What Are We Learning In SM Physics from the LHC*?Sabine LammersIndiana University

May 19, 2015

*focus on ATLAS and CMS, LHCb and ALICE results will be covered in other sessions

Twelfth Conference on the Intersections of Particle and Nuclear Physics

1

Tuesday, May 19, 15

Introduction• Run I of the LHC provided the discovery of the Higgs Boson, the first observation

of a fundamental scalar particle• Big question for Run II: Is there new physics at TeV scale?

• Higgs mass value seems to indicate unitarity and vacuum stability are ok

• No indirect evidence for NP from precision flavor physics

• should be resolved by next CIPANP• Goals of this talk

• Familiarize audience with major progress in SM measurements at LHC

• Point out a couple of interesting things to watch for in Run II

2

Tuesday, May 19, 15

Electroweak Physics

3

Tuesday, May 19, 15

4

Tuesday, May 19, 15

Outline

• Higgs

• Top quark

• W and Z physics

• High-energy Jets

There are hundreds of measurements within and outside of these topics which shed light on the Standard Model. Time constraints require me to make a very limited (and biased) selection. Apologies....

5

Tuesday, May 19, 15

Higgs Physics

gg fusion

VBF

ttH

Production..

...and decay modes

Rich scalar sector, giventhe myriad of possibilitiesfor production and decay

VH

6

Tuesday, May 19, 15

Higgs Production Modes

Parameter value μ = signal strength = σobservedσSM

→ value of 1 ⇒ SM agreement

Combining all decay modes for a single production mechanism:

7

Tuesday, May 19, 15

Higgs Decay Modes

The rate at which we see Higgs Bosons is exactly what we expect from the SM predictions, regardless of production or decay mechanism. 8

Tuesday, May 19, 15

Higgs Mass Measurements

2 precise decay modesfor measuring Higgs mass

H→ZZ→l+l-l+l-

H→𝛄𝛄

Clear mass peaks

Other modes are smeared due to

presence of neutrino or hadronic particles 9

ATLAS

ATLAS

CMS

CMS

Tuesday, May 19, 15

Higgs Mass Measurements

mH = 125.09 ± 0.21 (stat) ± 0.11 (sys) GeV

10

Tuesday, May 19, 15

Higgs Properties

see talk in parallel session by Sarah Demers

Upshot: so far it looks like the SM Higgs

Tightest constraints on Higgs widthfrom ratio of on-shell and off-shell H→ZZΓW < 22 MeV @ 95% CL (5.4x SM exp)

Phys. Lett. B 736 (2014) 64

ATLAS-CONF-2015-008

Some alternatives to SM Higgs spin and parity

hypotheses excluded at >95% CL

Angular observables sensitive to Higgs spin, parity:

Test of scaling of couplingswith the masses of SM

particles shows no deviationfrom SM expectation

Tuesday, May 19, 15

Top Quark Physics

12

Tuesday, May 19, 15

tt cross section• Increased experimental precision

coupled with strong theoretical progress

• Precise cross section allows for extraction of pole mass

13

Tuesday, May 19, 15

top mass• Precise measurements of top mass shed light on consistency of SM • Systematics have gradually tightened up

• tt modeling, jet energy scale and flavor uncertainties

• Run II will tell us if there’s any tension between Higgs and top sectors

14

Tuesday, May 19, 15

Differential tt measurements

15

arXiv:1502.05923

Reconstructed tt observables are unfolded to their particle-level counterpart based on

W and b signatures

avoids large model-dependent extrapolation corrections to the

parton level top quark

Careful comparisons to a variety of theory predictions will improve modeling of tt kinematics

Many BSM searches have

large irreducible tt backgrounds

Tuesday, May 19, 15

top asymmetry• A few years ago, CDF published a result of the tt forward-backward asymmetry

that showed a 3σ enhancement over the theory prediction at the time.• We now have results from ATLAS, CMS (where the asymmetry changes from

forward-backward to narrow-wide) and D0, which are in good agreement with the current theory.

• The CDF measurement has not changed significantly, but the theory prediction has changed, improving the compatibility with the CDF result.

16

Tuesday, May 19, 15

single top and |Vtb|• Observation of single top production in t-channel at LHC

• systematics limited, in particular b-tagging

• Wt production also highly significant (4-6σ)

• |Vtb| extraction from measurements: 4-20% precision|Vtb| known far better

from unitarity constraints

17new combinations are imminent!Tuesday, May 19, 15

W and Z Physics

18

Tuesday, May 19, 15

Z pT

• Probes QCD ISR, pT distribution of partons in proton

• constrains gluon PDF in region important for Higgs boson production

• important input for searches with W and Z backgrounds, and particularly for W mass through improved parton shower tunes

Uncertainties < 1% below Z pT ~100 GeV

JHEP09(2014)145

19

Tuesday, May 19, 15

W and Z reconstructed as single jets• New heavy resonances can decay to highly boosted W and Z bosons. • Proof of principle that W and Z hadronic decay products can be distinguished from

partonic jets

• Hadronically decaying W and Z bosons reconstructed as broad single jets with pT>320 GeV and |η|<1.9, in pp collisions at √s=7 TeV.

• Cross section extracted from fit to jet mass, using massless jet constituents:

• Result is in good agreement with theory:

increasing boson pT

partonic jetboson decay:

2014 New J. Phys. 16 113013

NLO QCD prediction: 20

Tuesday, May 19, 15

Multiboson production

After some initial excitement intheory community over a mild W+W-excess in 7 TeV ATLAS data, CMS

measures the cross section in excellentagreement with SM predictions

using 8 TeV data.

Sensitive probe of anomalous triple gauge boson (aTGC) couplings

21

Tuesday, May 19, 15

Multiboson production

First evidence for 3-boson production in Wγγ final state !

• access to quartic gauge couplings (QGC)• NLO EW corrections generally not available

• potentially large effects at high pT and high mass region where anomalous QGC effects could be present

• 3.7σ significance• limits placed on anomalous couplings

22

Tuesday, May 19, 15

Vector Boson Scattering - Role of the Higgs

Without the Higgs, the VBS scattering cross section risesunbounded with increasing center-of-mass energy ⇒ unphysical! violates unitarity - integrated probability

density cannot be larger than 1

By including additional diagrams:

where H is the SM Higgs, an exact cancellation unitarizes the high energy behavior of σ(VV→VV) Alboteanu, Kilian and Reuter,

JHEP 0811:010,2008, arXiv: 0806:4145

for

23

σ (n

b)σ

(nb)

Tuesday, May 19, 15

Vector Boson ScatteringComplementary approach for studying Electroweak Symmetry Breaking• Verify if the newly discovered Higgs Boson fully restores the unitarity in VLVL scattering• Search for alternative mechanisms for the unitarity restoration: new resonances or strong vector boson interactions or ...

Expected significance: 2.8σObserved significance: 3.6σ

σfid = 1.3 ± 0.4 (stat) ± 0.2 (sys) fbsimilar sensitivity at CMS in agreement with SM prediction

W±W± channel: excellent background suppression

24

Tuesday, May 19, 15

W/Z+jets

• W+jets measurements reach 1 TeV of jet transverse energy

• Painstaking analysis of ~40 distributions• Theory generally can describe data, but there

are several regions with 2-3σ excursions

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

CMS result: Phys. Lett. B 741 (2015) 12

Important processes for studying pQCD, and to validate main background to many SM & BSM searches

25

Tuesday, May 19, 15

W/Z+jets

Double differential measurement:

~10% disagreement betweenmeasurement and Madgraphfor leading jet pTjet > 100 GeV and all y

Overall good description of data by MC models

in muon channel and over full rapidity acceptance of detector

CMS-PAS-SMP-14-009

26

Tuesday, May 19, 15

Z+b(b) - ATLAS• Z+b sensitive to b-quark content of proton;

Z+2b important background in Higgs and BSM searches

• Additional, unfolded differential cross sections in a variety of kinematic variables

• Comparable measurement & theory uncertainties• data in best agreement with predictions from 5-

flavor NLO predictions

JHEP10(2014)141

Results comparable between two experiments

QCD radiation and soft corrections not fully captured by non-perturbative corrections applied to theory

27

Tuesday, May 19, 15

High-Energy Jets

28

Tuesday, May 19, 15

Inclusive Jets

29

Precision tests of pQCD and important inputs to proton PDFs

JHEP02(2015)153

Measurements probe jet transverse energies up to 2 TeV

Tuesday, May 19, 15

Strong Coupling Constant

αs and its total uncertainty determinedusing a 2-loop solution to the RGE as afunction of momentum transfer Q= pT

First extraction from tt events.Results are in good agreement with world average.

arXiv:1410.6765 Eur. Phys. J. C (2013) 73:2604

Phys. Lett. B 738 (2014) 526

Eur. Phys. J. C (2015) 75:186 30

Tuesday, May 19, 15

Conclusions and Prospects• Run I measurements being finalized as Run II data collection gets underway.

• No major excursions of data from SM predictions - so no big hints of new physics in Run I dataset; but many high-precision measurements that help us to continually refine our understanding.

• Run II will continue to provide precision measurements in kinematic regions where new physics will be searched for; also for rare processes that will come into reach with higher √s and larger luminosity

Full set of results and associated documentation can be found on ATLAS and CMS Public Results webpages

Highlight of LHC Run I: Higgs discoveryHighlight of LHC Run II?: BSM physics discovery - we hope

With no further unknown free parameters of the Standard Model, the precision measurements of the SM parameters

will be a primary focus of the LHC Run II and beyond.

31

Tuesday, May 19, 15

Backup

32

Tuesday, May 19, 15

W massSummary slide from M. Boonekamp’s 2015 Moriond EW talk:

33

Tuesday, May 19, 15

Z pT

• FEWZ and DYNNLO: Fixed-order calculation, CT10 PDFs

• ResBos (NNLL): Resummed multiple and collinear gluon emissions, CT10 PDFs,

• NLO+NNLL: Banfi et al, CTEQ6m PDFs

Born-level combined result compared with predictions from

Divergence at low pT expected from lack of resummation; dynamic scale choice improves shape at high pT

Inclusion of scale uncertainties covers difference between data

and prediction

Uncertainties defined by resummation,renormalization and

factorization scale variations

JHEP09(2014)145

34

Tuesday, May 19, 15

Z+J/Ψ• Clean signature to investigate double parton scattering (DPS)• DPS dominates at low opening angle between Z and J/Ψ

Assuming DPS dominates first bin of ∆ϕ distribution, can set an upper limit on the level of DPS in signal

and, correspondingly, a lower limit on σeff

missing SPS?

35

Tuesday, May 19, 15

Z+jets• Some discrepancy between measurement

and predictions for 100 < pTjet < 450 GeV in 1 jet bin

• First Z+5 jet differential cross section measurements

) [GeV]5

(jT

p

-410

-310

-210

-110

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/

) [p

b/G

eV]

5(j T/d

pσd

) [GeV]5

(jT

p20 30 40 50 60 70 80 90 100

Sher

pa2/

Dat

a0.5

1

1.5

Stat. unc. (gen)

) [GeV]5

(jT

p20 30 40 50 60 70 80 90 100

Mad

Gra

ph/D

ata

0.5

1

1.5

Stat. unc. (gen)

CMS-PAS-SMP-13-007

36

Tuesday, May 19, 15

Z+jets

37

Tuesday, May 19, 15

EW Z+2jets

Representative LO EW Zjj contributions

VBF component (left) cannot be calculated independently without breaking gauge invariance

Motivations: • testbed for VBF Higgs• measurement of TGC for space-like momentum transfer (complementary to diboson production)

VBF Z production is Z+2jets at tree level

38

Tuesday, May 19, 15

EW Z+2jets

• Inclusive (Strong + EW) Zjj measured in 5 fiducial regions

• Theoretical predictions calculated with Powheg Box and Sherpa 1.4.3

39

Tuesday, May 19, 15

EW Z+2jetsJHEP04(2014)031

• Signal extraction performed using template fit to the dijet mass spectrum, varying the signal EW Zjj and background normalization independently.

• Number of EW Zjj events NEW extracted from fit and converted to cross section

• Result significance is evaluated using pseudoexperiments: background is excluded at >5σ confidence.

• Measurement is systematics dominated; largest contributions from

• Control region statistics

• Jet Energy Scale (experimental)

• Signal modeling, background modeling and signal/background interference (theoretical)

First 5σ validation of the EW Zjj process!

weighted average:

Powheg prediction:

40

Tuesday, May 19, 15

Z/γ*+jets

• Ratio expected to be constant above pT region where Z mass effects are important

• Test for potential large log effects at high energy, not always included in perturbative calculations

• 4 kinematic regimes: njets ≥ 1, 2, 3 and njets ≥ 1 with HT>300 GeV; pTZ/γ* always > 100 GeV - BSM searches phase spaces

• Fiducial measurement in agreement with theory; MadGraph can describe shape of ratio in pT but predicts ~20% normalization difference (at LO). Higher order effects are expected to be smaller than experimental uncertainties.

γ+jets CMS-PAS-SMP-14-005

41

Tuesday, May 19, 15

(R-jets)

• Increased precision due to cancellation of many systematic effects

• Probes difference between kinematics of the jet system recoiling against W or Z

• Very good description by NLO pQCD

W+jetsZ+jets

1-15% uncertainty over jet bins considered

Eur. Phys. J. C (2014) 74: 3168

0 1 2 3 442

Tuesday, May 19, 15

R-Jets

43

Tuesday, May 19, 15

Z+b(b)

44

Tuesday, May 19, 15

Z+b(b) - CMS• Z+b sensitive to b-quark

content of proton; Z+2b important background in Higgs and BSM searches

• b-tagging: simple secondary vertex (SSV) algorithm; mistags estimated from template fit to secondary vertex mass

• data in best agreement with predictions from 5-flavor NLO predictions

massive bmassless b

JHEP 1406 (2014) 120

45

Tuesday, May 19, 15

W+c

• Provides s-quark PDF information

46

Tuesday, May 19, 15

Introduction

47

Tuesday, May 19, 15