SUSY at the LHC

Yeong Gyun Kim (Sejong U. & KAIST)

HPC Asia 2007 (September. 9-12, 2007 Seoul, Korea)

Introduction (weak scale supersymmetry)

LHC signature of Mirage mediation

Tau polarization in SUSY cascade decay

Contents

We are entering exciting period in particle physics.

The LHC is about to explore for the first timethe TeV energy scale.

The origin of EWSB ?The nature of dark matter ?Supersymmetry ?Extra dimensions ?

Weak scale supersymmetry-Provides a solution for the naturalness problem

-Complies with gauge coupling unification

-Lightest Supersymmetric Particles (LSP) a natural candidate for non-baryonic Dark Matter

Minimal Supersymmetric Standard Model (MSSM)

SM fields plus an extra Higgs doublet and their superpartners

SU(3) x SU(2) x U(1) gauge symmetry and Renormalizability

R-parity conservation (to avoid fast proton decay)

( B: baryon number, L: lepton number S: spin )

3( ) 2( 1) B L SR

= +1 for ordinary particles= -1 for their superpartners

Soft Supersymmetry Breaking

Sparticles are produced in pairsThe Lightest SUSY Particle (LSP) is STABLE

Precise measurement of SUSY particle masses

Reconstruction of the SUSY theory (SUSY breaking mechanism)

Measurement of SUSY masses

SUSY events always contain two invisible LSPs

No masses can be reconstructed directly

One promising approach

Identify particular decay chain and measure kinematic endpoints using visible particles (functions of sparticle masses)

When a long decay chain can be identified, various combinations of masses can be measured in a model independent way

The SPS 1a benchmark scenario

A favorable scenario both for LHC and ILC

M_gluino = 595 GeVM_qL= 534 GeV, M_uR = 522 GeV

M_N2 = 177 GeV, M_N1 = 96 GeVM_eR = 143 GeV, M_eL= 202 GeV(M_eR < M_N2)

Dilepton invariant mass distribution after the cut

~ 77 GeV

Other invariant mass edges

In total, five endpoint measurements

Four invovled sparticle masses can be obtained

LHC signature of Mirage Mediation

In collaboration with

W.Cho, K.Y.Lee, C.Park, Y.Shimizu (KAIST)

Ref. JHEP 0704 (2007) 054

In KKLT-type moduli stabilization scenario

Modulus mediated contribution to SSB parameters at MGUT

Mirage Mediation

can be comparable to the anomaly mediated one O (m3/2 /4pi2) when the gravitino mass m3/2 ~ 10 TeV.

Depending upon the anomaly to modulus mediation ratio

the model can lead to a highly distinctive pattern of superpaticle masses at low energy scale.

The soft parameters at MGUT are determined to be

where aijk = ai + aj + ak, and ci parameterize the patternof the pure modulus mediated soft masses.

ba and gammai : beta function and anomalous dim.

An interesting consequence of this mixed modulus-anomaly mediation is that soft masses are unified at a mirage messenger scale

For instance,

A benchmark point for collider study

alpha = 1M0 = 500 GeVaM=cM=1/2aH=cH=0tan(beta)=10

K.Choi, YGK, K.Y.Lee, K.Okumura, Y.Shimizu (2006)

Mirage benchmark point alpha=1, M0=500 GeV, aM=cM=1/2, aH=cH=0, tanb=10(M1=367 GeV, M2=461 GeV, mu=475 GeV at EW scale)

m_gluino= 884 GeV, m_dL=776 GeV, m_t1=545 GeVm_N1 = 355 GeV, m_N2 = 416 GeV, m_eR = 382 GeV

0 02 1Rq e The cascade decay is open !

(m_N2 > m_eR)

Cross section for SUSY events ~ 6 pb

We generated SUSY events ( ~ 30 fb-1 luminosity)using PYTHIA (event generator) + PGS (detector simulation)

(cf. mSUGRA )

Precision measurements of sparticle masses at the LHC

When the cascade decay0 02 1Rq e is open,

a clean SUSY signal is l l + jets + missing TE events.

2q q

Re e

1e

jlm

llmjllm

Event Selection Cuts.

• Di-lepton invariant mass distribution

for the mirage pointwith 30 fb-1 lumi.

Mll (max) ~ 60 GeVwell matched withthe generated value

• Various distributions for the mirage point

m_squark, m_slepton, m_N2, and m_N1 can be determined.

Gluino and squark mass measurement

Di-jet invariant mass

Gluino and squark mass measurement

Di-jet invariant mass

Squark mass measurement

Stransverse mass m_qR vs m_N1

‘Model-Independent’ Masses

The mass ratio of gluino to LSP

which is quite distinctive from the predictionof other gaugino mass pattern (i.e anomaly, mSUGRA pattern)

Determination of model parameters

Gluino, squark and slepton masses

M0, alpha and cM

Neutralino masses

Mu (EW scale), tan(beta) cH and tan(beta)

Determination of model parameters

Conclusions (of mirage medication part)

We have investigated LHC signature of mirage mediation by performing a Monte Carlo study for a benchmark point.

SUSY particle masses are determined in a model independent way. In particular, the measured ratio well reproduce theoretical input value of the benchmark point. Therefore, the benchmark scenario may be distinguishable experimentally from other SUSY scenarios, for example, in which gaugino masses are unified at GUT scale.

Model parameters were obtained from a global fit to observable and well agree with the input values.

Tau Polarization in SUSY Cascade decays

In collaboration with

S.Y.Choi, K.Hagiwara, K.Mawatari, P.M Zerwas

Ref) hep-ph/0612237

Much attention has been paid in the recent past to the SPS1a cascade

So far, cascades have primarily been studied involving first and second generation leptons/sleptons.

Explore how the polarization of tau leptons can be exploited to study R / L chirality and mixing effects in stau and neutralino sector

Single pion decays of tau as polarization analyzer

At high energies, the fragmentation functions for pions

( z : energy fraction transferred from the polarized tau to the pion. R / L : tau chirality )

Pion from the right-handed polarized tau- is harder than the one from left-handed polarized tau-

Neutralino decay

On the contrary, results in soft pions.

results in hard pions

(for , gauginos)

Invariant mass distribution of tau-tau and pi-pi

Dependence of on the stau mixing angle

With fixed SPS1a values of

and

With pion momentum cutWithout pion momentum cut

m (pi-pi) distribution for SUSY (SPS1a) and UED’

SPS1a : LR typeUED’ : LL type

m (pi-pi) distribution for SUSY (SPS1a) and UED’

SPS1a : LR typeUED’ : LL type

Conclusions (tau polarization part)

The analysis of tau polarization in cascade decays provides valuable information on chirality-type and mixing of suspersymmetric particles.

By comparing the distribution of the SUSY cascade with UED-type predictions, the sensitivity of the method has been demonstrated.

Though pi-pi distributions have been analyzed in detail, the techniques can readily be applied to other tau decay modes.