M. V. Purohit, Univ. of S. Carolina, ICHEP 2004, Beijing, China _ A Search for D 0 D 0 mixing in Semileptonic decays, A search for CP Violation in D +  K + K -   decays and a Measurement of the Branching ratio _ A Search for D 0 D 0 mixing in Semileptonic decays, A search for CP Violation in D +  K + K -   decays and a Measurement of the Branching ratio Milind V. Purohit Univ. of South Carolina (for the BaBar collaboration)

M. V. Purohit, Univ. of S. Carolina, ICHEP 2004, Beijing, China The BaBar Collaboration China [1/5] Inst. of High Energy Physics, Beijing Germany [4/28] Ruhr U Bochum TU Dresden Phys. Inst., Heidelberg U Rostock France[5/60] LAPP, Annecy Ecole Polytechnique LAL Orsay LPNHE des Universités Paris 6/7 CEA, DAPNIA, CE-Saclay United Kingdom [10/72] U of Birmingham U of Bristol Brunel University U of Edinburgh U of Liverpool Imperial College Queen Mary & Westfield College Royal Holloway, University of London U of Manchester Rutherford Appleton Laboratory Italy [13/105] INFN Bari INFN Ferrara INFN Frascati INFN Genova INFN Milano INFN Napoli INFN Padova INFN Pavia INFN Perugia INFN Pisa INFN Roma INFN Torino INFN Trieste Canada [4/19] U of British Columbia McGill U U de Montréal U of Victoria Norway [1/3] U of Bergen Russia [1/11] Budker Inst., Novosibirsk Netherlands [1/5] NIKHEF USA [38/301] Caltech, Pasadena UC, Irvine UC, Los Angeles UC, San Diego UC, Riverside UC, Santa Barbara UC, Santa Cruz U of Cincinnati U of Colorado Colorado State Florida A&M Harvard U of Iowa Iowa State U LBNL LLNL U of Louisville U of Maryland U of Massachusets MIT U of Mississippi Mount Holyoke College U of Notre Dame Ohio State U of Oregon U of Pennsylvania Prairie View A&M Princeton SLAC Univ. of South Carolina Stanford U SUNY, Albany U of Tennessee U of Texas at Dallas U of Texas, Austin Vanderbilt U of Wisconsin Yale U (78 institutions, 609 Collaborators)

M. V. Purohit, Univ. of S. Carolina, ICHEP 2004, Beijing, China The BaBar Detector Silicon Vertex Tracker z hit resolution 15  m Drift CHamber  (p T )/p T = 0.14%  p T % Detector of Internally Reflected Cherenkov light K-  separation GeV ElectroMagnetic Calorimeter  E /E = 2.3%  E -1/4  1.4% RPC based Instrumented magnetic field Flux Return 18/19 layers of RPC in 60/65 cm of iron ~250 fb -1 of data collected so far.

M. V. Purohit, Univ. of S. Carolina, ICHEP 2004, Beijing, China Searching for New Physics in Charm CP violation with BaBar data CP violation in charm is expected to first manifest itself in Singly Cabibbo-suppressed (SCS) decays. Within the Standard Model, one expects CP violation asymmetries in SCS Decays ~10 -3, while New Physics can give CP violation asymmetries ~ [G. Burdman & I. Shipsey, Ann. Rev. Nucl. Part. Sci., 2003, hep- ph/ See also S. Bianco, F. L. Fabbri, D. Benson & I. Bigi, hep-ex/ ] Current experimental limits are ~ (2 – 5) x leaving a considerable window for new physics discovery. The analysis reported here is based on ~43,000 D +  KK  decays from ~80 fb -1. [BaBar has ~250 fb -1 of data.]

M. V. Purohit, Univ. of S. Carolina, ICHEP 2004, Beijing, China Standard Model interfering amplitudes: A ~V cs * ¢ V us A ~ V cs * ¢ V us, V cd * ¢ V ud, V cb * ¢ V ub In the Wolfenstein parameterization, the CKM matrix (below) clearly gives only a small CP violating asymmetry.

M. V. Purohit, Univ. of S. Carolina, ICHEP 2004, Beijing, China Data Sample and Analysis Our final sample contains ~43,000 D +  KK  decays from ~80 fb -1. We measure the asymmetry where We also measure the asymmetry in the  & K* regions.

M. V. Purohit, Univ. of S. Carolina, ICHEP 2004, Beijing, China KK  Yields ± 228 D + events ± 226 D - events ± 217 D s + events ± 214 D s - events Likelihood ratio cut uses p* and beam-spot constrained  2 Kaons have kaon ID, pions must not have kaon ID

M. V. Purohit, Univ. of S. Carolina, ICHEP 2004, Beijing, China A CP in ,   Regions of KK  Dalitz Plot 5452 ± 87 D + events 5327 ± 86 D - events  mass is required to lie within 10 MeV/c 2 of nominal  mass |cos(  H )| is required to be ≥ 0.2 ;  H is helicity angle in  rest frame 1. The  region:

M. V. Purohit, Univ. of S. Carolina, ICHEP 2004, Beijing, China 5247 ± 96 D + events 5113 ± 96 D - events K* mass is required to lie within 50 MeV/c 2 of nominal K* mass |cos(  H )| is required to be ≥ 0.3 ;  H is helicity angle in K* rest frame 2. The   region:

M. V. Purohit, Univ. of S. Carolina, ICHEP 2004, Beijing, China Systematic Errors on A CP Systematic errors on A CP estimated as: –Largest difference using other normalizations (0.8%) –Largest uncorrected asym. in control samples (1.1%) –From table (in units of ): Source KK   K *0 K MC simulation 0.06 Background estimate Event Selection Total

M. V. Purohit, Univ. of S. Carolina, ICHEP 2004, Beijing, China A CP Results

M. V. Purohit, Univ. of S. Carolina, ICHEP 2004, Beijing, China The Branching Ratio  (D +  K - K +   ) /  (D +  K -     ) Using measured yields and efficiencies in bins of the Dalitz plots, the total branching ratio is determined: ± ± Sources of systematic errors: SourceError (10 -2 ) PID, tracking 0.21 Background estimate 0.05 Event Selection 0.02 Total 0.22

M. V. Purohit, Univ. of S. Carolina, ICHEP 2004, Beijing, China The Branching Ratio Compared

M. V. Purohit, Univ. of S. Carolina, ICHEP 2004, Beijing, China Searching for New Physics in mixing with BaBar data For decays of neutral Ds R mix – The standard model predicts a low rate (~10 -7 ) of for the box diagram which goes up to ~10 -3 when long distance effects are included; nevertheless we would like to observe mixing as a first step. – New physics effects can easily produce > rates of mixing, and are the only way we can get CP violation in mixing. [G. Burdman & I. Shipsey, Ann. Rev. Nucl. Part. Sci., 2003, hep- ph/ See also S. Bianco, F. L. Fabbri, D. Benson & I. Bigi, hep-ex/ ] The analysis reported here is based on ~50,000 semi-electronic decays of neutral D mesons from ~87 fb -1 with mixing rate sensitivity down to ~10 -3.

M. V. Purohit, Univ. of S. Carolina, ICHEP 2004, Beijing, China (A. Petrov, hep/ph ) Possible enhancements due to new particles and interactions in new physics models: gluinos, squarks fourth generation quarks lepto-quarks, etc. No CP-violating effects expected in SM -- CP violation in mixing would be unambiguous signal of new physics x=  M/  y=  /2  x=  M/  mixing rate = |amplitude| 2 New Physics Mixing Predictions current experimental sensitivity Charm Mixing, continued SM Mixing Predictions

M. V. Purohit, Univ. of S. Carolina, ICHEP 2004, Beijing, China cc continuum event topology K e,   slow other charmed hadron (will hadronically reconstruct in next iteration of analysis) interaction point beamspotD0D0 D *+ D 0  + tag D 0 K + e - D *- D 0  - tag D 0 K - e + Wrong-sign mixed decays D *+ D 0  + tag K - e + D *- D 0  - tag K + e - Right-sign unmixed decays

M. V. Purohit, Univ. of S. Carolina, ICHEP 2004, Beijing, China The Analysis Strategy exponential envelope Quadratic time dependence mixing rate We use neutral D mesons from D* + decays: D* +  D 0   Flavor at birth is tagged by pion from D* decay Flavor at decay is tagged by electron: D 0  (K - /K* - ) e + e Clearly, an e + signifies a RS (Right Sign, or unmixed) D 0 while an e - would signify a WS (Wrong Sign or mixed) D 0 The mixing rate is given by where x   M / ,y   / 2  No DCS decay background exists

M. V. Purohit, Univ. of S. Carolina, ICHEP 2004, Beijing, China Semileptonic Mixing Analysis Technique A neural network event selector is used. Another neural network is used for p*(D 0 ) reconstruction. (p* is the c.m. momentum) An unbinned extended maximum likelihood fit using  M & transverse lifetime is then done, where  M  m(  D 0 ) – m(D 0 ) First, a fit to high-statistics RS sample gets –signal  M shape and –unmixed D 0 lifetime for use in WS pdf and to get N(unmixed), the normalization for R mix. Subsequent fit to WS sample for N(mix) R mix ≈ N(mix) / N(unmixed) Data sample: 80 fb -1 on resonance, 7.1 fb -1 off-resonance

M. V. Purohit, Univ. of S. Carolina, ICHEP 2004, Beijing, China Unbinned extended maximum likelihood fit to transverse lifetime and  M = M(D*)-M(D 0 ) with 15 floated parameters RS Unmixed Fit to 87 fb -1 of Data D+ D0 bkgd zero life  M signal region  M sideband D+ D0 bkgd zero life lifetime tails D0 sgnl Results of fit: Unmixed D0 yield: ± 324 evts (stat)  M and lifetime pdfs

M. V. Purohit, Univ. of S. Carolina, ICHEP 2004, Beijing, China WS Mixed D 0 Fit to 87 fb -1 of Data Mixed signal pdf parameters taken from high-statistics unmixed data fit –N i and zero lifetime triple Gaussian parameters floated (11 parameters) Random D + Random D 0 Zero Life  M projection D 0 signal Peaking D + Distribution of N(mix) from fits to an ensemble of 170 WS generic MC datasets with zero embedded mixed signal events (~5% probability of getting a larger result for R mix =0) Unblinded N(mix): 114 ± 61 evts

M. V. Purohit, Univ. of S. Carolina, ICHEP 2004, Beijing, China WS Mixed D 0 Fit to 87 fb -1 of Data zero life Lifetime projection showing mixed signal random D + random D 0 D 0 signal pkng D + Full lifetime projection

M. V. Purohit, Univ. of S. Carolina, ICHEP 2004, Beijing, China stat stat + syst 90% Confidence limit on number of mixing signal. Final result for semileptonic mixing The fit gives a yield of N mix =114 ± 61 wrong sign signal events. Systematics evaluated as fraction of statistical error: Normalising to number of right-sign events gives result on mixing.

M. V. Purohit, Univ. of S. Carolina, ICHEP 2004, Beijing, China Comparison to other results Summary of all BaBar D mixing measurements: Hadronic (K  ) analysis: R mix < 1.3 x Lifetime difference for D 0  KK and D 0   y CP = 0.8 ± % This (semileptonic) analysis: Rmix < 4.2 x (90% CL)

M. V. Purohit, Univ. of S. Carolina, ICHEP 2004, Beijing, China Conclusions We have demonstrated that A CP is consistent with zero. The measured values are: D +  KK  ± ± D +   ± ± D +  K*K  ± ± We find that the Branching Ratio for D +  KK  is: ± ± We find, using semi-electronic neutral D decays, that R mix < 4.2 x (90% CL)

M. V. Purohit, Univ. of S. Carolina, ICHEP 2004, Beijing, China Acknowledgements Thanks to all BaBar collaborators including, particularly: Francisco Yumiceva, South Carolina graduate student (D +  K + K -   decays) Kevin Flood, graduate student at the Univ. of Massachusetts, Amherst (semileptonic mixing analysis)

M. V. Purohit, Univ. of S. Carolina, ICHEP 2004, Beijing, China Backup Slides

M. V. Purohit, Univ. of S. Carolina, ICHEP 2004, Beijing, China The Status of CP Violation CP violation is necessary if the universe is indeed matter-antimatter asymmetric but the Big Bang is not Standard Model CP violation cannot explain CP violation in the universe New physics is needed, SM is not enough Charm may be a good place to look

M. V. Purohit, Univ. of S. Carolina, ICHEP 2004, Beijing, China Raw CP asymmetries in control samples D s +  K + K -   decays: +3.0 x D +  K -    + decays: -2.9 x 10 -3

M. V. Purohit, Univ. of S. Carolina, ICHEP 2004, Beijing, China Event Sample Nearly all Run 1, 2 on/off-resonance (R10 processing) –80.0 fb -1 on-resonance –7.1 fb -1 off-resonance SP4 generics Wrong-sign mixed D 0 lifetime: 100k events

M. V. Purohit, Univ. of S. Carolina, ICHEP 2004, Beijing, China Track Selection Pion candidates –GoodTracksVeryLoose –.45 <  lab < 2.5 –p* < 0.45 GeV/c –track fit prob. > –beamspot refit prob. > 0.01 –≥ 2 SVT r-phi (z) hits with at least 1 hit on inner 3 r-phi (z) layers –≥ 6 total SVT hits Multiple D 0 candidates –Veto events with more than one RS or WS D 0 candidate passing all selection criteria (~11% of RS signal lost after other cuts) Kaon candidates –GoodTracksVeryLoose –KLHVeryTight plus KMicroVeryTight (p lab > 2.1 GeV/c) –.45 <  lab < 2.5 Electron candidates –GoodTracksVeryLoose –PidLHElectrons (default) –.45 <  lab < –0.8 < E/p < 1.05 –  conversion veto K/e vertex –GeoKin vertex prob. > 0.01 –M(KeVtx) < 1.82 GeV/c 2 –Lifetime error < 2 D 0 lifetimes

M. V. Purohit, Univ. of S. Carolina, ICHEP 2004, Beijing, China Neural Network Event Selection Events are selected using a neural network with the following inputs taken from signal and generic MC: –p*(K/e vertex) –p*(  ) –thrust magnitude (w/o K, e) –Opening angle between p*(K/e) and thrust (w/o K, e) –opening angle between p*(K) and p*(e) RS/WS signal selection efficiencies are identical RS/WS signal/bkgd NN event selector output signal bkgd Lumi-scaled NN output signal bkgd Normalized NN output final cut optimized for best statistical sensitivity final cut

M. V. Purohit, Univ. of S. Carolina, ICHEP 2004, Beijing, China Novel use of two hidden-layer neural network to map NN input vector to signal p*(D 0 ) Momentum resolution fit to double gssn –phi core sigma/fraction: 82 mrad / 0.81 –theta core sigma/fraction: 80 mrad / 0.94 –total magnitude RMS: 371 MeV/c –transverse magnitude RMS: 350 MeV/c Trained with inputs from signal MC: –p*(K/e vertex) –p*(  ) –thrust vector (w/o K, e) –Opening angle between p*(K/e) and thrust (w/o K,e) –Opening angle between p*(  ) and thrust (w/o K,e) –opening angle between p*(K) and p*(e) –opening angle between p*(K/e) and p*(  ) Neural Network D 0 Reconstruction p*(D 0 ) Neural Network Residuals GeV/c rad

M. V. Purohit, Univ. of S. Carolina, ICHEP 2004, Beijing, China zero lifetime D+D+ WS mixed D 0 RS unmixed D 0 mis-reco’d D 0 1-d lifetime pdfs  M, Lifetime PDFs signal D + (RS only) 1-d  M pdfs random comb. signal (zoom) off-res data fit shape from MC shape from MC fit from RS fit  M = M(D*) - M(D 0 ) MC/fit

M. V. Purohit, Univ. of S. Carolina, ICHEP 2004, Beijing, China Testing the Mixed Fit with Generic MC and Embedded Mixed Events WS mixed fit tested with full fit on ~540 lumi-scaled generic MC datasets with different levels of embedded mixed events N(mix) pull plots (right) show no evidence of bias or improperly scaled errors in the fit number of N(mix) with or w/o the presence of mixed events

M. V. Purohit, Univ. of S. Carolina, ICHEP 2004, Beijing, China Goodness-of-Fit to Run 1,2 Data Toy MC datasets generated from RS/WS data fit pdfs and fit with unmixed/mixed fit models to determine goodness-of-fit Both RS/WS NLL values from data fits lie well within range predicted by the fits to toy MC NLL Distribution for WS Toy Datasets NLL distribution for RS toy datasets WS data fit NLL value RS data fit NLL value

M. V. Purohit, Univ. of S. Carolina, ICHEP 2004, Beijing, China No significant variations in the mixing rate were found when making the following changes: – TwoTrksVtx → Hadronic beamspot – GeoKin K,e vertex → FastVtx – KLHVeryTight → KMicroVeryTight – E/p <1.05 → 1.10 – Lifetime error cut +/- 10% – Separate fitting of initial D 0 and D 0 – Different NN event selector cuts Evaluation of Systematics Systematic checks fall into two categories: –reasonableness or “sanity” checks –systematic variations which encode lack of knowledge/ understanding and biases in the fit model First class demonstrates robustness of result Latter class determines quantitative estimation of the systematic error Reasonableness Checks

M. V. Purohit, Univ. of S. Carolina, ICHEP 2004, Beijing, China RS Unmixed  M, Lifetime PDF Fit Classes RS random  M D 0 lifetime RS D + RS random  M zero lifetime RS peaking  M D 0 unmixed lifetime full  M range MM MM MM MM MM MM MM cc

M. V. Purohit, Univ. of S. Carolina, ICHEP 2004, Beijing, China WS Mixed  M, Lifetime PDF Fit Classes Random comb.  M D 0 lifetime WS random  M D + lifetime Random comb.  M zero lifetime Peaking  M D + lifetime WS peaking  M D 0 mixed lifetime full  M range MM MM MM MM MM MM MM MM cc cc

M. V. Purohit, Univ. of S. Carolina, ICHEP 2004, Beijing, China  stat Floated unmixed fit RS signal  M shape parameters correlated, so N(mix) systematic error from this source calculated using RS fit correlation matrix Quantitative Systematic Error Total systematic error  sys List of systematic errors:

M. V. Purohit, Univ. of S. Carolina, ICHEP 2004, Beijing, China Semileptonic Mixing Summary R mix = ± (stat) ± (sys) R mix consistent with no mixing CP fit was performed and no CP-violating effects were found R mix < (95% C.L.) from NLL scan E791: r mix < 90% CL FOCUS: r mix < 90% CL r mix < 90% CL (using Feldman-Cousins) Stat error is ~0.1% FOCUS result is UNPUBLISHED (Plot courtesy of G. Burdman & I. Shipsey, hep/ph ) N(mix) NLL Scan