Jay WackerSLAC

34th Annual Johns Hopkins Workshop May 24, 2010

with M. Lisanti, J. Alwall, & M-P Le, and E. Izaguirre, & M. ManhartarXiv: 0803.0019, 0809.3264, 1003.3886, 1005.XXXX

O GLUINO,WHERE ART THOU?

Plan of TalkAn Odyssian Voyage

Where we have been (Tevatron)

Where we will be (14 TeV LHC)

Where we are now (7 TeV LHC)

All started a few years back...

Had an MSSM model that predicted a spectrum

70 GeV80 GeV

140 GeV

...

Surely this must be excluded!?!

The production cross section at the Tevatron is

I went through the 25 years of squark and gluino searchesThey all came back to versions of this:

mSUGRA(Five parameters to rule them all)

but where is?

mSugra has “Gaugino Mass Unification”

Most models look like this

A shocking lack of diversity (see the pMSSM)

Solution to Hierarchy Problem

Jets + MET

Dark Matter

Fewest requirements on spectroscopy

If the symmetry commutes with SU(3)C,new colored top partners(note twin Higgs exception)

Wimp Miracle: DM a thermal relic ifmass is 100 GeV to 1 TeV

Usually requires a dark sector,frequently contains new colored particles

Doesn’t require squeezing in additional states to decay chains

Spectrum in Different Theories

MSSM Universal Extra Dimensions

High Cut-Off Low Cut-Off

Large Mass Splittings Small Mass Splittings

Back to the question:

Is an 80 GeV standard-issue gluino allowed?

Hope to catch in Jets + MET

Require energetic jets and unbalanced momentum

Jets + Missing Energy Cuts at D0

(Not exclusive searches)

1fb-1 analysis

Which search will an 80 GeV gluino fall into?

Simple searches counting experiments on tail of SM distribution

A careful look at the signal

80 GeV particle going to 70 GeV LSP and 2 jets

In rest frame of each gluino: two 3 GeV “jets” and a LSP with 3 GeV momentum

Parton level Detector level

Totally invisible: faked by QCD with

Give the gluino big boost!

Jets merge and MET points in direction of jetMore energy, but looks like jet mismeasurement

Radiate off additional jetUnbalances momentum of gluinos

The Parameter Space in Gluino Searches

mSugra

Need to calculate:

Calculating Additional Jets

Matrix Elements

Necessary for well-separated jets

Includes quantum interference

Fixed order calculation

Computationally expensive

Limited number of partons

Parton Showering

QCD Bremstrahlung

Soft/Collinear Approximation

Resums large logs

Computationally Cheap

Unlimited number of partons

Matching merges best of both worlds

Necessary to avoid double counting

A big advance in Monte Carlo calculations over past 10 years

Calculating Additional Jets

Matrix ElementsP

arto

n S

how

erD

ecay

veto if

veto ifveto if

An Example

High MET cut doesn’t kill signal

Unmatched

Matched

Tail is enhance by a factor of 10!

Start with a model and design a search to discover it

Model Dependent Design

Design a set of searches that will catch anything

Most studies currently available are benchmarks within specific parameterizations (e.g. SU#, etc)

What is the efficacy of searches outside parameterizations?(let alone to different theories e.g. UEDs)

Make sure unexpected theories aren’t missed

Exclusive Jets + MET Search

4 Separate Searches, Individually Optimized

Maximize significance for each

Tevatron Summary

Necessary to consider multiple searches

Multiple cuts for &

Difficult to pull signal from background

Searches are challenging

Frequently low values of & are necessary

These are hard searches!

A Comparison Between Optimized Cuts and Original Cuts

Dijet most effective channel

Not easy...but they’re providing more information now

CDF (2.0 fb-1) 0811.2512

BG

Signal Signal

BG

Tevatron Reach

4 fb-1

An 80 GeV gluino is “ruled out”!

Where are we going to get to with the LHC?

A lot further, a lot faster!

The LHC is not a SuperTevatron (thankfully)

QCD

BackgroundsMadgraph+Pythia PGS

Matching crucial to getting MET tail vaguely right

4+jets

Signals

Should use same methods for signals as backgrounds

Parton Shower - Matrix Element Matching

Signal may be in a different place than expected

Extra jets aren’t a nuisance, they can qualitatively alter signal

Search DesignStart with a range of jet multiplicities

that can be statistically combined

Lepton veto, MET separated from hardest 3 jets

Lore is that only multijet is useful

Based most from benchmark studies

“Susy Without Prejudice” found multijets more useful,but didn’t go away from ATLAS cuts

New Initial StatesPossible at higher order

Parton Luminosities

Spectrum of Radiation Harder for New Physics

Cross section for background is large due to lower SM CM energy

When LSP is heavy(rest mass of LSP is unobservable)

Spectrum of Radiation Harder for New Physics

Consider the additional cost of energy for radiating a jetoff a particle, X, of mass m

Identify

Spectrum of Radiation Harder for New Physics

Cross section for background is large due to lower SM CM energy

Equalizes CM energy for signal and backgroundIncreases S/B significantly

When LSP is heavy(rest mass of LSP is unobservable)

Radiate off a jet with

Works because we’re beyond last SM threshold at the LHC

Multijet Universality

Never found lower jet multiplicity to significantly enhance discovery

Tried many different event shape variables and search strategies

Degenerate spectra

Light Squarks, Heavy Gluinos

Qualitatively different than the Tevatron

14 TeV

3 Searches

High MET

Alpha

Mid MET

Gluinos, Squarks & Degenerate Spectra

Gluinos, Squarks

Cascade Decays

The Searches

High MET Search

Introduced by L. Randall & D. Tucker-Smith

The Alpha Variable

Modified by CMS to multijet searches

Group to minimizemomentum imbalance

Discovery ReachAlpha Search

AlphaHigh MET

Directly decaying SquarksDirectly decaying gluinos

AlphaHigh MET

Multijet still more effective than dijets

Cascade Decays

Mid MET Search

High MET

Alpha

Mid MET

Lowers MET in Events

Extended Cascade Decays

LSP is great-granddaughter

Momentum is divided many different ways

Reduces MET dramatically

Worse case scenario

Need a low MET search

7 TeV

High MET

Interpolating from Tevatron to 14TeV LHC

(in progress)

Base Search

Direct Gluino Decays

Doubling the reach in the next year!

Tevatron

High MET

Direct Squark Decays

High MET

Cascade Gluino Decays

High MET

Base

ConclusionO GLUINO,

WHERE ART THOU?Comin’ soon to a collider near you!

Lessons from Tevatron (and before) onhow not to design/present searches

Simple search strategies will provideextensive coverage

Discovery at the LHC in Jets + MET much easierthan at the Tevatron