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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

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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

  • 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 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


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


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


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?

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

Ronan McNulty, LHCEWWG, 5.04.2011


Going forward increases AFB

HORACE: Born

7TeV.

89.2<m<93.2.

Ronan McNulty, LHCEWWG, 5.04.2011


Going forward increases sensitivity…

HORACE: Born

7TeV.

86.2<m<96.2.

Ronan McNulty, LHCEWWG, 5.04.2011


HORACE: Born

7TeV.

Stat uncertainty 10fb-1

Stat uncertainty 50fb-1

Ronan McNulty, LHCEWWG, 5.04.2011


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 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 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 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

  • Is it worth trying to measure AFB at LHC?

  • …. Probably.

Ronan McNulty, LHCEWWG, 5.04.2011


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