na64++ - indico.cern.ch

��NA64++ S.N. Gninenko

(for the NA64 Collaboration)

1.

S.N. Gninenko – NA64++ – PBC BSM WG, CERN, March 1–2, 2017

NA64: Search for dark sector physics in missing energy events !

Approved in March’16 for the A´->inv decay search with e- beam.

The proposed NA64++ research program is significantly extended by the inclusion of searches for dark sector physics, new sub-GeV states coupled to leptons and/or quarks , new symmetries …with leptonic (e,μ) and hadronic (π, K, and p) beams at the CERN SPS.


2.

Goal to explore theoretically interesting parameter space !ε  ∼ 10-6 ‒ 10-3 ; mA´ ~ sub-GeV range (e.g. two-loop GUT interaction) Two runs in 2016: focus on the A´ parameter space suggested for (g-2)μ anomaly.!Growing activities, high intensity/sensitivity experiments in JLab, SLAC, FNAL,…. !Large literature, many recent theoretical and experimental results. !

3. Search for A´-> invisible decays in July run 2016.

!

NA64 July’16 PRL(2017)

arXiv:1702.03327 BABAR Collab.

Explanation of (g-2)µ with invisible A´ is excluded.


µ+µ-

Method: active beam dump + missing energy.

No signal Observation of QED dimuons

4. !

October run 2016 and further plans ! !


•  October run 2016 went well ‣  Good performance at 5x106 e-/spill ‣  4x1010 eot are collected. ‣  Data analysis in progress. •  2017 run ‣  Improved e- tagging: tracker+SRD ‣  Tests at intensity (7–8)x106 e-/spill ‣  Goal (2–3)x1011 eot. •  Plans for 2018 and 2020–2024 ‣  Fully explore the NA64 potential. ‣  Accumulate 1012 -1013 eot.

(bckg free case)!

( P. Crivelli AWG talk )

5. !

Search for Invisible decays of Dark Scalars. Oct’16 run ! !


•  Dark Scalar mediators (S) coupled to electrons

•  S decays predominantly invisibly into lighter dark sector particles ( χχ, χξ, ..)

•  Can be searched for in the reaction eZ -> eZ S; S -> χχ

First results on the search for

S-> invisible decays in October 2016 run

are under preparation for publication.

s -> χχ

NA64


6.

The 8Be excess

(J. Feng, this WS)

7/43

A new light X from 8Be transition ? !


7Li(p,γ)8Be, M A´ =16.7 MeV !

10101011

10121013

E774

E141

OrsayKEK

E137

Ν-Cal I �Π0�

CHARMNOMAD& PS191

aΜ ae

HADES

Dark�Light

APEX

HPS

SINDRUMKLOEWASA

APEXA1

BaBar

10�2 10�1 1

10�7

10�6

10�5

10�4

10�3

10�2

mΓ' �GeV�

Ε

Br(X à e+e-)=1, ε2~ 10-7

GEANT4 +!A´emission!

A´ spectra, 100 GeV e-

NA64 can observe X with ~ 5x1010 eot in 2017, SES ~ 2x10-10/eot.


8. Search for the X(A´)->e+e- decay !X,

E0= EW+ EECAL signature

Two separated showers in the WCAL and ECAL. Oct’16 run, ~0.5x1010 eot (preliminary)

WCAL, GeV

σx/σγ~10-10, τx~10-13 s

e-, 100 GeV

S.Andreas et al., arXiv: 1312.3309!S.G., PRD(2014)!

X,


9.

µ beam

Search for new light states coupled to muon

(M. Pospelov, this and Sept’16 WS)

10.


Search for Zµ in muon missing-energy events at SPS

Signature: •  in: 150 GeV µ- •  out: < 100 GeV µ- •  E≈0 in the hermetic ECAL+ HCAL •  Sensitivity ~ gµ

2 !

Remaining explanation of (g-2)µ anomaly: new massive Zµ from the broken U(1)Lμ － Lτ symmetry!

that coupled predominantly to µ and τ

Proposal for experiment at M2 beam of NA: •  clean 150 GeV µ- beam •  initial µ state can be tagged with BMS. A study is needed. Test run at M2 beam would be useful: •  π/µ < 10-(5-6) purity? •  initial, final µ state tagging purity? •  trigger rate? •  calorimeter hermeticity?

Zµ νν M Zµ < 2 mµ

M2 BMS


11.

Expected sensitivity

Signature in (Eµ´ ; Etot (FS)) plane for !  µZ->µ´Z Zµ; Zµ -> νν - muonic Vector   µZ->µ´Z aµ ; aµ -> inv - muonic Scalar aµ .

Chen, Pospelov, Zhong arXiv:1701.07437

  µ -> τ ->µνν LFV µ-τ conversion !

Expected sensitivity for Z´from U(1) Lμ-Lτ symmetry

BBN

exc

lude

d

150 GeV μ-

1012 mot

Preliminary feasibility study:!SG, Krasnikov, Matveev PRD(2015)!Background-free case.


12.

π, Κ, p beams

Search for π0,η,η’,ΚS, ΚL invisible decays

13.

Source of M0: charge exchange reactions: π-, K-+p -> M0+ n !


K0L -> νν is complementary to K0

L -> π0 νν

SG, Krasnikov PRD(2015)!SG PRD(2014)!

Main components :

•  20–50 GeV π,Κ- beam

•  MM/GEM tracker, ECAL-Veto target

•  4π fully hermetic ECAL+ HCAL Signature: •  in: 20–50 GeV π, Κ-track •  out: no energy in ECAL, Veto, HCAL Complete missing of beam energy !

Decay ! Current limits, PDG

Expected limits

π0 νν! <2.7 x10-7 <10-8

η inv! <1.0x10-4 <10-7

η’ inv! <5x10-4 <10-6

KS->inv! Never tested <10-8

KL->inv! Never tested <10-7

M0=π0, η, η´, KL, KS yield is not known! Plan to measure at NA64 in 2018 .!

14.


Search for GeV DM in pA interactions (prelim.)

p, 150 GeV

pA -> X +Z´; Z´-> χχ Z´ – leptophobic boson αZ´ – q-Z´ coupling const.

109 pot Exclusion region in (MZ´;αZ´) plane α

Z´

a’la CALICE

Emiss

p, 200 GeV

Source of Z´:


15.

Process New Physics Sensitivity

1. e-Z ->e-Z + Emiss

  A´-> e+e-   A´-> invisible   alps   milli-Q

Dark Sector:!Dark Photons and DM!New light states (V,S)!weakly coupled to e-!

8Be excess!

10-3<ε<10-6

M A´ ~ sub-GeV! mQ <10-5-10-7 e

MmQ ~ sub-GeV!

2. μ- Z->μ- Z+ Emiss

  Zμ-> νν, μ+μ-!

  aμ   μ->τ conversion

(g-2)μ anomaly,!New Zµ from Lμ-Lτ gauged symm., scalars coupled toμ

LFV

αμ< 10-11-10-9

σµτ/σµ< 10-9-10-8

3. π(K)p-> M0n + Emiss

  KL-> invisible   KS-> invisible   π0, η,η´-> invisible

CP, CPT symmetry Bell-Steinberger Unitarity,

new WC particles: NHL, φφ, VV

Br <10-8-10-6,

Complementary to K->πνν

Br< 10-8-10-7

4. pA -> Z´+ Emiss

  leptophobic Z´ ~ GeV DM σZ´<10-7-10-8 /p

Physics prospects


16. Tentative beam schedule

e-, A´->inv

X,A´->ee 1012-1013

Test Run H4

5x106/spill

July, October run

2x1011 eot 5x1010 eot 8Be excess

3x1011eot

Detector upgrade

3x1011eot

µ- µZ->µΖZµ µZ->τZ 1012-1013

M2 BMS performance

study.

Test run at M2?

BMS tagging 107µ-/spill

Detector design and proposal preparation

Test run at M2

BMS tagging 107µ-/spill

π-, K- π0,η,η->in KS,KL->inv 1012-1013

πA->π0,η,η´A KA->K0A

cross sect. measurem.


p pA->pAZ´Z´->χχ



17.

Tentative beam schedule

e-, A´->inv A´->ee

3x1011eot

3x1011eot

3x1011eot

µ- µZ->µΖZµ µZ->τZ

π-, K- π0,η,ηKS,KL->inv

Test run

Test run ~1010pot

~1010kot

p pA>pAZ´ Z´->χχ ~>1012

Test run

Test run ~1010pot


18. Summary !

•  The proposed searches of dark sector physics in missing-energy events with leptonic and hadronic beams at CERN have unique sensitivity and are highly competitive to similar projects. Some of the proposed experiments (on Zμ, KL->inv, X of 8Be) has never been done before.

•  The search for dark photons at NA64 could continue till LS3 in order to accumulate 1012 – 1013 eot and to cover significant area of the A´ parameter space. The X from 8Be excess could be studied in 2017 run with possible continuation in 2018. The use of H4 line is crucial.

The runs till LS2 will provide better understanding of background, rate capability and improved sensitivity for other light particle search. •  The opportunity to perform the search for Zμ and other light states

coupled to µ with the M2 muon beam at CERN is rather unique. For optimal design of the setup a study of the M2 BMS performance is needed to see whether it meet the NA64 requirements. A test run at M2 in 2018 would be useful.

•  To evaluate background level and sensitivity of the π0, η,η´, KS KL->

invisible decay searches measurements of the yield for the neutral meson charge-exchange production are required. This could be done at a π, Κ beam during a short run at H2, H4, H8.

na64++ - indico.cern.ch

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