Transverse spin asymmetries at low momentum transfer at STAR

Transcription

1 Trnsverse spin symmetries t low momentum trnsfer t STAR Dmitry Svirid (ITEP) for the STAR Collbortion EDS Blois th Workshop on Elstic nd Diffrctive Scttering, Qui Nhon, Vietnm, December 15-21, 2011

2 Amplitudes nd observbles s, t M s, t M s, t M s, t M s, t M 4 tot Im s d dt 1 3 t 0 spin non flip double spin flip spin non flip double spin flip single spin flip s (, ) d 4 * AN s t Im dt s (, ) d 4 2 * * ANN s t 2 Re dt s A Amplitudes nd observbles SS d 4 ( s, t) Re 2 dt s * * A N Coulomb nucler interference Ech mplitude hs hdronic nd electromgnetic prts:, EM HAD s t s, t s, t i i i Min contribution to A N (, ): d 8 ( s, t) Im 2 dt s EM * HAD HAD* EM 5 5 EM terms re clculble from QED? A N t HAD HAD HAD ( 1 3 ) / 2 tot hd t Prmetriztion: 5 r5 Im m p HAD t [ Re Im ] 2 Re Im t t c t t c r r r r 2 m tc t N. H. Buttimore et. l. Phys. Rev. D59, (1999) Dmitry Svirid for the STAR Collbortion EDS Blois

3 A N mesurements in the CNI region pp Anlyzing Power E704@FNAL p = 200 GeV/c PRD48(93)3026 HJet@RHIC p = 100 GeV/c PRD79(09) no hdronic spin-flip no hdronic spin-flip pc Anlyzing Power pp2pp@rhic s = 200 GeV/c PLB632(06)167 no hdronic spin-flip E950@AGS p = 21.7 GeV/c PRL89(02) no hdronic spin-flip with hdonic spin-flip Dmitry Svirid for the STAR Collbortion EDS Blois

4 Romn pots t STAR Vert. RPs Scttered protons hve very smll trnsverse momentum nd trvel with the bem through the ccelertor mgnets Romn pots llow to get very close to the bem without breking ccelertor vcuum Optiml detector position is where scttered prticles re lredy seprted from the bem nd their coordinte is most sensitive to the scttering ngle through the mchine optics Bem trnsport equtions relte mesured position t the detector to the scttering ngle. x y D x D D y D = Horz. RPs x L eff L y eff 44 STAR x y 0 * x 0 * y detector Horz. RPs Detector Pckge Vert. RPs x 0, y 0 : Position t interction point Θ* x, Θ* y : Scttering ngle t IP x D, y D : Position t detector Θ x D, Θ y D : Angle t detector The most significnt mtrix elements re L eff, so tht pproximtely x D L x eff Θ x * y D L y eff Θ y * Dmitry Svirid for the STAR Collbortion EDS Blois

5 In the tunnel Romn Pot bove the bem Horizontl Romn Pots on both sides of the bem To STAR IR Romn Pot below the bem Integrtion of RPs with STAR for RUN-2009: STAR Trigger system STAR Dt qusition system STAR BBC or VPD for normliztion Additionl opportunities for other gols centrl production etc. Dmitry Svirid for the STAR Collbortion EDS Blois

6 Si detector pckge 4 plnes of 400 µm Silicon microstrip detectors: 4.5 x 7.5 cm 2 sensitive re 100 um pitch => good resolution, low occupncy Redundncy: 2X- nd 2Y-detectors in ech pckge Closest proximity to the bem ~10 mm 8 mm trigger scintilltor with two PMT redout Totl 32 silicon plnes by Hmmtsu Photonics in 8 pckges Only 5 ded/noisy strips per ~14000 ctive strips. Trigger Scintilltor Si SVX chips Detector bord Al strips: 512 (Y), 768 (X), 50µm wide 100 µm pitch implnted resistors bis ring gurd ring 1 st stripedge: 490 µm LV regultion Michel Rijssenbeek Dmitry Svirid for the STAR Collbortion EDS Blois

7 Detector performnce nd Elstic cuts Accurte hit cluster selection bsed on individul chnnel pedestls, cluster width nd totl chrge Excellent signl/noise rtio ~20, high detector efficiency >97% Combine clusters in different plnes of ech side into trcks using lignment dt from overlpping regions Convert trck coordintes to IP ngles using trnsport mtrix Anlyze the event for elsticity bsed on 2, number of trcks nd number of contributing plnes Efficiencies of 31 out of 32 Si plnes >97% Elstic correltion: Θ* EAST = Θ* WEST Width is dominted by the ngulr spred in IP ( ) X ( Y ) ( (, mrd X) ( Y) ) / Cut : 2 5 (8.2% elstic event loss) Dmitry Svirid for the STAR Collbortion EDS Blois

8 Inner detector Outer detector STAR System cceptnce nd t rnges Full 2 cceptnce in zimuth ngle 5 ( t ) rnges up to 0.03 (GeV/c) 2 Top detector Number of events in ech t-rnge Bem t<0.005 (Gev/c) < t< < t< < t< < t Bottom detector Dmitry Svirid for the STAR Collbortion EDS Blois

9 Clcultion of symmetry A N ( ) N Squre root formul: don t need externl normliztion, cceptnce symmetry nd luminosity symmetry cncel out We hve ll bunch polriztion combintions:,,, -- cn build vrious symmetries ( PB PY ) AN cos N ( ) N ( ) N ( ) N ( ) 1 ( ) N ( ) N ( ) N ( ) N ( ) B ( ) PA cos N B N ( PB PY ) AN cos N ( ) N ( ) N ( ) N ( ) N ( ) 1 ( ) N ( ) N ( ) N ( ) N ( ) where N ( ) N ( ) N ( ) N ( ) B B B B N ( ) N ( ) N ( ) N ( ) B B B B 2 2 ( ) PB PY ( ANN cos ASS sin ) Both bems polrized hlf of the sttistics, but effect ~ (P B +P Y ) One bem polrized, the other unpolrized full sttistics, but effect is only ~P B (or P Y ) Opposite reltive polriztion effect ~ (P B P Y ) should be close to 0 systemtics check Bem polriztion: P B = 0.602±0.026 P Y = 0.618±0.028 P B P Y = 0.372±0.023 (P B +P Y ) = 1.221±0.038, (P B P Y ) = 0.016±0.038 = 0.013(P B +P Y ) Dmitry Svirid for the STAR Collbortion EDS Blois

10 Rw single spin symmetry N =A N *P N ~ (P B +P Y ) NY ~ P Y NB ~ P B N ~ (P B P Y ) Typicl result for single t-rnge As expected, N N 2.0 B Y N N Low sttisticl errors 2-3% Single bem symmetries use the sme sttistics, but independent polriztion vribles cn be combined N is consistent with 0 proof of 2 sttements: (P B P Y ) ~ 0 nd Low systemtic shifts reflects smll devition of the bem spin from verticl direction the sme by ll clcultions Dmitry Svirid for the STAR Collbortion EDS Blois

11 A N results nd r 5 estimtes Only sttisticl errors shown NO ccount for polriztion nd t uncertinties pp2pp (2003) result Re r 5 = ± Im r 5 = ± 0.56 No significnt contribution of hdronic spin-flip mplitude: r 5 ~ 0 Accurcy improved ~20 times compred to pp2pp (2003) Dmitry Svirid for the STAR Collbortion EDS Blois

12 Normliztion nd N systemtics checks Normliztion is bsed on inelstic event counts ssuming their negligible polriztion dependence Two independent STAR subsystems, both hving 2 cceptnce for forwrd prticles in est nd west: BBC bem-bem counters VPD vertex position detector Normlized counts: K +/ = N +/ /V +/, N +/ -- elstic event counts for certin spin combintion, V +/ -- normliztion fctor from BBC/VPD V ++ V + V + V N ( PB PY ) AN cos K ( ) K ( ) N ( ) 1 ( ) K ( ) K ( ) V +/ differs beyond sttisticl error (0.25%) for VPD/BBC two different physics processes verge Asymmetry vlue in good greement Smll systemtic errors High normliztion qulity but my not be good enough for A NN & A SS N / N N = 1.01 Dmitry Svirid for the STAR Collbortion EDS Blois

13 A NN nd A SS Cnnot use squre root formul hve to rely on normlized counts K +/ All t-rnges 2 2 NN ( ) PB PY ( ANN cos ASS sin ) ( K ( ) K ( )) ( K ( ) K ( )) ( K ( ) K ( )) ( K ( ) K ( )) Double spin effects re seen nd not consistent with 0 Both A NN nd A SS re very smll ~10 3 (except for the lowest t-rnge where lrger systemtic shifts my occur) Need better systemtic error studies current normliztion uncertinties re of the order of the effect Dmitry Svirid for the STAR Collbortion EDS Blois

14 Conclusions nd plns SUMMARY Romn Pots instlled t STAR IR nd integrted into STAR detector for low t studies ~ elstic events recorded in 40 hours of dt tking in 5 dys with RPs in 2009 t s=200 GeV nd specil mchine optics *=21 m Excellent detector performnce provides extremely clen dt set Single spin symmetry A N obtined with unprecedented 2% ccurcy in 5 t-rnges No significnt contribution of hdronic spin-flip mplitude seen: r 5 ~ 0 Double spin effects re seen, but need more ccurte normliztion studies THE WAY TO THE FINAL RESULT Accurte MC simultions of trnsport nd comprison with dt done Finlize detector lignment bsed on dt nd MC done Derive finl vlues of systemtic uncertinties in t, A N, r 5 in progress Normliztion studies for double spin symmetries in progress. FURTHER PLANS Mesurements of A LL t s=200 GeV longitudinl polriztion is possible with STAR spin rottors Mesurements t s=500 GeV: TOT, diffrction cone slope b, A N (expect r 5 ~0) Dmitry Svirid for the STAR Collbortion EDS Blois