By Alessandro Tricoli (CERN)

By Alessandro Tricoli (CERN) Presenting results from LHC, Tevatron and HERA experiments

EPS-‐HEP, Vienna 22-‐29 July 2015

¡  Our understanding and modelling of QCD interactions have direct impact on the potential for precision measurements and discoveries §  Accurate modeling of Soft and Hard QCD processes is of paramount importance for the success of

collider physics programs

Alessandro Tricoli EPS-‐HEP, Vienna 22-‐29 July 2015 2



¡  We experimentally probe and test different aspects of QCD calculations and modelling to improve the understanding of SM physics §  In addition we can improve descriptions of QCD production mechanisms, backgrounds to rare

processes, e.g. EW, new physics channels and can enhance sensitivity to new physics, e.g. jets, V+jets, VV




¡  We experimentally probe and test different aspects of QCD calculations and modelling to improve the understanding of SM physics §  In addition we can improve descriptions of QCD production mechanisms, backgrounds to rare

processes, e.g. EW, new physics channels and can enhance sensitivity to new physics, e.g. jets, V+jets, VV

¡  How well do we know QCD ? §  Meticulous and systematic work of exploration of different corners of the Standard Model is on-‐

going to accurately test predictions ▪  Studies of many processes spanning may orders of magnitude in cross-‐section



¡  Great progress made in past years in calculations and modeling of QCD production mechanisms, driven by higher and higher experimental accuracy

¡  QCD measurement are becoming more and more precision measurements §  Reaching the percent level on experimental uncertainties


¡  Great progress made in past years in calculations and modeling of QCD production mechanisms, driven by higher and higher experimental accuracy

¡  QCD measurement are becoming more and more precision measurements §  Reaching the percent level on experimental uncertainties

¡  Despite this great theoretical progress in recent years there are still theory uncertainties related to various sources which can be constrained by data

§  Many measurements have reached sensitivity to QCD effects beyond the NLO accuracy at hadron colliders ▪  However most of SM processes are known to NLO in pQCD in hadron colliders, so we need

more NNLO differential calculations to match experimental precision §  Measurements constrain soft QCD modeling, proton parton densities (PDF), prompt new

developments in MC generators


¡  MC are a critical tool in HEP §  Correct for detector and selection effects §  Test for the SM and measuring its parameters §  Estimate new signal properties and their backgrounds

¡  Our conception of QCD interactions as implemented in MC generators


¡  Our conception of QCD interactions as implemented in MC generators §  Hard Interaction



¡  Our conception of QCD interactions as implemented in MC generators §  Hard Interaction §  Initial/Final state Radiation (implemented by parton

showering)




showering) §  Hadronisation




showering) §  Hadronisation §  Multiple Parton Interaction (part of the underlying

event)




showering) §  Hadronisation §  Multiple Parton Interaction (part of the underlying

event)

¡  All these aspects can/must be constrained by experimental measurements


¡  Much recent work to make them more and more precise §  Including state of the art High-‐Order pQCD Calculations matched to Parton

Showering and modeling of Soft-‐Physics (PDF, Underlying event)

¡  Will show impact of recent (and selected) QCD measurements on understanding of SM physics



1.  Improvements on modeling of Soft QCD interactions

§  Minimum Bias interactions §  Underlying Event §  Multiple Parton interactions §  diffractive and exclusive processes -‐> not discussed here (refer to QCD parallel session)





2.  Tests of high-‐order perturbative QCD calculations and MC simulations §  Inclusive, multiple-‐jet production cross-‐sections §  V+jets production






3.  Measurements of fundamental Standard Model parameter αS






3.  Measurements of fundamental Standard Model parameter αS 4.  Constraining of models of Parton Density Functions


¡  Soft particle production cannot be calculated: free model parameters are tuned using data ¡  Charged particle distributions are measured at different √s up to 13 TeV!

§  Track-‐based analysis of MB properties from dedicated low-‐pileup runs §  Comparison with predictions of models tuned to a wide range of measurements


ATLAS-CONF-2015-028!




Ø  Precision of analyses highlights clear differences between models and measurements

Ø  EPOS and shown Pythia8 tunes reproduce the data the best




¡  Measurement of Nch energy dependence §  Lever arm of 13 TeV data helps constraining energy dependence of models!


Ø  Precision of analyses highlights clear differences between models and measurements

Ø  EPOS and shown Pythia8 tunes reproduce the data the best

arXiv:1507.05915!


¡  UE comprises all particles from the collision except those from the hard process of interest

¡  Experimental studies of UE activity in different processes and √s shed light on process dependence and energy evolution of UE activity


¡  UE comprises all particles from the collision except those from the hard process of interest


-‐ Z Boson -‐ Leading Track -‐ Leading Jet


Ø  Consistent UE activity across processes within known selection bias

Eur.Phys.J.C(2014)74:3195!




Ø  Modern tunes reproduce well the energy dependence

Eur.Phys.J.C(2014)74:3195!CERN-PH-EP-2015-176!




Ø  Modern tunes reproduce well the energy dependence up to √s = 13 TeV!

Ø  Difficult for MC tunes to describe simultaneously Minimum Bias and UE observables well (see EPOS and Herwig++ as examples)

Eur.Phys.J.C(2014)74:3195!


ATL-PHYS-PUB-2015-019!

CERN-PH-EP-2015-176!

¡  Measurements of production properties of low-‐pT particles of different species are important input for the modeling of soft parton interactions and hadronisation processes

¡  ALICE has measured production properties of prompt π±, K±, p, p at √s=7 TeV §  Combination of 5 techniques (sub-‐detectors) for particle identification that cover a wide pT range


_

arXiv:1504.00024!

Ø  Shapes of spectra reasonably reproduced by most models Ø  No model can simultaneously describe the yield of π, K and p Ø  These results can help constrain hadron production models

¡  Bose-‐Einstein Correllations (BEC): higher emission probability of two identical bosons with very similar momenta


arXiv:1502.07947!

Ø  Saturation effect of R at high multiplicities at R =2.28±0.32 fm

§  predicted by Pomeron-‐based models as consequence of overlap of colliding protons Phys. Lett. B703,288(2011); Nucl. Phys. Proc. Suppl.219-220,10(2011)!

q  Recent experimental results at pp, pPb and PbPb and different √s (CMS, ALICE etc.)

q  Recent ATLAS result in pp collisions including high track multiplicities

§  Measurement of emitting source effective radius R

Double Parton Interactions (DPI)

⌅ D P I i s c h a r a c t e r i s e d b y t h e e ↵ e c t i v e a r e ap a r a m e t e r , � e ↵ ( s ) , w h i c h i s a s s u m e d t o b ei n d e p e n d e n t o f p h a s e s p a c e a n d p r o c e s s

⌅ P r e v i o u s l y a n u m b e r o f m e a s u r e m e n t s h a v e b e e np e r f o r m e d i n pp a n d pp̄ c o l l i s i o n s a t

ps = 6 3

G e V , 6 3 0 G e V , 1 . 8 T e V a n d 1 . 9 6 T e V

⌅ M e a s u r e d v a l u e s r a n g e f r o m 5 m b a t l o w e n e r g i e su p t o 1 5 m b a t T e v a t r o n e n e r g i e s

⌅ I n t e r e s t i n D P I a t t h e L H C d u e t o⇤ Higher centre-of-mass enhances parton densities so

expect larger impact of DPI on many signatures⇤ Higher energy and luminosity means multiple

interactions occur at higher transverse momentum

W+

⌫

¯̀

qg

q

g

⌫q

¯̀

W+

⌦

q̄

20 of 25


Single Parton Interact. (SPI)

Double Parton Interact. (DPI)

¡  Potential contribution to precision measurements (e.g. Higgs, WW) and new physics searches ¡  Rapid increase with rising √s ¡  Difficult to measure as buried in other signal

L.&Di&Ciaccio&I&LHCP&2013&I&May&2013&& 27&

DPI in W + 2 jets !

Fraceon&of&DPIIproduced&in&W+2j&events&at&detector&level&&

σeff = effective area parameter assumed to be independent of phase space and process => need to prove this assumption experimentally


⌅ DPI is characterised by the e↵ective areaparameter, �e↵(s), which is assumed to beindependent of phase space and process

⌅ Previously a number of measurements have beenperformed in pp and pp̄ collisions at

ps = 63

GeV, 630 GeV, 1.8 TeV and 1.96 TeV

⌅ Measured values range from 5mb at low energiesup to 15mb at Tevatron energies

⌅ Interest in DPI at the LHC due to⇤ Higher centre-of-mass enhances parton densities so



W+

⌫

¯̀

qg

q

g

⌫q

¯̀

W+

⌦

q̄

20 of 25


⌅ D P I i s c h a r a c t e r i s e d b y t h e e ↵ e c t i v e a r e ap a r a m e t e r , � e ↵ ( s ) , w h i c h i s a s s u m e d t o b ei n d e p e n d e n t o f p h a s e s p a c e a n d p r o c e s s

⌅ P r e v i o u s l y a n u m b e r o f m e a s u r e m e n t s h a v e b e e np e r f o r m e d i n pp a n d pp̄ c o l l i s i o n s a t

ps = 6 3

G e V , 6 3 0 G e V , 1 . 8 T e V a n d 1 . 9 6 T e V

⌅ M e a s u r e d v a l u e s r a n g e f r o m 5 m b a t l o w e n e r g i e su p t o 1 5 m b a t T e v a t r o n e n e r g i e s

⌅ I n t e r e s t i n D P I a t t h e L H C d u e t o⇤ Higher centre-of-mass enhances parton densities so



W+

⌫

¯̀

qg

q

g

⌫q

¯̀

W+

⌦

q̄

20 of 25


Single Parton Interact. (SPI)

Double Parton Interact. (DPI)

¡  Potential contribution to precision measurements (e.g. Higgs, WW) and new physics searches ¡  Rapid increase with rising √s ¡  Difficult to measure as buried in other signal

L.&Di&Ciaccio&I&LHCP&2013&I&May&2013&& 27&

DPI in W + 2 jets !

Fraceon&of&DPIIproduced&in&W+2j&events&at&detector&level&&

σeff = effective area parameter assumed to be independent of phase space and process => need to prove this assumption experimentally


⌅ DPI is characterised by the e↵ective areaparameter, �e↵(s), which is assumed to beindependent of phase space and process

⌅ Previously a number of measurements have beenperformed in pp and pp̄ collisions at

ps = 63

GeV, 630 GeV, 1.8 TeV and 1.96 TeV

⌅ Measured values range from 5mb at low energiesup to 15mb at Tevatron energies

⌅ Interest in DPI at the LHC due to⇤ Higher centre-of-mass enhances parton densities so



W+

⌫

¯̀

qg

q

g

⌫q

¯̀

W+

⌦

q̄

20 of 25 Ø  DPI contributions studied in various processes by measuring kinematic correlations §  4jets, W+2jets, double-‐J/ψ, Z+D, W+J/ψ, §  Z+J/ψ, §  γ+3jets, §  2b-‐jets +2jets §  γγ+2jets, §  J/ψ +Υ

ATLAS Z+J/ψ (2015)

D0Note-6470-CONF!D0Note-6472-CONF!

D0Note-6470-CONF!

CMS-PAS-FSQ-13-010!

ATLAS Eur.Phys.J.C75(2015)229!

CMS-PAS-FSQ-12-017!


¡  Jet production cross-‐sections are excellent probes of QCD dynamics and modeling over many orders of magnitudes

§  test pQCD calculations and interplay with non-‐perturbative effects §  sensitive to strong coupling constant αS, PDF and Multi Parton Interactions

¡  Jet production cross-‐sections are excellent probes of QCD dynamics and modeling over many orders of magnitudes

§  test pQCD calculations and interplay with non-‐perturbative effects §  sensitive to strong coupling constant αS, PDF and Multi Parton Interactions


Ø  Many experimental results at Hera, Tevatron and at LHC at different √s §  Covering scales from few GeV to multi-‐TeV §  Measurements performed with different jet clustering algorithm radii to probe interplay

between Hard and Soft QCD effects §  Measurements are compared to fixed-‐order NLO and MC generators


JHEP02(2015)153!

[GeV/c]T

Jet p30 40 100 200 1000 2000

GeV

/cpb

dy Tdp

σ2 d

-510

-310

-110

10

310

510

710

910

1110

1310 = 8 TeV CMS Preliminaryspp

21

(low PU runs)-1 = 5.8 pbint

open: L (high PU runs)-1 = 10.71 fbintfilled: L

NP ⊗NNPDF 2.1 NLO

)5 10×0.0 <|y|< 0.5 ( )4 10×0.5 <|y|< 1.0 ( )3 10×1.0 <|y|< 1.5 ( )2 10×1.5 <|y|< 2.0 ( )1 10×2.0 <|y|< 2.5 ( )0 10×2.5 <|y|< 3.0 ( )-1 10×3.2 <|y|< 4.7 (

)5 10×0.0 <|y|< 0.5 ( )4 10×0.5 <|y|< 1.0 ( )3 10×1.0 <|y|< 1.5 ( )2 10×1.5 <|y|< 2.0 ( )1 10×2.0 <|y|< 2.5 ( )0 10×2.5 <|y|< 3.0 ( )-1 10×3.2 <|y|< 4.7 (

CMS-PAS-FSQ-12-031!CMS-PAS-SMP-12-012! Ø  LHC Measurements cover jet pT range 20 GeV-‐2 TeV, precision reaches ~5% level Ø  Very good agreement with NLO QCD calculations ¡  Complementary measurements of incl. jet, di-‐jet, 3-‐jet cross sections at HERA and LHC

§  Different sensitivity to underlying sub-‐processes and parton densities, e.g. gluon at high-‐x §  Full correlation across measurements allows for simultaneous use as inputs in QCD fits


¡  New measurement by CMS at 2.76 TeV

CMS-SMP-14-017 !

Six |y| bins (0.0-‐3.0), pT range 74-‐592 GeV



CMS-SMP-14-017 !

Six |y| bins (0.0-‐3.0), pT range 74-‐592 GeV Ø  Sensitivity to PDF



CMS-SMP-14-017 !


¡  Ratios of jet cross-‐sections at different √s allows for partial cancellation of uncertainties when correlations are accounted for ¡  Precise test of QCD at different √s and input to PDF fits

o  e.g. recently ATLAS 2.76 TeV / 7 TeV [EPJC(2013)73 2509]!

Ø  Sensitivity to PDF



CMS-SMP-14-017 !

CMS-SMP-14-017 !

Ø  CMS 2.76 TeV / 8 TeV ratio in range 0.1-‐14% and decreases with increasing jet pT => good agreement with NLO theory


¡  Ratios of jet cross-‐sections at different √s allows for partial cancellation of uncertainties when correlations are accounted for ¡  Precise test of QCD at different √s and input to PDF fits

o  e.g. recently ATLAS 2.76 TeV / 7 TeV [EPJC(2013)73 2509]!

Ø  Sensitivity to PDF

¡  ATLAS 4-‐jets cross-‐sections at 8 TeV, differentially in several variables depending on the jet momenta and angular distributions, in various event topologies §  Test of LO (PS and ME+PS) and NLO predictions up to multi-‐TeV scales !




Ø  Δφmin3j: 2-‐vs-‐2 from 1-‐vs-‐3 topologies

p(1)T > 100 GeV

p(1)T > 400 GeV

p(1)T > 700 GeV

p(1)T > 1000 GeV




p(1)T > 100 GeV

p(1)T > 400 GeV

p(1)T > 700 GeV

p(1)T > 1000 GeV




p(1)T > 100 GeV

p(1)T > 400 GeV

p(1)T > 700 GeV

p(1)T > 1000 GeV

Ø  NLO predictions BlackHat/Sherpa and NJet/Sherpa: compatible with data within large theoretical uncertainties (O(30%) at low momenta)

Ø  HEJ (all-‐order resummation) provides a good description of angular variables

¡  Dijet azimuthal decorrelations is complementary to multi-‐jet analyses §  Gain insight on multi-‐jet production without measuring jets beyond the leading two §  Experimental uncertainty on normalised distribution reach percent level at ΔφDijet ≈π


ΔφDijet= | φjet1 – φjet2 |

ΔφDijet ≈π

ΔφDijet ≈2π/3

ΔφDijet -‐> 0

CMS-PAS-SMP-14-015!

NLO

LO

Ø  Good agreement with 3-‐jet NLO calculation (NLOJet++)

in NLO range

Ø  Multi-‐jet 2-‐>4 MC (Madgraph+Pythia6) provides best description overall

¡  αs is a fundamental QCD quantity which many QCD measurements are sensitive to §  Inclusive jet cross section, 3-‐jet mass, 3-‐jet to 2-‐jet cross section ratio (R32), event shapes, tt cross-‐

section etc. ¡  Sensitive to new physics

§  The running of the strong coupling constant can be measured to unprecedented scales Q, in different processes at the LHC


Ø  Good agreement with 2-‐loop solution of the RGE as a function of the scale Q up to TeV scale

Incl. jets 3-‐jet mass

R32 tt

)!/d

(co

s "

)d#

(1/

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

Data (exp. unc.)

NLO pQCD (th. unc.)

= 7 TeVs ATLAS -1L dt = 158 pb $Preliminary

CT10 NNLO

jets R = 0.4tanti-k

) = 0.1173Z

(ms%

!cos

-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8

Da

ta /

Th

eo

ry

0.9

1

1.1

¡  New measurement by ATLAS data using event shapes, as a continuation of αS measurements at e+e-‐ colliders (PETRA-‐PEP, TRISTAN,LEP-‐SLC) §  Jet-‐based transverse energy-‐energy correlation


§  Experimental distributions in agreement with NLO calculation

Ø  Extraction of αS at Q=MZ


¡  Excellent compatibility with World Average and with jet-‐based measurements at hadron and e-‐p colliders

Ø  NNLO calculations needed for jet processes to improve precision on αS at hadron colliders

§  Theoretical scale uncertainty dominate over exp. uncertainties

ATLAS Energy Energy Correlations

Preliminary

32ATLAS N

ATLAS-CONF-2013-041 (2013)

Malaescu & Starovoitov ATLAS Inclusive jet

Eur. Phys. J. C 72 (2012) 2041

32CMS R

Eur. Phys. J. C 73 (2013) 2604

CMS inclusive jet cross section

Eur. Phys. J. C 75 (2015) 288

CMS 3-jet mass

Eur. Phys. J. C 75 (2015) 186

CDF Inclusive jet cross sections

Phys. Rev. Lett. 88 (2002) 042001

D0 Inclusive jet cross sections

Phys. Rev. D 80 (2009) 111107

D0 Jet angular correlations

Phys. Lett. B 718 (2012) 56

p!ZEUS Inclusive jet cross sections in

Nucl. Phys. B 864 (2012) 1

in ep collisions2H1 Multijet production at high Q

Eur. Phys. J. C 75 (2015) 65

H1 + ZEUS Inclusive jet cross sections in ep collisions

H1prelim-07-132, ZEUS-prel-07-025

World average 2014

Chin. Phys. C 38 (2014) 090001

)Z

(mS"

0.11 0.12 0.13 0.14 0.15 0.16 0.17

Experimental Uncertainty

Total Uncertainty

PDG Total UncertaintyPreliminary ATLAS


Ø  V+jets probe different aspects of QCD calculations Ø  Overall good data-theory

agreement over 5 orders of magnitude in cross-sections

Ø  High experimental accuracy

exposes discrepancies with predictions

New CMS γγ+jets at 7 TeV CMS-SMP-14-021!(see backup) !


q  Tevatron legacy on V+jets analyses and still many new results are coming…


q  Tevatron legacy on V+jets analyses and still many new results are coming… q  Larger cross-sections at LHC and larger integrated luminosity, different Bjorken-x, parton

densities and subprocesses

jetsN 1≥ 2≥ 3≥ 4≥ 5≥ 6≥ 7≥

-310

-210

-110

1

10

210

310

Data

2j@NLO 3,4j@LO + PS)≤Sherpa2 (

4j@LO + PS)≤Madgraph + Pythia6 (

CMS Preliminary (8 TeV)-119.6 fb

(R = 0.5) JetsTanti-k| < 2.4 jetη > 30 GeV, |jet

Tp

ll channel→*γZ/

[pb

]je

ts/d

Nσd

jetsN 1≥ 2≥ 3≥ 4≥ 5≥ 6≥ 7≥

Sher

pa2/

Dat

a

0.5

1

1.5

Stat. unc. (gen)

jetsN 1≥ 2≥ 3≥ 4≥ 5≥ 6≥ 7≥

Mad

Gra

ph/D

ata

0.5

1

1.5

Stat. unc. (gen)

CMS-PAS-SMP-13-007! Eur.Phys.J.C(2015)75:82!

Ø  Unprecedented kinematic reach Ø  Discrepancies between data and theory

§  These results already used to improve MC simulations


q  Tevatron legacy on V+jets analyses and still many new results are coming… q  Larger cross-sections at LHC and larger integrated luminosity, different Bjorken-x, parton

densities and subprocesses

q  Great theoretical advances in recent years/months

§  NLO calculations up to W+5 partons §  NNLO for W/Z+1 parton §  NLO MC matched to Parton

Showering §  Resummed calculations

jetsN 1≥ 2≥ 3≥ 4≥ 5≥ 6≥ 7≥

-310

-210

-110

1

10

210

310

Data

2j@NLO 3,4j@LO + PS)≤Sherpa2 (

4j@LO + PS)≤Madgraph + Pythia6 (


(R = 0.5) JetsTanti-k| < 2.4 jetη > 30 GeV, |jet

Tp

ll channel→*γZ/

[pb

]je

ts/d

Nσd

jetsN 1≥ 2≥ 3≥ 4≥ 5≥ 6≥ 7≥

Sher

pa2/

Dat

a

0.5

1

1.5

Stat. unc. (gen)

jetsN 1≥ 2≥ 3≥ 4≥ 5≥ 6≥ 7≥

Mad

Gra

ph/D

ata

0.5

1

1.5

Stat. unc. (gen)

CMS-PAS-SMP-13-007! Eur.Phys.J.C(2015)75:82!

Ø  Unprecedented kinematic reach Ø  Discrepancies between data and theory

§  These results already used to improve MC simulations


q  Theoretical uncertainties on W/Z+heavy flavour jets are larger than for light jets §  heavy-quark content in the proton §  modeling of gluon splitting (initial state, final state) §  massive vs massless b-quark in calculations

q  Test of QCD predictions with various implementations (LO multileg+PS, NLO, NLO+PS)

q  Very important processes as background to Higgs and searches

¡  W+c is sensitive to strange-‐PDF and gluon splitting §  ATLAS and CMS showed results compatible with strange enhancement §  DO carried out measurement sensitive to gluon splitting vs c-‐jet pT


dominating contribution

W

c _ c Increasingly

important at high pT

jet




W

c _ c Increasingly


jet

W+c-‐jet

PLB 743 (2015) 6-14!

W+c-‐jet:

Underestimated g-‐splitting? strange-‐quark enhancement?


¡  W+b is sensitive to gluon splitting and intrinsic-‐b PDF §  DO cross-‐section measurement vs b-‐jet pT



W

c _ c Increasingly


jet

W+b-‐jet

PLB 743 (2015) 6-14!

W+c-‐jet

PLB 743 (2015) 6-14!

W+c-‐jet:

Underestimated g-‐splitting? strange-‐quark enhancement?

W+b-‐jet : missing higher-‐order corrections Overall poor description of

NLO calculations

¡  Simultaneous analysis of W+light-‐jet, W+b and W+c, by LHCb in forward region §  W-‐>µν with 2.0<|ηµ|<4.5 and 2.2<|ηjet|<4.2 and pT

jet>20 GeV


¡  Simultaneous analysis of W+light-‐jet, W+b and W+c, by LHCb in forward region §  W-‐>µν with 2.0<|ηµ|<4.5 and 2.2<|ηjet|<4.2 and pT

jet>20 GeV

¡  Production cross-‐section ratios and charge asymmetries


Ø  Wc/Wj and Wb/Wj ratios consistent with NLO QCD (4-‐flavour scheme MCFM with CT10 PDF)

Ø  no sensitivity to intrinsic-‐b below O(10%) level Ø  agreement with strange-‐quark fraction in CT10 PDF

Ø  Charge asymmetry for Wc smaller than predicted Ø  could suggest an s-‐s asymmetry

_

arXiv:1505.04051!

v  Higgs boson production depends on gluon PDF (gluon fusion) v  Very large PDF uncertainties in phase-‐spaces relevant for new heavy particles v  PDFs dominant syst. for precision SM measurements, e.g. MW


¡  PDFs are determined from global fits to many observables (DIS, Vector Boson production, Jets, Heavy quark production)

PDG 2014 Chin.Phys.C38 090001!

NNPDF3.0

v  Higgs boson production depends on gluon PDF (ggF) v  Very large PDF uncertainties in phase-‐spaces relevant for new heavy particles v  PDFs dominant syst. for precision SM measurements, e.g. MW


¡  PDFs are determined from global fits to many observables (DIS, Vector Boson production, Jets, Heavy quark production)

Ø  New generations of PDF's include LHC data to improve quark-‐flavour separation and gluon PDF ¡  W/Z and W+c are sensitive to quark PDF, e.g. strange fraction ¡  Inclusive jet production is sensitive to the large-‐x gluon and quark PDF’s

arXiv:1410.8849!

PDG 2014 Chin.Phys.C38 090001!

¡  HERA provides most important dataset to measure PDF ¡  HERA II yields significant improvements in precision at high x-‐Q2 region

§  Combination of H1 and ZEUS inclusive DIS NC and CC cross-‐sections in HERA I and II §  QCD analysis at LO, NLO and NNLO => HERAPDF2.0 §  Simultaneous measurement of gluon-‐PDF and αS(MZ) after inclusion of HERA jet and charm data


H1 and ZEUS

0

0.2

0.4

0.6

0.8

1

1.2

10 3 10 4

mr,

NC

–

Q2/GeV2

HERA NC e p 0.4 fb–1–

HERA I

3s = 318 GeV

xBj = 0.008

xBj = 0.032

xBj = 0.08

xBj = 0.25

arXiv:1506.06042 !

§  Large kinematic range and unprecedented precision

(up to few%)

¡  HERA provides most important dataset to measure PDF ¡  HERA II yields significant improvements in precision at high x-‐Q2 region

§  Combination of H1 and ZEUS inclusive DIS NC and CC cross-‐sections in HERA I and II §  QCD analysis at LO, NLO and NNLO => HERAPDF2.0 §  Simultaneous measurement of gluon-‐PDF and αS(MZ) after inclusion of HERA jet and charm data


H1 and ZEUS

0

0.2

0.4

0.6

0.8

1

1.2

10 3 10 4

mr,

NC

–

Q2/GeV2

HERA NC e p 0.4 fb–1–

HERA I

3s = 318 GeV

xBj = 0.008

xBj = 0.032

xBj = 0.08

xBj = 0.25

arXiv:1506.06042 !

0.2

0.4

0.6

0.8

1

-410 -310 -210 -110 1

HERAPDF2.0 NLO

HERAPDF1.0 NLO

HERAPDF2.0 NLO

HERAPDF1.0 NLO

x

xf

2 = 10 GeV2fµ

vxu

vxd 0.05)×xS (

0.05)×xg (

H1 and ZEUS

arXiv:1506.06042 !

§  Large kinematic range and unprecedented precision

(up to few%)

§  Valence quark and gluon PDF become slightly harder

Ø  Important input for LHC Run-‐II predictions => HERA Legacy


Inclusive photon ET



Z+Njets distribution Drell-‐Yan distribution

CMS-DP-2015-015!

[GeV]T

p210×4 210×5 210×6 210×7 210×8

[pb/G

eV]

y d Tp/dσ2 d

-110

1

10

210PreliminaryATLAS

-113 TeV, 78 pb| < 0.5y=0.4; |R jets, tanti-k

uncertaintiesSystematic

Non-pert. corr.×NLOJET++ (CT10)

Data

Relative uncertainty of 9% in the integrated luminosity not included


Inclusive jet cross-‐section

W MT distribution


CMS DP-2015-017!

Di-‐jet mass distribution


Ridge in pp

J/ψ-‐from-‐b cross-‐section

LHCb-PAPER-2015-037!

invariant mass [GeV]-µ+µ1 10 210

Even

ts /

GeV

1

10

210

310

410

510

610

710

810

ω

φψJ/

'ψ

sBΥ

Z

Trigger pathsφψJ/'ψsB

Υlow mass double muon + trackdouble muon inclusive

(13 TeV)-120 pb

CMSPreliminary

Di-‐µ mass distribution

CMS DP-2015/01!

¡  Understanding QCD is central in hadron collider physics

¡  Both experimentalists and theorists are striving to improve our knowledge of QCD further and further

¡  New and more and more precise results from Hera, Tevatron and LHC experiments are prompting further theoretical developments on QCD §  NLO-‐>NNLO QCD differential calculations is the next frontier to improve data-‐theory agreement in

many processes at hadron colliders §  Improve PDF (e.g. quark and gluon PDFs) and models for (multi-‐)particle production dynamics §  Constrain Monte Carlo simulation, e.g. gluon splitting

¡  Thanks to wide kinematic reach at the LHC we test validity of SM to unprecedented phase spaces §  scale dependence of αS now tested to the TeV energy scale §  Jet production to multi-‐TeV scales §  V+jets to high jet multiplicity and TeV-‐scale jets

¡  Many more results are to come and we look forward to LHC Run-‐2 to provide further insight on QCD dynamics in a new energy regime



Back-‐up


¡  Data from different experiments used as inputs to tunes of MC parameters ¡  Data input with largest weight is shown in table

¡  Some tunes focused on describing Minimum Bias (MB) distributions others to describe UE distributions

¡  Bose-‐Einstein Correlations (BEC) §  correlations between two identical bosons

§  BEC effect corresponds to an enhancement in two identical boson correlation function when the two particles are near in momentum space Q.

§  BEC probe space-‐time geometry of the hadronization region and allow the determination of the

size and the shape of the emitting source.

§  Dependence of BEC on particle multiplicity and transverse momentum helps understand the multi-‐particle production mechanism.


Probability to observe two particles with momenta p1 and p2

Probability to observe one particle with momentum p1 or p2

R= effective radius λ = strength parameter (incoherence or chaoticity factor)

¡  Recent ATLAS result in pp collisions §  Experimental construction of C2(Q) correlation function:

§  Construct double ratio (Data / MC with no BEC) to reduce uncertainties


§  Analysis of 900 GeV and 7 TeV data §  Including high track multiplicities ~240 at 7 TeV (first time in BEC analyses) Ø  Saturation effect of R at high multiplicities at R =2.28±0.32 fm predicted by Pomeron-‐based models

Reference sample particle (track) pairs Q distribution => no BEC

Like-‐sign (ls) particle (track) pairs Q distribution => signal with BEC

arXiv:1502.07947!

Phys. Lett. B703,288(2011)!Nucl. Phys. Proc. Suppl.219-220,10(2011)!!

¡  CMS has studied 2 b-‐jets + 2 jet production at 7 TeV in low-‐pileup 2010 sample


§  Measurements of normalised differential cross-‐sections as a function of many correlation variables between jets (similarly to previous 4jet analysis)

§  ΔS is angular variable most sensitive to MPI at low ΔS

Ø  ΔS not well described by any prediction => need of UE tune to hard MPI

MPI-‐sensitive region

S (rad)Δ0 0.5 1 1.5 2 2.5 3

MC/

data

0.20.40.60.8

11.21.41.6

S [1

/rad]

Δ/d

σ) d

σ(1

/

-210

-110

1

10

210

2 b + 2 j + X→ (7 TeV), pp-13 pb

| < 2.4η > 20 GeV, |T

2 b-j: p| < 4.7η > 20 GeV, |

T2 j: p

CMSPreliminary

MADGRAPH+P6 Z2*POWHEG+PYTHIA6 Z2'CUETP8S1-CTEQ6L1HERWIG++ UE-EE-5-CTEQ6L1CUETP8S1-CTEQ6L1 MPI offDATATotal Uncertainty

Correlated jet topology (2b and 2j are back-‐to-‐back)

Uncorrelated jet topology

CMS-PAS-FSQ-13-010!


¡  Complementary measurements of incl. jet, di-‐jet, 3-‐jet cross sections at HERA and LHC §  Different sensitivity to underlying sub-‐processes and to parton densities §  Full correlation across measurements allows for simultaneous use as inputs in QCD fits

Ø  Sensitivity to PDF, e.g. gluon at high-‐x Ø  3-‐jet mass is used by CMS to extract strong coupling constant αS

1412.1633v2!

3-‐jet vs mjjj and ymax

3-‐jet vs mjjj and Y*

Eur.Phys.J.C(2015)75!


CMS-SMP-14-017 !

¡  New measurement by CMS at 2.76 TeV and ratio 2.76 TeV / 8 TeV

CMS-SMP-14-017 !

Inclusive jet cross-‐section at 2.76 TeV Inclusive jet cross-‐section ratio 2.76 TeV / 8 TeV

¡  Dijet azimuthal decorrelations is complementary to multi-‐jet analyses §  Gain insight on multi-‐jet production without measuring jets beyond the leading two §  Experimental uncertainty on normalised distribution reach percent level at ΔφDijet ≈π


ΔφDijet= | φjet1 – φjet2 |

ΔφDijet ≈π

ΔφDijet ≈2π/3

ΔφDijet -‐> 0

CMS-PAS-SMP-14-015!

NLO

LO

Good agreement with 3-‐jet NLO calculation (NLOJet++) in NLO range Multi-‐jet 2-‐>4 MC (Madgraph+Pythia6) provides best description overall

Alessandro Tricoli EPS-‐HEP, Vienna 22-‐29 July 2015 69 EPJ C75 (2015) 65!

¡  Simultaneous and correlated Measurements of inclusive jet, di-‐jet and three-‐jets at HERA (H1) §  Jet acceptance: -‐1<η<2.5, 5-‐7 GeV <pT

jet<50 GeV

Ø  Experimental precision higher than theory uncertainty (scales)

Ø  Overall good description of data by NLO calculation (NLOJET++ corrected for hadronisation and EW effects)

Ø  Extraction of competitive value of strong coupling constant αS(MZ) §  Most precise from jet cross-‐sections

0.60.8

11.2

0.60.8

11.2

0.60.8

11.2

0.60.8

11.2

0.60.8

11.2

7 10 20 300.60.8

11.2

7 10 20 30 7 10 20 30

Inclusive Jet Dijet Trijet

[GeV]TjetP [GeV]2�T

jtP� [GeV]3�TjtP�

Rat

io to

NLO

2 < 200 GeV2150 < Q

2 < 270 GeV2200 < Q

2 < 400 GeV2270 < Q

2 < 700 GeV2400 < Q

2 < 5000 GeV2700 < Q

2 < 15000 GeV25000 < Q

H1 Data ew c� had c�NLO Sys. Uncertainty 0.118 =s _MSTW2008,

NLOJet++ with fastNLO

H1

¡  D* production at HERA gives insight on High-‐Order QCD corrections and charm-‐fragmentation §  Combination of H1 and ZEUS results with full HERA II dataset

§  Single and double differential cross-‐section in various variables §  Full D-‐meson reconstruction §  Clean signal in distribution


Dominant charm-‐production mechanism

Ø  Data yields much higher precision than theory

Ø  NLO QCD theory is in reasonable agree with data, but Higher-‐Order calculations will reduce theory uncertainty

(D*)

(nb/

GeV

)T

/dp

md

-410

-310

-210

-110

1

(D*) (GeV)T

p2 3 4 5 6 7 8 9 10 20

ratio

to H

ERA

0.6

0.8

1

1.2

HERA-IINLO QCDNLO QCD customised

± D*ANLO QCD b

2 < 1000 GeV25 < Q0.02 < y < 0.7

(D*) > 1.5 GeVT

p(D*)| < 1.5d|

X H1 and ZEUS± eD*A ep

arXiv:1503.06042!

¡  Studies of jet properties can constrain models of jet formation §  ATLAS analysis on Jet Charge in dijet events (two well-‐balanced jets)


pT-‐weighted track charge for tracks associated to a jet κ=regularisation param. to control fluctuations due to soft-‐radiation

1st , 2nd moments of Jet Charge distribution measured vs jet pT

Ø  Data is 10% above MC predictions §  PDF uncertainties do not cover discrepancy => likely source is fragmentation modeling

§  Jet charge increases with jet pT following increase of up-‐flavour jets in dijet sample

(PDF evolution)



arXiv:1412.1115

Ø  NNLO QCD calculations are necessary to describe Drell-Yan data

JHEP 06 (2014) 112


Njets0 1 2 3 or 4

/dN

jets

σ d

σ1/

2−10

1−10

1 (7 TeV)-15.0 fb

CMSPreliminary

Data

SHERPA

aMC@NLO

0 1 2 3 or 4

SHER

PA /

Dat

a

00.5

11.5

22.5

3

0 1 2 3 or 4

aMC

@N

LO /

Dat

a

00.5

11.5

22.5

3

1j≥, close ,j}γ R{Δ

1 1.5 2 2.5 3 3.5 4 4.5 5 5.5

1j

≥, cl

ose

,j}

γ R

{Δ

/dσ

dσ

1/

2−10

1−10

(7 TeV)-15.0 fb

CMSPreliminary

Data

SHERPA

aMC@NLO

GoSam

1 1.5 2 2.5 3 3.5 4 4.5 5 5.5

SHER

PA /

Dat

a

00.5

11.5

22.5

3

1 1.5 2 2.5 3 3.5 4 4.5 5 5.5

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00.5

11.5

22.5

3

1 1.5 2 2.5 3 3.5 4 4.5 5 5.5

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am /

Dat

a

00.5

11.5

22.5

3

q  Differential γγ+jets cross section at 7 TeV by CMS

§  Event selection: o  photon pT> 40, 25 GeV o  jet pT > 25 GeV (anti-‐kT R=0.5)

Ø  Sherpa (LO multi-‐leg) and aMC@NLO (NLO up to 2 jets) agree well with data §  NLO calculation less affected by scale uncertainties

Ø  GoSam (fixed-‐order NLO for 1 or 2 jets corrected for N.P. effects) shows discrepancies with data

in γ-‐jet angular correlations


Ø  Extraordinary agreement between experiments and theory over 5 orders of magnitude in cross-sections

Ø  High experimental accuracy exposes discrepancies with predictions

Eur.Phys.J.C(2015)75:82!

[pb/

GeV

]T

1 je

t)/dp

≥ +

νµ

→(Wσd -510

-410

-310

-210

-110

1

10 DataBlackHat+Sherpa (NLO)Sherpa (LO)MadGraph+Pythia (LO)

-1 = 7 TeV 5.0 fbsCMS

(R = 0.5) jetsTanti-k| < 2.4jetη > 30 GeV, |jet

Tp

selectionνµ→W

[GeV]T

Leading jet p100 200 300 400 500 600 700 800

Theo

ry/D

ata

0.5

1

1.5

BlackHat+Sherpa (1 jet NLO)

Theory stat. + syst.

[GeV]T

Leading jet p100 200 300 400 500 600 700 800

Theo

ry/D

ata

0.5

1

1.5

NNLOσSherpa, normalized to

Theory stat.

[GeV]T

Leading jet p100 200 300 400 500 600 700 800

Theo

ry/D

ata

0.5

1

1.5

NNLOσMadGraph+Pythia, normalized to

Theory stat.

Phys. Lett. B 741 (2015) 12 q  W+jets at 7 TeV by ATLAS and CMS


q  Mismodelings seen in W+jets, Z+jets and γ+jet separately mostly cancel in Ratios §  Ratio measurements allow for cancellations of uncertainties (exp. and theory)

Ø  Significant discrepancies with theory in some regions of phase space Ø  Z/γ: over-estimation of ratio by a flat 10-20% by NLO calc. and LO multi-leg MC

W+jets (W + ≥ 2jets) Rjets=W+jets / Z+jets

Eur.Phys.J.C(2014)74: 3168!Eur.Phys.J.C(2015)75:82!

Z+jet / γ+jet

[GeV]γZ/T

p100 200 300 400 500 600 700 800

γ T/d

pσ

/ d

Z T/d

pσd

0.005

0.010

0.015

0.020

0.025

0.030

0.035

0.040

0.045

0.050

Data

Stat.+syst.

BlackHat

MadGraph

CMS (8 TeV)-119.7 fb

|<1.4V|y

arXiv.1505.06250!


q  Ratio measurements allow for cancellations of uncertainties (exp. and theory) §  Experimental: jet calibration uncertainties, lumi etc. §  Theory: scale+PDF uncertainties: 20% (W+1j) -‐> 2-‐4% on W+1j/Z+1j at jet pT=800 GeV

W+jets W+jets / Z+jets

Eur.Phys.J.C(2014)74: 3168!Eur.Phys.J.C(2015)75:82!

Ø  Accurate test of SM predictions Ø  Important for background estimation in searches


Ø  Z/γ: over-estimation of ratio by a flat 10-20% by NLO calc. and LO multi-leg MC

[GeV]γZ/T

p100 200 300 400 500 600 700 800

γ T/d

pσ

/ d

Z T/d

pσd

0.005

0.010

0.015

0.020

0.025

0.030

0.035

0.040

0.045

0.050

Data

Stat.+syst.

BlackHat

MadGraph

CMS (8 TeV)-119.7 fb

|<1.4V|y

Z+jet / γ+jet

[GeV]γZ/T

p100 200 300 400 500 600 700 800

Mad

Gra

ph/D

ata

0.6

0.8

1.0

1.2

1.4

MadGraph stat. error

[GeV]γZ/T

p100 200 300 400 500 600 700 800

Blac

kHat

/Dat

a

0.6

0.8

1.0

1.2

1.4

PDF Scale

CMS

(8 TeV)-119.7 fb

arXiv.1505.06250! arXiv.1505.06250!


q  Test limit of validity of NLO pQCD calculation (where large logs are expected or missing higher orders) q  Fixed-order NLO fails at large pT

Z/pT 1st jet due to missing higher predictions

§  3-jet emission only at LO in BlackHat

q  Parton shower adds soft jets and provides better description of high tails

)j1T

/pZT

(p10

log-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8

)j1 T/pZ T

(p10

/d lo

gσd

10

210

310

410

>40 llT

2, p≥ jets, N-l+ l→ *γZ/

data

stat+syst

)Z+2jetBlackHat(

NNLOSherpa k

NNLOMadGraph k

Preliminary CMS (8TeV)-119.7fb

Z-jet are back-to-back

Z pT < jet pT

3rd jet is relevant (NLO becomes LO)

arXiv.1505.06250!


q  First double differential measurement: leading jet pT and rapidity (like in jet measurements) §  also suitable for PDF fitting

q  Extended jet rapidity range, up to |η| = 4.7

[GeV]T

Leading jet p60 80 100 120 140 160 180

Theo

ry/D

ata

0.4

0.6

0.8

1

1.2

1.4

1.6

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4j@LO≤Sherpa Z +1,2j @NLO,

Total experimental unc|<4.7

j 3.2<|y


[GeV]T

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Theo

ry/D

ata

0.4

0.6

0.8

1

1.2

1.4

1.6

4j @LO≤MadGraph Z+

4j@LO≤Sherpa Z +1,2j @NLO,

Total experimental unc|<2.0

j 1.5<|y


Ø  Experimental precision of central jets is higher than prediction-‐to-‐prediction differences §  up to ±20% data-‐theory discrepancies (Madgraph, Sherpa MEPS@NLO) in high pT tails of 1st jet

CMS-PAS-SMP-14-009!


q  Theoretical uncertainties on W/Z+heavy flavour jets are larger than for light jets §  heavy-quark content in the proton §  modeling of gluon splitting (initial state, final state) §  massive vs massless b-quark in calculations

q  Test of QCD predictions with various implementations (LO multileg+PS, NLO, NLO+PS)

q  Very important processes as background to Higgs and searches

arXiv:1407.3643 (ATLAS)! JHEP 12 (2013) 39 (CMS) !

Ø  Distribution shapes generally well described by predictions

Ø  Except for configurations with nearby b-jets, dominated by gluon splitting


W+b*• Very*challenging*due*to*large*

backgrounds*

• Measurement*of:*- W+b*- W+b+1*jet*

• bWtagging*used*to*discriminate*signal*processes*

Produc4on*processes*

Gluon*splixng*in*PS*

bWquark*in*ini4al*state*

DoubleWparton*interac4ons*

11*b-tagging discriminante (Neural Network output)


backgrounds*









backgrounds*








q  Descriptions of “b-‐initiated processes” §  4 flavors number scheme (4FNS): b-‐quark generated through gluon splitting §  5 flavors number scheme (5FNS): b-‐quark generated in the initial state by DGLAP evolution

W+b-jets b

b

Z

g

(a)

b

b

Z

g

(b)

q

q

b

b

Z

(c)

q Z

b

bq

(d)

Figure 1: Main diagrams for associated production of a Z boson and one ormore b-jets.

larity silicon pixel and microstrip detectors allow for the re-construction of secondary decay vertices. The electromagneticcalorimeter uses lead absorbers and liquid argon as the activematerial and covers the rapidity range |!| < 3.2, with high lon-gitudinal and transverse granularity for electromagnetic showerreconstruction. For electron detection the transition region be-tween the barrel and end-cap calorimeters, 1.37 < |!| < 1.52,is not considered in this analysis. The hadronic tile calorime-ter is a steel/scintillating-tile detector that extends the instru-mented depth of the calorimeter to fully contain hadronic par-ticle showers. In the forward regions it is complemented bytwo end-cap calorimeters using liquid argon as the active ma-terial and copper or tungsten as the absorber material. Themuon spectrometer comprises three large air-core supercon-ducting toroidal magnets which provide a typical field integralof 3 Tm. Three stations of chambers provide precise trackinginformation in the range |!| < 2.7, and triggers for high mo-mentum muons in the range |!| < 2.4. The transverse energyET is defined to be Esin", where E is the energy associatedwith a calorimeter cell or energy cluster. Similarly, pT is themomentum component transverse to the beam line.

3. Collision data and simulated samples

3.1. Collision dataThe analysis presented here is performed on data from pp

collisions at a centre-of-mass energy of 7 TeV recorded by AT-LAS in 2010 in stable beams periods and uses data selectedfor good detector performance. The events were selected on-line by requiring at least one electron or muon with high trans-verse momentum, pT. The trigger thresholds evolved withtime to keep up with the increasing instantaneous luminositydelivered by the LHC. The highest thresholds applied in thelast data taking period were ET > 15 GeV for electrons andpT > 13 GeV for muons. The integrated luminosity after beam,detector and data-quality requirements is 36.2 pb!1(35.5 pb!1)

!ln tan("/2). The distance !R in ! ! # space is defined as !R =!

!#2 + !!2.

for events collected with the electron (muon) trigger, measuredwith a ±3.4% relative error [13, 14].

3.2. Simulated events

The measurements will be compared to theoretical predic-tions of the Standard Model, using Monte-Carlo samples ofsignal and background processes. The detector response to thegenerated events is fully simulated with GEANT4 [15].

Samples of signal events containing a Z boson decayinginto electrons or muons and at least one b-jet have been sim-ulated using the ALPGEN, SHERPA, and MCFM generators,using the CTEQ6.6 PDF set [16]. All three generators includeZ/$" interference terms. The ALPGEN generator is interfacedto HERWIG [17] for parton shower and fragmentation, andJIMMY for the underlying event simulation [18]. For jets orig-inating from the hadronisation of light quarks or gluons (here-after referred to as light-jets), the LO generator ALPGEN usesMLM matching [19] to remove any double counting of iden-tical jets produced via the matrix element and parton shower,but this is not available for b-jets in the present version. There-fore events containing two b-quarks with !R < 0.4 (!R > 0.4)coming from the matrix element (parton shower) contributionare removed. SHERPA uses the CKKW [20] matching for thesame purpose. The MCFM NLO generator lacks an interfaceto a parton shower and fragmentation package, hence to com-pare with the data we apply correction factors describing theparton-to-particle correspondence, obtained from particle-levelLO simulations. For all Monte-Carlo events, the cross-sectionis normalised by rescaling the inclusive Z cross-section of therelevant generator to the NNLO cross-section [21].

The dominant background comes from Z + jets events, withthe Z decaying into electrons, muons or tau leptons, where onejet is a light or c-jet which has been incorrectly tagged as ab-jet. These events are simulated using the same generatorsas the signal. Other background processes considered includet t pair production simulated by MC@NLO [22, 23], W(# l%)+ jets simulated by PYTHIA [24], WW/WZ/ZZ simulated byALPGEN, and single-top production simulated by [email protected] cross-sections for these processes have been normalisedto the predictions of [25, 26] (approximate NNLO) for t t pairproduction, [21] (NNLO) for W(# l%) + jets, [3] (NLO) forWW/WZ/ZZ, and the MC@NLO value for single-top.

Events have been generated with the number of collision ver-tices drawn from a Poisson distribution with an average of 2.0vertices per event. Simulated events are then reweighted tomatch the observed vertex distribution in the data.

4. Reconstruction and selection of Z + b candidates

Events are required to contain one primary vertex with atleast three high-quality charged tracks. As the final state shouldcontain a Z boson, the selection of events closely follows theselection criteria used by ATLAS for the inclusive Z analysis[27]. In the e+e! channel, two opposite sign electron candi-dates are required with ET > 20 GeV and |!| < 2.47. Electron

2

b

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bq→Wbq gq→Wbbq

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g

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q  Experimental analysis strategy: §  b-‐jet tagging

o  Exploit long life-‐time and large masses of b-‐hadrons (e.g. secondary vertex and large impact parameter)

§  Signal extraction based on fit to distributions sensitive jet-‐flavour o  i.e. b-‐tagging weight distribution o  Templates based on MC, but checked in data control regions

4FN

4FN 5FN

5FN

4FN


q  W+c sensitive to strange quark content in proton §  gluon splitting treated as background in ATLAS and CMS

v  Strange-quark usually suppressed by factor ½ wrt down-quark in PDF §  as suggested by ν-N DIS (NuTev)

v  ATLAS W/Z cross section measurements favour strange-quark enhancement

q  Charm candidates identified with two strategies §  Soft muon tagged inside a jet §  Exclusive decays of the charmed hadrons D± and D*±

q  Use the W-‐charm charge correlation to suppress backgrounds (e.g. gluon splitting, multijet, etc..) §  Same-‐sign contribution is subtracted ⇒  Measuring OS-‐SS yields

90% sg→Wc

10% dg→Wc


(W + c) [pb]σ0 20 40 60 80 100 120

= 7 TeVs at -1L = 5.0 fbCMS

Total uncertainty

Statistical uncertainty

CMS 2011 4.9 (syst.) pb± 2.0 (stat.) ±84.1

MSTW08 pb

PDF -1.7 +1.4 78.7

CT10 pb

PDF -5.2 +6.2 87.3

NNPDF23 pb PDF 3.3 ±78.2

collNNPDF23 pb PDF 11.8±102.7

| < 2.5jetη > 25 GeV, |jetT

p

| < 2.1lη > 35 GeV, |lT

p

Predictions:NLO MCFM + NNLO PDF

Ø  Overall agreement with NLO QCD predictions

Ø  Cross section depends on PDF Ø  ATLAS data suggests s-‐quark enhancement (ATLAS-‐

epWZ12 and NNPDF2.3coll with enhanced strange) §  Consistently with inclusive W/Z data results

Ø  CMS data in better agreement with suppressed strange

JHEP02(2014)013 (CMS) !

JHEP05(2014)068 (ATLAS)!


Source J. Rojo (NNPDF)

¡  Impact of HERA jet and charm data on αS measurement §  Inclusive ep data alone cannot constrain αs(M2

Z) well ¡  Simultaneous fit of PDFs and αs(M2

Z): HERAPDF2.0Jets §  Extracted αs(M2

Z) value very close to fixed one §  αs(M2

Z) value compatible with world average


H1 and ZEUS

0

20

40

0.105 0.11 0.115 0.12 0.125 0.13

r2 - rm

in2

NLOinclusive + charm + jet data, Q2inclusive + charm + jet data, Qmin = 3.5 GeV2

inclusive + charm + jet data, Q2inclusive + charm + jet data, Qmin = 10 GeV2

inclusive + charm + jet data, Q2inclusive + charm + jet data, Qmin = 20 GeV2

0

20

40

0.105 0.11 0.115 0.12 0.125 0.13

r2 - rm

in2

NLOinclusive data only, Q2inclusive data only, Qmin = 3.5 GeV2

inclusive data only, Q2inclusive data only, Qmin = 10 GeV2


0

20

40

0.105 0.11 0.115 0.12 0.125 0.13

_s(MZ2)

r2 - rm

in2

NNLOinclusive data only, Q2inclusive data only, Qmin = 3.5 GeV2



arXiv:1506.06042!

¡  ZEUS-‐H1 combined data of inclusive DIS cross-‐sections in ep scattering can be used to set limits on physics Beyond the SM ⇒  effective radius of electroweak charge of quarks

¡  Extension of HERAPDF2.0 analysis by ZEUS Coll. accounting for possible effects of new physics with quark charge as additional model parameter ¡  New interactions can modify cross-‐section at high Q2 and may be mistakenly absorbed into PDF fits


Classical quark Form Factor approach:

)2 (GeV2Q310 410

SMm/

m

1

-1p 0.5 fb+HERA NC e-1p 0.4 fb-HERA NC e

HERAPDF2.0 total unc.

)2 (GeV2Q310 410

SMm/

m

1

Quark Radius Limit at 95% CL

(prel.)2m)-1810u = (0.45q 2R

310 410

0.95

1

1.05

310 410

0.95

1

1.05

ZEUS preliminary )2 (GeV2Q310 410

SMm/

m

1

-1p 0.5 fb+HERA NC e-1p 0.4 fb-HERA NC e

HERAPDF2.0 total unc.

)2 (GeV2Q310 410

SMm/

m

1

Quark Radius Limit at 95% CL

(prel.)2m)-1810u = (0.45q 2R

310 410

0.95

1

1.05

310 410

0.95

1

1.05

ZEUS preliminary

Improvement wrt previous ZEUS and similar to L3 limit

ZEUS-prel-15-004!ZEUS-prel-15-004!

Date post:	19-Jan-2023
Category:	Documents
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By Alessandro Tricoli (CERN)

Documents