Search Potential for True at LHCb

Xabier Cid Vidal, Philip Ilten, Jonathan Plews, Brian Shuve, Yotem Soreq

Hadronic Contributions to New Physics Searches 2019

Paper: Discovering True Muonium at LHCb, arXiv:1904.08458

Jonathan Plews True Muonium at LHCb - HC2NP 2019 26th September 2019 1 / 11 True Muonium

∗ SM predicted QED Mixing with γ gives similar of µ+µ− phenomenology to the dark 3 , S1 is most 2 TM 10− promising state Belle II FASER + − HPS SeaQuest e e , 98% 10 3 + TM → − LHCb µ µ− SHiP 0 LHCb D∗

4 10−

properties predicted [unitless] byTM QED [1]: ε TM 5 10− mTM = 2mµ BE 211 MeV 6 − ≈ 10− 2 −5 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 TM = α /2 2.66 10 ≈ × m [GeV] 5 τTM 6/α mµ 1.8 ps ≈ ≈ parameter space. (Grey) excluded, (coloured) current and future analyses [1]

Jonathan Plews True Muonium at LHCb - HC2NP 2019 26th September 2019 2 / 11 Motivation

Deviations from SM predictions could indicate New Physics coupled to :

Dark , Lµ Lτ gauge , scalars or ALPs − Can be tested by precision measurements: mass (via BE), lifetime, decay rates and spectroscopy TM Motivated by other experimental discrepancies in the sector; namely (g 2)µ[2] and charge radius [3] −

Jonathan Plews True Muonium at LHCb - HC2NP 2019 26th September 2019 3 / 11 Dissociation

Major difference from dark photon: can dissociate into constituent muons in material interactions TM σ( µµ) 13Z 2 b TM → ≈

100 LHCb VELO (Run-III) [4]: signal signal w/out 250 µm thick Al RF-foil Pdis background 1 200 µm thick Si sensors 10− ] 1 − Inner radius 5.1 mm [mm dr dσ 1 σ 2 10− Each material interaction has dis 90% P & 3 10− 0 2 4 6 8 10 PYTHIA 8 simulation with r (radial flight distance) [mm] material map gives 50% of + − Radial flight distance for e e signal and B expected to dissociate background [1] TM Jonathan Plews True Muonium at LHCb - HC2NP 2019 26th September 2019 4 / 11 Proposed LHCb Search: Production

behaves like a dark photon, so signal rate calculated from off-shell TMphoton rate

Dominant γ∗ source: η γγ∗ → Signal cross-section estimated using values from PYTHIA 8 simulation

tot σpp = 100 mb fid Nη = 0.83 per event

Using BR(η γ ) = 4.8 10−10 [5], cross-section in fiducial region: → TM × σfid = σtot Nfid BR(η γ ) 40 pb TM pp η → TM ≈

Jonathan Plews True Muonium at LHCb - HC2NP 2019 26th September 2019 5 / 11 Proposed LHCb Search: Selection

Two proposed search strategies for Run-III (2021 - 24):

η γ γe+e− → TM→ Inclusive: Select e+e− pair with a good vertex

Reconstruct in 2σm mass window TM ee Exclusive: Same as for inclusive Also select photon

Reconstruct η in 2σmγee mass window

Aside: Muons from dissociation cannot be used to reconstruct produced colinearly and indistinguishable from photon conversionsTM −

Jonathan Plews True Muonium at LHCb - HC2NP 2019 26th September 2019 6 / 11 Proposed LHCb Search: Backgrounds

Potential sources of e+e− background: Heavy decays - B dominate, D hadrons decay outside of kinematic region Photon conversions, pair production in material - reduced by VELO material veto η e+e−γ decays - vetoed by a displacement cut → B decay backgrounds can be reduced with the following techniques: candidate is isolated, require large distance of closest approach (DOCA)TM between and other tracks in the event Require opening angle, θ, between flight vector and momentum vector is consistent with zero TM

Jonathan Plews True Muonium at LHCb - HC2NP 2019 26th September 2019 7 / 11 Proposed LHCb Search: Expectation

Table 1: Expected signal and background yields in 15fb−1 of Run-III data for the ee (eeγ) final state label asi(ii), assuming 100 % final state reconstruction efficiency

(i) (i) (ii) (ii) requirement STM Btot STM Btot base 3.4 × 103 3.2 × 107 1.6 × 103 5.4 × 106 DOCA 3.0 × 103 8.5 × 106 1.3 × 103 1.1 × 106 θ 1.5 × 103 1.8 × 104 6.4 × 102 1.9 × 103 efficiency 4.4 × 10−1 5.6 × 10−4 4.0 × 10−1 3.5 × 10−4

Also have to consider efficiency of reconstructing the final state, f , currently unknown for Run-III

Make estimates based on previous analyses: ∗0  + − > 10% - from B J/ψK analysis [6] e e →  + − 0.3 + − > 3% - from ratio of χc to J/ψ analysis [7] γe e ≈ e e Jonathan Plews True Muonium at LHCb - HC2NP 2019 26th September 2019 8 / 11 Proposed LHCb Search: Expectation

Significance limited by statistical uncertainty, given as r STM f σstat L−1 ≈ √Btot 15 fb 30 f is left as an unknown 25 15 fb−1 expected in 20 LRun-III ≥ ] 1 − 15 [fb

L A 5σ discovery of can 10 be made with: TM + 5 (i) e e− + f > 20% for inclusive (ii) e e−γ 0 0.00 0.05 0.10 0.15 0.20 0.25 0.30 f > 12% for exclusive εf [unitless] Realistic improvement to Integrated luminosity for 5σ discovery as a efficiencies with triggerless function of final reconstruction efficiency, f [1] readout in Run-III

Jonathan Plews True Muonium at LHCb - HC2NP 2019 26th September 2019 9 / 11 Conclusions

30

25

20 ] 1 − 15 [fb L 10

+ 5 (i) e e− + (ii) e e−γ 0 0.00 0.05 0.10 0.15 0.20 0.25 0.30 εf [unitless] Measurements of properties allow precise tests of SM predictions TM Deviations could be indications of new physics coupling to muons LHCb can make a5 σ discovery of during Run-III TM Paper: Discovering True Muonium at LHCb, arXiv:1904.08458

Jonathan Plews True Muonium at LHCb - HC2NP 2019 26th September 2019 10 / 11 References

[1] X. C. Vidal et al. “Discovering true muonium at LHCb”. In: Phys. Rev. D 100 (5 Sept. 2019), p. 053003. doi: 10.1103/PhysRevD.100.053003. [2] G. W. Bennett et al. “Final Report of the Muon E821 Anomalous Magnetic Moment Measurement at BNL”. In: Phys. Rev. D73 (2006), p. 072003. doi: 10.1103/PhysRevD.73.072003. arXiv: hep-ex/0602035 [hep-ex]. [3] C. E. Carlson. “The Proton Radius Puzzle”. In: Prog. Part. Nucl. Phys. 82 (2015), pp. 59–77. doi: 10.1016/j.ppnp.2015.01.002. arXiv: 1502.05314 [hep-ph]. [4] L. Collaboration. LHCb VELO Upgrade Technical Design Report. Tech. rep. CERN-LHCC-2013-021. LHCB-TDR-013. Nov. 2013. [5] Y. Ji and H. Lamm. “Scouring meson decays for true muonium”. In: Phys. Rev. D99.3 (2019), p. 033008. doi: 10.1103/PhysRevD.99.033008. arXiv: 1810.00233 [hep-ph]. [6] M. Nicol. “Analysis of the rare decay B0 → K ∗0e+e− at LHCb”. PhD thesis. Orsay, LAL, 2012.

[7] R. Aaij et al.√ “Measurement of the ratio of prompt χc to J/ψ production in pp collisions at s = 7 TeV”. In: Phys. Lett. B718 (2012), pp. 431–440. doi: 10.1016/j.physletb.2012.10.068. arXiv: 1204.1462 [hep-ex].

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