Future prospects for K experiments

1
Future prospects for K experiments

• A. Nappi
• University of Perugia and INFN
• EPS HEP 2001 - Budapest 13/7/01

2
Outline

• What is still to be learned from the K system
• Prospects of ongoing programs
• KLOE _at_ DAPHNE
• NA48 _at_ CERN
• E949 _at_ BNL
• E391a _at_ KEK
• New projects
• KOPIO _at_ BNL
• KAMI _at_ FNAL
• CKM _at_ FNAL

?
3
Physics issues

• Overconstrain flavour structure of S.M.
• FCNC decay channels
• exploit suppressions ( 2nd order weak
  interactions, GIM , CP violation ) for enhanced
  sensitivity to new physics
• Simmetry violations
• CP, T narrow the gap between experiment and
  predictions using improved experimental
  techniques
• Charge asymmetries , T violating observables
• CPT Tighten constraints from Bell-Steinberger
  sum rule KS/KL semileptonic decays ?
• Sharpen the theoretical tools
• ?PT tests parameter determination
• framework for interpretation of more fundamental
  processes

4
A few loop diagrams ...
K0 ? l?l
5
FCNC decays (1)

• KL???
• Experimental effort concluded
  B.R.(7.18?0.17)10-9
• Information on short range contribution limited
  by interpretation
• Dominating absorptive contribution from gg
• (7.07?0.18)10-9
• Better experimental information on
  KL????,ee?,eeee,ee?? needed to constrain long
  range dispersive contributions
• KL???0ee?,?0?? ?
• Direct CP violation component has to be
  disentangled from
• Indirect CP
• 2 g CP conserving long range contribution
• Experimental information on KS???0ee? , KL???0
  ?? valuable
• Prohibitive physical background from ??ee? ,
  ???? ?

6
FCNC decays (2)
h

• K??????
• Unique theoretical cleanliness
• no long range contribution
• matrix elements of quark operators related to Ke3
  decays
• KL decay dominated by direct CP
• Experiments challenging
• B.R. 1011 , kinematics underconstrained,
  background from channels with much larger decay
  rates

rih
1-r-ih
a
b
g
r
1
Known to 2 precision
Small additional uncertainty from mC
7
CPT tests

• CPT violation in K0 mass matrix L M iG/2
  characterized by

• PDG 2000
• from
• CPLEAR error 3.3104
• neglecting CPT in pp decay amplitude
• known to precision 2.5105
• from B.S. sum rule Im D to 5105

ImD
ReD
8
CPT tests

• Bell-Steinberger sum rule ( unitarity )
• ImD limited by
• h000 and Re e
• Semileptonic charge asymmetries KS vs KL

• dL(32.71.2)104
• ( 1974 5107Kl3 decays )
• dS from KLOE ?
• error 103 with design L

0 if no DS DQ , CPT violating
9
KLOE

• Tagged KL/KS decays from ?? KL/KS
• design luminosity 51032cm2/s
• even before that has interesting program of KS
  measurements
• branching ratios for dominating decays
• KS semileptonic branching ratios
• rare KS decays
• Machine performance improved
• 21031cm2/s peak L , 1 pb 1/day reached, but
  large backgr.
• 35 pb1 logged
• Performance demonstrated by preliminary data on
  KS??e?
• 283 events in 11.5 pb1 sample
• 4 present world statistics ( CMD-2 75 ev.)
• 200 pb1 goal for 2000 running

10
data yield for 200pb1
11
CERN NA48

• 2001 ends ?/? program
• 2 extensions approved
• NA48/1 ( 2002 )
• KS rare decays
• NA48/2 ( 2003 ... )
• K/K CP asymmetries
• High statistics study of K?e??? pp
  scattering length ? ?0??q q ?0?

• Drift chambers rebuilt ( operational from 2001 )
• TRD will be installed before NA48/2

12
NA48 KS rare decays

• 31010 decays in typical 1 year run

• KS???0ee with a SES 6 1010
• 1.51012lt BRCPdir(KL???0ee? )lt51012
• BRCPind(KL???0ee ) ?
• 3103 BR(KS???0ee)
• 51010lt BR(KS???0ee )lt5108
• 7 events with B.R. in the middle of expected
  range

• Sizable samples for channels of interest for ?PT
  phenomenology
• KS???
• exp BR 2.1106
• 24000 events
• KS??0??
• exp BR 3.8108 (mgggt220MeV/c2)
• 114 ev.
• . . .

• Bounds on h000 of 102
• 8106 events for 1.2tS lt t0 lt 4.7tS
• Control of acceptance to 10 3/ctS
• Precision of B.S. sum rule to 2102

13
NA48 K program

• Main goal ??? Dalitz plot slope asymmetry
• Present experimental limit Ag(-75)103 Ford
  .. 70
• HyperCP has 3.9/1.6?108 K/K decays yielding
  DAg 5104 stat, gt103 syst
• S.M. theoretical predictions range from 106 to
  104
• no DI1/2 rule suppression
• FSI phases

• NA48 aims at 104 DAg
• 7.3/4.4?109 / decays/year
• DAg0.7104(stat)
• Simultaneous K beams B field reversal to
  symmetrize efficiencies
• DAg 0.5104(sys)

14
KEK E391a

• Ground breaking experiment for KL???0???
• Approved december 97 . Addressing relevant
  experimental issues in a systematic way
• Detector inefficiency measurements ( physics
  limited)
• Beam survey ( Dec. 2000 )
• Prospects
• Data taking from Oct 2003, aiming at sensitivity
  1?10-10
• Test bed for experiment at JHF aiming at
  sensitivity 3?10-14

15
BNL E949

• Upgrade of E787
• with 1 event in 1995-97
• 98 data of comparable size
• Key features
• Redundant kinematic information on p
• hermetic veto coverage
• looks for p above end point for K?pp0
• E 949
• improved sensitivity ( 14 )
• data for 2 additional years
• expect to reach 1011/ evt by 2004 ( 7 events for
  S.M. BR prediction)

16
Progress in K?? ???

• Dedicated FNAL expt CKM
• aims at 100 events with S.M. branching ratio
• approved ( end june )
• TDR in 12-18 months

( courtesy of L.Littenberg)
17
CKM at FNAL M.I.

• Features
• First attempt of in-flight measurement of K??
  ???
• Superconducting RF separated beam
• Hadron purity gt 70
• 33MHz 22GeV/c K
• redundant determination of K and p momentum
• spectrometer RICH
• veto with total inefficiency for p0 from p p0
  107
• expects 100 signal with 10 background events

18
KAMI

• Aiming at 100 ??0??? events with SB 41
• Veto inefficiencies 106 required
• Recently discussed by FNAL PAC and not recommended

19
KOPIO new way to ?0???

• In addition to vetos as many kinematical
  constraints as possible
• photon energy, position and angle
• KL momentum via TOF allows transformation to CM
  system
• RF bunched beam , ltpgt 0.8GeV/c

• Tracking preradiator for g direction measurement
• E measurement combining prerad Shashlik
• Hermetic veto coverage including beam hole

20
KOPIO layout
21
KOPIO existence proofs

• Many critical parameters established by test
  measurements
• Beam bunching 280 ps achieved with 33MHz, 30 kV
  cavity
• final scheme with 25MHz, 150kV additional
  harmonic cavity at 100MHz
• Preradiator angle resolution 25-30 mr for 250 MeV
  ??
• Energy resolution in Shashlik 6.7 for 250MeV ?
• In combination with preradiator Monte-Carlo
  indicates
• Veto efficiencies from E787 measurements, only
  slightly upgraded for better sampling ( low E )
  and larger number of radiation lengths ( high E )

22
KOPIO kinematics at work

• Transformation to CM and full g reconstruction
  provides region where 2p0 background negligible
• kinematics complementary to vetos ( small Ep ?
  higher veto efficiency)

23
KOPIO expected results
24
KOPIO discovery potential
Expected error band for B.R.2.2?10-9
Expected error band for B.R.3?10-11
90 UL for 0 events
25
Conclusions

• K system still has potentialities for exciting
  physics
• With the e/e saga come to an end, the next few
  years will see
• polishing of precision results
• a more complete phenomenological picture of K
  decays and CP violation
• room for surprises
• Great potentialities of two new ambitious
  projects for studies of the FCNC in the K sector
• Together with B results, capable to put severe
  constraints on the flavour structure of the S.M.
• No technical show stopper
• It would be a pity if they are missed for lack of
  funding