Search for Hidden Particles (SHiP): an experimental proposal for the SPS

ship.web.cern.ch/ship

Mario Campanelli

University College London

SM and beyond

● All SM particles have been discovered (apart from ντ)● Higgs mass does not require nor exclude new physics

● Points towards a metastable universe, but SM may be valid up to the Plank scale

● Naturalness problem only thereif a new active particle hasmass between the EW andPlank

Many open problems

● Even forgetting naturalness, we do not understand:– Baryon Asymmetry of the Universe

– Smallness of neutrino masses

– Dark Matter (non-baryonic, “cold”)

– Inflation

– Possible new interactions (in the absence of new particles) before the Plank mass

● The “default” answer, SUSY, starts to suffer from naturalness problems as well, and limits to other models are pushed to O(TeV) masses

A different approach● We can think that new physics has not been observed

not because of its mass, but of its very coupling, even smaller than weak interactions

● These particles would be ideal dark matter candidates, and not introduce further naturalness problems. To be of any relevance to us, they should be able to transform into SM particles through a coupling between the SM Lagrangian and the new physics one

SM particles as “portals”

● Lowest-order SM operators could be the bridge between the two Lagrangians

● Experimentally, we could detect missing energy/mass, or “oscillations” between SM and hidden particles through interactions with portals

Vector and scalar portals

Recent BaBar result

Neutrino portal

Indications for mass ranges

Favourd masses for Heavy Neutral Leptons similar to those of other fermionsThis leads to Yukawa couplings similar to those of the electron, or smaller.

The MSM𝛎

● Symmetrises the SM lepton sector by adding 3 HNL N1, N

2, N

3

● With M(N1) ~ few KeV, it is a good DM candidate (or DM can be

generated outside of this model through decay of inflaton)

● With M(N2, N

3) ~ GeV, could explain Barion Asymmetry of Universe

(via leptogenesis), and generate neutrino masses through see-saw.

T.Asaka, M.Shaposhnikov PL B620 (2005) 17M.Shaposhnikov Nucl. Phys. B763 (2007) 49

Production of HNL

Interaction with Higgs vev leads to a mixing with active neutrinos

Several past searches; PS191 used neutrinos from K decays, while other experiments not sensitive to mixings of cosmological interest.

Latest result: LHCb with B decays obtained U2≈10-4, arXiv:1401.5361

Further exploration needed of the region with higher masses and smaller mixings

HNL decaysInteraction with Higgs vev would make it oscillate back into a virtual neutrino, that produces a muon and a W ( hadrons, eg pions)→Exact branching fractions depend n flavor mixing

Due to small couplings, ms lifetimes, decay paths O(km)

High-mass searches at the LHC

But the cosmologically-interesting region is at low couplings high intensity→

Experimental considerations (model-independent)

● We have to look for very weakly interacting particles:

– Production BR O(1E-10)

– Lifetimes O(km)

– Can travel through ordinary matter

● Cosmologically interesting masses O(GeV)

– Produced through decays of mesons

– Can decay to mesons or charged leptons

– Full final-state reconstruction and particle ID

● To have high intensities:

– fixed-target against a beam dump

– followed by a long decay tunnel and a spectrometer at the end

More in detail:● Use protons from CERN's SPS: 500 kW is 4x1E13 protons/7 s ->2E20 in 5y

● Slow (ms 1s) and uniform extraction → to reduce detector occupancy and combinatorics

● HS particles produced by mesons (mainly charm) decays; need to absorb all SM decay products to minimise BG heavy material thick target, with wide beam →to dilute energy deposition (different from neutrino facility)

● Muons cannot be absorbed by target: muon shield, possibly magnetised

● Long decay tunnel away from external walls to minimise rescattering of muons and neutrons close to detector

● Vacuum in decay tunnel to reduce neutrino interactions

● Far-away detector with good PID and resolutions

Schematic view

40-50m 5m

50m

pFilter

magnet ντ detectorMUON

UTECALSTRAWS

UV TC

HCALLSV

A more realistic view

Overall layout

General detector philosophy

● Almost no R&D to do, we can make it with detectors already built in the past, optimizing the parameters

● For muon detector, baseline now is extruded scintillator bars read out by SiPM —> experience from SuperB, but also RPC are considered.

● Trigger and DAQ: a simplified version of the HLT of LHCb upgrade (i.e. no L0)

Active muon filter

Spectrometer magnet

A dipole magnet very similar to the LHCb one but with 40% less iron and three times less power

LHCb: 4Tm and aperture ~ 16 m2

This design:

- aperture 20 m2 - Two coils Al-99.7 - peak B field ~ 0.2 T - field integral ~ 0.5 Tm su 5 m

Tracking and veto

Straw tubes similar to NA62 with 120 m space μresolution, 0.5% X0/X.

Main difference to NA62:

A. 5m lenght B. vacuum 10-2 mbarC. 2kHz/straw of 1cm

diam

Calorimeter: possible design

Spiral Shashlik ECALUniformity few %, time resolution 1ns σ∼and (E)/E=6.5%/√E 1%σ ⊕

Bonus: tau neutrino detectorEmulsion based detector with the LNGS OPERA brick technolgy, but with a much smaller mass (750 bricks) very compact (2m), upstream of the HNL decay tunnel —> with B field and followed by a muon detector (to suppress charm background)

Even replacing 10 times

the emulsion bricks

during the run

—> still 5% of OPERA

Trigger and DAQ● Event building on all data and trigger

decision at EF

● TFC system generates the clock

● All sub-systems send data through ethernet links (no need for radiation hardness) to Event Filter Farm via a switch

● Fraction of data sent to Monitoring Farm to evaluate performance

● Smallest time slice that could potentially contain all data from one pot (100 ns)

● Since some events spread over more than one frame, 100 frames are combined into package, with 1 overlap

Ship sensitivity to HNL

Most of the cosmologically-allowed region below the charm mass will be accessible to SHIP, at least in the inverted hierarchy case

ShiP sensitivity to dark photons

only e+e- and + - decays: arxiv.org/1411.4007𝜇 𝜇

Ship sensitivity to light scalar (Higgs portal)

Active neutrino physics

● Current status of tau neutrino observations:

DONUT observed 9 events (from charm) with a background of 1.5

OPERA observed 4 events (from oscillations)

No tau antineutrino has been even observed

Ship can increase by 200 the current tau neutrino sample, and discover tau antineutrinos

● Measurement of tau neutrino differential cross-section in CC interactions

● Measurement of charm production for muon neutrinos and antineutrino (factor of 100 increase wrt CHORUS)

A good fraction of the old OPERA collaborators are joining SHiP to build the neutrino sub-detector and analyse its data.

Status of the collaborationSPC EOI-2013-010 + addendum submitted October 2013

Interaction with the SPSc referees and discussion at the January 2014 meeting.

SPSc recommendation: The Committee received with interest the response of the proponents to

the questions raised in its review of EOI010.

The SPSC recognises the interesting physics potential of searching for heavy neutral leptons and investigating the properties of neutrinos.

Considering the large cost and complexity of the required beam infrastructure as well as the significant associated beam intensity, such a project should be designed as a general purpose beam dump facility with

the broadest possible physics programme, including maximum reach in the investigation of the hidden sector.

To further review the project the Committee would need an extended proposal with further developed physics goals, a more detailed technical

design and a stronger collaboration.

Recent developments● Since then, collaboration expanded to 11 countries

● First general meeting held in April in Zurich

● Technical paper received from CERN beam division on 2/7/2014, including cost estimation

● Second general meeting on December 15 at Cern, with formalisation of the collaboration

● Physics case being extended

● A Technical Proposal is under preparation, couple with a theory paper on detector performance

ShIP in the UK

● Imperial College London has been involved since the very beginning, and expresses the spokesperson (Andrei Golutvin); main activity active muon filter

● UCL (N.Brook, M.C) to work on trigger/DAQ

● RAL PPD expressed strong interest (engineering support, but also physicists like S.Ricciardi)

● Warwick, Manchester?

● Liverpool will probably join in a second stage

● Bristol?? ;-)

General considerations on the future of particle physics

● LHC Run 1 results, especially those from precision measurements, leave limited room for BSM discoveryin Run 2 (being a member of Atlas, I hope to be disproven soon, but I would not bet on it)

● In current (and foreseable) resource climate, a next big brute-force, general-purpose collider is difficult

● Particle physics could reinvent itself in becoming smaller and smarter, designing experiments that target specific problems (dark matter, neutrinos, etc.)

Perspectives for ShiP● A relatively simple and focussed detector, the best

laboratory to study the hidden sector in the cosmologically relevant parameter space

● The collaboration is being formed now, but many studies are already quite advanced

● Plan to submit a SoI to STFC with the same time scale as the TP

● So far reaction from Cern and other funding agencies (e.g. INFN) very positive, let's keep the momentum...