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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 - PowerPoint PPT Presentation
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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)
05-07/03/2012 Alessandro De Falco 2
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?
05-07/03/2012 Alessandro De Falco 3
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
05-07/03/2012 Alessandro De Falco 4
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
05-07/03/2012 Alessandro De Falco 5
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)
05-07/03/2012 Alessandro De Falco 6
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)
05-07/03/2012 Alessandro De Falco 7
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)
05-07/03/2012 Alessandro De Falco 8
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)
Box: stat+syst. error
NA60 In-In ( pT > 1.1 GeV)NA49 Pb-Pb (KK, pT < 1.6 GeV)NA50 Pb-Pb (, pT > 1.1 GeV)
Box: stat+syst. error
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)
05-07/03/2012 Alessandro De Falco 9
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
05-07/03/2012 Alessandro De Falco 11
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
05-07/03/2012 Alessandro De Falco 13
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
05-07/03/2012 Alessandro De Falco 14
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?
05-07/03/2012 Alessandro De Falco 15
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
05-07/03/2012 Alessandro De Falco 16
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
05-07/03/2012 Alessandro De Falco 18
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
05-07/03/2012 Alessandro De Falco 20
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
05-07/03/2012 Alessandro De Falco 22
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
05-07/03/2012 Alessandro De Falco 23
arXiv:1112.2222
pT-differential cross sections
05-07/03/2012 Alessandro De Falco 24
arXiv:1112.2222
05-07/03/2012 Alessandro De Falco 25
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
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