ew @ lhcb: future look

EW @ LHCb: Future Look

Ronan McNulty (UCD)

EW meeting 29th November 2011

Working Group on Electroweak precision measurements at the LHCTuesday, Nov 29th, 2011

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Channels Z W W/Z W+/W- (W asymmetry) Afb

Low mass DY Z + jets W + charm

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General Comments 2010->2011 Luminosity for 2011 is 1.1 fb-1 (factor 30) Average number of interactions is 1.7 Due to luminosity levelling, same running conditions

throughout fills and throughout year Triggers unchanged *Very stable* for analysis Since almost everything is data-driven, most

systematics are statistical in nature Factor 5.5 improvement

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ZSource 2010 2011

Statistics 2.2% (2000 Z) 0.4% (60,000 Z)

Efficiency 4.0% 0.7%

Purity 0.1% 0.0%

FSR 0.0% 0.0%

Luminosity 3.5% 2.5%

2010 measurement dominated by statistics (sys. are statistical in nature)2011 dominated by luminosity. How well can we know this?

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WSource 2010 2011

Statistics 0.7% (20,000 W) 0.1% (600,000 W)

Efficiency 2.8% 0.5%

Purity 3.1% 1.0% {?}

FSR 0.0% 0.0%

Luminosity 3.5% 2.5%

2010 measurement dominated by statistics (sys. are statistical in nature)2011 dominated by luminosity. How well can we know this?

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How can we improve luminosity?

QED processUncertainty <1%

Well known process studied by all LHCexperiments.

• A.G.Shamov and V.I.Telnov, NIM A 494 (2002) 5156, 2002.

• J. Vermaseren, Nucl. Phys. B229, 347,1983.• CMS PAS DIF-07-001• Bryan Caron, CERN-THESIS-2006-024• CERN-LHCb-CONF-2011-022

Difficulty is in selecting a pure enough signal.

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Exclusive J/psi(not background subtracted)

Candidates for di-photon produced dimuons

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Fit elastic and inelastic components

Shape for inelastic events

Note: this time we have simulation thatpredicts the shape for the three contributions.

Fit to signal events

Background shape from dataSignal shape from simulation.

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Luminosity through pp->pmmpSource 2010 2011

Statistics 16% 2.3%

Efficiency 8% 1%

Purity 2% 0.3%

Note: Better than N improvement in 2011 due to lower average number of proton-proton interactions

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W/Z (Remove luminosity)

Source 2010 2011

Statistics 2.2% 0.4%

Efficiency 2.8% 0.5%

Purity 3.1% 1.0% {?}

FSR 0.0% 0.0%

Luminosity 0.0% 0.0%

2010 measurement dominated by statistics (sys. are statistical in nature)2011 dominated by statistics & W bkg: 1% measurement looks possible

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W+/W-Source 2010 2011

Statistics 1.5% 0.3%

Efficiency 0.0% 0.0%

Purity 0.2% 0.2%

FSR 0.0% 0.0%

Luminosity 0.0% 0.0%

2010 measurement dominated by statistics (sys. are statistical in nature)2011 dominated by statistics: Most sensitive experimental test of SM (<0.5%)

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W asymmetryEta range 2010 2011

2 < < 2.5 0.014 0.003

2.5 < < 3. 0.014 0.003

3 < < 3.5 0.016 0.003

3.5 < < 4. 0.022 0.004

4 < < 4.5 0.058 0.010

2010 measurement dominated by statistics (sys. are statistical in nature)2011 dominated by statistics Most sensitive experimental test of SM

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Indicative uncertaintieswith 2011 data

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Z boson: AFB

60,000 Z with 2011 data Precision of 0.004 on Afb. Precision of ~0.001 on sin2W

(Similar to precision from Afb0l from one LEP experiment)

(see WG meeting 5th April)

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*-> below Z

Backgrounds appear controllable down to 10 GeV (x~2.10-5)

Statistical uncertainty ~ as for Z Systematics under study: background description likely

to be dominant. Purity ~ 25%. Results hopefully for early 2012. Excellent method for constraining gluon pdf at low x.

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Z+jets

Z sample for 2011 being analysed using anti-kt, cone 0.5.

Requires jet energy calibration difficult at LHCb EM calorimeter saturation Can’t use jet balancing techniques

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W+charm

Possible once jet energy calibration understood ….

Require evidence for secondary vertices generic HF tagging IP of high pt tracks (as in Z->) D meson reconstruction

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Summary

W,Z limited by luminosity uncertainty which can improve using pp

Ratios become systematic limited at ~ 1% New measurements: Afb, low mass DY,

Z+jets, W+charm