Resummed QCD Power Corrections and Di-Hadron Correlations

1. Resummed QCD Power Corrections and Di-Hadron Correlations Ivan Vitev Iowa State University, Ames, IA 50011 AGS-RHIC Annual Users’ Meeting May 10 – May 14, 2004 Brookhaven National Lab, Upton NY Ivan Vitev, ISU Ivan Vitev, ISU

2. Motivation: Modification of Di-HadronCorrelations in the Nuclear Environment K.Filimonov, nucl-ex/0403060 J.Adams et al., Phys.Rev.Lett. 91 (2003) • Small broadening (and/or attenuation) is observed • in d+Au • Large attenuation is observed in Au+Au (sensitive • to the orientation relative to the reaction plane) – • clearly a final state effect J.Rak, hep-ex/0403038 Address the (relatively) small effects in d+Au Ivan Vitev, ISU Ivan Vitev, ISU

3. Calculating Power Corrections in DIS x = xB U-quark, CTEQ5 LO Dynamical nuclear shadowing: generated by the multiple final state scattering of the struck quark Scale of higher twist QM shift operator: Scale of higher twist J.W.Qiu and I.V., hep-ph/0309094 Ivan Vitev, ISU Ivan Vitev, ISU

4. Results for A- and Bjorken x- Dependence Q2dependence, Longitudinal structure function J.W.Qiu and I.V., hep-ph/0309094 Ivan Vitev, ISU Ivan Vitev, ISU

5. Power Corrections in Neutrino-Nucleus DIS Valance quark shadowing and QCD sum rules: examples where dipole models will fail 1 20 10 3 Q2 D.J.Gross and C.H Llewellyn Smith , Nucl.Phys. B 14 (1969) J.W.Qiu, I.V., Phys.Lett.B 587 (2004) Ivan Vitev, ISU Ivan Vitev, ISU

6.  +,- Power Corrections in p+A Collisions Resum the multiple final state scattering of the parton “d” with the remnants of the nucleus A p Starting point:LO pQCD • Interested in the maximum coherent rescattering of the small xb • parton in the nucleus • Other interactions are less coherent (elastic) and sppressed at • forward rapidity by a large scale 1/u, 1/s - standard parton distribution functions - standard parton distribution functions Isolate all thexbdependence of the integrand: Ivan Vitev, ISU Ivan Vitev, ISU

7. Power Correction Contributions to LO pQCD 1. Recall that the two gluon ladder generates the scale of higher twist - c 2. For a fixed number of interactions (2N) we take all possible cuts d New contributions to the cross section 3. Sum over all possible N The results look like LO pQCD with the substitution: I.B.P • Driven by the Mandelstam invariant(-t) the resulting suppression will be • sensitive to pTand rapidity y. Cd = 1 for quarks, CA/CF = 9/4 for gluons J.W.Qiu, I.V., hep-ph/0405068 Ivan Vitev, ISU Ivan Vitev, ISU

8. Similar power corrections • modification to single and double • inclusive hadron production - increases with rapidity • disappears at high pTin accord with • the QCD factorization theorems • Dominated by dynamical gluon • shadowing • single and double inclusive • shift in ~ 2 /t Numerical Results for the Power Corrections - increases with centrality J.W.Qiu, I.V., hep-ph/0405068 Ivan Vitev, ISU Ivan Vitev, ISU

9. Observing the Acoplanarity and the Power Corrections • Consider di-hadron correlations associated with hard • (approximately) back-to-back scattering Before the hard scatter After the hard scatter If Ivan Vitev, ISU Ivan Vitev, ISU

10. Dijet Acoplanarity in d+Au and Au+Au Estimate from: J.W.Qiu, I.V., Phys.Lett.B 570 (2003); hep-ph/0405068 <|kTy|>pA = 1.25 GeV <z><|kTy|>AA = 1.25 - 1.45 GeV p+A From: <z> = 0.75, <|kTy|>pp = 1.05 GeV A+A (2.5pTtrigg4.0)(1.0pTassoc2.5) Feedback? pp: <z><|kTy|> pp: <|jTy|> J.Rak, hep-ex/0403038 Very interesting! P.Constantin, N.Grau Ivan Vitev, ISU Ivan Vitev, ISU

11. Only small broadening • versus centrality • Looks rather similar at • forward rapidity of 2 • The reduction of the area • is rather modest • Apparently broader • distribution • Even at midrapidity a small • reduction of the area • Factor of 2-3reduction of the • area at forward rapidity of 4 Dihadron Correlation Broadening and Attenuation Midrapidity and moderate pT J.Adams et al., Phys.Rev.Lett. 91 (2003) Forward rapidity and small pT Trigger bias can also affect: J.W.Qiu, I.V., Phys.Lett.B 570 (2003); hep-ph/0405068 Ivan Vitev, ISU Ivan Vitev, ISU

12. At x2 = 2 x 10-4 and • pT = 1.25 GeV hard • scattering is • similar in p+p and p+A • There isn’tmono • jettiness or g-fusion • I think that the p+A • analysis has under and • over estimated the • away-side area X2 = 1.94 x10-4 STAR • There may be room for • some suppression due • to power corrections X2 = 2.51 x10-4 Power Corrections at Forward Rapidity Preliminary: L.Bland, [STAR Colaboration] What the author concluded Are suppressed in d+Au relative to p+p at small <xF> and <pT,p> Spp-SdAu= (9.0 ± 1.5) % Consistent with CGC picture Are consistent in d+Au and p+p at larger <xF> and <pT,p> As expected by HIJING 25<Ep<35GeV 35<Ep<45GeV Statistical errors only Ivan Vitev, ISU Ivan Vitev, ISU

13. Conclusions • Dynamical nuclear shadowing in DISfrom resummed QCD power corrections. Results consistent with its x-, Q2- and A- dependence. Neutrino-nucleus DIS. Modification of the QCD sum rules. • First calculations of dynamical power corrections for hadronic collisions, .Results for the centrality and rapidity dependent suppression of single inclusive spectra and the dihadron correlations. • In d+Au collisions midrapidity and moderate pT the dominant effect is small broadening of the correlations. • At very forward rapidity (y=4) and small pTthe power corrections give a factor of 2-3reduction of the area of the away side correlations. • If the preliminary STAR results at forward y correlations persist – there isn’t monojettines or high density gluon fusion effects at x=2x10-4 in Au. • Will be interesting to measure neutral pions at forward y and compare the suppression effect (RAA) to the suppression for charged • Given the results of correlation analysis one can go back and rethink their favorite d+Au suppression scenarios Ivan Vitev, ISU Ivan Vitev, ISU