Long lived LSPs

Long lived LSPs

SLAC ATLAS forum, 5 December 2007

Ignacio Aracena (SLAC)Ignacio Aracena (SLAC)Keith Bechtol (Stanford)Keith Bechtol (Stanford)Dan Silverstein (Stanford)Dan Silverstein (Stanford)Claus HornClaus Horn (SLAC) (SLAC)

SLAC ATLAS forum, 5 Dec 2007

Claus Horn: Long-lived LSPs

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Content of this Talk

Motivation Signatures Reach studies Generator level studies Reconstruction Next steps

Working in collaboration with the ATLAS Hidden Valley group



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Motivation

L number violating

B number violating

Should not exclude L / B violating effects a priori !

• We have seen L violating effects in neutrino sector. • A HE theory should include B violation to explain baryon asymmetry.

In RP conserving SUSY models these terms are neglected which ensures a stable LSP and, if neutral, a CDM candidate.

The general SUSY Lagrangian contains L and B violating terms:

• There are also RPV scenarios with dark matter candidates.• There are many other motivations for supersymmetry.

However:

Advantage of RPV: Possibility to directly reconstruct sparticle masses.

Striking signature: high pT DVs, no MET



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Existing limits on RPV couplings

Source Best Limits Comment

Tevatron & HERA ’, ” < 10-2 Mostly squark mass dependent

Low Energy

experiments

’, “ < 10-2 ml/100GeV Proportional to sfermion mass

Proton decay ’” < 10-11 No limit on single couplings!

Cosmology , ’, ” < 5 10-7 Model dependent!

If couplings are small, we will not observe RPV in production, but displaced vertices!



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Signatures

Other possible LSPs:(gravitino) sneutrino, slepton, squark (disfavoured by cosmology)

LLE

Signature ( LSP)Superpotential

’ LQD

’’ UUD

Search for displaced vertices with 2jets+X or 2 leptons.

‘Underlying SUSY event’ from main IP + Displaced vertex

2 jets + l±/

l+ l- +

3 jets

l*

l

l

l

LSP

l*

l

q

q’

q*

q

q

q”

Focusing on LSP case



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Reach on RPV couplings

Decays in muon-spectrometerDecays in calorimeter

Decays in inner detectorb-tagging region

d ~ ( ) ml

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2 m5

Effective coupling

Decay length:

Covering 4 orders of magnitude; Largest region covered by ID

Reach additionally extended due to ml and exp(d/d0) dependence.

’

LQD



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Decay Regions

x-axis : decay length for =1Additional dependencies:

Considering 10K simulated events per .

Classifying displaced vertexposition into 5 diff regions.

• EKin m()-m(q)

• Integrated lifetime distribution

(ID includes b-tag)

Decay probability for a single LSP

Study decay region dependence on lifetime

ID=Decay in Inner detectorMS=Decay in Muon-Spectrometer



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Combined Probability

Both decaying in ID

Both decaying in calorimeter

Ptot approaches 1 in end region.

Maximal 16% of events have two decays in the calorimeterfor any lifetime.

Calculate combined probability:

P2ID = PID2

PID+CAL = 2*PID*PCAL

5 decay regions (b-tagging, tracker, Calorimeter, MuonSpectrometer,ETmiss)-> In total 15 combinations.

[cm]

[cm]

Two DV requirement may be important background discriminator.



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Event Generation with Pythia

Setting sparticle masses by hand Suppressing long decay chains Allow long decay length of LSP in

Pythia Switch explicitly off neutrino decays Suppress decays involving third

generation quarks Modified Pythia interface:

introduce new flags to select different RPV couplings

qqqqqR 01

~~

Sparticle mass spectrum

m( g ) = 5137 GeV

m( dL,R ) ≈ 700 GeV

m( uL,R ) ≈ 698 GeV

m( t1,2,b1,2 ) ≈ 5000 GeV

m( lL,R ) ≈ 5000 GeV

m( ) = 800 GeV

m( 01 ) = 494 GeV

Resulting event: Squark pair production+



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Generator level Studies

Neutralino:

Jets:

etapT

Applying simple jet finder to construct jets out of tracks from DV:



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Dependence on E

Average deltaR of decay products

Mean electron pT increases with increasing neutralino energy.

Decay products are well separated even for high neutralino energies.

Electron pT for different E.



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Sample Production

Simulation in Geant4

Digitization (-> RDO)

Samples

7mm 800 evts100mm 50 evts700mm 50 evts

Reconstruction (->ESD)

Conversion job (->AOD)

Athena analysis (->AANT ntuple)

Generation in Pythia

Change tracking cuts, very slow

Using production transforms, run on the grid

Create Track Selections

ROOT analysis



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Experimental HandlesDecays in the Inner Detector

Decays in the calorimeter

Decays in the muon spectometer

Jets without tracksHigh em/had energy fraction

Clusters of muon ROIs

High mass displaced vertices

GeneralTwo DV decays in each eventCommon DV mass (neutralino)

Missing ET to be studied

Main backgroundsSecondary vertices within jetsMaterial reactions

NoisePi0-jets

Very high pT jets



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Event DisplaysShown are all stable truth particles

Dashed line: electron

Displaced Vertices:Red & blue

(intermediate particles are not shown)

Black:Underlying SUSY from IP

Green:Neutalino



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c = 7mm

x-y view y-z view

Stable truth particles

Leptons and jets well seperated



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c = 700 mm Example



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Reconstruction-Overview

c=7mm

c=1m

Tracking

Jet finding

Vertex finding

Many standard cuts have to be adjusted:

Lepton ReconstructionMatch tracks to DV instead of IPOptimize shower shape variables

Release constraints on vertex positionOptimize for different regions

Optimization for DV tracks

Match calorimeter clusters to DV tracks



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Reconstruction Strategy

• Standard calorimeter jet finder (jets from IP)

• Track jets, on pre-selected tracks (cut on impact parameter)

Vertexing methods: fitting tracks from one vertex/ topological

High vertex mass requirement

Secondary vertices within jets

Vertices within dead material map

Pre-select all tracks within these jets (match at calo surface)

Reject:



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Impact Parameter

Red: QCD

Blue: RPV(c=7mm)

Many track with d0 of order of cm Tails much wider for RPV sample



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Impact Parameter SignificanceStandard cuts Extended cuts

QCD

SUSY

QCD

RPV

Impact parameter distribution indicates existence of DVs



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Jets in the 700 mm sampleRunning cone (0.4) tower jet finder on calorimeter clusters

Next step: study efficiency as function of decay length

Red: Truth, Black: Reconstructed

Decays beyond the cal will lead to not reconstructed jets

DeltaR



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Conclusions

Exciting new analysis effort started.

ATLAS covers a large region of unexplored RPV coupling space.

Many adjustments are needed in reconstruction

Small RPV couplings lead to striking signatures with disp. vertices.

High pT displaced vertices may enable an early discovery.



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Backup slides



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Triggering

Introduction of specific triggers:

Events may be triggered by jets/leptons from main IP

Triggering on DV properties may extend trigger reach

Decays in calorimeter: low EEM/EHAD

Decays in MuonSpectrometer: large # muon ROIs



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pions

photonsFrom IP

From DV

Documents

Long lived LSPs