2010

1

Christopher Rogan

1

Christopher Rogan

The Path to Discovery

2010

2

Outline Standard Model candles and handles

towards discovery - Z/W+jets: separation Detector/reconstruction commissioning NP search bkg estimations

Example: Search for SUSY All hadronic analysis - “Jets+MET+X” Re-engineered approach to maximize

discovery potential “tail search” to “bump hunt”

Example: H → ZZ → 4l

Branch of LHC inverse problem: Measuring new resonances’ JPC

2

Pre-requisites: Candles and Handles

Search: Innovative analyses

SIG

BKG

SIG

BKG

SIG

BKG

Log(

N)

Log(

N)

x x’

Characterize: What did we discover?

2010

3

Candles and Handles - Z/W+jets

3

☐ FULLY DATA-DRIVEN METHODS FOR STUDYING W/Z+jets PRODUCTION, USING candles/handles TO: study detector and reconstruction performance - estimate bkgs to BSM searches - probe pQCD - …

aka “Berends-Giele” (BG) scaling

W

Z CDF

CONSTANTSLOPE

2010

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W/Z+jets Analysis Strategy

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Background control samples

Maximum Likelihood Fits

Tests of the Fit

Event Reconstruction and Cut-Based W+jets,

Z+jets selection

sPlots

Z boson “Candle”

MET characterization/

corrections

Probe of NP

Background estimation

Fit PDF validation

High Eff. Selection

MF Fits

Candle Apps

Scaling/Ratios

Modular strategy with staged and varied physics applications

2010

5

W/Z+jets control samples

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Inverting lepton isolation and vertexing requirements → QCD control sample → background shapes for ML Fit

Analysis strategy works “out-of-the-box”

QCD MT shape taken from

control sample and used in

signal extraction ML fit

Excellent agreement btw Data/MC

2010

6

Candles and Handles

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With the ML fit, statistical background subtraction (sPlots) yields a “pure” Z(ll)+jets “candle” sample

Z()+jets bkg normalization

from Z()+jets → Reproduces Z()+jets MET

distribution

MET correction for W()+jets derived from Z()+jets →

Recovers sharp Jacobian peak

Low jet multiplicities can be used to predict high mult.

yields - deviations from BG scaling can indicate new physics contributions

more SUSY

emer

ging

di

scre

panc

y

2010

7

W(l)/Z(ll) Data

LINT = 0.0111pb-1

Nsig = 43.4 +/- 7.3NQCD = 44.6 +/- 7.4

V+jets program 2 years in the making is yielding first results

Yield, with from MC, agrees with NLO x-section (28 nb)

within 10%

2010

8

The Search for SUSY

SIG

BKG

SIG

BKG

SIG

BKG

Log(

N)

Log(

N)

x x’

All hadronic SUSY search has a number of challenges: Controlling W/Z and top backgrounds → W/Z+jets methodology essential component Controlling QCD backgrounds →

especially important in the context of jet/MET reconstruction

We repeat the ‘canonical’ jets+MET SUSY search Looking for excess of events in MET or HT tails Studying this approach allows us to identify its

strengths/weaknesses

Re-engineered SUSY search:new variables, higher signal efficiency, more control over

background distributions, distinctive signature: tail search becomes

bump hunt

2010Kinematic Variables for SUSY

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Two variables I designed to be used together for discovery and characterization of SUSY

Doesn’t involve MET Uses both transverse and

longitudinal information Invariant under long. boosts

Peaks for signal:

Presented at PLANCK2010arXiv:1006.2727v1 [hep-ph]

2010Kinematic Variables for SUSY

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Dimension-less variable used for S/B discrimination Not only suppresses backgrounds, but also shapes their

distributions in the variable in a predictable and well-understood way - the Razor

Two variables I designed to be used together for discovery and characterization of SUSY

Presented at PLANCK2010arXiv:1006.2727v1 [hep-ph]

2010

11

MR and R in CMS

Razor cut shapes surviving background events, falling ~exponentially

Using just trigger requirements and a cut on R

gives excellent S/B discrimination with ~40%

signal efficiency w.r.t. inclusive SUSY x-section

2010

12

Discovery Potential

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3 Observation 5 Discovery

Analysis approach using MR and R is potentially a very powerful discovery toolAllows for characterization of SUSY mass scale

Variables designed to reduce/remove sensitivity to anomalous signals/noise which is problematic for ‘canonical’ search

2010

13

MR and R in Data

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DATAQCD MC

Loos

e R

cut Behavior of MR and R is confirmed

with data both qualitatively and quantitatively

2010

14

Looking towards the Higgs

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Int. Lumi

W/Z+jets SUSY Higgs These variables have many applications in the program of

NP discovery and characterization

MR peaks at 1/2 the Higgs mass. R cut efficiency is stable as a function of Higgs mass →

variables can be used in a mass independent analysis for Higgs discovery and

characterization in the leptons + MET final state

MR and R can be used to study any final state featuring pair-production of heavy particles decaying to visible SM and weakly interacting particles:

MSSM Higgs sector UED Little Higgs Leptoquarks …

2010

15

Higgs ZZ 4l Discovery and Characterization

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Neyman-Pearson hypothesis tests are used, with ML fits, to distinguish between different

Higgs Look-a-likes (HLL’s)arXiv:1001.5300To be published in PRD

In order to improve Higgs discovery and allow for direct measurement of its quantum numbers JPC we consider the Z decay and Higgs production angles

Calculate the PDF’s for these angles as a function of the most general spin 0, 1 and 2 couplings

Running 10’s of trillions of toy experiments with a detector simulation, we build multi-dimensional numerical PDF’s

Decay angles

Production angles

2010

16

Higgs and its Imposters

Correlations between

observables are very important and must be taken into

account

SM H

iggs

vs.

pse

udos

cala

r

Table shows number of signal events required for

the mean expected significance for rejecting in favor of (assuming

is true) to exceed

In some cases, JPC of HLL can be measured near the moment of discovery

2010

17

Higgs and its Imposters: 0+ vs. J = 1

Most general spin 1 Lagrangian

Can distinguish between SM 0+ and general J=1 case at 5 withfor

Can I exclude all J=1 possibilities when I have an SM Higgs?

Can I exclude an SM Higgs when I have the J = 1 case?

2010

18

Outlook Standard Model candles and handles

towards discovery - W/Z+jets: separation Detector/reconstruction commissioning NP search bkg estimations

Example: Search for SUSY All hadronic analysis - “Jets+MET+X” Re-engineered approach to maximize

discovery potential “tail search” to “bump hunt”

Example: H → ZZ → 4l Branch of LHC inverse problem:

Measuring new resonances’ JPC

18

Pre-requisites: Candles and Handles

Search: Innovative analyses

Characterize: What did we discover?

A comprehensive discovery/characterization program that is already underway - some aspects already being adopted by the LHC experiments

2010

19

EXTRA SLIDES

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2010

20

W+jets and top separation

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ML fit based on the transverse mass is split into two categories Categories based on b-tag variables Heavy flavor (h.f.) enriched category is predominantly top h.f. depleted category is predominantly W+jets

sPlots statistical background subtraction allows one to study derived pure “W+jets” or “top” samples

2010

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h.f. variable control samples

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2010

22

Higgs and its impostersMedian expected significance for differentiating between SM 0+ and

general J=1 case should exceed 5 withfor

Most general spin 1 Lagrangian

J=0 composite Higgs Lagrangian

We find that at low masses, discrimination between SM 0+ and a

composite Higgs is possible - discrimination is degraded at higher masses - need to appeal to ratios of

2010

23

H(ZZ 4l) discovery

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Although there is a fairly large irreducible background from ZZ production, this can be statistically “subtracted” using a fit+weighting scheme called sPlots

Hence, for discriminating between different JPC hypotheses we use a signal-only sample and quantify the expected power of discrimination as a function of the number of these observed signal events

Likelihood fits using the Higgs mass and decay

angles (with correlations) reduce the mean int.

luminosity needed for discovery by 30-50%