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Recent Advances in Charm Physics

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  1. Why charm physics? Searches for new physics using D meson decays Mixing CP violation Measurements which provide input to QCD Decay processes Charm semileptonic decays Lifetimes Production mechanisms What to expect from future experiments Conclusions Recent Advances in Charm Physics Alex Smith University of Minnesota Physics in Collisions June 20-22, 2002 Alex Smith University of Minnesota

  2. Why Charm? Charm contributes to a variety of important topics in HEP… • Searches for new physics: • D mixing • CP violation • Measurements which guide QCD • Necessary in order to extract standard model parameters • Form factors and decay constants -> B decay CKM elements • Final state interactions, resonances in multi-body decays • Lifetimes, masses, branching fractions • Charmonium production mechanisms • Spectroscopy of light mesons/glueball candidates • Dalitz plot fits of D meson decays (see talk by Brian Meadows) • J/y radiative decays (see talk by Shen Xiaoyan) Alex Smith University of Minnesota

  3. D0-D0bar Mixing x mixing: Channel for new physics… x Two types of mixing: y (long-range) mixing: SM background… Standard model prediction: y • All mixing contributions doubly Cabibbo suppressed • - Factor of tan4qc in rate • Further GIM suppression of x possible * New physics will enhance x but not y * CP violation in mixing would be a smoking gun for new physics …although long-distance contributions could increase these Alex Smith University of Minnesota

  4. mixing (x2+y2) doubly Cabibbo suppressed (RD) Cabibbo Favored (CF) “Wrong sign” D0-D0bar Mixing Look for mixing in “wrong signed” (WS) decays of D0… Notation:“right-signed” (RS) => Cabibbo-favored decays “wrong-signed” (WS) => Mixing or doubly Cabibbo-suppressed decays Mixing is not the only way to get to “wrong sign” hadronic states… Need to fit proper decay time in order to distinguish mixing (both x and y) from doubly Cabibbo-suppressed (DCS) decays… Complication: phase difference, dKp, between CF and DCS amplitudes can lead to observable quantities x’ and y’, related to x and y by a rotation Alex Smith University of Minnesota

  5. Current Status of D0-D0 Mixing • Current measurements cutting into range of some non-SM predictions • Much room for improvement before we hit SM background y x “Typical” upper SM predictions “Typical” non-SM predictions (many higher and lower, however) Alex Smith University of Minnesota

  6. Currently, best constraints come from this mode if assumptions about strong phaseare made Unknown strong phase difference weakens these limits CLEO measurement remains the strongest constraint on x X, y, and RD from D0->K+pi- Alex Smith University of Minnesota

  7. X, y, and RD from D0->K+pi- y CLEO limit (still best constraint on x) FOCUS x-y limit x Alex Smith University of Minnesota

  8. Belle and BaBar have new WS rate measurements RWS from D0->K+pi- Alex Smith University of Minnesota

  9. Belle and BaBar Significant improvements in RWS x’ and y’ proper time fits soon! Information in multi-body modes not yet fully exploited x, y, CP violation Measurements of the Wrong Sign Rate RWS in multi-body hadronic modes • Situation more complicated • Dalitz plot fits of RS and WS required to get limits on x, y, CPV • Need lots of statistics RWS in D0->K+p- Alex Smith University of Minnesota

  10. Measurement of ratio of D0 rates into K0Lp0 and K0Sp0 can be used to disentangle the CF and DCS amplitudes: K0L content of K0 and K0 is equal K0L content of K0 and K0 is opposite in sign to K0S Get DCS rate from interference between the two D0->K0pi0 First measurement! Very important measurement! Uncertainty still too large to limit dKp, but more data on the way… Alex Smith University of Minnesota

  11. D0->K0spipi Overview • Measure x and y rather than x’2 and y’ • RS and WS occupy the SAME Dalitz plot: • Simultaneous measurement of relative strong phase between CF and DCS • Only mode with sensitivity to sign of x! • Doubly-Cabibbo-suppressed modes • y sensitivity comparable to CP eigenstate (eg., D0->K+K-) analyses • Better scaling of sensitivity to x with int. luminosity than D0->K+p- analysis • Complicated Dalitz plot and proper time fit required y x Alex Smith University of Minnesota

  12. Time-independent Dalitz fit so far… Rich resonance structure r, K*-, … Interference effects Fit results shown in projections fit data D0->K0spipi CLEO Alex Smith University of Minnesota

  13. D0->K0spipi CLEO Final fit with intermediate states: (Breit-Wigner resonance line shape) Wrong sign Phase convention: Right sign First measurement of strong phase difference between CF and DCS! Alex Smith University of Minnesota

  14. CLEO will have RD, x, y, and ACP measurements very soon BaBar analysis is in progress Difficult analysis Many systematic uncertainties will scale with statistics D0->K0spipi Babar 15,753 events! Alex Smith University of Minnesota

  15. D0->K+K- and D0->pi+pi- y can be determined by measuring the lifetime difference between D0 decays to CP-even and CP-odd final states: Experimentally, it is easier to measure the lifetime difference of a CP-even decay relative to the non-CP final state D0->K-p+ (assumes no CP violation): Many systematic errors will cancel in the ratio These were some of the first D mixing results to come out of the B factories Alex Smith University of Minnesota

  16. Technique, resolution, and systematics are quite different at fixed target experiments (FOCUS, E791) and e+e- (Belle, BaBar, CLEO) D0->K+K- and D0->pi+pi- Alex Smith University of Minnesota

  17. FOCUS measurement is high relative to both CLEO and FOCUS D0->K+p- limits Unknown strong phase difference New BaBar and Belle measurements pull yCP back towards D0->K+p- limits D0->K+K- and D0->pi+pi- y yCP from D0->K+K-/p+p- x Alex Smith University of Minnesota

  18. Sensitive to mixing only (no DCS decays): Will need separate measurement of y if that turns out to be larger or comparable to x Measurements from E791 (D0->Kln): CLEO (D0->K*ln): Sensitivity estimate from FOCUS B factories should have results soon Accessible to future experiments Hadron machines Lepton helps triggering CLEO-c Opposite side tag Measurements of the Mixing Rate Using Wrong Sign Semileptonic D0 Decays y x Alex Smith University of Minnesota

  19. 2 D f Three Types of CP Violation Decay (AD) |Af|  |Af | 2 D  f 2 2 D0 D0 D0 D0  Mixing (AM) f f 2 2 D0 D0 f f Interference between mixing and decay (f)  + + D0 D0 D0 D0 f f Alex Smith University of Minnesota

  20. Ingredients for observing non-standard model physics through CPV in D decays Decay amplitude with contributions from at least two diagrams with different weak phases Non-negligible strong phase shift Likely to be non-zero in charm decays, since SU(3) flavor symmetry is badly violated SM predictions: O(10-3) or below in SCS modes: Due to interference of tree and penguin amplitudes No SM CPV in DCS and CF modes Any observation is new physics Non-SM predictions: Up to O(10-2) Searches for CP Violation Alex Smith University of Minnesota

  21. Measurements of charm semileptonic branching fractions and form factors can be used to improve estimates of corresponding quantities in the B sector Leads to improved estimates of |Vub| and |Vcb| Several experiments are working on other semileptonic modes: D0->pln , rln , Kln Ds-> fln Charm Semileptonic Decay Rates and Form Factors (FOCUS also sees first evidence for an S-wave component) New FOCUS result is a dramatic improvement (tiny backgrounds)! Alex Smith University of Minnesota

  22. Non-perturbative QCD effects are important in weak decays of charmed particles Motivation to Measure Charmed Particle Lifetimes External Spectator Internal Spectator W Annihilation W Exchange Helicity and Wavefunction Suppressed Color-suppressed • Which processes are important in charmed meson and baryon decays? Challenge for theory is to reproduce the observed lifetime hierarchy in charmed baryons and mesons Alex Smith University of Minnesota

  23. D Meson Lifetimes Large observed ratio is understood to be due to destructive interference in diagrams contributing only to D+ decays New precise measurements of t(D0) and t(D+) from FOCUS Alex Smith University of Minnesota

  24. Unlike charmed mesons, decays of charmed baryons are not color or helicity suppressed W-exchange diagrams may be important Charmed Baryon Lifetimes Alex Smith University of Minnesota

  25. Theory now describes most of the observed lifetime hierarchy Still some notable discrepancies with theory, however: Further measurements will help guide theory New and more precise lifetimes Further analyses of charmed hadron decays (like Lc+) Tuning with data will yield better theoretical tools Charmed Particle Lifetimes Alex Smith University of Minnesota

  26. Tevatron Run 1A: CDF and D0 observe O(10-100) surplus in charmonium production cross section above NRQCD predictions Something is missing in the model. Color-octet? Gluon splitting? Can test NRQCD using e+e- collisions at lower energies Prompt charmonium production I Dominant Dominant at py* endpoint Small O(10%) Alex Smith University of Minnesota

  27. Some NRQCD calculations predict a large yield in the endpoint region due to color-octet e+e-J/yg This was not observed! By comparing on/off resonance: Cross sections for 2.0 GeV/c< p* < p*max: Prompt charmonium Production PRL 88, 052001, (2002) e+e-J/yg not observed in endpoint region Alex Smith University of Minnesota

  28. Prompt_charmonium Production Clear threshold At 2*mc J/y Side band Alex Smith University of Minnesota

  29. Use D*+->D0p+, D0->Kp, KK, Kppp, Ks0pp, Kpp0 Prompt Charmonium Production e+e-J/yD*+X e+e-J/yD0X • Use D0->Kp, KK modes Alex Smith University of Minnesota

  30. Use JETSET rates to convert s(e+e-J/yD(*)X) to s(e+e-J/ycc) Compare with measured s(e+e-J/yX): Recall that prediction was only O(0.1)! Prompt Charmonium Production Alex Smith University of Minnesota

  31. D0 mixing: New measurements ofx’ and y’ from Belle and BaBar using D0->K+p- dKpfrom Belle by measuring different D->Kp isospin states Can get x and y from D0->K+p- Time-dependent CP asymmetry measurements in D0->K+K-, p+p- Dalitz analyses: D0->Ks0p+p- Best sensitivity to x with B factory samples (including its sign) RS and WS interfere since they have the same final state CLEO will have mixing/CPV limits soon Babar is working on this mode with 3X the CLEO statistics QCD input from charm Necessary ingredient to improve measurements of standard model parameters Semileptonic branching ratios and form factors (several new FOCUS results imminent) fD and fDs measurements (Belle, BaBar) More lifetime measurements and spectroscopy at B factories Further understanding of charmonium production puzzle The Near Future in Charm Physics Alex Smith University of Minnesota

  32. The Near Future in Charm Physics: D Mixing • Does not include B factory results, for which sensitivity estimates have not been shown: • D0->K0sp+p- • D0->K+p- • D0->K*+l-n • Can expect great improvement when these measurements are added y x Alex Smith University of Minnesota

  33. e+e- machines: Belle, BaBar--- running CLEO-c: 2003 : L~(1-4)x1032/cm2s BESIII: 2005-6 : L~1033/cm2s Clean environment Easy triggering Lower cross section than in hadronic collisions Hadron machines: CDF, D0, BTeV , LHCb, Compass, Hera-b Difficult triggering on hadronic final states Large cross section for charm (also 10X that for b’s) Future Experiments in Charm Physics Alex Smith University of Minnesota

  34. 2003: 3 fb-1 at y(3770) L~3.6x1032/cm2s 30M events, 6M taggedD decays 310 times MARK III 2004: 3 fb-1 at ~sqrt(s)=4100 MeV L~3.0x1032/cm2s 1.5M Ds pairs, 0.3M taggedDs decays 480X MARK III, 130X BESII 2005: 1 fb-1 at the J/y(3100) L~1.0x1032/cm2s 1 billion J/y decays 170 times MARK III, 20X BESII CLEO-c Experiment Alex Smith University of Minnesota

  35. Absolute branching fractions Semileptonic form factors D mixing searches CP violation searches Rare D decays CLEO-c Experiment CLEO-c reach for some key measurements… Alex Smith University of Minnesota

  36. CDF Up to 107D0->Kp => ~15,000 WS D0->K+p- Assumes current trigger rate holds up Assumes same RS/WS efficiency ratio as B factories CPV reach of 10-3? LHCb Trigger not optimal for charm BTeV Up to 108 D0->Kp => ~150,000 WS D0->K+p- Many assumptions in this number CPV reach down to 10-4? Future Charm Physics at Hadron Machines Alex Smith University of Minnesota

  37. Many exciting new results from existing data Including many other important results I did not have time to cover Several new results expected within a year or less B factories: Data is coming in fast Eagerly awaiting results from analyses in progress CDF: SVX triggers are taking charm! Great potential if charm stays within the trigger bandwidth budget Future experiments Funding decision soon on CLEO-c, first data in 2003 Many uncertainties in charm physics potential at hadron machines, however: Potential for huge gains in sensitivity Preliminary Run II CDF charm plots show that it can be done! BTeV trigger should be quite good for charm We can look forward to great advances in charm physics which will improve our understanding of the standard model and beyond Summary and Outlook Alex Smith University of Minnesota