Search for a Dark Photon: proposal for the experiment at VEPP–3. I.Rachek, B.Wojtsekhowski, D.Nikolenko IEBWorkshop Cornell University June 18, 2015 I.Rachek dark photon at VEPP-3 June 18, 2015 1
Latest results of dark photon searches BABAR (2014): e + e − → γ A ′ , A ′ → e + e − , µ + µ − NA48/2: π 0 → γ e + e − 2 KLOE ε WASA ) σ (3 2) e − (g -5 10 HADES APEX (g 2) − µ A1 -6 10 BaBar E774 NA48/2 E141 -7 10 2 10 10 2 m (MeV/c ) A’ KLOE 2015 e + e − → γ ( e + e − ) results of 2013-2015 10 − 4 π 0 → γ ( e + e − ) KLOE ( φ → η e + e − ) WASA 2013 PLB 726 (2013) 187 φ → η ( e + e − ) KLOE 2013 PLB 720 (2013) 111 WASA 10 − 5 ( g − 2) µ 5 σ e + e − → γ ( µ + µ − ) KLOE 2014 arXiv:1404.7772 HADES APEX KLOE ( µ + µ − γ ) ( g − 2) µ ± 2 σ e − N → e − N ( e + e − ) ε 2 MAMI-A1 2014 PRL 112 (2014) 221802 A1 favored KLOE ( e + e − γ ) 10 − 6 π 0 , η → γ ( e + e − ) PHENIX 2014 arXiv:1409.0851 preliminary BaBar ( g − 2) e pN → X ( e + e − ) prelim. HADES 2014 PLB 731 (2014) 265 E774 e + e − → γ ( e + e − ) 10 − 7 KLOE 2015 arXiv:1501.05173 E141 π 0 → γ ( e + e − ) NA48/2 2015 arXiv:1504.00607 1 10 100 1000 m U (MeV/c 2 ) no A’ signal observed to date I.Rachek dark photon at VEPP-3 June 18, 2015 2
Latest results of dark photon searches BABAR (2014): e + e − → γ A ′ , A ′ → e + e − , µ + µ − NA48/2: π 0 → γ e + e − 2 KLOE ε WASA Decay of A’ to invisible particles ) σ (3 2) e − (g -5 10 − − A' is excluded 4 4 10 10 HADES A' is 'welcome' APEX a µ (g 2) − µ A1 a µ − − 5 5 10 10 -6 10 BaBar BaBar → π BNL (K A') − − 6 6 2 10 10 E774 ε a e NA48/2 E141 -7 10 2 10 10 2 m (MeV/c ) A’ − − 7 10 7 KLOE 2015 e + e − → γ ( e + e − ) 10 results of 2013-2015 10 − 4 π 0 → γ ( e + e − ) KLOE ( φ → η e + e − ) WASA 2013 PLB 726 (2013) 187 − − 8 8 φ → η ( e + e − ) 10 KLOE 2013 10 PLB 720 (2013) 111 WASA 10 − 5 ( g − 2) µ 5 σ e + e − → γ ( µ + µ − ) KLOE 2014 arXiv:1404.7772 HADES APEX − − − − 2 2 1 1 KLOE ( µ + µ − γ ) 10 10 10 10 1 ( g − 2) µ ± 2 σ e − N → e − N ( e + e − ) 1 ε 2 MAMI-A1 2014 PRL 112 (2014) 221802 A1 favored m (GeV) KLOE ( e + e − γ ) 10 − 6 A' π 0 , η → γ ( e + e − ) PHENIX 2014 arXiv:1409.0851 preliminary BaBar ( g − 2) e pN → X ( e + e − ) prelim. HADES 2014 PLB 731 (2014) 265 E774 e + e − → γ ( e + e − ) 10 − 7 KLOE 2015 arXiv:1501.05173 E141 π 0 → γ ( e + e − ) NA48/2 2015 arXiv:1504.00607 1 10 100 1000 m U (MeV/c 2 ) no A’ signal observed to date I.Rachek dark photon at VEPP-3 June 18, 2015 2
A ′ from annihilation of beam’s positrons and target electrons instead of standard two-photon annihilation e + e − → γ + γ CM LAB photon photon e + γ electron positron cm lab positron θ γ θ γ γ - e photon photon . . . annihilation with the production of dark photon e + e − → A ′ + γ : CM LAB A' boson e + A' electron positron cm lab positron γ θ γ θ γ - e photon photon ε -3 E =500 MeV, =10 + e A'), nbarn differential cross section (in Lab System): 10 � � dy ≈ ε 2 · π r 2 (1+ µ ) 2 d σ 1 − ( y + µ ) − 2 y 0 y γ + γ → − e where 1 + (e σ γ / E + , µ = M 2 y = E lab A / s 0 5 10 15 20 m , MeV A' I.Rachek dark photon at VEPP-3 June 18, 2015 3
Kinematic correlations in annihilation Photon energy depends on its emission angle and the mass of the 2nd particle: 1 − M 2 A / s E γ ≈ E + · 1 + γ + (1 − cos θ γ ) , s = 2 m e ( E + + m e ) for E + = 500 MeV → √ s = 22 . 6 MeV : 500 450 γ γ 400 350 [MeV] M 300 =10 MeV A' 250 M Lab =15 MeV A ' 200 γ E 150 M =20 MeV 100 A ' 50 0 1 1.5 2 2.5 3 3.5 4 4.5 5 Θ Lab γ [deg] I.Rachek dark photon at VEPP-3 June 18, 2015 4
The concept of search in annihilation measure energy and emission angle of γ -quantum search for a “bump” on top of QED background A’-boson should appear in a missing mass spectrum as a peak above QED background: peak width is defined by energy and angular resolutions of the γ -detector gamma background M =15 MeV, veto on 2nd cluster 5 A 8 8 10 → γ all events + + e +H e H background only 5 7 7 10 6 6 4 10 4 10 [deg] [deg] 5 5 e + e + +e -- events +e -- → 3 → 10 4 4 γ 3 γ γ 10 A' for M γ γ Θ Θ 3 3 2 10 =15 MeV A' 2 2 2 10 10 → γ e + +H e + H 1 1 1 50 50 60 60 70 80 90100 70 80 90100 200 200 300 300 400 400 0 2 4 6 8 10 12 14 16 18 20 22 E E γ γ [MeV] [MeV] M , MeV missing I.Rachek dark photon at VEPP-3 June 18, 2015 5
VEPP–3 approach positron beam repeatedly crosses the internal hydrogen gas target working with the new injector complex, which provides 2 · 10 9 e + per second; staying at injector energy E e + = 500 MeV – no energy ramping in VEPP–3 6 bunches in VEPP–3; every 10 seconds the oldest bunch is replaced by a new one with up to 2 · 10 10 positrons, stored in the injector’s cooler ring; designed luminosity of the experiment: 10 33 cm − 2 s − 1 special magnetic system providing free flight for γ –quanta from target to detector is needed using a segmented EM-calorimeter placed at a distance of ∼ 8 m from the target searching for a peak in a missing mass distribution. VEPP-3 beam microstructure: 6-bunches mode revolution period = 249 ns 41.5 ns 1ns T 1 2 3 4 5 6 1 bunch # I.Rachek dark photon at VEPP-3 June 18, 2015 6
1st configuration for the experiment at VEPP–3 Three dipole magnets in the 2nd straight section of VEPP-3 Pump 2,3 o 4.5 Pump 1 = Θ γ o 2.6 γ = Θ D2 Photon Detector Pump 5 Storage Cell Sextupole Q1 Q2 Q3 10.7 o o Valve Valve D1 D3 Pump 4 Sandwich Cold Head 217 cm arXiv:1207.5089 I.Rachek dark photon at VEPP-3 June 18, 2015 7
1st configuration for the experiment at VEPP–3 Three dipole magnets in the 2nd straight section of VEPP-3 Pump 2,3 o 4.5 Pump 1 = Θ γ o 2.6 γ = Θ D2 Photon Detector Pump 5 Storage Cell Sextupole Q1 Q2 Q3 10.7 o o Valve Valve D1 D3 Pump 4 obvious drawbacks Sandwich Cold Head very busy space – difficult to clean-up the path from the target to the calorimeter 217 cm arXiv:1207.5089 VEPP–3 becomes completely unavailable for other programs (SR,KEDR,VEPP-4) when the dipoles are installed I.Rachek dark photon at VEPP-3 June 18, 2015 7
2nd configuration: The ByPass at VEPP–3 SR + e 3B8A 1B1B BYPASS along the 4th straight section of VEPP–3 – where the FEL was previously situated • vacuum chamber with pumping system • 3 dipole magnets • 6 quadrupoles • elements of beam diagnostics I.Rachek dark photon at VEPP-3 June 18, 2015 8
2nd configuration: The ByPass at VEPP–3 kG/cm D1: 12.0 Q1: −0.86 CsI calorimeter Q2: 0.45 D2: 13.4 Q3: −0.57 D3: 19.6 distance = 8 m Q4: 0.54 Target Q5: −0.19 Q6: 0.28 L/L = 0.5% ∆ 4.5 D2 Q5 Q6 Q2 Q1 D3 D1 V Q4 Q3 e+ 3B8A 1B1B length of bypassed segment of VEPP−3 = 1830 cm BYPASS along the 4th straight section of VEPP–3 – where the FEL was previously situated • vacuum chamber with pumping system • 3 dipole magnets • 6 quadrupoles • elements of beam diagnostics I.Rachek dark photon at VEPP-3 June 18, 2015 8
Photon detector The desired specifications: energy resolution σ E / E ≤ 5% in the range E γ = 50 ÷ 500 MeV angular resolution ∆ θ ∼ 0 . 1 ◦ angular acceptance in θ lab : 1 . 5 ◦ ÷ 4 . 5 ◦ – corresponds to θ CM = 90 ◦ ± 30 ◦ angular acceptance in φ : 360 ◦ I.Rachek dark photon at VEPP-3 June 18, 2015 9
Photon detector The desired specifications: energy resolution σ E / E ≤ 5% in the range E γ = 50 ÷ 500 MeV angular resolution ∆ θ ∼ 0 . 1 ◦ angular acceptance in θ lab : 1 . 5 ◦ ÷ 4 . 5 ◦ – corresponds to θ CM = 90 ◦ ± 30 ◦ angular acceptance in φ : 360 ◦ Considering an option of using the crystals from the CLEO EM–calorimeter CsI(Tl) crystals 1650 rectangular crystals in endcaps crystal size: 5 × 5 × 30 cm 3 (16.2X 0 ) 4 Hamamatsu S1790 photodiodes per crystal I.Rachek dark photon at VEPP-3 June 18, 2015 9
Calorimeter based on CsI(Tl) crystals from CLEO 608 crystals are assembled in a “ring” calorimeter is placed at a distance of 8 m from the target based on CLEO measurements with 180 MeV positrons: energy resolution σ E = 3 . 8% spatial resolution σ x = 12 mm ⇒ angular resolution: σ θ = 0 . 09 ◦ event rate at threshold 25 MeV and luminosity 10 33 : total background rate: 850 kHz maximum per a crystal < 20 kHz I.Rachek dark photon at VEPP-3 June 18, 2015 10
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