1. June 20, 2002Alex Smith University of Minnesota Recent Advances in Charm Physics 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 Alex Smith University of Minnesota Physics in Collisions June 20-22, 2002

2. June 20, 2002Alex Smith University of Minnesota Why Charm? 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/  radiative decays (see talk by Shen Xiaoyan) Charm contributes to a variety of important topics in HEP…

3. June 20, 2002Alex Smith University of Minnesota D0-D0bar Mixing x mixing: Channel for new physics… y y (long-range) mixing: SM background… x Standard model prediction: …although long-distance contributions could increase these * New physics will enhance x but not y but not y * CP violation in mixing would be a smoking gun for new physics 1)All mixing contributions doubly Cabibbo suppressed - Factor of tan 4  c in rate 2)Further GIM suppression of x possible Two types of mixing:

4. June 20, 2002Alex Smith University of Minnesota D0-D0bar Mixing 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,  K , between CF and DCS amplitudes can lead to observable quantities x’ and y’, related to x and y by a rotation doublyCabibbosuppressed (R D ) mixing (x 2 +y 2 ) CabibboFavored (CF) (CF) “Wrong sign” Notation: “right-signed” (RS) => Cabibbo-favored decays “wrong-signed” (WS) => Mixing or doubly Cabibbo-suppressed decays “wrong-signed” (WS) => Mixing or doubly Cabibbo-suppressed decays Look for mixing in “wrong signed” (WS) decays of D 0 …

5. June 20, 2002Alex Smith University of Minnesota Current Status of D 0 -D 0 Mixing “Typical” non-SM predictions (many higher and lower, however) “Typical” upper SM predictions - Current measurements cutting into range of some non-SM predictions - Much room for improvement before we hit SM background x y

6. June 20, 2002Alex Smith University of Minnesota X, y, and RD from D0->K+pi- Currently, best constraints come from this mode if assumptions about strong phase are madeCurrently, best constraints come from this mode if assumptions about strong phase are made Unknown strong phase difference weakens these limitsUnknown strong phase difference weakens these limits CLEO measurement remains the strongest constraint on x CLEO measurement remains the strongest constraint on x

7. June 20, 2002Alex Smith University of Minnesota X, y, and RD from D0->K+pi- x y FOCUS x- y limit CLEO limit (still best constraint on x)

8. June 20, 2002Alex Smith University of Minnesota RWS from D0->K+pi- Belle and BaBar have new WS rate measurementsBelle and BaBar have new WS rate measurements

9. June 20, 2002Alex Smith University of Minnesota Measurements of the Wrong Sign Rate R WS in D 0 ->K +   R WS in multi-body hadronic modes Belle and BaBar –Significant improvements in R WS –x’ and y’ proper time fits soon! Information in multi-body modes not yet fully exploited –x, y, CP violation Situation more complicated Dalitz plot fits of RS and WS required to get limits on x, y, CPV Need lots of statistics

10. June 20, 2002Alex Smith University of Minnesota D0->K0pi0 Measurement of ratio of D 0 rates into K 0 L  0 and K 0 S  0 can be used to disentangle the CF and DCS amplitudes: K 0 L content of K 0 and K 0 is equal K 0 L content of K 0 and K 0 is opposite in sign to K 0 S Get DCS rate from interference between the two Very important measurement! Uncertainty still too large to limit  K , but more data on the way… First measurement!

11. June 20, 2002Alex Smith University of Minnesota 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., D 0 ->K + K - ) analyses Better scaling of sensitivity to x with int. luminosity than D 0 ->K +  - analysis Complicated Dalitz plot and proper time fit required x y

12. June 20, 2002Alex Smith University of Minnesota D0->K0spipi CLEO Time-independent Dalitz fit so far… Rich resonance structure – , K *-, … –Interference effects Fit results shown in projectionsfitdata

13. June 20, 2002Alex Smith University of Minnesota D0->K0spipi CLEO Phase convention: Final fit with intermediate states: Right sign First measurement of strong phase difference between CF and DCS! Wrong sign (Breit-Wigner resonance line shape)

14. June 20, 2002Alex Smith University of Minnesota D0->K0spipi Babar 15,753 events! CLEO will have R D, x, y, and A CP measurements very soonCLEO will have R D, x, y, and A CP measurements very soon BaBar analysis is in progressBaBar analysis is in progress Difficult analysisDifficult analysis Many systematic uncertainties will scale with statisticsMany systematic uncertainties will scale with statistics

15. June 20, 2002Alex Smith University of Minnesota D0->K+K- and D0->pi+pi- y can be determined by measuring the lifetime difference between D 0 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 D 0 ->K -  + (assumes no CP violation): These were some of the first D mixing results to come out of the B factories Many systematic errors will cancel in the ratio

16. June 20, 2002Alex Smith University of Minnesota D0->K+K- and D0->pi+pi- Technique, resolution, and systematics are quite different at fixed target experiments (FOCUS, E791) and e + e - (Belle, BaBar, CLEO)

17. June 20, 2002Alex Smith University of Minnesota D0->K+K- and D0->pi+pi- y CP from D 0 ->K + K - /  +   FOCUS measurement is high relative to both CLEO and FOCUS D 0 ->K +  - limits –Unknown strong phase difference New BaBar and Belle measurements pull y CP back towards D 0 ->K +  - limits x y

18. June 20, 2002Alex Smith University of Minnesota Measurements of the Mixing Rate Using Wrong Sign Semileptonic D 0 Decays 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 (D 0 ->K l ): –CLEO (D 0 ->K * l ): Sensitivity estimate from FOCUS B factories should have results soon Accessible to future experiments –Hadron machines Lepton helps triggering –CLEO-c Opposite side tag x y

19. June 20, 2002Alex Smith University of Minnesota Three Types of CP Violation f D 0 f D f 2 D f 2 22   f ff D0D0 f 2 D0D0 2  ++ Mixing (A M ) Interference between mixing and decay (  ) Decay (A D ) |A f |  |A f |

20. June 20, 2002Alex Smith University of Minnesota Searches for CP Violation 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 )

21. June 20, 2002Alex Smith University of Minnesota Charm Semileptonic Decay Rates and Form Factors 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 |V ub | and |V cb | Several experiments are working on other semileptonic modes: – D 0 ->  l  l  K l – D s ->  l New FOCUS result is a dramatic improvement (tiny backgrounds)! (FOCUS also sees first evidence for an S-wave component)

22. June 20, 2002Alex Smith University of Minnesota Motivation to Measure Charmed Particle Lifetimes Non-perturbative QCD effects are important in weak decays of charmed particles ExternalSpectatorInternalSpectator W Exchange W Annihilation Color-suppressed Helicity and Wavefunction 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

23. June 20, 2002Alex Smith University of Minnesota 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  (D 0 ) and  (D + ) from FOCUS

24. June 20, 2002Alex Smith University of Minnesota Charmed Baryon Lifetimes Unlike charmed mesons, decays of charmed baryons are not color or helicity suppressedUnlike charmed mesons, decays of charmed baryons are not color or helicity suppressed –W-exchange diagrams may be important

25. June 20, 2002Alex Smith University of Minnesota Charmed Particle Lifetimes 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  c + ) –Tuning with data will yield better theoretical tools

26. June 20, 2002Alex Smith University of Minnesota Prompt charmonium production I DominantDominant at p  * endpoint O (10%) Small 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

27. June 20, 2002Alex Smith University of Minnesota Prompt charmonium Production PRL 88, 052001, (2002) Some NRQCD calculations predict a large yield in the endpoint region due to color-octet e + e -  J/  gSome NRQCD calculations predict a large yield in the endpoint region due to color-octet e + e -  J/  g –This was not observed! By comparing on/off resonance:By comparing on/off resonance: Cross sections for 2.0 GeV/c< p * < p * max :Cross sections for 2.0 GeV/c< p * < p * max : e + e -  J/  g not observed in endpoint region

28. June 20, 2002Alex Smith University of Minnesota Prompt_charmonium Production Clear threshold At 2*m c J/  Sideband

29. June 20, 2002Alex Smith University of Minnesota Prompt Charmonium Production e + e -  J/  D *+ X e + e -  J/  D 0 X Use D *+ ->D 0  +, D 0 ->K , KK, K , K s 0 , K  0Use D *+ ->D 0  +, D 0 ->K , KK, K , K s 0 , K  0 Use D 0 ->K , KK modesUse D 0 ->K , KK modes

30. June 20, 2002Alex Smith University of Minnesota Prompt Charmonium Production Use JETSET rates to convert  (e + e -  J/  D (*) X) to  (e + e -  J/  cc) Compare with measured  (e + e -  J/  X): Recall that prediction was only O (0.1)!

31. June 20, 2002Alex Smith University of Minnesota The Near Future in Charm Physics D 0 mixing:D 0 mixing: –New measurements of x’ and y’ from Belle and BaBar using D 0 ->K +  - –  K  from Belle by measuring different D->K  isospin states Can get x and y from D 0 ->K +  -Can get x and y from D 0 ->K +  - –Time-dependent CP asymmetry measurements in D 0 ->K + K -,  +  - –Dalitz analyses: D 0 ->K s 0  +  -D 0 ->K s 0  +  - –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 charmQCD input from charm –Necessary ingredient to improve measurements of standard model parameters –Semileptonic branching ratios and form factors (several new FOCUS results imminent) –f D and f Ds measurements (Belle, BaBar) –More lifetime measurements and spectroscopy at B factories –Further understanding of charmonium production puzzle

32. June 20, 2002Alex Smith University of Minnesota The Near Future in Charm Physics: D Mixing Does not include B factory results, for which sensitivity estimates have not been shown:Does not include B factory results, for which sensitivity estimates have not been shown: D 0 ->K 0 s  +  - D 0 ->K +  - D 0 ->K* + l - Can expect great improvement when these measurements are addedCan expect great improvement when these measurements are added x y

33. June 20, 2002Alex Smith University of Minnesota Future Experiments in Charm Physics e + e - machines: –Belle, BaBar--- running –CLEO-c: 2003 : L ~(1-4)x10 32 /cm 2 s –BESIII: 2005-6 : L ~10 33 /cm 2 s –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)

34. June 20, 2002Alex Smith University of Minnesota CLEO-c Experiment 2003: 3 fb -1 at  (3770) –L ~3.6x10 32 /cm 2 s –30M events, 6M tagged D decays –310 times MARK III 2004: 3 fb -1 at ~sqrt(s)=4100 MeV –L ~3.0x10 32 /cm 2 s –1.5M D s pairs, 0.3M tagged D s decays –480X MARK III, 130X BESII 2005: 1 fb -1 at the J/  (3100) –L ~1.0x10 32 /cm 2 s –1 billion J/  decays –170 times MARK III, 20X BESII

35. June 20, 2002Alex Smith University of Minnesota CLEO-c Experiment CLEO-c reach for some key measurements… Absolute branching fractions Semileptonic form factors D mixing searches CP violation searches Rare D decays

36. June 20, 2002Alex Smith University of Minnesota Future Charm Physics at Hadron Machines CDF –Up to 10 7 D 0 ->K  –=> ~15,000 WS D 0 ->K +   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 10 8 D 0 ->K  –=> ~150,000 WS D 0 ->K +   Many assumptions in this number –CPV reach down to 10 -4 ?

37. June 20, 2002Alex Smith University of Minnesota Summary and Outlook 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