ISR Physics at B-factories Vladimir Druzhinin BINP, Novosibirsk

2 Initial State Radiation (ISR) Method e + e detected hadrons 21º < θ < 138º θ 170º High luminosity at B-factories allows to use this method for measurements of e + e - f cross sections at energies below s Wide energy interval in single experiment Greatly reduced point-to- point uncertainty

3 Initial State Radiation Studies at BABAR Регистрация всех конечных частиц. 10% событий радиационного возврата фон от e + e - адроны при Е=10 ГэВ, 0 имитирует фотон слабая зависимисть эффективности регистрации от массы и динамики процесса измерение сечений от порога до 3-5 ГэВ Без регистрации фотона масса больше 3 ГэВ выигрыш в статистике (5-8 раз) начиная с 3.5 ГэВ нет фона от e + e - адроны, но есть двухфотонный, e + e - e + e - + адроны изучение редких процессов при энергии выше 3.5 ГэВ 10 ГэВ - эксклюзивные адронные сечения малы нет вклада излучения конечных частиц Rely on tagged photon for identification, loose hadronic selection High fiducial efficiency : –Wide-angle ISR forces hadronic system into the detector fiducial region –Collimated hadronic system due to boost. –Weak dependence on details of fragmentation Harder momentum spectrum due to boost: –fewer problems with soft particles. Kinematic fit: –excellent mass resolution –background suppression Most dangerous background, e + e - f 0, can be estimated from data and subtracted

4 Objective : Precise cross section measurements for all significant processes, e + e - f, from threshold to c.m. energy ~ 4.5 GeV Purpose : Significantly improve understanding of the spectroscopy of J PC = states, and of their resonant substructure Combine the cross section measurements to obtain improved precision on the c.m. energy dependence of R in this region Reactions for which results have been published : e + e - p p e + e e + e , K + K - + -, 2K + 2K - e + e , K + K Work in progress on : + -, K K, K K 0, K K, , ,,,, d d,….. Initial State Radiation Studies at BABAR

5 (e + e - hadrons) s [GeV/c 2 ] Contributions to had magnitude errors Burkhardt, Pietrzyk 2001

6 Build R from Sum Over Exclusive Final States K+K-K0SK0LK+K-K0SK0L K + K - K + K - K + K - K + K - K 0 K pp J/ 6 2K+4 DD* (2S) s' [GeV] R Units Results published by BABAR Analyses in Progress

e + e - pp (232 fb -1 ) Phys. Rev. D 73, (2006)

8 The cross section depends on two form factors, electric and magnetic. From the total cross section we obtain effective form factor Ratio of form factors can be extracted from analysis of angular dependence Advantage of ISR measurement: weak dependence of detection efficiency on mass and proton polar angle Model-independent measurement of cross section.

9 + - K + K - pp 0 uds pp data 5.9 ± ± ± 3213 ± 326 ± 43737± J/ (2S) 232 fb -1 Mass spectrum

10 Angular distributions angular distributions associated with G E and G M are: G E dominates near m2 GeV/c 2 Inconsistent with PS170 measurements G M in Blue G E in Red 2.025

11 Cross section In reasonable agreement with e + e - previous measurements Negative steps at M ~ 2.2 and 3 GeV (!?)

12 pp : effective form factor Reasonable agreement with pp- annihilation results Steep behaviour at threshold can be manifestation of subthreshold pp-bound state

e + e - Phys. Rev. D 70, (2004) (90 fb -1 )

14 e + e - PDG: МэВ/c 2 PDG : МэВ PDG: 1670 ± 30 МэВ/c 2 PDG: 315 ± 35 МэВ Key process for study excited -like state

15 e + e - N J/ = B(J/ )% BABARPDG 2004BES ± ± ±0.12 M 3 [GeV/c 2 ] SND DM2 BaBar 90 fb -1 systematic error - 5% and -meson parameters are in agreement with world averages Consistent with SND data for M

e+e- 4h: updated new (232 fb -1 ) (90 fb -1 ) Phys. Rev. D 71, (2005)

17 e e 2 2 cross section Good agreement with direct e e measurements Most precise result above 1.4 GeV Systematic errors: 12% for m 4 < 1 GeV, 5% for 1 < m 4 < 3 GeV, 16% for higher masses PRD 71, (2005) 90 fb -1 a 1 (1260) - dominant, f 0 (1370) final state is seen.

18 e + e - K + K K + K - 0 0, K + K + K - K - Systematic error – 7-15% Intermediate states: K*(890)K dominant, KK Structures in K + K - cross section near 1.8, 2.2, 2.4 GeV. 232 fb -1 e + e - K + K - K + K - Systematic error – 25% 90 fb -1

e + e - 6h: (232 fb -1 ) Phys. Rev. D 73, (2006)

20 6π final states Large improvements upon existing measurements. Structure around 1.9 GeV, already seen by DM2 and FOCUS (diffractive photoproduction) Little substructure (~1 /event) J/ψ Large improvement in precision Similar Structure around 1.9 GeV substantial substructure – seen – f …. present

21 Fit to e + e - 6π cross section data e + e - e + e - FOCUS: PL B514, 240 (2001) M = MeV G = MeV G = MeV M(GeV/c 2 )G(GeV)phase BABAR 1.88 ± ± ± 40 BABAR 1.86 ± ± ± 15 FOCUS 1.91 ± ± ± 30 J/ψ

22 e + e - K + K - 2( + - ) Clear signals for K* 0, J/ and (2S) signal in K + K - spectrum ; mainly from J/ decay Clear signals for K* 0, J/ and (2S) signal in K + K - spectrum ; mainly from J/ decay J/ (2S) J/ (2S) K* 0 J/ K* 0 (K + K - 2( + - )) (nb) Band

23 J/ and (2S) decays ModeBaBar BFPDG 2004 J/ (2.18±0.19)%(1.50±0.20)% J (3.61±0.26±0.26) (4.0±1.0) J K + K - (6.09±0.50±0.53) (7.2±2.3) J 2K + 2K - (6.7 ±1.0±1.1) J 3 3 (4.40±0.29±0.29) (4.0±2.0) J (1.65±0.10±0.18) J (1.47±0.41±0.15) (1.58±0.16) J K + K (5.09 ±0.42±0.35) (3.1±1.3) J 2 2 (1.77 ±0.35±0.12) (1.60±0.32) J pp(2.22 ±0.16) (2.17 ±0.08) ModeBaBar BFPDG 2004 (2S) 2 2 (5.3±1.6±0.6) (2S) K + K (2.1 ±1.0±0.2) (2S) pp(3.3 ±0.9) (2.36 ±0.24) BES (2.10 ± 0.12 ) % We actually measure BF(J/f) x ee Branching fractions are obtained using ee = (5.40±0.18) keV [PDG] New better worse

24 DD mass spectrum Mass spectrum fitted with interfering: Presence of structure at 3.9 GeV (Not due to a new charmonium state but to a threshold effect predicted by E. Eichten et al.,Phys.Rev. D21 (1980) 203.) Preliminary

25 e + e - Y(4260) + - J/ (2S) 232 fb fb -1 ISR photon need not be detected Confirmation by CLEO-c: e + e - scan Y(4260) событий Mass МэВ Width МэВ max 50 пб Not seen in total hadronic cross section small electron width, but large ( + - J/ ) Exotic structure: 4q, hybrid, mesonic or baryonic molecular Search for similar states containing light quarks ( ). PRL 95, (2005)

26 e + e - f 0 (980)

27 e + e - f 0 (980) Phase space: 2 / =81/51 Resonance: 2 / =38/47 Fitted resonance parameters: M=2175±10±15 MeV =58±16±20 MeV ss partner of Y(4260)? f 0 have large ss content ssss state

28 Cross section measurements: –Continuous coverage from threshold to E cm ~4.5 GeV for many processes. –Eventually combine exclusive cross section measurements to obtain precise s dependence of R: ~1% below 1 GeV, ~5% for 1-3 GeV Spectroscopy of J PC = 1 -- states: – Parameters of excited -, -, -states – New, possibly exotic states: dip at 1900 MeV in e + e - 6π cross section, Y(4260), structure in f 0 at 2175 MeV Large luminosity is needed both for R measurement (~1-2% accuracy can be reached for 1-5 GeV range) and for spectroscopy.

29 50 ab -1 ISR luminosity for 50 ab ab ab -1 detected hadrons 21º < θ < 138º θ 170º s, GeV IL,fb VEPP fb-1 BES-III 20 fb-1 Resonances produced and detected: J/ x10 9 (2S) – 0.14x10 9 (1S) – 0.6x10 9 (2S) – 0.5x10 9 (3S) – 0.8x10 9