# Presentation: 679414

## The case for CESR operating as a -charm factory

- Introduction
- Physics highlights
- Conclusions

- Presented by
- Marina Artuso,
- Syracuse University

- Marina Artuso

- Cornell, 9/8/2000

## Introduction

- The competition at the (4S):
- BaBar/Belle now running at a peak luminosity of 2x1033 cm-2s-1 and very high efficiency.
- Both are planning upgrades to 1034 cm-2s-1  in 2003 and eventually up to 3x1034 cm-2s-1.
-  b-factories are the main competition also in charm physics
******-charm has important advantages**:
- D production cross section ~10 time higher at -charm region
- Reconstruction efficiency is much better
- Some measurements are unique to this mode of operation
- Mark III accumulated  0.01 fb-1 at the (3770) and BES accumulated 0.02 fb-1 at Ecm=4.04 GeV

- Marina Artuso

- Cornell, 9/8/2000

## Primary charm yields at -charm

| ECM | Channel | (nb) | #of DD (Lint =1 fb-1) |
| --- | --- | --- | --- |
| 3.770 | DoDo | 5.80.8 | 5.8x106 |
| 3.770 | D+D- | 4.20.7 | 4.2x106 |
| 4.028 | DsDs | 0.80.2 | 0.8x106 |
| 4.140 | DsDs* | 0.90.2 | 0.9x106 |
| 4.140 | DoDo* | 1.6 | 1.6x106 |
| 4.140 | D+D-* | 1.6 | 1.6x106 |

- Marina Artuso

- Cornell, 9/8/2000

## Do tagged samples for Lint = 1 fb-1

**D****o******

- vs B decays: low multiplicity final state B 10 times smaller we do not have to detect subsequent charm decays.

- Marina Artuso

- Cornell, 9/8/2000

## D+ tagged samples for Lint = 1 fb-1

**D****+******

- Marina Artuso

- Cornell, 9/8/2000

## Ds tagged samples for Lint = 1 fb-1

**D****s******

- Marina Artuso

- Cornell, 9/8/2000

## D tagged samples for Lint = 1 fb-1

- All the tags allow us to use powerful kinematical constraints to look at the “other side”
- Most of them are “flavor specific”

- Marina Artuso

- Cornell, 9/8/2000

## The physics case: charm as a laboratory for new physics discovery

- DoDo mixing

- x is the most likely to be “signature” of new physics

- Marina Artuso

- Cornell, 9/8/2000

## Theoretical “guidance”

- From compilation of H.N.Nelson hep-ex/9908021

**Triangles** are  SM x  **Squares** are SM y
**Circles **are NSM x

- Predictions  encompass **15 orders magnitude** for Rmix (but not all of them are created equal!)

- Marina Artuso

- Cornell, 9/8/2000

**Notes:**
These are results from a compendium of H.N. Nelson from CLEO giving about 50 papers which predict values for the x (mass mixing) and y (width mixing) parameters. They span roughly 7 orders of magnitude which implies a rough 15 order of magnitude range of predictions for pure semileptonic mixing. I gather from this that mixing amplitudes on the order of a few percent certainly are “not out of the question” theoretically.

## CLEO enlivened this subject considerably...

**CLEO assuming CP**

**CLEO allowing CPV**

**E791  WS semilep circle**

**E791  K********/ KK lifetime band**

**D****0**

- K+-

- DCSD

- CAD

**95% CL**

**Assuming small ******

- Marina Artuso

- Cornell, 9/8/2000

**Notes:**
The CLEO Letter has a great plot on the right which I borrowed which reviews the present experimental situation on mixing using all three methods. The circle shows the 95% cl limit obtained by E791 based on wrong sign D* (Kl) events.  This is an upper limit Rmix = (x**2 + y**2)/2 and thus forms a circle in x and y. The band is the E791 measurement of the lifetime difference between Kpi and KK and is therefore a direct measurement of pure y which as you can see is also consistent with 0. The ellipse and kidney beam shaped region are due to CLEO who measure the the time evolution of their  WS D* (K) events. The smaller (elliptical region) is the result of a fit which assumes CP symmetry, while the larger kidney bean region does not. Much of the information comes from the interference between the  DCSD and mixing  term which is proportional to y’ times time. CLEO can measure the sign of y but not the sign of x’
CLEO doesn’t technically measure pure x or y but measures a rotated set of variables called x’ and y’ . It is technically only legitimate to compare to the E791  y band if one assumes a very small rotation angle do to the phase shift between mixing and DCSD. This has been the going assumption for several years but it has been recently challenged by Falk, Nir and Petrov. 

## Present experimental status

- The comparison to CLEO **is only valid if** one assumes a small strong phase difference 
- FOCUS has essentially the same sensitivity to the CLEO CP constrained fit but are getting the opposite sign!

_**FOCUS **_
**y****CP** **= 3.42 ******** 1.39 ******** 0.74 %**

**95% CL**

**E791**

- _Previous Measurements_
**E791: y****CP**** =(+0.8 ********  2.9 ********1)%**
- CLEO -5.8 % < y’ < 1% (95% CL)

- CLEO

- Marina Artuso

- Cornell, 9/8/2000

**Notes:**
We modified CLEO’s figure a bit to add our result which we converted to a 95% CL band. I also re-quote our “official number” and compare that to E791 and CLEO. We are completely consistent with E791 but have significantly smaller errors.
The CLEO comparison is only really a valid if one assumes a small phase angle. There is a very small overlap of the 95% CL regions with CLEO but only on their least restrictive CP conserving fit. We seem to be getting the same magnitude as CLEO ( 3.42% as opposed to ~2.4% ) but the opposite sign. We do get the same sign as E791 but their result is , of course, very consistent with 0.

## -charm Projected yields for DoDoK+-K+- + C.C.

- Sensitivity can be enhanced by adding other modes (such as K+-o).
- Standard Model predictions quite uncertain. We will not span the full range of Standard Model predictions, but we are likely to make a measurement if there is **new physics**.

- Marina Artuso

- Cornell, 9/8/2000

## One important goal: x, y measurement

- We can separate y contribution if we study the wrong sign to right sign ratio from the initial state **D****o****D****o**********in absence of CP violation it is relate to:

- 3rD+8()tan2cc+4tan2c|c|2

- To be determined  with this measurement

- Amplitude for DCSD

- Marina Artuso

- Cornell, 9/8/2000

## CP violation in charm decays

- Direct CP:
- SM effects in Cabibbo suppressed modes  *O*(0.1%)
- New physics can produce enhancements up to O(1%) in some modes.
- Present experimental data:
- FOCUS  most precise measurement
**   ****A****cp****(D****+********K****-****K****+********+****)=-0.001********0.022********0.015**, compared with an error of  about ******0.01** that CLEO could have in -charm mode with **1fb****-1**.

- Marina Artuso

- Cornell, 9/8/2000

## CP measurement sensitivities

- Self tagging modes (D+, Ds)

| Mode | Acp(Lint=1 fb-1) | Acp(Lint=10 fb-1)  | SM predictions |
| --- | --- | --- | --- |
| D++ | 0.014 | 0.0044 | O(10-3) |
| D++ | 0.011 | 0.0034 | O(10-3) |
| D++K*o | 0.015 | 0.0048 | O(10-3) |

- Marina Artuso

- Cornell, 9/8/2000

## We may also look into

- CP involving DoDo oscillations
- Do ******K****+****K****-  ****vs **Do ******K****+****K****-**** **
**Measurement needs to be done with initial state D****o****D****o******for which **<CP>****time****=2sqrt(2r****D****)Im[********(D *********f*****)]**
** ****Optimum energy for D****o****D****o********initial state needs to be determined. To look for 1% asymmetry requires about 5x10****6 ****D****o****D****o********events (about 5 fb****-1 ****if coming from D****0****D*****0****).**
**Present FOCUS result ****A****cp****(K****+****K****-****)=-0.001********0.022 ********0.015**
- Other observables like angular correlations in VV final states ....

- Marina Artuso

- Cornell, 9/8/2000

## Yet another approach

- We can establish CP by looking at the reaction
******D****o****D****o *********f******+ ******f******+****** or f******- ******f******-***
- (*f*+=K+K-,+-,Ks...
- Preliminary estimates give B=1%  1fb-1 would give a sample of about 112,000 single tags in these modes  may be a viable way to prove CP in D decays.

- Marina Artuso

- Cornell, 9/8/2000

## Charmed Mesons Decay constants

- Where do we stand now:

- Marina Artuso

- Cornell, 9/8/2000

## Charm meson decay constants 

- Where we could stand with 1 fb-1 of data

- Marina Artuso

- Cornell, 9/8/2000

## Rare and forbidden decays

- Some D decays are forbidden: Standard Model expectations are several order of magnitude below any experimental reach laboratory for “Standard Model background free” searches for new physics
- the -charm region has the advantage of high efficiency and low background both for charged particle final states and final states including  and o.
- e.g. Do**** o   24 events for Lint=1fb-1 if B = 0.25x10-5.

- Marina Artuso

- Cornell, 9/8/2000

## D absolute branching fraction

- Crucial input to several B physics results (Vcb,...)
- Present status: absolute B is DoK-+
- B/B(DoK-+)=2.3%
- B/B(D+K-+)=8%
- B/B(DS+)=23%
- Lint =1fb-1 

******B****/****B****(D****o********K****-********+ ****)=0.4%**
******B****/****B****(D****+********K****- ********+********+****)=0.3%**
******B****/****B****(D****s********+ ****)=2.9%**

- Marina Artuso

- Cornell, 9/8/2000

## Summary of the physics opportunities 

- absolute branching charm fractions 0.3%-2,9% depending upon the mode in 1 fb-1
- decay constants to a few % in 1 fb-1
- CP violation asymmetries with an error of  0.01 in many modes with 1 fb-1
- evidence for mixing in  10 fb-1 if rD  10-4 & potential to disentangle all the mixing parameters with sufficient luminosity,
- sensitivity to a variety of rare decay modes down to 10-6 in 1 fb-1 potential to explore inclusive rare decays

- Marina Artuso

- Cornell, 9/8/2000

## Conclusion

- the move to a -charm center-of-mass energy will be the best opportunity to produce first class physics, a strong plea by the people that put years of effort in building CLEO III

- Marina Artuso

- Cornell, 9/8/2000

## Conclusions I 

- My study is supported by a significant amount of work done previously by -charm proponents in various part of the world
- The main questions is whether the machine will deliver the needed Lint. We need this information ASAP

- Marina Artuso

- Cornell, 9/8/2000

## Conclusions II

- A CLEO study group can pursue several important topics, changing the impressionist picture that I have drawn into a Vermeer. In particular:
- understand background levels in multi-body modes to determine mixing and CP
- understand tagging efficiency for mixing mediated CP
- understand errors vs luminosity in extracting mixing and CP parameters from **D****o****D****o******
- understand efficiency for inclusive rare decays,
- understand achievable accuracy in Cabibbo suppressed semileptonic decays (form factors/ Vcd/Vcs)

- Marina Artuso

- Cornell, 9/8/2000