SUSY searches at ATLASmoriond.in2p3.fr/QCD/2016/MondayMorning/Lorenz.pdf · 21.3.2016 J. Lorenz, SUSY searches at ATLAS 17 SUSY summary. 21.3.2016 J. Lorenz, SUSY searches at ATLAS

SUSY searches at ATLASJeanette Miriam Lorenz (LMU München)

On behalf of the ATLAS Collaboration

Moriond QCD 2016, 21.3.2016

21.3.2016 J. Lorenz, SUSY searches at ATLAS 2

Searches for Supersymmetry in early Run 2

[http://inspirehep.net/record/1326406]

SUSY: well motivated theory beyond the SM→ predicting supersymmetric partners

to SM particles.

Extensive search program during LHC Run 1,but nothing found.

Early LHC Run 2: Cross sections of gluinos and squarks significantly increased with respect to Run 1.

→ Early Run 2 SUSY searches mainly look for gluino and squark pair- production, but also for stops and sbottoms.

Example signatures


Search strategies

Large sensitivity gain/discovery potential => Aimed to have simple and robust analyses for first data. => In most cases simple (cut-and-count) signal regions, in contrast to (sometimes)

complicated Run 1 analysis configurations.

Analyses optimized on discovery.

Background estimation strategies essentially as in Run 1:

● Based on control regions for irreducible backgrounds and data-driven approaches for reducible backgrounds.

● Simultaneous fits (and hypotheses tests etc.) to calculate final background estimates, to calculate p0-values and to derive limits.

Matrix method, jet smearing...


Overview on results

Presented at the CERN seminar before Christmas (partly updated):

● 0 lepton + >= 2-6 jets: ATLAS-CONF-2015-062● 0 lepton + >= 7 jets: http://arxiv.org/abs/1602.06194● 1 lepton + >= 2-6 jets: ATLAS-CONF-2015-076● 2 same-sign leptons/3 leptons: http://arxiv.org/abs/1602.09058● 2 opposite-sign leptons + Z requirement: ATLAS-CONF-2015-082● 0/1 lepton + >= 3 b-jets: ATLAS-CONF-2015-067● 0 leptons + 2 b-jets: ATLAS-CONF-2015-066

New:

● Searches for stop in final states with 1 lepton: ATLAS-CONF-2016-007● Searches for stop in final states with 2 leptons: ATLAS-CONF-2016-009

All ATLAS SUSY results at: https://twiki.cern.ch/twiki/bin/view/AtlasPublic/SupersymmetryPublicResults

Searches for gluino and squark pair production


Zero lepton + jets + ETmiss

0-lepton + >= 2-6 jets + ET

miss

0-lepton + >= 7 jets

7 inclusive signal regions (>= 2 to >= 6 jets), using e.g. criteria on ET

miss and mef = Σ pT (jets) + ETmiss

etc.

Data and background estimates in good agreement.

Targeting more complex final states with high jet multiplicity.

→ Using signal regions with and without requiring b-tagged jets and requiring harder or less hard jets.

Data agrees with background estimates.[arXiv:1602.06194]

Updated

[ATLAS-CONF-2015-062]


1 electron or muon + jets + ETmiss

→ Two analysis parts: soft pT lepton (7/6 < pT(e/μ) < 35 GeV) and high pT lepton (pT > 35 GeV)

● 6 diferent signal regions (jet multiplicity, ETmiss, mef,

mT = and spherical variables).● Main backgrounds, ttbar and W+jets, estimated using

control regions.● Data in good agreement with background estimates

within 2.0 sigma.

hard

√2 pTl ET

miss(1−cos([Δ φ( p⃗T

l , p⃗Tmiss

)]))


soft


2 same-sign leptons/3 leptons

Events with same-sign leptons predicted in many BSM models, but rare in SM.→ low background expectations (tt+V, diboson)

=> Four signal regions, with or without b-tagged jets, criteria on ETmiss and mef

Data agrees with background prediction.

[arXiv:1602.09058]

Updated


2 opposite-sign leptons + Z requirement + ETmiss

[Eur

. Phy

s. J.

C75

(201

5) 3

18]Searching for gluino or squark

pair-production with a Z as decay product.

→ in Run 1 search: 3 (1.7) σ in ee (µµ) channel.=> Re-look at the same SR in Run 2.

Run 2 analysis:

● Small changes to the signal region due new tracking layer and updates in reconstruction software – backgrounds due to misidentified hadrons now negligible.

● Selection: 2 (e + e − or μ+ μ− ) with pT > 50,25 GeV and 81 < m(ll) < 101 GeV, 2 jets with ∆φmin ( ETmiss , jets) > 0.4, ET

miss > 225 GeV and HT > 600 GeV● Extensive background estimation studies, validation

regions look all very fine: Z + jets from γ + jets control region, top and diboson events from diferent-flavor control region.

=> 21 observed versus 10.3 +- 2.3 expected (2.2 σ), symmetric in ee and µµ channels.


Searches for stops and sbottoms


0-lepton + 2 b-tagged jets + ETmiss

Search for direct sbottom pair production:● Two sets of signal regions – for large and small mass

diferences between sbottom and LSP.● For large mass diferences cut on cotransverse mass:

m2CT(v1 , v2 ) = [ET(v1 ) + ET(v2 )]

2 − [pT(v1 ) − pT(v2 )]2

→ for ttbar events clear endpoint at 135 GeV.● For small mass diferences use recoil against ISR jet.● Backgrounds: W+jets, Z+jets and top events from control

regions with 1 or 2 leptons.

Data in good agreement with background expectation.



0/1 lepton + 3 b-jets

Searching for sbottom and stops in gluino decay using 3 b-tagged jets.

Three sets of signal regions:● 0 leptons + >= 4 jets + ET

miss and mef etc. → sbottom● 0 leptons + >= 8 jets + ET

miss and mef etc. → stop● 1 lepton + >= 6 jets + ET

miss and mef etc. → stopData in good agreement with background expectation.

New: Combination of 0 lepton and 1 lepton signal regions to improve sensitivity to stop.



Searching for stops in final states with 1 lepton

→ Due to int. luminosity currently more sensitive to gluino production

● Three signal regions requiring >= 1 b-tagged jet, 1 isolated e or µ, jets, mT, mT2 etc.

● Using large R-jets in boosted regimes towards low stop masses.

Data in good agreement with background estimates within 2.3 σ (region SR1)

SR1, resolved

SR2 and SR3, boosted

Targets gluino-mediated stop quark production and direct stop quark pair production.

New



Searching for stops in final states with 2 leptons

● Requiring two isolated e or µ with opposite charge + 2 b-tagged jets + ET

miss

● 2 signal regions with same or diferent flavor of the leptons.● Criteria on mll , mT2 , ET

miss/mef and ● Dominant backgrounds (diboson and ttbar) estimated using control

regions.

Data in good agreement with background prediction.

p⃗Tbl l= p⃗T

miss+ p⃗T

l1 + p⃗Tl2

New



Outlook

Very productive year 2015 for SUSY searches for gluinos or stops/sbottoms.→ Searches focused on a simple analysis strategy to validate the first Run 2

data and to fully benefit from the increased discovery potential.

● Strong limits on gluinos, stops and sbottom significantly superseding the Run 1 limits.● Few analyses reported small discrepancies in the order of 2 σ, as can be expected when

looking at so many signal regions.

Looking forward to clarify the situation with the 2016 data and to extend the search program to electroweak and RPV SUSY.

x.3.2016 J. Lorenz, SUSY searches at ATLAS 16

Backup


SUSY summary


More summary plots


Background estimations using control regions

[Eur.Phys.J. C75 (2015) 153]


0-lepton + >= 2-6 jets + ETmiss


Signal regions – lower jet multiplicities targetting squark pair-production, higher jet multiplicities gluino pair-production and longer decay chains.


0-lepton + >= 2-6 jets + ETmiss

Important backgrounds (top, W+jets, QCD multi-jet, Z → neutrinos) constrained in control regions



0-lepton + >= 7 jets [arXiv:1602.06194]

Signal regions


0-lepton + >= 7 jets [arXiv:1602.06194]

Background composition in the signal regions requiring jets with pT > 50 GeV

● Multi-jet backgrounds estimated via using ET

miss/sqrt(HT) templates at lower jet multiplicities

● Leptonic backgrounds estimated via control regions with 1 lepton




Example for a signal region requiring a high pT lepton + associated control regions




Example for a signal region requiring a low pT lepton + associated control regions


2 same-sign leptons/3 leptons[arXiv:1602.09058]

Signal regions




Definition of signal, control and validation regions.

Good agreement between background estimates and data in validation regions.




Background estimation techniques:

● ttbar, WW, Wt (flavor-symmetric backgrounds) from 'flavor-symmetry method' using eµ control sample; cross-checked with a side-band fit

● Z/gamma* + jets: small background, estimated data-driven from gamma+jets events

● WW/ZZ: 30% in signal region, taken from MC and validated in validation regions

● ttbarW, ttbarZ and ttbarWW taken from MC


0-lepton + 2 b-tagged jets + ETmiss

[ATLAS-CONF-2015-066]Signal regions


0/1 lepton + 3 b-jets[ATLAS-CONF-2015-067]

→ Example of the signal regions requiring 1 lepton and the associated control regions


Searching for stops in final states with 1 lepton[ATLAS-CONF-2016-007]

Control and validation regions for background estimation

● amT2: variant of the mT2 variable with special focus on dileptonic ttbar events● mT2:

→ see e.g. JHEP 03 (2015) 100


Searching for stops in final states with 2 leptons[ATLAS-CONF-2016-009]

→ Selected distributions in control regions

Documents

SUSY searches at ATLASmoriond.in2p3.fr/QCD/2016/MondayMorning/Lorenz.pdf · 21.3.2016 J. Lorenz, SUSY searches at ATLAS 17 SUSY summary. 21.3.2016 J. Lorenz, SUSY searches at ATLAS