Low mass dielectrons in pp, p-pb and Pb-Pb collisions measured by the ALICE experiment

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Mervin Copeland
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Clustr Univrs on bhalf of th ALICE Collaboration 56 th

1 Low mass dilctrons in, Pb and PbPb collisions masurd by th ALICE xrimnt Ivan Vorobyv nis Univrsität Münn, Excllnc Clustr Univrs on bhalf of th ALICE Collaboration 56 th Intrnational Wintr Mting on Nuclar Physics 4..8, Bormio, Italy

2 A Larg Ion Collidr Exrimnt Low mass dilctron studis A. Drs, Nucl. Phys. A83 (9) 435 Producd during all stags of collisions with ngligibl finalstat intractions Highnrgy havyion collisions: Inmdium modifications of vctor msons hrmal radiation from QGP Enrgy loss of corrlatd havy flavour quarks Protonion collisions: Cold nuclar mattr ffcts Protonroton collisions: Mdiumfr rfrnc Havy flavour crosssctions Nw hnomna in highmultilicity vnts? MADAI Collaboration. fm/c Initial stat fm/c Prquilibruim fm/c QGP and xansion Hadronization Hadronic has and frzout LM in ALICE I. Vorobyv Bormio 8 t

3 A Larg Ion Collidr Exrimnt h ALICE Exrimnt at CERN LHC Innr racking Systm racking, vrtx, PID (de/dx) im Projction Chambr racking, PID (de/dx) im Of Flight dtctor PID (OF masurmnt) LM in ALICE I. Vorobyv Bormio 8 3

4 A Larg Ion Collidr Exrimnt h ALICE Exrimnt at CERN LHC Innr racking Systm racking, vrtx, PID (de/dx) im Projction Chambr racking, PID (de/dx) im Of Flight dtctor PID (OF masurmnt) LM in ALICE I. Vorobyv Bormio 8 3

5 A Larg Ion Collidr Exrimnt h ALICE Exrimnt at CERN LHC Innr racking Systm racking, vrtx, PID (de/dx) im Projction Chambr racking, PID (de/dx) im Of Flight dtctor PID (OF masurmnt) V scintillators riggr, cntrality stimation In this talk: Collision systm N of vnts riggrs at s = 7 V ~ 37 M min. bias at s = 3 V ~4 M + 48 M min. bias + high mult. Pb at snn = 5. V ~5 M min. bias PbPb at snn =.76 V ~ M % cntrality LM in ALICE I. Vorobyv Bormio 8 3

6 ) A Larg Ion Collidr Exrimnt s = 7 V: invariant mass sctrum Cocktail of known hadronic sourcs: Rsonanc and Dalitz dcays: π, η, ϕ and J/ψ masurmnts, othr sourcs (η, ρ, ω) from m scaling Havyflavour corrlatd smiltonic dcays: masurd K cc and bb cross sctions, sha from PYHIA simulations D l + Dtctor tanc and rsolution ffcts νl c c D K + l νl Data in agrmnt with cocktail calculations within uncrtaintis Finalisation of rsults is ongoing (havyflavour cross sction, dirct hotons, air DCA analysis) (mb/gv/c dσ dm cocktail sum, s=7 V π γ η γ >. GV/c η γ η <.8 φ & φ η 3 ω & ω π ρ J/ψ & J/ψ γ cc (PYHIA, 8.5 mb) Data/Cocktail ALI PREL m (GV/c ) LM in ALICE I. Vorobyv Bormio 8 4

7 A Larg Ion Collidr Exrimnt s = 7 V: air DCA analysis Ida: sarat romt and nonromt contributions using air vrtx osition (nonromt) Obsrvabl: DCA = DCA + DCA Obtain DCA tmlats from MC, normalis to cocktail and comar with data Good dscrition of data in all mass rgions Lowmass rgion: romt and nonromt sourcs, can sarat thm Intrmdiatmass rgion: nonromt sourcs, saration of cc and bb (/σ) dn ddca N v norm. Pull ALICE Prliminary s = 7 V data cocktail sum light flavour + (X) (MC) + cc (MC) bb + (MC) >.4 GV/c, η <.8, < 5 GV/c,. < m <. GV/c ALI PREL 5974 norm. Pull DCA (σ) ALI PREL 5978 ALICE Prliminary s = 7 V data cocktail sum light flavour + (X) (MC) cc + (MC) bb + (MC) J/ψ + (MC) >.4 GV/c, η <.8, < 5 GV/c,. < m <.7 GV/c DCA (σ) LM in ALICE I. Vorobyv Bormio 8 5

8 A Larg Ion Collidr Exrimnt Nw hnomna in high multilicity vnts? Production / dstruction of ρ mson, dirct hotons, on havy flavour? Ida: roduc a ratio of (uncorrctd) dilctron sctra: N (HM ) / N (HM ) N (MB) / N (MB) Min. bias triggrd data: coincidnc of VA & VC signals High mult. triggrd data: coincidnc of VA & VC signals, thrshold on VM N (HM) / N (MB) = 4.36 (masurd at η ~ ) Naiv xctation (for light flavour): signal ~ N ) ((GV/c ) dn/dm /N v ALIPERF ALICE Prliminary s = 3 V ϕ V MB L int >. GV/c, η <.8 < for m <. GV/c HM.8 nb, L int 83 nb Minimum bias HM (.% VM) 7 8 ALIPREL m (GV/c ) LM in ALICE I. Vorobyv Bormio 8 6

9 A Larg Ion Collidr Exrimnt s = 3 V: cocktail calculations vs multilicity Lightflavour dcays: Prliminary ALICE π ± masurmnts as inut, m scaling for othr hadrons Modification of sctrum in vnts with highr argd articl multilicitis Ratio to INEL> ALICE, Phys. Ltt. B 753, 39 (6) ALI PUB 54 ALICE,, Data, N N N N = 6.7, N = 9.4 ( < N N N MC, slction on N s = 3 V, argd articls, η <.8 < N EPOS LHC, N =. PYHIA 8 (Monash3), N >.5 GV/c) =. (GV/c) LM in ALICE I. Vorobyv Bormio 8 7

10 A Larg Ion Collidr Exrimnt s = 3 V: cocktail calculations vs multilicity Lightflavour dcays: Prliminary ALICE π ± masurmnts as inut, m scaling for othr hadrons Modification of sctrum in vnts with highr argd articl multilicitis Havyflavour contribution: PYHIA simulation of on arm roduction Multilicity dndnt roduction of D mson in at s = 7 V Rough xctation: N cc! (HM)/hN (HM)i N cc! (MB)/hN (MB)i.5 N/dyd ) / d N/dyd (d ALICE s = 7 V, y <.5 D mson, < < GV/c Ratio to INEL> ALICE, Phys. Ltt. B 753, 39 (6) ALI PUB 54 ALICE,, Data, N N N N = 6.7, N = 9.4 ( < N N N MC, slction on N s = 3 V, argd articls, η <.8 < N EPOS LHC, N =. PYHIA 8 (Monash3), N ALICE, JHEP 9, 48 (5) N/dyd ) / d N/dyd (d >.5 GV/c) =. (GV/c) ALICE s = 7 V, y <.5 D mson, < <4 GV/c + D mson, < <4 GV/c + D* mson, < <4 GV/c +6%/3% normalization unc. not shown ± 6% unc. on (dn /dη) / dn /dη not shown +6%/3% normalization unc. not shown ± 6% unc. on (dn /dη) / dn /dη not shown B fddown unc ALI PUB B fraction hyothsis: / () at low (high) multilicity (dn /dη) / dn /dη B fddown unc..4 B fraction hyothsis: / () at low (high) multilicity ALI PUB 99 (dn /dη) / dn /dη LM in ALICE I. Vorobyv Bormio 8 7

11 A Larg Ion Collidr Exrimnt s = 3 V: high multilicity data analysis Rsults ar in agrmnt with cocktail xctations Intrmdiat mass: in agrmnt with Dmson rsults at 7 V (HM) (MB) N (HM)/ N N (MB)/ N ALICE Prliminary s = 3 V >. GV/c, η <.8 N MB L int (HM) / N.8 nb HM, L int (MB) = nb data (.% VM) cocktail m (GV/c ) ALIPREL9668 LM in ALICE I. Vorobyv Bormio 8 8

12 A Larg Ion Collidr Exrimnt s = 3 V: high multilicity data analysis Rsults ar in agrmnt with cocktail xctations Intrmdiat mass: in agrmnt with Dmson rsults at 7 V Low mass: ratio > du to ang of hadron sctrum and tanc cut Analysis of mor data (x5) is ongoing (HM) N (HM)/ N (MB) N (MB)/ N ALICE Prliminary s = 3 V >. GV/c, η <.8 N MB L int (HM) / N.8 nb HM, L int (MB) = nb (.% VM) data cocktail m (GV/c ) ALIPREL9668 ALIPREL9684 LM in ALICE I. Vorobyv Bormio 8 8

13 ) A Larg Ion Collidr Exrimnt Pb snn = 5. V: invariant mass sctrum Cocktail calculations: Rsonanc and Dalitz dcays: π ± and J/ψ masurmnts, m scaling for othr hadrons Havy flavour contributions: cross sction xtraolatd from at 7 V masurmnts Data consistnt with cocktail within uncrtaintis ((GV/c ) dn /dm NSD /N vt 3 4 ALICE Prliminary Pb NSD s NN >. GV/c η <.8 = 5. V Cocktail sum with uncrtaintis π γ η γ ω and ω π φ and φ η η' γ ρ cc (<N bb (<N Pb coll Pb coll > x PYHIA MNR, σ > x PYHIA MNR, σ (Liksign subtractd) J/ψ and J/ψ γ cc bb = 6.9mb) = µb) 5 data/cocktail ALIPREL6975 m (GV/c ) LM in ALICE I. Vorobyv Bormio 8 9

14 ) A Larg Ion Collidr Exrimnt Pb snn = 5. V: diffrntial analysis Diffrntial analysis in m : Snsitiv to cc and bb cross sctions Cold nuclar mattr ffcts? ) ((GV/c) dn /d NSD /N vt 3 ALICE Prliminary Pb NSD s NN = 5. V >. GV/c.4 < m η <.8 <.75 GV/c Cocktail sum with uncrtaintis η γ ω and ω π η' γ ρ Pb cc (<N > x PYHIA MNR, σ = 6.9mb) coll cc ) ((GV/c) dn /d NSD /N vt 3 4 ALICE Prliminary Pb NSD s NN = 5. V >. GV/c.75 < m η <.8 <. GV/c Cocktail sum with uncrtaintis ω and ω π φ and φ η ρ Pb cc (<N > x PYHIA MNR, σ = 6.9mb) coll cc (Liksign subtractd) ((GV/c) dn /d NSD /N vt Cocktail sum with uncrtaintis 3 4 ALICE Prliminary Pb NSD s NN = 5. V >. GV/c. < m η <.8 < 3 GV/c Pb cc (<N > x PYHIA MNR, σ = 6.9mb) coll cc Pb bb (<N > x PYHIA MNR, σ = µb) coll bb (Liksign subtractd) J/ψ and J/ψ γ data/cocktail (GV/c) ALIPREL6973 data/cocktail (GV/c) ALIPREL69739 data/cocktail (GV/c) ALIPREL69747 x5 mor Pb data in Run : dtaild studis vs m and ar forsn LM in ALICE I. Vorobyv Bormio 8

15 A Larg Ion Collidr Exrimnt PbPb snn =.76 V: invariant mass sctrum Light flavour cocktail: π masurmnts, m scaling for othr hadrons Havy flavour cocktail: PYHIA calculations normalisd to at 7 V masurmnts, xtraolatd to.76 V and scald with Ncoll (GV/c ) dn dm N vt PbPb, s NN =.76 V Cntrality % >.4 GV/c, η <.8 ALICE Prliminary total cocktail π γ η γ η' γ ρ ω & ω φ & φ cc bb (cc) π η Data comatibl with cocktail within larg uncrtaintis Room for additional sourcs m (GV/c ) ALIPREL6 data / cocktail PbPb, s NN ALICE Prliminary =.76 V, Cntrality % >.4 GV/c, η < m ALIPREL893 LM in ALICE I. Vorobyv Bormio 8 (GV/c )

16 A Larg Ion Collidr Exrimnt PbPb snn =.76 V: invariant mass sctrum Light flavour cocktail: π masurmnts, m scaling for othr hadrons Havy flavour cocktail: PYHIA calculations normalisd to at 7 V masurmnts, xtraolatd to.76 V and scald with Ncoll Data comatibl with cocktail within larg uncrtaintis Room for additional sourcs Data comard to hadronic cocktail + QGP and HG radiation with modifid ρ and ω inmdium sctral functions [, ] Rducd snsitivity to masur thrmal radiation Run 3 data (aftr dtctor ugrad): mor rcis studis, ss to init (GV/c ) dn dm N vt Data/Cocktail ALICE Prliminary ALIPREL488 PbPb s NN =.76 V Cntrality % >.4 GV/c, η <.8 data hadronic cocktail w/o vacuum ρ hadronic cocktail + Ra: QGP and HG Ra: sum of QGP and HG (inmdium ρ) Ra: QGP Ra: HG (inmdium ρ sctral function) Ra: HG (vacuum ρ sctral function) Adv. HEP 3 (3) 4853 and PRC 63 () m (GV/c ) [] R. Ra, Adv. High Enrgy Phys. 3 (3) 4853 [] R. Ra, Phys. Rv. C63 () 5497 LM in ALICE I. Vorobyv Bormio 8

17 A Larg Ion Collidr Exrimnt PbPb snn =.76 V: virtual dirct hotons Fit dilcton mass sctrum (m 3 MV/c, and 4 GV/c) f (m ) = r f dir (m ) + ( r) f LF (m ) + f HF (m ) r = virtual dirct γ / inclusiv Dirct virtual hotons dscribd by KrollWada (m << ) (GV/c ) dn dm N vt ALICE Prliminary PbPb, =.76 V s NN Cntrality % >.4 GV/c, η <.8 < < GV/c data Hadronic cocktail r f + (r) f LF +f dir HF f LF f HF f dir N γ dn = α.m. dm 3π 4m m (+ m m ) m Rsults comatibl with ALICE and RHIC dirct hoton masurmnts of r ~.. [, ] m (GV/c ) ALIPREL87 incl / γ dir = γ r % C.L. ALICE Prliminary PbPb s NN =.76 V Cntrality % 9% C.L [] ALICE Collaboration, Phys. Ltt. B 754 (6) 3548 [] PHENIX Collaboration, Phys. Rv. Ltt. 4 () 33 ALIPREL (GV/c) LM in ALICE I. Vorobyv Bormio 8 3

18 A Larg Ion Collidr Exrimnt Summary and outlook collisions Mdiumfr baslin for havy ions studis First lowmass dilctron analysis of highmultilicity vnts Rsults ar dscribd with cocktail calculations of known hadronic sourcs Pb collisions Studis of ossibl cold nuclar mattr ffcts Comatibl with hadronic cocktail within uncrtaintis PbPb collisions Challnging analysis, rsults comatibl with hadronic cocktail within uncrtaintis Room for additional contributions Mor rsults ar coming soon! LM in ALICE I. Vorobyv Bormio 8 4

19 A Larg Ion Collidr Exrimnt Backu slids LM in ALICE I. Vorobyv Bormio 8 5

A Larg Ion Collidr Exrimnt Dilctron air analysis Physics signal: S = N + B R Combinatorial background: gomtric man of liksign airs from sam vnt B = N ++ N Pair tanc

20 A Larg Ion Collidr Exrimnt Dilctron air analysis Physics signal: S = N + B R Combinatorial background: gomtric man of liksign airs from sam vnt B = N ++ N Pair tanc corrction factor (from mixd vnts) R = N + MIX N ++MIX N MIX Convrsion rjction tniqus: V tagging, air orintation rlativ to th magntic fild LM in ALICE I. Vorobyv Bormio 8 6

21 A Larg Ion Collidr Exrimnt s = 7 V: dirct hotons Fit dilcton mass sctrum (m 4 MV/c, > GV/c) with f (m ) = r f dir (m ) + ( r) f LF (m ) + f HF (m ) (mb/ GV/c ) d σ dm d ALICE rliminary, s=7 V >. GV/c η <.8.4 < < 3. GV/c π η φ data f γ,dir (r)*f cocktail + cocktail sum η ω c r*f γ,dir r = virtual dirct γ / inclusiv Dirct virtual hotons dscribd by KrollWada (m << ) N γ dn = α.m. dm 3π 4m m (+ m m ) m Rsults comatibl with NLO QCD calculations c 3 ) (b GV 3 σ/d 3 d E 3 4 ALI PREL (GV/c ) ALICE rliminary, s=7 V 95 % C.L. γ dirct γ incl m = r (PCM) γ dirct (W.V.) NLO µ=.5 µ=. µ=. γ incl 6 5 ALI PREL (GV/c) LM in ALICE I. Vorobyv Bormio 8 7

22 A Larg Ion Collidr Exrimnt s = 7 V: air DCA analysis Ida: sarat romt and nonromt contributions using air vrtx osition racks from D or B dcays (cτ ~ 5 µm) do not oint back to vnt vrtx Obsrvabl: DCA = DCA + DCA (DCAi Distanc of Closst Aroa of track i) Obtain DCA tmlats from MC, normalis to cocktail and comar with data (/σ) dn ddca N v 4 ALICE Prliminary s = 7 V (/σ) data cocktail sum light flavour + (X) (MC) + cc (MC) bb + (MC) dn ddca N v 4 ALICE Prliminary s = 7 V data cocktail sum light flavour + (X) (MC) cc + (MC) bb + (MC) ALICE Prliminary s = 7 V (/σ) data cocktail sum light flavour + (X) (MC) cc + (MC) bb + (MC) J/ψ + (MC) dn ddca N v 5 ALICE Prliminary s = 7 V data cocktail sum cc + (MC) bb + (MC) J/ψ + (MC) nonromt J/ψ + (MC) 5 >.4 GV/c, η <.8, < 5 GV/c,.8 < m <.4 GV/c 5 >.4 GV/c, η <.8, < 5 GV/c,. < m <. GV/c >.4 GV/c, η <.8, < 5 GV/c,. < m <.7 GV/c 6 >.4 GV/c, η <.8, < 5 GV/c,.8 < m < 3. GV/c norm. Pull ALI PREL 597 norm. Pull 8 DCA (σ) ALI PREL 5974 DCA (σ) 5978 norm. Pull DCA (σ) ALI PREL 598 DCA (σ) LM in ALICE I. Vorobyv Bormio 8 8

23 A Larg Ion Collidr Exrimnt s = 7 V: DCA rsolution DCA rsolution should b smallr than obsrvabl (cτ of D mson ~ 5 µm) Pair DCA analysis is don for >.4 GV/c rsolution (µm) d,xy ALICE s = 7 V data, ions data, kaons data, rotons MC, ions MC, kaons MC, rotons rsolution (µm) d,xy ALICE argd articls Pb s PbPb = 7 V s NN = 5. V s NN =.76 V 5 ALI PUB (GV/c) ALI PUB 763 (GV/c) LM in ALICE I. Vorobyv Bormio 8 9

24 A Larg Ion Collidr Exrimnt Nw dvlomnts: main larning mthods Elctron idntification: imrovs fficincy whil king hadron contamination low Dilctron signal: surss convrsions, rduc combinatorial background Usag of th mthods ar forsn in th dilctron analysis of, Pb and Pb Pb Run data Normalisd Yild ALICE simulation s = 3 V PYHIA 8. (Monash 3 uns) lctrons ions rotons kaons muons total MVA Outut ALISIMUL59 ALIPERF58 ALISIMUL5 LM in ALICE I. Vorobyv Bormio 8

25 A Larg Ion Collidr Exrimnt s = 3 V: S / B and significanc Naiv xctation: signal is roortional to N, combinatorial background grows lik N Signal / background ratio is lowr for high multilicity vnts Significanc is comarabl in backgrounddominatd mass rgion / B S 4 3 ALICE Prliminary s = 3 V ϕ V MB L int >. GV/c, η <.8 < for m <. GV/c HM.8 nb, L int 83 nb Minimum bias HM (.% VM) S / S + B 4 3 ALICE Prliminary s = 3 V ϕ V MB L int >. GV/c, η <.8 < for m <. GV/c HM.8 nb, L int 83 nb Minimum bias HM (.% VM) 3 4 ALIPREL (GV/c ) m ALIPREL (GV/c ) m LM in ALICE I. Vorobyv Bormio 8

26 A Larg Ion Collidr Exrimnt s = 3 V: MB and HM triggrs Min. bias triggr: coincidnc of VA & VC signals (forward raidity) High mult. triggr: coincidnc of VA & VC signals, thrshold on VM N (HM) / N (MB) = 4.36 (masurd at η ~ ) Evnts 8 7 ALICE Prformanc s = 3 V η <. MB triggr HM triggr 6 5 ALIPERF dn /dη dn /dη ALI PERF 8369 LM in ALICE I. Vorobyv Bormio 8

27 A Larg Ion Collidr Exrimnt PbPb snn =.76 V: virtual dirct hotons (GV/c ) dn dm N vt ALICE Prliminary PbPb, =.76 V s NN Cntrality % >.4 GV/c, η < < GV/c <.8 (GV/c ) dn dm N vt ALICE Prliminary PbPb, =.76 V s NN Cntrality % >.4 GV/c, η <.8 < < 4 GV/c Hadronic cocktail Hadronic cocktail + virtual hotons (r =.7) m (GV/c ) ALIPREL Hadronic cocktail Hadronic cocktail + virtual hotons (r =.) m (GV/c ) ALIPREL835 data / cocktail ALICE Prliminary PbPb, =.76 V s NN Cntrality % >.4 GV/c, η <.8 < < GV/c data / cocktail ALICE Prliminary PbPb, =.76 V s NN Cntrality % >.4 GV/c, η < < 4 GV/c <.8 Hadronic cocktail Hadronic cocktail + virtual hotons (r =.7) m (GV/c ) ALIPREL8358 Hadronic cocktail Hadronic cocktail + virtual hotons (r =.) m (GV/c ) ALIPREL836 LM in ALICE I. Vorobyv Bormio 8 3

28 A Larg Ion Collidr Exrimnt Ur limit on virtual dirct hotons Masur fraction of virtual hotons in N = 4 simulatd xrimnts Random samling of data around bst fit curv and moving of data cohrntly by fraction of thir systmatic uncrtaintis Ur limit (9% CL) xtractd from intgration of obtaind r distributions counts ALICE Prliminary PbPb s NN =.76 V Cntrality % < < GV/c counts ALICE Prliminary PbPb s NN =.76 V Cntrality % < < 4 GV/c 9% C.L. gaussian fit 9% C.L. gaussian fit r = r(χ min ) ALIPREL833 min r = r(χ min ) ALIPREL8338 min LM in ALICE I. Vorobyv Bormio 8 4

29 A Larg Ion Collidr Exrimnt Run collctd data Statistics collctd in 6 (3 V), Pb 6 (5 V) and PbPb 5 (5 V) 6 Rcordd triggrs, 9 ALICE Prformanc 6, Pb s = 5 V MB: 764M Nov 5 Nov Nov 3 Nov 7 Dc LM in ALICE I. Vorobyv Bormio 8 5

30 A Larg Ion Collidr Exrimnt Dirct hoton rsults PHENIX AuAu GV [] ALICE PbPb.76 V [] [] ALICE Collaboration, Phys. Ltt. B 754 (6) 3548 [] PHENIX Collaboration, Phys. Rv. Ltt. 4 () 33 LM in ALICE I. Vorobyv Bormio 8 6

31 A Larg Ion Collidr Exrimnt ALICE Ugrad for Run 3 () Major ugrads of main tracking systms Comltly nw 7layr IS dtctor Nw PC GEMbasd radout ambrs Highr radout rat u to 5 khz in PbPb (x5 comard to Run ) LM in ALICE I. Vorobyv Bormio 8 7

32 A Larg Ion Collidr Exrimnt ALICE Ugrad for Run 3 () Ddicatd low B fild =. to incras tanc of low & mass airs Exctd statistics:.5 x 9 PbPb vnts in 4 wks of PbPb data taking Excss abov GV is dominatd by thrmal QGP radiation of arly stags without blu shift % statistical and % systmatic uncrtaintis in IMR LM in ALICE I. Vorobyv Bormio 8 8

ON A MISSED MECHANISM OF DIELECTRON PRODUCTION IN NUCLEUS-NUCLEUS COLLISIONS.

ON A MISSED MECHANISM OF DIELECTRON PRODUCTION IN NUCLEUS-NUCLEUS COLLISIONS. O A MISSED MECHAISM OF DIELECRO PRODUCIO I UCLEUS-UCLEUS COLLISIOS. A.S. Khrykin IR, Dubna, Moscow Rgion, Russia. MEU 00 un, Collg William and Mary, Williamsburg, Virginia, USA. OULIE Introduction h cas