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LNF-19-Jan-06
R measurement at DAFNE-2
G. Venanzoni LNF
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What is DAFNE-2?

• Upgraded Dafne with 1 interaction region

Energy (cm) (GeV) 1.02 lt2.5
Peak luminosity gt (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!
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Competitors (on R)
Machine Physics Program on R Energy range Starting date
VEPP-2000 L 1032 ScanISR(?) 0.4lt?slt2 GeV gt2007
BESIII L1033 _at_ y(3770), ISR(?) 2.4lt?slt4.2 GeV gt2007
CESR-c ? 3lt?slt5 GeV Working
Babar ISR Thr.lt?slt10 GeV Working
Belle ISR (?) Thr.lt?slt10 GeV Working
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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.

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

• 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)

Big work from Karlsruhe/Katowice group (Kühn,
Czyz) to provide generators for ISR processes
(Phokhara) at 0.5 accuracy!
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Status of R measurements (?s lt10 GeV)
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Topics on R in the region 2mplt?slt2.4 GeV

• Exclusive analysis
• 2p channel (the biggest contribution to (g-2)m )
• Threshold region below 600 MeV poorly covered
  by data (error between 1 and 3)
• Around the r 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 with 2p spectral
  function from t
• Above 1 GeV O(1-4) from CMD-2
• pp-p0 , 2p2p-, p p- p0p0 , KK-pp-, 3(p
  p-), 2(p p-) p0p0 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.

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2p spectrum 0.35lt?slt.95 GeV2

• Discrepancy with tau data
• KLOE and CMD-2 lower than t data at high Mpp2
• Error on theoretical corrections (I.B., FSR)
  underestimated?
• New tau data available from B factories

Comparison of ee- data

• Most likely this issue will continue (hopefully
  solved) in the next years
• New data KLOE,BABAR, Belle(?), CMD-2, will
  hopefully bring the error lt1. However the path
  to reach few per-mill accuracy is still long

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2p threshold region

• It contributes for 20 of ampp
• ampp (2mpltElt600 MeV) 100? 10-10
• This region is poorly covered by data
• Different authors use different ranges for
  analytical expansion
• t data do not agree so well (F.J. 01), also
  with ep?epg data (NA7 ,1987) extrapolated in
  timelike.

s (nbarn)
s (GeV2)
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KLOE Data at off peak (1 GeV)(started at mid of
Dec. 05)
spp-p0 329.8 nb spp-g 4.4 nb

• stat. error on a? 1.5-2.5?10-10 (300-100
  pb-1)
• comparible with the expected syst.error
  (dsppg/sppg )syst 2 from region lt 0.35 GeV2

spp-p0 6 nb, sqrt(s)1003.71 MeV (from SND,
PRD66 (2002) 032001)
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Impact of DAFNE-2 on the threshold region
bin width 0.01 GeV2 efficiency 50 flat
1) total accuracy better than 3 in the region
lt0.35 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)
(dsppg/sppg )stat
during the KLOE data taking campaign _at_ ?s 1 GeV
we can learn a lot
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Issues in the region 1-2 GeV
from Burkhardt Pietrzyk, PRD72 (2005) 057501
1) the most critical region for Dahad and
the second relevant one for amhlo 2) significant
difference btw inclusive and sums of exclusive
measurements 3) most recent inclusive
measurements from DC1 and ADONE ( 1981!!)
d2Dahad
1.05-2GeV
40 of the total error
from Martin et al., EPJ,C19 (2001) 681
R(s)
?s (GeV)
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How DAFNE-2 can improve this region 1-2.4 GeV

• 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)
• 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) Babar Belle (?) ISR at Tau/charm
factories?
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Energy scan
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Impact of DAFNE-2 on inclusive measurement
20 pb-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 d(Dahad)/Dahad ? O(5) systematic error will
be reduced as well 4) a precise comparison
exclusive vs. inclusive can be carried out
Lint (nb-1)

• MEA, 14 points, Lett. Nuovo Cim.30 (1981) 65
• B antiB, 19 points, Phys.Lett.B91 (1980) 155

?s (GeV)
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Impact of DAFNE-2 on the range 1-2 GeV (4p)
BaBar, with the published Lint per point BaBar,
with 10 ? (the present Lint ) DAFNE-2, with 20
pb-1 per point

• comparison among the present BaBar analysis, an
  (O(1 ab-1)) BaBar update,
• and Lint 20 pb-1 per energy point
• _at_ DAFNE-2, in the impact on d(Dahad) /Dahad
• 2p2p- O(2) O(0.7) O(0.5)

statistical dshad / shad ()
?s (GeV)
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Impact of DAFNE-2 on the range 1-2 GeV (2K2p)
comparison among the present BaBar analysis, an
(O(1 ab-1)) BaBar update, and Lint 20 pb-1 per
energy point _at_ DAFNE-2, in the impact on d(Dahad)
/Dahad p- pK- K O(15) O(5) O(3)
BaBar, with the published Lint per point BaBar,
with 10 ? (the present Lint ) DAFNE-2, with 20
pb-1 per point
statistical dshad / shad ()
?s (GeV)
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Impact of DAFNE-2 on the range 1-2 GeV (3p)
BaBar, with the published Lint per point BaBar,
with 10 ? (the present Lint ) DAFNE2, with 20
pb-1 per point
comparison among the present BaBar analysis, an
(O(1 ab-1)) BaBar update, and Lint 20 pb-1 per
energy point _at_ DAFNE-2, in the impact on d(Dahad)
/Dahad p- p p0 O(9) O(3) O(1)
statistical dshad / shad ()
?s (GeV)
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Radiative Return _at_ 2.4 GeV
ISR differential luminosity

• q0 is the minimum polar angle of ISR photon. In
  the following, we will assume to tag the photon,
  with q020o.
• e is the overall efficiency, we will use 10.
• m is the invariant mass of the hadronic system
  (pp-, pp- p0, 2 p0 pp-, 2 p2p-, )
• x is 2Eg/?s, ?s ee- c.m. energy
• L0 is the total integrated luminosity

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ISR Luminosity for different c.m. energies

• We integrated dL/dm for 25 MeV bin sizes.

2fb-1 _at_ ?s1.02 GeV
nb-1/25MeV
2fb-1 _at_ ?s2.4 GeV
1pb-1
89fb-1 _at_ ?s10.6 GeV
2fb-1 _at_ 2.4 GeV 89fb-1 _at_ 10.6 GeV
1
GeV
GeV
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Impact of DAFNE-2 on the range 1-2 GeV (3p)
using ISR _at_ 2.4 GeV
BaBar, with the published Lint per point BaBar,
with 10 ? (the present Lint ) DAFNE-2, with 2
fb-1 _at_ 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 _at_ DAFNE-2, in the impact
on d(Dahad) /Dahad p- p p0 O(9)
O(3) O(8)
statistical dshad / shad ()
On the other channels the improvement can be
larger
?s (GeV)
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ISR _at_ 2.4 GeV vs scan

• Assuming to tag the ISR g, 2fb-1_at_ 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 _at_1032 cm-2 sec-1 .
• 2fb-1 _at_ 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 _at_ 2.4 GeV vs B-factories
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Different event topology btw 2.4 and 10.6
GeV 2p2p- channel
?s2.4 GeV
Eg
min(qg,p)
?s10.6 GeV
BABAR

• At 10.6 GeV
• Hard photon Eg 3-5.3 GeV at ?s 0-7 GeV.
• Þ No fakes from beam-gas processes.
• Hadronic system collimated by recoil.
• Harder spectrum Þ better detection efficiency.

GeV
degrees
Ep

• At 2.4 GeV
• Hard photon Eg lt 1.1 GeV.
• Distribution of particles and photon uniform
  distributed

GeV
degrees
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Conclusions

• F. J. aks for shad at 1 up to the ?. L. Roberts
  will also be happy!

• Tough task! However big activities around the
  world

• pp 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. 2p threshold also
  very important KLOE off-peak data will help.

• 1.02-2.4 GeV energy range the most important
  for Dahad 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 t/charm factory (BES-III).

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spares
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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 dL/L 0.3 and d?s 50
  keV, with Bhabha events), a good dE/dx resolution
  should not be neglected for good p/K separation
  (see V. Pateras talk)
• Electromagnetic calorimetry it is crucial for
  good measurements of time, direction and energy
  of the gs from p0, h (e.g. a completely neutral
  inclusive R measurement), for efficient trigger
  criteria and for e/p 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 Domenicos talk)

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Conclusions and perspectives

• in the future years the impact of amhlo and
  Dahad is conditioned to different factors
• KLOE and VEPP-2M are successfully covering the
  pp 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

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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 _at_1032 cm-2 sec-1 for single point gives
  higher statistics then B-factories even at
  1000fb-1. However for am or aem . what really
  matters is also the systematics.

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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 doesnt required a
  dedicated program. However statistically limited,
  compared with full luminosity B-factories.Systemat
  ics 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!

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Different topology btw 2.4 and 10.6
GeV pp-p0g channel
?s2.4 GeV
Eg
min(qg,p)
?s10.6 GeV
BABAR

• At 10.6 GeV
• Hard photon Eg 3-5.3 GeV at ?s 0-7 GeV.
• Þ No fakes from beam-gas processes.
• Hadronic system collimated by recoil.
• Harder spectrum Þ better detection efficiency.

GeV
degrees
Ep

• At 2.4 GeV
• Hard photon Eg lt 1.1 GeV.
• Distribution of particles and photon more
  symmetric in polar angle.

GeV
degrees
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Event Yeld with 1fb-1_at_ 2.4 GeV
pp-p0g
2p2p-g
20oltqglt160o e10
N/fb-1/25MeV
Above 1 GeV Statistical error for single point
at 5-10 level. However what matters for am or
aem is the systematic error (which must be kept
below 5).
GeV
GeV
pp-2p0g
mm-g
GeV
GeV
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ppg/mmg with 1fb-1_at_ 2.4 GeV inclusive
measurement
N/25MeV
mm-g qglt20o
mm-g qggt20o
e10
pp-g qglt20o
GeV
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KLOE impact with 2 fb-1
only ISR at the NLO for both processes 50o lt qp,
qg lt 130o , Eg gt 50 MeV, bin 0.01 GeV2 L 2
fb-1 , e 50 flat in s', in both channels
ds/ds' (nb/GeV2)
ppg mmg
s (GeV2)
s (GeV2)
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Hadronic regions contributions and errors
based on estimates from Davier et al., EPJ,C27
(2003) 497
a?had
?? had(MZ)
8 2mp - 0.5 GeV 54 0.6 - 1.0 GeV 10
rest lt 1.8 GeV
? 2?? had
? 2a?had
8 2mp - 0.5 GeV 34 0.6 - 1.0 GeV 31
rest lt 1.8 GeV
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Contribution to Da(5)had from F. Jegerlehner
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Comparison of different evaluations of Da(5)had
Da(5)had Method Ref
0.0280 ?0.00065 datalt12 GeV S.Eidelman F.Jegerlehner 95
0.02777 ? 0.00017 datalt1.8 GeV J.H.Kuhen, M.Steinhauser 98
0.02763 ?0.00016 datalt1.8GeV M.Davier, A.Höcker 98
0.027730?0.000148 Euclideangt2.5 GeV F.Jegerlehener 99
0.027426?0.000190 scaled data, pQCD 2.8-3.7, 5-? A.D.Martin et al. 00
0.027896?0.000391 datalt12 GeV (new data CMD2 BES) F.Jegerlehner 01
0.02761 ? 0.00036 datalt12 GeV (new data CMD2 BES) H.Burkhardt,B.Pietrzyk 01 ( 05)
0.00007 (0.00005) ds1 up to J/y (ds1 up to ?)
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Hadronic contributions to amhad
Calculations based on Davier, Eidelman, Höcker,
Zhang
a?had
lt1.8 GeV
?2a?had
lt1.8 GeV
1
ee- data only!
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Burkhardt Pietrzyk 2001
Contributions to Dahad
magnitude
errors
Including KLOE results, a preliminary analysis of
B. P. found a value of Da(5)(mZ2) which confirms
their 2001 estimate Da(5)(mZ2) 0.027610.00036
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Current activities ISR events
the MC code Phokhara with full NLO ISR
corrections Kühn et al., EPJ,C24 (2002) 71
standard way (energy scan) measuring se e-
? hadrons(s) by varying e? beam energy
alternative approach given a fixed ?s, by
studying Initial State Radiation events
H radiation function qmin emitted g min. ang.
ISR vs.
SCAN

• 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

• 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.
  r-w), and the only way for the 2mp threshold

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Impact of DAFNE-2 on the range 1-2 GeV (4p)
using ISR _at_ 2.4 GeV
BaBar, with the published Lint per point BaBar,
with 10 ? (the present Lint ) DAFNE-2, with 2
fb-1 _at_ 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 _at_ DAFNE-2, in the impact
on d(Dahad) /Dahad 2p2p- O(2.5)
O(0.8) O(1)
statistical dshad / shad ()
?s (GeV)
41
Impact of DAFNE-2 on the range 1-2 GeV (2K2p)
using ISR _at_ 2.4 GeV
BaBar, with the published Lint per point BaBar,
with 10 ? (the present Lint ) DAFNE-2, with 2
fb-1 _at_ 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 _at_ DAFNE-2, in the impact
on d(Dahad) /Dahad p- pK- K O(15)
O(5) O(5)
statistical dshad / shad ()
?s (GeV)
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e e- ? pp-p0g
Babar _at_89 fb-1
N/25MeV
Results obtained with Phokhara 5, NLO ISR
D2_at_2fb-1
GeV
We have assumed a 10 eff. in both cases.
2fb-1_at_ 2.4 GeV 89fb-1_at_ 10.6 GeV
Number of events for Babar consistent with
publication (hep-ex/0408078)
GeV
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Issues in the region 1-2 GeV
from Burkhardt Pietrzyk, PRD72 (2005) 057501
1) the most critical region for Dahad and
the second relevant one for amhlo 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
R(s)
?s (GeV)
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ISR Luminosity for different c.o.m. energies

• We integrated dL/dm for 25 MeV bin sizes. L0 1
  fb-1

nb-1/25MeV
1fb-1 _at_ ?s1.02 GeV
1fb-1 _at_ ?s2.4 GeV
ISR L _at_ 2.4 GeV ISR L _at_ 10.6 GeV
1fb-1 _at_ ?s10.6 GeV
GeV
GeV
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