LHC SUSY SPIN MEASUREMENTS SPIN PRAHA Spin Measurements in Supersymmetry at the LHC Christopher Lester Cavendish Laboratory, Cambridge (on behalf of the ATLAS collaboration)

LHC SUSY SPIN MEASUREMENTS SPIN PRAHA This talk is Backwards

LHC SUSY SPIN MEASUREMENTS SPIN PRAHA not upside down !

LHC SUSY SPIN MEASUREMENTS SPIN PRAHA Conclusions ATLAS does not yet know the circumstances (models, masses, integrated luminosities) in which the spins of supersymmetric particles will be unambiguously measurable There are lots of good and promising ideas – both within ATLAS and outside some are partly tested some are un-tested plenty of work remains to be done!

LHC SUSY SPIN MEASUREMENTS SPIN PRAHA What is “Discovering SUSY” ? What makes Supersymmetry different to Universal Extra Dimensional (UED) models? One part of the answer: SPIN

LHC SUSY SPIN MEASUREMENTS SPIN PRAHA We will see two important themes: Mass measurements will precede ( * ) spin determinations “Spin measurement” ( ** ) should not be confused with “sensitivity to spin” (*) or will at best be simultaneous with (**) Here “spin measurement” means “determining unambiguously the correct nature (scalar, fermion, vector) of one or more particles in a decay chain or model

LHC SUSY SPIN MEASUREMENTS SPIN PRAHA The methods considered here Spins in “QLL chain” A.Barrhep-ph/ ATL-PHYS Smillie et alhep-ph/ (including ATLAS member) Biglietti et al ATL-PHYS-PUB (Study of second lightest neutralino spin measurement with ATLAS detector at LHC Matchev et al arXiv: Slepton Spin (pair production) A.Barr hep-ph/ ATL-PHYS-PUB

LHC SUSY SPIN MEASUREMENTS SPIN PRAHA Other interesting methods Gluino chain spin Alvez, Eboli, Plehnhep-ph/ MAOS method Cho, Kong, Kim, Park arXiv: Spins in chains with charginos Wang and Yavinhep-ph/ Smillie hep-ph/ Spins in chains radiating photons Ehrenfeld et alarXiv:

LHC SUSY SPIN MEASUREMENTS SPIN PRAHA Spin Consistency Check

LHC SUSY SPIN MEASUREMENTS SPIN PRAHA Spin Consistency Check Di-Lepton Invariant Mass (GeV) Relative Frequency Straight line Consistent with: Phase-space Scalar slepton (SFSF) Fermion KK lepton (FVFV)

LHC SUSY SPIN MEASUREMENTS SPIN PRAHA QL Spin Determination (A.Barr) “NEAR” “FAR” How can we tell from ? 2 problems : How can we distinguish the ‘near’ lepton from the ‘far’ lepton? hep-ph/ ATL-PHYS

LHC SUSY SPIN MEASUREMENTS SPIN PRAHA Quark+NearLepton invariant mass distributions for: sin ½ θ* Back to back in  2 0 frame QL + QL - Phase space (spin-0) Probability density QUARKS L+ L- and sin ½ θ* Back to back in  2 0 frame QL - QL + Phase space (spin-0) Probability density ANTI -QUARKS L+ L- and __ _ hep-ph/ ATL-PHYS

LHC SUSY SPIN MEASUREMENTS SPIN PRAHA Experimental problem Cannot reliably distinguish QUARKs from ANTI QUARKs In experiment, can only distinguish RED(QL+,_ L+) from BLUE(QL-,_L-) Can only distinguish lepton charge RED(QL+,QL+) from BLUE(QL-,QL-)

Expect QUARK and ANTI-QUARK contributions to cancel: QL + _ QL - _ SUM jL + SUM jL -

But LHC is Proton-Proton machine More Quarks than Anti-Quarks! So get: QL + _ QL - _ SUM jL + jL - Asymmetry! hep-ph/ ATL-PHYS

LHC SUSY SPIN MEASUREMENTS SPIN PRAHA “Far” Lepton washout? (though compare with later comments Matchev arXiv: ) “NEAR” “FAR”

LHC SUSY SPIN MEASUREMENTS SPIN PRAHA jL + So define m jL +, m jL - asymmetry parton-level detector-level Asymmetry “A” spin-0 Spin-½ M jL / GeV  sin ½ θ* where jL - hep-ph/ ATL-PHYS fb-1 M(QL)

Charge asymmetry at detector level Susy spins compared only with no spin (i.e. with phase space) Points are for 500 fb -1 detector level no spin parton level x 0.6 Barr hep-ph/ ATL-PHYS (similar to SU3) M(QL)

LHC SUSY SPIN MEASUREMENTS SPIN PRAHA Tested further in ATLAS ATL-PHYS-PUB Biglietti et al Preselection cuts Dilepton selection cuts Parametrised Simulation (ATLFAST)

LHC SUSY SPIN MEASUREMENTS SPIN PRAHA Di-lepton mass spectra ATL-PHYS-PUB Biglietti et al SU1 – MC truth SU3 – MC truth Here at SU1 there are two sleptons (ê L =255 GeV, ê R =155 GeV) below chi 2 =264 GeV. Chi 1 =137 GeV Here at SU3 there is only one accessible slepton below chi2 Chi 2 =219, ê R =155, Chi 1 =118 GeV M(LL)

LHC SUSY SPIN MEASUREMENTS SPIN PRAHA Jet-lepton mass spectra ATL-PHYS-PUB Biglietti et al SU1 – MC truth SU3 – MC truth M(QL)

LHC SUSY SPIN MEASUREMENTS SPIN PRAHA Truth Asymmetry ATL-PHYS-PUB Biglietti et al where A SU3 – MC truth 30 /fb M(QL)

Truth Asymmetry ATL-PHYS-PUB Biglietti et al SU1 – MC truth Near lepton Left slepton Near lepton Right slepton Far lepton Right slepton Far lepton Left slepton A A A A 220 /fb M(QL) Shows asymmetry depends on particle identities

Backgrounds ATL-PHYS-PUB Biglietti et al Main background is SUSY Mostly defeated by flavour subtraction Main Standard Model backgrounds are Di-top + jets W / Z + jets

LHC SUSY SPIN MEASUREMENTS SPIN PRAHA Fast simulation results ATL-PHYS-PUB Biglietti et al SU1 – ATLFAST SU3 – ATLFAST Note... Flavour subtraction

LHC SUSY SPIN MEASUREMENTS SPIN PRAHA Fast simulation results ATL-PHYS-PUB Biglietti et al AA SU1 – ATLFAST SU3 – ATLFAST Note... Flavour subtraction 30 /fb100 /fb Sufficient power to eliminate null hypothesis M(JL)

LHC SUSY SPIN MEASUREMENTS SPIN PRAHA Safety check ATL-PHYS-PUB Biglietti et al SU1 – ATLFAST SU3 – ATLFAST Expect to see NO ASYMMETRY in these OFOS lepton plots. Confirmed! 30 /fb100 /fb M(JL)

LHC SUSY SPIN MEASUREMENTS SPIN PRAHA QUACK ! SUSY UED Not all things that quack are ducks!

LHC SUSY SPIN MEASUREMENTS SPIN PRAHA UED SUSY SPS1a masses UED type masses UED and SUSY not distinguished by dilepton mass spectrun hep-ph/ Compare ratios of dilepton invariant mass distributions for different spin configurations (SUSY is horizontal) : M(LL) 2

LHC SUSY SPIN MEASUREMENTS SPIN PRAHA Jet + lepton asymmetry not good at distingusihing UED and SUSY either UED massesSPS 1a masses Not resolvable for UED masses, maybe for SUSY Charge asymmetry due to quark vs antiquark excess

LHC SUSY SPIN MEASUREMENTS SPIN PRAHA UED massesSPS 1a masses Similar form, different magnitude Not detectable for UED masses Jet + lepton asymmetry not good at distinguishing UED and SUSY either.

LHC SUSY SPIN MEASUREMENTS SPIN PRAHA “ANY-Spin” Determination (Smillie et.al.) Later fuller follow-up (Matchev, Kong, et al) F FFF SFS hep-ph/ arXiv: M(JL) 2 (SUSY) (UED) relative probability Cannot distinguish:

LHC SUSY SPIN MEASUREMENTS SPIN PRAHA Direct di-slepton production A.Barr hep-ph/ ATL-PHYS-PUB Event selection: two single leptons transverse missing energy > 100 GeV no jets with pT> 100 GeV no b-jets mT2(l+, l-) < 100 GeV Mll< 150 GeV |missing pT+ pT(l+), pT(l-)| <100 GeV Lepton pT(l1) > 40 GeV, pT(l2) > 30 GeV

LHC SUSY SPIN MEASUREMENTS SPIN PRAHA Look at slepton production angle A.Barr hep-ph/ ATL-PHYS-PUB

LHC SUSY SPIN MEASUREMENTS SPIN PRAHA Have some access to desired angle Distribution of is correlated with decay angle A.Barr hep-ph/ ATL-PHYS-PUB

LHC SUSY SPIN MEASUREMENTS SPIN PRAHA Fast simulation plot Outer error bars: after SUSY & SM background subtraction Significance strongly dependent on mass spectrum A.Barr hep-ph/ ATL-PHYS-PUB

LHC SUSY SPIN MEASUREMENTS SPIN PRAHA End Notes QLL chain Some spin “sensitivity” – but no strong UED/SUSY separation Reduced discriminatory power when considering general couplings (Matchev/Kong). Di-slepton production Better chance of separating UED/SUSY Still model dependent Both require large cross sections

LHC SUSY SPIN MEASUREMENTS SPIN PRAHA Backup slides

LHC SUSY SPIN MEASUREMENTS SPIN PRAHA M T2 -assisted spin determination assign 4-momenta SUSY UED Cho, Choi,Kim,Park,

LHC SUSY SPIN MEASUREMENTS SPIN PRAHA Cross sections imply spins Datta, Kane, Toharia hep- ph/ Higher spins mean higher cross sections (for given masses)

LHC SUSY SPIN MEASUREMENTS SPIN PRAHA SU1 (stau co-annihilation) point

LHC SUSY SPIN MEASUREMENTS SPIN PRAHA SU3 bulk point

LHC SUSY SPIN MEASUREMENTS SPIN PRAHA SU3 bulk point

LHC SUSY SPIN MEASUREMENTS SPIN PRAHA Helicity dependence Process 1 (SUSY) Process 1 (UED, transverse Z*: P /P = 2x) Both prefer highinvariant mass TL

LHC SUSY SPIN MEASUREMENTS SPIN PRAHA Example mass spectra SPS1a mass spectrum: (GeV) UED-type mass spectrum: (GeV) (R -1 ~ 800 GeV)