cLFV & BNV - CERNcds.cern.ch/record/2280092/files/Onderwater.pdfcLFV & BNV Searches @ LHCb Gerco...

cLFV & BNVSearches @ LHCb

Gerco Onderwateron behalf of the LHCb collaboration

Flavour2017, Qui Nhơn, Việt Nam, 13-19 August 2017

Outline

LHCb Experiment

LFV with muons : τ→μμμ

LFV with electrons : D0→eμ

LFV with taus?

BNV & LNV

Conclusion

Gerco Onderwater, Flavour2017

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τ

μ

B+

π

ντπ

πK+

LHCb

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LHCb : precision measurement

Triggerhigh efficiency esp. muon triggers

Int. J. Mod. Phys. A 30, 1530022 (2015)

Muon IDidentification ε ~ 97% misID ~ 2%

RICHPID ε(K) ~ 95% for MisID(π→K) ~ 5%

VELO IP resolution 15+29/(pT/GeV) μm

Tracking Δp/p0.4% @ 5 GeV/c – 1.0% @ 200 GeV/c

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http://www.worldscientific.com/doi/abs/10.1142/S0217751X15300227

Recent LHCb results

D0 → eμ PLB 754 (2016) 167 LFV

B0 → D*+ τντ / μνμ PRL 115, 111803 (2015) LNU Julian

τ → μμμ JHEP 02 (2015) 121 LFV

B+ → K+μμ / ee PRL 113, 151601 (2014) LNU Julian

B– → π+μ–μ– PRL 112, 131802 (2014) LNV

τ– → pμ–μ– PLB 724 (2013) 36 BLNV

D+ → π–μ+μ+ PLB 724 (2013) 203 LNV

B0 → eμ PRL 111 (2013) 141801 LFV

(s)

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http://www.sciencedirect.com/science/article/pii/S0370269316000411

http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.115.111803

http://link.springer.com/article/10.1007/JHEP02(2015)121






μ detection

μ

μ

μ

τ

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Challenge : τ decays at hadron collider

B factory

✘ Babar & Belle ~3x109 τ-pairs

✓ e+e‒ → τ+τ‒ extremely clean

✓ tag with opposite τ possible

LHC

✓ LHCb ~3.5x1011 τ's in detector acceptance in 2011 & 2012

✘ Nearly no direct τ production, mainly from Ds decay

✘ No “production traces” in Ds → τντ

✘ Charm decay with missing particles similar to τ signature

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τ → 3μ search

Approach:■ trigger on muon and secondary vertex■ multivariate analysis to discriminate signal and background■ control sample for normalization and calibration

μ

μ

μ

τ

Dsprimary vertex

secondary vertex

ν

main tauproduction viadecay of Ds

JHEP 02 (2015) 121

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Signal candidate selection

Trigger■ muons not “in beampipe” (pT > 1.48 GeV/c)■ two-, three- or four-track secondary vertex■ at least one particle does not point to collision point

Analysis■ no tracks may point to collision point■ good 3-track vertex■ decay-time compatible with τ decay (ct > 100 μm)■ τ momentum must point back to PV

Background elimination■ |M(μ+μ‒)−M(Φ)| > 20 MeV/c² Ds‒ → Φ(μ+μ‒)π‒

■ M(μ+μ‒) > 450 MeV/c² Ds‒ → η(μ+μ‒γ)μ‒νμ■ M(μ‒μ‒) > 250 MeV/c² reconstructed from same particle

JHEP 02 (2015) 121

misID

missing mis-reconstructed

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Signal & background discrimination

Three likelihoods to distinguish signal from background

I. L3body : decay topology

II. LPID : μ identification

III.L3μ : tau selection

L3body

LPID

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M3μ distribution

■ Shape determined using Ds‒ → Φ(μ+μ‒)π‒

■ Analyze 5x5 best bins in LPID and L3body

Blind analysis

LPID : [0.65, 1.0]L3body : [0.725, 1.0]

JHEP 02 (2015) 121

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M3μ distribution

Bkgd Signal Bkgd

■ Shape determined using Ds‒ → Φ(μ+μ‒)π‒

■ Analyze 5x5 best bins in LPID and L3body

LPID : [0.65, 1.0]L3body : [0.725, 1.0]

JHEP 02 (2015) 121

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dashed : expected solid : observed

68%

95%

Result

– Robust analysis method – Statistics limited – No significant evidence for excess of events

B(τ‒ → μ‒μ+μ‒) < 4.6 x 10-8

@ 90% C.L.

Belle 2.1 x 10-8 @ 90% C.L.

BaBar 3.3 x 10-8 @ 90% C.L.

@Run2: LHCb may overtake Belle… which will then be overtaken by Belle-II

JHEP 02 (2015) 121

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e detectione

μ

D0

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D0 → eμ

e

μ

D0

D*+

π+

Belle : Br(D0 → eμ) < 2.6x10–7 (90% CL)

RPV SUSY : ~10–7 Leptoquarks : 4x10–8

LHCb analysis based on 3 fb–1 collected @ √s = 7 & 8 TeV

D*+ → D0 π+

↳ D0 → eμ Signal ↳ D0 → K– π+ Normalization

PLB 754 (2016) 167

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Bremsstrahlung

e → eγ

also study w/B+ → J/ψ K+

↳e+e–

PLB 754 (2016) 167

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Mis-Identification

Probability forπ+π– → eμ mis-ID~ (1–2)x10–8

Kπ

π+π–

PLB 754 (2016) 167

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Unbinned simultaneous fits

BKGD-like

intermediate

Signal-like

-7±15 events

m(eμπ)-m(eμ) → MD*-MDm(eμ) → MD

Signal + bkgd

D0→eμ (signal)

PLB 754 (2016) 167

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dashed : expected solid : observed

Result

–Robust analysis method –Statistics limited –No significant evidence for excess of events

B(D0 → eμ) < 1.3 x 10-8

@ 90% C.L.

20x improvement over previous resultEffectively deal with backgroundsBremsstrahlung complicates analysis

PLB 754 (2016) 167

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Other channels under investigation

B(s) → eμ

B0 → K*0eμ

Bs → Φeμ

B(s) → J/Ψ(→eμ) X

B+ → K+eμ

Expect to improveexisting limits

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τ detectionOpportunities for

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Some existing limits

J/ψ(1S) → μτ < 2x10–6

Υ(1S) → μτ < 6x10–6

Υ(2S) → μτ < 3x10–6

Υ(3S) → μτ < 3x10–6

Z0 → μτ < 1x10–5

h0 → μτ < 1.5%

J/ψ(1S) → eτ < 9x10–6

Z0 → eτ < 1x10–6

O(few x 10-6)@ 90-95% CL

Particle Data Group

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Reconstruction – I

Interesting possibilityShort lifetime prohibits direct detection

τ

μ

B0

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Reconstruction – II

τ

μ

B0

μ

νμ

ντ

Interesting possibilityShort lifetime prohibits direct detectionNeutrinos remain undetected

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Reconstruction – III

τ

μ

B0

π

ντπ

π

Interesting possibilityShort lifetime prohibits direct detectionNeutrino remains undetected Br ~ 9%

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Reconstruction – IV

τ

μ

B+

π

ντπ

πK+

Interesting possibilityShort lifetime prohibits direct detectionNeutrino remains undetected

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Reconstruction – V

τ

μ

π

ντπ

π

Interesting possibilityShort lifetime prohibits direct detectionNeutrino remains undetected

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Possibly interesting channels

B(s) → e/μτ

B+ → K+e/μτ

Υ(nS) → e/μτ

Benefit from B0 → D*+τντ & B(s) → ττ

τ

μ

π

ντπ

π

τ

μ

B+

π

ντπ

πK+

τ

μ

B0

π

ντπ

π

Phys. Rev. Lett. 115, 111803 (2015)Phys. Rev. Lett. 118, 251802 (2017)

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https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.115.111803

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.118.251802

BNV & LNV

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LHCb LNV & BNV results

B– → D*+ μ– μ– < 2.4x10–6

→ D0π+ μ– μ– < 1.5x10–6

→ D+ μ– μ– < 6.9x10–7

→ Ds+ μ– μ– < 5.8x10–7

→ K+ μ– μ– < 5.4x10–8

→ π+ μ– μ– < 4.0x10–9

Ds–→ π+ μ– μ– < 1.4x10–7

D– → π+ μ– μ– < 2.5x10–8

τ– → pμ– μ– < 5.4x10–7 *

→ pμ+μ+ < 4.6x10–7

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Search for Majorana ν's

Best limits to date, stillto be improved

Note: B–L not conserved(except *)

PRL 112 (2014), 131802 PLB 724 (2013), 36PLB 724 (2013), 203 PRL 108 (2012), 101601

PRD 85 (2012), 112004

LNV / BNV / (B–L) conserving

D0 → p μ–

B0(s) → p μ–

B0(s) → Λc μ–

Λ0(b) → K+ μ–

Λ0b → D+(s) μ–

Λ+c → μ+μ+μ–

M0 → B+ ℓ– (0,0) → (+1,+1)B0 → M+ ℓ– (–1,0) → (0,+1)B+ → ℓ+ℓ+ℓ– (+1,0) → (0,–1)

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Bein

g in

vestig

ate

d

Conclusion

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Take away message

LHCb : diverse program studying flavor physics with all three quark & lepton generations

With LHC Run-I data LHCb sharpened limits for manyLFV, LNV, and BNV channels

No significant deviations from SM seen

Demonstrated sensitive BSM searches @ hadron collider

Many more options around, lots of additional dataexpected in Run-II & Run-III

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Thank you for your attention!


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