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Measurements of transverse spin effects in the forward region with the STAR detector  [PDF]
L. Nogach,for the STAR collaboration
Physics , 2009,
Abstract: Measurements by the STAR collaboration of the cross section and transverse single spin asymmetry (SSA) of neutral pion production at large Feynman x (x_F) in pp-collisions at \sqrt{s}=200 GeV were reported previously. The x_F dependence of the asymmetry can be described by phenomenological models that include the Sivers effect, Collins effect or higher twist contributions in the initial and final states. Discriminating between the Sivers and Collins effects requires one to go beyond inclusive \pi^0 measurements. For the 2008 run, forward calorimetry at STAR was significantly extended. The large acceptance of the Forward Meson Spectrometer (FMS) allows us to look at heavier meson states and \pi^0-\pi^0 correlations. Recent results, the status of current analyses and near-term plans will be discussed.
Measurements of Transverse Spin Effects with the Forward Pion Detector of STAR  [PDF]
L. Nogach,for the STAR collaboration
Physics , 2006, DOI: 10.1063/1.2750839
Abstract: Measurements by the STAR collaboration of neutral pion production at large Feynman x (x_F) in the first polarized proton collisions at $\sqrt{s}=200$ GeV were reported previously. Cross sections measured at $\eta=3.3$, 3.8 and 4.0 are found to be consistent with next-to-leading order perturbative QCD calculations. The analyzing power is consistent with zero at negative x_F and at positive x_F up to ~0.3, then grows more positive with increasing x_F. This behavior can be described by phenomenological models including the Sivers effect, the Collins effect or higher twist contributions in the initial and final states. Forward calorimetry at STAR has been extended, and there are plans for further expansion. An integrated luminosity of 6.8 pb^${-1}$ with average beam polarization of 60% from online polarimetry measurements was sampled with the upgraded FPD in the 2006 RHIC run. This data sample will allow for a detailed map of the \pi^0 analyzing power over kinematic variables bounded by 0.3 < x_F < 0.6 and 1.2 < p_T < 5.0 GeV/c at $\sqrt{s}=200$ GeV. The expanded FPD has observed multi-photon final states expected to have "jet-like" characteristics. The transverse spin dependence of jet-like events can discriminate between the Collins and Sivers effects and lead to further progress in understanding the origin of single spin asymmetries in forward particle production. Data were also obtained at $\sqrt{s}=62.4$ GeV for x_F -> 1 to test predictions based on phenomenological fits to earlier STAR results. Recent results, the status of the analysis of 2006 run data and near-term plans will be discussed.
Forward Neutral Pion Cross Section and Spin Asymmetry Measurements at STAR  [PDF]
S. Gliske,J. Drachenberg for the STAR collaboration
Physics , 2013,
Abstract: The STAR endcap electromagnetic calorimeter (EEMC) was designed to allow measurement of cross sections and spin observables in the forward direction, $1 < \eta < 2$ and with the full azimuth. Using the EEMC to measure double longitudinal spin asymmetries in photonic channels---such as inclusive neutral pions, prompt photon, and prompt photon + jet---allows access to $\Delta G$ within a low Bjorken-$x$ region ($0.01 < x < 0.33$ at $\sqrt{s}=200$) where $\Delta G$ is poorly constrained. Additionally, transverse spin asymmetries, shown to be zero at $\eta$ near zero and as large as 10\% at $\eta$ near 4, occupy a previously unmeasured region in the 3D pseudorapidity, transverse momentum, and $x$-Feynman phase space when measured with the EEMC. The neutral pion cross section measurement verifies that the signal of interest can be properly reconstructed and isolated from the background. Pion reconstruction techniques in the STAR EEMC will be discussed and preliminary cross-section and transverse single spin asymmetry measurements presented.
Jet-like correlations between Forward- and Mid- rapidity in p+p, d+Au and Au+Au collisions from STAR at 200 GeV  [PDF]
Levente Molnar
Physics , 2007, DOI: 10.1088/0954-3899/34/8/S51
Abstract: In this proceedings we present STAR measurements of two particle azimuthal correlations between trigger particles at mid-rapidity ($|\eta|<$ 1) and associated particles at forward rapidities (2.7 $<|\eta|<$ 3.9) in p+p, d+Au and Au+Au collisions at $\sqrt{s_{NN}} $= 200 GeV. Two particle azimuthal correlations between a mid-rapidity trigger particle and forward-rapidity associated particles preferably probe large-x quarks scattered off small-x gluons in RHIC collisions. Comparison of the separate d- and Au-side measurements in d+Au collisions may potentially probe gluon saturation and the presence of Color Glass Condensate. In Au+Au collisions quark energy loss can be probed at large rapidities, which may be different from gluon energy loss measured at mid-rapidity.
Forward- and Mid-Rapidity Jet-like correlations  [PDF]
Fuqiang Wang,for the STAR Collaboration
Physics , 2007, DOI: 10.1142/S0218301307009166
Abstract: Mid-rapidity azimuthal correlations probe di-jets originating mainly from gluon-gluon hard-scattering. Measurements of such correlations have revealed significant (gluon-)jet modification in central Au+Au collisions. Azimuthal correlations of hadrons at forward rapidity with a mid-rapidity high-$\pt$ hadron, on the other hand, probe asymmetric partonic scatterings involving large-x quarks and small-x gluons. We present preliminary results from STAR on correlations of charged hadrons at forward rapidity in the forward TPCs ($2.7<|\eta|<3.9$, $\pt<2$ GeV/$c$) with high-$\pt$ charged hadrons at mid-rapidity from the main TPC ($|\eta|<1$, $\pt>3$ GeV/$c$) in $pp$, d+Au, and Au+Au collisions at $\snn=200$ GeV. The implications of the results for small-x gluon distributions (Color Glass Condensate formation) and the energy loss of quark jets at forward rapidity in nuclear medium are discussed. %Their measurements in d+Au collisions, separately at the d-side and the Au-side, may be sensitive to Color Glass Condensate in the Au-nucleus. Their measurements in Au+Au collisions may probe quark-jet modification in nuclear medium.
Small-x Physics and Forward Jet Production at THERA  [PDF]
Hannes Jung,Leif Lonnblad
Physics , 2001,
Abstract: We discuss some aspects of forward jet production as a signature for small $x$ physics at THERA energies.
QCD predictions for polarised deep inelastic scattering accompanied by a forward jet in the low x region of possible HERA measurements  [PDF]
J. Kwiecinski,B. Ziaja
Physics , 1999, DOI: 10.1016/S0370-2693(99)01338-6
Abstract: We estimate the cross-section and asymmetry relevant for the production of forward jets in polarised deep inelastic scattering in the region of small values of $x$ which can be probed at possible polarised HERA measurements. The kinematical cuts implemented in our analysis are the same as those which were used in the unpolarised deep inelastic scattering at HERA. The calculations are based on the double ln^2(1/x) resummation which controls the polarised deep inelastic scattering for small values of the Bjorken parameter x. We show that this resummation substantially enhances the corresponding cross-section and asymmetry. The predicted value of the asymmetry is found to vary between -0.01 and -0.04 within the small x region which can possibly be probed at polarised HERA measurements.
Recent CMS Results on Forward and Small-x QCD Physics  [PDF]
Benoit Roland,on behalf of the CMS Collaboration
Physics , 2012,
Abstract: Recent CMS results on Forward and Small-x QCD Physics are presented. Those include the measurement of the Underlying Event activity and the study of jet production at large rapidity separation.
Analyzing Powers for Forward p+p->pi0+X at STAR  [PDF]
G. Rakness,for the STAR Collaboration
Physics , 2002, DOI: 10.1063/1.1607167
Abstract: Preliminary results of the analyzing power for the production of forward, high-energy pi0 mesons from collisions of transversely polarized protons at sqrt(s)=200 GeV from STAR are presented. The kinematic ranges covered by the data are x_F=0.2-0.6 and p_T=1-3 GeV/c. The analyzing power at sqrt(s)=200 GeV is found to be comparable to that observed at sqrt(s)=20 GeV.
Small x QCD effects in DIS with a forward jet or a forward pi0  [PDF]
J. Kwiecinski,A. D. Martin,J. J. Outhwaite
Physics , 1999, DOI: 10.1007/s100529900091
Abstract: We compare predictions based on small x (QCD) dynamics with recent data for deep inelastic events containing forward jets or forward pi0 mesons. We quantify the effect of imposing the (higher order) consistency condition on the BFKL equation and study uncertainties inherent in the QCD predictions. We also estimate the cross-section for the forward production of two jets.
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