Cracking the Unitarity Triangle B physics at Ba
Cracking the Unitarity Triangle: . . B physics at Ba. Bar Gabriella Sciolla Massachusetts Institute of Technology On behalf of the Ba. Bar Collaboration APS/DPF Meeting Philadelphia, April 5 - 8, 2003 March 14, 2001 Gabriella Sciolla - MIT
The Beauty of the Unitarity Triangle (r, ) All sides are ~ O(1) measure independently: a n 2 sides: n g (0, 0) n b B mixing, Vub, Vcb, … 3 angles: n CPV in B decays (1, 0) This allows us to: n test CP sector of SM quantitatively n CPV as a probe for New Physics April 5, 2003 B physics at Ba. Bar 2
Outline n Introduction n The angles: n n sin 2 b: the golden mode, the penguin modes, D*+D*The angle a: B 0 p+p-, B 0 rp The angle g: progress in B+ D 0 CPK+ The sides: n n n The experimental apparatus: PEP-II and Ba. Bar CP violation in the B system: theory and analysis technique Inclusive measurement of Vub Prospects for Vtd from b dg Summary and conclusion April 5, 2003 B physics at Ba. Bar 3
The PEP-II accelerator As of April 3, 2003: n Asymmetric B factory n n Results based on 89 M BB pairs n Peak luminosity n n B physics at Ba. Bar Design: 3 x 1033 cm-2 s-1 Achieved: 5 x 1033 cm-2 s-1 Integrated Luminosity n April 5, 2003 9. 0 Ge. V e- beam 3. 1 Ge. V e+ beam Delivered: Recorded: 118 fb-1 113 fb-1 4
The BABAR Detector 1. 5 T solenoid DIRC (PID) Cs. I(Tl) EMC e+ (3. 1 Ge. V) Silicon Vertex Tracker Drift Chamber Instrumented Flux Return e- (9 Ge. V) n n n Tracking: (p. T)/p. T = 0. 13% p. T 0. 45% DIRC: K-p separation: > 3. 5 for p<3. 5 Ge. V/c EMC: E/E = 2. 3% E-1/4 1. 9% April 5, 2003 B physics at Ba. Bar 5
CP violation in B 0 decays mixing y ( f) a dec Scenario 1 Only one diagram contributes: ACP(t) = - Iml sin(Dmt) CPV in interference between mixing and decays Iml=sin 2 b, sin 2 a, etc. April 5, 2003 Scenario 2 More than one diagram contributes both sin and cos terms will survive - Sf: depends on Iml sensitive to UT angles - Cf: depends on |l|, direct CP B physics at Ba. Bar 6
How to measure CPV at Ba. Bar. e. U(4 S) e. Ingredient #1: Exclusive reconstruction Breco B 0 e+ Ingredient #3: Btag Flavor tagging (coherent state) m+ B 0 m- p p+ Dz~ b c Dt Ingredient #2: Dt determination April 5, 2003 B physics at Ba. Bar 7
The measurement of b a g April 5, 2003 bb B physics at Ba. Bar 8
0 B charmonium b 0 K The “golden channels”: n n n Theoretically well understood Experimentally clean Relatively large BF (~10 -4) ACP(t) = sin 2 b sin. Dmt CP sample: Mode CP Nevents J/y. Ks, Y(2 s)Ks, c. Ks -1 1506 J/y. KL +1 988 mixed 147 J/y. K*0(Ks p 0) Full CP sample 2641 April 5, 2003 B physics at Ba. Bar 9
b B flavor tagging D*- B 0 n l+ D 0 p-(soft) p- K+ D*- B 0 W+ p+(hard) Tagging parameters measured from data using B 0 flavor eigenstates in time dependent B 0 mixing analysis. Category etag (%) w (%) eeff (%) Lepton 9. 1 0. 2 3. 3 0. 6 7. 9 0. 3 Kaon 1 16. 7 0. 2 9. 9 0. 7 10. 7 0. 4 Kaon 2 19. 8 0. 2 20. 9 0. 8 6. 7 0. 4 Inclusive 20. 0 0. 3 31. 6 0. 9 2. 7 0. 3 ALL 65. 6 0. 5 April 5, 2003 28. 1 0. 7 B physics at Ba. Bar 10
b sin 2 b CP fit Unbinned maximum likelihood fit to Dt distribution CP=-1 CP=+1 sin(2 b) = 0. 741 ± 0. 067 stat ± 0. 033 syst April 5, 2003 B physics at Ba. Bar 11
Testing the “usual assumptions” Assumptions made in the sin 2 b measurement: n Same lifetime for BH and BL n SM No CP/T/CPT violation in the mixing SM CP/T CPT Very good approximation in SM But can we test them? April 5, 2003 B physics at Ba. Bar z=0 SM 12
Fit for the “usual assumptions” Fit B CP and B 0 flavor eigenstates floating DG/G, q/p, z and l. CP: 90% C. L. Direct limit on DG/G Test of CPT invariance Indirect CP in mixing The “usual assumptions” work! April 5, 2003 B physics at Ba. Bar 13
Unitarity Triangle constraints b sin 2 b vs indirect UT constraints: n Excellent agreement Observed CP asymmetry consistent with CKM mechanism being the dominant source of CPV at low energies n This means: n n sin 2 b from Ba. Bar vs. indirect constraints April 5, 2003 B physics at Ba. Bar New Physics contribution is small OR New Physics is not small but does not appear in this particular decay because of accidental cancellations Can we test this hypothesis? . 14
More measurements of sin 2 b b Why do we need them? measure sin 2 b in many modes characterized by: n completely different Feynman diagrams n theoretically clean and well understood and compare results. Significant differences will be indication of New Physics. Modes under study: n n n B charmonium K 0 B 0 f. KS B 0 ’KS B 0 D*D* B 0 D*D April 5, 2003 B physics at Ba. Bar 15
0 B f. K S: b theory ss ss ss dd n Pure penguin modes: b sss n |A/A|=1 within 4% n Another clean measurement of sin 2 b! f KS Grossman, Worah PLB 395, 241 (1997) Grossman, Isidori, Worah PRD 58, 057505 (1998) ACP(t)= - sin 2 b sin. Dm. Dt n ACP(FKS)~ACP(J/YKS) n If difference > few% Clear signal of New Physics April 5, 2003 B physics at Ba. Bar 16
sin 2 b in 0 B f. K S: the results Results: n B 0 tag 64 signal events Fit with both S and C terms: Sf. Ks = -0. 18 ± 0. 51 ± 0. 07 Cf. Ks = -0. 80 ± 0. 38 ± 0. 12 n b B 0 tag Background Assuming no direct CP (C=0): Sf. Ks = -0. 26 ± 0. 51 n Hints of New Physics? n Compare Sf. Ks with sin 2 b(J/YKS)=0. 73± 0. 05 n 2 effect --- C+S __ S only . April 5, 2003 B physics at Ba. Bar 17
b sin 2 b in B 0 ’KS Another penguin dominated mode n Tree is Cabibbo and color suppressed s s s d ’ u W– KS d Compared to B f. KS n u b s d ’ KS ~70 candidates Larger Branching Fraction: BFBa. Bar= (5. 54 0. 52) x 10 -5 More challenging final state: 0 + n ’ r g and p p n n April 5, 2003 B physics at Ba. Bar 18
CP fit of B 0 ’KS Ba. Bar B 0 tag n b Results of CP fit: S ’Ks = 0. 02 0. 34 0. 03 C ’Ks = 0. 10 0. 22 0. 03 Background B 0 tag n Hints of New Physics? n n April 5, 2003 Compare S ’Ks with sin 2 b(J/YKS)=0. 73± 0. 05 2 effect B physics at Ba. Bar 19
b 0 *+ *B D D n n Tree measures sin 2 b from b ccd transitions Penguin expected to be small in SM (<10%) n But could be enhanced by New Physics Transversity analysis used to measure CP odd component: R =0. 07 0. 06 (stat) 0. 03 (syst) Mainly CP even! April 5, 2003 B physics at Ba. Bar 20
0 *+ *B D D : the CP fit b Nsignal= 126 12 n CP fit: Im(l)=-0. 31 0. 43 0. 13 |l| = 0. 98 0. 25 0. 09 n Indication for large Compare with sin 2 b(J/YKS)=0. 73 0. 05 penguin contribution April 5, 2003 B physics at Ba. Bar 21
sin 2 b summary b Statistical fluctuation or first signs New Physics? April 5, 2003 B physics at Ba. Bar 22
The measurement of a a g April 5, 2003 bb B physics at Ba. Bar 23
a a from B 0 p+p. T = Tree P = Penguin Significant contribution from both diagrams: n n n P/T ~ 1/3 from Br(B Kp)/Br(B pp) Spp sin 2 aeff related to angle a through isospin Cpp direct CP violation April 5, 2003 B physics at Ba. Bar 24
0 + B p p : n K-p separation is a must n n n Br(B 0 K+p-) ~ 4 x Br(B 0 p+p-) PID gives >3. 5 up to 3. 5 Ge. V * Continuum background n n analysis technique a rejected by Fisher discriminant Low branching fraction D 0 p+ data BR(B 0 p+p-) ~ 5 x 10 -6 p+p- MC n PID and Fisher included in maximum likelihood fit April 5, 2003 B physics at Ba. Bar m. ES data sideband Bkg MC 25
B 0 p+p-: the CP fit a Npp=157 20 No asymmetry seen in p+p- yet… April 5, 2003 B physics at Ba. Bar 26
0 + B p p : n Dm. B = (0. 52 0. 05) ps-1 Extensive cross-checks: n n n the validation a Possible two-body vertexing systematics CP asymmetry in the background Fit method Likelihood function t. B = (1. 56 0. 07) ps Some examples: n Measure mixing in B 0 K+p– n Dmd = (0. 52 0. 05) ps-1 OK! Measure t. B in B 0 p+p– n n t. B = (1. 56 April 5, 2003 0. 07) ps OK! B physics at Ba. Bar 27
0 B r p n Similar to B 0 p+p-… n n Measures both mixing-induced CP(a) and direct CP …just more challenging! n n n and 0 B r K a Not a CP eigenstate 4 configurations: 0 0 n B r p , B r p n 3 p final state combinatorics r-, pp+, r+ Analysis strategy n Pseudo two-body analysis n n n avoid interference regions of Dalitz plot Continuum background suppressed by NN Simultaneous fit for r+p- and r+KApril 5, 2003 B physics at Ba. Bar 28
0 B r p and 0 B r K a Combined Maximum Likelihood fit measures: n BF(B 0 rp)= (22. 6 1. 8 2. 2) 10 -6 BF(B 0 r. K)= (7. 3 1. 3) 10 -6 n and 6 other parameters related to CP: n N(rp) = 428 34 April 5, 2003 Indication for small penguins N(r. K) = 120 20 B physics at Ba. Bar 29
B 0 r p (K ) : the CP fit n Time integrated direct CP: n Time dependent CP: a -- B backg. -- all backg. n Asymmetry between rates: First step towards a measurement of a in B rp decays. Full Dalitz analysis in progress. April 5, 2003 B physics at Ba. Bar 30
Prospects for g n Clean measurement will eventually come from BS D+K- n In the mean time B factories can constrain g using: n B ® D 0 CP K n n B 0 ® D(*)+ pn n n Theoretically clean (Gronau & Wyler, Dunietz 1991) Interference between b u (cs) and b c (us) Small accessible Branching Fractions ~ 10 -7 Theoretically clean measurement of 2 b+g Interference between b u (cd) and b c (ud) B ® pp, Kp n Interference between penguin and tree diagrams n Take ratios of Br’s to eliminate dependence on strong phases n Model dependent - relies on assumptions of factorizaton, SU(3) April 5, 2003 B physics at Ba. Bar 31
Progress in n Isospin analysis n Measurements: April 5, 2003 0 B D CP K B physics at Ba. Bar 32
The measurement of the sides B 0 wg a Vtb*Vtd * Vcd. Vcb g April 5, 2003 b B physics at Ba. Bar 33
Why another measurement of Vub? Indirect constraints vs sin 2 b world average n sin 2 b is now very well known n n (sin 2 b) ~5% (Ba. Bar+Belle) Measurement of the “decay side” ~ |Vub/Vcb| is not as well known n n (Vcb) ~ 5% (Vub) ~16 -20% Better measurement of Vub needed for a more stringent test of CP side of Standard Model April 5, 2003 B physics at Ba. Bar 34
A new measurement of Vub pl*>1 Ge. V/c The idea: n n n Vub One B exclusively reconstructed (4 K/fb-1) Inclusively measure Br(b uln) on recoiling B Many kinematical variables: p*lepton, Q 2, MX Reduce systematics measuring: B(Xuln)/B(Xln) Better purity and smaller model dependence! April 5, 2003 B physics at Ba. Bar 35
Vub The result S/B ~ 1. 7! April 5, 2003 B physics at Ba. Bar 36
Vub inclusive: summary Vub This measurement: total error 13% April 5, 2003 B physics at Ba. Bar 37
Vtd B rg and B wg EW penguin dominated by top quark: BF(b dg) ~ |Vtd|2 constraints on UT d B 0 0 n n n r 2 p (w 3 p) + high energy g Continuum suppressed by NN PID rejects B K*g B+ + Mode 90% CL (10 -6) SM Expectation (10 -6) B(B 0 r 0 g) <1. 2 0. 49 ± 0. 21 B(B+ r+g) <2. 1 0. 85 ± 0. 40 B(B 0 wg) <1. 0 ~ 0. 5 B 0 Ali and Parkhomenko (hep-th 0105302) April 5, 2003 B physics at Ba. Bar 38
Summary Ba. Bar is attacking the UT from all sides and angles: a is coming… n CPV in B 0 p+p- and B 0 rp a New Vub measurement n Vtd from EW penguins n The power of statistics! g g is tough! n B DCPK- b sin 2 b is well established n n April 5, 2003 B rg complements mixing golden mode used as calibration new modes: B 0 f. KS, ’KS, D*D*, … …and much more in parallel sessions! B physics at Ba. Bar 39
Conclusion n n Despite the fierce attack, the Standard Model is still holding remarkably well… Although, some interesting shifts observed in sin 2 b from penguin modes and D*D*: n n n Hints of New Physics? ? ? Statistics will tell… And much more data is coming: n n n Run-3 in progress (>24 fb-1 so far) >500 fb-1 by 2006 >1 at-1 by 2009 if physics case remains compelling April 5, 2003 B physics at Ba. Bar 40
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