Ralf Averbeck State University of New York at Stony Brook INT/RHIC Winter Workshop, Seattle, December 13-15, 2002 Lepton and Charm Measurements in the First Two Years of RHIC: An Experimental Overview

Ralf Averbeck, SUNY Stony Brook INT/RHIC, Seattle, 12/14/2002 l lepton & charm measurements at RHIC  PHENIX l PHENIX experiment: how to measure leptons l Run-1: Au +  s NN = 130 GeV l single electrons from charm decays (c  D  e + X) l Run-2: Au + Au and  s NN = 200 GeV l single electrons refined l dielectron continuum l charmonium measurements –J/   e + e - in p+p and Au+Au –J/       in p+p l summary and outlook Outline

Ralf Averbeck, SUNY Stony Brook INT/RHIC, Seattle, 12/14/2002 PHENIX experiment l electrons: two central arms l muons: two forward arms l Run-1: l Au+Au at  s NN = 130 GeV l central arms partly instrumented l Run-2: l Au+Au at  s NN = 200 GeV l p+p events at  s = 200 GeV l central arms fully instrumented l one muon arm instrumented Two forward muon spectrometers Two central electron/photon/hadron spectrometers l only RHIC experiment optimized for lepton measurements

Ralf Averbeck, SUNY Stony Brook INT/RHIC, Seattle, 12/14/2002 All charged tracks BG Net e ± e ± cand. l high resolution tracking and momentum measurement l drift chamber and pad chambers |  | 0.2 GeV/c l electron identification l ring imaging Cherenkov detectors and electromagnetic calorimeters Electron measurement in PHENIX e-e- Run-1: half of one arm only energy/momentum (E/p)

Ralf Averbeck, SUNY Stony Brook INT/RHIC, Seattle, 12/14/2002 Muon measurement in PHENIX South muon identifier (MuID) 5 gaps per arm filled with planes of transversely oriented Iarocci tubes South muon tracker (MuTR) 3 octagonal stations of cathode strip chambers per arm l muon identification, tracking, momentum measurement in south muon arm forward muons: 1.2 < |  | < 2.2 l p TOT > 2.0 GeV/c

Ralf Averbeck, SUNY Stony Brook INT/RHIC, Seattle, 12/14/2002 l charm production in heavy-ion collisions l production mainly via gg fusion in earliest stage of collision l additional thermal production at very high temperature l propagation through dense (deconfined?) medium l energy loss by gluon radiation?  softening of D-meson spectra? l baseline measurement for charmonium suppression l same arguments hold for bottom measurements l NO data available from heavy-ion collisions (except quarkonia) Charm measurements: why are they important? sensitive to initial gluon densitysensitive to initial temperaturesensitive to state of nuclear medium

Ralf Averbeck, SUNY Stony Brook INT/RHIC, Seattle, 12/14/2002 l ideal but very challenging l direct reconstruction of charm decays (e.g. ) Charm measurements: why are they difficult? D0  K- +D0  K- + l alternative but indirect l charm semi leptonic decays contribute to single lepton and lepton pair spectra l 1 st approach at RHIC: analyze inclusive e ± spectra

Ralf Averbeck, SUNY Stony Brook INT/RHIC, Seattle, 12/14/2002 Inclusive e ± spectra from Au+Au at 130 GeV l how to extract the contribution from open charm decays? l cocktail method l model known sources as precisely as possible l compare with data l main sources contributing to the e ± spectra l “photonic” sources –conversion of photons from hadron decays in material –Dalitz decays of light mesons (  0, , ,  ’,  ) l “non-photonic” sources –semi leptonic decays of open charm (beauty) PHENIX: PRL 88(2002)192303

Ralf Averbeck, SUNY Stony Brook INT/RHIC, Seattle, 12/14/2002 l light hadron cocktail input:  0 (dominant source at low p T ) –p T spectra from PHENIX  0,  ± data –power law parameterization l other hadrons –m T scaling: –relative normalization to  at high p T from other measurements at SPS, FNAL, ISR, RHIC l photon conversions –material known in acceptance l excess above cocktail l increasing with p T l expected from charm decays Separation of non-photonic e ± : cocktail method  conversion  0   ee    ee, 3  0   ee,  0 ee   ee,  ee   ee  ’   ee

Ralf Averbeck, SUNY Stony Brook INT/RHIC, Seattle, 12/14/2002 l compare excess e ± spectra with PYTHIA calculation of semi leptonic charm decays (c  e + X) l tuned to fit SPS, FNAL, ISR data (  s<63 GeV) l for pp at 130 GeV –cross section  cc = 330  b l scale to Au+Au using the number of binary collisions l reasonable agreement between data and PYTHIA Non-photonic e ± spectra from Au-Au at 130 GeV l corresponding charm cross section per binary collision from data l assumption: all e ± are from charm decays l fitting PYTHIA to data for p T > 0.8 GeV/c l consistent with binary scaling (within large uncertainties) PYTHIA direct  (J. Alam et al. PRC 63(2001)021901) b c PHENIX: PRL 88(2002)192303

Ralf Averbeck, SUNY Stony Brook INT/RHIC, Seattle, 12/14/2002 Energy dependence of charm production PHENIX PYTHIA ISR NLO pQCD (M. Mangano et al., NPB405(1993)507) PHENIX: PRL 88(2002)192303

Ralf Averbeck, SUNY Stony Brook INT/RHIC, Seattle, 12/14/2002 Photon converter in Run-2 l additional photon converter installed in parts of the 200 GeV run in PHENIX central arms l 1.7 % X 0 brass close to beam line l additional material increases the number of e ± from photon conversions by a fixed factor ratio between Dalitz decays and photon conversions is fixed by relative branching ratios Dalitz/ , which is very similar for  0 and  conv  e+e- e+e- l comparison of spectra with and without converter allows for complete separation of contributions from non-photonic and photonic sources l complementary to cocktail method l completely different systematics

Ralf Averbeck, SUNY Stony Brook INT/RHIC, Seattle, 12/14/2002 Converter method: proof of principle l e ± spectra with converter: N c l e ± spectra without converter: N l if no contribution to e ± from non-photonic sources  N/N c  const. l but spectra approach each other with increasing p T l indication for strong non-photonic source

Ralf Averbeck, SUNY Stony Brook INT/RHIC, Seattle, 12/14/2002 Non-photonic e ± spectra from Au-Au at 200 GeV l non-photonic e ± yield at 200 GeV l larger than at 130 GeV l consistent with PYTHIA, assuming binary scaling PYTHIA for pp at 200 GeV:  cc = 650  b l spectral shape l consistent with PYTHIA prediction l dominant uncertainties l at high p T : statistical error in converter measurement l at low p T : systematical error in material budget

Ralf Averbeck, SUNY Stony Brook INT/RHIC, Seattle, 12/14/2002 Centrality dependence at 200 GeV

Ralf Averbeck, SUNY Stony Brook INT/RHIC, Seattle, 12/14/2002 Observations from single e ± data l inclusive e ± are consistent with binary scaling within the current statistical and systematical uncertainties l a factor of ~3-4 suppression of high p T hadrons is observed relative to binary scaling l no large effect observed in e ± from charm decays l possibly less energy loss of charm quarks in medium due to “dead cone” effect (Y.L. Dokshitzer and D.E. Kharzeev, Phys. Lett. B519(2001)199) l NA50 has inferred a factor of ~3 charm enhancement from dimuon measurements at SPS (NA50: Eur. Phys. J. C14(2000)443) l no large effect observed at RHIC l possible cross check: dileptons at RHIC l next steps (work in progress): l charm in p+p as reference l complementary leptonic channels

Ralf Averbeck, SUNY Stony Brook INT/RHIC, Seattle, 12/14/2002 Dielectron continuum l why is it interesting? intermediate mass region (IMR): between the  and the J/  mass –may be dominated by charm decays at RHIC –another charm measurement with completely different systematics low mass region (LMR): below the  mass –dominated by light hadron decays –excess dielectron observed at SPS (NA45/CERES) and attributed to in-medium modifications of the  meson due to the restoration of approximate chiral symmetry l and why it is so difficult to measure? l combinatorial background needs to be subtracted to extract small signal Real and Mixed e + e - distributionsReal - Mixed = e + e - signal

Ralf Averbeck, SUNY Stony Brook INT/RHIC, Seattle, 12/14/2002 Dielectron continuum: results l comparison with cocktail including l light hadron decays using vacuum masses and branching fractions l charm decays from PYTHIA l integrated yield in PHENIX expectated from cocktail l LMR ( GeV): ~9.2 x l IMR ( GeV): ~1.5 x l PHENIX preliminary data net e + e - e + e - from charm (PYTHIA) e + e - from light hadron decays l reasonable agreement within huge uncertainties l improvement requires future Au+Au run at RHIC design luminosity

Ralf Averbeck, SUNY Stony Brook INT/RHIC, Seattle, 12/14/2002 J  physics l why is it interesting? l possible signature of the deconfinement phase transition J/  yield in heavy ion collisions can be –suppressed, because of Debye screening of the attractive potential between c and c in the deconfined medium –enhanced, because of cc coalescence as the medium cools important to measure J/  in Au+Au, p+p (Run-2), and d+Au (Run-3) to separate “normal” nuclear effects l preliminary data from PHENIX J/   e + e - and J/        in p+p at  s = 200 GeV J/   e + e -  in Au+Au at  s NN = 200 GeV

Ralf Averbeck, SUNY Stony Brook INT/RHIC, Seattle, 12/14/2002 J   e + e - in p+p collisions at  s = 200 GeV ~ 1.0 billion pp collisions sampled with el.magn. calorimeter hardware trigger (single e ± /  ) l represents about half of total p+p statistics N J/  = 24  6 (stat)  4 (sys)

Ralf Averbeck, SUNY Stony Brook INT/RHIC, Seattle, 12/14/2002 J    +  - in p+p collisions at  s = 200 GeV l ~1.7 billion pp collisions sampled with muon level-1 hardware trigger

Ralf Averbeck, SUNY Stony Brook INT/RHIC, Seattle, 12/14/2002 J  p T distribution in p+p collisions at  s = 200 GeV 1.2<y<2.2 l shape of p T distribution is consistent with a PYTHIA calculation l average p T l y=1.7 = 1.66 ± 0.18 (stat.) ± 0.09 (syst.) GeV/c l slightly larger than measured at lower energies l consistent with a PYTHIA extrapolation to RHIC energy

Ralf Averbeck, SUNY Stony Brook INT/RHIC, Seattle, 12/14/2002 J  rapidity distribution & integrated cross section l combination of muon measurement at forward rapidity and electron measurement at central rapidity  rapidity distribution l integrated cross section consistent for l Gaussian fit l shape from PYTHIA

Ralf Averbeck, SUNY Stony Brook INT/RHIC, Seattle, 12/14/2002  s dependence of J/  production in p+p l comparison with lower energy data and model predictions CEM predictions (J.F. Amundson et al.:Phys.Lett.B390: ,1997)

Ralf Averbeck, SUNY Stony Brook INT/RHIC, Seattle, 12/14/2002 J   e + e - in Au+Au collisions at  s NN = 200 GeV l e + e - invariant mass analysis l very limited statistics l split minimum bias sample into 3 centrality classes N=10.8  3.2 (stat)  3.8 (sys)

Ralf Averbeck, SUNY Stony Brook INT/RHIC, Seattle, 12/14/2002 Centrality dependence of J/  yield J/  B-dN/dy per binary collision compared to different models for J/  absorption patterns J/  scale with the number of binary collisions J/  follow normal nuclear absorption with given absorption cross sections J/  follows same absorption pattern as observed by NA50 (Phys. Lett. B521(2002)195) =791 p+p =297 =45 Attention: all curves are normalized to the p+p data point! present accuracy NO discrimination power between different scenarios

Ralf Averbeck, SUNY Stony Brook INT/RHIC, Seattle, 12/14/2002 l open RHIC l single e ± : no direct charm measurement, but as close as it gets l Au+Au  cc: little room for large in-medium effects l p+p  cc: reference data are needed dielectron continuum and J/ RHIC l capability to measure rare probes has been demonstrated studies of continuum and J/  suppression/enhancement pattern require more statistics to draw conclusions l long runs of p+p (Run-3), d+Au (Run-3), and Au+Au (Run-4) are needed at RHIC design luminosity Summary and outlook