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Studies of PDF uncertainties for the measurement of the mass of the W boson at the LHC Stefano Camarda (DESY) October 21, 2014 October 21, 2014 Stefano Camarda 1 PDF uncertainties on m W ATL-PHYS-PUB-2014-015 Studies of theoretical

slide-1
SLIDE 1

Studies of PDF uncertainties for the measurement

  • f the mass of the W boson at the LHC

Stefano Camarda (DESY) October 21, 2014

October 21, 2014 Stefano Camarda 1

slide-2
SLIDE 2

PDF uncertainties on mW

ATL-PHYS-PUB-2014-015 “Studies of theoretical uncertainties for the measurement of the mass of the W boson at the LHC”

Introduction Theory predictions and PDF uncertainties Event selection and methodology W polarization and PDF uncertainties Charm-initiated W production and PDF uncertainties Detector effects and summary of PDF uncertainties Parton shower uncertainties Conclusions

Points of discussion for a coherent treatment of PDF uncertainties between ATLAS and CMS

October 21, 2014 Stefano Camarda 2

slide-3
SLIDE 3

Introduction

The extraction of mW from the pℓ

T spectrum, is likely to be

limited by theoretical uncertainties. This study addresses PDF uncertainties, and non-perturbative QCD uncertainties related to the parton shower model We need not only a precise estimation of PDF and other theoretical uncertainties, but also a roadmap to control and reduce them, by mean of precise experimental measurements

  • f alternative observables

The idea is to perform a breakdown of the physical mechanisms behind the PDF uncertainties, and estimate which are the most relevant sources of uncertainties. By pointing out the largest uncertainties, the idea is to provide a pattern to reduce them, rather than a precise estimation to be used in our measurement

October 21, 2014 Stefano Camarda 3

slide-4
SLIDE 4

Introduction

PDF uncertainties for the extraction MW from pℓ

T at the

Tevatron are 9 MeV (CDF) and 11 MeV (D0) It has been suggested in Eur. Phys. J. C 69 (2010) 379397 [Krasny, Dydak, Fayette, Placzek, Siodmok, ’10] that PDF uncertainties in proton-proton collisions could be larger than in proton-antiproton collisions for

1st quark generation effect: u and d PDF uncertainties on W boson polarisation 2nd quark generation effect: strange-quark PDF uncertainty

  • n charm-initiated W boson production

3rd quark generation effect: bottom quark mass uncertainty in the extraction of non pertubative parameters from pZ

T

The idea of this study is to estimate such effects with standard tools for theory predictions and Monte Carlo, and get feedback from the theory community

Are we missing something important? Do we need better, additional theoretical predictions to estimate these effects?

October 21, 2014 Stefano Camarda 4

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SLIDE 5

Introduction - disclaimer

The emphasis is on tracking the physical sources of the uncertainties, we are not estimating the uncertainties to be used in the measurement This is not the ATLAS final word on PDF and PS uncertainties for the W mass, and on theory uncertainties We are considering in this study:

u and d valence and sea PDF uncertainties Strange PDF uncertainties PS uncertainties, assuming they can be extrapolated from the measurement of pZ

T to the modelling of pW T

Detector effects on the muon momentum resolution

We are not considering in this study:

Gluon PDF uncertainties in all-order resummation (gluon PDF is varied only at NLO) Heavy flavour masses in the matrix-element calculations Differences in the heavy flavour content of W and Z production when propagating PS uncertainties from pZ

T to pW T

Any QED FSR, and NLO EW effect Detector effects on the measurement of the hadronic recoil

October 21, 2014 Stefano Camarda 5

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SLIDE 6

Theory predictions

EW scheme

Gµ-scheme: with GF, MZ, MW as inputs from PDG 2012, α and θW calculated at tree level ΓZ and ΓW measured value from PDG 2012 CKM from PDG 2012, but Vtx = 0, no top in the initial state

Theory predictions and tools

MCFM

W+j production at LO O(αs), which is the real part of W inclusive calculation at NLO finite width, leptonic decay, spin correlations

CuTe

differential W pT at NNLL with matching corrections at O(αs) (NLO+NNLL) zero width approximation no decay of the W

APPLGRID: Fast PDF convolution

Need to combine the two codes, MCFM and CuTe, to get a realistic prediction of the lepton pT spectrum

October 21, 2014 Stefano Camarda 6

slide-7
SLIDE 7

CuTe

Infrared Safety from the Collinear Anomaly [Becher, Neubert, Wilhelm ’11] The factorisation scale is set to µ = q∗ + qT, with q∗ ∼ 1.82 GeV The non-perturbative scale q∗ ∼ e−C/αs(mV ) protects the processes from receiving large long-distance hadronic contributions Allows to calculate the derivative of pW ,Z

T

for pT → 0 with perturbative QCD One additional non perturbative parameter ΛNP = 0.6 GeV introduce a gaussian smearing for hadronic non-pQCD effects Public C++ code, very fast

October 21, 2014 Stefano Camarda 7

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SLIDE 8

Theory predictions - benchmark

[pb/GeV]

+

W T

/dp σ d 10

2

10

3

10

4

10

5

10

6

10 = 7 TeV s ;

+

W → pp

NLO (fixed order) CuTe CT10nlo MCFM CT10nlo

[GeV]

+

W T

p 20 40 Ratio 0.98 1 1.02 [pb/GeV]

  • W

T

/dp σ d 10

2

10

3

10

4

10

5

10

6

10 = 7 TeV s ;

  • W

→ pp

NLO (fixed order) CuTe CT10nlo MCFM CT10nlo

[GeV]

  • W

T

p 20 40 Ratio 0.98 1 1.02

Perfect agreement between the two codes, at fixed order O(αs), zero width, no decay.

October 21, 2014 Stefano Camarda 8

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SLIDE 9

Theory predictions - combination

Reweighting function defined as r(pT) = NLO+NNLL

NLO

The reweighing is applied, in the range 0.1 < qT < 150 GeV,

  • utside this range the weight is set to 0

[GeV]

+

W T

p 20 40 60 80 100 120 140 [pb/GeV]

T

/dp σ d 10

2

10

3

10

4

10

5

10

+

W → CuTe; pp NLO (fixed order) NLO+NNLL [GeV]

  • W

T

p 20 40 60 80 100 120 140 [pb/GeV]

T

/dp σ d 10

2

10

3

10

4

10

5

10

  • W

→ CuTe; pp NLO (fixed order) NLO+NNLL [GeV]

+

W T

p 20 40 60 80 100 120 140 Ratio 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

+

W → CuTe; pp NLO NLO+NNLL [GeV]

  • W

T

p 20 40 60 80 100 120 140 Ratio 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

  • W

→ CuTe; pp NLO NLO+NNLL

October 21, 2014 Stefano Camarda 9

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SLIDE 10

CKM decomposition of the reweighting function

The NLO+NNLL/NLO ratio has a significant dependence on the flavour of the quarks initiating the W -boson production process: heavy quarks result in a harder pW

T spectrum and a

harder ratio between resummed and fixed order predictions The reweighting function is decomposed in terms of the CKM matrix: 6 × 2 functions are the NLO+NNLL/NLO ratios evaluated by setting to 0 all the CKM matrix except the Vxy term, separately for W + and W −

[GeV]

+

W T

p 20 40 60 80 100 120 140 Reweighting function 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

+

W → CuTe; pp

ud

V

us

V

ub

V

cd

V

cs

V

cb

V [GeV]

  • W

T

p 20 40 60 80 100 120 140 Reweighting function 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

  • W

→ CuTe; pp

ud

V

us

V

ub

V

cd

V

cs

V

cb

V October 21, 2014 Stefano Camarda 10

slide-11
SLIDE 11

Theory predictions - benchmark

[pb/GeV]

+

W T

/dp σ d

2

10

3

10

4

10 = 7 TeV s ;

+

W → pp

NLO+NNLL CuTe MCFM+CuTe

[GeV]

+

W T

p 20 40 Ratio 0.95 1 1.05 [pb/GeV]

  • W

T

/dp σ d

2

10

3

10

4

10 = 7 TeV s ;

  • W

→ pp

NLO+NNLL CuTe MCFM+CuTe

[GeV]

  • W

T

p 20 40 Ratio 0.95 1 1.05

Good agreement at NLO+NNLL after reweighting. PDF uncertainties reproduced at high pT, at low pT CuTe has larger PDF uncertainties. In CuTe the factorisation scale is set to µ = q∗ + qT, with q∗ ∼ 1.82 GeV, → CuTe is sensitive to larger PDF uncertainties associated with the low x region. In MCFM prediction, the factorisation scale is set to 80 GeV.

October 21, 2014 Stefano Camarda 11

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SLIDE 12

Dedicated PDF set

A dedicated PDF set has been produced to study the PDF uncertainties for MW extraction from pl

T

Simple setup which allows breakdown of uncertainties, not intended for final estimate of PDF uncertainties NLO Fit to HERA I data Starting scale Q2

0 = 1.7 GeV2

charm mass mc = 1.38 GeV bottom mass mb = 4.75 GeV top mass mt = 3.5 TeV → 5 flavour strange fraction rs = s/¯ d = 1 13p parametrisation 26 hessian variations 4 model variations: mc = 1.32, 1.44, rs = 0.72, 1.25 Total of 30 variations

October 21, 2014 Stefano Camarda 12

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SLIDE 13

PDF at the starting scale

x

  • 4

10

  • 3

10

  • 2

10

  • 1

10 1 )

2

(x,Q

V

xu 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

2

= 1.7 GeV

2

Q MW-NLO exp+mod MW-NLO exp x

  • 4

10

  • 3

10

  • 2

10

  • 1

10 1 )

2

(x,Q

V

xd 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4

2

= 1.7 GeV

2

Q MW-NLO exp+mod MW-NLO exp x

  • 4

10

  • 3

10

  • 2

10

  • 1

10 1 )

2

xg(x,Q

  • 1
  • 0.5

0.5 1 1.5 2 2.5 3

2

= 1.7 GeV

2

Q MW-NLO exp+mod MW-NLO exp x

  • 4

10

  • 3

10

  • 2

10

  • 1

10 1 )

2

(x,Q Σ x 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

2

= 1.7 GeV

2

Q MW-NLO exp+mod MW-NLO exp x

  • 4

10

  • 3

10

  • 2

10

  • 1

10 1 )

2

(x,Q u x 0.1 0.2 0.3 0.4 0.5

2

= 1.7 GeV

2

Q MW-NLO exp+mod MW-NLO exp x

  • 4

10

  • 3

10

  • 2

10

  • 1

10 1 )

2

(x,Q d x 0.1 0.2 0.3 0.4 0.5

2

= 1.7 GeV

2

Q MW-NLO exp+mod MW-NLO exp x

  • 4

10

  • 3

10

  • 2

10

  • 1

10 1 )

2

xs(x,Q 0.1 0.2 0.3 0.4 0.5 0.6

2

= 1.7 GeV

2

Q MW-NLO exp+mod MW-NLO exp x

  • 4

10

  • 3

10

  • 2

10

  • 1

10 1 )

2

)(x,Q d + u )/( s x(s+ 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

2

= 1.7 GeV

2

Q MW-NLO exp+mod MW-NLO exp

Blue band: experimental (hessian) uncertainties Red band: experimental uncertainties plus model variations, rs and mc

October 21, 2014 Stefano Camarda 13

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SLIDE 14

PDF uncertainties at the scale of MW

x

  • 4

10

  • 3

10

  • 2

10

  • 1

10 1

ref

)

2

(x,Q

V

)/xu

2

(x,Q

V

xu 0.8 1 1.2

2

= 6464 GeV

2

Q MW-NLO exp+mod MW-NLO exp x

  • 4

10

  • 3

10

  • 2

10

  • 1

10 1

ref

)

2

(x,Q

V

)/xd

2

(x,Q

V

xd 0.8 1 1.2

2

= 6464 GeV

2

Q MW-NLO exp+mod MW-NLO exp x

  • 4

10

  • 3

10

  • 2

10

  • 1

10 1

ref

)

2

)/xg(x,Q

2

xg(x,Q 0.8 1 1.2

2

= 6464 GeV

2

Q MW-NLO exp+mod MW-NLO exp x

  • 4

10

  • 3

10

  • 2

10

  • 1

10 1

ref

)

2

(x,Q Σ )/x

2

(x,Q Σ x 0.8 1 1.2

2

= 6464 GeV

2

Q MW-NLO exp+mod MW-NLO exp x

  • 4

10

  • 3

10

  • 2

10

  • 1

10 1

ref

)

2

(x,Q u )/x

2

(x,Q u x 0.8 1 1.2

2

= 6464 GeV

2

Q MW-NLO exp+mod MW-NLO exp x

  • 4

10

  • 3

10

  • 2

10

  • 1

10 1

ref

)

2

(x,Q d )/x

2

(x,Q d x 0.8 1 1.2

2

= 6464 GeV

2

Q MW-NLO exp+mod MW-NLO exp x

  • 4

10

  • 3

10

  • 2

10

  • 1

10 1

ref

)

2

)/xs(x,Q

2

xs(x,Q 0.8 1 1.2

2

= 6464 GeV

2

Q MW-NLO exp+mod MW-NLO exp x

  • 4

10

  • 3

10

  • 2

10

  • 1

10 1

ref

)

2

)(x,Q d + u )/( s )/x(s+

2

)(x,Q d + u )/( s x(s+ 0.8 1 1.2

2

= 6464 GeV

2

Q MW-NLO exp+mod MW-NLO exp

Valence PDF dominated by experimental uncertainties from the HERA I data ¯ u, ¯ d and strange PDF dominated by model variations, rs and mc

October 21, 2014 Stefano Camarda 14

slide-15
SLIDE 15

Methodology and event selection

Event selection

|ηl| < 2.4 pν

T > 30 GeV

MT > 60 GeV 30 < pl

T < 50 GeV

Generate a test sample with MW = 80.385 Estimate only statistical experimental uncertainty in 5 fb−1, assuming no efficiency loss Consider normalised pl

T distribution, in bins of 0.5 GeV

Calculate a χ2 profile as a function of MW , in the region ±100 MeV (80.286 < MW < 80.484), in steps of 2 MeV Fit the χ2 profile with a parabolic function to find minimum and sigma at ∆χ2 = 1 Compute the minimum for each PDF variation of a given PDF set, calculate PDF uncertainty as the difference between the minimum for the central PDF and each PDF variation Repeat the analysis for W + only, W − only and both W + and W −

October 21, 2014 Stefano Camarda 15

slide-16
SLIDE 16

Methodology and event selection - Example of χ2 profile

[MeV]

W

M 80300 80350 80400 80450 80500

2

χ

  • 200

200 400 600 800

+

W

  • W
  • and W

+

W 5.0 ± 80385.2 5.8 ± 80385.1 3.8 ± 80385.2

The procedure gives us a rough estimate of the statistical uncertainty expected from the 2011 data set at 7 TeV. Detector resolution effect are not yet included in this plot The statistic of the MC sample is much higher, the statistical bias on the central value of MW = 80.385 is below 0.2 MeV

October 21, 2014 Stefano Camarda 16

slide-17
SLIDE 17

W polarization and PDF uncertainties

The production of W by u and d quarks at LO, at a given rapidity y can be decomposed in two terms corresponding to λ = +1, −1 helicity states: σW +(y) ∝ u(x1) · ¯ d(x2) + ¯ d(x1) · u(x2) (1) σW −(y) ∝ d(x1) · ¯ u(x2) + ¯ u(x1) · d(x2) (2) x1,2 = MW

√s · e±y

At central rapidity y = 0, x1 = x2, the two terms are equal, → unpolarised W For y = 0, the two terms are different, the W is polarised on average The uncertainty in the u and d valence and sea PDF determines an uncertainty in the average polarisation of the W , which in turns propagates into an uncertainty on the pl

T spectrum.

October 21, 2014 Stefano Camarda 17

slide-18
SLIDE 18

W polarization and PDF uncertainties

  • λ = −1

zlab ℓ+ (WRF) ν (WRF) θ∗

  • λ = 0

zlab ℓ+ (WRF) ν (WRF) θ∗

  • λ = +1

zlab ℓ+ (WRF) ν (WRF) θ∗

)

*

θ cos(

  • 1 -0.8-0.6-0.4-0.2 0

0.2 0.4 0.6 0.8 1 0.5 1 1.5 2 2.5 3 3.5 4

=-1 λ =+1 λ =0 λ =-1,0,+1 λ =-1,1 λ

The λ = +1, −1, and 0 helicity states correspond to different distribution of the polar angle θ∗ between the direction of the momentum of the incoming quark in the laboratory frame, assumed to be parallel to the beam axis, and the direction of the leptons momenta in the W -boson rest frame

October 21, 2014 Stefano Camarda 18

slide-19
SLIDE 19

W polarization and PDF uncertainties

The uncertainty on the u and d valence and sea PDF translates into an uncertainty in the average W polarisation, which affects the pl

T distribution

Simple setup to disentagle the effect of W polarisation Keep only Vud = 0 and set all the other terms of the CKM matrix to 0 Apply a random rotation to the decay angle of the leptons in the W rest frame → No spin correlations Apply a sign flip to the lepton momentum in W rest frame → λ = ±1 symmetric Switch on spin correlations and compare PDF uncertainties Thanks to Paolo Nason for the idea of randomising the lepton momenta to switch off spin correlations

October 21, 2014 Stefano Camarda 19

slide-20
SLIDE 20

W polarization and PDF uncertainties

*) θ cos(

  • 1
  • 0.5

0.5 1 *) [pb] θ /dcos( σ d 1000 2000 3000 4000 5000 6000 7000 = 7 TeV s ;

+

W → pp

MCFM+CuTe No spin correlations 1 symmetric ± = λ Spin correlations

*) θ cos(

  • 1
  • 0.5

0.5 1 *) [pb] θ /dcos( σ d 500 1000 1500 2000 2500 3000 3500 4000 = 7 TeV s ;

  • W

→ pp

MCFM+CuTe No spin correlations 1 symmetric ± = λ Spin correlations

cos θ∗ distributions in the 3 samples The dashed bands show PDF uncertainties, only in the sample with spin correlations the PDF uncertainties affect the average W polarisation

October 21, 2014 Stefano Camarda 20

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SLIDE 21

W polarization and PDF uncertainties

[pb / GeV]

l T

/dp σ d ⋅ σ 1/

  • 2

10

  • 1

10 = 7 TeV s ;

+

W → pp

Spin correlations No spin correlations

[GeV/c]

l T

p 30 35 40 45 50 Ratio 0.995 1 1.005 [pb / GeV]

l T

/dp σ d ⋅ σ 1/

  • 2

10

  • 1

10 = 7 TeV s ;

  • W

→ pp

Spin correlations No spin correlations

[GeV/c]

l T

p 30 35 40 45 50 Ratio 0.995 1 1.005

Dramatic shrink of the PDF uncertainties on pℓ

T distribution

when spin correlations are switched off

October 21, 2014 Stefano Camarda 21

slide-22
SLIDE 22

W polarization and PDF uncertainties

PDF member 1 6 11 16 21 26 [MeV]

W

m 80360 80370 80380 80390 80400

80384.8 +3.1 -3.0 80386.2 +3.1 -3.3 80385 +17 -21 No spin correlations

+

W 1 symmetric ± = λ

+

W Spin correlations

+

W

PDF member 1 6 11 16 21 26 [MeV]

W

m 80365 80370 80375 80380 80385 80390 80395 80400 80405

80384.5 +5.6 -5.5 80386.4 +6.8 -6.1 80385 +28 -27 No spin correlations

  • W

1 symmetric ± = λ

  • W

Spin correlations

  • W

Sets 1-26, hessian variations Set 27 mc = 1.32, Set 28 mc = 1.44 Set 29 rs = 0.72, Set 30 rs = 1.25 ∼ 20 MeV effect in W +, mostly due rs variations ∼ 25 MeV effect in W −, spread across eigenvector variations

October 21, 2014 Stefano Camarda 22

slide-23
SLIDE 23

W polarization and PDF uncertainties

PDF member 1 6 11 16 21 26 [MeV]

W

m 80365 80370 80375 80380 80385 80390 80395 80400

80384.7 +3.4 -3.5 80386.3 +3.8 -3.7 80385 +15 -17 No spin correlations

±

W 1 symmetric ± = λ

±

W Spin correlations

±

W

Since PDF variations are different between W + and W −, when W + and W − spectra are used simultaneously, the uncertainty is reduced to ∼ 15 MeV

October 21, 2014 Stefano Camarda 23

slide-24
SLIDE 24

W polarization and PDF uncertainties

Why rs variations affects the W -boson polarisation, when only u- and d- initiated W production is considered?

x

  • 4

10

  • 3

10

  • 2

10

  • 1

10 1

ref

)

2

)(x,Q d /

V

)/x(d

2

)(x,Q d /

V

x(d 0.8 1 1.2

2

= 6464 GeV

2

Q MW-NLO exp+mod MW-NLO exp var

s

MW-NLO r

DIS data constrains the sum of ¯ d and strange PDF In the medium and high x region, variations of the ratio of the strange-quark PDF over the ¯ d PDF, corresponding to rs = 0.72 and rs = 1.25, give a significant contribution to the total PDF uncertainty of the dV /¯ d ratio.

October 21, 2014 Stefano Camarda 24

slide-25
SLIDE 25

Charm quark in the initial state and strange PDF

A charm in the initial state is expected to alter the kinematic

  • f the W productions

Roughly, a kick of the order of mc = 1.4 GeV in the pW

T

spectrum is expected Randomise decay angle of the leptons in the W rest frame → unpolarised W Switch between a setup with only Vud term in the CKM matrix, and a setup with Vud and Vcs terms However, the amount of charm initiated W production will also alter the balance between valence quark initiated and sea quark initiated production, which in turns affect the W polarisation and the W pl

T spectrum

October 21, 2014 Stefano Camarda 25

slide-26
SLIDE 26

Charm mass effect

]

  • 1

[GeV

+

W T

/dp σ d ⋅ σ 1/

  • 3

10

  • 2

10

  • 1

10 = 7 TeV s ;

+

W → pp

CuTe NLO+NNLL

ud

V

cs

V

cs

and V

ud

V

[GeV]

+

W T

p 20 40 Ratio 0.6 0.8 1 1.2 ]

  • 1

[GeV

  • W

T

/dp σ d ⋅ σ 1/

  • 3

10

  • 2

10

  • 1

10 = 7 TeV s ;

  • W

→ pp

CuTe NLO+NNLL

ud

V

cs

V

cs

and V

ud

V

[GeV]

  • W

T

p 20 40 Ratio 0.6 0.8 1 1.2

As expected, the pW

T spectrum acquires a kink from

charm-initiated production Notice that the charm is treated as massless in the ME calculation, the effect of the charm mass we see is encoded in the PDF, as a threshold between 3 and 4 flavours

October 21, 2014 Stefano Camarda 26

slide-27
SLIDE 27

Charm quark in the initial state and strange PDF

[pb / GeV]

l T

/dp σ d ⋅ σ 1/

  • 2

10

  • 1

10 = 7 TeV s ;

+

W → pp

cs

and V

ud

V

ud

V

[GeV/c]

l T

p 30 35 40 45 50 Ratio 0.995 1 1.005 [pb / GeV]

l T

/dp σ d ⋅ σ 1/

  • 2

10

  • 1

10 = 7 TeV s ;

  • W

→ pp

cs

and V

ud

V

ud

V

[GeV/c]

l T

p 30 35 40 45 50 Ratio 0.995 1 1.005

Significant shrink of the PDF uncertainties on pℓ

T distribution

when charm-initiated W production is switched off

October 21, 2014 Stefano Camarda 27

slide-28
SLIDE 28

Charm quark in the initial state and strange PDF

PDF member 1 6 11 16 21 26 [MeV]

W

m 80376 80378 80380 80382 80384 80386 80388 80390 80392 80394

80384.8 +3.1 -3.0 80384.9 +8.4 -6.9

ud

V

+

W

cs

and V

ud

V

+

W

PDF member 1 6 11 16 21 26 [MeV]

W

m 80375 80380 80385 80390 80395

80384.5 +5.6 -5.5 80384.6 +11.6 -9.5

ud

V

  • W

cs

and V

ud

V

  • W

Sets 1-26, hessian variations Set 27 mc = 1.32, Set 28 mc = 1.44 Set 29 rs = 0.72, Set 30 rs = 1.25 ∼ 5 MeV effect in W + and W − due to rs variations

October 21, 2014 Stefano Camarda 28

slide-29
SLIDE 29

Charm quark in the initial state and strange PDF

PDF member 1 6 11 16 21 26 [MeV]

W

m 80375 80380 80385 80390 80395

80384.7 +3.4 -3.5 80384.8 +9.4 -7.7

ud

V

pm

W

cs

and V

ud

V

±

W

Since the rs variations are correlated between W + and W −, there is no significant reduction of the uncertainty when W + and W − pℓ

T spectra are used simultaneously

October 21, 2014 Stefano Camarda 29

slide-30
SLIDE 30

Total PDF uncertainties

Consider altogether polarisation and charm-initiated effects, by using normal spin correlations and SM CKM matrix Observed a partial cancellation of the two effects

PDF member 1 6 11 16 21 26 [MeV]

W

m 80375 80380 80385 80390 80395

80385 +12 -11 80385 +20 -19 80385 +11 -10

+

W

  • W
  • and W

+

W

October 21, 2014 Stefano Camarda 30

slide-31
SLIDE 31

Detector effects - Muon pT smearing

Implemented detector pT smearing for muons from arXiv:1404.4562, to asses the impact of detector smearing on PDF uncertainties

October 21, 2014 Stefano Camarda 31

slide-32
SLIDE 32

Detector effects - Muon pT smearing

[MeV]

W

m 80300 80350 80400 80450 80500

2

χ 100 200 300 400

+

W with detector effects

+

W 5.0 ± 80385.2 5.7 ± 80384.9

PDF member 1 6 11 16 21 26 [MeV]

W

m 80375 80380 80385 80390 80395

80385 +12 -11 80385 +13 -12

+

W with detector effects

+

W

[MeV]

W

m 80300 80350 80400 80450 80500

2

χ

  • 50

50 100 150 200 250 300 350

  • W

with detector effects

  • W

5.8 ± 80385.1 6.5 ± 80385.2

PDF member 1 6 11 16 21 26 [MeV]

W

m 80375 80380 80385 80390 80395 80400

80385 +20 -19 80385 +22 -21

  • W

with detector effects

  • W

Small effect, increase of the PDF uncertainties by ∼ 10% However, detector effects on the hadronic recoil are not considered

October 21, 2014 Stefano Camarda 32

slide-33
SLIDE 33

Summary of PDF uncertainties

MW-NLO CT10nlo MSTW2008CPdeutnlo NNPDF30 nlo as 118 W + +13 -12 +18 -22 +11 -10 +8 -10 W − +22 -22 +18 -23 +11 -10 +8 -9 W ± +11 -11 +14 -18 +7 -7 +6 -5

CT10nlo scaled to 68 cl The dedicate PDF set used for the study has a reasonable uncertainty compared to the global PDF set The larger W − uncertainty is due to missing constraints from additional dataset like Tevatron (and LHC) W asymmetry

October 21, 2014 Stefano Camarda 33

slide-34
SLIDE 34

Summary of PDF uncertainties

Difference between the input value of mW = 80385 MeV and the extracted value of mW , when using CT10nlo as PDF for the reference pℓ

T spectrum, and another PDF for the test spectra with

various values of mW

MW-NLO CT10nlo MSTW2008CPdeutnlo NNPDF30 nlo as 118 W +

  • 9
  • 0.1
  • 20
  • 1.2

W − +48 +0.2 +13 +12 W ± +16 0.0

  • 6

+5

Large, unrealistic shift for the dedicated PDF set MW-NLO for W − production Known issue related to the limited number of parameters (13 parameters), and not enough constraints from HERA data on the d valence PDF

October 21, 2014 Stefano Camarda 34

slide-35
SLIDE 35

Low pW

T modelling uncertainty

Exploit the pZ

T data to constrain the non perturbative QCD

parameters at low pT of Pythia8: Tune AZ Propagate the data uncertainty to the pW

T by mean of

eigentunes hessian uncertainties

[GeV]

Z T

p 1 10

2

10 Prediction/Data 0.8 0.9 1 1.1

Data uncertainty PYTHIA8 4C PYTHIA8 AZ

ATLAS

  • 1

Ldt = 4.7 fb

∫

= 7 TeV; s [GeV]

Z T

p 1 10

2

10 Prediction/Data 0.8 0.9 1 1.1

Data uncertainty POWHEG+PYTHIA8 4C POWHEG+PYTHIA8 AZNLO

ATLAS

  • 1

Ldt = 4.7 fb

∫

= 7 TeV; s

Tune AZ AZNLO 4C Primordial kT [GeV] 1.71 ± 0.03 1.75 ± 0.03 2.0 αISR

s

(mZ ) 0.1237 ± 0.0002 0.118 (fixed) 0.137 ISR cut-off [GeV] 0.59 ± 0.08 1.92 ± 0.12 2.0 χ2

min/dof

45.4/32 46.0/33

  • October 21, 2014

Stefano Camarda 35

slide-36
SLIDE 36

Low pW

T modelling uncertainty

[GeV]

µ T

p

30 32 34 36 38 40 42 44 46 48 50 Ratio to AZ 0.995 0.996 0.997 0.998 0.999 1 1.001 1.002 1.003 1.004 1.005 Central tune Variation 1+ Variation 2+ Variation 3+

[GeV]

µ T

p

30 32 34 36 38 40 42 44 46 48 50 Ratio to AZ 0.995 0.996 0.997 0.998 0.999 1 1.001 1.002 1.003 1.004 1.005 Central tune Variation 1- Variation 2- Variation 3-

Tune Variation Positive Negative 1± 3 −4 2± 3 −4 3± 3 −4 Total 5 7

October 21, 2014 Stefano Camarda 36

slide-37
SLIDE 37

Low pW

T modelling uncertainty

[GeV]

+

W T

p 10 20 30 40 50 ]

  • 1

[GeV

T

/dp σ d ⋅ σ 1/ 0.01 0.02 0.03 0.04 0.05 0.06 0.07 CuTe NLO+NNLL

+

W → pp

ud

V

us

V

ub

V

cd

V

cs

V

cb

V [GeV]

  • W

T

p 10 20 30 40 50 ]

  • 1

[GeV

T

/dp σ d ⋅ σ 1/ 0.01 0.02 0.03 0.04 0.05 0.06 0.07 CuTe NLO+NNLL

  • W

→ pp

ud

V

us

V

ub

V

cd

V

cs

V

cb

V [GeV]

Z T

p 10 20 30 40 50 ]

  • 1

[GeV

T

/dp σ d ⋅ σ 1/ 0.01 0.02 0.03 0.04 0.05 0.06 0.07 CuTe NLO+NNLL Z → pp u u d d s s c c b b

Heavy flavour production results in different distorsions of the W and Z pT spectrum Differences in the heavy flavour content of W and Z production when propagating PS uncertainties from pZ

T to pW T

are not accounted

October 21, 2014 Stefano Camarda 37

slide-38
SLIDE 38

Summary and conclusions

Performed a breakdown of most important PDF uncertainties for the MW extraction from pℓ

T, by tracking the physical

mechanism which give rise to PDF uncertainties Large contribution of polarisation, of the order of 10 − 20 MeV, can be improved by better knowledge of u, d valence and sea PDF Strange-quark PDF uncertainty due to charm-initiated W production is at the level of 5 MeV, but partially cancel the effect of strange-quark PDF on polarisation Preliminary and partial estimation of parton shower uncertainties at the level of 5 − 7 MeV

October 21, 2014 Stefano Camarda 38

slide-39
SLIDE 39

POINTS FOR DISCUSSION

With inputs from Luca Perozzi and Maria Rosaria D’Alfonso

October 21, 2014 Stefano Camarda 39

slide-40
SLIDE 40

Coherent treatment of PDF uncertainties between ATLAS and CMS

Various theory predictions can be used to evaluate PDF uncertainties: MCFM, RESBOS, DYRES, POWHEG, aMC@NLO. Should we expect such tools to provide the same estimation of PDF uncertainties? Should we agree on which prediction(s) can be safely used? Various PDF set are available on the market, at least CT10, MSTW, NNPDF, but also ABM, JR, HERAPDF, and recently also ATLAS and CMS PDF sets. Do we want to agree on a common PDF set? We should at least be sure that ATLAS and CMS results can be combined accounting for the correlation of PDF uncertainties Prescription for evaluating PDF uncertainties: single set? envelope as in PDF4LHC prescription? META-PDF?

October 21, 2014 Stefano Camarda 40

slide-41
SLIDE 41

How to reduce PDF uncertainties for mW

Is the measurement of mW at different collider energies, 7, 8, 13 TeV, beneficial for the reduction of PDF uncertainties? Which LHC measurements can further constrain the PDF uncertainties for mW ?

October 21, 2014 Stefano Camarda 41

slide-42
SLIDE 42

BACKUP

October 21, 2014 Stefano Camarda 42

slide-43
SLIDE 43

Choice of ptsqmin 4.0 in POWHEG+PYTHIA8

ptsqmin 0.2 ptsqmin 0.8 ptsqmin 2.0 1 2 3 4 5 10 20 30 40 50 60 70 80 PZ

T [GeV]

dσfid./dPZ

T [pb/GeV]

October 21, 2014 Stefano Camarda 43