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Resonances production from the NA60 experiment. Results for the f m + m - channel in In-In collisions Results for the f K + K - channel in In-In collisions Comparison between the hadronic and leptonic channels Comparison between In-In and other systems

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Resonances production from the na60 experiment

Resonances production from the NA60 experiment

  • Results for the fm+m-channel in In-In collisions

  • Results for the fK+K-channel in In-In collisions

  • Comparison between the hadronic and leptonic channels

  • Comparison between In-In and other systems

  • r production in In-In collisions

Eur.Phys.J.C64:1 (2009)

Phys.Lett.B699:325 (2011)

Alessandro De Falco (University and INFN Cagliari)

Resonance Workshop at UT Austin

March 5-7 2012

Alessandro De Falco

The f puzzle
The f puzzle

Historic facts on

NA49 fKK vs NA50 fmm

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

 fpuzzle:in-medium effects on f and kaons +kaon absorption and rescattering leading to reduced yield and hardened pT spectrum in hadronic channel?

  • CERES hadronic yield and inverse slope similar to NA49.

    Within large errors leptonic yield also compatible with NA49  No f puzzle?

Alessandro De Falco

The na60 detector layout

2.5 T dipole magnet

muon trigger and tracking (NA50)

beam tracker

vertex tracker

magnetic field


hadron absorber



Origin of muons can be accurately determined

Improved dimuon mass resolution

(~20 MeV/c2 at  instead of 80 MeV/c2)

Additional bend by the dipole field extends the

dimuon coverage down to low pt

High luminosity mm experiment: possible with radiation tolerant detectors and high speed DAQ

The NA60 detector layout

Concept of NA60: place a silicon tracking telescope in the vertex region to measure the muons before they suffer multiple scattering in the absorber and match them (in both angles and momentum) to the tracks measured in the spectrometer

Alessandro De Falco

Data sample
Data sample

  • In-In collisions at 158 AGeV Incident beam energy

    • 5 weeks in Oct.-Nov. 2003

    • ~ 4 ∙ 1012 ions delivered

    • ~ 230 million dimuon triggers

  • Data analysis for dimuons

    • Select events with

      only one reconstructed vertex

      in target region

      (avoid re-interactions)

    • Match muon tracks from

      Muon Spectrometer with

      charged tracks from

      Vertex Tracker (candidates

      selected using weighted distance

      squared  matching c2)

    • Subtract Background

Alessandro De Falco

Extraction of differential spectra

We select the events on the f peak and use two side mass windows to estimate the pT,y and decay angle distribution of the continuum under the peak

5 centrality bins

Extraction of differential spectra

Mmm (GeV/c2)

4000 A data set only

Systematic error: variation of analysis cuts and parameters

Acceptance: Overlay Monte Carlo tuned to

data with an iterative process

Alessandro De Falco

F mm multiplicity

Yield integrated in centrality:

  • Direct method:

  • J/y Calibration:

fmm: Multiplicity

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

Centrality Dependence (average of the 2 methods)

f scales faster than Npart

Box: stat+syst. error

Box: stat+syst. error

Alessandro De Falco

F mm 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)

fmm: transverse mass distributions

Alessandro De Falco

T slopes in in in and pb pb collisions
T slopes in In-In and Pb-Pb collisions

NA60 fits at high pT(NA50 range)

NA60 fits at low pT (NA49 range)

NA60 In-In (mm, pT < 1.6 GeV)‏

NA49 Pb-Pb (KK, pT < 1.6 GeV)‏

NA50 Pb-Pb (mm, pT > 1.1 GeV)‏

NA60 In-In (mm, pT > 1.1 GeV)‏

NA49 Pb-Pb (KK, pT < 1.6 GeV)‏

NA50 Pb-Pb (mm, pT > 1.1 GeV)‏

Ceres Pb-Pb (KK, pT > 0.75 GeV)

Ceres Pb-Pb (ee, pT < 1.5 GeV)

Box: stat+syst. error

Box: stat+syst. error

NA60low vs high pT: maximal difference in T slopes only ~ 15 MeV presumably related to radial flow

well below difference between NA50 and NA49 (~ 70 MeV) in the most central bin  significant extra hardening of hadronic channel beyond radial flow?

Alessandro De Falco

F kk in in in collisions


MC f mass


s=7.8 MeV

MKK (GeV/c2)

fKK in In-In collisions

  • No PID: all tracks assumed to be kaons Huge combinatorial background

  • Events are accepted if there is one and only one vertex

    • All triggers are taken (dominated by dimuon trigger)

  • Event mixing technique

  • Cuts on tracks: c2<3, pT > 0.2 GeV/c, 2.9 < y < 3.7

  • Cut on pairs: 0.005 < qKK < 0.15

  • Acceptance correction evaluated with an overlay Monte Carlo

  • The expected mass resolution is 7.8 MeV (20 MeV in muons)

Alessandro De Falco

F kk in in in collisions1
fKK in In-In collisions

  • Residual background present in spectra

  • Mass spectra fitted with a function that describes the MC f mass peak + the BKG Several functions used to describe the residual background. Differences taken into account in the systematic error

  • Different selections are applied to check the consistency of the results

  • Peak position and width correctly reproduced when left as free parameters, independent of centrality

Alessandro De Falco

F kk m t distributions
fKK: mT distributions

  • pT and mT distributions are obtained fitting the mass spectra in pT slices

  • High background at low pT: fit limited to pT>0.9 GeV/c

  • Spectra normalized to the multiplicity in 4p (discussed in next slides)

  • 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

Phys.Lett.B699:325 (2011)

Spectra normalized

to multiplicity

Alessandro De Falco

Yield vs n part in kk compared to mm
Yield vs Npart in KK compared to mm

  • Multiplicity obtained for pT>0.9 GeV/c for each centrality bin

  • Data corrected for the integrated acceptance in 4p and branching ratioTeff from KK in (semi)central collisions, from mm in (semi)peripheral collisions

f multiplicity vs Npart in the kaon channel in agreement with the results in muons

Alessandro De Falco

Sensitivity to rescattering absorption
Sensitivity to rescattering-absorption

Modelslike AMPT predicteffects due to rescattering/absorptionconcentratedatlowpT

Common coverage of the NA60 mm and KK chanels for mT– m0> 0.34 GeV

The localTeffvalue in thisregionwoulddiffer by 30-50 MeVin the twochannels

Fractionallossin kaonswould be 35-50%Notseen in NA60 data

For lowermT:Extreme hypothesis: assume Teffvaluemeasured by NA49 in Pb-Pb (330 MeV) for formT– m0< 0.34 GeV

Thisvariationwouldlead to a reduction of the fyield in kaons by 12%




Alessandro De Falco

T and f n part in central collisions
T and <f>/Npartin central collisions

  • Inverse slope: increase fast at low Npart, less pronounced at high Npartlower value observed by NA50

  • Yield per participant: in In-In collisions the dilepton and hadron channels, differences within 22% in full pT<f>/Npart in In-In exceeds the one measured in Pb-Pb (KK) by about 30%NA50 point higher by a factor of 2

  • Suppression of the kaon channel in Pb-Pb below experimental sensitivity in In-In?

Alessandro De Falco

Peripheral nch 30 in in collisions

Eur.Phys.J.C 49 (2007) 235

Peripheral (Nch<30) In-In collisions

Well described by meson decay ‘cocktail’: η, η’, ρ, ω, f and contributions(Genesis generator developed within CERESand adapted for dimuons by NA60).

A. Uras, QM2011


Similar cocktail describes NA60 p-A collisions, 400 GeV data

Alessandro De Falco

More central in in collisions
More central In-In collisions

  • Clear excess of data above decay ‘cocktail’ describing peripheral events

  • Excess isolated subtracting the measured decay cocktail (without r) independently for each centrality bin, based on local criteria for h,w,f (2-3% accuracy)

  • Advantages:

    • no need for reference data (pA, peripheral collisions, models)

    • Less uncertainties (e.g. strangeness enhancement: h,f)

Phys. Rev. Lett. 96 (2006) 162302

Alessandro De Falco


Resonances production from the na60 experiment

  • No cocktail rand noDDsubtracted

NA60 LMR excess dimuons

Evolution of the excess with centralitystudied with precision with a rather fine binning in multiplicity

  • Eur.Phys.J.C 49 (2007) 235

data – cocktail (all pT)

  • Clear excessabove the cocktail ,centeredat the nominalr poleand rising with centrality

  • monotonic broadening with centrality

  • “melting” of the r

Centrality dependence of lmr excess
Centrality dependence of LMR excess

NA60, In-In 158A GeV

Eur.Phys.J.C 49 (2007) 235


peak: R=C-1/2(L+U) continuum: 3/2(L+U)cocktail ρ is fixed by ρ/ω=1.0

Excess rises faster than linear with multiplicity: compatible with emission from annihilation processes

  • rapid initial increase of total - already 3 at dNch/dh=Npart=50

  • strong increase of continuum (by a factor of >10)

  • Precision measurement of excess yield (r-clock):

  • -the most precise constraint in the fireball lifetime (6.5±0.5 fm/c) in heavy ion collisions to date!

Alessandro De Falco

Resonances production from the na60 experiment

LMR excess: r dropping mass vs broadening

Rapp-Wambach: hadronic model predicting strong broadening/no mass shift

Brown/Rho scaling: dropping mass due to dropping of chiral condensate

Predictions for In-In by Rapp et al (2003) for dNch/d = 140, covering all scenarios

Theoretical yields normalized to data in mass interval < 0.9 GeV

After acceptance filtering,data and predictions displayspectral functions, averaged over space-time and momenta

Only broadening of (RW) observed, no mass shift (BR)

Excess mass spectrum up to 2 5 gev
Excess mass spectrum up to 2.5 GeV

  • All known sources (hadro-cocktail, open charm, DY) subtracted

  • Acceptance corrected spectrum (pT>0.2 GeV)

  • Absolute normalization → comparison to theory in absolute terms!

  • thermalpp g mm(M<1 GeV)

  • && thermalqq g mm(M >1 GeV) suggested dominant by Teff vs M (supported by R/R, D/Z)

  • also multipion processes (H/R)

  • Eur. Phys. J. C 59 (2009) 607

  • Planck-like mass spectrum; falling exponentially

  • Agreement with theoretical models up to 2.5 GeV!

Alessandro De Falco

  • 20


  • 20

Dimuon m t distributions
Dimuon mT distributions

  • Phys. Rev. Lett. 100 (2008) 022302

  • Eur. Phys. J. C 59 (2009) 607

  • all mT spectra exponential for mT-M > 0.1 GeV; <0.1 GeV ??

  • IMR

  • LMR

  • fit with 1/mT dN/mT ~ exp(-mT/Teff)

Evolution of inverse slope t eff with mass
Evolution of inverse slope Teff with mass

Phys. Rev. Lett. 100 (2008) 022302

Strong rise of Teff with dimuon mass, followed by a sudden drop for M>1 GeV

Rise consistent withradial flow of a hadronic source(here pp→r→mm) , taking the freeze-out ρ as the reference

Drop signals sudden transition tolow-flowsource, i.e.source of partonic origin (here qq→mm)

Alessandro De Falco

Low mass dimuons in the lhc era alice
Low mass dimuons in the LHC era: ALICE


  • Dimuon mass spectrum in p-p collisions at 7 TeV described by hadronic cocktail + open charmMass resolution at the f peak of about 60 MeV

Alessandro De Falco

W f p t differential cross sections
w,f pT-differential cross sections




Alessandro De Falco


  • f production in In-In (kaons vs muons):results in the KK channel agree with the ones in mm both for T and multiplicity

    Compared to Pb-Pb central collisions:-TEFF values in In-In significantly lower than kaon points in Pb-Pb (NA49/ CERES) higher than NA50(mm) points in Pb-Pb- <f>/NPART in In-In much lower than the NA50 result slightly higher than results in kaon pairs and dielectrons - mm vs KK in Pb-Pb still leave room for a physical effectHowever, CERES measurements in kaons and dielectrons agree

  • Excess in dilepton emission:Good agreement with models of thermal emissionFaster than linear scaling with NchargedPlanck-like mass spectraTeff rising with mass in LMR and, after sharp drop, flat in IMR

No f puzzle in In-In collisions

Alessandro De Falco