andrey golutvin imperial college london€¦ · andrey golutvin imperial college london . 2. 3 3 sm...
TRANSCRIPT
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Andrey Golutvin Imperial College London
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SM may well be a consistent effective theory all the way up to the Plank scale
ü MH < 175 GeV à SM is a weakly coupled theory up to the Plank energies !
ü MH > 111 GeV à EW vacuum is stable or metastable with a lifetime greatly exceeding the age of our Universe (Espinosa et al)
ü No sign of New Physics seen
Stable vacuum is perfectly admi6ed by present data
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Hard to believe that this is a pure coincidence !
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No sign of New Physics seen
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No sign of New Physics seen
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Most stringent limits come from observables in K0 & B0 mixing
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Theoretical motivation
• Discovery of the 126 GeV Higgs boson à Triumph of the Standard Model The SM may work successfully up to Planck scale ! Short comings of the SM: - Neutrino masses & oscillations - Excess of matter over antimatter in the Universe - The nature of non-baryonic Dark Matter Strong motivation to search for physics BSM
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Search for BSM physics: how and where ?
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New light hidden particle must be singlet with respect to the gauge group of the SM à they may couple to different singlet composite operators (portals) of the SM ü Dim 2: Hypercharge U(1) field, Bµν : vector portal. New particle – massive vector photon (paraphoton, secluded photon, …); renormalisable coupling – kinetic mixing à εΒµνF’µν
ü Dim 2 Higgs field , : Higgs portal. New particle – hidden (dark) scalar; renormalisable coupling à ü Dim 5/2 Higgs-lepton : neutrino portal. New particles Heavy Neutral Leptons, HNL; renormalisable coupling à ü Dim 4 Axion-like Particles, ALP, pseudo-scalars: axion portal Non-renormalisable couplings à
Hidden portals: impressive list of ideas in the past
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Vector portal
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Higgs portal
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Neutrino portal (Heavy Neutral Leptons)
Axion portal
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Vector portal observables Kinetic mixing of dark (massive) photons with our world
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SHIP sensitivity to dark photons
Use the following decays of neutral mesons: ü π0 à γγ ü η à γγ ü ω à π0γ ü η’à γγ
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Higgs portal observables ( inflaton )
If µ << v, the new scalar χ may be long-lived
Synergy with search for inflaton at LHCb
Recent example – a model to produce 7 keV N1 (DM candidate) and inflate the Universe in accordance with BICEP and Planck
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Neutrino portal observables: (Heavy Neutral Leptons) νMSM ( T.Asaka, M.Shaposhnikov PL B620 (2005) 17 ) explains all short comings of the SM at once by adding 3 HNL: N1, N2 and N3
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See-saw generation of neutrino masses
Most general renormalisable Lagrangian of all SM particles (+3 singlets wrt the SM gauge group):
Majorana term which carries no gauge charge
Yukawa term: mixing of NI with active neutrinos to
explain oscillations
The scale of the active neutrino mass is given by the see-saw formula: where - typical value of the Dirac mass term
Example: For M ~ 1 GeV and mν ~ 0.05 eV it results in mD ~ 10 keV and Yukawa coupling ~ 10-7
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0.2 0.5 1.0 2.0 5.0 10.010!9
10!7
10!5
0.001
0.1
M !GeV"
"!s"
BAU NBAU I
Seesaw NSeesaw I
BBN
Masses and couplings of HNLs • N1 can be sufficiently stable to be a DM candidate, M(N1)~10keV
• M(N2) ≈ M(N3) ~ a few GeVà CPV can be increased dramatically to explain Baryon Asymmetry of the Universe (BAU) Very weak N2,3-to-ν mixing (~ U2) à N2,3 are much longer-lived than the SM particles
µ
!µ"
sµ
!µ
D
D
#
#
N2,3
N2,3H
HExample: N2,3 production in charm
N2,3
µ
!
"µ
N2,3
e
µ"µ
"e
#
#
H
H
and subsequent decays
• Typical lifetimes > 10 µs for M(N2,3) ~ 1 GeV Decay distance O(km)
• Typical BRs (depending on the flavour mixing): Br(N à µ/e π ) ~ 0.1 – 50% Br(N à µ-/e- ρ+) ~ 0.5 – 20% Br(N à νµe) ~ 1 – 10% 19
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Dark Matter candidate HNL N1
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MN5
Dark Matter candidate HNL N1
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Constraints on DM HNL N1
ü Stability à N1 must have a lifetime larger than that of the Universe
ü Production à N1 are created in the early Universe in reactions ll à νN1 , qq à νN1 etc. Need to provide correct DM abundance ü Structure formation à N1 should be heavy enough ! Otherwise its free streaming length would erase structure non-uniformities at small scales ( Lyman-α forest spectra of distant quasars and structure of dwarf galaxies ) ü X-ray spectra à Radiative decays N1àγν produce a mono-line in photon galaxies spectrum.
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Allowed parameter space for DM HNL N1
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Searches for DM HNL N1 in space
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Two recent publications in arXiv: • arXiv 1402.2301 Detection of an unidentified emission line in the stacked X-ray spectrum of Galaxy Clusters, Eγ ~ 3.56 keV • arXiv 1402.4119 An unidentified line in X-ray spectra of the Andromeda galaxy and Perseus galaxy cluster, Eγ ~ 3.5 keV
New line in photon galaxy spectrum ???
Will soon be checked by Astro-H with better energy resolution
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0.2 0.5 1.0 2.0 5.0 10.010!9
10!7
10!5
0.001
0.1
M !GeV"
"!s"
BAU NBAU I
Seesaw NSeesaw I
BBN
Masses and couplings of HNLs • M(N2) ≈ M(N3) ~ a few GeVà CPV can be increased dramatically to explain Baryon Asymmetry of the Universe (BAU) Very weak N2,3-to-ν mixing (~ U2) à N2,3 are much longer-lived than the SM particles
µ
!µ"
sµ
!µ
D
D
#
#
N2,3
N2,3H
HExample: N2,3 production in charm
N2,3
µ
!
"µ
N2,3
e
µ"µ
"e
#
#
H
H
and subsequent decays
• Typical lifetimes > 10 µs for M(N2,3) ~ 1 GeV Decay distance O(km)
• Typical BRs (depending on the flavour mixing): Br(N à µ/e π ) ~ 0.1 – 50% Br(N à µ-/e- ρ+) ~ 0.5 – 20% Br(N à νµe) ~ 1 – 10% 26
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Baryon asymmetry
• CP is not conserved in νMSM 6 CPV phases in the lepton sector and 1 CKM phase in the quark sector (to be compared with only one CKM phase in the SM) • Deviations from thermal equilibrium
ü HNL are created in the early Universe ü CPV in the interference of HNL production and decay
ü Lepton number goes from HNL to active neutrinos
ü Then lepton number transfers to baryons in the equilibrium sphaleron processes
PS Explanation of DM with N1 reduces a number of free parameters à Degeneracy of N2,3 masses is required to ensure sufficient CPV
Sakharov conditions:
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28 0.2 0.5 1.0 2.0 5.0 10.0
10!9
10!7
10!5
0.001
0.1
M !GeV"
"!s"
BAU NBAU I
Seesaw NSeesaw I
BBN
Masses and couplings of HNLs Very weak N2,3-to-ν mixing (~ U2) à N2,3 are much longer-lived than the SM particles
µ
!µ"
sµ
!µ
D
D
#
#
N2,3
N2,3H
HExample: N2,3 production in charm
N2,3
µ
!
"µ
N2,3
e
µ"µ
"e
#
#
H
H
and subsequent decays
• Typical lifetimes > 10 µs for M(N2,3) ~ 1 GeV Decay distance O(km)
• Typical BRs (depending on the flavour mixing): Br(N à µ/e π ) ~ 0.1 – 50% Br(N à µ-/e- ρ+) ~ 0.5 – 20% Br(N à νµe) ~ 1 – 10%
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0.2 0.5 1.0 2.0 5.0 10.010!12
10!10
10!8
10!6
M !GeV"
U2
BAU
BAU
Seesaw
BBN
PS191
NuTeV
CHARM
Experimental and cosmological constraints
Strong motivation to explore cosmologically allowed parameter space
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- Recent progress in cosmology
- The sensitivity of previous experiments did not probe the interesting region for HNL masses above the kaon mass
Proposal for a new experiment at the SPS, SHIP to search for new long-lived particles produced in charm decays (more details can be found at http://ship.web.cern.ch/ship ) Experimentally this domain has not been very well explored !
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(rad)!0 0.1 0.2 0.3 0.4
fract
ion
of m
uons
/(8 m
rad)
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
Experimental requirements • Search for HNL in Heavy Flavour decays
Beam dump experiment at the SPS with a total of 2×1020 protons on target (pot) to produce large number of charm mesons
• HNLs produced in charm decays have significant PT
Detector must be placed close to the target to maximize geometrical acceptance Effective (and “short”) muon shield is essential to reduce muon-induced backgrounds (mainly from short-lived resonances accompanying charm production) 30
Polar angle of µ from Nàµπ
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31 31 Generic setup, not to scale!
W-‐target
Fe/Pb
Magnet Detector volume
e.m, hadrons
neutrino
Shield (W, Fe)
KL, KS, Λ, n, υ
Occupancy (KL)
p(400 GeV) π,K
π
µ
Vacuum
Mul2ple sca3ering
Hard-‐momentum µ (η,ρ,ω)
Low-‐mid-‐momentum µ from fast decays of π,K
Return field Mul2ple sca3ering
Ν2,3
Initial reduction of beam induced backgrounds - Heavy target (50 cm of W) - Hadron absorber - Muon shield: optimization of active and passive shields is underway
Secondary beam-line (incompatible with conventional neutrino facility)
Acceptable occupancy <1% per spill of 5×1013 p.o.t. spill duration 1s à < 50×106 muons spill duration 10ms à < 50×103 muons
spill duration 10µs à < 500 muons
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Detector concept (based on existing technologies)
HNL
π+
µ-
• Long vacuum vessel, 5 m diameter, 50 m length Background from active neutrino interactions becomes negligible at 0.01 mbar
• 10 m long magnetic spectrometer with 0.5 Tm dipole magnet and 4 low material tracking chambers 32
• Reconstruction of the HNL decays in the final states: µ-π+, µ-ρ+ & e- π+ Requires long decay volume, magnetic spectrometer, muon detector and electromagnetic calorimeter, preferably in surface building
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Detector concept (cont.) Geometrical acceptance • Saturates for a given HNL lifetime as a function of detector length • The use of two magnetic spectrometers increases the acceptance by 70% Detector has two almost identical elements
Veto station
50m
5m
Vacuum vessel
Dipole
Trackingchambers
2.5m 2.5m
Muon IDCalorimeter
~2m
5m
muon shield
wall / earth
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Arb
itrar
y un
its
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Expected event yield (cont.) Assuming Uµ
2 = 10-7 (corresponding to the strongest experimental limit currently for MN ~ 1 GeV) and τN = 1.8×10-5 s ~12k fully reconstructed N à µ-π+ events are expected for MN = 1 GeV
34 120 events for cosmologically favoured region: Uµ
2 = 10-8 & τN = 1.8×10-4s
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Status of the SPSC review
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Physics case for general beam dump facility
ü Study of ντ interactions (guarantied SM physics) Ideally suited since ντ is produced in Ds à τντ with similar to HNL kinematics ü Search for any weakly interacting yet unstable particles such as HNL, low mass SUSY or paraphotons or … ü Review of the SHIP sensitivities for ντ physics and wide class of models with hidden portals is ongoing Expect significant improvement of currently available measurements and constrains everywhere !
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SM: ντ physics with 2×1020 pot
Expect ~3400 ντ interactions in 6 tons emulsion target ( 5% of OPERA )
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h6p://ship.web.cern.ch/ship Strengthen collaboration …
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1st SHIP workshop, 10-12 June, Zurich
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41 Activate SHIP collaboration at this session
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Next steps: schedule of the SHIP facility
A few milestones: ü Form SHIP collaboration à June-August 2014 ü Technical proposal à 2015 ü Technical Design Report à 2018 ü Construction and installation à 2018 – 2022 ü Data taking and analysis of 2×1020 pot à 2023 - 2027
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Conclusion
• The proposed experiment will search for NP in the largely unexplored domain of new, very weakly interacting particles with masses below the Fermi scale • Detector is based on existing technologies Ongoing discussions of the beam lines with experts • The impact of HNL discovery on particle physics is difficult to overestimate ! • The proposed experiment perfectly complements the searches for NP at the LHC and in neutrino physics A collaboration is currently being setup Let us know if you are interested to join !
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BACK UP SLIDES
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Axion portal observables Axion-like particles (or pseudo-Nambu- Goldstone bosons), dark matter, SUSY, …
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Muon shield optimization
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Muon shield optimization
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Experimental requirements (cont.) • Minimize background from interactions of active neutrinos in the detector decay volume
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2×104 neutrino interactions per 2×1020 pot in the decay volume at atmospheric pressure à becomes negligible at 0.01 mbar
Requires evacuation of the detector volume
Momentum spectrum of the neutrino flux after the muon shield
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Residual backgrounds
Use a combination of GEANT and GENIE to simulate the Charged Current and Neutral Current neutrino interaction in the final part of the muon shield (cross-checked with CHARM measurement) yields CC(NC) rate of ~6(2)×105 per int. length per 2×1020 pot
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• ~10% of neutrino interactions in the muon shield just upstream of the decay volume produce Λ or K0 (as follows from GEANT+GENIE and NOMAD measurement ) • Majority of decays occur in the first 5 m of the decay volume • Requiring µ-id. for one of the two decay products à 150 two-prong vertices in 2×1020 pot
Instrumentation of the end-part of the muon shield would allow the rate of CC + NC to be measured and neutrino interactions to be tagged
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Detector concept (cont.) Magnetic field and momentum resolution • Multiple scattering and spatial resolution of straw tubes give similar contribution to the overall δP / P • For M(N2,3) = 1 GeV 75% of µ π decay products have both tracks with P < 20 GeV
• For 0.5 Tm field integral σmass ~ 40 MeV for P < 20 GeV
Ample discrimination between high mass tail from small number of residual KL à π+µ-ν and 1 GeV HNL 51
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KL produced in the final part of the muon shield have very different pointing to the target compared to the signal events Use Impact Parameter (IP) to further suppress KL background • IP < 1 m is 100% eff. for signal and leaves only a handful of background events • The IP cut will also be used to reject backgrounds induced in neutrino interactions in the material surrounding the detector
Bckg.
Signal
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Detector concept (cont.) Impact Parameter resolution
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Low energy SUSY sector
Light s-goldstinos (super-partners of SUSY goldstinos), e.g. D à πX with X à µµ
R-parity violating neutralinos in SUSY goldstinos, e.g. D à µ with
D.S. Gorbunov (2001)
A. Dedes, H.K. Dreiner, P. Richardson (2001)
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Detector apparatus based on existing technologies
• Experiment requires a dipole magnet similar to LHCb design, but with ~40% less iron and three times less dissipated power • Free aperture of ~ 16 m2 and field integral of ~ 0.5 Tm - Yoke outer dimension: 8.0×7.5×2.5 m3 - Two Al-99.7 coils - Peak field ~ 0.2 T - Field integral ~ 0.5 Tm over 5 m length
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Courtesy of W. Flegel
LHCb diplole magnet
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NA62 vacuum tank and straw tracker - < 10-5 mbar pressure in NA62 tank
- Straw tubes with 120 µm spatial resolution and 0.5% X0/X material budget Gas tightness of NA62 straw tubes demonstrated in long term tests
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Detector apparatus (cont.) based on existing technologies
NA62 straws
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LHCb electromagnetic calorimeter - Shashlik technology provides economical solution with
good energy and time resolution
LHCb ECAL
Detector apparatus (cont.) based on existing technologies
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Expected event yield • Integral mixing angle U2
is given by U2 = Ue2 + Uµ
2 + Uτ2
• A conservative estimate of the sensitivity is obtained by considering only the decay N2,3 à µ- π+ with production mechanism D à µ+ NX, which probes Uµ
2 • U2 Uµ
2 depends on flavour mixing
• Expected number of signal events: npot = 2 × 1020
χcc = 0.45 × 10-3
BR(Uµ
2) = BR(D à N2,3 X) × BR(N2,3à µπ) BR(N2,3 à µ-π+) is assumed to be 20% εdet (Uµ
2) is the probability of the N2,3 to decay in the fiducial volume and µ, π are reconstructed in the spectrometer 57
Nsignal = npot × 2χcc × BR(Uµ2) × εdet(Uµ
2)
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Expected event yield (cont.)
• ECAL will allow the reconstruction of decay modes with π0 such as N à µ-ρ+ with ρ+ à π+π0, doubling the signal yield • Study of decay channels with electrons such as N à eπ would further increase the signal yield and constrain Ue
2
In summary, for MN < 2 GeV the proposed experiment has discovery potential for the cosmologically favoured region with 10-7 < Uµ
2 < a few × 10-9
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