Soft probes of high density QCD physics with CMS

The CMS heavy-ion program will probe QCD matter under extreme conditions. Its capabilities for the study of global observables and soft probes are described.Comment: 6 pages, 10 figures. Presented at the International Conference on Strangeness in Quark Matter 2007, Levoca, Slovakia, 28 June 200

Large Angle Hadron Correlations from Medium-Induced Gluon Radiation

Final state medium-induced gluon radiation in ultradense nuclear matter is examined and shown to favor large angle emission when compared to vacuum bremsstrahlung due to the suppression of collinear gluons. Perturbative expression for the contribution of its hadronic fragments to the back-to-back particle correlations is derived. It is found that in the limit of large jet energy loss gluon radiation determines the yield and angular distribution of | Delta phi | > Pi/2 di-hadrons to transverse momenta pT2 of the associated particles. Clear transition from enhancement to suppression of the away-side hadron correlations is established at moderate pT2 and its experimentally accessible features are predicted versus the trigger particle momentum pT1.Comment: 5 pages, 3 figures. Figures 1 and 2 and some of the text revised. Footnote added. As published in Phys. Lett.

High pT leading hadron suppression in nuclear collisions at sqrt(s_NN) = 20 -- 200 GeV: data versus parton energy loss models

Experimental results on high transverse momentum (leading) hadron spectra in nucleus-nucleus collisions in the range sqrt(s_NN) = 20 -- 200 GeV are reviewed with an emphasis on the observed suppression compared to free space production in proton-proton collisions at the corresponding center-of-mass energies. The transverse-momentum and collision-energy (but seemingly not the in-medium path length) dependence of the experimental suppression factors measured in central collisions is consistent with the expectations of final-state non-Abelian parton energy loss in a dense QCD medium.Comment: Two typos correcte

Status of Zero Degree Calorimeter for CMS Experiment

The Zero Degree Calorimeter (ZDC) is integral part of the CMS experiment, especially, for heavy ion studies. The design of the ZDC includes two independent calorimeter sections: an electromagnetic section and a hadronic section. Sampling calorimeters using tungsten and quartz fibers have been chosen for the energy measurements. An overview of the ZDC is presented along with a current status of calorimeter's preparation for Day 1 of LHC.Comment: 8 pages, 5 figures, 1 table, to appear in the proceedings of CALOR06, June 5-9, 2006 Chicago, US

Elliptic Flow and Fixed p_T Suppression in a Final State Interaction Model

It has been shown that a final state interaction model, used to describe J/psi suppression, can also describe the fixed p_T suppression of the pi^0 (and charged pions) yield at all values of p_T, with a final state interaction cross-section sigma close to one milibarn. We propose an extension of the model to the pion motion in the transverse plane - which introduces a dependence of the suppression on the azimuthal angle theta_R. Using the same value of sigma, we obtain values of the elliptic flow v_2 close to the experimental ones, for all values of p_T, including the soft p_T region.Comment: 21 pages, 6 figure

Small-x QCD studies with CMS at the LHC

The capabilities of the CMS experiment to study the low-x parton structure and QCD evolution in the proton and the nucleus at LHC energies are presented through four different measurements, to be carried out in Pb-Pb at sqrt(s_NN) = 5.5 TeV: (i) the charged hadron rapidity density $dN_{ch}/d\eta$ and (ii) the ultraperipheral (photo)production of Upsilon; and in p-p at sqrt(s) = 14 TeV: (iii) inclusive forward jets and (iv) Mueller-Navelet dijets (separated by $Delta\eta\gtrsim$ 8).Comment: Quark Matter'06 Proceedings. To appear in J.Phys.

Exclusive Photoproduction of Υ\Upsilon and lepton pairs in Pb-Pb at 5.5 TeV

Electromagnetic interactions of heavy-ions give access to a unique programme of photon-induced studies in the QCD and QED sectors of the Standard Model. On the one hand, exclusive photoproduction of bottomonium ($\gamma\,A \rightarrow \Upsilon\,A$, where the nucleus $A$ remains intact) offers a useful means to constrain the small-$x$ nuclear gluon density. On the other, two-photon exclusive dilepton production ($\gamma\,\gamma\rightarrow l^{+}\,l^{-}$) allows us to study QED at field-strengths close or above the Schwinger limit ($E_{\rm crit}\approx$~1.5 $\times$10$^{16}$~V/cm). We present full simulation studies of exclusively photo-produced $\Upsilon$ and high-mass dileptons in Pb-Pb collisions at the LHC