Study of W/Z differential distributions and properties of W and Z production from CMS !

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Study of W/Z differential distributions and properties of W and Z production from CMS

PING TAN

^,

University of Iowa 

 

on behalf of   the CMS experiment

ICHEP 2014, July 2-9, Valencia, Spain !

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Introduction

8 TeV

✦ Started with a handful of events at W/Z discoveries (UA1/UA2)

✦ LHC is a W/Z factory   → ~ 100 million W(µν) 

→ ~ 10 million Z(µµ) (recorded by CMS in LHC Run I.)  

Extreme high-precision electro-weak measurements:  

W mass, weak mixing angle, … 

→ indirect hints for beyond-the-SM physics

W 

Z

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Introduction (cont.)

✦ Leading order production at LHC: quark anti-quark annihilations

fa, fb: PDF hard interaction W: high pT - lepton + Missing ET 

Z: two high pT-leptons

scale

variation <1%

C. Anastasiou et. al., Phys. Rev.

PDF errors:

~3-4%

PDF4LHC

✦ Test high-precision

perturbative QCD prediction at the NNLO: 

αS2(Z) ~ α(Z), photon-induced background, … 

✦ Constrain PDFs at the LHC kinematic region: 

Drell-Yan production,  

W charge asymmetry (next talk by Saranya Ghosh) 

CMS constraints on PDF

(Katerina Lipka in QCD session)

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Inclusive W/Z production at 8 TeV - a standard candle

✦ W/Z production is a standard candle when exploring new energy scale/new phenomena

✦ Low-pileup data (~20 pb^-1) taken with dedicated LHC runs: 

→ loose isolated single electron trigger, ET>22 GeV, |η| < 2.5 

→ non-isolated single muon trigger, pT>15 GeV, |η| <2.1

✦ Offline lepton selection: 

isolation,  

ET(pT)>25 GeV, |η|<2.5 (<2.1 for muons) 

EWK+ttbar: ~6% 

QCD: by MET fit

backgrounds:

~0.4%

Phys. Rev. Lett. 112 (2014) 191802 

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Inclusive W/Z production at 8 TeV - standard candles (cont.)

CMS 8 TeV

Systematic uncertainties:  

lepton efficiency (1-3%), momentum (energy) scale, MET modeling, background subtraction  theoretical uncertainty (acceptance): ~2 %  

luminosity: 2.6%

✦ With only 0.1% of 2012 full CMS data, it can challenge the state-of-the-art theoretical predictions, e.g. NNLO (FEWZ) + MSTW2008NNLO

Fiducial results

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Double differential cross section d ² σ/dydp T

✦ Vector boson pT:  

complicate dynamics (intrinsic parton motion/soft gluon radiation/

perturbative QCD/PDF)

✦ Unique sensitivity to

perturbative QCD and gluon PDF at high pT 

 ~1 % statistical precision at Z pT

~ mZ

Analysis Overview

✦ Trigger: 

single isolated muon trigger, pT>24 GeV, |η| < 2.1

✦ Offline selections: 

leading muon pT>25 GeV, |η| < 2.1 

next-to-leading muon pT>10 GeV, |η| < 2.4  81<m(µµ)<101 GeV

✦ Background composition has rather strong pT dependence  Drell-Yan (ττ), W+jets, ttbar, and single top

✦ Data-driven background estimation from e-µ data (except WZ/ZZ)

CMS-PAS-SMP/13-013 Full 2012 CMS data of 19.7 fb-1, ~10 M Z(µµ) events

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Double differential cross section d ² σ/dydp T

(cont.)

✦ Absolute/normalized fiducial cross section in 5 bins of Z rapidity and 10 bins of pT

✦ Unfold to pre-FSR with response matrix from MC simulation: 

correcting for data/MC scale/resolution difference and Z boson pT kinematics Shape discrepancy between data and MC predictions

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Differential cross section dσ/dm and d ² σ/dydm - introduction

New results with full 2012 CMS data, 19.7 fb^-1, in

both ee/µµ channels CMS-PAS-SMP/14-003

HERA w/wo CMS 7 TeV result A classical process: 

 one of benchmark channels to test QCD calculations and study PDFs at hadron colliders

CMS 7 TeV result: JHEP 12 (2013) 30

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Differential cross section dσ/dm and d ² σ/dydm - analysis overview

✦ Double lepton trigger:  

pT>17/8 GeV with |η| < 2.4

✦ Offline selections: 

lepton pT >20/10 GeV, |η| < 2.4 

one candidate per event: based on highest dilepton mass (e) or vertex probability (µ)

✦ Weight NLO POWHEG MC to NNLO level with FEWZ  

→ good data/MC agreement without any other correction, particularly at low mass region

✦ Unfold result to after-FSR (“bare”) and pre-FSR (“born”): 

matrix inversion technique,  correction for acceptance/

efficiency at “bare” level γ-induced background  

significant at high mass region

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Differential cross section dσ/dm

State-of-the-art theoretical calculation works across ~ 10 orders of magnitude.

✦ Variations of evaluated systematic uncertainties across mass bins

✦ Electron and muon channel are consistent

✦ BLUE method for ee/µµ combination considering correlated syst. unc.:

acceptance, modeling, and luminosity.

✦ Corrected to full acceptance with a mass range of [15, 2000] GeV

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Double differential cross section d ² σ/dydm

✦ Fiducial differential cross section dσ/dy in 6 mass bins:  

[20, 30, 45, 60, 120, 200, 1500] GeV

✦ Good agreement with NNLO predictions based on CT10/NNPDF2.1 PDFs.

20-30 GeV 60-120 GeV 200-1500 GeV

syst. unc.: <1%

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Differential cross section dσ/dm - ratio between 7 and 8 TeV

✦ Ratio of normalized (to inclusive Z cross section) differential cross section between 7 and 8 TeV

✦ Cancellation of luminosity uncertainty and reduction of theoretical uncertainties:  

M. Mangano and J. Rojo, http://arxiv.org/abs/1206.3557.

✦ Fully correlated experimental uncertainties between 7 and 8 TeV measurements: acceptance, modeling, and FSR

Ratios between 7/8 TeV for Drell-Yan production are explored for the first time! 

 Limited by statistical uncertainties of 7 TeV measurement for mll>160 GeV

! !

!

CMS 7 TeV result: JHEP 12 (2013) 30

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Double differential cross section d ² σ/dydm - ratio between 7 and 8 TeV

✦ Good agreement with CT10 in general, however different features between data and CT10 are evident.

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Conclusion

✦ High precision W/Z physics is one of key physics programs at the LHC

✦ Inclusive W/Z cross sections serve as standard candles at new energy frontier

✦ Latest differential cross sections (d

²

σ/dp

T

dy, dσ/dm, and d

²

σ/dydm) with full CMS 8 TeV data are presented

✦ Good agreement with state-of-art theoretical predictions in many order of magnitude

✦ Explore vector boson pT dynamics to improve/validate theoretical tools for LHC phenomenology

✦ Provide valuable datasets to improve constraints on proton PDFs

✦ For the first time ratios between 7/8 TeV in Drell-Yan process are shown

✦ Many more high-precision measurements are to come:  

W mass, weak mixing angle, …

✦ Wish all these beautiful/hard measurements could help shed light on the hunting for

the BSM physics

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Backup

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The LHC and CMS experiment

pp collisions: 0.9, 2.36, 7.0, 8.0 TeV (13/14 TeV in 2015)  delivered luminosity:  

2010: 40 pb^-1, 2011: ~6 fb^-1, 2012: ~24 fb^-1

_

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Systematic uncertainty - Drell-Yan differential

cross section

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Study of W/Z differential distributions and properties of W and Z production from CMS !