Physics with KLOE at DAFNE phase 2

F. Bossi, LNF

Frascati September 16, 2005

The purpose of this talk is to discuss some relevant physics issues that can be studied at the new machine using the KLOE detector

I will emphasize:

What KLOE has achieved up to now and what part of this can be improved with further statistics

Which portion of the original KLOE program can be addressed only with an integral luminosity ≥ 20 fb1

What are the possible ways to improve the detector performance

Much of this talk has to be taken as a guideline for discussion and does not pretend to be exhaustive

KLOE has proven to be perfectly suited to cover a wide variety of physics issues, spanning from charged and neutral K decays, to low-energy hadron spectroscopy, to quantum interferometry studies

This is demonstrated by the number of published results which have given to KLOE worldwide reputation

00 PLB 537, 21 (02)

0 PLB 536, 203 (02)

+0 PLB 561, 55 (03)

' PLB 541, 45 (02)

l+l PLB 608, 199 (05) + PLB 606, 12 (02)

KS PLB 538, 21 (02)KL PLB 566, 61 (03)

K+ +00 PLB 597, 49 (04)

KS e PLB 535, 37 (02)

KS 000 PLB 619, 61 (05)

KL main submitted to PLB

KL lifetime accepted by PLB

PLB 591, 49 (04)

+ PLB 606, 12 (05)

KLOE physics papers

E.M: Calorimeter:

Full angular coverage

Exceptional timing capabilities

Large lever arm

Drift Chamber:

Good momentum resolution

Large tracking volume

Minimization of materials

Good 0 reconstruction capabilities

Excellent e/ separation based on t.o.f.

Full kinematical reconstruction of events

Maximization of efficiency for long-lived particles (K± ,KL)

The ingredients of success

KL 30 decay time

L/βc (ns)

6 – 24.8 ns40 – 165 cm

0.37 L

e

+0

+

Lesser of pmiss Emiss in or hyp. (MeV)

KL decays at KLOE

Measurements of kaon partial rates provide at present by far the most accurate test of Unitarity (i.e. of Universality as P.F. points out)

| Vud|2 + |Vus|2 + |Vub|2 = 0.9998 ± 0.0011

The study of KL decays has been the driving force in the design and operation of KLOE. However DANE has proven to be almost without competitors under other respects.

KS decays: 3x105 tagged KS mesons delivered / pb1

decays: 4x104 mesons delivered / pb1

No way to obtain the same purity at any hadron machine: some decays can be studied only here.

KLOE has already the largest sample of mesons collected to date.

Quantum interferometry

KLOE reached the highest sensitivity on decoherence effects

I will discuss all of the three items above, but, because of personal preparation and prejudice, I will emphasize KS decays mostly

KS e decays

Sensitivity to CPT violation through the charge asymmetry:

AS AL signals CPT in mixing and/or in S Q decay amplitudes

Sensitivity to CP violation in K0-K0 mixing:

AS = 2 Re assuming CPT symmetry

(KS e) provides test of S Q rule:

S(e)/L(e) 1 4 Re x

Can obtain |Vus| from measurements of (KS e)

AS,L =(KSL +e) (KSL e+)

(KSL +e) + (KSL e+)

KS e decays

Use of TOF and kinematics to reject the huge + background

t texp (+e) (ns)

t

te

xp (

e+)

(ns) Need to associate DC

tracks to calorimeter’s clusters

Non negligible loss in signal acceptance

Present overall efficiency ~ 6%

KS e decays

KLOE current results ( ~ 400 pb1) :

BR( KS +e) = ( 3.53 ± 0.05 ± 0.03) x 104

BR( KS e+) = ( 3.54 ± 0.06 ± 0.04) x 104

BR( KS e) = ( 7.06 ± 0.08 ± 0.06) x 104

AS = ( 1.5 ± 10 ± 5 ) x 103

Present KLOE run aims at AS ~ 3 x 103 i.e ~ 2 Re

A 3 measurement of AS requires ~ 20 fb1

KS e decays

Can we do better than that?

B (kG)

(KLCrash + Ks DC selection)

Present analysis, MC with detailed field map400 pb MC with LSF=0.5, with uniform axial B field

0.1

0.2

3 540

0.15

0.05

Magnetic field value dramatically affects signal acceptance. Can improve up to a factor ~ 2

Proper balancing with consequent loss in momentum resolution yet to be studied

T. Spadaro

KS decays

• Same motivations of the KSe3, but more difficult:• Lower BR: expect 4×104

• Background events from KS : same PIDs of the signal• Troublesome charge identification for the signal

• Anyway, measurement never done before

Emiss Pmiss ( hyp) (MeV) 0 20 20

Can reach a statistical accuracy of ~ 3% with present data

• 2002 data MC MC MC

This channel begs for more statistics !

KS 30 decays

This decay violates CP. SM branching ratio is 2 x 109

MCEff. Stat. =5.3 data

450 pb1

’01+’02 data

Analysis based on counting and kinematic fit on 20 and 30 hypotesis

2 22 2

23

23

Nbck (MC) = (3.13 ± 0.82 ± 0.37)

KLOE 450 pb1 Nobs = 2

BR ≤ 1.2 x 107 90% C.L.

Cf. NA48 (05): BR ≤ 7.4 x 107 90% C.L.

KS 30 decays

Background mostly due to photon clusters double splittings

Preliminary studies show that there is room for “algorithmic” improvements in background rejection without big losses in signal efficiency

Study of the entire KLOE data set crucial for a better assessment of the real potentialities of the analysis

Ideally, with 20 fb1 one can reach a limit ~ 5x109

KS +0 decays

Decay mainly CP-conserving (I = 3/2)BR useful to constrain K 3 amplitudes PDG ’04: BR = (3.2+1.2

-1.0) 10-7

Never observed directly

Preliminary results with 740 pb1:

• Signal efficiency: ~ 1.5%

• Candidates: 6 events

• Background (sidebands): ~ 3.5 events

• Number of events observed consistent with expectation

• Statistical error: ~ 100%

• Evaluation of systematic error in progress

2 from kin. fit

MC background

MC signal (L x 100)

KS +0 decays

Scaling above numbers:

With 20 fb1 one can reach a statistical precision of ~ 15%

At least one of the two tracks has low momentum:

36% efficiency due only to acceptance

Note:

Use lower magnetic field could potentially greatly increase efficiency

KS 0 e+e decays

Fundamental to assess indirect CPV contribution to parent KL decay

Measured by NA48 on the basis of 7 events (plus 6 +)

Theoreticians’ dream: measurement at 15% accuracy

BR = (5.8 ± 3) x 10-9

What efficiency can reasonably be expected for KLOE?

Quoting my presentation at a previous meeting ( May 2005):

“Based on 3 experience, Matthew bets for 4%”

KS 0 e+e decays

Feasibility study performed on the basis of ~ 480 pb1 equivalent MC all- events, and 2x105 signal events

First step: usual Ks tagging plus preselection criteria sig ~ 13%

Surviving background events accounted by:

KS 20 + 10 dalitz decay

KS 20 + 20 dalitz decay (double dalitz)

KS 20 + conversion

Badly reconstructed K+K events

Badly reconstructed 0 events

KS +

6095

277

93

2

115

16

( M. Moulson, M. Palutan, T. Spadaro)

KS 0 e+e decays

Further selection based on cuts on 5 independent variables

e+e inv. mass 2 kinem. fit

MC MC

DATA 400 pb1 DATA 400 pb1

signal

signal

KS 0 e+e decays

Cuts tuned on MC: 0 events retained < 4.8 ev / fb1 @ 90% CL

Detailed studies of problematic topologies:

single dalitz : 880 pb1 : 0 events < 2.6 ev / fb1

double dalitz: 4200 pb1 : 0 events < 0.55 ev / fb1

K+K : 880 pb1 : 0 events < 2.6 ev / fb1

Overall efficiency on signal: 4.3%

Check on data (~ 400 pb1) : 0 observed (0.12 expected)

Optimistically (no further bkg) ~ 5 events observed in 20 fb1

Quantum Interferometry

Measurements of decay time differences between KS and KL decays into various combinations of +, 00, l can determine the entire set of parameters describing the neutral kaon system

From fit on KSKL ++

m = (5.34 ± 0.34) x109 hs1

At 20 fb1 m = 0.05 x 109 hs1

Compare with :

PDG 04 : m = 0.016 x 109 hs1

Best (KTeV 03) : m = 0.043 x 109 hs1

DataFit result

(380 pb1)

Quantum Interferometry

tmeeetI ttt LSSL cos12 ;, 2/

interference term modified introducing a decoherence parameter .

From fit on KSKL ++ (380 pb1)

SYSTSTAT 008.0037.0043.0 SL

5SYSTSTAT00 1002.020.024.0

KLOE preliminary result:

STAT005.0

5STAT 1003.0

At 20 fb1

Compare with :16.013.0 SL

7.04.000 (from CPLEAR data)

meson decays

With 20 fb1 as many as 6x108 mesons produced

Channels presently studied with KLOE:

Decay BR ana Expectation @ 20 fb-1

( 39.43 ± 0.26 ) % 70% 2.4× 108 evts

( 32.51 ± 0.29 ) % 45% 1.3× 108 evts

( 22.6 ± 0.4 ) % 36.5% 0.7 ×108 evts

( 4.68 ± 0.11 ) % 46% 1.8 ×107 evts

( 8.0 ± 2.7 ) × 105 4.63% 3000 evts

< 1.3×105 < 1×108

< 1.6×105 20% < 1×108

With 20 fb1, can largely improve UL’s on 0l+l, e+e, +

A note on tracking

In most of the above mentioned decays, low-momentum charged particles are produced

A too high magnetic field not only affects the acceptance, but also worsens the pattern recognition and the track reconstruction performance, producing higher splitting probabilities and non-gaussian resolution tails

Further complications are posed by the coarse cell granularity and the z-coordinate reconstruction in the full-stereo geometry

pions fromKS +0

decays

A note on tracking – an explicative example from K+K

Split track Split track, no VTX reconstructed

A digression – measurment of the neutron FF

Many people have asked whether KLOE can be used to perform the measurement of nucleon form factor.

The key issue here is to know the efficiency of the calorimeter in detecting low energy neutrons. At present nobody can really state how large it is. A dedicated test is needed.

In the meantime we are following the idea (B. Sciascia) of searching for neutrons in hadronic interactions of K on the beam pipe and the inner DC wall (a background for her analysis!). The method is still under developement but has shown promising preliminary results.

Conclusions and remarks

A factory delivering 20 fb allows an interesting and various physics program to be pursued

KLOE has proven to be perfectly tailored for it, although improvements can still be considered:

Beside this, the goal of keeping KLOE running beyond 2010 is by no means trivial: careful maintenance and precise studies have to be undertaken to prove the feasibility of this

♣ Insertion of a vertex chamber closer to the IP

♣ Implementation of better z coordinate reconstruction by charge division

♣ Optimization of the magnetic field value with respect to Ks physics and interferometry

♣ Improvement of reconstruction algorithms, both for charged and neutral particles

♣ Redesign of the IR and the connected instrumentation