resonances production from the na60 experiment

05-07/03/2012 Alessandro De Falco 1

Resonances production from the NA60 experimentAlessandro De Falco (University and INFN Cagliari)

Resonance Workshop at UT Austin

March 5-7 2012

• Results for the channel in

In-In collisions • Results for the channel in In-In collisions• Comparison between the hadronic and leptonic channels• Comparison between In-In and other systems• production in In-In collisions

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

Phys.Lett.B699:325 (2011)


The puzzle

Historic facts on NA49 KK vs NA50

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

puzzle: in-medium effects on 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 puzzle?


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

Origin of muons can be accurately determinedImproved dimuon mass resolution (~20 MeV/c2 at instead of 80 MeV/c2)Additional bend by the dipole field extends thedimuon coverage down to low pt

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

2.5 T dipole magnet

hadron absorber

targets

beam tracker vertex trackermuon trigger and tracking (NA50)

mag

netic field

>10m<1m


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 2)– Subtract Background


We select the events on the peak and use two side mass windows to estimate the pT,y and decay

angle distribution of the continuum under the peak

Systematic error: variation of analysis cuts and parameters

5 centrality bins

4000 A data set only

Extraction of differential spectra

Acceptance: Overlay Monte Carlo tuned to data with an iterative process

M (GeV/c2)


Multiplicity

b7.005.001.7 16.001.062.1 2.004.048.1

Yield integrated in centrality:• Direct method: • J/ Calibration:

Results in full phase space and corrected for BR = 2.86 · 10-4

Centrality Dependence (average of the 2 methods)

Box: stat+syst. errorBox: stat+syst. error

scales faster than Npart

Multiplicity determined either directly with the cross section measurement orextracted using the J/ (corrected for the nuclear and anomalous suppression)


transverse mass distributions

Box: stat+syst. error

Tm

TT

Tekdm

dN

m/1

Spectra fitted with the function:

Depends on the fit range in presence of radial flowEffective temperature (larger T at low pT)


T slopes in In-In and Pb-Pb collisions

NA60 In-In ( pT < 1.6 GeV)NA49 Pb-Pb (KK, pT < 1.6 GeV)NA50 Pb-Pb (, pT > 1.1 GeV)

NA60 fits at low pT (NA49 range)


NA60 In-In ( pT > 1.1 GeV)NA49 Pb-Pb (KK, pT < 1.6 GeV)NA50 Pb-Pb (, pT > 1.1 GeV)


NA60 low 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?

NA60 fits at high pT (NA50 range)

Ceres Pb-Pb (KK, pT > 0.75 GeV) Ceres Pb-Pb (ee, pT < 1.5 GeV)


MC mass spectrum

MKK (GeV/c2)

dN

/dM

KK

=7.8 MeV

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: 2<3, pT > 0.2 GeV/c, 2.9 < y < 3.7

• Cut on pairs: 0.005 < KK < 0.15

• Acceptance correction evaluated with an overlay Monte Carlo

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

05-07/03/2012 Alessandro De Falco10

KK in In-In collisions

Npart NMB(*106) NRAW(*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

• Residual background present in spectra

• Mass spectra fitted with a function that describes the MC 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


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 4(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

Spectra normalizedto multiplicity

Phys.Lett.B699:325 (2011)

05-07/03/2012 Alessandro De Falco12

Yield vs Npart in KK compared to

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

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

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

collisions

Sensitivity to rescattering-absorption


KK

Models like AMPT predict effects due to rescattering/absorption concentrated at low pT

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

The local Teff value in this region would differ

by 30-50 MeV in the two channels

Fractional loss in kaons would be 35-50%

Not seen in NA60 data

For lower mT:Extreme hypothesis: assume Teff value

measured by NA49 in Pb-Pb (330 MeV) for for mT – m0< 0.34 GeV

This variation would lead to a reduction of the yield in kaons by 12%

RESCATTERING-ABSORPTION MODEST OR ABSENT IN In-In

T and <>/Npart in central collisions


Inverse slope: increase fast at low Npart, less pronounced at high Npart

lower value observed by NA50

Yield per participant: in In-In collisions the dilepton and hadron channels, differences within 22% in full pT

<>/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?


Peripheral (Nch<30) In-In collisions Well described by meson decay ‘cocktail’: η, η’, ρ, ω, and

contributions(Genesis generator developed within CERES and adapted for dimuons by NA60).

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

DD

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

A. Uras, QM2011

p-A


16

•Clear excess of data above decay ‘cocktail’ describing peripheral events•Excess isolated subtracting the measured decay cocktail (without ) independently for each centrality bin, based on local criteria for (2-3% accuracy)•Advantages:

• no need for reference data (pA, peripheral collisions, models)• Less uncertainties (e.g. strangeness enhancement: )

Phys. Rev. Lett. 96 (2006) 162302

More central In-In collisions

17

• Clear excess above the cocktail , centered at the nominal pole and rising with centrality

•No cocktail and no DD subtracted

data – cocktail (all pT)

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

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

monotonic broadening with centrality

“melting” of the

NA60 LMR excess dimuons


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

NA60, In-In 158A GeVEur.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

Centrality dependence of LMR excess

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

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

Precision measurement of excess yield (-clock):

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

19

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

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

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

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

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

LMR excess: dropping mass vs broadening

Excess mass spectrum up to 2.5 GeV

2020

20

thermal (M<1 GeV) && thermal qq (M >1 GeV) suggested dominant by Teff vs M (supported by R/R, D/Z) also multipion processes (H/R)

All known sources (hadro-cocktail, open charm, DY) subtractedAcceptance corrected spectrum (pT>0.2 GeV)Absolute normalization → comparison to theory in absolute terms!

Planck-like mass spectrum; falling exponentially Agreement with theoretical models up to 2.5 GeV!

Eur. Phys. J. C 59 (2009) 607


all m T spectra exponential for m T-M > 0.1 GeV; <0.1 GeV ?? IMR LM

R

Phys. Rev. Lett. 100 (2008) 022302 Eur. Phys. J. C 59 (2009) 607

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

Dimuon mT distributions


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

Rise consistent with radial flow of a hadronic source (here →→) , taking the freeze-out ρ as the reference

Drop signals sudden transition to low-flow source, i.e. source of partonic origin (here qq→)

Phys. Rev. Lett. 100 (2008) 022302

Evolution of inverse slope Teff with mass

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 peak of about 60 MeV


arXiv:1112.2222

pT-differential cross sections


arXiv:1112.2222


Summary• production in In-In (kaons vs muons):

results in the KK channel agree with the ones in 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() points in Pb-Pb- <>/NPART in In-In much lower than the NA50 result

slightly higher than results in kaon pairs and dielectrons - 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 Ncharged

Planck-like mass spectraTeff rising with mass in LMR and, after sharp drop, flat in IMR

No puzzle in In-In collisions

resonances production from the na60 experiment

Documents

pbpb collisionsna60

mev leptonic high pt

low pt na49 rangebox

gevna49 pbpb kk

falco university

hardened pt spectrum

errorna60 low vs high

gevna49 pbpbkk