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
