


Backup 21/18Backup: full PDF

i f1i f2i Fi0 a+a∗+ + a−a

∗− + b+b∗+ + b−b

∗− 1 1

1 a+a∗+ − a−a∗− + b+b∗+ − b−b

∗− P cos θ

2 a+a∗+ − a−a∗− − b+b∗+ + b−b

∗− αΛ cos θ1

3 a+a∗+ + a−a∗− − b+b∗+ − b−b

∗− P αΛ cos θ cos θ1

4 −a+a∗+ − a−a∗− + 1

2b+b∗+ + 1

2b−b

∗− 1 1

2(3 cos2 θ2 − 1)

5 −a+a∗+ + a−a∗− + 1

2b+b∗+ −

12b−b

∗− P 1

2(3 cos2 θ2 − 1) cos θ

6 −a+a∗+ + a−a∗− −

12b+b∗+ + 1

2b−b

∗− αΛ

12

(3 cos2 θ2 − 1) cos θ1

7 −a+a∗+ − a−a∗− −

12b+b∗+ −

12b−b

∗− P αΛ

12

(3 cos2 θ2 − 1) cos θ cos θ1

8 −3Re(a+a∗−) P αΛ sin θ sin θ1 sin2 θ2 cosφ1

9 3Im(a+a∗−) P αΛ sin θ sin θ1 sin2 θ2 sinφ1

10 − 32Re(b−b

∗+) P αΛ sin θ sin θ1 sin2 θ2 cos(φ1 + 2φ2)

11 32Im(b−b

∗+) P αΛ sin θ sin θ1 sin2 θ2 sin(φ1 + 2φ2)

12 − 3√2Re(b−a

∗+ + a−b

∗+) P αΛ sin θ cos θ1 sin θ2 cos θ2 cosφ2

13 3√2Im(b−a

∗+ + a−b

∗+) P αΛ sin θ cos θ1 sin θ2 cos θ2 sinφ2

14 − 3√2Re(b−a

∗− + a+b∗+) P αΛ cos θ sin θ1 sin θ2 cos θ2 cos(φ1 + φ2)

15 3√2Im(b−a

∗− + a+b∗+) P αΛ cos θ sin θ1 sin θ2 cos θ2 sin(φ1 + φ2)

16 3√2Re(a−b

∗+ − b−a

∗+) P sin θ sin θ2 cos θ2 cosφ2

17 − 3√2Im(a−b

∗+ − b−a

∗+) P sin θ sin θ2 cos θ2 sinφ2

18 3√2Re(b−a

∗− − a+b∗+) αΛ sin θ1 sin θ2 cos θ2 cos(φ1 + φ2)

19 − 3√2Im(b−a

∗− − a+b∗+) αΛ sin θ1 sin θ2 cos θ2 sin(φ1 + φ2)


Backup 22/18

q MC weighted using the fit results

2F

1 0.5 0 0.5 1

Events

/ 0

.1

0

20

40

60

80

100

120

140

160

180

200

databΛ+bΛ0

bΛReweighted 0

bΛPythia

Background

test prob: 0.982χATLAS

1 L dt = 4.6 fb∫ = 7 TeV, s

4F

0.5 0 0.5 1

Events

/ 0

.05

0

50

100

150

200

250

300

350

databΛ+bΛ0

bΛReweighted 0

bΛPythia

Background


1 L dt = 4.6 fb∫ = 7 TeV, s

6F

1 0.5 0 0.5 1

Events

/ 0

.04

0

50

100

150

200

250

databΛ+bΛ0

bΛReweighted 0

bΛPythia

Background


1 L dt = 4.6 fb∫ = 7 TeV, s

18F

0.4 0.2 0 0.2 0.4

Events

/ 0

.02

0

20

40

60

80

100

120

140

databΛ+bΛ0

bΛReweighted 0

bΛPythia

Background


1 L dt = 4.6 fb∫ = 7 TeV, s


cos θ112 (3 cos2 θ2 − 1)

12 sin θ1 sin θ2 cos θ2 cos(φ1 + φ2) 1

2 sin θ1 sin θ2 cos θ2 sin(φ1 + φ2)

Backup 23/18Sidebands comparison

4F

0.5 0 0.5 1

Eve

nts

/ 0

.1

0

100

200

300

400

[5560, 5680] MeV

[5400, 5520] MeV

[5720, 5840] MeV

ATLAS

1 L dt = 4.6 fb∫ = 7 TeV, s

6F

1 0.5 0 0.5 1

Eve

nts

/ 0

.04

0

100

200

300

[5560, 5680] MeV

[5400, 5520] MeV

[5720, 5840] MeV

ATLAS

1 L dt = 4.6 fb∫ = 7 TeV, s

18F

0.4 0.2 0 0.2 0.4

Eve

nts

/ 0

.05

0

100

200

300[5560, 5680] MeV

[5400, 5520] MeV

[5720, 5840] MeV

ATLAS

1 L dt = 4.6 fb∫ = 7 TeV, s

19F

0.4 0.2 0 0.2 0.4

Eve

nts

/ 0

.05

0

100

200

300[5560, 5680] MeV

[5400, 5520] MeV

[5720, 5840] MeV

ATLAS

1 L dt = 4.6 fb∫ = 7 TeV, s


12 (3 cos2 θ2 − 1) 1

2 (3 cos2 θ2 − 1) cos θ1

12 (sin θ1 sin θ2 cos θ2 cos(φ1 + φ2) 1

2 (sin θ1 sin θ2 cos θ2 sin(φ1 + φ2)

Backup 24/18

q Other angular variables

θcos

1 0.5 0 0.5 1

Fra

ctio

n /

0.1

0

0.02

0.04

0.06

0.08

0.1

Flat PDF

=1b

α

=0.3b

α

=1b

α

ATLAS

Simulation

[rad]1

φ

3 2 1 0 1 2 3

/16

) ra

dπ

Fra

ctio

n /

(

0

0.01

0.02

0.03

0.04

0.05

0.06

Flat PDF

=1b

α

=0.3b

α

=1b

α

ATLAS

Simulation

[rad]2

φ

3 2 1 0 1 2 3

/16

) ra

dπ

Fra

ctio

n /

(

0

0.01

0.02

0.03

0.04

0.05

0.06

Flat PDF

=1b

α

=0.3b

α

=1b

α

ATLAS

Simulation

[rad]2

φ+1

φ

3 2 1 0 1 2 3

/16

) ra

dπ

Fra

ctio

n /

(

0

0.01

0.02

0.03

0.04

0.05

Flat PDF

=1b

α

=0.3b

α

=1b

α

ATLAS

Simulation


Backup 25/18Backup: Λ0

b → ψ(2S)Λ0 selection

Λ0b and Λ0

b

) [MeV]0

Λ ψm(J/

5400 5500 5600 5700 5800 5900

Events

/ 1

0 M

eV

0

100

200

300

400

500

600

700

800ATLAS

1 = 8 TeV, 20.6 fbs0bΛ

89± = 3523 sigN

Data

Fitted model

signal0bΛ

reflection0

B

) [MeV]0

Λ ψm(J/

5400 5500 5600 5700 5800 5900

Events

/ 1

0 M

eV

0

100

200

300

400

500

600

700ATLAS

1 = 8 TeV, 20.6 fbs0

bΛ

92± = 3414 sigN

Data

Fitted model

signal0

bΛ

reflection0

B

Threshold function

A · (m −mp −mπ−)B · exp[C · (m −mp −mπ−) + D · (m −mp −mπ−)2]


ATLAS b0 Baryon Studies...Introduction 0 b reconstructionLifetime measurementHelicity study 0 b!...

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Transcript of ATLAS b0 Baryon Studies...Introduction 0 b reconstructionLifetime measurementHelicity study 0 b!...