the hidden valley and atlas dan ventura u.washington particle theory journal club 01 june 2007
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The Hidden Valley and ATLAS
Dan Ventura
U.Washington Particle Theory Journal Club
01 June 2007
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1 June 2007 U. Washington PTJC 2
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1 June 2007 U. Washington PTJC 3
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
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1 June 2007 U. Washington PTJC 4
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)
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1 June 2007 U. Washington PTJC 5
Conceptual Diagram
• The heavy communicators that carry both SM and Gv charge were rarely produced at LEP and LEPII
Energy
Inaccessibility
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1 June 2007 U. Washington PTJC 6
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
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1 June 2007 U. Washington PTJC 7
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
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1 June 2007 U. Washington PTJC 8
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
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1 June 2007 U. Washington PTJC 9
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
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1 June 2007 U. Washington PTJC 10
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
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1 June 2007 U. Washington PTJC 11
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 =
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1 June 2007 U. Washington PTJC 12
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
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1 June 2007 U. Washington PTJC 13
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
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1 June 2007 U. Washington PTJC 14
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
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1 June 2007 U. Washington PTJC 15
Jet
2nd v does not produce a jet -- the decay products are not energetic enough and are too spread out to form a jet
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1 June 2007 U. Washington PTJC 16
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
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1 June 2007 U. Washington PTJC 17
Muons from displaced verticesLongitudinal Impact Parameter
Reconstructed Muon track
v decay vertex
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1 June 2007 U. Washington PTJC 18
Muon Impact Parameters
Reconstructed longitudinal impact parameter -- Distance from the IP
Reconstructed radial impact parameter
1.5 m
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1 June 2007 U. Washington PTJC 19
Triggering on muons from HV decays
7.5 m
2.5 m
Level 1 triggers
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1 June 2007 U. Washington PTJC 20
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
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1 June 2007 U. Washington PTJC 21
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
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1 June 2007 U. Washington PTJC 22
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
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1 June 2007 U. Washington PTJC 23
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
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1 June 2007 U. Washington PTJC 24
For a particular model. Others may differ by ~ factor of 10
100 events/year
Z’Z’
v production via the Z´
Many v-hadrons are formed. ±
v and v-nucleons are stable -- give MET
0v decay to bb ()
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1 June 2007 U. Washington PTJC 25
Z´ decay to v
Pixel detector ~12 cm
EM Cal ~1.1 m
v decays inside the HCal -- will cause punch through
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1 June 2007 U. Washington PTJC 26
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
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1 June 2007 U. Washington PTJC 27
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