# Presentation: 880779

## Recent Charm Physics Results from Fixed Target Experiments

**Harry W.K. Cheung, Fermilab**

**Results from 3 Fermilab experiments:**

- Data in 1990/1991 - 500 GeV/c  p  beam

- -

**E791**

**FOCUS**

- Data in 1996/1997 - 50-300 GeV/c photon beam

**SELEX**

- Data in 1996/1997 - 600 GeV/c  p  and S  beam

- -

- -

**D - D  Mixing**

**0**

**0**

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- Concentrate on

- and

**CP Violation**

- related topics

## Results receiving the most attention

**Results receiving the most attention**

**Phenomenology:**

**Assume CP conservation and use approximations for charm:**

- d = strong phase difference
-     between CF and DCS

## M(Kp)

**Looking at the decay rate difference**

- FOCUS has measured a lifetime difference:

- M(Kp)

- M(KK)

- looser Kp separation

- M(KK)

- Y=119738

- Y=10331

- Y=16532

## Corrections from a

- pure exponential decay:

- (statistical error only)

**Looking at the decay rate difference**

## Comparison of Results

**Comparison of Results**

- These results have provoked a large

- Comparison to CLEO and E791 results

- Valid for small d (strong phase difference)

- amount of theoretical interest

- centred on the following:

- IF true values of y and y' are within

- 1s of measured values

- Expectation for d (SU(3) breaking)

- SM expectation for y

- Results still consistent with no mixing

- (or much smaller values of x and y)

## Theoretical analysis of the comparison of FOCUS and CLEO Results

**Theoretical analysis of the comparison of FOCUS and CLEO Results**

- Bergmann, Grossman, Ligeti, Nir and Petrov - Phys. Lett. B486 (2000) 418

- Model independent analysis of FOCUS and CLEO results (IF within 1s of these)

- y ~ few % even with CP violation and x 1 0

- Need d large than about 45 degrees (this is zero in SU(3) limit)

- Gronau and Rosner - hep-ph/0010237

- Study of SU(3) breaking within D decays

- Can get  up to 20 degrees but 45 degrees not accommodated in their scheme

- Bigi and Uraltsev - Nucl. Phys. B592 (2001) 92

- Reanalysis of SM short-range and long-range contributions to mixing

- higher level quark level contributions can give x,y ~ 10

- Only estimated!

- -3

- (without LD contributions)

- Dispersive LD calculations have phases like d in the calculation, set to 0

- SU(3) breaking for exculsive versus inclusive rates

- x ~ y and matrix elements too small; or local quark-hadron duality violation

- Still need better understanding of SM expectation for x and y AND more data

##  Signal/Background lower than in CLEO:

-  Signal/Background lower than in CLEO:

- Double mis-ID Cabibbo favoured decay:

- Single Mis-ID and multi-body (KK, pp, Kpp , Klu,...)

- 0

- New method to handle these to increase observed signal

- Monte Carlo study

##  Fit the Kp mass in 1 MeV bins of D - D mass difference:

-  Fit the Kp mass in 1 MeV bins of D - D mass difference:

- *

##  Fit the real D yields vs D - D mass difference:

-  Fit the real D yields vs D - D mass difference:

- *

- Yield(RS) = 36760 ± 195

- Yield(WS) = 149 ± 31

- Interpretation in the possible presence of mixing?

## Interpretation in the possible presence of mixing gives a profile:

- Interpretation assuming zero mixing:

## Data is still inconclusive

- Results consistent with zero (small) mixing

- Even IF y ~ few %, x must be measured

- Cannot infer New Physics from a single
- measurement, need many, e.g. d

- (Much like for B physics)

- Wait with interest for data from B factories!

- Expected sensitivity from semileptonic
- decays from FOCUS is shown

## Search for CP Violation in Charm

- Need to normalize out production asymmetries as well as use tagging

- Summary of measured Asymmetries

- Sensitivities now at the few % level

**New results from FOCUS**

- A LONG way to go to the SM ~ 10   level

- -3

- Still sensitive to new physics (at least if seen in multiple decay modes!)

## Dalitz Plot Analyses of Hadronic Decays

**Search for CP Violation in Charm**

**and**

- Dalitz plot (amplitude) analysis needed for multi-body decays to study

- New results from E791 for the decay modes:

- CP violation

- Mixing (Rate difference) % of CPeven and CPodd states

- New results to come from FOCUS on many Dalitz plot analyses

- - New for spin 1/2 initial state

- Will phases become an area of theoretical interest?

- - study of the f

- - evidence for broad scalar s

- - evidence for broad scalar k

- 0

- ÞLaboratory for study of light quark physics

## Charm Lifetime Measurements

- Lifetime resolution is very important in mixing studies

- New lifetimes from SELEX for D  (10210 events) and for the L

- 0

- c

- Compared to PDG2000, preliminary FOCUS and CLEO values:

- Number of L

- c

- Lifetime resolution

- SELEX

- FOCUS

- CLEO II.V

- 20 fs

- 1630

- 30 fs

- 8520

- 4749

- ~140 fs

- Fixed target results will provide a benchmark for B-factories

## Summary

- Data is still inconclusive

- Results still consistent with zero (small) mixing

- Even IF y ~ few %, x must be measured, other quantities like d also helpful

- Cannot infer New Physics from a single measurement, need many
- and look for inconsistencies (much like for B physics)

- Wait with interest for charm data analyses from B factories!

- Current Fixed Target dataset probably will not be
- able to provide conclusive (5s) measurement of non-zero x and y

**CP Violation**

- Sensitivities in the few % level

- New Physics if see % level CP violation in multiple decay modes

- Not likely to see SM CP violation in charm decays at B factories

- Will probably need to wait for an experiment like BTeV

**D - D  Mixing**

**0**

**0**

**_**