R measurement at DAFNE-2

LNF-19-Jan-06

G. Venanzoni LNF

What is DAFNE-2?

•Upgraded Dafne with 1 interaction region

Energy (cm) (GeV) 1.02 <2.5

Peak luminosity > (cm-1sec-2) 8 1032 1032

Total integrated luminosity (fb-1) 20 3

Start time ~2011

•Discussion on detector upgrade has started

I will not discuss in this talk this issue!

Machine Physics Program on R Energy range Starting date

VEPP-2000 L = 1032

Scan+ISR(?)0.4<s<2 GeV >2007

BESIII L=1033 @ (3770), ISR(?) 2.4<s<4.2 GeV >2007

CESR-c ? 3<s<5 GeV Working

Babar ISR Thr.<s<10 GeV Working

Belle ISR (?) Thr.<s<10 GeV Working

Competitors (on R)

Radiative Return vs Energy Scan

Energy scan seems the natural way of measuring hadronic cross section. However experience at KLOE and BABAR have shown that the Radiative Return has to be considered a (working) complementary approach.

Advantages:•Data comes as a by-product of the standard program of the machine•Systematic errors from luminosity, acceptance, normalization, s,… enters only once•It allows fine tuning of the binning (expecially important in the resonances region)

Disadvantages:•High order process (radiative corrections must be kept under control at high precision)•Requires a high suppression of FSR and or background •Needs high integrated luminosity: for 2 at Dafne statistics is not problem, but it can be just at the limit for DAFNE-2

Big work from Karlsruhe/Katowice group (Kühn, Czyz) to provide generators for ISR processes (Phokhara) at 0.5% accuracy!

Status of R measurements (s <10 GeV):

Region Covered by DAFNE-2

Topics on R in the region 2m<s<2.4 GeV

•Exclusive analysis: •2 channel (the biggest contribution to (g-2) ):

• Threshold region: below 600 MeV poorly covered by data (error between 1 and 3%)•Around the peak: syst. error of 0.6% from CMD-2, 1.3% from SND, KLOE. Not perfect agreeement on the spectra between different experiments, and discrepancy with2 spectral function from •Above GeV: O(1-4%) from CMD-2

• 22 + - 00 , K+K-, 3(+ -, 2(+ -) 00; accuracy in the range 5 to 20%, recently presented by BABAR

•Inclusive analysis: • Old data, inconsistency between inclusive measurements and the sum of exclusive channels.

2 spectrum 0.35<s<.95 GeV2

Discrepancy with tau data:

•KLOE and CMD-2 lower than data at high M

•Error on theoretical corrections (I.B., FSR)

underestimated?

•New tau data available from B factories:

Most likely this issue will continue (hopefully solved) in the next years•New data KLOE,BABAR, Belle(?), CMD-2, will hopefully bring the error <1%. However the path to reach few per-mill accuracy is still long…

• CMD-2 (‘04) and KLOE agree @ high M

• disagreement btw KLOE and CMD-2/SND at peak

MM22 (GeV (GeV22))

interpolation ofKLOE 60 data points

from 0.35 to 0.95 GeV2

+10%

-10%

s (GeVs (GeV22))

+10%

-10%

hep-ex/0512071

Comparison of e+e- data

•It contributes for 20% of a

ameV100 10-10

•This region is poorly covered by data;

•Different authors use different ranges for analytical expansion

• data do not agree so well (F.J. ’01), also with ee data (NA7 ,1987)

extrapolated in timelike.

s (GeVs (GeV22))

(n

barn

)(n

barn

)

2 threshold region

nb, sqrt(s)=1003.71 MeV

(from SND, PRD66 (2002) 032001)

nbnb

6

5

4

3

2

1

01010

10

10

( ( aa

))st

atst

at

• stat. error on a:: [1.5-2.5]10-10 (300-100 pb-1)

• comparible with the expected syst.error

()syst ~ 2% from region < 0.35 GeV2

KLOE Data at off peak (1 GeV)(started at mid of Dec. 05)

Impact of DAFNE-2 on the threshold region

()stat1) total accuracy better than 3% in the

region <0.35 GeV2 ( ~3 × 10-10) is a hard

task for KLOE

2) This accuracy could be improved in the

future, using ISR at DAFNE-2 (off-peak)

bin width = 0.01 GeV2

efficiency = 50% flat

during the KLOE

data taking campaign @ s = 1 GeV

we can learn a lot

Issues in the region [1-2] GeVfrom Burkhardt & Pietrzyk, PRD72 (2005)

057501

s (GeV)s (GeV)

R(s)R(s)

1) the most critical region for had and the

second relevant one for ahlo

2) significant difference btw inclusive and

sums of exclusive measurements

3) most recent inclusive measurements

from DC1 and ADONE (~ 1981!!)

from Martin et al., EPJ,C19 (2001) 681

had

1.05-2GeV

40% of the total error

How DAFNE-2 can improve this region [1-2.4 GeV]

1. Energy Scan: • 20 pb-1 per single point (2-3 days at 1032 cm-2 sec-1)• Allows inclusive measurement with high statistics• Needs a dedicate programme• Knowledge of s at with O(10-4) accuracy, using bhabha events (?)

(without resonant depolarization)

2. ISR at 2.4 GeV:• 2 fb-1 (1 year at 1032 cm-2 sec-1)• Compatible with other programs• Statistics can be an issue

Competitors: VEPP-2000 (up to 2 GeV)BabarBelle (?)ISR at Tau/charm factories?

Energy scan

Impact of DAFNE-2 on inclusive measurement

s (GeV)s (GeV)

Lin

t (n

b-1)

o MEA, 14 points, MEA, 14 points, Lett. Nuovo Cim.30 (1981) 65Lett. Nuovo Cim.30 (1981) 65

• B antiB, 19 points, B antiB, 19 points, Phys.Lett.B91 (1980) 155Phys.Lett.B91 (1980) 155

20 pb20 pb-1-1

1) the most recent inclusive

measurements are from MEA and B

antiB, with total integrated luminosity of

200 nb-1 (on hour of data taking at 1032

cm-2 sec-1).10% stat.+ 15% syst.

errors

2) With 20 pb-1 per energy point, stat.

errors on hadhad O(5%);

systematic error will be reduced as well

4) a precise comparison exclusive vs.

inclusive can be carried out

Impact of DAFNE-2 on the range [1-2] GeV (4)st

atis

tica

lst

atis

tica

l

h

ad

had

h

adhad

s (GeV)s (GeV)

BaBar, with the published BaBar, with the published LLintint per point per point

BaBar, with 10 BaBar, with 10 (the present (the present LLint int ))

DAFNE-2, with 20 pbDAFNE-2, with 20 pb-1-1 per point per point

comparison among the present BaBar

analysis, an (O(1 ab-1)) BaBar update,

and Lint = 20 pb-1 per energy point

@ DAFNE-2, in the impact on hadhad:

: O(2%) | O(0.7%) | O(0.5%)

Impact of DAFNE-2 on the range [1-2] GeV (2K2)st

atis

tica

lst

atis

tica

l

h

ad

had

h

adhad

s (GeV)s (GeV)

comparison among the present

BaBar analysis, an (O(1 ab-1)) BaBar

update, and Lint = 20 pb-1 per energy

point @ DAFNE-2, in the impact

on hadhad :

: O(15%) | O(5%) | O(3%)

BaBar, with the published BaBar, with the published LLintint per point per point

BaBar, with 10 BaBar, with 10 (the present (the present LLint int ))

DAFNE-2, with 20 pbDAFNE-2, with 20 pb-1-1 per point per point

Impact of DAFNE-2 on the range [1-2] GeV (3)st

atis

tica

lst

atis

tica

l

h

ad

had

h

adhad

s (GeV)s (GeV)

BaBar, with the published BaBar, with the published LLintint per point per point

BaBar, with 10 BaBar, with 10 (the present (the present LLint int ))

DAFNE2, with 20 pbDAFNE2, with 20 pb-1-1 per point per point

comparison among the present

BaBar analysis, an (O(1 ab-1))

BaBar update, and Lint = 20 pb-1

per energy point @ DAFNE-2, in

the impact on hadhad :

: O(9%) | O(3%) | O(1%)

Radiative Return @ 2.4 GeV

is the minimum polar angle of ISR photon. In the following, we will assume to tag the photon, with 20o.

is the overall efficiency, we will use 10%.- m is the invariant mass of the hadronic system (,

…- x is 2E/s, s= e+e- c.m. energy - L0 is the total integrated luminosity

0

2

022

cos,1

2)

1

1log)22((

)(

Cs

mx

Ls

mCx

C

Cxx

xdm

dLdm

dLm

dm

dN

born

hadree

ISR differential luminosity

ISR Luminosity for different c.m. energies - We integrated dL/dm

for 25 MeV bin sizes. 2fb-1 @ s=1.02 GeV

2fb-1 @ s=2.4 GeV

89fb-1 @ s=10.6 GeV[n

b- 1/2

5MeV

]2fb-1 @ 2.4 GeV89fb-1 @ 10.6 GeV

GeVGeV

1pb-1

1

Impact of DAFNE-2 on the range [1-2] GeV (3) using ISR @ 2.4 GeV

stat

isti

cal

stat

isti

cal

h

ad

had

h

adhad

s (GeV)s (GeV)

BaBar, with the published BaBar, with the published LLintint per point per point

BaBar, with 10 BaBar, with 10 (the present (the present LLint int ))

DAFNE-2, with 2 fbDAFNE-2, with 2 fb-1-1 @ 2.4 GeV @ 2.4 GeV

comparison among the present

BaBar analysis, an (O(1 ab-1))

BaBar update, and Lint = 2 fb-1 at

2.4 GeVper energy point @

DAFNE-2, in the impact on

hadhad :

: O(9%) | O(3%) | O(8%)

On the other channels theimprovement can be larger

ISR @ 2.4 GeV vs scan

- Assuming to tag the ISR , 2fb-1@ 2.4 GeV, translates in a luminosity for single point in the range [100 nb-1 - few pb-1] which would correspond to [few hours - a day] of data taking with a scan @1032 cm-2 sec-1 .

- 2fb-1 @ 2.4 GeV is statistically competitive with current results from B factories (90 fb-1). The much higher ISR probability of photon emission at lower s, compensates for the lower luminosity. However we should keep in mind that the planned luminosity of B factories is 1000 fb-1.

- In any case different systematics, background, etc…

ISR @ 2.4 GeV vs B-factories

Different event topology btw 2.4 and 10.6 GeV:2+2-channel

Es=2.4 GeVs=10.6 GeV min

degrees

degreesGeV

GeV

E

• At 10.6 GeV:• Hard photon: E* = 3-5.3 GeV at s’ = 0-7 GeV.

No fakes from beam-gas processes.• Hadronic system collimated by

recoil.• Harder spectrum better

detection efficiency.

BABAR

• At 2.4 GeV:• Hard photon: E* < 1.1 GeV.• Distribution of particles and photon

“uniform” distributed

F. J. aks for had at 1% up to the . L. Roberts will also be happy!

Conclusions

Tough task! However big activities around the world:

region: 1.3% of syst. err. from KLOE/SND; 0.6% from CDM-2. Not perfect

agreement among data, needs additional clarification. New data from KLOE

and B-factories will help. 2 threshold also very important: KLOE off-peak data

will help.

[1.02-2.4] GeV energy range: the most important for had; DAFNE-2 could

give a relevant contribution (expecially with a scan). Other competitive

experiment are running (B-Factories) or are expected to taka data in few years

(VEPP-2000, BESIII with ISR(?)). All these efforts are very welcome (almost

mandatory): 1% accuracy needs confirmation from different experiments!

Region above 2.4 GeV: ISR at B-factories, scan at/charm factory (BES-III).

spares

Detector requirements: a wishlist

Momentum measurement: charged particles selection, kinematic fitting

and/or identification of the several processes require good momentum

resolution, furthermore, with a scan R-measurement, luminosity and s need

good accuracy (e.g. in KLOE L/L ~ 0.3% and s ~ 50 keV, with Bhabha

events), a good dE/dx resolution should not be neglected for good

separation (see V. Patera’s talk)

Electromagnetic calorimetry: it is crucial for good measurements of time,

direction and energy of the ’s from , (e.g. a completely neutral inclusive R

measurement), for efficient trigger criteria and for e/ particle identification

Vertex detector: in the multitrack channels, a vertex detector is really

helpful, matching similar requirements of the interferometry in the

semileptonic channels (see A. Di Domenico’s talk)

in the future years the impact of ahlo and had is conditioned to

different factors

KLOE and VEPP-2M are successfully covering the region,

waiting for B factories results;

despite of KLOE, VEPP-2M and BaBar results there is still room

for improving the R measurement in the future

DAFNE2 can give major contributions mostly on the threshold

region and in the [1.02-2] GeV energy range

Conclusions and perspectives

Conclusions - A scan at Dafne-2 will allow to improve - Statistical error expected at the level of 5-10% for

single point (in ISR case). Systematics and background are different.

- A scan @1032 cm-2 sec-1 for single point gives higher statistics then B-factories even at 1000fb-1. However for a or em . what really matters is also the systematics.

Conclusions -II- Crucial point:

- Time schedule of the data above phi in D2 (2015?)

- Keep in mind:- Scan:

- Better than B-factories. However also VEPP-2000 will enter in the game in few fears from now (2008?), with a scan up to 2 GeV at 1032 cm-2 sec-

1.

- ISR: - Compatible with other D2 programs at 2.4 GeV (NN,gg physics, etc…).

It doesn’t required a dedicated program. However statistically limited, compared with full luminosity B-factories.Systematics are different.

- In any case keep in mind that for precision physics the more data you have the better it is. And systematics are different!

• At 10.6 GeV:• Hard photon: E* = 3-5.3 GeV at s’ = 0-7 GeV.

No fakes from beam-gas processes.• Hadronic system collimated by

recoil.• Harder spectrum better

detection efficiency.

Different topology btw 2.4 and 10.6 GeV:+-0channel

Es=2.4 GeVs=10.6 GeV min

degrees

degreesGeV

GeV

E

BABAR

• At 2.4 GeV:• Hard photon: E* < 1.1 GeV.• Distribution of particles and photon

more symmetric in polar angle.

Event Yeld with 1fb-1@ 2.4 GeV

GeV GeV

GeV GeV

N/f

b-1/2

5MeV +-0 +2-

+-20 +-

20o<<160o

=10%

Above 1 GeV Statistical error for single point at 5-10% level.However what matters for a or em is the systematic error (which must be kept below 5%).

with 1fb-1@ 2.4 GeV: inclusive measurement

GeV

N/25MeV

+-

=10%

+-

+-

KLOE impact with 2 fb-1

s’ (GeVs’ (GeV22))

dd/ds/ds′ (nb/GeV′ (nb/GeV22))

s’ (GeVs’ (GeV22))

′′′′

′′

only ISR at the NLO for both processes

EMeV, bin = 0.01

GeV2

L = 2 fb-1 , = 50% flat in s′, in both channels

Hadronic regions: contributions and errors

ahad:

had(MZ):

12 - 5 - 12 (+)3.7 - 5 (+J/, )1.8 - 3.743 (+,)2 > 4 (+KK)

< 1.8 GeV< 1.8 GeV 8% [2m - 0.5 GeV] 54% [0.6 - 1.0 GeV]10% [rest 1.8 GeV]

2[ahad]: 2[

had]:

8% [2m - 0.5 GeV] 34% [0.6 - 1.0 GeV]31% [rest 1.8 GeV]

based on estimates from Davier et al., EPJ,C27 (2003) 497

Contribution to had from F. Jegerlehner

Comparison of different evaluations of had

had Method Ref

0.0280 0.00065 data<12 GeV S.Eidelman F.Jegerlehner ’95

0.02777 0.00017 data<1.8 GeV J.H.Kuhen, M.Steinhauser ’98

0.02763 0.00016 data<1.8GeV M.Davier, A.Höcker ’98

0.0277300.000148 Euclidean>2.5 GeV F.Jegerlehener ’99

0.0274260.000190 scaled data, pQCD 2.8-3.7, 5-

A.D.Martin et al. ’00

0.0278960.000391 data<12 GeV (new data CMD2 & BES)

F.Jegerlehner ’01

0.02761 0.00036 data<12 GeV

(new data CMD2 & BES)

H.Burkhardt,B.Pietrzyk ’01 ( ’05)

0.00007

(0.00005)

up to J/up to )

Hadronic contributions to ahad

12 - 5 - 12 (+)3.7 - 5 (+J/, )1.8 - 3.743 (+,)2 > 4 (+KK)

< 1.8 GeV

ahad

2[ahad]

<1.8 GeV

<1.8 GeV

1%

Calculations based onDavier, Eidelman, Höcker, Zhang

e+e- data only!

2 contrib. ahad

8% [2m - 0.5 GeV] 54% [0.6 - 1.0 GeV] 10% [Rest<1.8 GeV]

2 contrib. ahad

8% [2m - 0.5 GeV] 34% [0.6 - 1.0 GeV] 31% [Rest< 1.8 GeV]1GeV

magnitude errors

Burkhardt & Pietrzyk

2001Contributions to

had

Including KLOE results, a preliminary analysis of B.& P. found a value of (5)(mZ

2) which confirms their 2001 estimate: (5)(mZ

2) =0.02761±0.00036

Current activities: ISR events

standard way (energy scan):measuring e+ e- hadrons(s) by varying e beam energy

alternative approach:given a fixed s, by studying Initial State Radiation events

)cosθ,H(M)(MσdM

)(MdσM min

22

ee2

2

γee2hadhadhadrons

had

hadhadronshad

H = radiation function

min = emitted min. ang.

uncertainties related to the beam energy and the luminosity are the

same for each Mhad2 value

it may be performed in parallel with other measurement programs the ideal solution for interference region (e.g. -), and the only way

for the 2m threshold

cleaner topology: minor impact

from FSR corrections and the H

function

the resolution is that of s rather

than that of Mhad

an inclusive R measurement can

be performed with smaller

systematic uncertainty wrt ISR

experiments

ISR vs. SCANISR vs. SCAN

the MC code Phokhara

with full NLO ISR corrections

[Kühn et al., EPJ,C24 (2002) 71]

Impact of DAFNE-2 on the range [1-2] GeV (4) using ISR @ 2.4 GeV

stat

isti

cal

stat

isti

cal

h

ad

had

h

adhad

s (GeV)s (GeV)

BaBar, with the published BaBar, with the published LLintint per point per point

BaBar, with 10 BaBar, with 10 (the present (the present LLint int ))

DAFNE-2, with 2 fbDAFNE-2, with 2 fb-1-1 @ 2.4 GeV @ 2.4 GeV

comparison among the present BaBar

analysis, an (O(1 ab-1)) BaBar update,

and Lint = 2 fb-1 at 2.4 GeVper energy

point @ DAFNE-2, in the impact on

hadhad :

: O(2.5%) | O(0.8%) | O(1%)

Impact of DAFNE-2 on the range [1-2] GeV (2K2) using ISR @ 2.4 GeV

stat

isti

cal

stat

isti

cal

h

ad

had

h

adhad

s (GeV)s (GeV)

BaBar, with the published BaBar, with the published LLintint per point per point

BaBar, with 10 BaBar, with 10 (the present (the present LLint int ))

DAFNE-2, with 2 fbDAFNE-2, with 2 fb-1-1 @ 2.4 GeV @ 2.4 GeV

comparison among the present

BaBar analysis, an (O(1 ab-1)) BaBar

update, and Lint = 2 fb-1 at 2.4

GeVper energy point @ DAFNE-2, in

the impact on hadhad :

: O(15%) | O(5%) | O(5%)

e+ e- +-0

Babar @89 fb-1

D2@2fb-1

2fb-1@ 2.4 GeV89fb-1@ 10.6 GeV

N/25MeV

We have assumed a 10% eff. in both cases.

Results obtained with Phokhara 5, NLO ISR

Number of events for Babar consistent with publication(hep-ex/0408078)

GeV

GeV

Issues in the region [1-2] GeV

from Burkhardt & Pietrzyk, PRD72 (2005)

057501

s (GeV)s (GeV)

R(s)R(s)

1) the most critical region for had and the

second relevant one for ahlo

2) significant difference btw inclusive and

sums of exclusive measurements

3) most recent inclusive measurements

from DC1 and ADONE (~ 1981!!)

from Martin et al., EPJ,C19 (2001) 681

ISR Luminosity for different c.o.m. energies - We integrated dL/dm

for 25 MeV bin sizes. L0 = 1 fb-1

1fb-1 @ s=1.02 GeV

1fb-1 @ s=2.4 GeV

1fb-1 @ s=10.6 GeV

[nb- 1

/25M

eV]

ISR L @ 2.4 GeVISR L @ 10.6 GeV

GeVGeV