and NA62 (Neutral Pion Form Factor) On behalf of the NA62 - PowerPoint PPT Presentation

Recent results from NA48/2 (LFV, DP) and NA62 (Neutral Pion Form Factor) On behalf of the NA62 collaboration Nicolas Lurkin School of Physics and Astronomy, University of Birmingham XIIIth International Conference on Heavy Quarks and Leptons, 24-05-2016

Outline  NA48/2 - 𝐎𝐁𝟕𝟑 𝐒 𝐋 experiment Lepton Number Violating (LNV) decay 𝑳 ± → 𝝆 ∓ 𝝂 ± 𝝂 ±  Search for resonances in 𝑳 ± → 𝝆 ∓ 𝝂 ± 𝝂 ± and 𝑳 ± → 𝝆 ± 𝝂 + 𝝂 −  Dark Photon (DP) searches in 𝝆 𝟏 decay  𝝆 𝟏 electromagnetic transition form factor (TFF) measurement  Nicolas Lurkin, HQL2016,24-05-2016 2

CERN NA48/NA62 experiments Experiments history Earlier NA31 Jura mountains 𝑆𝑓 𝜁 ′ /𝜁 France 1997 NA48 ( 𝐿 𝑇 / 𝐿 𝑀 ) Discovery of NA48/NA62: 2001 direct CPV SPS Centre of the LHC Switzerland Rare 𝐿 𝑇 and hyperon 2002 NA48/1 LHC ( 𝐿 𝑇 /hyperons) decays 2003 NA48/2 Direct CPV, Rare 𝐿 + / 𝐿 − decays ( 𝐿 + / 𝐿 − ) 2004 ± /𝐿 ± Geneva airport 2007 NA62 R K 𝑆 𝐿 = 𝐿 𝑓2 𝜈2 ( 𝐿 + / 𝐿 − ) 2008 𝐿 + → 𝜌 + 𝜉 𝜉 , Rare 2014 NA62 𝐿 + and 𝜌 0 decays ( 𝐿 + ) Kaon decay in flight experiment NA62: currently ~ 200 participants, 29 institutions from 13 countries

Experimental Setup (NA48/2 – 𝐎𝐁𝟕𝟑 𝐒 𝐋 )  Principal subdetectors  Scintillator hodoscope (HOD)  Low-level trigger, time measurement (150 ps)  Magnetic spectrometer (4DHCs)  4 views/DCH high efficiency  𝜏 𝑞 𝑞 = 1.02% ⊕ 0.044% ⋅ 𝑞 [GeV/ c ] NA48/2 = 0.48% ⊕ 0.009% ⋅ 𝑞 [GeV/ c ] NA62 R K  Liquid Krypton EM calorimeter (LKr)  High granularity, quasi-homogeneous NA48/2 𝑄 𝐿 = 60 ± 3 GeV/ c  𝐹 ⊕ 𝜏 𝐹 𝐹 = 3.2 9 𝐹 ⊕ 0.42 % [E in GeV] 3-track vertex trigger 𝐿 + 𝐿 − beam Simultaneous  𝜏 𝑦 = 𝜏 𝑧 = 4.2 𝐹 ⊕ 0.6 mm [E in GeV] 𝐎𝐁𝟕𝟑 𝐒 𝐋 (1.5 mm @ 10 GeV) 𝑄 𝐿 = 74 ± 2 GeV/ c 𝐿 𝑓2 trigger 𝐿 + 𝐿 − beam Alternate Nicolas Lurkin, HQL2016,24-05-2016 4

LNV in the 𝑳 ± → 𝝆𝝂𝝂 decays  Majorana Neutrinos  Asaka-Shaposhnikov model ( 𝜉 MSM) [PLB 620 (2005) 17]: three sterile neutrinos N i in the SM to explain Dark Matter ( N 1 , 𝒫 (keV)) + Baryon Asymmetry and low 𝜉 mass ( N 2,3 𝒫 (100 MeV – few GeV))  Effective vertices with 𝑋 ± , 𝑎 and SM leptons with 𝑉 mixing matrix  Production of N 2,3 in 𝐿 ± decays and N 2,3 decay for 𝑛 2,3 < 𝑛 𝐿 − 𝑛 𝜈 𝐿 ± → 𝜈 ± 𝑂, 𝑂 → 𝜌 ± 𝜈 ∓ For this result 4  BR 𝐿 ± → 𝜈 ± 𝑂 × BR 𝑂 → 𝜌 ∓ 𝜈 ± ~ 𝑉 𝜈4  Inflatons  Shaposhnikov-Tkachev model [PLB 639 (2006) 414]: 𝜉 MSM + real scalar field (inflaton 𝜓 ) with scale-invariant couplings to explain universe homogeneity and isotropy on large scales/structures on smaller scales 𝜓 -Higgs mixing ( 𝜄 ), 𝜓 -Higgs coupling → universe reheating, 𝜐 𝜓 ~ 10 −8 − 10 −12   Production in Kaon decays: 2 𝑞 𝜓 𝑛 𝜓 < 354 MeV/𝑑 2 and BR 𝐿 ± → 𝜌 ± 𝜓 = 1.3 × 10 −3 𝜄 2 𝑁 𝐿 Nicolas Lurkin, HQL2016,24-05-2016 5

LNV: Same-Sign Muon Sample  Blind analysis: M 𝜌 ∓ 𝜈 ± 𝜈 ±  Selection based on simulation of 𝐿 ± → 𝜌 ∓ 𝜈 ± 𝜈 ± and 𝐿 ± → 𝜌 ± 𝜌 + 𝜌 − (background, similar topology)  3-track vertex topology, 2 same-sign muons, 1 odd-sign pion, no missing momentum  First-order cancellation of systematic effects  Control region: 𝑁 𝜌𝜈𝜈 < 480 MeV/𝑑 2  Signal region: 𝑁 𝜌𝜈𝜈 − 𝑁 𝐿 < 5 MeV/𝑑 2  Results:  Event in Signal Region: 𝑂 𝑝𝑐𝑡 = 1  Expected background from MC: 𝑂 exp = 1.163 ± 0.867 𝑡𝑢𝑏𝑢 ± 0.021 𝑓𝑦𝑢 ± 0.116 𝑡𝑧𝑡𝑢  From Rolke-Lopez statistical method: 𝐶𝑆 𝐿 ± → 𝜌 ∓ 𝜈 ± 𝜈 ± < 8.6 × 10 −11 @ 90% CL Nicolas Lurkin, HQL2016,24-05-2016 6

LNC: Opposite-Sign Muon Sample  Selection M 𝜌 ± 𝜈 + 𝜈 −  Similar to same-sign  3-track vertex, 2 opposite-sign muons, 1 pion, no missing momentum  First-order cancellation of systematic effects  Signal region: 𝑁 𝜌𝜈𝜈 − 𝑁 𝐿 < 8 MeV/𝑑 2  Results  Event in Signal Region: 3489 𝐿 ± → 𝜌 ± 𝜈 + 𝜈 − candidates M 𝜈 + 𝜈 −  Background: 0.36 ± 0.10 % M 𝜌 ± 𝜈 ∓  See [Phys. Lett. B697 (2011) 107] for previous measurement of BR and FF  Search for resonances in 𝑁 𝜌𝜈 and 𝑁 𝜈𝜈 invariant masses  step= 0.5𝜏 𝑁 𝑠𝑓𝑡 and window= ±2𝜏 𝑁 𝑠𝑓𝑡  Limit using Rolke-Lopez from 𝑂 𝑝𝑐𝑡 and 𝑂 𝑓𝑦𝑞 for each hypothesis 7

LNV and LNC: Resonances searches  Search for 𝑳 ± → 𝝂 ± 𝑶 𝟓 𝑶 𝟓 → 𝝆 ∓ 𝝂 ± decays, 284 mass hypotheses 2 possibilities for 𝑁 𝜌 ∓ 𝜈 ± , closest to 𝑁 𝑠𝑓𝑡 chosen  Never exceeds +3𝜏 : no signal observed and UL BR ~10 −10 for 𝜐 < 100 ps   Upper limit on 𝐂𝐒 𝑳 ± → 𝝂 ± 𝑶 𝟓 𝐂𝐒 𝑶 𝟓 → 𝝆 ∓ 𝝂 ± UL(BR) vs. 𝑁 𝑠𝑓𝑡 N obs vs. 𝑁 𝑠𝑓𝑡 UL 𝑂 𝑡𝑗𝑕  𝑉𝑀 BR = 𝑂 𝐿 ∗𝐵𝑑𝑑𝑓𝑞𝑢𝑏𝑜𝑑𝑓  Statistical significance 𝑂 𝑝𝑐𝑡 −𝑂 𝑓𝑦𝑞  𝑨 = 𝜏 𝑂 𝑝𝑐𝑡 ⊕𝜏 𝑂 𝑓𝑦𝑞 𝑨 vs. 𝑁 𝑠𝑓𝑡 Nicolas Lurkin, HQL2016,24-05-2016 8

LNV and LNC: Resonances searches  Search for 𝑳 ± → 𝝂 ± 𝑶 𝟓 𝑶 𝟓 → 𝝆 ∓ 𝝂 ± decays, 284 mass hypotheses 2 possibilities for 𝑁 𝜌 ∓ 𝜈 ± , closest to 𝑁 𝑠𝑓𝑡 chosen  Never exceeds +3𝜏 : no signal observed and UL BR ~10 −10 for 𝜐 < 100 ps   Search for 𝑳 ± → 𝝂 ± 𝑶 𝟓 𝑶 𝟓 → 𝝆 ± 𝝂 ∓ decays, 280 mass hypotheses Never exceeds +3𝜏 : no signal observed and UL BR ~10 −9 for 𝜐 < 100 ps   Upper limit on 𝐂𝐒 𝑳 ± → 𝝂 ± 𝑶 𝟓 𝐂𝐒 𝑶 𝟓 → 𝝆 ∓ 𝝂 ± N obs vs. 𝑁 𝑠𝑓𝑡 UL(BR) vs. 𝑁 𝑠𝑓𝑡 UL 𝑂 𝑡𝑗𝑕  𝑉𝑀 BR = 𝑂 𝐿 ∗𝐵𝑑𝑑𝑓𝑞𝑢𝑏𝑜𝑑𝑓  Statistical significance 𝑂 𝑝𝑐𝑡 −𝑂 𝑓𝑦𝑞  𝑨 = 𝜏 𝑂 𝑝𝑐𝑡 ⊕𝜏 𝑂 𝑓𝑦𝑞 𝑨 vs. 𝑁 𝑠𝑓𝑡 Nicolas Lurkin, HQL2016,24-05-2016 9

LNV and LNC: Resonance searches  Search for 𝑳 ± → 𝝂 ± 𝑶 𝟓 𝑶 𝟓 → 𝝆 ∓ 𝝂 ± decays, 284 mass hypotheses 2 possibilities for 𝑁 𝜌 ∓ 𝜈 ± , closest to 𝑁 𝑠𝑓𝑡 chosen  Never exceeds +3𝜏 : no signal observed and UL BR ~10 −10 for 𝜐 < 100 ps   Search for 𝑳 ± → 𝝂 ± 𝑶 𝟓 𝑶 𝟓 → 𝝆 ± 𝝂 ∓ decays, 280 mass hypotheses Never exceeds +3𝜏 : no signal observed and UL BR ~10 −9 for 𝜐 < 100 ps   Search for 𝑳 ± → 𝝆 ± 𝒀 𝒀 → 𝝂 + 𝝂 − decays, 267 mass hypotheses Never exceeds +3𝜏 : no signal observed and UL BR ~10 −9 for 𝜐 < 100 ps   Upper limit on 𝐂𝐒 𝑳 ± → 𝝂 ± 𝑶 𝟓 𝐂𝐒 𝑶 𝟓 → 𝝆 ∓ 𝝂 ± N obs vs. 𝑁 𝑠𝑓𝑡 UL(BR) vs. 𝑁 𝑠𝑓𝑡 UL 𝑂 𝑡𝑗𝑕  𝑉𝑀 BR = 𝑂 𝐿 ∗𝐵𝑑𝑑𝑓𝑞𝑢𝑏𝑜𝑑𝑓  Statistical significance 𝑂 𝑝𝑐𝑡 −𝑂 𝑓𝑦𝑞  𝑨 = 𝜏 𝑂 𝑝𝑐𝑡 ⊕𝜏 𝑂 𝑓𝑦𝑞 𝑨 vs. 𝑁 𝑠𝑓𝑡 Nicolas Lurkin, HQL2016,24-05-2016 10

Dark Photon Searches  Simplest hidden sector model: Extra U(1) symmetry with gauge boson 𝑩 ′ [B.Holdom, Phys. Lett. B166 (1986) 196] 𝑓 −  QED-like interactions with SM fermions 𝐵 ′ ℒ ~𝑕 ′ 𝑟 𝑔 𝜔 𝑔 𝛿 𝜈 𝜔 𝑔 𝑉 𝜈 ′  𝑓 +  Coupling constants and charges generated through kinetic mixing between QED and the new U(1) gauge bosons ℒ 𝑛𝑗𝑦 = − 𝜗 𝐵 ′ 𝑅𝐹𝐸 𝐺 𝜈𝜉 𝛿  2 𝐺 𝜈𝜉 𝑒𝑏𝑠𝑙  Motivations:  Possible explanation for positron excess in cosmic rays (PAMELA, 𝑓 + 𝐵 ′ FERMI, AMS-02) by dark matter annihilation 𝜓 𝑓 − ~ TeV 𝑓 + 𝐵 ′ 𝛿 𝜓  Possible solution to the muon g-2 anomaly 𝑓 − ~G eV 𝐵 ′ 𝜈 𝜈 Nicolas Lurkin, HQL2016,24-05-2016 11

DP: 𝝆 𝟏 → 𝜹𝑩 ′ Decay  Production Batell, Pospelov and Ritz, [PRD80 (2009) 095024] 3 2 𝑛 𝐵′  BR 𝜌 0 → 𝛿𝐵 ′ = 2𝜁 2 1 − BR 𝜌 0 → 𝛿𝛿 2 BR 𝜌 0 → 𝛿𝐵 ′ vs. 𝑛 𝐵 ′ 𝑛 𝜌0  Mixing parameter 𝜁 and dark photon mass 𝑛 𝐵 ′ Valid for 𝜁 2 ≪ 1  Loss of sensitivity as 𝑛 𝐵 ′ approaches the 𝑛 𝜌 0 threshold  For 𝜁 2 > 10 −7 and 𝑛 𝐵 ′ > 10 MeV/𝑑 2 mean free path is negligible and prompt decay is assumed  Signature similar to 𝜌 𝐸 0 0 → 𝛿𝑓 + 𝑓 − ; 𝜌 0 → 𝛿𝐵 ′ 𝜌 𝐸 ↳ 𝑓 + 𝑓 −  Decay Batell, Pospelov and Ritz, [PRD79 (2009) 115008] 𝑩 ′ decay BRs 𝑩 ′ decay width into SM fermions  Accessible in 𝜌 0 decay, 𝑓 + 𝑓 − Assuming 𝜁 2 = 10 −4 assuming only into SM 𝜈 + 𝜈 − fermions 𝒏 𝝆 𝟏 𝐵 ′ ≈ Γ 𝐵 ′ → 𝑓 + 𝑓 − 𝟑𝒏 𝝂 Γ ≈ 𝛽𝜁 2 𝑛 𝐵 ′ /3 𝒏 𝝆 𝟏 𝑛 𝐵 ′ > 2𝑛 𝜌 0 : hadronic hadrons decay contribution Nicolas Lurkin, HQL2016,24-05-2016 12