Top Measurement Prospects with LHCb · Experiment Trigger [JINST8(2013)P04022] • RunInumbershere • movableL0thresholdsand softwareHLT • highp T andjettriggers L0 µ: pT >1.5GeV

Top Measurement Prospects with LHCb

Philip Iltenon behalf of the LHCb Collaboration

Massachusetts Institute of Technology

September 27, 2014

Ilten Top with LHCb September 27, 2014 1 / 18

Introduction

Introduction

• forward top production• reduced gg-scattering• increased charge asymmetry• low and high x gluons

• experiment• detector• trigger• reconstruction• jet tagging• datasets

• expectations• cross-sections• asymmetries• gluon PDF

• discussion


Experiment

Experiment


Experiment

Detector [JINST 3 (2008) S08005]

VELO

RICH1

TT

magnet

OT

IT

T1T2

T3

RICH2

M1

M2M3M4M5

HCAL

ECALmuon system5 m

5 m 15 mz-axis →

y-ax

is→

SPD/PRS

• fully instrumented between 2 < η < 5• momentum resolution between 0.4% at 5 GeV to 0.6% at 100 GeV• impact parameter resolution of 13− 20 µm for tracks• secondary vertex reconstruction with precision of

0.01− 0.05(0.1− 0.3) mm in xy(z)Ilten Top with LHCb September 27, 2014 4 / 18

http://iopscience.iop.org/1748-0221/3/08/S08005

Experiment

Trigger [JINST 8 (2013) P04022]

• Run I numbers here• movable L0 thresholds and

software HLT• high pT and jet triggers

L0

µ: pT > 1.5 GeV340 kHz

µµ:√

p1Tp2

T > 1.3 GeV75 kHz

h: ET > 3.5 GeV405 kHz

e: ET > 2.5 GeV160 kHz

γ: ET > 2.5 GeV80 kHz

µ: pT > 4.8(1) GeV0.7(5) kHz

µµ: m > 2.7(1)GeV1.2(1.3) kHz

track: pT > 1.7 GeV33 kHz

e: pT > 10 GeV

. . .

µ: pT > 10(4.8) GeV

µµ: m > 4.8(3) GeV

displaced vertex

inclusive topologicalbeauty BBDT

inclusive andexclusive charm

. . .

15 MHz 5 kHz

HLT1 HLT2

1 MHz 50 kHz


http://arxiv.org/abs/1211.3055

Experiment

Topological Trigger [JINST 8 (2013) P04022]

• 2, 3, 4-body vertex inclusiveB-hadron trigger

• discrete BDT (Bonsai BDT)• γ, µ(µ), e, or h at L0• single track at HLT1• εTOS w.r.t offline candidates

variable pre-cut (2, 3, 4-body)

Σ |pT| > 3, 4, 4 GeVpminT > 0.5 GeV

m < 7 GeVmcor −DOCA < 0.2 mmIP χ2 −FD χ2 > 100



Experiment

Muon and Jet Reconstruction [JHEP 01 (2014) 033]

• event (pT(µ) > 20 GeV)• ≈ (91± 0.1)% event

multiplicity efficiency• muon (pT > 20 GeV)

• efficiencies from data withtag-and-probe

• ≈ (80± 0.6)% triggerefficiency

• ≈ (90± 0.6)% track efficiency• ≈ (99± 0.3)% ID efficiency

• jet (pT > 30 GeV)• particle flow with anti-kT• efficiencies from simulation• ≈ (95± 8)% efficiency• ≈ (10− 15)% energy

resolution

VELO TT

OTECAL

muon system

tag

test

HCAL

probe



Experiment

Jet Tagging [Phys. Rev. Lett. 113 (2014) 082003]

• pseudo-topological tagger(pTOPO)

• uses TOPO BBDT• bb̄ forward-central asymmetry

(published)• Z + b-jet cross-section (in

review)• pTOPO tagged jet

(pT > 20 GeV)• b-efficiency ≈ 40%• light mis-tag < 0.1%

• dedicated b, c-tagger undervalidation

• from simulation• b-efficiency ≈ 60%• light mis-tag < 0.1%

mcor =√

m2 + p2 sin θ2 +p sin θ



Experiment

Collected Datasets [2012 JINST 7 P01010]

• 2011 at√

s = 7 TeV• 1.1 fb−1

• 2012 at√

s = 8 TeV• 2.1 fb−1

• 2015− 2017 at√

s = 13 TeV• ≈ 5 fb−1

• 2020− 2030 at√

s = 14 TeV• ≈ 50 fb−1

2011

date [day/month]28/02 09/04 19/05 29/06 08/08 18/09 28/10

L[ fb−

1]

0

1

2

3

4

5

6

LHCbATLASCMS

2012

date [day/month]28/02 18/04 05/06 23/07 09/09 27/10 14/12

L[ fb−

1]

0

5

10

15

20

25

30

LHCbATLASCMS



Expectations

Expectations


Expectations

Cross-sections (1) [LHCb-PUB-2013-009]

• Gauld• lb, lbj , lbb, lbbj , l+l−, and l+l−b final states

• 2 < η(µ, jet) < 4.5• pT(l) > 20(7, 10) GeV• pT(jet) > 60(20) GeV

• b-efficiency 70%• light mis-tag 1%• charm mis-tag 15%

• selection can be considerably improved

state σ(7 TeV) [fb] σ(8 TeV) [fb] σ(14 TeV) [fb]

lb 285± 52 504± 94 4366±663lbj 97± 21 198± 35 2335±323lbb 32± 6 65± 12 870±116lbbj 10± 2 26± 4 487± 76l+l− 44± 9 79± 15 635±109l+l−b 19± 4 39± 8 417± 79


https://cds.cern.ch/record/1557385

Expectations

Cross-sections (2) [LHCb-PUB-2013-009]



Expectations

Asymmetries (1) [Phys. Rev. Lett. 107 (2011) 082003]

• Kagan, Kamenik, Perez, Stone• forward asymmetry

At ≡(

N (t)−N (t̄)N (t) + N (t̄)

)2<η<5

• select µ and b-jet• 2 < η(µ, jet) < 5• pT(µ) > 20 GeV• pT(jet) > 50 GeV• b-efficiency 50%• light mis-tag 1%

• backgrounds• single top• W + light, b-jet• QCD multi-jet (light or b)



Expectations

Asymmetries (2) [LHCb-PUB-2013-009]

• Gauld• charge asymmetry

Ac ≡N (∆ |y| > 0)−N (∆ |y| < 0)N (∆ |y| > 0) + N (∆ |y| < 0)

• select µ and b-jet• 2 < η(µ, jet) < 4.5• pT(µ) > 20 GeV• pT(jet) > 60 GeV• b-efficiency 70%• light mis-tag 1%• charm mis-tag 15%

• backgrounds• single top• W + light, b-jet

7 TeV 8 TeV 14 TeV

At 0.69+0.12−0.11 0.55+0.10

−0.09 0.27+0.13−0.12

Alb 2.23+0.43−0.68 0.97+0.74

−0.45 0.54+0.39−0.31

Ac 1.75+0.67−0.47 1.64+0.58

−0.67 1.08+0.27−0.32



Expectations

Asymmetries (3) [LHCb-PUB-2013-009]

• asymmetry can improve with more sophisticated selection



Expectations

Gluon PDF (1) [JHEP 02 (2014) 126]

• Gauld• constrain high x gluon PDF

Q2(x) =

xs uppere±2|η|x2√s left/rightm2

min lower

x-610 -510 -410 -310 -210 -110 1

Q2[ G

eV2]

1

10

210

310

410

510

610

710

LHCbTevatronHERAfixed target



Expectations

Gluon PDF (2) [JHEP 02 (2014) 126]



Discussion

Discussion

• LHCb now has the tools and analyses in place to make a topmeasurement

• using 2012 data, observation should be possible• large statistical uncertainty• possible inclusive combined t and tt̄ cross-section?

• what measurements are needed in the future?• separation of t and tt̄• what is the ideal suite of top measurements LHCb could make?• differential in what?• asymmetries, or just cross-sections?


Documents

Top Measurement Prospects with LHCb · Experiment Trigger [JINST8(2013)P04022] • RunInumbershere • movableL0thresholdsand softwareHLT • highp T andjettriggers L0 µ: pT >1.5GeV