The Hidden Valley and ATLAS Dan Ventura U.Washington Particle Theory Journal Club 01 June 2007.

The Hidden Valley and ATLAS

Dan Ventura

U.Washington Particle Theory Journal Club

01 June 2007

1 June 2007 U. Washington PTJC 2


Outline

• Introduction to Hidden Valley models– Specialize to QCD-like Hidden Valley with 2 light

flavors

• Production of Hidden Valley particles– Via the Higgs and the Z´

– Experimental signatures & issues of Hidden Valley type models


What is a Hidden Valley

• SM extended by a non-abelian gauge group Gv – SM → SM x Gv

• All SM particles are neutral under Gv

• There are new “light” particles (v-particles) charged under Gv and neutral under the SM

• Interactions between the v-particles and SM are mediated by new heavy communicators (Z´ or loop of heavy particles carrying both SM and Gv charges)


Conceptual Diagram

• The heavy communicators that carry both SM and Gv charge were rarely produced at LEP and LEPII

Energy

Inaccessibility


Hidden Valley

• Let Gv = U(1)´ x SU(nv)

• The U(1)´ is broken by a scalar expectation value giving a Z´ a mass of ~3 TeV

• The SU(nv) confines on a scale of

~100 GeV < v < 1 TeV


QCD-like Hidden Valley

• Consider a Hidden Valley with 2 light flavors ( UV & CV )

• mU ~mC << V-QCD • Particle spectrum controlled by approximate v-

isospin symmetry • v-hadrons decay promptly to v-pions & v-nucleons• V-nucleons are stable• The SM neutral v

± are stable unless FCNC allows CV→UV


v0 Decays

v0 has the wave function UU - CC and

can decay via QVQV→ Z´→ f f

v0 decays predominately to heavy flavor

( b b or for m < 2 mt)

Free Parameters


v Production via the Higgs

• The potential for the scalar fields is:– V= -2 |H|2 - ||2 + |H|4 + ||4 + ||2 |H|2

• After SSB, H and fields mix– The produced higgs state is: cos|h> + sin|>– Then the SM higgs can decay into the HV through

the

ˆ

v0

Mixing

h hv

v0

g

g


Hidden Valley in ATLAS

Rome La SapienzaGuido Ciapetti Carlo DionisiStefano Giagu Daniele DePedisMarco ResignoLucia Zanello

Barbara Mele*

U. WashingtonHenry LubattiGiuseppe SalamannaLaura BodineDan Ventura

Matt Strassler*

Rome1 - Seattle Collaboration

*Theoretical consultants (not ATLAS members)

• Rome1-Seattle working group formed in Sept. 2006

• All work presented is property of the ATLAS collaboration and was preformed by members of the Rome1-Seattle WG


Parameters

• Parameters used in the current study: – mh = 140 GeV mZ´ = 3 TeV

– m = 40 GeV

250 mm -- for v from higgs decays

100 mm -- for v from Z´ decays

Lifetimes were chosen to give a distribution of decay positions throughout the inner detector

{c =


Event Signatures

Pixel Layers

Silicon Layers

TRT

Radial Position of “truth” vertices

For gluon fusion:• Highly displaced vertices O(10 cm - 1m)– Jets with few tracks

• SM Backgrounds: Interaction of neutrals with detector material


Jets from HV decaysgg→h→v v

Number of reconstructed jets per eventNumber of reconstructed tracks per jet

nTracks

Jet cut: ET > 35 GeV

• Final state has 4 b quarks -- not 4 b jets• Number of jets depends on the boost and

decay position of v


gg→h→v v

Pixel detector

Silicon tracker

TRT

50 - 120 mm

300 - 520 mm

640 - 1030 mm

White tracks are MC “truth” tracks Green tracks are reconstructed

v decay ~ 50 cm from the interaction point (IP)

v decay ~ 5 cm from IP with associated tracks


Jet

2nd v does not produce a jet -- the decay products are not energetic enough and are too spread out to form a jet


Muons from HV decays

• Muons are produced from the semi-leptonic decays of B-mesons (or decays)

• Produced at large distances from the IP

• Backgrounds: SM ± and K decays in flight


Muons from displaced verticesLongitudinal Impact Parameter

Reconstructed Muon track

v decay vertex


Muon Impact Parameters

Reconstructed longitudinal impact parameter -- Distance from the IP

Reconstructed radial impact parameter

1.5 m


Triggering on muons from HV decays

7.5 m

2.5 m

Level 1 triggers


Triggering on muons from HV decaysLevel 2 triggers

• Full granularity of data is available within region of interest (RoI) around the “infinite momentum path” as defined by level 1

• Refined PT measurement preformed• Outside-in tracking is preformed to match the

muon spectrometer track to an inner detector track

• If PT < threshold or if no matching track is found, the trigger fails


Muon Trigger results

≥ 6 GeV~17% of events

≥ 10 GeV~13% of events ≥ 20 GeV

~6% of events

Level 1 muon triggers

Level 2 muon triggers

≥ 2 GeV“loose” trigger ≥ 6 GeV

≥ 20 GeV


Other higgs production mechanisms

• Vector Boson Fusion

– Higgs produced with 2 forward jets

• Higgsstrahlung

– Higgs recoils against the W

h0

W/Z

W/Zq

q

q1

q2

q3

q4

h0W/Z

W/Z


Longer lifetimes or boosted v

W decayv decays inside ID

2nd v decays at the end of the HCal Hadronic shower occurs inside the Muon Spectrometer


For a particular model. Others may differ by ~ factor of 10

100 events/year

qq

qq

QQ

QQ

Z’Z’

v production via the Z´

Many v-hadrons are formed. ±

v and v-nucleons are stable -- give MET

0v decay to bb ()


Z´ decay to v

Pixel detector ~12 cm

EM Cal ~1.1 m

v decays inside the HCal -- will cause punch through


Trigger Rates

• Jet triggers:– ~75% of events pass

Level 1 single jet triggers

– ~70% pass level 1 multi-jet triggers

• Muon triggers:– 80% of events pass

level 1 6 GeV muon trigger

– 8.2% pass level 2 muon trigger

• ~10% of these muon triggers are caused by punch through


Work in progress …

• Level 1 triggers are hardware based– Cannot be changed at this point

• Level 2 triggers are software based– Still being written/implemented

• Can still be modified -- We are currently looking for a set of level 2 trigger objects that will keep our events without letting in SM backgrounds

The Hidden Valley and ATLAS Dan Ventura U.Washington Particle Theory Journal Club 01 June 2007.

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