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CP violation studies at B A B AR Philip Clark University of Colorado.

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Presentation on theme: "CP violation studies at B A B AR Philip Clark University of Colorado."— Presentation transcript:

1 CP violation studies at B A B AR Philip Clark University of Colorado

2 Philip J. Clark CP violation studies at BaBar Page 2 Talk overview Introduction to CP violation PEPII and the B A B AR experiment The charmonium system Various  c results B A B AR CP violation results Summary

3 Philip J. Clark CP violation studies at BaBar Page 3 The Standard Model Gravitational, weak, EM and strong 1) fermions which experience the forces quarks “confined” eg.  + (ud), p(uud) leptons don’t experience strong force 2) bosons which transmit the forces Two types of fundamental particle: Four fundamental forces:

4 Philip J. Clark CP violation studies at BaBar Page 4 Symmetries and conservation laws C = Charge Conjugation particle  antiparticle Relation between symmetry and conservation laws Noether’s theorem Symmetries  conservation laws -y x z -x y -z q q B. Cahn CP = P = Parity: x  -x T = time reversal “run the film backwards”

5 Philip J. Clark CP violation studies at BaBar Page 5 C and P symmetry and the weak interaction C P C and P are violated maximally

6 Philip J. Clark CP violation studies at BaBar Page 6 CP symmetry Is CP, a good symmetry for all interactions including the weak interaction? Cosmology: CP violation is one of the three necessary conditions to produce a global excess of matter in the Universe (Andreï Sakharov, 1967) 1964 : Christenson, Cronin, Fitch and Turlay CP violation in the decay of neutral kaons A CP-violating process offers an absolute way of distinguishing a world of anti-matter from a world of matter CPLEAR

7 Philip J. Clark CP violation studies at BaBar Page 7 Perhaps the answer to why the Universe looks like this not that??? Matter-antimatter asymmetry

8 Philip J. Clark CP violation studies at BaBar Page 8 The CKM model 1973 : M. Kobayashi and T. Maskawa made the connection CP violation  third generation of quarks udud cscs tbtb quark doublets d s b uctuct uctuct CP violation in the Standard Model   ≠   Wolfenstein parametrization: WW b u V ub ub  Cabibbo-Kobayashi-Maskawa matrix V : Complex matrix described by 4 independent real parameters (e.g. three angles, one phase) WW d u V ud ud 

9 Philip J. Clark CP violation studies at BaBar Page 9 The Unitarity Triangle V ud V cd V td V us V cs V ts V ub V cb V tb = V ud V us V ub V cd V cs V cb V td V ts V tb * * * * * * * * *  V ud V ub + V cd V cb + V td V tb = 0 *** V ud V us V ub V cd V cs V cb V td V ts V tb * * * * * * * * * V ud V cd V td V us V cs V ts V ub V cb V tb = The CKM Matrix is complexand unitary 9 unitarity relations The Unitarity Triangle Experimentally: constraints on the coordinates of the apex of the Rescaled Triangle in the complex plane The Rescaled Unitarity Triangle CP Violation  area of the Triangle

10 Philip J. Clark CP violation studies at BaBar Page 10 Precision test of the CKM model Phys. Rev. Lett. 89 (2002) B A B AR World average ( B A B AR +Belle+…) Heavy Flavor Averaging Group 2003 Main experimental constraints on the apex of the UT CP violation in the kaon system Measurements of | V ub | ( b → u transitions) B  and B s mixing frequencies

11 Philip J. Clark CP violation studies at BaBar Page 11 Is the CKM mechanism sufficient? CP violation in the quark sector is not enough to generate the baryon asymmetry of our Universe Antimatter in the Universe ? Understand the origin of CP violation in the Standard Model The Kobayashi & Maskawa mechanism can it account for all the effects of CP violation that are observed in the quark sector? What can we do? and if possible, reveal inconsistencies between experimental data and theoretical predictions Possible manifestations of New Physics? Evidence for new sources of CP violation?

12 Philip J. Clark CP violation studies at BaBar Page 12 PEP II/B A B AR at SLAC PEP II Asymmetric B Factory design peak: best peak: total recorded: x    cm  s  x    cm  s   fb  PEP-II/ BABAR at SLAC Luminosity records Started construction in1994 Completed in 1999 Reached design luminosity in GeV e  on 3.1 GeV e +

13 Philip J. Clark CP violation studies at BaBar Page 13 SVT  -T Solenoid The BABAR detector SVT EMC IFR DCH DIRC

14 Philip J. Clark CP violation studies at BaBar Page 14 B Mixing Certain mesons can do a neat little trick (K 0, D 0, B 0 ) A B 0 meson can change into an anti B 0 meson (B 0 ) This is called “mixing”. It means these particles can (and do) oscillate into their anti-particles and back again The oscillation frequency is about 0.5 ps -1 !

15 Philip J. Clark CP violation studies at BaBar Page 15 Measurement of sin2  0 tag B Coherent BB production Identify B or anti-B Identify B or anti-B z x y Full reconstruction of B   c K s 0 Full reconstruction of B   c K s 0 cc K+K+  t  z/c    

16 Philip J. Clark CP violation studies at BaBar Page 16 Observable CP Asymmetry (perfect experiment with sin2  = 0.6) Different  t spectrum for B 0 and B 0 Positive and negative  t Visible asymmetry A CP = nB 0 -nB 0 /(nB 0 +nB 0 ) t spectrum of CP eigenstates sin 2 

17 Philip J. Clark CP violation studies at BaBar Page 17 CP asymmetry

18 Philip J. Clark CP violation studies at BaBar Page 18 The new mode:- B 0   c K s In the  c analysis group we have studied B    c K  and B 0   c K s in the  c decay modes: cc _ b d c _ d c s _ K0K0 B0B0 W The two dominant modes measured have the following branching fractions BR(B 0   c K 0 ) x BR( c K 0 K    ) 36.8  11.6  6.0 x10 -6 BR(B 0   c K 0 ) x BR( c K + K -  0 ) 11.3  5.1  2.4 x10 -6 Combining gives us our CP sample:

19 Philip J. Clark CP violation studies at BaBar Page 19 CP asymmetry using B→  c K

20 Philip J. Clark CP violation studies at BaBar Page 20 Sin2  per Charmonium mode Good consistency between the measurements

21 Philip J. Clark CP violation studies at BaBar Page 21 Summary of “sin2  ” results “reference” sin2 pure penguin mostly penguin? heavily supressed tree with competing penguin suppressed tree penguin pollution The other B A B AR measurements agree with the reference sin2 Statistical conspiracy or hint of unexpected physics effect? within two standard deviations, or better but… consistently on the low side “sin2” 0.741

22 Philip J. Clark CP violation studies at BaBar Page 22 The Charmonium system Bound state of two spin ½ particles (fermions) The  c meson consists of a charm and anti-charm quark J = J 1 + J 2 the triplet state the singlet state J = 0 (½ - ½ ) J = 1 (½ + ½) m = 0 m = -1, 0, 1 The combined angular momenta J = |j 1 -j 2 |, |j 1 -j 2 |+1, …, (j 1 +j 2 )-1, (j 1 +j 2 ) and m =m 1 +m 2 gives: Other examples are the: hydrogen atom ( e - p ) positronium (e + e - ) EnEn singlet triplet hyperfine splitting Discrete energy levels and splittings exist and can give information on the strong force

23 Philip J. Clark CP violation studies at BaBar Page 23 Striking similarity Missing singlet state  c (2S) “Introduction to High Energy Physics” D. Perkins 4 th edition April 2000 singlet triplet singlet triplet  c singlet J/  triplet charmonium (cc)positronium (e + e - ) J/  (2S) triplet

24 Philip J. Clark CP violation studies at BaBar Page 24  c at BABAR photon-photon production ? mass and total decay width  c width  c mass  c mass and total width  c (2S) mass and total width

25 Philip J. Clark CP violation studies at BaBar Page 25 Charming, but strange mesons D+D+ D+sD+s D s + = cs D s - = cs mass = MeV D s + = cs D s - = cs mass = MeV D + sJ (2317)  D + s  0

26 Philip J. Clark CP violation studies at BaBar Page 26 Large amount of theoretical interest 32 new preprints

27 Philip J. Clark CP violation studies at BaBar Page 27 Summary  Prequisites The Standard Model The discrete symmetries C P and T C and P violated maximally in weak interation CP violation in the kaon system Cosmological implications  Formalism The Standard Model mechanism for CP violation Testing the unitarity of the CKM matrix  Measurement of Sin2 General methodology Manifestation of CP violation by BaBar Comparison to other measurements  Charmonium B   c K transitions and branching fractions Using the  c to measure sin 2 Charmonium system and measurement of  c (2S)  New particle D sJ + resonance What we have covered:

28 Philip J. Clark CP violation studies at BaBar Page 28 The  c and the Charmonium System : fundamental scalar state of the charmonium system, hyperfine partner of the to hadrons through virtual photon radiative In the  c group we are studying the following decay modes:

29 Philip J. Clark CP violation studies at BaBar Page 29 Resonant structure M(K ±  ± ) M(K 0 s  ± )  c  (K s K)  resonant structure  c Dalitz analysis and Branching fraction large 4.9 ± 1.8 % ( c ) 1.28% ( ±  ± ) cf. 1.26% ( c K s K ±  ± ) No result from Belle resonant structure –  c a 0 ) – Should look for  c )

30 Philip J. Clark CP violation studies at BaBar Page 30 B physics at hadron machines Geant3 LHCb event display Advantages: LHC cross-section 500 mb bb pairs/year at 2x10 32 cm -2 s -1 (down by 5 at Tevatron ) Challenges: Event complexity Triggering Bunch spacing: 25 ns (LHC) 132 ns (Tevatron) What next?

31 Philip J. Clark CP violation studies at BaBar Page 31 Comparison of yield and purity SampleN tagged Purity J/ K s ( +  - ) 97497% J/ K s ( 0  0 ) 17089% (2S) K s 15097%  c1 K s 8095% cKscKs 13273% Total150692%

32 Philip J. Clark CP violation studies at BaBar Page 32 SLAC-PUB-8970 At 10 36

33 Philip J. Clark CP violation studies at BaBar Page 33 Mixing and Sin2  analysis procedure Reconstruct one B fully in CP eigenstate or flavour eigenstate Other B partially reconstructed and flavour tagged Measure  z Fit for  t  z/c     PDF(  t)  exp(–|  t|/  B ) ( 1 ± (1-2  ) sin2  sin(  m  t) )  R (  t) CP violation:- PDF(  t)  exp(–|  t|/  B ) ( 1 ± (1-2  ) cos(  m  t) )  R (  t) B Mixing:- (1-2  ) is the “dilution” due to mistag R (  t) is the vertex resolution function

34 Philip J. Clark CP violation studies at BaBar Page 34 Silicon Vertex Tracker (SVT) Five layer double-sided Si Very low mass Stand-alone tracking device for P T < 120 MeV/c Radiation hard z-resolution of 70  m on CP vertex 580 mm

35 Philip J. Clark CP violation studies at BaBar Page 35 Drift Chamber Tracking resolution

36 Philip J. Clark CP violation studies at BaBar Page 36 Detector of Internally Reflected Cherenkov Light (DIRC): cos  c =1/n   c resolution:

37 Philip J. Clark CP violation studies at BaBar Page 37 Cherenkov angles for  and K from D * D 0    D 0 K -   K 

38 Philip J. Clark CP violation studies at BaBar Page 38 Electromagnetic calorimeter Radiation length1.85 cm (16 -18X 0 ) Moliere radius3.8 cm Peak emission565 nm Density4.53 g/cm 3 Time constant940 ns Light yield40-50k photons/MeV

39 Philip J. Clark CP violation studies at BaBar Page 39 Time-Dependent Asymmetries Use the large statistics B flav data sample to determine the mis-tagging probabilities and the parameters of the time-resolution function CP-violating asymmetry using the B CP sample Mixing using the B flav sample: for example

40 Philip J. Clark CP violation studies at BaBar Page 40 Large solid angle coverage for muon id (P>1 GeV/c) and to detect neutral hadrons (K 0 L ) Barrel section of IFR   ID efficiency and  fake rate Instrumented Flux Return (IFR)

41 Philip J. Clark CP violation studies at BaBar Page 41 Speaking of Direct CP violation … Uncertainty ~5%!

42 Philip J. Clark CP violation studies at BaBar Page 42 Separating Signal from Background (II)  The other powerful thing we can do is to exploit the “event shape”  In the CM, the decay products of the B are distributed roughly spherically. This is because the pair of B mesons weigh only slightly less than the . They are essentially produced at rest  The continuum is light quark pair production, so there is lots of extra energy. All the decay products bunch into “jets”  We define variables that measure the degree of “jettiness” of the decay to tell us how more or less likely it is to be signal or background e+e+ e-e- e+e+ e-e- qq Signal B Other B


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