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Wrong Sign D Group
D⁰ mixing and/or Doubly Cabibbo Suppressed Decays (DCSD)
(Mirror at LNS)

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D⁰ mixing is the name given to a process whereby certain types of matter transmute into antimatter. Analogous processes have actually been observed in elementary particles that resemble the D⁰, known as the K⁰ and the B⁰. However, the popular expectation is that the D⁰ will not transmute at a large rate, in contrast to the K⁰ and the B⁰.

We are nonetheless seeking evidence that the D⁰ turns into antimatter, in our data. If we see D⁰ mixing, the existence of some new (and predicted) particles might be implied.

There is a process that resembles D⁰ mixing, known as `Doubly Cabibbo Suppressed Decay (DCSD)'. That process is not well quantified, and our work will help pin DCSD down, even if we don't detect D⁰ mixing.

Most of the links below are rather technical. We'll work on a simpler description and provide a link to it soon.

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Links to pages, which now have a lot of information, of members of our working group:

• David Asner
• Gary Gladding
• Tony Hill
• Mike Marsh
• Chris Sedlack
• Harry Nelson
• Craig Prescott
• Alex Smith

Meeting minutes

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Writeup for Kaon 99. (aka hep-ex/9909028) (Spires)
Lepton-Photon Conference Paper (aka hep-ex/9908040) (Spires)

• y' versus x' limit plot, in .ps, .eps
• x' limit plot, showing inconsistencies with predictions, in .ps, .eps

CBX 99-39 on our Search for D0 Mixing (access to CLEO members only)
Figures portraying the preliminary results for the early summer, 1999
Transparencies presented Harry Nelson at Kaon99.
Transparencies presented by the CLEO `gang of four' (Tony Hill, Chris Sedlack, Mike Marsh, and David Asner) at the APS Centennial Meeting at Atlanta, March 22, 1999.
Jeff Gronberg's draft writeup for DPF 1999 at UCLA
David Asner's Talk at the 1999 Lake Louise Winter Institute
CBX on the mixing analysis
Jeff Gronberg's Talk at DPF 1999 at UCLA
Plots showing limits, for Early 1999
Jan. `99 APS/DPF Abstract (here is the TeX file)
Heavy Quarks `98 Talk Transparencies (10/12/98)
Plots for early Summer, 1998
APS Talk Transparencies (4/17/98)
APS Abstract (here is the TeX file)

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Useful Links:

• Two pages on D0>K+pi- from the talk of Luigi Moroni at Tampere, Finland at the 1999 Europhysics HEP Conference, from the FOCUS collaboration. Some numbers that characterize the FOCUS sensitivity are:
  • FOCUS reports 7222+-88 right-sign D0>K-pi+ events in 40% of their data sample; one can extrapolate that their complete sample should have 18055+-220 right sign events; CLEO II.V has 16126+-127 right sign events, reported in the Lepton-Photon contributed paper.
  • FOCUS reports a resolution in delta-M of 860 KeV; the CLEO II.V resolution is 190 KeV.
  • FOCUS reports a background level of about 0.023 wrong-sign per right-sign in a 4-sigma delta-M region. CLEO II.V reports 0.0032 wrong-sign per right-sign in a 4-sigma delta-M region, a factor of seven lower than FOCUS. Other comparable background levels: Aleph reported 0.012, CLEO-II reported 0.0062, Argus reported 0.0060, and CLEO-I.5 reported 0.0050, all in wrong-sign background per right-sign signal per 4 sigma delta-M region.
  • S^2/B, for FOCUS's full data set, is a factor of 5.7 lower than for CLEO II.V's full data set.
• Memo and figures of theoretical predictions for the numerical level of D0-D0bar mixing.
• Table of theoretical predictions for the numerical level of D0-D0bar mixing, with hyperlinked references.
• LNS Journal Club talk of Mike Sokoloff, 3/12/99.
• E791 has released a preprint in which they report comparison of the D0 lifetime, as measured with both D0>Kpi and D0>KK; the numbers are the same as below. Nice work!
• E791 reported a limit on the difference between the D0 lifetime, as measured with Cabibbo-favored D0>K-pi+ and with the first-Cabibbo suppressed CP eigenstate D0>K-K+, at the DPF `99 Meeting at UCLA. The two key transparencies are part of a longer talk given by David Sanders.
  The summary is that y, which is (Delta-Gamma/2/Gamma), is limited by these data to be, at 90% C.L., between -0.042 and 0.058; actually, Sanders quotes only the second of those values.
  The limit is based on comparing a D0>K-pi+ lifetime of 413+-3+-4 fs (60581+-353 events) with a D0>K-K+ lifetime pf 410+-11+-6 fs (6683+-161 events). Then Delta-Gamma is evaluated to be 40+-140+-50 ns^-1, from which the limits on y can be deduced.
  BTW, for comparison, CLEO II.V has a D0 life measurement of 408.5+-4.1+-3.1 fs. E791 also reported a D_S^+ life measurement of 518+-14+7 fs (1662+-56 events), compared with CLEO II.V's measurement of 486.3+-15+-4.1 fs (2167+-64 events, based on 41% of CLEO II.V's total data sample).
  
  The E791 results are an update of those presented by Michael Sokoloff at ICHEP `98 in Vancouver. The Kpi/KK mass plots shown there give a feeling for the S/B; the number of D0>K-K+ of 6683+-161 is the same as presented at UCLA. The lifetimes are determined form the proper time plot.
  The result then was 407+-3(stat) fs for the lifetime to Kpi, and 404+-11 fs for the lifetime to KK; the systematic error was not reported. Delta-Gamma was reported as 22+-73(stat) ns^-1; then the result for y is 0.005+-0.015(stat); the systematic error was expected to be the similar to the statistical error, which would have yielded y of 0.005+-0.015+-0.015, which would then limit y to be between -0.029 and 0.040, at 90% C.L.
• Aleph's Vancouver Paper... the Aleph collaboration has reported to Physics Letters a whopping R_DCSD of [1.84 +- 0.59(stat) +- 0.34 (sys)] per cent. Wow! Big wrong sign from the Atlantic's wrong side! The citation is Phys. Lett. B436 211-221 (1998); here is the spires reference.
  (Aleph's Vancouver Page)
  Some useful points:
  • They report about 1040 right sign events.
  • Per right sign per 4 sigma in delta-M, the background is about .012 (roughly twice as high as the CLEO-II result below); resolution in delta-M is 0.65 MeV; their resolution in m_D0 is about 14 MeV.
  • They reverse the dE/dx to estimate some backgrounds such as double misid of K-pi+(pi0).
• The page that the Sheldon-Webster group at Vanderbilt University keeps on talks and publications of the FOCUS experiment, a fixed target charm experiment at Fermilab. Of particular note are the talks at the bottom of the page.
• CLEO CBX 98-26 on the calibration of dE/dx in the CLEO 2/SVX data.
• CLEO's D0>K+pi- paper, Spires, CLEO CBX 93-38. Some useful points:
  • Visible cross section for right sign is 1.2 picobarns (p_D*>3.1GeV, sqrt(s) is about 10.6 GeV), from 2200 events in 1.8 1/fb.
  • Background level is 2.4 fb/MeV. Per right sign per 4 sigma in delta-M, the background is about .0062; resolution in delta-M is 0.77 MeV.
  • The signal, relative to right sign, was .0077+-0.0025+-0.0025.
• CLEO's D0>K+pi-pi0 paper; Spires reference.
• CLEO CBX 95-71 on a CLEO search for D0-D0bar mixing, where the decay mode D0>X lepton nu is used.
• Argus' 1992 D0>K+pi- DESY report 92-056. This report does not appear to have been published; it is not listed in the Review of Particle Properties. Some useful points from it:
  • Visible cross section for right sign is 0.62 picobarns (p_D*>3.1 GeV, sqrt(s) is about 10.6 GeV) from 224 events in 360 1/pb; they also get 36 right sign events from B0>D*+l-nu, but those events are not so important, and are not included in the visible cross section computed.
  • Background level is 1.5 fb/MeV. Per right sign per 4 sigma in delta-M, the background is about .0060; resolution in delta-M is 0.61 MeV.
  • They note that the center of mass decay angle, which they call theta*_K, of the K w/r to the D0 boost direction, is correlated with the tendency of other modes such as D0>K+K-, D0>pi+pi-, and D0>K-pi+ to get in the D0>K+pi- signal region. That correlation is also explored in CLEO CBX 98-25.
  • Their upper limit on BR(D0>K+pi-)/BR(D0>K-pi+) is 0.9 percent, at the 90 percent confidence level.
• CLEO 1.5 1991 paper (CLNS 91/1058, CLEO 91-2, PRD44:3383,1991) on unusual decay modes of the D0, including D0>K+pi-. Some useful points:
  • Visible cross section for right sign is 0.90 picobarns, from 420 events in 466 1/pb.
  • Background level is 1.6 fb/MeV. Per right sign per 4 sigma in delta-M, the background is about .0050; resolution in delta-M is 0.70 MeV.
  • Their upper limit on BR(D0>K+pi-)/BR(D0>K-pi+) is 1.1 percent, at the 90 percent confidence level.
  • There is also a limit on BR(D0>K+pi-pi+pi-)/BR(D0>K-pi+pi-pi+) < 1.4 percent, at 90% CL, based upon 393 right sign events. Indeed, the delta-M resolution looks about the same for this mode, but the background looks about 2-3 times as big.
• All 1998 PDG pages on the D0. Pages 2 and 3 have discussions of delta-M and delta-Gamma; Wrong-sign discussion starts on page 38.
• 1996 PDG pages on wrong sign and forbidden D0 Decays.
• Guy Blaylock's talk at the 1997 Heavy Flavor Symposium.
• E791's D0>(hadronic wrong sign) paper.
  
• E791's D0>(X lepton-) paper. I have a small quandry with this paper... the result is r=0.11+0.30-0.27%; it seems that the 90% CL limit is then computed to be 0.11+0.30*1.28=0.494 approximately 0.50%. The quandry is: why use the single sided 90% CL, which is 1.28 sigma? The region of r<0 is non-physical. It looks to me like 65.8% of the distribution is physical, or above 0. So, I get that the 90% CL is about 1.508 sigma, or 0.56%. If exactly 50% of the distribution were physical, the 90% CL is 1.64 sigma, coincidently equal to the `double sided' limit... that would give a limit of 0.60% at 90% CL.
  
• E791's D0>KK,pipi paper. This paper reports on 609 tagged D0/D0bar>K+K- events, with about 3/1 Signal/Background; also there are 343 tagged D0/D0bar>pi+pi- events, with about 1/1 Signal/Background.
  
• A short discussion on sensitivity of D mixing to supersymmetry.
• Ted Liu's Papers:
  • 1997 Santa Monica Talk
  • 1995 Argonne Talk (42pp.)
  • 1994 Talk at Charm 2000
• 1997 Paper of Woo and Cline on a new techniqe to search for D0-D0bar mixing; (Spires reference).
• Hitoshi Yamamoto's Papers:
  • 1995 EPS writeup, LANL Server Abstract.
• Some good papers from the 1989 Tau-Charm Factory Workshop:
  • Uri Karshon's paper in which estimates of the number of reconstructed, flavor-tagged CP eigenstates are made, for one year of tau/charm factory running, and for production from D*0D0bar>gamma D0 D0bar.
    CLEO-II/SVX now has numbers of events that are nearly equal to the estimates of Karshon!
    This comparison is relevant for sensitivity to CP violation in D0 mixing: and to be fair, for the same number of events, the D*D>gamma DD production mechanism has a factor of 2 advantage in sensitivity, due to constructive interference in the C+ DD state produced.
    For pure mixing, without CP violation, the tau-charm factory would have had sensitivity that exceeds the CLEO-II/SVX data by a factor of 4 or so.
    Here is the spires reference.
  • Gary Gladding's paper, which has nice discussions of the experimental techniques.
    Here is the spires reference.
  • I.I. Bigi's paper in which the phenomenology of D0-D0bar mixing is reviewed.
    Here is the spires reference.
• Theory Papers:
  • A 1998 paper by Azimov on the use of final states from D decay that involve neutral K0 mesons to deduce the D mixing and DCSD parameters.
  • A bunch of references, mainly directed toward rates of D0>PP, are here.
  • 1998 paper C. Meca and J. Silva on detecting new physics contributions to D0-D0bar mixing via the measurements in B Decays; (Spires reference).
    
  • 1998 paper of Iain Stewart on the natural width of the D^* (Spires reference).
    
  • 1998 paper of Golowich and Petrov; (Spires reference).
    
  • D Mixing Pages from Bigi's 1997 Moscow lectures on CP violation. Here it the LANL server abstract; (Spires reference).
  • 1997 paper of Pakvasa on Flavor Changing Neutral Currents in Charm Sector (Spires reference).
  • 1996 paper of Yosef Nir on Supersymmetric CP violation; there is a good discussion of CP violation in mixing in the D system; (talk from the Workshop on K Decays, Orsay, France, 1996 (Spires reference).
  • 1996 paper of Buccella, Lusignoli, and Pugliese, with the latest version of their fit to hadronic charm decays, including DCSD. There is a prediction for Delta-Gamma near the end: although pipi and KK intermediate states would contribute a y of about 0.02, piK-Kpi apparently comes in and saves the day, and drags y down to .0007; (Spires reference).
  • 1996 paper of Blaylock, Seiden, and Nir, where they emphasize the interference caused by the combination of either strong phases and/or CP violation and dispersive (Delta-M) mixing; (Spires reference).
  • 1995 paper of Yosef Nir on searching for new physics with charm mixing; this paper has a nice summary of various extentions to the Standard Model and their impact on charm mixing. (Spires reference).
  • 1995 paper of JoAnne Hewett on searching for new physics with charm. (Spires reference).
  • 1994 paper Chau and Cheng, where they describe the somewhat high CLEO-II result on (D0>K+pi-)/(D0>K-pi+); (Spires reference).
  • 1993 paper of Hall and Weinberg, where they suggest that D mixing might have good sensitivity to flavor-changing scalar interactions: indeed, they suggest that D mixing is the best probe of their model; (Spires reference).
  • 1992 paper of Georgi (Spires reference) (a good starting point, because this paper has been often cited, so clicking on the `cited by' button gets good results; the long version of this paper is here (Spires reference). Kaeding 1995 questions Georgi... (Spires reference).
    
  • 1986 paper of Bigi and Sanda, on CP violation in D mixing; (Spires reference).
  • Citations of Wolfenstein's 1985 paper on D0 mixing; (Spires reference).

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hnn@charm.physics.ucsb.edu 10/21/99