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New results from NA60
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The NA60 detector beam tracker vertex tracker 2.5 T dipole magnet
hadron absorber targets beam tracker vertex tracker muon trigger and tracking + ZDC (NA50) magnetic field >10m <1m Radiation-hard silicon pixel vertex tracker Muons from the NA50 spectrometer matched to tracks in the vertex region: Improved mass resolution offset wrt the vertex ( @ ~20 GeV) prompt vs open charm (ct=123,312 mm) separation Dipole improves low-mass and low-pT acceptance Matching rejects decay kinks improved S/B Selective trigger, high luminosity P. Cortese – NA60 collaboration HEP09
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NA60 In-In: low mass region
Clear excess of data above decay ‘cocktail’ describing peripheral events Phys. Rev. Lett. 96 (2006) Excess isolated subtracting the measured decay cocktail (without r), independently for each centrality bin Based solely on local criteria for the major sources: η, ω and f 2-3% accuracy. No need of reference data (pA, peripheral data, models) Less uncertainties (e.g. strangeness enhancement: ,) P. Cortese – NA60 collaboration HEP09 3
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NA60 In-In: intermediate mass region
Eur.Phys.J. C59 (2009) 607 Fit range Mass spectrum is similar to NA50: Good description by Drell-Yan + ~2Open Charm (extrapolated from pA data) Prompt ~50mm ~1mm Such explanation is rejected by the spectra of dimuon offsets wrt the interaction vertex! 1.120.17 Data Prompt: 0.08 Charm: 0.16 Fit 2/NDF: 0.6 Prompt Offset fit shows that the enhancement is not due to Open Charm the excess is prompt P. Cortese – NA60 collaboration HEP09 4
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Effective temperature of excess dileptons
M<1 GeV thermal dilepton production largely mediated by the broad vector meson ρ via pp→r→g→mm annihilation. Hadronic nature supported by the rise of radial flow up to M=1 GeV M>1 GeV sudden fall of radial flow of thermal dimuons occurs, naturally explained as a transition to a qualitatively different source, i.e. mostly partonic radiation, qq→g→μμ Phys. Rev. Lett (2006) Phys. Rev. Lett (2008) P. Cortese – NA60 collaboration HEP09
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Absolute comparison with thermal models
All known sources (hadro-cocktail, open charm, DY) subtracted Acceptance corrected spectrum (pT>0.2 GeV) Absolute normalization → comparison to theory in absolute terms! thermal pp g mm (M<1 GeV) && thermal qq g mm (M >1 GeV) suggested dominant by Teff vs M (supported by R/R, D/Z) also multipion processes (H/R) Planck-like mass spectrum; falling exponentially Agreement with theoretical models up to 2.5 GeV! 6 Eur. Phys. J. C 59 (2009) 607 P. Cortese – NA60 collaboration HEP09 6 6 6
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NA60 excess vs pT: comparison to theory
J.Phys. G 35 (2008) Absolute normalization both for theory and data Differences at low masses reflect differences in the tail of r spectral function Differences at high masses, pT reflect differences in flow strength P. Cortese – NA60 collaboration HEP09
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Absence of polarization of excess dileptons
Analysis in CS reference frame. Same results in Gottfried Jackson reference frame Lack of any polarization in excess supports emission from thermalized source. Submitted to PRL, nucl-ex/ P. Cortese – NA60 collaboration HEP09
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The f puzzle Historical discrepancy NA49 fKK vs NA50 fmm
Yields in hadronic channel lower than in leptonic channel by factor ~4 in central collisions Inverse slopes in central collisions Hadronic (low pT) ~ 300 MeV Leptonic (high pT) ~ 230 MeV f puzzle: in-medium effects on f and kaons + kaon absorption and rescattering leading to reduced yield and hardened pT spectrum in hadronic channel? More recently: CERES hadronic yield and inverse slope similar to NA49. Within large errors leptonic yield also compatible with NA49 No f puzzle? New NA50 analysis confirms previous results within 8% P. Cortese – NA60 collaboration HEP09
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fKK in In-In collisions
No PID: all tracks assumed to be kaons huge combinatorial background Event mixing technique (pools by target, multiplicity, reaction plan) Single tracks distributions are reproduced by the event mixing within a precision of few permil Fit with f peak + the residual background Different functions and selections to check systematics Npart NMB(*106) NfRAW(*103) S/B 39 1.47 14 5 1 / 167 75 4.40 120 15 1 / 212 132 9.59 616 40 1 / 271 183 7.11 631 50 1 / 412 0.8 < pT < 1.8 GeV/c <Npart> = 75 <Npart> = 132 <Npart> = 183 P. Cortese – NA60 collaboration HEP09
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fKK and fmm mT distributions
pT and mT distributions are obtained fitting the mass spectra in pT slices High background at low pT: fit limited to pT>0.8 GeV/c Spectra normalized to the multiplicity in 4p Due to limited statistics in the peripheral data, the pT distributions can be extracted only in the two most central bins Systematic error on T of ~ 5 MeV Clear agreement between the mT distributions measured in In-In collisions in the hadronic and dileptonic channels T=252 11 MeV (stat) T=258 14 MeV (stat) Spectra normalized to multiplicity Spectra normalized to multiplicity P. Cortese – NA60 collaboration HEP09
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Teff vs other measurements
central collisions In In-In collisions the measurements in kaon and muon pairs are in agreement Central collisions: NA49 and CERES (KK) measurements in Pb-Pb are above the In-In result by about 30 MeV The difference betweeen NA50 and NA49 results is of ~ 70 MeV P. Cortese – NA60 collaboration HEP09
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Yield vs Npart KK compared to mm
μμ multiplicity determined either directly or compared to J/ψ (corrected for the nuclear and anomalous suppression) KK determined for pT>0.8 GeV/c for each centrality bin and then corrected for the integrated acceptance in 4p and for the branching ratio Yield integrated in centrality: Direct method: J/y Calibration: Teff taken from fmm scales faster than Npart KK: syst ~ 0.2 μμ box: stat+syst. f multiplicity vs Npart in the kaon channel in agreement with the results in muons P. Cortese – NA60 collaboration HEP09
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<f>/Npart compared with other measurements
Unambiguous comparison to NA50 in full phase space not feasible due to the observed differences in the T value An extrapolation with the extreme hypoteses T=220 MeV (NA50 value, blue open symbols) and T=300 MeV (NA49 value, lines) leads to values significantly higher than In-In f/Npart in central In-In collisions exceeds the corresponding values in Pb-Pb collisions in kaons and dielectrons Central collisions P. Cortese – NA60 collaboration HEP09
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Evidence for ω in-medium modification
Determine suppression vs pT with respect to (extrapolated from pT>1GeV/c) Account for difference in flow effects using the results of the Blast Wave analysis Eur.Phys.J. C (2009), in press nucl-ex/ Reference line: f/Npart = f.ph.s. (central coll.) Consistent with radial flow effects Reference line: ω/Npart = f.ph.s. Strong centrality-dependent suppression at pT<0.8 GeV/c , beyond flow effects P. Cortese – NA60 collaboration HEP09
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The A dependence of J/ production
Study of charmonium production/suppression in pA collisions Production models (CSM, NRQCD, CEM, ....) Initial/final state nuclear effects (shadowing, dissociation,...) Reference for understanding dissociation in a hot medium (Relatively) large amount of fixed-target data (SPS, FNAL, HERA) HERA-B (I. Abt et al., arXiv: ) p-Cu (p-Ti) p-W, 920 GeV, -0.34<xF<0.14, pT<5 GeV E866 (M.J.Leitch et al., PRL84(2000) 3256) p-Be p-Fe p-W 800 GeV,-0.10<xF<0.93, pT<4 GeV NA50 (B. Alessandro et al., EPJC48(2006) 329) p-Be p-Al p-Cu p-Ag p-W p-Pb, 400/450 GeV, -0.1<xF<0.1, pT<5 GeV NA3 (J. Badier et al., ZPC20 (1983) 101) p-p p-Pt, 200 GeV, 0<xF<0.6, pT<5 GeV pA 158 GeV pA 400 GeV New results from NA60 P. Cortese – NA60 collaboration HEP09
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Cross section ratios W Pb Cu In U Be Al
When calculating the J/ cross section ratios, the beam luminosity factors Niinc cancel out (apart from a small beam attenuation factor), since all the targets were simultaneously exposed to the beam no systematic errors The acceptance and reconstruction efficiencies do not cancel out completely because each target sees the vertex spectrometer under a (slightly) different angle Need to compute these quantities, and their time evolution for each target separately P. Cortese – NA60 collaboration HEP09
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Efficiency corrections
Reconstruction efficiency does not cancel in the ratio Estimate based on a Monte-Carlo approach Inject realistic VT efficiencies (follow their time evolution) Finest granularity (at the pixel level where statistics is enough) Use “matching efficiency” and its time evolution as a check of the goodness of the procedure Matching rate MC Matching rate data Efficiency map (4th plane, sensor 0) Matching efficiency P. Cortese – NA60 collaboration HEP09
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Differential distributions: dN/dy
158 GeV 400 GeV Gaussian fit at 158 GeV gives y=0.05±0.05, y=0.51±0.02 (in agreement with NA3) y-distribution wider at 400 GeV, as expected Peak position not well constrained at 400 GeV Imposing y=-0.2 (NA50 at 400 GeV) y=0.81±0.03 (NA50 got 0.85) P. Cortese – NA60 collaboration HEP09
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Comparison with previous experiments
HERA-B observes, at 920 GeV, a displacement of the center of the xF distribution towards negative values, increasing with A (by a small amount, xF< 0.01) HERA-B NA50 NA50 observes, at 400 GeV, a strong backward displacement (y=0.2, corresponding to xF= 0.045) Mutually incompatible observations? NA60 data not precise enough to discriminate between the two scenarios P. Cortese – NA60 collaboration HEP09
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Differential distributions: dN/dpT
pT broadening (Cronin effect) observed at both 158 and 400 GeV 158 GeV 400 GeV P. Cortese – NA60 collaboration HEP09
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Comparison with previous experiments
<pT2>= <pT2>pp+ gN L Fit pT2 for various nuclei as <pT2>= <pT2>pp+ (A1/3-1) <pT2>pp shows an increase vs s Does increase with s? Disagreement NA60 vs NA3 (200 GeV) at low energy Agreement NA60 vs NA50 at 400 GeV P. Cortese – NA60 collaboration HEP09
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Relative cross sections vs A
158 GeV 400 GeV A-dependence fitted using the Glauber model Shadowing neglected, as usual (but not correct!) at fixed target 6.4±0.5 mb at 158 GeV (exp vs L) abs J/ (158 GeV) = 7.6 ± 0.7(stat) ± 0.6(syst) mb abs J/ (400 GeV) = 4.3 ± 0.8(stat) ± 0.6(syst) mb We get (158 GeV) = ± ± 0.008 (400 GeV) = ± ± 0.009 Using P. Cortese – NA60 collaboration HEP09
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Comparison with other experiments (1)
Recent results on vs xF from HERA-B, together with older data from NA50, E866 (no NA3, biased by use of p-p) In the region close to xF=0, increase of with √s NA60 400 GeV: very good agreement with NA50 158 GeV: smaller , hints of a decrease towards high xF ? Systematic error on for the new NA60 points ~0.01 P. Cortese – NA60 collaboration HEP09
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Comparison with other experiments (2)
Pattern vs x1 at lower energies resembles HERA-B+E866 systematics Shadowing effects scale with x2, clearly other effects are present P. Cortese – NA60 collaboration HEP09
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Shadowing at 400/158 GeV We have evaluated (and corrected for) the (anti)shadowing effect expected for our data points, within the EKS98 and EPS08 scheme 158 GeV, EKS98 400 GeV, EKS98 abs J/,EKS (158 GeV)=9.3±0.7±0.7 mb abs J/,EPS (158 GeV)=9.8±0.8±0.7 mb abs J/,EKS (400 GeV)=6.0±0.9±0.7 mb abs J/,EPS (400 GeV)=6.6±1.0±0.7 mb The Glauber fit now gives Significantly higher than the “effective” values P. Cortese – NA60 collaboration HEP09
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Anomalous suppression (preliminary)
abs J/ (158 GeV) > abs J/ (400 GeV) smaller anomalous suppression with respect to previous estimates (where abs J/ (400 GeV) was used) In-In Pb-Pb New reference Anomalous suppression still well visible in PbPb In In-In the effect becomes quite small Unexpected pattern in In-In careful study of systematics in progress! P. Cortese – NA60 collaboration HEP09
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Conclusions Low and intermediate masses
The dimuon excess has been characterized and absolutely quantified Absence of any polarization: fully consistent with the interpretation of the observed excess as thermal radiation Planck-like shape of mass spectra, temperature systematics, agreement of data with thermal models Thermal interpretation more plausible than ever before production In-In (kaons vs muons): results in the KK channel agree with the ones in mm both for T and multiplicity In-In vs other systems: Cannot explain the difference between NA50 and NA49 New high statistics and high precision measurements in Pb-Pb would be welcome J/ψ production 400 GeV Energy/kinematic domain already investigated (with higher statistics) by NA50 good agreement on differential spectra and nuclear effects 158 GeV Same kinematic domain of NA50/NA60 A-A collisions Nuclear effects more important wrt 400 GeV Still present anomalous beyond nuclear effects Overall picture of cold nuclear effects on pA still not clear No scaling of or abs with any investigated variable P. Cortese – NA60 collaboration HEP09
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The NA60 collaboration Lisbon CERN Bern Torino Yerevan Cagliari Lyon
Clermont Riken Stony Brook Palaiseau Heidelberg BNL ~ 60 people 13 institutes 8 countries R. Arnaldi, R. Averbeck, K. Banicz, K. Borer, J. Buytaert, J. Castor, B. Chaurand, W. Chen, B. Cheynis, C. Cicalò, A. Colla, P. Cortese, S. Damjanović, A. David, A. de Falco, N. de Marco, A. Devaux, A. Drees, L. Ducroux, H. En’yo, A. Ferretti, M. Floris, P. Force, A.A. Grigoryan, J.Y. Grossiord, N. Guettet, A. Guichard, H. Gulkanyan, J. Heuser, M. Keil, L. Kluberg, Z. Li, C. Lourenço, J. Lozano, F. Manso, P. Martins, A. Masoni, A. Neves, H. Ohnishi, C. Oppedisano, P. Parracho, P. Pillot, T. Poghosyan, G. Puddu, E. Radermacher, P. Ramalhete, P. Rosinsky, E. Scomparin, J. Seixas, S. Serci, R. Shahoyan,P. Sonderegger, H.J. Specht, R. Tieulent, E. Tveiten, G. Usai, H. Vardanyan, R. Veenhof and H. Wöhri P. Cortese – NA60 collaboration HEP09
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Backup slides P. Cortese – NA60 collaboration HEP09
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Comparison with new RHIC results (2)
Results are shown as a function of a the multiplicity of charged particles (~ energy density, assuming SPS~RHIC) Phenix results from Tony Frawley @ ICT Trento 09 The relation between the charged multiplicity and NPart is obtained AuAu using PHOBOS data (Phys.Rev.C (2002) PbPb using NA50 data (Phys.Lett.B (2002) 43-55) Good agreement between PbPb and AuAu P. Cortese – NA60 collaboration HEP09
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NA60 IMR excess (1.16 < M < 2.56 GeV/c2)
Mass (GeV/c2) Mass shape and yield close to Open Charm contribution measured agrees within ~20% with from NA50 pA data (same kinematical domain |cosCS|<0.5) no strong modifications. Scales with centrality faster than Drell-Yan (~Nbin.coll), but less faster than Eur.Phys.J. C59 (2009) 607 Much softer in pT than Drell-Yan: rules out higher-twist DY? [Qiu, Zhang, Phys. Lett. B 525, (2002) 265] P. Cortese – NA60 collaboration HEP09 32
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Polarization of excess dileptons
Collins Soper (CS) frame ϕ pprojectile ptarget z axis CS pµ+ y x Viewed from dimuon rest frame θ is the angle between the positive muon pμ+ and the z-axis. The z axis is the bisector between pproj and - ptarget In principle once all measured, l, m, n can be re-computed in any other frame with a simple transformation (Z. Phys. C31, 513 (1986)) Data analysis in the “natural” reference frame minimizes uncertainties P. Cortese – NA60 collaboration HEP09 33 33
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Reference frames zHE zGJ zCS y Commonly used reference frames:
The degree of polarization may depend on the chosen frame pprojectile Viewed from dimuon rest frame ptarget zCS y zGJ zHE Commonly used reference frames: Collins-Soper pprojectile Viewed from dimuon rest frame ptarget z axis x y reaction plane decay plane m+ ϕ z axis parallel to the bisector of the angle between beam and target directions in the J/ rest frame Helicity z axis coincides with the J/ direction in the target-projectile center of mass frame Gottfried-Jackson z axis parallel to the beam momentum in the J/ rest frame P. Cortese – NA60 collaboration HEP09
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Absence of polarization for and f
Analysis in CS reference frame. Same results in Gottfried Jackson r.f. P. Cortese – NA60 collaboration HEP09
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η polarization P. Cortese – NA60 collaboration HEP09
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EM form factors in In-In peripheral collisions
Acceptance-corrected data (after subtraction of , and peaks) fitted by three contributions: pole approximation: Confirmed anomaly ofF wrt the VDM prediction. Improved errors wrt the Lepton-G results. Removes FF ambiguity in the ‘cocktail’ In-In, peripheral P. Cortese – NA60 collaboration HEP09 (hep-ph/ , submitted to PLB)
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fmm: transverse mass distributions
Box: stat+syst. error Spectra fitted with the function: Depends on the fit range in presence of radial flow Effective temperature (larger T at low pT) P. Cortese – NA60 collaboration HEP09
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fmm: Multiplicity Centrality Dependence (average of the 2 methods)
Multiplicity determined either directly with the cross section measurement or extracted using the J/y (corrected for the nuclear and anomalous suppression) Results in full phase space and corrected for BRmm = 2.86 · 10-4 Yield integrated in centrality: Direct method: J/y Calibration: Centrality Dependence (average of the 2 methods) f scales faster than Npart Box: stat+syst. error Box: stat+syst. error P. Cortese – NA60 collaboration HEP09
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fKK analysis No PID: all tracks assumed to be kaons Huge combinatorial background Events are accepted if there is only one vertex Event mixing technique Pools defined by target, multiplicity and reaction plane Single tracks distributions are reproduced by the event mixing within a precision of few ‰ Acceptance correction evaluated with an overlay MC MC f mass spectrum MKK (GeV/c2) dN/dMKK s=7.8 MeV P. Cortese – NA60 collaboration HEP09
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Invariant mass spectra and fits
Fit the reconstructed invariant mass spectrum as a superposition of the various expected sources: Drell-Yan, J/, ’, open charm DY J/, ’ DD PC muons, all targets VT muons, Pb target 2/ndf = 1.24 (PC 158 GeV) VT scartati a 400 GeV 7300 J/ statistics, after analysis cuts 158 GeV, NJ/PC = 2.5104, NJ/VT= 1.0 104 400 GeV, NJ/PC = 1.6104, NJ/VT= 6.0 103 P. Cortese – NA60 collaboration HEP09
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Comparison with new RHIC results
Measured/Expected SPS results are compared with AuAu RHIC RAA results normalized to RAA(CNM) Phenix results from Tony Frawley @ ICT Trento 09 Both Pb-Pb and Au-Au seem to depart from the reference curve at NPart~200 For central collisions more important suppression in Au-Au with respect to Pb-Pb Systematic errors on the CNM reference are shown for all points P. Cortese – NA60 collaboration HEP09
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Comparison with new RHIC results (2)
Results are shown as a function of a the multiplicity of charged particles (~ energy density, assuming SPS~RHIC) Phenix results from Tony Frawley @ ICT Trento 09 The relation between the charged multiplicity and NPart is obtained AuAu using PHOBOS data (Phys.Rev.C (2002) PbPb using NA50 data (Phys.Lett.B (2002) 43-55) Good agreement between PbPb and AuAu P. Cortese – NA60 collaboration HEP09
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