Physical program for the new VEPP-2000 e+e− collider

ELSEVIER

Nuclear Physics B (Proc.

SUPPLEMENTS

369-374

126 (2004)

Suppl.)

www.elsevierphysics.cclm

Physical program for the new VEPP-2000 S.I.Serednyakov* Budker Institute

e+e- collider

of Nuclear Physics, Novosibirsk State University,

Novosibirsk,

630090, Russia

The description of the new VEPP-2000 e+e- collider now under construction in Novosibirsk is given. Two upgraded collider detectors SND and CMD-3 are intended for experiments in the available energy range 23=0.4-2.0 GeV. The physical program includes precise measurements of the total hadronic cross section, exclusive hadronic channels, two photon physics, test of higher order quantum elecrodynamics processes. The important item of the program is the study of nucleon form factors at the threshold in the reaction e+e- + pp, nA.

1. VEPP-2000

collider

The VEPP-2000 project was proposed to continue the VEPP-2M [l] physical program in the higher energy range. In year 2000 the VEPP2M was dismantled and on its place the construction of the new VEPP-2000 collider [2], [3] (fig.1) started. The maximum energy of the new collider is limited by the size of the experimental hall. The injection system (linac, synchrotron, booster) remains without significant changes.The main parameters of VEPP-2000 are the following:

Layout

of

the

VEPP-2000

l

the perimeter - 24.5 m,

l

the beam current - 200 mA (E=0.9 GeV),

l

the beam length - 3.4 cm (E=0.9 GeV),

l

the beam energy spread - 0.7 MeV (E=0.9 GeV),

Though the VEPP-2000 luminosity is less than the luminosity of e4e--factories, nevertheless it is by 2-3 orders of magnitudes higher than the luminosity of the machines (DCI, ADONE), earlier operating in the energy range l-2 GeV. The expected integrated luminosity for 5 years of VEPP2000 running is about 3 fb-I.

complex

2.

CMD-3

detector

The CMD-3 [4] is upgraded version of CMD2 detector, operated at VEPP-2M from 1992 to 2000. CMD-3 (fig.2) is the general purpose magnetic detector

Figure 1. General view of VEPP-2000 plex.

l

energy

range

S.C. 1.5 T solenoid,

drift

cham-

com-

0.4 - 2.0 GeV,

2E=

8 the luminosity L depends on energy: 2E=l.O GeV L = 1031cm-2sec-1, 2E=2.0 GeV L = 1032cm-2sec-1, *e-mail:[email protected]; 0920-5632/S - see front matter doi: 10.1016/~j.nuclphysbps.2003.1

with

ber for tracking, and muon system. The three component electromagnetic calorimeter includes 8 X0 liquid xenon and 5 X0 CsI(T1) in barrel and BGO in endcaps. The expected energy resolution for photons with energy 0.1-1.0 GeV is cEy/Ey = 3 f 6%. Angular resolution for photons is about 0.3”. 3.

at at

B.V

All rights

detector

SND [5] is a nonmagnetic detector with three spherical layer NaI(T1) calorimeter with 1620 crystals (fig.3). Due to its spherical shape SND

FAX: f7 (3832) 342163

0 2004 Elsevier 1.O62

SND

reserved

XI.

370

Serednyakov/Nucleur

Physics

Figure 2. CMD-3 detector; 1 - beam pipe, 2 - drift chamber, 3 - BGO endcap calorimeter, 4 - Z-chamber, 5 - S.C. solenoid, 6 - LXE calorimeter, 7 - CsI calorimeter, 8 - iron yoke, 9 - focusing S.C. solenoids

has the uniform response to photons over 90% of the solid angle. At present the following SND system are under upgrade [6] - the new tracking system based on 9 layer drift chamber is constructed, the aerogel cherenkov counter for separation between pions and kaons is under test. Electronics and DA& system are upgraded too. Both detectors CMD-3 and SND are located in opposite straight sections of VEPP-2000 and will take data in parallel (fig.1). 4. Physical

program

for VEPP-2000

The total e+e- -+ hadrons cross section is of the fundaThe value R = u$~~~?$$‘?p) mental importance in &CD. In the first approximation R = 3. C,ei and for the first three quarks R _N 2. The region of VEPP-2000 2E 5 2.0 GeV is the resonance region because the cross sections sharply change with energy. The present experimental data (fig.4) in general agree with the QCD prediction at the energy 2E > 1.4 GeV. The systematic errors in the cross section measurements in the energy range 2E = 1.1 + 2.0 GeV are still too large - 10 + 20%. The goal of VEPP-2000 experiments is to reduce the errors to the level of N 3%.

B (Proc.

S~ppl.)

126 (2004)

369-374

Figure 3. SND detector; 1 - beam pipe, 2 drift chamber, 3 - aerogel counters, 4 - NaI(T1) counters, 5 - vacuum phototriodes, 6 - iron absorber, 7 - streamer tubes, 8 - scintillation counters

The value R and fundamental constants. The anomalous magnetic moment of muon = 9 is the fundamental quantity in pary:le physics. In the recent BNL experiment [7] a, was measured with the accuracy 0.7 ppm (1 ppm=10e6). The Standard Model prediction for afi [8] agrees with experiment and has similar uncertainty 0.9 ppm. In the calculation of a, the experimental data on e+e- -+ hadrons cross section are used [9]: the lower energy - the more contribution. The VEPP-2000 range 2E < 2.0 GeV gives about 90% of the contribution to a,. Theoretical uncertainty in acL is also limited by the accuracy of R measurements at 2E < 2.0 GeV. New future data from VEPP-2000 will be of great help for more accurate a, calculations. The fine structure constant oepn in quantum electrodynamics is the function of energy s = 4E2. Its value rises with the energy. At Z-mass c+, -N l/129, which is considerably higher than 01,,(s = 0) N l/137. Because the precisely measured Z-bozon parameters are used for Standard Model tests, the accuracy of the LY,,(S = Mz) calculation plays important role in such tests. Similar to a, calculation, the value R gives the significant contribution to CY’,,(S = A4:), but the

S.I. Serednyukoo/Nuclear

Physics B (Proc. Suppl.) 126 (2004) 369-374

The parameters of these states were obtained from the cross section measurements of the corresponding exclusive hadronic channels. The experimental data for &K&‘T’ and KsK+rfinal states are shown in figs.5,6. One can see large systematic errors in the first figure and poor statistical accuracy in the second figure. This is typical picture for all processes (l), because the integrated luminosity in all previous experiments was only N 5 pb-I. At VEPP-2000 we expect to have N 3 fb-l of integrated luminosity, so the accuracy will be much higher.

RT : NY

‘iI 10

l

-

: a ;i 1 6: 4-

ND, CMO. CMD2. SND

)

i a .; i-r: . MD1 * C:‘O LITpoco

f I

-ir:.

h il i I

i

fi

i

;i 2 y ;.i ,I ,,.;q.+q: ; *, , ,I,

I

00

6

2

4

371

i’,.C! .~I ‘i;$,.i 1 8 .A, ‘GO&

Figure 4. Experimental data on value R = u(e+e- -thadrons) a(e+e---t/J+@-) and QCD predictions.

region of VEPP-2000 gives here only 20% of the total contibution, which is less than in up, but still considerable. So VEPP-2000 data can improve the calculated value of aern(s = Mi). Exclusive hadronic channels The value R is determined by the sum of the cross sections of all channels of efe- annihilation into hadrons: e+e- -+ 27r, 3n, 4r, 5n, Kl?, KI?n, Nfi,

...

(1)

At the energy 2E < 1.0 GeV the processes e+e- + 27r, 3n have the largest cross section, while at 1.0 < 2E < 2.0 GeV the eSe- ---) 47r process dominates. Each channel from (1) is described rather well by extended vector dominance model. Besides the old well known states p(770), u(783), qS(1020), there are heavier vector states in the Tables [lo], which are supposed to be radial or orbital excitations of low lying states: /I( 1450): ~(1700): ~(2150): ~(1420): ~(1650): d(1680):

M=1465&25; M=1700f20; M=2149f17; M=1419f31; M=1649f24; M=1680&20;

P=31Oz!z60; l?=240&60; I’=363+50; l?=174&60; I?=220&35; r=150&50;

47r; 4n; K+K-; 37r;

Figure 5. Experimental data of the e+e- ---t r+Yr”?ro process cross section

Test of CVC hypothesis, (fig.7). The CVC hvnothesis establishes the relation between r-lepton decay spectra in JPG = l-+ state and the cross section of the corresponding e+e--+ hadrons isovector process eSe- -+ 27r, 47r, wn”, r]~+r-, . . .. The CVC relation has the following form:

dMh -zz dq2

G$COS2& (1 + SEW) 327r2a2m3t ’

Wfb;

K*K;

+ 2q2).w(q2), +4 - q2). Cm?

S.I. Seuednyukov/Nucleur

372

Physics B (Proc. Suppl.) 126 (2004) 369-374

Figure 7. CVC diagrams

4s (MeV)

Figure 6. Experimental data of the e+eKsKSr- process cross section

-+

where $$$ and CL;:- (q2) are the r mass spectrum and e+e- cross section as a fun.ction of energy, respectively. At present the CVC hypothesis is under test for main isovector channels of e+e--annihilation. Fig 8 shows how the e+e- -+ UQTOprocess cross section [II] ‘agrees with -r-lepton data (CLEO). In general, if one considers the CVC tests for main channels, it turns out, that the r-data are higher by -2 s.d. than e+e--data. To resolve this descrepancy, new more accurate ese--data are needed and VEPP-2000 could produce such data. Production of Nn pairs At VEPP-2000 the measurements of proton and neutron electromagnetic formfactors becomes possible in the reactions: e+e- + pp, nfi The existing

(2) data in the region close to the

threshold are shown in Figs.S,lO. One can see that there are few data with Tkin <50 MeV and there is no data at all with Tkin
Figure 8. Comparison of e+e- -+ km0 process cross section (SND) with CVC prediction from r-lepton data (CLEO).

New measurements

at VEPP-2000

will allow

S.I. Serednyakov/Nuclear

Physics B (Proc. SuppI.) 126 (2004) 369-3 74

to study whether proton (Gp) and neutron (G”) formfactors rise to threshold and what their ratio g is. Separate measurements of electric and magnetic formfactors of nucleon are possible if the detector measures polar angles B of produced nucleons. There are data, indicating possible existence of a narrow state (I’ N 10 MeV) in e+e-annihilation [13],[14] and in photoproduction [15]. The position of this state B! _N 1.90 GeV is close to the nucleon production threshold, so there are speculations about its IV3 origin. Future high statistics experiments at VEPP-2000 could give answer as to the nature of this state and its relation to the Nfi bound state. The pp pairs from the reaction (2) have low kinetic energy and stop in material of beam pipe or drift chamber inner wall. The antiproton annihilation star gives events with displaced vertex and can be identified by the detector (SND and CMD-3). The n7i. events are more difficult for reconstruction because both neutron and antineutron penetrate deep inside the detector. Neutrons at the threshold of their production are nearly invisible. Antineutrons give an annihilation star somewhere far from the detector center. Some n% events look like beam or cosmic background, other resemble physical processes with production of KL mesons, for instance, efe- -9 KLKsT’. Now the problem of nfi detection in SND is considered. Other items of VEPP-2000 program. - ISR production of hadrons [16]. In N 3fb-1 data sample with energy 2E = 1.1 + 2.0 GeV we expect production of about N 107pmesons and - lO”w-mesons. This amount is comparable with what we have now in direct production of these states. So, the parameters of these states and their contribution to fundamental constants can be measured at VEPP-2000 in the independent way. We plan to mea- two photon physics. sure the cross section of the processes e+e- -+
Experimental data on proton Figure 9. electromagnetic formfactor in timelike rigion. Horizontal line corresponds to the VEPP-2000 energy range.

ity is direct measurement of tensor meson production in the proceses efe--+ ~~(1320) -+ n7r”, fi( 1260) -+ 7r07ro. Latest measurements at VEPP-2M [17] gave upper limits on electron width close to the expected values. - test of higher order QED in 2 --+ 4,5 processes with emission of all particles at large angles e - 1:

e+e- 4 e+e-e+e-,

yyyyy, e+e-e+e-y,

...

(3)

Some of these processes were studied earlier, for instance the process e+e- 4 4y was observed at VEPP-2M with the -ND detector [18] The expected number of these events at VEPP-2000 is - lo3 f 104. These proceses are of interest because of QED test and development of diagram technique. Another motivation is that these QED processes are an important source of background in a search for rare processes. For instanse, the reaction e+e- ---f 5y is a serious problem in study of the process e’e- 4 w7r” 4 57.

S.I. Serednyakov/Nucleuv

374

e+e-3

Physics B (Pvoc. Suppl.) 126 (2004) 369-374

N Nbar

Points - exp. data 1’ m FENICE

4. 5. 6.

t

7. 8. 9. 10.

11. Figure 10. Experimental data on neutron electromagnetic formfactor in timelike rigion. Horizontal line corresponds to the VEPP-2000 energy range.

5. Conclusions The suggested physical program could be done in experiments at the VEPP-2000 collider with integrated luminosity AL - 3 fb-i during -5 year data taking run with CMD-3 and SND detectors.

Acknowledgement. The author expresses his gratitude for fruitful discussions to Yu.M.Shatunov, I.A.Koop, B.I.Khazin and S.I.Eidelman. This work is supported in part by the Russian Foundation for Basic Research, grants No. 02-0216269-a, 03-02-16581 and Sci.School-1335,2003.2. REFERENCES 1. G.M.Tumaikin, in: Proc. 10th Intern. Conf. on High Energy Particle Accelerators (Serpukhov, 1977), Vol.1, p.443 2. I.A.Koop et al, in: Proc. Frascati Physics Series, (Frascati, Nov.16-19, 1999) Vol.XVI, p.393-404 3. Yu.M.Shatunov et al, in: Proc. 7-th European Particle Accelarators Conference EPAC2000.

12. 13. 14. 15. 16. 17. 18.

(Vienna, Austria, 2000) p.439 R.R.Akhmetshin et al., Preprint Budker INP 2001-45, Novosibirsk, 2001 M.N.Achasov et al., NIM A449, 2000, 125 G.N.Abramov et al, Preprint Budker INP 2001-29, Novosibirsk, 2001 G.W.Benaett et al., (Muon (g-2) Collaboration), hep-ex/0208001 M.Davier et al., LAL 02-81, hep-ex/0208177 R.R.Akhmetshin et al., Phys.Lett. B527, 2002,161 Particle Data Group. Review of Particle Physics, The European Physical Journal, v.15, No.l-4, (2000) M.N.Achasov et al., Phys.Lett. B486, 2000, 29-34 A.Antonelli et al., Nucl.Phys., B517, 1998, 3 A.B.Clegg, A.Donnache, Z.Phys. C34, 1987, 257 A.Antonelli et al., Phys.Lett., B365, 1996, 427 PFrabetti et al, Phys.Lett, B514, 2001, 240 V.Benayoun et al., Mod.Phys.Lett., Al4, 1999, 2605 M.N.Achasov et al., Phys.Lett. B492, 2000, 8-12 S.I.Dolinsky et al., PhysRep. 202, 1991, 99170