Recent results from the NA64 experiment at CERN
SPS
D.V. Kirpichnikov
August 22 2021

XXth LOMONOSOV CONFERENCE ON ELEMENTARYPARTICLE PHYSICS
Moscow State University, Moscow, 19-25 August, 2021

D. V. Kirpichnikov (INR RAS)

prospects for NA64++

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Outline
Motivation: Light Dark Matter, (g − 2)µ anomaly
Vector Portal to Dark Sector
NA64e (invisible mode setup)
Prospects for Light Dark Matter (invisible and semi-visible decaymode)
prospect for ALPs (visible and invisible decays)
NA64e (visible mode setup)
Prospects for visible decays and ATOMKI anomaly
Probing (g − 2)e with NA64
e + -beam, e − beam: resonant DP production, e + e − → A0NA64µmoun beam: prospects for (g − 2)µ anomaly, Z 0 and millicharges
Combined NA64e and NA64µ projection
Conclusion
D. V. Kirpichnikov (INR RAS)

prospects for NA64++

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Motivations for searching for light vectors and ALPs
They are popular candidates for solution of experimental anomalies: (g − 2)µ ,MinoBooNE, 8 Be, KOTO, XENON1T
They could act as a mediator to a Dark Dector (DS). DS consists of particles and fields
which are singlets with respect to the gauge group of the SM. It interacts with the SM
presumably via gravity and possibly via a new interaction transmitted by the mediator.

DARK MATTER ←→ MEDIATOR ←→ STANDARD MODEL
The most popular models of Dark Matter χ: Scalar Dark Matter, Majorana Dark
Matter, Pseudo Dirac Dark Matter

D. V. Kirpichnikov (INR RAS)

prospects for NA64++

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Additional motivation for NA64 is (g − 2)µ anomalyaµ =gµ − 2, ∆aµ = aµexp − aµth = (251 ± 59) · 10−112B. Abi et al. Muon g-2 collaboration Phys. Rev. Lett. 126, 141801
T. Aoyama et al. Phys. Rept. 887 (2020) 1-166
Sz. Borsanyi et al Nature volume 593, pages 5155 (2021)
NA64: 1-Loop contribution from Dark Sector (A0 , Z 0 )D. V. Kirpichnikov (INR RAS)

prospects for NA64++

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Vector Portal to Dark Sector

Okun, Holdom (1986) αD = eD2 /(4π): new masssive boson A0 (darkphoton) which has kinetic mixing with ordinary photon :
1 0 2 
1 20++ Fµν Fµν+ Lint (A0 − DM)
L ⊃ − Fµν
F44 µν
2Production: A0 -bremsstrahlung e − N → e − NA0 ,Decays:– Mostly Visible: A0 → e + e − , µ+ µ− , hadrons, assuming
mA0 > 2me , 2mµ ...
– Mostly Invisible: A0 → χχ if mA0 > 2mχ assuming
αD ∼ αQED  
D. V. Kirpichnikov (INR RAS)

prospects for NA64++

5 / 21NA64 experiment setup (invisible mode)∼ 50 researchers from 12 institutes.
Proposed in 2014, first test runs in 2015

D. V. Kirpichnikov (INR RAS)

prospects for NA64++

6 / 21NA64 location

D. V. Kirpichnikov (INR RAS)

prospects for NA64++

7 / 21NA64 photograph

D. V. Kirpichnikov (INR RAS)

prospects for NA64++

8 / 21NA64 experiment setup (invisible mode)

S.Andreas et al., arXiv: 1312.3309 S.G., PRD(2014)
Main Components: a) clean E0 = 100 GeV e − beam; b) e − tagging
system: tracker+SRD; c) hermetic ECAL+HCAL;
Signature:a) in: 100 GeV e − track; b) out: EECAL < E0 shower in ECAL; c) noenergy in Veto and HCAL;
Background:a) µ, π, K decays in flight; b) upstream interaction; c) Tail < 50 GeV
in the e − beam; d) energy leack from ECAL+HCAL
D. V. Kirpichnikov (INR RAS)

prospects for NA64++

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DM processes simulation: DMG4 toolkit
Fully GEANT4 compatible package DMG4 is developed (Kirsanov etal, 2021, Computer physics communication, 2102.12192) . Can
be used in any full simulation program based on GEANT4 toolkit
Bremsstrahlung process of electrons and muons (like eN → eNA0 ),gamma conversion to ALP, annihilation processes (likee + e − → A0 → χχ)DM messengers: vector (A0 ), axial vector, scalar, pseudoscalar
invisible and visible (to SM particle) decays
For the total cross-section we use the full matrix element
calculation (ETL) (1712.06706) through K-factors applied to theIWW cross-section
We continue development the package (more exact WW
differential cross-section)
D. V. Kirpichnikov (INR RAS)

prospects for NA64++

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NA64e design for invisible mode

120

1031003101008080

102
EHCAL , GeV

EHCAL , GeV

120604010II20102

B60402010AI0020Ebeam ' EHCAL + EECAL

C4060
EECAL, GeV

80100

100204060
EECAL, GeV

80100

1NA64e allows to probe invisible decays of Dark Matter mediators: eN → eNX (X → χχ̄), where X is a general
hidden boson (spin 0, spin 1, spin 2) the mediator between SM and DM particle χ (Scalar, Dirac or Majorana).
Signal box (A) of missing energy signature: no events in EECAL . 50 GeV && EHCAL . 1 GeV

D. V. Kirpichnikov (INR RAS)

prospects for NA64++

11 / 21Current and future sensitivity to Dark Photon (, mA0 ) and (y , mχ )10−2E787, E949𝑎𝜇𝑎𝜇 favored

prospects
5x10^12 EOT𝑎𝑒𝜖BaBar62
NA10−310−4NA64
current
2.84x10^11 EOT

prospects
10^13 EOT

10−5

projected sensitivity
5x10^12 EOT before LS3
10−6
10−3

10−2

10−1𝑚𝐴′ , 𝐺𝑒𝑉

110Invisible mode data taking: 2016-2017-2018 (combined analysis 2.84 × 1011 EOT )Long Shutdown 2: 2019-2020
data taking 11th August 2021 (5 weeks)
GOAL: Beam setup and electronics upgrade → reduce background from electro nuclearinteractions along the beam line.
GOAL: to accumulate few 1011 EOT in 2021 and 5 × 1012 EOT before LS3

D. V. Kirpichnikov (INR RAS)

prospects for NA64++

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Semivisible Decay of A0 in NA64: update 2107.02021 [hep-ph]
Δ = 0.4𝑚𝜒1 , 𝑚𝐴 = 3𝑚𝜒1 , 𝛼𝐷 = 0.1
10−1LEPnew

10−2𝜖BaBar

10−310−4(𝑔 −)𝜇(𝑔−2NA642) 𝑒c
Reli

NuCalcennda

Abutercat7S
E13E137 Decay

PRELIMINARYCHARM

10−510−2

110−1𝑚𝐴′ , 𝐺𝑒𝑉

Motivation: (g − 2)µ anomaly and Light Dark
Matter production
E. Izaguirre, et al. PRD 96, 055007 (2017)
G. Mohlabeng, PRD 99, 115001 (2019)
Y. Tsai, et al., PRL126, 181801 (2021)
Signature: Missing energy + SM particles pair
D. V. Kirpichnikov (INR RAS)

prospects for NA64++

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NA64 semivisible modes: ALPs

ALPs predominantly coupled to photons produced via Primakoff effect1
L ⊃ − aFµν F̃µν
4Signature:– No signal on veto and HCAL1– A: visible decay into γγ on HCAL2 || HCAL3– B: Decays after HCAL3 No activity in HCAL2 and HCAL3
D. V. Kirpichnikov (INR RAS)

prospects for NA64++

14 / 21Current limits and projection for ALPs

10−1Z
KSV

10−2 E141

LEP𝑔𝑎𝛾𝛾 , 𝐺𝑒𝑉 −1

DFSZ

10−3BaBar

PrimExNuCal

10−410NA64−5E137

CHARM

10−610−2−110𝑚𝑎 , 𝐺𝑒𝑉

1Left plot is a current limit for EOT = 2.84 · 1011 (PRL, 2020)
Right plot is projected limit for EOT = 5 × 1012 (PRD, 2020)
Future Plans: to consider invisible decay into DM,Br (a → χχ) ' 1
D. V. Kirpichnikov (INR RAS)

prospects for NA64++

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Probing (g − 2)e with NA64
∆aeLKB = aeexp − aeth = (4.8 ± 3.0) · 10−13 LKB, L. Morel, Zh. Yao, P. Clade,and S. Guellati-Khelifa, Nature (London) 588, 61 (2020).
aeB = aeexp − aeth = (−8.8 ± 3.6) · 10−13 Berkley, R. H. Parker, C. Yu, W.
Zhong, B. Estey, and H. Muller, Science 360, 191 (2018)

X (J P = 0± , 1± ) → invis.: Motivation is to exclude the explanation of(g − 2)e puzzle due to X decaying invisibly.
NA64 collaboration, Phys. Rev. Lett. 126, 211802
D. V. Kirpichnikov (INR RAS)

prospects for NA64++

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Visible mode of Dark Photon and ALPs coupled mostly toThe ATOMKI experimentelectrons
10−2

KLOE-2013

HADES
PHENIXATOMKI

𝐵𝑒

E141

𝑒E774−2)

10−4(𝑔10−42) 𝑒E774

BaBar

𝜖8−𝜖

NA4810−3(𝑔10−3NA64
NA64CHARM

E141

10−2𝑚𝐴′ , 𝐺𝑒𝑉

10−1

10−2𝑚𝑎 [𝐺𝑒𝑉 ]10−1of (Krasznahorkay et al. 2016)
has reported the observationof a 6.8 σ excess of events inthe invariant mass distributionsof e + e − pairs producedin the nuclear transitionsof excited ∗ Be 8 and ∗ He 4
This anomaly
can be associated withX-boson of mX = 16.7 MeV.

GOAL: to perform invariant mass reconstruction:
Increase the length of decay tube to resolve e + e − tracks.
TOP VIEW, visible 2018
More compact WCAL
St1-2

S1 V0

SRD ΜM
5-6
S2
W2

MBPL1&2

vacuum pipe, 3.1m

θ= 13mrad

MM3-4
Vacuum pipe

D. V. Kirpichnikov (INR RAS)

Wcat

St3-4

V2ECALHCAL1-4S4Wcal

prospects for NA64++

GEM1-4DESYtable
St5-6

VETO

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New result!
Resonance annihilation channel using the secondary positrons present
in the EM shower in the target induced by the initial electron beam
Improvement limit on  up to factor 10 in the resonant region
10−7

10−7

LSND

NA64
BaBar

10−9

NucleonFermionScalar

10−10

c

10−12

E137

MB-e

LSNDliic
Reel
R licnioar RermalFe
Sc anaacoriraj-DM
doeuPs

10−13

10−11

1010−310−210−1𝑚𝜒 , 𝐺𝑒𝑉1Fermion
ScalarMB-e

E137

10−12Do-rFeniomcira

10−1310Nucleon

icelR licearal a R
Sc ranoajMlicRedeu

𝛼𝐷 = 0.5

10−14−15Detection

MB-N

10−910−10Ps

𝛼𝐷 = 0.1

10−14Direct

NA64BaBarDetection

MB-N

10−1110−8Direct𝑦 = 𝜖2 𝛼𝐷 (𝑚𝜒 /𝑚𝐴′ )4

𝑦 = 𝜖2 𝛼𝐷 (𝑚𝜒 /𝑚𝐴′ )4

10−8−1510−310−210−1𝑚𝜒 , 𝐺𝑒𝑉

1PRELIMINARY: probing resonant e + e − → A0 → χχ production withelectron beam (2108.04195 [hep-ph])NEXT STEP is to probe the resonance e + e − → A0 with positron beam
D. V. Kirpichnikov (INR RAS)

prospects for NA64++

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∈NA64e and NA64µ for large mass region mX ∼ 1 GeV
10−2NA64µPreliminary

10−310−41010 MOT1011 MOT1012 MOT(g-2)µ ± 2σ10−510−310−2

10−11mV [GeV]APPROVED: pilot muon beam run (M2 channel) - November 2021
GOAL: millicharged particles (more effective production in Na64µ than in NA64e)
GOAL: probing muon (g − 2) anomaly at NA64µ within Lµ − Lτ anomaly free gauge extension (exact tree levelcross-section µN → µNZ 0 without relaying on widely used IWW approach)

D. V. Kirpichnikov (INR RAS)

prospects for NA64++

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Combined NA64e and NA64µ limits
10−710−8LSND

10−7DirectDetection

BaBar

LSND

10−8Nucleon

DirectMB-N

10−910−10r

ala
Sc
ic
st elicela R
In na&rajo
ic
st Ma
laMB-e10−11E137
E

10−1210−13ac
Dir

1264
A

5×TO

E10T

13N

134 10A6OTE+2×10MONlicReo-deuPsniomr
FeceliR𝑦 = 𝜖2 𝛼𝐷 (𝑚𝜒 /𝑚𝐴′ )4𝑦 = 𝜖2 𝛼𝐷 (𝑚𝜒 /𝑚𝐴′ )4NA64

𝛼𝐷 = 0.510−1410−1510−310−210−1110−12𝛼𝐷BaBar

2×10OMTAN10−1𝑚𝜒 , 𝐺𝑒𝑉

1NA64 1013 EOT + 2 × 1013 MOT

NA64 5 × 1012 EOT

NA64

𝛼𝐷
𝛼𝐸𝑀+0.5

Majorana Thermal DM
10−1

NA64LSND

BaBar

10−210𝛼𝐸𝑀

E137−3LSND

MB-NMB-e

10−210−1

110−410−3𝑚𝜒 , 𝐺𝑒𝑉

D. V. Kirpichnikov (INR RAS)

64

EO

4π1

Pseudo-Dirac Thermal DM−310−410−313T1310100.5

NA64 5 × 1012 EOT

1010−21 TeV Landau Pole

110−210𝛼𝐷 = 0.1

10−1510−31 TeV Landau Pole

NA64 1013 EOT + 2 × 1013 MOT

MB-e×10−134π

1010−15c64eliARrN
alalicSc
Reicnst elic
E137
iolaRerm
In naFe&cra
joic
irast Ma-D
doElaeuPsTOE

1210−10Detection
Nucleon

MB-N

10−14
110−1𝑚𝜒 , 𝐺𝑒𝑉

NA64BaBar

10−910−210−11𝑚𝜒 , 𝐺𝑒𝑉

prospects for NA64++

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SummaryDark sector physics interesting framework to explain dark matter
NA64 is an ideal experiment for testing benchmark scalar, Majorana andpseudo-Dirac thermal sub-GeV dark matter models
Prospects before LS3:
New area at H4 and setup upgrade to run at high intensity
Main goal to explore LDM parameter space with goal & 5 × 1012 EOTStart searches of dark sectors weakly coupled to muons with NA64µ:(g − 2)µ and Lµ − Lτ → Z 0 : pilot run at M2
Probing light dark matter parameter space for mA0 > 100 MeV
Increase sensitivity to A0 → e + e − decays and explore X 17 → e + e −remaining parameter space in 2022: in case of signal-like eventsreconstruct the invariant mass with precision at few percent level.
All DM physics is simulated by the newly developed DMG4 package
Exploration of LDM with NA64 has just began. Full physics potential
to be exploited in the coming years!
D. V. Kirpichnikov (INR RAS)

prospects for NA64++

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