The Collaboration Univ. of California-Davis, CBPF-Rio de Janeiro, CINVESTAV-Mexico City, Univ. Colorado-Boulder, FERMILAB, Laboratori Nazionali di Frascati, Univ. of Illinois-Urbana-Champaign, Indiana Univ.-Bloomington, Korea Univ.-Seoul, INFN and Univ.-Milano, INFN and Univ.-Pavia Univ. of North Carolina-Asheville, INFN and Univ.-Pavia, Univ. of Puerto Rico-Mayaguez, Univ. of South Carolina-Columbia, Univ. of Tennessee-Knoxville, Vanderbilt Univ.-Nashville, Univ. of Wisconsin-Madison

CHARM MIXING AND CP VIOLATION IN FOCUS AT FERMILAB CHARM MIXING AND CP VIOLATION IN FOCUS AT FERMILAB EPS-HEP2001, Budapest, july 12-18, 2001 EPS-HEP2001, Budapest, july 12-18, 2001 SERGIO P. RATTI INFN and Dipartimento di Fisica Nucleare e Teorica - PAVIA for the FOCUS COLLABORATION

Outline of the talk Basic phenomenolgy: D o -D o mixing: lifetime mixing: y CP =  DCS decay D o  K +  - (from D*) Comparison with other experiments D-D asymmetries: search for CP Conclusions

NEUTRAL MESON LIFETIME MIXING IN THE CHARM SECTOR IS A VERY INTERESTING ISSUE: THE TIME EVOLUTION OF A NEUTRAL FLAVOUR EIGENSTATE IS GIVEN BY THE SCHRODINGER EQUATION (as for the old K o 1 - K o 2 case): NEUTRAL MESON LIFETIME MIXING IN THE CHARM SECTOR IS A VERY INTERESTING ISSUE: THE TIME EVOLUTION OF A NEUTRAL FLAVOUR EIGENSTATE IS GIVEN BY THE SCHRODINGER EQUATION (as for the old K o 1 - K o 2 case): D o -D o MIXING MASS AND WIDTH DIFFERENCES ARE PARAMETRIZED AS: x  m/  ; y  /2  with      MASS AND WIDTH DIFFERENCES ARE PARAMETRIZED AS: x  m/  ; y  /2  with      The MASS EIGENSTATES, IF CP IS CONSERVED, are: D 1,2 =1/  2(D o ±D o )

INTEGRATING |A mix | 2 OVER TIME, MIXING IS DESCRIBED BY: D o -D o MIXING THE MIXING AMPLITUDE SQUARE IS:

For a HADRONIC DECAY D o  K +  - R WS R WS =  (D o  K +  - )/  (D o  K -  + )  e -  t [R DCS +R’/2 t 2 +y’ t  R DCS e -  t [R DCS +R’/2 t 2 +y’ t  R DCS ] R WS R WS =  (D o  K +  - )/  (D o  K -  + )  e -  t [R DCS +R’/2 t 2 +y’ t  R DCS e -  t [R DCS +R’/2 t 2 +y’ t  R DCS ] D o  K -  + is C.F. WRONG SIGN D o  K +  - is WRONG SIGN D.C.S D.C.S. or mixing box diagram from mixing box diagram D o  K -  + is C.F. WRONG SIGN D o  K +  - is WRONG SIGN D.C.S D.C.S. or mixing box diagram from mixing box diagram STRONG PHASE  y’= y cos  x sin  x’= x cos  y sin  R’=(x’ 2 +y’ 2 )/2 STRONG PHASE  y’= y cos  x sin  x’= x cos  y sin  R’=(x’ 2 +y’ 2 )/2 DCS BOX or

Theoretical “guidance” From compilation of H.N.Nelson hep-ex/ Triangles are SM x Squares are SM y Circles are NSM x 15 orders of magnitude Predictions encompass 15 orders of magnitude for R mix (only 7 orders of x or y!)

ONLY MESON GOLDEN MODES ±3011 D* signal seen without cuts

D o -D o lifetime mixing D o -D o lifetime mixing

LIFETIME MIXING assuming CP conserved : CP|k + k - > =+1; CP |k -  + > =equal mixture. Therefore: Thus:

M kk SAMPLE HANDLING D o  KK is CP=+1 D o  KK is CP=+1 need over 10,000 ev. to reach  1% error in  need over 10,000 ev. to reach  1% error in 

Fit spanning over ~10  !! Fit spanning over ~10  !! Fitting  (D o [K  ]) and y cp 10,331 events 119,738 events  MEASUREMENTS

Results Mass (GeV) Phys. Lett. B485, 62 (2000) y CP = 3.42  1.39  0.74 %   =  1.34  ?? fs

SPECULATIONS  (KK)=   =(395.8±5.5) fs  2 = (415.5 ± 11.5) fs Purely speculative:  ns  Just for the fun of it!!! From: 2 1  (K  ) = and y CP get  (KK)= ;  1 +  2  1  1 -  2 y cp = get  - =1/  2 ; get .  1 +  2 From:

Comparison of y CP measurements semileptonic

D o  K +  - from D* D o  K +  - from D*

WRONG SIGN STUDIES The CLUE of the WRONG SIGN STUDIES when the nature of the D o meson is identified by the parent D* K  AMBIGUITY is the RESPONSE OF THE CERENKOV COUNTERS to solve the K  AMBIGUITY MORE SO since we have to directly compare K -  + to K +  - single misidentification implies “regular background” DOUBLE MISIDENTIFICATION WOULD RETAIN THE EVENT BUT IN THE WRONG CATEGORY!!!! WRONG SIGN STUDIES The CLUE of the WRONG SIGN STUDIES when the nature of the D o meson is identified by the parent D* K  AMBIGUITY is the RESPONSE OF THE CERENKOV COUNTERS to solve the K  AMBIGUITY MORE SO since we have to directly compare K -  + to K +  - single misidentification implies “regular background” DOUBLE MISIDENTIFICATION WOULD RETAIN THE EVENT BUT IN THE WRONG CATEGORY!!!! STARTING FROM OVER 200,000 D* EVENTS, this study required a sistematic Montecarlo investigation to sort out the wrong sign K +  - signal (either DCS decay or BOX diagram decay) from the overwelming background. STARTING FROM OVER 200,000 D* EVENTS, this study required a sistematic Montecarlo investigation to sort out the wrong sign K +  - signal (either DCS decay or BOX diagram decay) from the overwelming background.

Simulate 3 different types of background, i.e.: D o  +  - ; D o  K + K - ; partially reconstructed D’s and D o  K  double misidentified; double misid.D o ‘s handled with adequate Cerenkov cuts. Subdivide the  M distribution into 1 MeV bins and fit the remaining backgrounds plus signal to M(K  ). Simulate 3 different types of background, i.e.: D o  +  - ; D o  K + K - ; partially reconstructed D’s and D o  K  double misidentified; double misid.D o ‘s handled with adequate Cerenkov cuts. Subdivide the  M distribution into 1 MeV bins and fit the remaining backgrounds plus signal to M(K  ). When the wrong K  have mass around the right K  !  M=M D* -M D is at the peak! When the wrong K  have mass around the right K  !  M=M D* -M D is at the peak!

Make a total of 80 fits (wrong sign and right sign) on 40 1 MeV strips

Y=36760 ± 195 Y=148.5 ± 31.3 MM

We obtain: R WS =(0.405 ± ± 0.025)% Of course -as we have seen- R WS becomes a function of t in presence of mixing We obtain: R WS =(0.405 ± ± 0.025)% Of course -as we have seen- R WS becomes a function of t in presence of mixing Consistent with SM Cabibbo tg 4  Phys. Rev. Lett. 86,2955, ± 0.25 ± ± ± ± 0.040CLEOE791ALEPH CLEO II.V Events R DCSC (%)

with mixing assumption and  t/  =1.578±.008  (t/    =3.61±.03 estimate  t/  and  (t/    using MC R ws =(0.404 ±.085 ±.025

CP asymmetries CP asymmetries

CP asymmetry for D mesons 1623± ± ± ± ± ± ± ±282

Parameter A for D mesons Comparison to other experimentss No evidence for CP violation so far. Our limit on K + K - needs tagged D o ‘s from D *, which cuts our sample by ~80%. Our limits: most precise published measurements reflecting our large statistics. Our limits: most precise published measurements reflecting our large statistics.

ConclusionsConclusions can we speculate that Do-Do mixing is  0? y CP =(3.42±1.39±0.74)% has a 90% CL limit  0. R ws =(0.404 ±.085 ±.025)% would be R DCSD in absence of mixing if mixing R ws compatible with CLEO II No evidence for CP violation at 1% level semileptonic decays still to be tackled CP=-1 states still to be adressed can we speculate that Do-Do mixing is  0? y CP =(3.42±1.39±0.74)% has a 90% CL limit  0. R ws =(0.404 ±.085 ±.025)% would be R DCSD in absence of mixing if mixing R ws compatible with CLEO II No evidence for CP violation at 1% level semileptonic decays still to be tackled CP=-1 states still to be adressed