A Precision Measurement of the Neutral Pion Lifetime: the PRIMEX Experiment!"#$%&'()'*+, -,'.+#('/$%"0%&1((1234(+//(6%5*3+#(/%5*3+#(/ 1,7%/3+ 8!9&:;%<"==1>"#1/'",? 5%(3"#/%#+.'+@%"0%! 0!""? A3+%8!9&:;%+BC+#'*+,/%1/%DE1>? :=+2/#"*1F,+/'2%21='>#1/'",%#+12/'",(?!+(4=/(%0"#%/3+%! G ='0+/'*+? 8!9&:;%1/%HI%J+K L'B/3%9,/+#,1/'",1=%<",0+#+,2+%",%8+#(C+2/'.+(%',%M17#",'2%83$('2( A#'+(/+%N 9/1=$6%&1$%HIOHP6%IGGQ
A short review of! 0!"" : discovery! HRSQT%U4)1@1%C"(/4=1/+(%1%,+4/#1=% *+(",%>1(+7%",%">(+#.1/'",(%"0% 231#F+%',7+C+,7+,2+%"0%/3+%VV% 0"#2+! HRWGT%L1)1/1%+(/'*1/+(%#! HG OHP (% 0"#%/3+%! G 0#"*%%%%%%=""C%7'1F#1*%% pp? HRWQT%%XCC+,3+'*+#%(4FF+(/(%/31/%! G% 7+21$(%1#+%#+(C",('>=+%0"#%F1**1% >12)F#"4,7(%',%3'F3%1=/'/47+%2"(*'2% #1$(? HRYGT%%! G 7'(2".+#+7%1/%Z+#)+=+$% 7% %Z % <$2="/#",%
A short review of! 0!"" : era of current algebra?a3+%("0/oc'",%='*'/%"0%8<5<%c#+7'2/(%5[!!""$%\%g? 57=+#6%Z+==6%D12)'@%1,7%Z1#7++, 7'(2".+#%/#'1,F=+%%%%%%%%%%%% 7'1F#1*(%/31/%1=/+#%8<5<%C#+7'2/'",(%0"#%! " 7+21$ # $ % $ &
A short review of! 0!"" : era of QCD and effective interactions? ]+((6%^4*',"%1,7%]'//+, 2",(/#42/%1,"*1="4(% X[C W _%=1F#1,F'1,%/31/%C+#*'/(%/#1,('/'",(%>+/@++,% +.+,%1,7%"77%,4*>+#(%"0%C(+47"O(21=1#%*+(",( (21=1#%*+(",(? A3+%23'#1=%1,"*1=$%31(%(C+2'1=%(/1/4(%',%`<aT% /3+#+%1#+%,"%="@%+,+#F$%2",(/1,/(%',%=1F#1,F'1, F F I ' V2 I *! S )! S I YbP! d! & G! $ 2! ( "" * * bcbiybiy +K
A short review of! 0!"" : era of chiral dynamics? <"##+2/'",(%74+%/"% ['_%4O 7O e41#)%*1((+( [''_%%'("(C',%>#+1)',F%[!6%+6%1,7%+%+ %1,7%+ *'B',F_%C#"C"#/'",1=% /"%e41#)%*1((%7'00+#+,2+(?!+2+,/%21=24=1/'",(%',%vex%<38a%f'.+( f & G ( "" $ * QcHG +K )!! Yg%3'F3+#%/31,%EX6%@'/3%4,2+#/1',/$%"0%=+((%/31,%Hg %J % %Z % 7%Z % = %83 % % % % 7% ' Dc%J"'/$6%5c%Z+#,(/+',6%1,7%Zc%M"=(/+',6%83$(c%!+.c%aPPTGbPGHW6%IGGI6%1,7% Zc%5,1,/31,1#1$1,%1,7%Zc%&"4((1==1*6%DM:8GY%[IGGI_%GYIc%
Experimental results used in PDG average V"%2"=='7+#%#+(4=/(% + h + O ("";; 1#+%',%/3'(% %/3' % 1.+#1F+ ' `<a%(4*%#4=+%21=24=1/'",t%zc%9"00+6%5c%xf1,+('1,6%83$(c%e+//c%zpwb6%sqr%[iggb_c
Direct Measurement of Lifetime (CERN 1984)!# OHP!,HBHG (+2%-/""%(*1==%/"%*+1(4#+!L"=4/'",T%%%<#+1/+%+,+#F+/'2%! G i(6 E%\%.#! :j*! &+1(4#+%! G 7+21$%=+,F/3% d"#%:\%hggg%j+k %HGGG%J+K6%E%E *+1,, HGG%!*! )[! G (""_%\%bcsw+k.schg[/"/1=_ a"*',1,/%($(/+*1/'2%+##"#t -,2+#/1',/$%',%8! [.HcYg_ 12 11 π 0 γγ Decay Width (ev) 10 9 8 QCD Sum Rule +/-1.5% NLO, +/-1% Leading Order 7 CERN (Direct) 0 1 2 3 4 5 6 7 Experiments
Primakoff Reaction dσ/dθ, µbarn/rad 30 25 20 E γ =5.2GeV HI <%/1#F+/ 15 8#'*1)"00 V42=c%<"3+#+,/ 10 5 9,/+#0+#+,2+% V42=c%9,2"3c 0 0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 2.25 2.5 θ 0 π (degr.) d d 8 3 2 3 4 1 Pr ' Z 0 E 2 2 * )"" F..( Q) sin / 3 4 e m! 2 m! Q <31==+,F+T%%:B/#12/%/3+%8#'*1)"00%1*C='/47+
Previous Primakoff Experiments 5==%C#+.'"4(%+BC+#'*+,/(%4(+7T! -,/1FF+7%>#+*((/#13=4,F%" " >+1*! <",.+,/'",1=%8>OF=1((%21="#'*+/#$ 12 11 π 0 γγ Decay Width (ev) 10 9 8 QCD Sum Rule +/-1.5% DESY (Primakoff) NLO, +/-1% Leading Order 7 Cornell (Primakoff) Tomsk (Primakoff) 0 1 2 3 4 5 6 7
PRIMEX Collaboration Arizona State University, Tempe, AZ, Catholic University of America, Washington, DC, Chinese Institute of Atomic Energy, Beijing, China, Eastern Kentucky University, Richmond, KY, George Washington University, Washington, DC, Hampton University, Hampton, VA, Institute for High Energy Physics, Chinese Academy of Sciences, Beijing, China, Institute for High Energy Physics, Protvino, Moscow region, Russia, Institute for Theoretical and Experimental Physics, Moscow, Russia, Kharkov Institute of Physics and Technology, Kharkov, Ukraine, Massachusetts Institute of Technology, Cambridge, MA, Norfolk State University, Norfolk, VA, North Carolina A&T State University, Greensboro, NC, North Carolina Central University, Durham, NC, Thomas Jefferson National Accelerator Facility, Newport News, VA, Tomsk Polytechnical University, Tomsk, Russia, Idaho State University, Pocatello, ID, University of Illinois, Urbana, IL, University of Kentucky, Lexington, KY, University of Massachusetts, Amherst, MA, University of North Carolina at Wilmington, i Wilmington, i NC, University i of Virginia, i i Charlottesville, VA, Yerevan Physics Institute, Yerevan, Armenia
" DE1>%M1==%Z%3'F3%#+("=4/'",%3'F3 ',/+,('/$%C3"/",%/1FF',F%012'='/$ " V+@%C1'#%(C+2/#"*+/+#%0"# C3"/",%0=4B%2",/#"=%1/%3'F3 ',/+,('/'+( " V+@%3'F3%#+("=4/'",%3$>#'7 F $ *4=/'O231,,+=%21="#'*+/+# [MU<5E_
Jefferson Lab Photon Tagger
PRIMEX Targets: 12 C and 208 Pb Lead target :00+2/'.+%,4*>+#%"0%1/"*(j2* % 0% I ',%/3+%/1#F+/(T% <1#>",%),"@,%/"%k GcGWg E+17%),"@,%/"%k GcWg 34jA\GcSg
Pair Spectrometer "!+=1/'.+%C3"/",%0=4B%*",'/"#T >$%7+/+2/',F%+ h + O C1'#(%0#"*% >+1*%74#',F%/3+%+BC+#'*+,/ " <"*>',1/'",%"0T%! HP%lJB&%7'C"=+%*1F,+/! I%/+=+(2"C+(%"0%IBQ% (2',/'==1/',F%7+/+2/"#(
Stability of relative tagging ratios 8Lh/1FF+#! &",'/"#+7%>$%8L%74#',F%C#"742/'",%71/1%/1)',Fc A1FF+# %(
8#'*:B%M$>#'7%<1="#'*+/+#%%O M$<1= 5%3'F3=$%(+F*+,/+7%3$>#'7% 21="#'*+/+# N YbP%=+17OF=1((%7+/+2/"#(% [WcGG)WcGG)WG%2* GG)WG%2* S _ N HHYI%=+17O/4,F(/1/+% 7+/+2/"#(% [IcHIY)IcHIY)IHcY%2* S _ N +,+#F$%#+("=4/'",%HcSg N C"('/'",%#+("=4/'",%HcS%**
QED calibration reaction I: pair production on
Differential cross sections for pair production [mb] dσ dx 450 400 350 300 250 200 150 100 50 0 Run 5141 x min x max σ exp. σ theory = 0.4 = 0.755 = 115.612 mb = 115.566 mb 0.2 0.4 0.6 0.8 1 x = E e -/E γ " 9,/+F#1/+7%2#"((%(+2/'",(%',%1F#++*+,/%@'/3%/3+"#$%1/% " 9,/+F#1/+7%2#"((%(+2/'",(%',%1F#++*+,/%@'/3%/3+"#$%1/% /3+%(4>OC+#2+,/%=+.+=
`:a%21='>#1/'",%#+12/'",%99t%<"*c/",%(21//+#',f% " 6 e ( " 5 6 e5
Latest results for the! 0 lifetime
Extracting Elastic Pion Yields versus /! : : H : H 6 I /1FF+77" & "" A3#++%F#"4C(%1,1=$m+7%/3+%71/1%',7+C+,7+,/=$T% C $ :c<=',/",%[-&1((_6%ac%&2v4=/$%[&9ajde1>_%1,7%9c%e1#',%[9a:8_
π o yield per 0.02 o per 10 12 incident γ s 400 300 200 100 a'00+#+,/'1=%<#"((%(+2/'", π 0 Photoproduction Yield (crystal only) Elastic π 0 Yield 12 C target dσ/dθ per 0.02 o, µbarn/rad 35 30 25 20 15 10 5 12 C target 0 0 0.5 1 1.5 2 2.5 θ π o, (degr.) 0 0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 2.25 2.5 θ π o, (degr.) :BC+#'*+,/1=%U'+=7% C+#%38! GEANT:! 122+C/1,2+(n! +00'2'+,2'+(n%! #+("=4/'",(n a'00c%2#"((%(+2/'",
d'/%/"%:b/#12/%"[! G (""_%a+21$%]'7/3 " Theoretical angular distributions smeared with experimental resolutions are fit to the data HI < IGQ 8>
IGQ8> dn/dθ, events/0.02 deg. HI< dn/dθ, events/0.02 deg. <"*>',+7%L4*4=/1,+"4(%d'/%/"%Z"/3%A1#F+/( 285.3 600 Γ CS-C φ-c CI-C CS-Pb φ-pb CI-Pb 500 400 300 / 243 7.947 1.238 1.064 0.9482 1.028 1.049 1.088 0.1281 0.2109E-01 0.4236E-01 0.5091E-01 0.5521E-01 0.6672E-01 0.1784 200 100 0 0 0.25 0.5 0.75 1 1.25 1.5 1.75 0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 2.25 2.5 θ(π ), degrees 285.3 Γ CS-C φ-c CI-C CS-Pb φ-pb CI-Pb 0 / 243 7.947 1.238 1.064 0.9482 1.028 1.049 1.088 2 2.25 2.5 0.1281 0.2109E-01 0.4236E-01 0.5091E-01 0.5521E-01 0.6672E-01 0.1784 10 10 1 θ(π0), degrees 2
5,1=$('(%5.+#1F+(%0"#%)[! G!""_ Target )&! 9!""$ HI < bcqp%k GcIH%+K IGQ 8> <"*>',+7%21#>",h=+17 bcrr%k GcHQ%+K bcrs%k GcHQ%+K
:(/'*1/+7%L$(/+*1/'2%:##"#( Contributions 83"/",%0=4B A1#F+/%,4*>+# Z12)F#"4,7%(4>/#12/'", Errors HcGg GcHg GcRg :.+,/%(+=+2/'", GcYg MU<5E%#+(C",(+% 04,2/'", Z+1*%C1#1*+/+#( 522+C/1,2+ &"7+=%+##"#(%[/3+"#$_ 83$('2(%>12)F#"4,7 Z#1,23',F%#1/'"%[8aJ_ GcYg GcWg GcSg GcIYg GcIWg GcGSg Total 1.6%
Current PrimEx Result )[!(""_%\%bcrs+k.icsg.hcpg &*
d4/4#+%de1>%!4,%
PrimEx Program at 12 GeV JLAB PrimEx Program at 12 GeV JLAB ]+%C#"C"(+%/"%*+1(4#+T N A@"O83"/",%a+21$%]'7/3(T% "[#$o!!_ o!!_6%"[# %"[#"$o!!_% HH%J+K%+ C3"/"C#"742/'",% /' ",%C#"/", N A#1,('/'",%d"#*%d12/"#%d ""p "0%% G 6%#%1,7%# %#%1,7%#" 1/%="@%`I [GcGGHOOGcY%J+K I j2 I _.'1%/3+%%8#'*1)"00%+00+2/c
Fundamental input to physics: # a+/+#*',1/'",%"0%e41#)%*1((%#1/'" 2! 2 m m 1 Q 7 2 * s, where mˆ * ( m 2 2 u m m 7 m 6 2 d d u # +-+ *'B',F # 9,/+#12/'",%#17'4(%"0%! 0 6%+ 1,7%+ # 9(%/3+ + 1,%1CC#"B'*1/+%J"=7(/",+% >"(",q )
8!9&:;%1/%HI%J+KT%J=4+;%7+/+2/"#%',% DE1>%M1==%a
Summary and Conclusions " ]+%1#+%',%/3+%C#"2+((%"0%0',1='m',F%/3+%% " ='0+/'*+ 1,1=$('(c%%X4#%#+(4=/%'(T )! G * bcrs. GcHQ. ("" GcHS+K " X4#%#+(4=/%'(%',%1F#++*+,/%@'/3%EX%1,7%VEX%<38A6%1,7% /3+%`<a%(4*%#4=+%21=24=1/'",c%% " 577'/'",1=%#4,,',F%21,%#+742+%"4#%2"*>',+7%(/1/'(/'21=% 1,7%($(/+*1/'2%+##"#(%>$%1>"4/%rc%]+%1#+%1CC#".+7% 0"#%1,"/3+#%#4,%1/%D+00+#(",%E1>c% " 5%8#'*1)"00%C#"F#1*%1/%HI%J+K%3"=7(%F#+1/%C#"*'(+% C F F C 0"#%(/47'+(%"0%/3+%C(+47"O(21=1#%*+(",(