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A FB at LHC. Myfanwy Liles (University of Liverpool) Ronan McNulty (University College Dublin) Tara Shears (University of Liverpool). LHCEWWG 5.04.2011. Outline. Is it worth trying to measure A FB at LHC? Rather simple and unsophisticated study Horace Pythia

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a fb at lhc

AFB at LHC

Myfanwy Liles (University of Liverpool)

Ronan McNulty (University College Dublin)

Tara Shears (University of Liverpool)

LHCEWWG 5.04.2011

Ronan McNulty, LHCEWWG, 5.04.2011

outline
Outline
  • Is it worth trying to measure AFB at LHC?
  • Rather simple and unsophisticated study
    • Horace
    • Pythia
  • Motivate discussion and ideas

Ronan McNulty, LHCEWWG, 5.04.2011

current precision on sin 2 q w
Current precision on sin2qW

Unsatisfactory that two most precise measurements are >3s apart, and that W.A. is marginally consistent with either.

Would like to make

measurement with precision

of ~0.0001.

Ronan McNulty, LHCEWWG, 5.04.2011

a fb away from z pole

HORACE: O()+-ind.

7TeV.

All rapidities.

AFB away from Z pole
  • Strong dependence with mass due to -Z interference. (To first order, zero on pole).

“Asymmetry greater further from pole”

Ronan McNulty, LHCEWWG, 5.04.2011

a fb away from z pole1
AFB away from Z pole
  • On pole, due to different RH, LH Z coupling…
  • Small positive value

HORACE: O()+-ind.

7TeV.

All rapidities.

Ronan McNulty, LHCEWWG, 5.04.2011

a fb on z pole
AFB on Z pole

AFB in muon channel at LHC is about 5 times larger than at LEP.

But sensitivity coming more from Al rather than Au or Ad

Ronan McNulty, LHCEWWG, 5.04.2011

where are we most sensitive
Where are we most sensitive?

HORACE: Born

7TeV.

All rapidities.

Greatest sensitivity per event

at 82 GeV

About 2/3 that sensitivity at 91 GeV

But much more stats.

So measurement on pole appears

most sensitive to sin2q

far from pole

HORACE: Born

7TeV.

All rapidities.

near pole

Ronan McNulty, LHCEWWG, 5.04.2011

problems for lhc
Problems for LHC

Ronan McNulty, LHCEWWG, 5.04.2011

going forward increases a fb
Going forward increases AFB

HORACE: Born

7TeV.

89.2<m<93.2.

Ronan McNulty, LHCEWWG, 5.04.2011

going forward increases sensitivity
Going forward increases sensitivity…

HORACE: Born

7TeV.

86.2<m<96.2.

Ronan McNulty, LHCEWWG, 5.04.2011

slide11

HORACE: Born

7TeV.

Stat uncertainty 10fb-1

Stat uncertainty 50fb-1

Ronan McNulty, LHCEWWG, 5.04.2011

50fb 1 at 14 tev measures sin 2 q 0 0001
50fb-1 at 14 TeV measures sin2q~0.0001

1fb-1

HORACE: Born

14TeV.

10fb-1

50fb-1

Stat uncertainty 10fb-1

Stat uncertainty 50fb-1

Ronan McNulty, LHCEWWG, 5.04.2011

50fb 1 at 14 tev measures sin 2 q 0 00011
50fb-1 at 14 TeV measures sin2q~0.0001

1fb-1

HORACE: Born

14TeV.

10fb-1

50fb-1

Stat uncertainty 10fb-1

  • How confident are we:
  • - of theory?
  • - of PDF uncertainties?
  • of detector systematics?

Stat uncertainty 50fb-1

Ronan McNulty, LHCEWWG, 5.04.2011

uncertainty due to pdf
Uncertainty due to PDF

Uncertainty from PDF

(from one PDF set)

about the same as

statistical uncertainty.

With time, this should

improve (~ 50%?)

For 3<yZ<4

0.0004

AFB calculated

MSTW Eigenvector number

Ronan McNulty, LHCEWWG, 5.04.2011

uncertainty due to pdf1
Uncertainty due to PDF

HORACE: Born

7TeV.

86.2<m<96.2.

Difference between

two (old) PDF sets

about the same as

statistical uncertainty.

0.0004

Ronan McNulty, LHCEWWG, 5.04.2011

conclusions
Conclusions
  • Is it worth trying to measure AFB at LHC?
  • …. Probably.

Ronan McNulty, LHCEWWG, 5.04.2011

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