Hidden Valley Higgs Decays in the ATLAS detectorThe ATLAS Collaboration

L.Bodine, G.Ciapetti, A.Coccaro, D.Depedis, C.Dionisi, S.Giagu, H.Lubatti, F.Parodi, M.Rescigno, G.Salamanna, C.Schiavi, A.Sidoti, M.Strassler, D.Ventura, L.Zanello

The Hidden Valley

“Hidden Valley” models predict a new dynamic accessible (may be) at LHC energies

Hidden Valley and SM communicate through a mediator communicator(Higgs, Z’,LSP)

All v-particles are neutral under the SM

The lightest v-particles (v) are stable in the v-

sector and decay (weakly) only in the SM

v decay in heavy quarks (heavy leptons) pairs

(bb,)

Hidden Valley models are a general class of models that predict neutral, long-lived particles

M. Strassler and K. Zureck ,Phys.Lett.B 661:263(2008) Phys.Lett.B 651:374(2007)

NEED A SIGNATURE DRIVEN TRIGGER STRATEGY

v proper c (mm)

Hidden Valley Monte Carlo simulation based on Pythia Simulated process:Higgs → v v

Decay length choosen to provide v decays throughout the ATLAS detector

Model parameter

hv production and decay:

M(hv)=140 GeV

M( v )=40 GeV

c=1500mm

Hidden Valley: parameters of the model

Is the ATLAS detector able to cope with “unexpected” long-lived neutral particles?

v d

eca

y p

robabili

ty

Displaced high multiplicity neutral vertices Unique topological signature

No SM process can mimick those signatures, HV processes almost

background free

Displaced high multiplicity neutral vertices Non-pointing tracks and no charged track in the

Inner DetectorLow efficiencies for “conventional” trigger selections (jet trigger, muon triggers, tracking

algorithms in Inner Detector) and reconstruction algorithms

BUT

v decaying in the calorimeter Small energy deposit in Electromagnetic calorimeters Large deposit in Hadronic calorimeters No tracks associated in IDv decaying in the Muon

Spectrometer Large multiplicity Tracks not pointing to nominal interaction vertex No tracks in ID No energy in calorimeters

“Atlantis” ATLAS event display“Pythia” event display (no detector simulation)

ATLAS “Hidden Valleys” TriggersImplemented Level-2 triggers specific for Hidden Valley decays selection

Jet Log(EHAD/EEM):

Jet ET>35 GeV in | |<2.5 log(EHAD/EEM)>1 no reconstructed tracks

pT>1GeV/c

Muon Cluster:

at least 3 Level-1 muon candidates pT>6GeV/c contained in a cone of R=0.4 isolated (R=0.7) from jets

Trackless Jet with muon:

Jet ET>35 GeV in | |<2.5 1 Level-1 muon candidate with pT>6GeV/c No tracks with pT>1GeV/c contained within the jet cone

(R=0.4)

2.2

Muon

Higgs production: gluon fusion

4.4

Jet

Conventional Triggers

HV Specific Trigger Selection (Level-1&Level-2)

15.7

Total HV Triggers

9.0

MuonCluster

3.8

Trackless jet with muon

18.55.04.7

Total all Triggers

Log (EHAD/EEM)

Total

2.2

Muon

Higgs production: gluon fusion

4.4

Jet

Conventional Triggers

HV Specific Trigger Selection (Level-1&Level-2)

15.7

Total HV Triggers

9.0

MuonCluster

3.8

Trackless jet with muon

18.55.04.7

Total all Triggers

Log (EHAD/EEM)

Total

Expected Level1&Level2 background trigger rate from HV triggers:

~3 Hz at L=1033 cm-2s-1

evaluated with minimum bias and dijet samples

* *

* Overlap removed

HV Calorimetric trigger

v decaying in Hadronic Calorimeter

Ratio of energy deposit in calorimetersLog(EHAD/EEM) vs v decay distance

Di-jet sample

70 < ET< 140 Gev 140 < ET< 280 Gev

v decaying in Inner Detector or in the EM calorimeter appears as “usual” jets

HV muon trigger

Mean number of Level-1 Muon Candidates vs v decay lengthLarge Level-1 multiplicity <NCandidates> ~ 3

Number of LVL-1 Muon Candidates in cluster with R=0.4 around v line of flight

Level-2 efficiency (%)

1 Jet

ET>160 Gev

2 Jets

ET>120 Gev

3 Jets

ET>65 GevTotal (overlap removed)

Higgs:

Gluon fusion3.3 1.7 1.7 4.4

Calorimetric Triggers

Level-1 efficiency (%)

1 Jets

ET>80 Gev

2 Jets

ET>55 Gev

3 Jets

ET>35 GevTotal (overlap removed)

Higgs:

Gluon fusion13.1 8.3 5.0 16.4

Muon Triggers

Level-1 efficiency (%)

1 pT>6 Gev

1 pT>20 Gev

2 pT>6 Gev

Higgs:

Gluon fusion13.1 8.3 5.0

Level-2 efficiency (%)

1 pT>6 Gev

1 pT>20 Gev

2 pT>6 Gev

Higgs:

Gluon fusion2.2 0.3 ~0