Th mchanisms of antihydrogn formation E.Lodi Rizzini, L.Vnturlli, N.Zurlo, (ATHENA Collaboration) Prsntd by L.Vnturlli Brscia Univrsity & INFN (Italy) 2.5 cm 10 4 pbars 10 8 + 3T 1
Antihydrogn Exprimnts Hot Hbars: rlativistic - 1996: PS210 @ CERN (First 10 antihydrogn) - 1997: E862 @ Frmilab (othr 100 antiatoms) Cold Hbars: 10 2 K - 2002 Sptmbr: Athna @ CERN (First 50000 cold Hbars) - 2002 Novmbr: Atrap @ CERN (othr cold antiatoms) -Now @ CERN-AD, 3 Collaborations ar working towards antihydrogn spctroscopy: Atrap (AD-2), Asacusa (AD-3), Alpha (AD-5) Thy nd: nough # of Hbars vry cold Hbars Hbars in low n stats magntic trapping s Csar s talk 2
Antihydrogn production mchanisms: Rfrnc procdur to produc Hbars is th ovrlapping of pbars and + Th xpctd Hbar formation mchanisms ar: p + + H + γ (1) Radiativ rcombination (2-BR) p + + + + + H + (2) 3-body rcombination (3-BR) Hbar productions rats of (1) and (2) dpnd diffrntly on th + plasma paramtrs (+ plasma dnsity, tmpratur, ) Hbars producd in (1) and (2) hav diffrnt charactristics (binding nrgy, ) Th knowldg of (1) and (2) is crucial for th bst optimization of th cration of Hbars for spctroscopy Not yt solvd 3
Faturs of th Hbar production mchanisms: Naiv xpctations Expctd rat (in Athna) (*) som 10 Hz High (>>10Hz) (*) Assuming complt ovrlapping of 10 4 pbars with + plasma (n + =2 10 8 cm -3 @ 15K) 4
Atrap What w xprimntally know Notxhaustiv Notxhaustiv dtctd Hbars with n about 60 2-BR Athna Maximum Hbar production rat (pr cycl) = 440 +- 40 Hz 2-BR 15 K no incras in Hbar formation from lasr stimulation in n=11 2-BR Rsults from tmpratur dpndnc (2 diffrnt xprimnts) 3-BR 5
Rsults from tmpratur dpndnc (1st xprimnt) Athna M. Amortti t al., PLB (2004) Hbar production dcrass whn tmpratur incrass (still prsnt @ room tmpratur) No powr law rproducs th data. Howvr bst fit: No simpl mixing of 2-BR and 3-BR T Proportional to th total numbr of dtctd hbar in a mixing cycl 0.7± 0.2 3-BR Opning angl xcss 15 K 175 K 500 K 3500 K Tot. numbr of triggrs in 180 sc Pak triggr rat 6
Rsults from tmpratur dpndnc (2nd xprimnt) Athna M.C.Fujiwara t al., PRL in prss bst fit T 1.1± 0.4 In agrmnt with th 1st xp. rsult 3-BR T 1.1± 0.4 T 9 2 Priodic hating of + plasma Tim + tmpratur 7
N.B. Th rsults appar to b in contradiction Th dtctd Hbars ar th ons that surviv to th r-ionization (du to + and trap potntials) 3-body Mont Carlo for ATHENA F.Robichaux PRA 2004 Doubling T th # of dtctd hbars dcrass of a factor 2.5 only (instad of 20 with 9 2 ) T Diffrnt rsults btwn MC and naiv xpctations sinc: pbars rpaditly cross + plasma; Hbar formation is a multistp procss; rionization. 8
What about th + dnsity dpndnc? A tmptativ alrady don (s Int.Nucl.Confrnc 2004 Gotborg) but th rsults dpnd on th radial distribution of th pbars cloud Athna NOW nw analysis -> 9
ATHENA Collaboration @ CERN-AD Workd @ Crn-AD(Antiproton Dclrator) during 2000-2004 Univ. of Aarhus, Dnmark Univ. of Brscia, Italy CERN, Gnva, Suiss Univ. of Gnova, Italy Univ. of Pavia, Italy Univ. of Rio, Brazil Univ. of Swans, Wals (UK) Univ. of Tokyo, Japan ~ 40 mmbrs Univ. of Zurich, Suiss INFN, Italy Rikn, Japan 10
Antiproton Dclrator (AD) at CERN 0 5 10m. Scal AD PROJECT ATRAP ASACUSA DEM A T H E AN Antiproton production, captur, dclration, cooling 100 MV/c (5.3 MV) Pulsdxtraction 2-4 x 10^7 antiprotons pr puls of 100 ns lngth 1 puls / 85 sconds Antiprotonic atom/ion formation and spctroscopy; Antihydrogn formation and spctroscopy; Atomic collisions; Nuclar collisions In opration 2000-2004 and rstartd in 2006 AD is th only low-nrgy p sourc ATHENA xprimntal ara 11
Main goal: production & studing of cold H Th ATHENA Exprimnt lttr to Natur Natur 419, 456-459 (2002) Antiproton Accumulation & Mixing with positrons 3 T suprconducting solnoid Cryostat Positron Accumulator + Na-22 Sourc Antiproton Captur Trap Dtctor Mixing Trap 0 1 m CsI crystals Si strip dtctors Antihydrogn Dtctor 0 10 cm 12
π How ATHENA workd 2.5 cm Si strips 10 4 pbars γ 10 8 + H π 10 4 p & 10 8 + ar mixd in Pnning trap H form and fly away γ π 3T H annihilat on trap wall CsI crystals Offlin slction of H annihilation: Coincidnc in spac & tim (<5μs) of: p annihilation (chargd pion vrtx) + annihilation (2 back-to-back 511 kv γ) 13
Nw Data Analysis Prliminary Prliminary Prvious data analyss basd on Cold Mixing Data (CM) (standard conditions for H production) Nw data analysis uss mainly Elctron through Positron Data (ETP) Hot spot p annihilations vrtics Hot spot p annihilations vrtics H H x y x y Protonium N.B. Aftr 2D dconvolution alghoritm Protonium N.B. Aftr 2D dconvolution alghoritm p p Som difficultis to disantangl signal (Hbar) from background (protonium, Hot Spots) Lss background (no protonium) ETP: continuos mixing and + stacking mix + and antiprotons and cool nw antiprotons at th sam tim stack 10 + shots in th mixing trap 14
Vrtx tim distributions ETP Data Prliminary Prliminary Slctd vnts Imix=2 Diffrnt slops Z-vrtx (cm) Tim of annihilation vrtics (ms) why diffrnt slops in diffrnt tim intrvals? do th diffrnt slops corrspond to diffrnt Hbar production mchanisms (2-BR, 3-BR)? 15
Data analysis 1/2 Prliminary Prliminary Imix=2 dt dt ( N H ) BR ( N H ) 3 BR N = + dt H 2 dt 2 int ( N ) ε n + N Δt H 3BR 3BR dt int ( N ) ε n + N Δt H 2BR 2BR p p 3-body 2-body N dt H in Δt 1 =(1,5)s 2 ( Δt ) = c n + + c n + 1 Tim of annihilation vrtics (ms) 1 3-BR W call 2 2-BR N R N dt H dt H N dt H in Δt 2 =(30,60)s 2 ( Δt ) = c n + + c n + 2 2 ( Δt ) c1 n + + c2 n + 1 = 2 ( Δt ) c n + + c n + 2 2 If c n + >> c + (i.. if 2-BR is dominant in ΔT 2 ) thn 4 3 n 3 3 3-BR 4 4 2-BR dt N H = ε = = + dtctd Hbars # in Δt dtction fficincy n Positrons #/cm 3 int N p assumd to b constant in Δt = # of pbars intracting with positrons in Δt c R + + c 1 n 4 c c 2 4 16
Data analysis 2/2 Prliminary Prliminary Vrification of R a n + b + by fitting it to th data ETP Imix=2 ETP Imix=6 0 5 10 8 + dnsity (#cm -3 ) 0 5 10 8 + dnsity (#cm -3 ) Also with Cold Mix Data b a ETP imix=2 ETP imix=6 0.4 + 10% 0.5 + 10% 1.8 E-9 + 20% 1.6 E-9 + 20% Similar valus Cold Mix 0.3 + 10% 1.0 E-9 + 20% 0 5 10 8 + dnsity (#cm -3 ) at last for R n + n + < 2 10 8 cm 3 17
Data analysis 2/2 Prliminary Prliminary Vrification of R a n + b + by fitting it to th data ETP Imix=2 ETP Imix=6 0 5 10 8 + dnsity (#cm -3 ) 0 5 10 8 + dnsity (#cm -3 ) Also with Cold Mix Data b a N.B. hr + radius is is smallr ETP imix=2 ETP imix=6 Cold Mix 0.4 + 10% 0.5 + 10% 0.3 + 10% 1.8 E-9 + 20% 1.6 E-9 + 20% 1.0 E-9 + 20% Similar valus 0 5 10 8 + dnsity (#cm -3 ) at last for R n + n + < 2 10 8 cm 3 18
Rats Prliminary Prliminary Th masurd R (ratio) valus agr with th hypothsis that: Athna @ arly tims (first sconds) 3-BR dominats Imix=2 @ lat tims (> tns sconds) 2-BR dominats Tim of annihilation vrtics (ms) Th masurd rats: What about th rats? Man valu, not th pak To b incrasd by 2 du to th dtctor fficincy Rats @ lat tims ar consistnt with 2-BR xpctations 19
@ arly tims (Δt 1 ) (Possibl) xplanation Prliminary Prliminary p + Many pbars wll insid th + plasma @ lat tims (Δt 2 ) Rlvant # of antihydrogns producd by 3-BR xprinc lot # of collisions and will b nough boundd to b dtctd N dt dt dt Larg ( H ) 3BR ( N H ) BR >> ( N H ) 3 2BR F.Robichaux PRA 2004 p + Only fw pbars wll insid th + plasma (most of pbars ar on th dg) Antihydrogns producd by 3-BR asily r-ioniz (not dtctd) ( N dt H ) 3BR small dt dt ( N H ) BR << ( N H ) 3 2BR Th radial volution of pbars can b du to: cntrifugal sparation btwn pbars and + du to th diffrnt masss but in ATHENA it is xpctd to b slow (sparation tim = 1000 s) xhaustion of th cntral pbars (thy hav bn usd ) 20
Anothr topic Hot mixing data Prliminary Prliminary Hbars producd @room tmpratur Ar antihydrogn producd @ 10 000 K? 10000 K Only Protonium? 10000 K cos γγ distribution Tim of annihilation vrtics (ms) 10000 K Tim of annihilation vrtics (ms) masurd rat is 2 Hz To b compard with 0.5 Hz from 2-BR xpctation 21
Nxt analysis improvmnt R (ratio) vs dnsity with othr data sampls 2 T R (ratio) vs tmpratur ( R = 2?) 3 T 9 Mont Carlo simulations Natur of th Hot Spot (ar thy consqunc of th r-ionization?) 22
Conclusions Aftr th first cold Hbars dtction, many fforts to undrstand th antihydrogn formation mchanisms hav bn don Prliminary analysis of th tim volution of antihydrogn annihilations vs + plasma dnsity and rats stimations suggst that in Athna conditions: 3-body rcombination dominats @ arly-tims (first sconds) Radiativ rcombintion dominats @ lat-tims (> tns sconds) Mor confirmations can com from th dvlopmnt of th analysis (Athna has a lot of usful data!) Information on th antihydrogn production mchanisms will b usful for th goal of prcision spctroscopy of antihydrogn 23