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The Proton Radius Puzzle Μ The proton radius puzzle µ A. Antognini Paul Scherrer Institute ETH, Zurich Switzerland CREMA collaboration Laser spectroscopy of muonic atoms µ 2P 2S-2P Laser excitation Energy 2S 1S μ • 2S-2P p From 2S-2P • 2S-2P μd ꔄ charge radii • 2S-2P μ3He, μ4He Aldo Antognini Rencontres de Moriond 19.03.2017 2 Three ways to the proton radius p p e- H 2 e- µ- e--p scattering H spectroscopy µp spectroscopy 6.7 σ CODATA-2010 µp 2013 scatt. JLab µp 2010 scatt. Mainz H spectroscopy 0.82 0.83 0.84 0.85 0.86 0.87 0.88 0.89 0.9 Proton charge radius [fm] Pohl et al., Nature 466, 213 (2010) Antognini et al., Science 339, 417 (2013) Pohl et al., Science 353, 669 (2016) Aldo Antognini Rencontres de Moriond 19.03.2017 3 Extracting the proton radius from 훍p Measure 2S-2P splitting (20 ppm) 8.4 meV 2P F=2 and compare with theory 3/2 F=1 2P1/2 F=1 → proton radius F=0 ∆Eth . − . r2 . 2P −2S = 206 0336(15) 5 2275(10) p +00332(20) [meV] 206 meV 50 THz 6 µm fin. size: 3.8 meV F=1 2π(Zα) 2 2 2S ∆Esize = r |Ψnl(0)| 1/2 m ≈ 200m 3 p 23 meV µ e 4 2(Zα) 3 2 F=0 3 m r δl = 3n r p 0 Aldo Antognini Rencontres de Moriond 19.03.2017 4 Principle of the µp 2S-2P experiment Produce many µ− at keV energy − Form µp by stopping µ in 1 mbar H2 gas Fire laser to induce the 2S-2P transition Measure the 2 keV X-rays from 2P-1S decay µp formation Laser excitation Plot number of X-rays vs laser frequency ] n~14 2 P -4 7 Laser 6 1 % 99 % 2 S 5 2 P 4 2 S 3 2 keV 2 keV γ γ 2 delayed / prompt events [10 1 0 1 S 49.75 49.8 49.85 49.9 49.95 1 S laser frequency [THz] Aldo Antognini Rencontres de Moriond 19.03.2017 5 The setup at the Paul Scherrer Institute Aldo Antognini Rencontres de Moriond 19.03.2017 6 The first 훍p resonance (2010) Discrepancy: 5.0 σ ↔ 75 GHz ↔ δν/ν =1.5 × 10−3 ] -4 7 CODATA-06 our value 6 e-p scattering H2O 5 calib. 4 Systematics: 300 MHz Statistics: 700 MHz delayed / prompt events [10 3 2 1 0 49.75 49.8 49.85 49.9 49.95 laser frequency [THz] Pohl et al., Nature 466, 213 (2010) Aldo Antognini Rencontres de Moriond 19.03.2017 7 Politically in-correct discussion Everybody seems to be right!..? Aldo Antognini Rencontres de Moriond 19.03.2017 8 Is the 훍p experiment wrong? This is what I mean with politically incorrect Aldo Antognini Rencontres de Moriond 19.03.2017 9 Why is the 훍p theory reliable? ∆Eth . − . r2 . 2P −2S = 206 0336(15) 5 2275(10) p +00332(20) [meV] 1-loop eVP proton size 2-loop eVP µSE and µVP discrepancy 1-loop eVP in 2 Coul. recoil 2-photon exchange hadronic VP proton SE Discrepancy: 0.31 meV 3-loop eVP Th. uncert.: 0.0025 meV light-by-light -3 -2 -1 2 10 10 10 1 10 10 meV Pachucki, Borie, Eides, Karschenboim, Jentschura, Martynenko, Indelicato Pineda… Aldo Antognini Rencontres de Moriond 19.03.2017 10 Why is the 훍p theory reliable? ∆Eth . − . r2 . 2P −2S = 206 0336(15) 5 2275(10) p +00332(20) [meV] 1-loop eVP proton size 2-loop eVP µSE and µVP discrepancy 1-loop eVP in 2 Coul. recoil 2-photon exchange hadronic VP proton SE Discrepancy: 0.31 meV 3-loop eVP Th. uncert.: 0.0025 meV light-by-light -3 -2 -1 2 10 10 10 1 10 10 meV Pachucki, Borie, Eides, Karschenboim, Jentschura, Martynenko, Indelicato Pineda… Aldo Antognini Rencontres de Moriond 19.03.2017 11 Why is the 훍p theory reliable? ∆Eth . − . r2 . 2P −2S = 206 0336(15) 5 2275(10) p +00332(20) [meV] 1-loop eVP proton size 2-loop eVP µSE and µVP discrepancy 1-loop eVP in 2 Coul. recoil 2-photon exchange hadronic VP proton SE Discrepancy: 0.31 meV 3-loop eVP Th. uncert.: 0.0025 meV light-by-light -3 -2 -1 2 10 10 10 1 10 10 meV Pachucki, Borie, Eides, Karschenboim, Jentschura, Martynenko, Indelicato Pineda… Aldo Antognini Rencontres de Moriond 19.03.2017 12 Why is the 훍p theory reliable? ∆Eth . − . r2 . 2P −2S = 206 0336(15) 5 2275(10) p +00332(20) [meV] 1-loop eVP proton size 2-loop eVP µSE and µVP discrepancy 1-loop eVP in 2 Coul. recoil 2-photon exchange hadronic VP Pachucki, Carlson, Birse, McGovern, Pineda, proton SE Discrepancy: 0.31 meV Theory uncert.: 0.0025 meV Gorchtein, Pascalutsa, 3-loop eVP Vanderhaeghen, Alarcon, light-by-light Miller, Paz, Hill… -3 -2 -1 2 10 10 10 1 10 10 meV Pachucki, Borie, Eides, Hill, Paz, arXiv:1611.09917 Karschenboim, Jentschura, Birse, McGovern, arXiv1206.3030 Martynenko, Indelicato Hagelstein et al., arXiv:1512.03765 Pineda… Peset and Pineda, arXiv:1406.4524 Aldo Antognini Rencontres de Moriond 19.03.2017 13 Is the 2휸 exchange in 훍p reliable? Phenomenological: - dispersion relations - data - subtraction term Chiral EFT AGREEMENT OF TWO METHODS Subtraction term=-0.004 (1) meV Discrepancy=0.3 meV Aldo Antognini Rencontres de Moriond 19.03.2017 14 How reliable is e-p scattering? dσ dσ 1 2 2 2 2 = εGE(Q ) + τGM (Q ) ⇣dΩ⌘Ros. ⇣dΩ⌘Mott (1 + τ)⇣ ⌘ 2 dGE Q 2 ~2 ( ) hrpi = −6 dQ2 Q2=0 Extrapolation: - which function? - physical model? - constraining large-r? - which Q2 range? - sensitivity? 2 4 2 Q 2 Q 4 GE(Q )=1+ 6 hrpi + 120 hrpi + ... Aldo Antognini Rencontres de Moriond 19.03.2017 15 The proton charge radii 6.7 σ CODATA-2010 µp 2013 scatt. JLab µp 2010 scatt. Mainz H spectroscopy 0.82 0.83 0.84 0.85 0.86 0.87 0.88 0.89 0.9 Proton charge radius [fm] Aldo Antognini Rencontres de Moriond 19.03.2017 16 The proton charge radii Bernauer, Distler, arXiv:1606.02159 Various e-p scattering analysis in Sick, Trautmann, arXiv:1701.01809 agreement with muonic results Horbatsch, Hessels, Pineda, arXiv:1610.09760 Lee, Arrington, Hill, arXiv:1505.01489 BUT these analysis are opposed by the experts of the field. ꔄ Discrepancy still persists H(2S-4P) 2016 ?? µd, 2016 Horbatsch, 2016 Higinbotham, 2015 Hessels, 2015 Griffionen, 2015 Sick, 2015 Lee, 2015 µp 2013 dispersion 2012 e-p, JLab, 2011 CODATA-2010 µp 2010 e-p, Mainz, 2010 dispersion 2007 H/D 0.8 0.82 0.84 0.86 0.88 0.9 0.92 0.94 Proton charge radius [fm] Aldo Antognini Rencontres de Moriond 19.03.2017 17 How accurate is hydrogen spectroscopy? R∞ L Lth (r ) = 8171.636(4) + 1.5645 r2 MHz E ' + 1S 1S p p nS n2 n3 8S 4S 3S 3D 2S - 2P 2S-4P 2S-8D 1/2 1/2 2S1/2 - 2P1/2 2S - 2P 2S 2P 1/2 3/2 1S-2S + 2S- 4S1/2 1S-2S + 2S- 4D5/2 1S-2S + 2S- 4P1/2 1S-2S + 2S- 4P3/2 1S-2S + 2S- 6S1/2 1S-2S + 2S- 6D5/2 1S-2S + 2S- 8S 1S-2S 1/2 1S-2S + 2S- 8D3/2 1S-2S + 2S- 8D5/2 H = 0.8779 +- 0.0094 fm 1S-2S + 2S-12D3/2 avg µp : 0.84087 +- 0.00039 fm 1S-2S + 2S-12D5/2 1S-2S + 1S - 3S1/2 0.8 0.85 0.9 0.95 1 1S 4휎 only when averaging proton charge radius (fm) Aldo Antognini Rencontres de Moriond 19.03.2017 18 How accurate is hydrogen spectroscopy? Beyer, Ann. d. Phys. 525, 671 (2013) µp H Low sensitivity to Rp Large sensitivity to Rp ꔄ high-precision frontier ꔄ circumvent high-precision issues fight with systematics But difficult to see the signal ꔄ But “easy” to see the signal Explain the discrepancy by shifting the µp (2S-2P) 100 σ 75 GHz 4 Γ H (1S-2S) 4’000 σ 40 kHz 40 Γ σ · −4 Γ H (2S-4P) < 1.5 9 kHz 7 10 σ σ · −4 Γ : exp accuracy H (2S-2P) < 1.5 5 kHz 7 10 Γ : line width Aldo Antognini Rencontres de Moriond 19.03.2017 19 Is there room for BSM physics? ��� �����+ - �� ���� � � � →γ �����+ - -� - � �� ��� + � �� � μ →μ <� � / -�) ���� � (� μ σ (� ) < �% �� - →μνϕ ���� ������� �� � � � ℓ ����� ����� ξ ϵ ) �� ����� - μ→ �� � ������ ��� �� ( ��� � ����� ����� μ μ ����� �� � � (±� ) ) � ��� ���� � σ ���� -� ����� �� ( ����� ± ) ���� � - ) ( � ) (� � � (±� ��� σ ���� μ �� ��� σ ���� ��� � �� ��-� �� (���) ��� + - �� �����+ - �� ���� � � � →μ μ � �� �� �� �� �� � (���) →γ �����+ - -� � - � �� ϕ ��� + � �� τ � μ →μ ) <� ����/� (�-� σ μ � �� → - ���� ������� �� � � � ℓ X ����� ��� ξ ϵ �� ����� - μ→ �� � ��� ����� �� ����� + � �+ + - → ℓ ℓ = - ���� ��� ��� �� � ���� ��β����± =��� ��� = ± σ α ��� ��� ��� Some open regions best fit 2 ( X ) ���� ��� � �� ( ) �� ��� for MeV force carrier mX(MeV) still resist Aldo Antognini Rencontres de Moriond 19.03.2017 20 Is there room for BSM or unconventional physics? • Breakdown of Lorentz invariance? Gomes, Kostelecky, & Vargas (2014) • Unanticipated QCD corrections? G. Miller, (2013) • Breakdown of Lamb shift expansion due to non-smooth form factor Pascalutsa (2015) • Light sea fermions in e-p and µ-p interactions. Jentschura, G. Miller • Beyond perturbative QED: strong field physics. Pachucki, Jentschura (2014) • Higher-dimensional gravity(?) Dahia & Lemos (2015) • Renormalization group effects for effective particles. Glazek (2014) • Point-particle effective theories, Burgess, Haymann, Rummel, Zalavari (2017) • BSM coupling to muons and protons. Small or no coupling to other particles. • Tuning (e.g. vector vs axial-vector) New point-particle EFT • Targeted coupling (additional coupling to µ and p) predicts R(µp) < R(H), R(scatt.) • No UV completion and no full SM gauge invariance arXiv:1612.07334, arXiv:1612.07313 BSM pessimistic: Barger, Chiang, Keung, Marfatia (2011, 2012), Karshenboim, McKeen, Pospelov (2014) BSM optimistic: Tucker-Smith & Yavin (2011), Batell, McKeen & Pospelov (2011), Brax & Burrage (2011) Rislow & Carlson (2012, 2014), Marfatia & Keung (2015), Pauk& Vanderhaeghen (2015) Martens & Ralston (2016), Liu, McKeen & Miller (2016), Batell et.
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