Search for a Dark Photon: proposal for the experiment at VEPP 3.

Search for a Dark Photon: proposal for the experiment at VEPP 3. I.Rachek, B.Wojtsekhowski, D.Nikolenko IEBWorkshop Cornell University June 18, 015 I.Rachek dark photon at VEPP-3 June 18, 015 1

Latest results of dark photon searches BABAR (014): e + e γa, A e + e, µ + µ NA48/: π 0 γe + e ε KLOE WASA 5 (g ) e (3σ) (g ) µ HADES A1 APEX 6 BaBar KLOE 015 e + e γ(e + e ) ε 4 5 6 7 KLOE (φ ηe + e ) (g )µ 5σ HADES (g )µ ± σ A1 favored KLOE (e + e γ) preliminary (g BaBar )e prelim. E774 E141 WASA APEX KLOE (µ + µ γ) 1 0 00 mu (MeV/c ) 7 results of 013-015 E774 E141 NA48/ m A (MeV/c ) WASA 013 π 0 γ(e + e ) PLB 76 (013) 187 KLOE 013 φ η(e + e ) PLB 70 (013) 111 KLOE 014 e + e γ(µ + µ ) arxiv:1404.777 MAMI-A1 014 e N e N(e + e ) PRL 11 (014) 180 PHENIX 014 π 0, η γ(e + e ) arxiv:1409.0851 HADES 014 pn X (e + e ) PLB 731 (014) 65 KLOE 015 e + e γ(e + e ) arxiv:1501.05173 NA48/ 015 π 0 γ(e + e ) arxiv:1504.00607 no A signal observed to date I.Rachek dark photon at VEPP-3 June 18, 015

Latest results of dark photon searches BABAR (014): e + e γa, A e + e, µ + µ KLOE 015 e + e γ(e + e ) ε 4 5 6 7 KLOE (φ ηe + e ) (g )µ 5σ HADES (g )µ ± σ A1 favored KLOE (e + e γ) preliminary (g BaBar )e prelim. E774 E141 WASA APEX KLOE (µ + µ γ) 1 0 00 mu (MeV/c ) ε 5 6 ε 5 6 7 results of 013-015 (g ) µ E774 E141 NA48/: π 0 γe + e WASA Decay of A to invisible particles 4 7 a e NA48/ (g ) e (3σ) HADES KLOE A1 APEX BaBar m A (MeV/c ) WASA 013 π 0 γ(e + e ) PLB 76 (013) 187 KLOE 013 8 φ η(e + e ) PLB 70 (013) 111 KLOE 014 e + e γ(µ + µ ) arxiv:1404.777 MAMI-A1 014 e N e N(e + e 1 1 ) PRL 11 (014) 180 PHENIX 014 π 0 m A', η γ(e + (GeV) e ) arxiv:1409.0851 HADES 014 pn X (e + e ) PLB 731 (014) 65 KLOE 015 e + e γ(e + e ) arxiv:1501.05173 NA48/ 015 π 0 γ(e + e ) arxiv:1504.00607 no A signal observed to date A' is excluded a µ A' is 'welcome' a µ BNL (K πa') I.Rachek dark photon at VEPP-3 June 18, 015 BaBar

A from annihilation of beam s positrons and target electrons instead of standard two-photon annihilation e + e γ + γ photon e + γ CM photon LAB electron positron positron cm lab θ γ θ e- γ γ photon photon... annihilation with the production of dark photon e + e A + γ: e + A' CM electron γ positron cm θ e- γ photon A' boson photon LAB positron θ γ lab differential cross section (in Lab System): where y = E lab dσ dy ε πr 0 yγ + [ (1+µ) 1 (y+µ) y ] γ /E +, µ = M A /s, MeV 0 5 15 0 m A' I.Rachek dark photon at VEPP-3 June 18, 015 3 e γa'), nbarn + σ(e 1 E e +=500 MeV, -3 ε=

Kinematic correlations in annihilation Photon energy depends on its emission angle and the mass of the nd particle: E γ E + for E + = 500 MeV s =.6 MeV : 1 M A /s 1 + γ + (1 cos θ γ ), s = m e(e + + m e ) 500 450 [MeV] Lab E γ 400 350 300 50 00 150 γγ M A' = MeV M A' =15 MeV 0 M A' =0 MeV 50 0 1 1.5.5 3 3.5 4 4.5 5 Lab Θ γ [deg] I.Rachek dark photon at VEPP-3 June 18, 015 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 8 7 e + +H e + H γ 5 5 M A =15 MeV, veto on nd cluster all events background only [deg] Θ γ 6 5 4 3 -- e + +e γ -- e + +e γ γ A' for M A' =15 MeV 4 3 events 4 3 1 e + +H e + H γ 50 60 70 80 900 00 300 400 E γ [MeV] 1 0 4 6 8 1 14 16 18 0 M missing, MeV I.Rachek dark photon at VEPP-3 June 18, 015 5

VEPP 3 approach positron beam repeatedly crosses the internal hydrogen gas target working with the new injector complex, which provides 9 e + per second; staying at injector energy E e + = 500 MeV no energy ramping in VEPP 3 6 bunches in VEPP 3; every seconds the oldest bunch is replaced by a new one with up to positrons, stored in the injector s cooler ring; designed luminosity of the experiment: 33 cm 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 = 49 ns 1ns 41.5 ns 1 3 4 5 6 1 bunch # T I.Rachek dark photon at VEPP-3 June 18, 015 6

1st configuration for the experiment at VEPP 3 o Three dipole magnets in the nd straight section of VEPP-3 Valve Pump 1 D1 Q1.7 o Pump,3 Storage Cell Cold Head D 17 cm Pump 4 Θ γ =.6 Q Sandwich o o Θγ= 4.5 Pump 5 D3 Valve Sextupole Q3 Photon Detector arxiv:107.5089 I.Rachek dark photon at VEPP-3 June 18, 015 7

1st configuration for the experiment at VEPP 3 o Three dipole magnets in the nd straight section of VEPP-3 Valve Pump 1 D1 Q1.7 o Pump,3 Storage Cell obvious drawbacks Cold Head D Pump 4 Θ γ = Sandwich.6 o Q o Θγ= 4.5 Pump 5 D3 Valve Sextupole Q3 Photon Detector very busy space difficult to clean-up the path from the target to the calorimeter 17 cm VEPP 3 becomes completely unavailable for other programs arxiv:107.5089 (SR,KEDR,VEPP-4) when the dipoles are installed I.Rachek dark photon at VEPP-3 June 18, 015 7

nd 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, 015 8

nd configuration: The ByPass at VEPP 3 D3 CsI calorimeter Q6 distance = 8 m Q5 4.5 Q4 Q3 D Target Q D1: 1.0 D: 13.4 D3: 19.6 Q1 L/L = 0.5% D1 V kg/cm Q1: 0.86 Q: 0.45 Q3: 0.57 Q4: 0.54 Q5: 0.19 Q6: 0.8 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, 015 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, 015 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 30cm 3 (16.X 0 ) 4 Hamamatsu S1790 photodiodes per crystal I.Rachek dark photon at VEPP-3 June 18, 015 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 = 1 mm angular resolution: σ θ = 0.09 event rate at threshold 5 MeV and luminosity 33 : total background rate: 850 khz maximum per a crystal < 0 khz I.Rachek dark photon at VEPP-3 June 18, 015

Main background processes background QED processes 1 positron bremmstrahlung on hydrogen e + + H e + + X + γ Bhabha scattering with bremsstrahlung e + + e e + + e + γ 3 -photon annihilation e + + e γ + γ 4 3-photon annihilation e + + e γ + γ + γ Part of background events can be identified and rejected. The rest form a smooth substrate ; their fluctuations define a search sensitivity. For realistic background estimation a Monte Carlo simulation is required. Such simulation was performed using GEANT4 toolkit and a set of dedicated event generators. I.Rachek dark photon at VEPP-3 June 18, 015 11

1 e + + H e + + X + γ Event generators root class TFoam, dif. cross section dσ γ de γdω γ from classic paper Y-S. Tsai, Rev. Mod. Phys 46 815 (1974), Rev. Mod. Phys 49 41 (1977). e + + e e + + e + γ adapted event generator from CMD 3 A.B.Arbuzov, G.V.Fedotovich, F.V.Ignatov, E.A.Kuraev, A.L.Sibidanov, BINP preprint 004-70 3 e + + e γ + γ e + + e γ + γ + γ event generator based on an aproach from: F. A. Berends and R. Kleiss, Distributions for electron-positron annihilation into two and three photons, Nucl. Phys. B186 (1981) 4 e + + e γ + A root class TFoam, dif. cross section [ ] dσ dy ε πr 0 (1+µ) yγ + 1 (y+µ) y derived from P. Fayet, Phys.Rev. D 75 (007) 115017, Eq.55 I.Rachek dark photon at VEPP-3 June 18, 015 1

Identification of background events more than one γ-quantum in calorimeter a symmetrical (around θ CM = 90 ) calorimeter acceptance is required then events of -photon annihilation (and partially of 3-photon one) can be identified veto-counter for positrons bremsstrahlung is partially rejected rejection efficiency depends on configuration of veto-counter sandwich e + γ beam w 80000 70000 60000 50000 40000 30000 0000 000 Veto efficiency=43.% Entries 987767 γ 0 0 50 0 150 00 50 300 350 400 450 500 E, MeV all E sand >0.5 MeV ɛ = 43% f =.4 MHz p0 Entries 49998 e + scintillator γ beam 4000 3500 3000 500 000 1500 00 500 Veto efficiency=79.5% γ 0 0 50 0 150 00 50 300 350 400 450 500 E, MeV all E sand >0.5 MeV ɛ = 80% f = 17 MHz I.Rachek dark photon at VEPP-3 June 18, 015 13

Secondary sources of background events large flux of bremsstrahlung photons, emitted at small angle: miss the calorimeter, but are able to produce a shower, passing 8m of air (0.06X 0) can be dumped by a blocker: 0cm-long tungsten rod at the exit of the dipole Target Magnet positron veto counter W blocker charged veto scintillator to calorimeter h1_0 events 000 8000 6000 4000 000 Air W blocker Entries 1087 0 0 0.5 1 1.5.5 Θ γ, deg positrons that lost a small fraction of energy in the target are bent in the dipole magent and hit the vacuum chamber wall, producing showers. Install: Pb shields wherever it is possilble; vacuum pocket close to magnet exit (where there is no room for Pb-shield) guiding positrons to shielded area vacuum pocket e + γ Pb calorimeter acceptance I.Rachek dark photon at VEPP-3 June 18, 015 14

The configuration accepted for Monte Carlo simulation I.Rachek dark photon at VEPP-3 June 18, 015 15

Entries 3058 Mean 0.988 RMS 0.04718 Monte Carlo: energy and angular resolution cluster 3 3 crystals is analyzed; threshold = MeV Signal = energy depositon + noise; noise = coherent + individual noise parameters from CLEO paper [NIM A65(1988)58]: σ coh = 0.3 MeV, σ ind = 0.6 MeV Energy resolution Angular resolution measured simulated simulated E γ 3000 he Eγ=180 MeV Events 500 000 1500 FWHM=9.0% 7000 6000 5000 Eγ= 50 MeV 0 σ θ =0.091 θ γ hd Entries 15974 Mean -0.009 RMS 0.0917 500 400 Eγ=400 MeV 0 σ θ =0.059 θ γ hd Entries 7995 Mean -0.005996 RMS 0.05948 Events 4000 Events 300 00 3000 00 500 000 0 00 0 0.8 0.85 0.9 0.95 1 1.05 1.1 1.15 E cluster /E γ 1.06 0-0.5-0.4-0.3-0. -0.1 0 0.1 0. 0.3 0.4 0.5 θ θ, deg cluster γ 0-0.5-0.4-0.3-0. -0.1 0 0.1 0. 0.3 0.4 0.5 θ θ, deg cluster γ σ E /E, % E e + = 180 MeV E e + = 180 MeV E e + = 50 MeV E e + = 400 MeV energy resolution 7 6 5 4 3 measurement (CLEO) Monte Carlo 1 1.15%+1.11%/ E[GeV] 0 0 50 0 150 00 50 300 350 400 450 E γ, MeV σ θ, deg 0.1 0.1 0.08 0.06 0.04 0.0 angular resolution measurement (CLEO) Monte Carlo 0 0 50 0 150 00 50 300 350 400 450 E γ, MeV I.Rachek dark photon at VEPP-3 June 18, 015 16

Monte Carlo: missing mass reconstruction Data analysis is aimed at selecting events with a single cluster in the calorimeter and searching for a peak in the missing mass distribution Results for 4 values of A -boson mass: m miss =5,,15,0 MeV Missing Mass events 5 4 3 = 5 MeV M A σ miss =1.9 MeV M A =0 MeV σ miss =0. MeV M A =15 MeV σ miss =0.5 MeV M A = MeV σ miss =1.0 MeV Entries 199575 48540 σ miss, MeV.5 1.5 1 missing mass resolution Constant 1.93 ± 0.05354 Slope -0.1343 ± 0.00735 0.5 1 0 4 6 8 1 14 16 18 0 M missing, MeV 0 4 6 8 1 14 16 18 0 M miss, MeV resolution is fitted by a function: σ miss (M A )= 3.6 e 0.13 M A [MeV] I.Rachek dark photon at VEPP-3 June 18, 015 17

9 7 4 Event selection: Monte Carlo: missing mass distributions E cluster > 5 MeV; 1.5 < θ cluster < 4.5 ; N cluster == 1; veto on signal in positron sandwich; veot on charged particle in the calorimeter aperture; events 5 4 3 M A = 5 MeV, veto on nd cluster all events background only events 5 4 3 M A = MeV, veto on nd cluster all events background only set: ε = 0.1 Cross sections, mbarn e + pγ 1.0 e + e γ 7.7 γγ 1.4 γγγ 0.7 5 0 4 6 8 1 14 16 18 0 M missing, MeV M A =15 MeV, veto on nd cluster all events background only 5 0 4 6 8 1 14 16 18 0 M missing, MeV M A =0 MeV, veto on nd cluster all events background only events 8 e + pγ e + e γ events: generated passed all cuts γγ 4 4 6 γγγ γa' events 3 events 3 5 3 0 1 3 4 5 6 reaction identifier 0 4 6 8 1 14 16 18 0 M missing, MeV 0 4 6 8 1 14 16 18 0 M missing, MeV I.Rachek dark photon at VEPP-3 June 18, 015 18

search conditions Beam energy E e + = 500 MeV luminosity L = 33 cm s 1 beam current 30 ma + target thickness 5 15 at/cm Run time T = 7 seconds half-year with 65% time utilization width of search window: ±σ mis Monte Carlo: search sensitivity A decays to e + e MC results M A M miss window ε MeV MeV (95% CL) 5 ±3.8 9.5 8 ±.0 8.5 8 15 ±1.0 5.4 8 0 ±0.4 3.0 8 VEPP-3 I.Rachek dark photon at VEPP-3 June 18, 015 19

Search sensitivity: decay mode-independent search of A Invisible decay of A ε 4 Existing constraints 5 6 a e DAΦNE A' is excluded a µ A' is 'welcome' a µ BNL (K πa') DarkLight BaBar decay mode-independent: muon (g µ ) electron (g e ) invisible: BaBar Υ(1S) γa BNL: K πa 7 8 VEPP-3 CESR 1 1 m A' (GeV) Proposed measurements L duration, s VEPP-3: 33, 7 CESR: 34, 7 DAΦNE: 8, 7 DarkLight 6 35 6 I.Rachek dark photon at VEPP-3 June 18, 015 0

Conclusion A decay mode independent search for a dark photon is effective in a setup with an intense positron beam and an internal hydrogen gas target. Crystals from the CLEO endcap EM-calorimeter would be a good choice for the photon-detector. If the proposal is accepted the measurement at the ByPass at VEPP-3 can be prepared and performed in 3-4 years. Budker Institute has a good opportunity to contribute to the worldwide hunt for a dark photon. D3 CsI calorimeter Q6 distance = 8 m Q5 Q4 4.5 Q3 D Target Q D1: 1.0 D: 13.4 D3: 19.6 L/L = 0.5% Q1 D1 V kg/cm Q1: 0.86 Q: 0.45 Q3: 0.57 Q4: 0.54 Q5: 0.19 Q6: 0.8 e+ ε 4 5 6 7 a e VEPP-3 DAΦNE a µ A' is excluded a µ A' is 'welcome' BaBar BNL (K πa') DarkLight CESR 3B8A 1B1B 8 length of bypassed segment of VEPP 3 = 1830 cm 1 1 m A' (GeV) I.Rachek dark photon at VEPP-3 June 18, 015 1

Conclusion A decay mode independent search for a dark photon is effective in a setup with an intense positron beam and an internal hydrogen gas target. Crystals from the CLEO endcap EM-calorimeter would be a good choice for the photon-detector. If the proposal is accepted the measurement at the ByPass at VEPP-3 can be prepared and performed in 3-4 years. Budker Institute has a good opportunity to contribute to the worldwide hunt for a dark photon. D3 CsI calorimeter Q6 distance = 8 m Q5 THANK YOU! Q4 4.5 Q3 D Target Q Q1 D1: 1.0 D: 13.4 D3: 19.6 L/L = 0.5% D1 V kg/cm Q1: 0.86 Q: 0.45 Q3: 0.57 Q4: 0.54 Q5: 0.19 Q6: 0.8 e+ ε 4 5 6 7 a e VEPP-3 DAΦNE a µ A' is excluded a µ BNL (K πa') DarkLight CESR A' is 'welcome' BaBar 3B8A 1B1B 8 length of bypassed segment of VEPP 3 = 1830 cm 1 1 m A' (GeV) I.Rachek dark photon at VEPP-3 June 18, 015 1