ew @ lhcb: future look
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EW @ LHCb: Future Look. Ronan McNulty (UCD) EW meeting 29 th November 2011. Working Group on Electroweak precision measurements at the LHC Tuesday, Nov 29 th , 2011. Channels. Z W W/Z W+/W- (W asymmetry) A fb Low mass DY Z + jets W + charm. General Comments 2010->2011. - PowerPoint PPT PresentationTRANSCRIPT
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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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Working Group on Electroweak precision measurements at the LHC. 29.11.2011 2
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