The First Stage of Polarization Program Spascharm at the Accelerator U-70 of Ihep
V.V.Abramov, N.A. Bazhanov, N.I. Belikov, A.A. Belyaev, A.A. Borisov, N.S. Borisov, M.A. Chetvertkov, V.A. Chetvertkova, Yu.M. Goncharenko, V.N. Grishin, A.M. Davidenko, A.A. Derevshchikov, R.M. Fahrutdinov, V.A. Kachanov, Yu.D. Karpekov, Yu.V. Kharlov, V.G. Kolomiets, D.A. Konstantinov, V.A. Kormilitsyn, A.B. Lazarev, A.A. Lukhanin, Yu.A. Matulenko, Yu.M. Melnik, A.P. Meshchanin, N.G. Minaev, V.V. Mochalov, D.A. Morozov, A.B. Neganov, L.V. Nogach, S.B. Nurushev, V.S.Petrov, Yu.A. Plis, A.F. Prudkoglyad, A.V. Ryazantsev, P.A. Semenov, V.A. Senko, N.A. Shalanda, O.N. Shchevelev, L.F. Soloviev, Yu.A. Usov, A.V. Uzunian, A.N. Vasiliev, V.I.Yakimchuk, A.E. Yakutin
aa r X i v : . [ h e p - e x ] D ec THE FIRST STAGE OF POLARIZATION PROGRAM SPASCHARM ATTHE ACCELERATOR U-70 OF IHEP
V.V. Abramov , N.A. Bazhanov , N.I. Belikov , A.A. Belyaev , A.A. Borisov ,N.S. Borisov , M.A. Chetvertkov , V.A. Chetvertkova , Yu.M. Goncharenko ,V.N. Grishin , A.M. Davidenko , A.A. Derevshchikov ,R.M. Fahrutdinov ,V.A. Kachanov , Yu.D. Karpekov , Yu.V. Kharlov ,V.G. Kolomiets , D.A. Konstantinov , V.A. Kormilitsyn , A.B. Lazarev ,A.A. Lukhanin , Yu.A. Matulenko , Yu.M. Melnik , A.P. Meshchanin , N.G. Minaev ,V.V. Mochalov , D.A. Morozov , A.B. Neganov , L.V. Nogach , S.B. Nurushev † ,V.S. Petrov , Yu.A. Plis , A.F. Prudkoglyad , A.V. Ryazantsev , P.A. Semenov ,V.A. Senko , N.A. Shalanda , O.N. Shchevelev , L.F. Soloviev , Yu.A. Usov ,A.V. Uzunian , A.N. Vasiliev , V.I. Yakimchuk , A.E. Yakutin (1) IHEP, Protvino, Russia (2)
JINR, Dubna, Russia (3)
KhPTI, Kharkov, Ukraine (4)
MSU, Physics Department, Moscow, Russia (5)
Skobeltsyn INP MSU, Moscow, Russia † E-mail: [email protected]
Abstract
The first stage of the proposed polarization program SPASCHARM includesthe measurements of the single-spin asymmetry (SSA) in exclusive and inclusivereactions with production of stable hadrons and the light meson and baryon reso-nances.In this study we foresee of using the variety of the unpolarized beams ( pions,kaons, protons and antiprotons) in the energy range of 30-60 GeV. The polarizedproton and deuteron targets will be used for revealing the flavor and isotopic spindependencies of the polarization phenomena. The neutral and charged particles inthe final state will be detected.
Introduction
In shaping the new polarization program at U-70 we were guided by three conditions:by our own experiences. by theoretical status of subject and the reliability of the newprogram.As concerns of the first condition one may refer on the comparative study ofpolarizations in the elastic scattering of particles and antiparticles by using the polarizedproton target [1], [2], measurements of the spin transfer tensor [3], [4] (HERA Collabo-ration), study of the SSA in the exclusive and inclusive charge exchange reactions at 40GeV/c [5] (PROZA Collaboration), study of polarization effects at 200 GeV/c by usingthe polarized proton and antiproton beams (E581/E704 Collaboration, FNAL) [6]. Thefourth example of polarization data came recently from the STAR Collaboration at energyin the center of mass √ s =200 GeV [7], [8]. 1he second condition is the status of the relevant theoretical models. Since the ener-gies and transfer momenta with which we are dealing are not large enough, so there isa doubt about the possible application of the perturbative quantum chromodynamicsp(QCD). Therefore either the specific models should be used for the interpretation of theexperimental data or the general asymptotic predictions might be applied.The third condition is relevant to the reliability of the experiment, that is, availabilityof robust equipments, manpower, money and other resources.Below we shall briefly describe all these conditions. In 1970-1976 at U70 Collaboration of physicists from Saclay (France), Protvino, Dubnaand Moscow (Russia) (HERA Collaboration) had performed the measurements of the po-larization parameters P and R (spin rotation parameter) in elastic scattering of particlesand antiparticles at ∼
40 GeV/c by using the polarized proton target. The polarizationdata are presented in Figure 1 with one panel for pair of particle and antiparticle.In papers [9] and [10]it was considered some consequences of the hypothesis of the ap-proximate γ invariance of the strong interactions. According to this hypothesis at highenergies and large momentum transfers s, -t ≫ m (m is the mass of the particles involvedin reactions) the polarization in any elastic scattering of particles or antiparticles shouldbe equal to zero. From Figure 1 the following results stem out of:1. polarizations are not zero in reactions induced by pions, protons and antiprotons.It means that the hypothesis of γ invariance does not work for that reactions yet,2. the polarizations are zero for reactions induced by kaons. It means that the hy-pothesis of γ invariance may work in these reactions. But the large error bars inthe measured polarizations make this statement doubtful. The future experimentsmeasuring the polarizations in kaon induced elastic scattering with better statisticsare needed.For all of above reactions the next comment follows. Though the asymptotic regimewas reached for s it’s not fulfilled for t, since for | t | > GeV /c ) the experimental errorsare large. This is the next item for the future measurements with high statistics. Thereis a good measurement of the polarization parameter in π ± p, K ± p, pp, ¯ pp elastic scatter-ing at 6 GeV/c [11]. In this case the γ invariance does not work too for all reactions,exception is ¯ pp , where polarization is compatible with zero in small -t region in frame ofthe large error bars. -0.1-0.0500.050.10 0.5 1 1.5 2 -t, (GeV/c) P -0.100.10.20 0.5 1 1.5 2 -t, (GeV/c) P -0.5-0.2500.250 0.25 0.5 0.75 1 -t, (GeV/c) P (a) (b) (c) Figure 1: (a)
P in elastic scattering: π − p ( • ) and π + p ( (cid:4) ). (b) P in elastic scattering: K − p ( • )and K + p ( (cid:4) ) . (c) P in elastic scattering:¯ pp ( • ) and pp ( (cid:4) ).2n paper [12] the study was made of the asymptotic relations between polarizations incross channels of a reaction. Using the crossing symmetry and Fragman - Lindeloff theo-rem they arrived at the following result: polarizations in the elastic scattering processes(see Figure 1) induced by particle and antiparticle at a given energy and a given angleshould be equal in magnitude and opposite in sign. If we look at Figure 1 one may notethat this statement is approximately correct for the pion induced reactions, not correctfor reactions initiated by proton and antiproton and ambiguous for reactions involvingkaons (thanks to the small statistics). Therefore the new elastic scattering experimentshould clarify this interesting problem by gathering a large statistics, specially at largetransverse momenta.The HERA Collaboration making use of the simple Regge pole model concluded thatthe elastic scattering polarizations induced by pions and kaons follow the predictions ofsuch model, while polarization in elastic pp scattering reveals the drastic deviation fromthe prediction of the Regge pole model. Such behavior may be explained by assumingthat at 40 GeV/c momentum the dominant contribution to the polarization in elasticpp scattering comes from the pomeron with the spin flip term of the order of 10% withrespect to the spin non flip term. Involving in the analysis the data on the spin rotationparameter [3], [4] they strengthened their conclusion. But the statistics are not so largeto be unambiguous in such conclusion. One needs more measurements.The PROZA Collaboration measured the single spin asymmetries in the charge ex-change binary and inclusive reactions at the incident beam momentum 40 GeV/c [5]. Withthe different statistics the results were obtained for the exclusive reactions containing inthe final states the mesons of the different mass and quantum numbers Figure 2 , Figure 3.The polarization data for reactions 1, 2 and 3 (the mesons in the final states arespinless) were extensively analyzed in frame of the different models. For example, in theasymptotic model [12] the polarizations in all of these three reactions should be zero. Butsuch predictions are in contrast to the experimental data (see Figure 2 ). In the Reggepole model with inclusion of the odderon [13], [14], the best approximation predicting thenew dip in polarization around the crossing point at -t ∼ . GeV /c ) was obtained in the -50-250250 1 2 3 -t, (GeV/c) P , % -500500 1 2 3 -t, (GeV/c) P , % -50050 0 0.25 0.5 0.75 1 -t, (GeV/c) A N , % (a) (b) (c) Figure 2: (a)
Polarization in reaction π − + p → π + n . (b) Polarization in reaction π − + p → η + n . (c) Polarization in reaction π − + p → η ′ + n .3odel [13]. After analyzing the reaction (Figure 2a) the authors of the paper [14] noted:The surprising results of the recent 40 GeV/c Serpukhov measurement of thepolarization in π − p → π n are shown to support the conjecture that thecrossing-odd amplitude may grow asymptotically as fast as is permitted bygeneral principles.This model in contrast to other ones predicts the shift of the left zero crossing pointfarther to left and the increase of polarization with growth of the incident momentum.This is an attractive subject for experimental check.The reactions 2,3 were also analyzed in frame of the Regge pole model and data are con-sistent with model prediction. Other reactions 4-6 showing also the significant spin effects(see Figure 3) did not yet attract the attention of theoreticians.These data are unique in the sense that nobody made (30 years later) the similar measure-ments at higher energies. This fact may confirm the assumption that the U-70 acceleratoroccupies a good niche for such studies of exclusive reactions dying rapidly with growth ofenergy.By using the experimental set-up PROZA the inclusive asymmetries were measuredat 40 GeV/c in the following charge exchange reactions: π − + p → π + X (1) .p + p → π + X (2)in the central, polarized target and unpolarized beam fragmentation regions [5].In centralregion the asymmetry about 30% was found at p T > p T > -75-50-2500 0.5 1 -t, (GeV/c) A N , % -50-250250 0.2 0.4 0.6 0.8 1 -t / , (GeV/c) A , % -75-50-250 0 0.5 1 -t, (GeV/c) A N , % (a) (b) (c) Figure 3: (a) asymmetry in reaction π − + p → ω + n . (b) asymmetry in reaction π − + p → a + n . (c) asymmetry in reaction π − + p → f + n .4 First stage of the SPASCHARM polarization pro-gram
In composing the new scientific program we are guided by the recent theoretical andexperimental developments in polarization physics. Its obvious also that this programis also strongly influenced by our own experiences, by resources and competitions withother collaborations over the world. Therefore we attempt of using efficiently our protonsynchrotron U70, existing experimental equipments and fit to the environmental require-ments. So we are going to propose the following first stage polarization program:1. Asymmetry measurements in charge exchange exclusive reactions at 34 GeV/c withemphasis to increase the statistics of the most of reactions shown in the Figures 2and 3 by approximately by factor 10 and move to the larger t region.2. Comparative studies of asymmetries induced by particles and antiparticles in binaryand inclusive reactions.3. Study of spin transfer mechanism by using the unstable spin carrying particles likehyperons, vector mesons, etc. We emphasize, that only fixed target experiments,like ours, may measure spin transfer tensors for stable final particles, like antiprotonsand protons.4. Asymmetry measurements in inclusive productions of various stable hadrons con-taining partons of different flavors (u,d,s,c quarks).5. The systematic studies of the isospin dependence of single spin asymmetry.6. The comparative studies of asymmetries in production of particles and antiparticlesin final state.7. Asymmetry studies by using the light ion beams and polarized target.8. Check more accurately the puzzle caused by differences of the single spin asymme-tries induced by pion and proton beams in the central and fragmentation regions at34 GeV/c.9. The new upcoming polarized proton beam will lead to the measurements of theinclusive single spin asymmetries with unprecedented precisions.10. Finally with the availability of the polarized beam and polarized target the way willbe opened for the intense studies of the double spin asymmetries in many reactions.For the inclusive reactions the extensive Monte Carlo simulations were made for beamparticles π, K , p and ¯ p for momentum of 34 GeV/c. For the sake of brevity we present,as an example, only the results of calculations for the ¯ p beam. According to the negativebeam composition the fraction of the ¯ p particles is only 0.3% at momentum of 34 GeV/c.Therefore the absolute flux of ¯ p beam is only 9 ∗ ¯ p/cycle . The yields of the secondaryparticles on this beam are very important for comparison to the yields of the same par-ticles in the proton beam. For detection of the secondary resonances with the rare decaymodes produced on the propandiole target the request was imposed: the energy deposit5n calorimeters should be > p interaction cross section with targetthe yields of the secondary particles with higher cross section for 30 days beam run arepresented in the next Table 1.Table 1. The estimated yields N EV of the secondary particles from the propandioletarget ( C H O , 20 cm long) stricken by the ¯ p beam of 34 GeV/c. One month beamrun was assumed (3 . interactions). B/S means the background to signal ratio. N EV * N EV B/S1 π + . × * 7 n 1 . × *2 π − . × * 8 ¯ n . × *3 K + . × * 9 ¯Λ → ¯ p + π + . × K − . × * 10 ¯Λ → ¯ n + π . × . × * 11 ¯∆ −− → ¯ p + π − . × p . × * 12 Ξ − → Λ + π − . × . It mens that such comparisons may bedone for sure for pions, kaons, barions, antibarions, but doubtful for Xi − . The estimateswere done for ideal apparatus and not taking into accounts the real backgrounds. The experimental apparatus for the SPASCHARM program consists of the following ele-ments:1. Beam apparatus consisting of the scintillation and Cherenkov counters, scintillationhodoscopes for detecting and identifying the beam particles (not shown in Figure4).2. The polarized proton (deuteron) target (target in Figure 4).3. The guard system surrounding the polarized target(PT).4. The polarization building-up and holding magnet (target magnet ).5. GEM1, GEM26. The large aperture magnetic spectrometer.7. Micro drift chambers (MDC).8. Two large aperture multichannel threshold Cherenkov counters for identificationsof the secondary particles.9. Multiwire proportional chambers (MWPC).10. Electromagnetic calorimeter(ECAL).11. Hadron calorimeter (HCAL). 62. Muon system.13. Scintillation hodoscopes.The layout of the SPASCHARM detectors is presented in Figure 4.Figure 4: Layout of the SPASCHARM experimental apparatus. Themainel-e-mentsoftheap-pa-ra-tus,theirstruc-ture,po-si-tionsandsizesare listed in the Table 2.Table 2. The parameters of the main elements of the experimental apparatus. L-distance from detector to polarized target (PT), DS-detector structure, WS-wire spacing,GS-gross size, N ch -number of channelsdetector L, m DS WS GS N ch GEM1 0.5 X, Y Strip 0.4 20 x 20 1000GEM2 0.75 X, Y Strip 0.4 30 x 30 15001.MDC 1.0 X, X’, Y, Y’, U, V’ 6 65 x 54 12002.MDC 1.5 X, X’, Y, Y’, U, V’ 6 111 x 81 19203.MDC 2.0 X, X’, Y, Y’, U, V’ 6 150 x 111 26104.MWPC 3.5 X, Y, U, V 2 150 x 100 25005.MWPC 6.5 X, Y, U, V 2 150 x 100 2500
Conclusions
The SPASCHARM program presents the natural extension of our previous polarizationexperiments. Proposed experiment will open new and wider perspectives due to the severalreasons. First it contains the magnetic spectrometer with the high resolution trackingdetectors allowing to register all secondary charged particles with precise angular andmomentum resolutions. Secondly it has the fast particle identification system allowing toreconstruct the resonances with high probability. Third, the electromagnetic and hadroniccalorimeters practically allow (together with threshold Cherenkov counters) to identifyall hadrons in final state having sufficiently large cross sections. The large angular and7omentum acceptances will finally allow to increase by a factor 0f 10 the statistics thanin previous PROZA experiments. Using the forward detectors with the guard countersaround the polarized target one can select the binary charge exchange reactions with oneorder better statistics and also detect new reactions. The detections of hyperons andvector mesons permit to study not only polarization but also the spin transfer mechanismin strong interaction. It is assumed that the full apparatus for the first stage of theSPASCHARM polarization program will be ready to 2013 beam run. The distinct featureof our program will be the comparative studies of the polarization phenomena inducedby the particles and antiparticles.The work was supported by State Atomic Energy Corporation Rosatom with partialsupport by State Agency for Science and Innovation grant N 02.740.11.0243 and RFBRgrants 08-02-90455 and 09-02-00198.
References [1] A. Gaidot et al., Phys. Let. (1975) 389.[2] A. Gaidot et al., Phys. Let. (1976) 103.[3] J. Pierrard et al., Phys. Let. (1975) 393.[4] J. Pierrard et al., Phys. Let. (1976) 107.[5] V.V. Mochalov, Proc. of the 18th. Int. Spin Physics Symposium, SPIN2000, Char-lottesville, Virginia, 6-11 October 2008, AIP Conf. Proc.
V.1149 (2008)pp.637-644[6] S.B. Nurushev, Fermilab polarization experiment E581/E704: polarization effects inpp and ¯ pp interactions at √ s = 19 . (1962) 317.[10] Y.Nambu, in Proceedings of International Conference on High Energy Physics,Geneva (1962), p. 153.[11] M. Borghini et al., Phys. Lett. (1970) 405.[12] S. M. Bilenky et al.,, Zh. Eksp. Teor. Fiz. (1964) 1098.[13] L.L. Enkovsky, B.V. Struminsky, On Polarization in the Recharge Reaction π − + p → π + n . Preprint of the Institute of Theoretical Physics, -82-160, Kiev, 1982.[14] P. Gauron et al. Polarisation in π − + p → π + nn