Report of Snowmass 2001 Working Group E2 : Electron-positron Colliders from the $φ$ to the Z

24 Pages·0.66 MB·English

by  Z. Zhao

APS/123-QED
Report of Snowmass 2001 Working Group E2 :
Electron-positron Colliders from the φ to the Z
Zhenguo Zhao
Beijing Institute of High Energy Physics
Gerald Eigen
University of Bergen
∗
Gustavo Burdman
Boston University
2
0
William Marciano
0
2 Brookhaven National Laboratory

n
a
J David Hitlin
California Institute of Technology
0
3

1 Mark Mandelkern
v University of California, Irvine
7
4
0
Abi Soffer
1
Colorado State University
0
2
0
/ David Cassel, Lawrence Gibbons
x
Cornell University
e
-
p
e
Klaus Moenig
h
DESY, Zeuthen
:
v
i
X
∗
Joel Butler , Penelope Kasper, Rob Kutschke, Paul Mackenzie, Stephen Pordes, Ron Ray, Tenaji Sen
r
a Fermilab
Diego Bettoni, Roberto Calabrese
University of Ferrara
Caterina Bloise
Frascati National Laboratory
Daniel Kaplan
Illinois Institute of Technology
∗
Nobu Katayama, Yasuhiro Okada, Yukiyoshi Ohnishi, Hitoshi Yamamoto
KEK
2
Andrei Gritsan
Lawrence Berkeley National Laboratory
Steve Dytman
University of Pittsburgh
∗
Jik Lee, Ian Shipsey
Purdue University
Yuri Maravin
Southern Methodist University
Franz-Joseph Decker, Gudrun Hiller, Peter Kim, David Leith,
Sibylle Petrak, Steven Robertson, Aaron Roodman, John Seeman
Stanford Linear Accelerator Center
Marina Artuso, Sheldon Stone
Syracuse University
Xinchou Lou
University of Texas, Dallas
Michael Luke
University of Toronto
Will Johns
Vanderbilt University
( E2 Working Group Convenor)
∗
(Dated: October15, 2001)
Wereport on thestatus and plansof experiments nowrunningor proposed for electron-positron
collidersat energiesbetweentheφandtheZ. Thee+e− Bandcharmfactories weconsidered were
PEP-II/BABAR,KEKB/Belle, superKEK,SuperBABAR,andCESR-c/CLEO-c. Wereviewedthe
programsattheφfactoryatFrascatiandtheproposedPEP-NfacilityatStanfordLinearAccelerator
Center. WestudiedtheprospectsforBphysicswithadedicatedlinearcolliderZ factory,associated
with the TESLA high energy linear collider. In all cases, we compared the physics reach of these
facilities with that of alternative experimentsat hadron colliders or fixedtarget facilities.
PACSnumbers: ValidPACSappear here
Introduction ring at Stanford Linear Accelerator. Section 3 presents
the physics potential of a proposed reorientation of the
CESRmachineandtheCLEOdetector,knownasCLEO-
In this report we review the status of ongoing and c, which would focus on topics in charm physics and
planned electron-positron collider facilities whose center QCD.Insection4,wediscuss the future evolutionofthe
of mass energies range from the mass of the φ meson two asymmetric e+e− B-factory facilities, KEKB/Belle
to that of the Z Boson. In Section 1 and 2, we discuss and PEP-II/BABAR to superKEK and SuperBABAR
the physics potential of two “low energy machines”, the and compare their B physics reach to that of existing
φ factory at Frascati and the proposed PEP-N storage and proposed hadron collider experiments. In section 5,
3
we discuss the potential of a dedicated Z factory asso-
TABLE I:Summary of KLOEPhysics Program
ciated with a Linear Collider, in this case TESLA, for
B physics studies and compare its strengths to those of
Physics Topic Integrated Luminosity
e+e− and hadron collider experiments. In section 6, we (pb−1)
present our conclusions. This report is a written version φ radiative decays (foγ,aoγ,ηγ,η′γ) 20-100
oftheE2SummaryTalkgivenatthefinalplenarysession Measurement of σ(ππ) (for g 2)
of Snowmass [1]. K semileptonic decays, Kl4, −
η/η′ mixing, ... 1000
Tests of CP and CPT violation and
measurement of rare K decays 5000
I. φ FACTORIES
The φ factory, DAφNE, at Frascati is a unique facil-
ity, in which electron and positron beams of energy 510
rent luminosity but the study of CP violation and rare
MeV collide [2]. There are no plans to build a simi-
kaon decays requires significant improvements.
lar facility elsewhere. While there are several aspects to
its physics program, the E2 working group concentrated
on the physics reachof the KLOE (KLOng Experiment)
C. Comparison of Physics Reach of KLOE to
as compared to planned fixed target Kaon experiments,
Planned Fixed Target Experiments
which will run at US facilities in the next severalyears.
Thecurrentstatusofmeasurementsof“directCPvio-
′
lation”throughthe quantityǫ/ǫinFixedTargetExper-
A. Status of DAφNE
iments at CERN(NA48) and Fermilab(KTeV) is shown
in Fig. 3. At a φ factory, the double ratio and interfero-
DAφNE consistsoftwoindependentstoragerings,one metric methods are complementary to the Fixed Target
for electrons of 510 MeV and one for positrons of 510 experiments. KLOE’s goal of measuring ǫ′/ǫ to an ac-
MeV. The beams intersect at an angle of 25 milliradians curacy of 2 10−4, which requires 5000 pb−1, will
at two locations. The bunch length is 3 cm. The hor- provide a m∼easu×rement comparable to the other experi-
izontal bunch size is 2 mm and the vertical size is 0.02 ments. However, the ability to extract Standard Model
mm. The design luminosity is 5 1032cm−2s−1. CP parameters from this quantity is, at present, limited
×
It has been a great challenge to obtain reasonable lu- by theoretical uncertainties.
minosity. Recently, a luminosity of 2.5 1031cm−2s−1 Another emphasis of future Fixed Target programs in
×
has been achieved. This is a significant improvement the US is rare kaon decays, in particular, measurement
over a year ago and, while still far below the design, is of the branching fractions of
sufficient to begin to do meaningful physics. Over the
last few months sustained running at 1.3pb−1/day has K+ π+νν¯ (1)
been achieved. An integrated luminosity of 200pb−1 is Ko → πoνν¯. (2)
expected by the end of calendar 2001. L →
The first of these provides a measurement of V and
td
the second is a direct indicator of the CKM parameter
B. The KLOE Experiment: Description, Goals, η. The branching fractions are very small, of order a
and Status few 10−11. Very high kaon fluxes are needed and Fixed
×
Targetexperimentsthatwanttodetectthemmustwith-
A main goal of KLOE is to study rare and CP violat- standformidablebackgroundsandrunatveryhighrates.
ing decays of the Ko mesons which are produced in the The φ factory has very desirable features for doing
L
decay φ KoKo. A schematic of the KLOE detector these measurements which avoid many of the problems
→ L s
is given in Fig. 1. It has a 5m diameter superconduct- of the Fixed Target experiments. However, even with
ing solenoid, which contains a drift chamber and a lead- 5000 pb−1, only about 1010 K K pairs will be pro-
L s
scintillator electromagneticcalorimeter. There is also an duced so the Standard Model expectations cannot quite
endcap electromagnetic calorimeter. The drift chamber bereached. Thebranchingfractionforthenowobserved
uses Helium gas to minimize multiple scattering and Ko decayK+ π+νν¯isalreadytoolowforKLOEtoreach.
L
regeneration. A CP violating Ko decay has a very clear However, i→f there is new physics, outside the Standard
L
signature in the detector, as shown in Fig. 2. Model, in the decay Ko πoνν¯, which currently has a
The physics program of KLOE is quite broad and is limitonlyoforder10−6L,t→his processcouldbe withinthe
described in Table I. The table includes physics topics range of the KLOE experiment. Thus, KLOE has a few
andthe approximateluminosity requiredto make mean- year window to push the sensitivity of Ko πoνν¯ in
L →
ingful measurments for each topic. It can be seen that the hope thatnew physicsmight be presentthere. If the
some measurements are already achievable with the cur- Standard Model processes are the dominant ones, then
4
FIG. 1: A schematic of theKLOEdetector
FIG. 2: A CP violating Ko decay as seen in KLOE
L
ultimately this decay will have to be observed in Fixed 100MeV<E <800MeV. Theaccessiblecenterofmass
e
Target kaon experiments. See [3] for further details. (CM)energyis1.2GeV<√s<3.15GeV. Thismachine
would run simultaneously with PEP-II operation at the
Υ(4S).
II. PEP-N There is a rich variety of important physics measure-
ments that are accessible at this collider. The most
PEP-N is a proposed novel extension of PEP-II. The prominentarethe high-precisionmeasurementof the ra-
machineisanasymmetriccolliderconsistingofthePEP- tio,R[5][6],ofthehadrontotalcrosssectiontothemuon
IILowEnergyRing(LER)(3.1GeV)andanewelectron pair crosssectionand the determination ofnucleon form
storage ring (Very Low Energy Ring, VLER) of energy factors [7]. Other physics topics which can be studied at
5
FIG. 3: World Results on ǫ′
ǫ
FIG.4: Current andexpected resultson rare Kdecays. Foreach mode, thetwo linescorresponding tothegreatest sensitivity
are for theKopio experiment (Ko πoνν¯) and the KAMI proposal (all three modes). NoteKAMI is not approved.
L →
PEP-N include meson form factors, vector meson spec- A. The Measurement of R
∗
troscopy, the search for non qq states and γγ interac-
tions.
TestingtheconsistencyoftheStandardModelrequires
In our view the most important single measurement avarietyofmeasurementsforwhichradiativecorrections
that PEP-N could contribute is the determination of R playa crucialrole. Two ofthe mostimportantexamples
with greatly improved precision. In this report we will are (a) Higgs mass bounds from precision measurements
focus solely on the physics motivation and challenges of at LEP and electroweak natural relations (i.e. the evo-
measuring R. lution of α to the Z pole), and (b) Interpretation of the
6
αEM(s)
! h
+ +
αEM(o) ∆α! ∆αHad
aµ≡(g−22)µ
+ ! + Z + ...
aµ(EW)
h
h + ! +
aµ(Had;1) aµ(Had; 2) aµ(L b L)
FIG. 5: Feynman diagrams for radiative corrections to αem
and (g 2)µ
−
FIG.6: R includingresonanceswiththeparameterization
had
of Burkhardt and Pietrzyk.
BNL g 2 experiment [8]. In addition, future higher
µ
−
precision experiments, such as Giga-Z, will depend on
radiative corrections being precisely known.
Theparametersoftheelectroweakmodelcanbetaken
as GF, αem(0), MZ, mH and the fermion masses and ∆α(s)=∆α (s)+∆α(5) (s) (4)
mixings. Inordertocomputephysicalquantitieswemust leptons hadrons
include radiative corrections which renormalize charges,
masses and magnetic moments as shown in Fig. 5. Al-
though the electroweakradiative correctionsare calcula- αs ∞ R(s′)
∆α(5) (s)= ds′ (5)
bthlee,lothweeshta-odrrdoenricharaddroiantiicvreacdoiarrteivceticoonrsreacrteionnost.caHnobweeovber- hadrons −3π Z4m2π s′(s′−s)
tained from e+e− hadrons using dispersion relations Our current knowledge of R below 10 GeV is shown in
→
and unitarity. The forward scattering amplitude for vir- Fig. 6. ∆α(M2) is of particular importance for pre-
Z
tual photons interacting with the vacuum is related to dicting the W mass and Z-pole asymmetries and has
the total cross section for that process by the Optical been calculated by many authors including Burkhardt
Theorem. and Pietrzyk (BP) [10]. BP find ∆α(5) (M2) =
hadrons Z
0.02761 0.00036 (1.3%) corresponding to 1/α(M2) =
± Z
128.936 0.046 (0.037%). The largest contributions to
1. The evolution of α to MZ the unce±rtainty in ∆α(5) (s) are from the measured
hadrons
values of R in the regions 1.05< √s <2.0 GeV and
In leading order perturbation theory:
2.0< √s <5.0 GeV, each contributing about 0.8% as
shown in Fig. 7 from Ref. [10]. The latter uncertainty
α s 5 decreased significantly after inclusion of the recent BES
∆α(s) = Q2N (ln )
3π f cf m2 − 3 (inclusive) data [11], even though the measurements be-
mX2f<<s f tween2 and 3 GeV have largeerrorsand potentially sig-
= ∆α (s)+∆α (s) (3) nificant systematic uncertainties. The uncertainties in
leptons hadrons
the contributionsfromdifferentintervalsaresystematics
This expression is inadequate for the hadronic contribu- dominated. However BP combines the errors in quadra-
tion, whichcanbe obtainedfromthe measurementofR. ture. If one were to sum the systematic errors, the un-
For (2m )2 >>s>>(2m )2 we have: certainty would be 3%.
t b
7
experimental uncertainty of 56 MeV. Measurements of
the effective leptonic sin2θ and the predictions of the
W
Standard Model with uncertainties due to ∆α(5) (M2)
had Z
and m from the LEPWG [12] are shown in Fig. 8.
t
The effective weak mixing angle, can be determined
from Z-pole asymmetry data, etc. without knowledge of
the top and Higgs masses. The Standard Model predic-
tion is given as a function of m with uncertainties due
H
to∆α(5) ,m ,andm . Theuncertaintyinsin2Θl
hadrons t Z eff
due to ∆α(5) is sin2Θl ∆α(5) 0.0001,
hadrons ∼ eff hadrons ∼ ±
that due to m is also about 0.0001, and that due to
t
M << 0.0001, compared to the experimental error of
Z
0.00017. Theoverallfittom fromallelectroweakdata,
H
showninFig.9,yieldsanestimateof 100+57GeVwhere
∼ −38
thedominantcontributiontotheuncertainty, 20GeV,
∼
(5)
is from ∆α .
had
2. (g 2)µ
−
We now consider hadronic corrections to the muon
magnetic moment. The Standard Model prediction for
a (g 2) /2 is:
µ µ
≡ −
FIG. 7: Relative contributions to ∆α(h5a)d(MZ2) in magnitude aµ(theory)=aµ(EW)+aµ(Had). (10)
and uncertainty from Burkhardt and Pietrzyk.
a (EW) a (QED)+a (Weak) is calculable to a few
µ µ µ
parts in 1≡011. The uncertainty in a is dominated by
µ
As noted in [5], the consistency of R measurements thatinaµ(Had)whichisusuallybrokenupintothelead-
between 3 and 4 GeV and between 5 and 8 GeV is poor. ingvacuumpolarizationcontributionaµ(Had;1)oforder
Absolutecrosssectionsaredifficulttomeasureandthere (απ)2, the higher order vacuum polarization contribution
maybesignificantsystematicerrorsinthemeasurements aµ(Had;2)oforder(απ)3,andthe hadroniclight-by-light
beyond those estimated by the experiments. contribution a (LbL), also of order (α)3. The first of
µ π
∆α(M2) enters in electroweak physics via these is related to R by a dispersion relation, and the
Z
second and third must be estimated.
πα 1
sin2Θcos2Θ= (6)
√2GFMZ2 1−∆r a (Had;1)=(αemmµ)2 ∞ dsK(s)R(s) (11)
where µ 3π Z4m2 s2
π
∆r =∆α(M2) f(sin2Θ)δρ+∆r +∆r (7) where
Z − Higgs other
and
3s x2
K(s) = x2(1 )
δρ √2GF3m2 (8) m2µ{ − 2
≃ 16π2 t
1 x2
+ (1+x)2(1+ ) ln(1+x) x+
x2 { − 2 }
∆rHiggs ≃ √21G6FπM2 W2 {cH(sin2Θ)(lnMmW2H2 − 56)}; + 11+xxx2lnx} (12)
−
m >>M (9)
H W with
cH(sin2Θ)andf(sin2Θ)aredependentonthedefinition
of sin2Θ, i.e. the renormalization method. In the on- 1 β 4m2
µ
shellscheme,for example,CWH =11/3andfW(sin2Θ)= x= 1−+β,β =r1− s . (13)
cot2Θ 3.35.
W
Theres≃ultingfractionaltheoreticaluncertaintyinM NotetheweightingofR(s)is1/s2,makingthelowenergy
W
is 0.23δ∆α. The contribution from the 0.0004 uncer- regime more important than for α(s). Some recentanal-
tai∼ntyin∆α(5) (s)isabout75MeV,comparedtothe yses have used τ decay data to supplement e+e− data.
hadrons
8
Here CVC is used to relate processes through the vector Preliminary
charged weak current to comparable processes through A0,l 0.23099 ± 0.00053
fb
theisovectorE.M.currentassumingnosecondclassweak A 0.23192 ± 0.00052
t
currents,whichimpliesthatthe contributionoftheaxial A 0.23117 ± 0.00061
vector current to G+ decays is zero. Thus annihilation e
A(SLD) 0.23098 ± 0.00026
cross sections with G = C( 1)I = +1 (G+, i.e. n l
− π A0,b 0.23240 ± 0.00031
even) are obtained fromthe rates of correspondingτ de- fb
cays. While τ decay data is useful at the currentlevelof A0,c 0.23262 ± 0.00080
fb
accuracy, I-spin violation and effects such as initial and <Q > 0.2322 ± 0.0010
fb
finalstateradiationmustbe understoodifwe areto rely
Average 0.23156 ± 0.00017
on it at smaller experimental errors, as emphasized by
c 2/d.o.f.: 15.5 / 6
Eidelman and Jegerlehner [13, 14]and by Melnikov [15]. 103
PQCD is used at energies> 12 GeV by all authors be-
]
V
causeofthelackofdata. TheresultofDavierandHocker e
G
(DH) [16], who use QCD sum rule constraints atlow en-
[
segerivrgviynagatisvtweheerleldsauosmltτiondfaaJntetag,ueinrslceaehrµnt(aeHrinaitsdy;61i9n)87=a(µ16.1912T)4.h(e62m)×or1e0c−o1n1-, m H102 DaDaamst==h(5 a0)1d.=71 410.8.30 ±2± 7 056..0110 ±G2 e0V.00036
0.23 0.232 0.234
The higher order hadronic vacuum polarization and sin2q lept
hadronic light-by-light contribution to aµ are compara- eff
ble. However while the uncertainty in the former is sev-
eral parts in 1011, the uncertainty in the latter is much FIG. 8: Measurements of the effective leptonic sin2θW and
thepredictionsoftheStandardModelwithuncertaintiesdue
larger. The detailed calculations done by Hayakawa and
Kinoshita [17] and by Bijkens, Pallante and Prades [18] to ∆α(h5a)d(MZ2) and mt.
givea negativeaLbL [19]. MarcianoandRoberts intheir
µ
recent review [21] combine in quadrature the DH re-
sult for a (Had;1) = 6924(62) 10−11 and a (LbL) =
µ µ
85(25) 10−11(the averageof×HK and BPP taking the 6
− × theory uncertainty
averageof the quoted uncertainties) for an overallresult DaDa (5) =
ofaSM =116591597(67) 10−11. Thisistobecompared had
withµthe BNL E821[8]re×sultof116592020(160) 10−11. 00..0022776318±±00..0000003260
The discrepancy is 423(173) 10−11 [19]. Other×authors 4
×
regard the light-by-light calculation as model-dependent
and less reliable [5]. BNL E821 ultimately anticipates 2
an uncertainty of 40 10−11. Clearly improved knowl-
× Dc
edge of a (Had;1) and a (LbL) are required to exploit
µ µ
2
high-precisionmeasurementsof(g 2) . Theformerwill
µ
greatly benefit from better e+e− d−ata below 3 GeV.
Excluded Preliminary
B. Experimental Requirements 0
2
10
Two methods can be used to measure R: m [GeV]
H
Inclusive approach: hadronic events are defined
•
inclusivelybyrequiringaminimumnumberofpar-
ticlesinthedetector. Inordertomeasurethecross FIG. 9: Light Higgs mass prediction of precision electroweak
section σ(e+e− hadrons) the acceptance is re- data, with uncertainty dueto hadroniccorrections.
→
quired. Due to the large number of contributing
channels,aMonteCarlosimulationisused,leading
topotentiallylargesystematicerrorsandrendering 1-2 % in R can be reached, as shown by the recent
thismethodunsuitableforahigh-precision(1-2%) VEPP-2M measurements.
measurement of R.
To measure R with a precision of the order of 2 % (or
Exclusive approach: the cross section of each better), the PEP-N experiment is designed to use the
•
individual channel contributing to R is measured. exclusive method. The detector has a large acceptance
Eventsmustbecompletelyreconstructedwithhigh and is able to measure the absolute position of charged
efficiency, and acceptances for each channel must and neutral particles. In addition, since σ(e+e− nn)
→
be well known. With this method an accuracy of is a sizeable fraction of the total hadronic cross section
9
Side view Up view
Magnet EM Calorimeter Magnet
TPC Chamber
Tracking Plane
Hadronic Cal
Aerogel
LER Beam Pipe VLEAR
27.56°
42.43°
EM Calorimeter
Coil
TPC Chamber
HER Beam Pipe LER Tracking Plane
Coil Hadronic Cal
Aerogel
-160 -120 -80 -40 0 40 80 120 160 200 240 280 320 cm -160 -120 -80 -40 0 40 80 120 160 200 240 280 320 cm
FIG. 10: PEP-N detector layout: side view (left) and top view (right).
(e.g. 2.5 % at √s = 2 GeV), nn detection capability is Another important feature of the PEP-Ndesignis the
needed. magnet. The magnetic field required to perform beam
TheproposedPEP-Ndetectormustsatisfythefollow- separation with minimal interference with PEP-II op-
ing requirements: eration is a weak dipole field (B 0.3 T). This field
≈
is also used by the experiment for the measurement of
Low mass tracking. IntheenergyrangeofPEP- charged particle momenta. Therefore, the tracking sys-
•
N multiple scattering contributes significantly to tem is housed inside the magnet gap which, as a con-
the momentum resolution ( 2%); sequence, has to be made big enough to give a suitable
≈
acceptance. Considerable effort has been expended to
Momentum measurement with good accu- design a magnet with a sufficiently uniform field.
•
racy. A high-precision measurement of R requires Assuming an average instantaneous luminosity of 5
the ability to reconstruct efficiently every individ- 1030cm−2s−1 and a detection efficiency of 50 %, the ex×-
ualfinalstate. Thiscanbedonebymeansoftopo- pected hadronic event rate for the measurement of R is
logicalselectionsandkinematicfitting. The ability 10,000 events per day. A 1-2 day data taking period
to identify eachchannelcontributing to R depends at each CM energy provides statistical accuracies better
crucially on a high-precision measurement of the than 1 %. PEP-N plans to take data at intervals of 10
momenta. MeV.Severalhundreddaysofdatatakingarerequiredto
cover the energy region between 1.2 GeV and 3.15 GeV.
Electromagnetic (EM) calorimetry. The EM
• Taking a maximum total cross section of 100 nb and
calorimeter provides the direction and energy of maximum instantaneous luminosities of 1031cm−2s−1,
photons with high precision and accuracy down to
the event rate (excluding backgrounds) is 1 Hz. Back-
100MeV orbelow,andidentifies Bhabhasusedfor
grounds will increase this rate but should present no
the luminosity measurement.
problem for the detector.
The proposed PEP-N detector layout is shown in fig.
Particle ID is necessary for π/K separation; this
• 10. Thecentraldetectorishousedinsidethemagnetgap.
featureiscrucialtodistinguishbetweenandrecon-
It consists of a time projection chamber (TPC) using a
struct efficiently final states containing pions and
slowHebasedgasprovidingσ =200 300µmanddE/dx
kaons.
−
capability. ItisproposedtouseGEMsforthereadoutto
Luminosity measurement with an accuracy of eliminate the E B term. The EM calorimetermodules
• ×
the order of 1 % or better. are located outside the magnet. Energy resolution of a
few percent down to 100 MeV and good time resolution
nn capability canbeachievedwithaleadandscintillatingfibertechnol-
•
ogy based on the KLOE design. Particle ID is achieved
AsPEP-Nisanasymmetricmachine,theCMistravel- withtwo10cmthickKEDRstyleaerogelcounters,which
ling at 0.6<β <0.94. In consequence,slowparticles achieve 4σ π/K separation between 600 MeV/c and 1.5
CM
intheCMframeareboostedtomomentarangingfroma GeV/c. The hadron calorimeter design was not chosen
few hundred MeV to 1-2 GeV, simplifying detection and at the time of writing this report. A scintillator based
reducing the angular coverage needed to obtain full ac- calorimeteroranextensionindepthoftheEMcalorime-
ceptance. The asymmetric operation has the additional ter were under investigation. The dipole magnet and
advantage of simplifying beam separation. the central detector are not centered on the interaction
10
point. Theyareshifted25cmintheforwarddirectionto luminosity has been too low, or have been carried out
increase the path inside the magnetic field for particles previously with meager statistics. They include:
produced in the forward direction.
The forward detector consists of two silicon aerogel 1. Charm decay constants fD,fDs;
countersforparticleID,additionaltrackingplanes (drift
2. Charm absolute branching fractions;
chambers)as well as EM andhadronic calorimeter mod-
ules. Also shown in fig. 10 are the HER (High Energy
3. Semileptonic decay form factors;
Ring), LER and VLER beam pipes.
TheproposedscheduleforPEP-Nisasfollows. Apro- 4. Direct determination of V & V ;
cd cs
posalreviewisplannedforsummerof2001. Ifapprovalis
granted, then in 2003 the injector gun, linac, and trans- 5. QCD studies including:
port lines would be installed. Also modifications to the Charmonium and bottomonium spectroscopy;
PEP-IILERandHERwouldbemade. Thefirstinjector Glueball and exotic searches;
beam test would be in October 2003. In summer 2004, MeasurementofRbetween3and5GeV,viascans;
the VLER ring, detector magnet, and detector would be and
installed. In October 2004, first VLER injected beam Measurement of R between 1 and 3 GeV, via ISR
tests areforeseen. InJanuary2005,firstcollisionswould (Initial State Radiation).
occur.
6. Search for new physics via charm mixing, CP vio-
lation and rare decays; and
C. Summary
7. τ decay physics.
The determination of R in this energy range is of The CLEO detector can carry out this program with
particular importance and is timely. The statistical only minimal modifications. The CLEO-c project is de-
error achievable is negligible. However, there was no scribed at length in [25]. It was also described in several
cleardemonstrationthattherequiredsystematicerrorof talks at this workshop: [26] - [34]. Theoretical issues
about2%(dominatedbyknowledgeoftheacceptance)is in charm physics were covered in talks [35] - [38]. A
achievable. StudiesstimulatedbytheE2groupareongo- very modest upgrade to the storage ring, described else-
ing to address this concern. In one approach, a CLEO-c where in these proceedings, is required to achieve the
109 J/Ψ run would yield precision J/Ψ absolute branch- required luminosity. Below, we summarize the advan-
ingratios,whichcouldbeusedbyPEP-Ninacalibration tagesofrunningatcharmthreshold,theminormodifica-
runattheJ/Ψforaprecisiondeterminationoftheaccep- tions required to optimize the detector, examples of key
tance. The PEP-Ndetector design appears to be sound. analyses, a description of the proposed run plan, and a
There is no new technology except for the GEM read- summary of the physics impact of the program.
out of the TPC. We conclude that the physics program
of PEP-N is well defined, important and unique and the
required number of events can be obtained in five years. A. Advantages of running at charm threshold
However, control of systematic errors needs to be care-
fully evaluated before proceeding. The B-factories, running on the Υ(4S) will have pro-
duced 500 million charm pairs from the underlying con-
tinuum by 2005. However, there are significant advan-
III. CHARM PHYSICS WITH CLEO-c
tages of running at charm threshold:
For many years, the CLEO experiment at the Cor- 1. Charmeventsproducedatthresholdareextremely
nell Electron Storage Ring, CESR, operating on the clean;
Υ(4S) resonance, has provided much of the world’s in-
formation about the B and B mesons. At the same 2. Double tag events, which are key to making abso-
d u
time, CLEO, using the copious continuum pair produc- lutebranchingfractionmeasurements,arepristine;
tion at the Υ(4S) resonance has been a leader in the
3. Signal/Backgroundis optimum at threshold;
study of charm and τ physics. Now that the asymmet-
ric B-factories have achieved high luminosity, CLEO is
4. Neutrino reconstruction is clean; and
uniquely positioned to advance the knowledge of heavy
flavorphysicsbycarryingoutseveralmeasurementsnear 5. Quantum coherence aids D mixing and CP viola-
charmthreshold,atcenterofmassenergiesinthe3.5-5.0 tion studies
GeV region. These measurements address crucial topics
which benefit from the high luminosity and experimen- These advantages are dramatically illustrated in Fig-
tal constraints which exist near threshold but have not ure 11, which shows a picture of a simulated and fully
been carried out at existing charm factories because the reconstructed ψ(3770) DD¯ event.
→