The WASA Collaboration - past, present, future -

Transcription

1 Magnus Wolke The WASA Collaboration - past, present, future - WASA at GSI/FAIR GSI, Nov 27, 2017

2 Magnus Wolke The WASA Collaboration - past, present, future - The past: from the LoI to CELSIUS, from CELSIUS to COSY The present: analysis of WASA-at-COSY data The future: WASA at GSI/FAIR

3 Wide Angle Shower Apparatus a little bit of history

4 Wide Angle Shower Apparatus a little bit of history from: Hans Calen, TSL symposium, Nov 2015 Mar 1984 Oct 1987 Letter of intent for a research program on elementary particle physics experiments at CELSIUS Wide Angle Shower Apparatus Proposal for a detector at CELSIUS from the WASA collaboration Jun Apr 1998 WASA/PROMICE experiments η meson production in proton-nucleon collisions

5 Wide Angle Shower Apparatus a little bit of history from: Hans Calen, TSL symposium, Nov 2015 Mar 1984 Oct 1987 Jun Apr 1998 Letter of intent for a research program on elementary particle physics experiments at CELSIUS Wide Angle Shower Apparatus Proposal for a detector at CELSIUS from the WASA collaboration WASA/PROMICE experiments 1998 CELSIUS/WASA commissioning proposal Jun Jun 2005 Oct 2004 CELSIUS/WASA experiments WASA-at-COSY proposal Jun Aug 2006 Move of WASA from to Apr Jun 2014 WASA-at-COSY experiments

6 COSY, March 2006 CELSIUS, October 2005 COSY, Jun 12, 2006 CELSIUS, Aug 29, 2005 WASA to COSY CELSIUS, June 2005 COSY, Aug 8, 2006 Picture Gallery COSY, October 2005 COSY, October 2005

7 Wide Angle Shower Apparatus a little bit of history from: Hans Calen, TSL symposium, Nov 2015 Mar 1984 Oct 1987 Jun Apr 1998 Letter of intent for a research program on elementary particle physics experiments at CELSIUS Wide Angle Shower Apparatus Proposal for a detector at CELSIUS from the WASA collaboration WASA/PROMICE experiments 1998 CELSIUS/WASA commissioning proposal Jun Jun 2005 Oct 2004 CELSIUS/WASA experiments WASA-at-COSY proposal Jun Aug 2006 Move of WASA from to Apr Jun 2014 WASA-at-COSY experiments

8 ABC first observation Lawrence Radiation Laboratory 184 inch cyclotron (p), d 2 gas target (Abashian, Booth, Crowe) A.Abashian, N.E.Booth, K.M.Crowe, Phys.Rev.Lett. 5 (1960) 258 pd 3 HeX, θ He = 11.5 at the time of PRL 5 (1960): "The data are inconsistent with the relativistically invariant phase space assumed. [...] Plausible explanations [...] are the existence of a new neutral particle or a resonant π π system."

9 Discovery of d * (2380) Why was it discovered by WASA-at-COSY and not by CELSIUS/WASA?

10 The ABC Gallery CELSIUS/WASA measurements pn dπ 0 π 0 1.0GeV pd 3 Heπ 0 π 0 0.9GeV data phase space dd 4 Heπ 0 π 0 1.0GeV data phase space data phase space PRL 2 (2009) PLB 637 (2006) 223 NPA 825 (2009) 71 WASA-at-COSY new exclusive measurements over the full region

11 Discovery of d * (2380) CELSIUS/WASA preliminary results from: M.Bashkanov, H.Clement, COSY proposal 183 (2007) CELSIUS/WASA prel DESY bubble chamber JINR bubble chamber without resonance with resonance

12 Lorentzian shaped energy distribution t-channel N * (1440) syst. error 4 times narrower compared with, peak 80MeV below 2m 2 orders of magnitude larger statistics compared to CELSIUS/WASA!... But how? Discovery of d * (2380) CELSIUS/WASA preliminary results from: M.Bashkanov, H.Clement, COSY proposal 183 (2007) CELSIUS/WASA prel DESY bubble chamber JINR bubble chamber without resonance with resonance σ [mb] data T p 1.0GeV 1.2GeV 1.4GeV WASA-at-COSY results P.Adlarson et al., PRL 6 (2011) pn dπ 0 dπ π 0 π d ππ threshold s [GeV]

13 2 orders of magnitude larger statistics compared to CELSIUS/WASA by... From CELSIUS to COSY: the d * (2380) example CELSIUS/WASA preliminary results σ [mb] WASA-at-COSY results pn dπ 0 π d ππ threshold s [GeV] strategic investments to remove bottlenecks: complete redesign of DAQ system improved pellet target reliability

14 First WASA-at-COSY Run April 2007: η 3π 0 Dalitz Plot GAMS-2000 ZPC 25 (1984) 225 Crystal Barrel PLB 417 (1998) 193 BNL E852 hep-ex/ SND JETPL 73 (2001) 451 Crystal Ball PRL 87 (2001) KLOE prelim. hep-ex/ (Moriond 2005) KLOE prelim [hep-ex] CELSIUS/WASA PRC 76 (2007) WASA-at-COSY submitted for publication Crystal Ball hep-ex/ <T π > - T π Γ A(z) 2 = c 0 (1+2αz) z = (ρ/ρ max ) 2 = 6 3 i=1 ( ) 2 E i - m π /3 m η - m π First step to compare dynamics with ChPT prediction: slope parameter α four days of data taking events combined CELSIUS/WASA statistics events (T π1 - T π2 )/ 3 A 2 /c radial density distribution reanalysis with M η = MeV/c PL B 677 (2009) z α note: historic slide covers only results until end of 2008!

15 significant increase in user community and collaboration size WASA - at CELSIUS and at COSY first CELSIUS/WASA publication first WASA-at-COSY publication

16 147 members 27 institutions Cracow Katowice Warsaw Lodz, Warsaw Dubna Moscow Novosibirsk WASA-at-COSY Collaboration (2014) Sofia Lanzhou Spokesperson: M.Wolke (Uppsala) Deputy: P.Moskal (Cracow) Mumbai Indore KEK Bochum Bonn Erlangen Jülich Münster Tübingen Physics Coordinator: A.Kupsc (Uppsala) Technical Coordinators: H.Calen (Uppsala) F.Goldenbaum (Jülich) IT Coordinator: V.Hejny (Jülich) Uppsala

17 Magnus Wolke The WASA Collaboration - past, present, future - The past: from the LoI to CELSIUS, from CELSIUS to COSY The present: analysis of WASA-at-COSY data The future: WASA at GSI/FAIR

18 heaviest of octet Goldstone bosons many open decay channels mass and all interactions vanish in the chiral limit basis for effective field theory approach (ChPT) What is special about the η meson? eigenstate of P, C, CP, and G, I G (J PC ) = 0 + (0 + ) first order strong and electromagnetic decays forbidden laboratory to study (non-)conservation of these discrete symmetries

19 η decays into neutrals with an odd number of photons KLOE PLB 591 (04) 49 Tests of C symmetry in rare η decays simplest case: η 3γ η γ + (γγ) J=0 forbidden for real γ (0 0 transition) η γ + (γγ) J=1 forbidden by Bose symmetry each (γγ) pair hase to have at least J=2 BR(η 3γ) η π 0 γ 0 0 transition BR(η π 0 γ) 9 5 η π 0 π 0 γ, η 3π 0 γ,... η decays into neutrals with an odd number of l + l Crystal Ball PRC 72 (05) η π 0 e + e -

20 Tests of C symmetry in rare η decays η decays into neutrals with an odd number of l + l Standard Model C conserving contribution: η π 0 γ γ e + e η π 0 ρ 0 γ e + e BR(η π 0 e + e ) T.P.Cheng, PR 162 (67) 1734 C invariance violating process: experiment: BR(η π 0 e + e ) M.R.Jane et al., PLB 59 (75) 99 PDG: BR(η π 0 e + e ) 4.0 5

21 preliminary preliminary η π 0 e + e with WASA-at-COSY F.S.Bergmann, PhD thesis, WWU Münster (2017) pd 3 HeX, after preselection missing mass m X invariant mass (e + e - γγ) preliminary invariant mass (γγ) invariant mass (e + e - ) preliminary remaining background: η π + π π 0, direct π + π π 0, ππ

22 preliminary η π 0 e + e with WASA-at-COSY F.S.Bergmann, PhD thesis, WWU Münster (2017) pd 3 HeX, signal selection signal selection cuts missing mass m X invariant mass (γγ) χ 2 e + e - γγ kinematic fit invariant mass (e + e - γγ) invariant mass (e + e - ) e + e - identification preliminary 3 events left after selection criteria 2 events expected (pd 3 Heπ + π π 0 ) preliminary result: BR(η π 0 e + e ) < 7.5 (9.5) 6 for VMD (phase space) decay of signal channel factor 6 (5) below present upper limit publication drafted

23 Magnus Wolke The WASA Collaboration - past, present, future - The past: from the LoI to CELSIUS, from CELSIUS to COSY The present: analysis of WASA-at-COSY data The future: WASA at GSI/FAIR

24 WASA at GSI/FAIR With the end of the experimental programme at COSY it has been the wish of the owners that the detector shall be used for excellent physics in future WASA FD in use at COSY WASA CD to GSI/FAIR: unique opportunity Key ingredients: strong physics case investment against bottlenecks user community, manpower infrastructure This workshop is the place to take important steps in these directions

25 The old CELSIUS/WASA DAQ Help Page... Even if some people may be tempted to think so, The WASA experiment Målning av Nils Stödberg och Jozef Zlomanczuk när VASA kantrar has (almost) nothing to do with what you see on the picture!

26 The WASA Facility an internal 4π detector H.-H.Adam et al. (proposal), nucl-ex/04138 www2.fz-juelich.de/ikp/wasa Solenoid Pellet line Tracking Detectors TOF Detector COSY beam Thin Plastic Scintillators EM Calorimeter 50 cm Range Hodoscope Central Detector...light meson decay products Superconducting Solenoid Plastic Scintillator Barrel Forward Detector...scattered projectiles and charged recoil particles Plastic Scintillators Forward Straw Tracker Straw Chamber Scintillator Electromagnetic Calorimeter

27 droplet stream before vacuum injection Pellet Target Typical Target Values: tdc hits per 5µs Forward Detector single rate: 8000/s pellet rate Pellet diameter 20-30µm 4 Pellet frequency Pellet velocity Effective thickness 5-12kHz 60-80m/s > 15 atoms/cm t[µs] Goal: always one "pellet in beam"

28 tdc hits per 5µs Pellet rates 12 8 Forward Detector single rate: 8000/s pellet rate average time "pellet in beam" 80-0µs t[µs] Goal for target operation: always one "pellet in beam" Higher droplet frequency Uniform time distribution Future developments: Pellet Tracking Improved vertex reconstruction Time and velocity distribution MC studies of pellet-beam interaction as preparation for PANDA

29 η tagging with WASA-at-COSY pd 3 Heη pp ppη lower cross section unbiased trigger 3 7 η mesons tagged precision studies for common decays larger cross section decay selective trigger required ~5 8 η mesons tagged large statistics studies, rare decays

30 η tagging with WASA-at-COSY pd 3 Heη pp ppη unbiased 3 He reconstructed pp reconstructed kin fit η π + π π 0 lower cross section unbiased trigger 3 7 η mesons tagged precision studies for common decays larger cross section decay selective trigger required ~5 8 η mesons tagged large statistics studies, rare decays

31 P.Adlarson et al., PLB 726 (2013) 187 Search π 0 γu with WASA Entries/(1 MeV) considerable background from γ conversion IM(e e ) [GeV] data MC sum π 0 e + e γ π 0 γγ accidentals

32 Search π 0 γu with WASA P.Adlarson et al., PLB 726 (2013) 187 Entries/(1 MeV) IM(e e ) [GeV] data π 0 e + e γ accidentals MC sum π 0 γγ considerable background from γ conversion Events/(1 mm) R [mm] but: vertex of conversion decays is not at the target point

33 target and conversion decays from reconstructed vertices Search π 0 γu with WASA P.Adlarson et al., PLB 726 (2013) 187 Entries/(1 MeV) considerable background from γ conversion IM(e e ) [GeV] data MC sum π 0 e + e γ π 0 γγ accidentals

34 Search π 0 γu with WASA P.Adlarson et al., PLB 726 (2013) 187 Entries/(1 MeV) IM(e e ) [GeV] data π 0 e + e γ accidentals MC sum π 0 γγ considerable background from γ conversion Events/(1 mm) Entries/(1 MeV) IM(e e ) [GeV] R [mm] but: vertex of conversion decays is not at the target point almost background free π 0 e + e γ events (~ 500k)

35 P.Adlarson et al., PLB 726 (2013) 187 SINDRUM PRL 68 (1992) 3845 WASA-at-COSY PLB 726 (2013) 187 KLOE PLB 720 (2013) 111 e g-2 µ g-2 PR D 86 (2012) preferred µ g-2 ±2σ Dark photon mixing parameter ε Γ(π 0 γu) Γ(π 0 γγ) -4 = 2ε 2 F(M 2 U) 2 (1 - ) 2 M 2 U M 2 M.Reece, L.-T.Wang, JHEP 0907 (2009) 051 UL 90% CL [MeV] M U