Post on 22-Dec-2015
Study of short-lived resonances in ALICE
A. Badalà – INFN Sezione di Catania
Contents
•Physics motivations
•Some SPS and RHIC results
•ALICE detector performance
•Some results from simulated p-p events @14 TeV
•Summary
A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/071
Why short-lived resonances?
Resonances are strongly decaying particles which have lifetimes of about a few fm/c (i.e resonance ~ fireball )
Resonances c (fm) (770) +- 1.3 f0(980) +- 2.6 K*(892)0 K 3.9(1520) Kp 13 (1020) K+K- 44
Modifications of properties of resonances (peak,width)
Partial chiral symmetry restoration
Interaction of the resonances and/or their daughters with fireball medium
Resonances may give information on the dynamics and on the chiral property of the hot and dense matter which is produced in the collision
A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 2
Resonances as a probe of chiral symmetry restoration
To study chiral symmetry restoration in terms of mass shift and width
broadening, resonance decays from the early
stage of the medium need to be extracted
The best probes are resonances reconstructed by their leptonic decay channel since leptons are
less likely to rescatter in the hadronic medium. However
regenerated resonances from the late hadronic phase feed
down into this signal
ρ0
ρ0
+
+
-
-
π- π+
ρ0
-
+
ρ0 ρ0π-
π+
π+
π-
Leptonic decay channel probes all
stages of the collision
Hadronic decay channel probes late stages of
the collision
A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 3
NA60 results
A significant excess of +- pairs is observed above the yield expected from neutral meson decay. Its shape is consistent
with a contribution from +- annihilation
Models based on in-medium broadening scenario seem able to reproduce data, while moving mass models
seem ruled outR. Arnaldi et al. (NA60 Collaboration) Phys. Rev.
Lett. 96(2006)162302
In-In@ 158AGeV
A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 4
Resonances from jets
High pT resonances from the away side jet could be modified by the partonic medium, but they are so fast to have low probability to be affected by the hadronic medium
Recently suggestion to study chiral symmetry
restoration by comparing resonance
production (reconstructed by their
hadronic decay) in event classes based on azimuthal distribution
respect to jet direction C. Markert, 23rd Winter Workshop on Nuclear Dynamics Big Sky, Montana, USA and SQM07, Levoca (Slovakia)
A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 5
(1020) from same/away side in/out of plane
side1
side2
near
away
No mass shift or width broadening
visible
side2
side1 near - side
away- side
•Trigger particle: hadron pT > 4.0 GeV/c • Associated particle: resonance (1020) <pT>~ 0.9 GeV/c
C. Markert, SQM07, Levoca (Slovakia)A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 6
Next step: with higher pt
Interactions of resonances in hadronic nuclear medium
No interaction
Rescattering
Due to the rescattering , resonances may not be reconstructed
Regeneration
Pseudo-elastic collisions may regenerate resonances
The yields of resonances detected by their hadronic decay can be influenced by effects of rescattering and regeneration which depends on:
•the time between the chemical and the thermal freeze-out
• the lifetime of the resonances
• the interaction cross-section of the decay particles.
The resonances may probe the timescale between the chemical and the kinetic freeze-out
A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 7
p+p and Au+Au @ sNN =200 GeV
Suppression of K* and *
Resonance/non-resonance ratio
B.I. Abelev (Star Collaboration) nucl-ex 0604019
At RHIC energies thermal models are able to reproduce the ratios of stable particles
Deviations from these ratios have been used to estimate the time interval between
thermal and chemical freeze-out
(UrQMD) = 13±3 fm/c
Lower limit (<4 fm/c, T=160 MeV) from measured K*/K and */ ratio by a thermal model with a rescattering phase (G. Torrieri and J. Rafelski, Phys. Lett. B509 (2001) 239 and
C. Market, J. Phys. G. Nucl. Part. Phys. 31 (2005) 1045)A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 8
(*) Extraction of the signal/yields
(*) Mass and widths of resonances
(*) Transverse momentum and transverse mass spectra
(*) Particle ratios
Elliptic flow
Nuclear modification factors: RCP and RAA
Main observables concerning the study of resonances
in pp and AA collisions
A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 9
K*(892) π K B.R. ~1 c = 4 fm
STAR Preliminary
STAR Preliminary
√sNN = 200 GeV √sNN = 200 GeV
√sNN = 62 GeV
STAR Preliminary
STAR collaboration, Phys. Rev. C71, 64902 (2005)
√sNN = 200 GeV
10
Σ(1385) Λ B.R. 0.88 c = 5.5 fm
Λ(1520) pK B.R. 0.45 c = 12.6 fm
Star collaboration, Phys. Rev. Lett. 96(2006)132301
STAR Preliminary
d+Au √sNN=200 GeVd+Au √sNN=200 GeV
p+p √sNN=200 GeV
Au+Au √sNN=200 GeV
11
Φ(1020) K+ K- B.R. 0.49 c = 44 fm
STAR Preliminary
PHENIX
d+Au √sNN=200 GeV
PHENIX
Au+Au √sNN=200 GeV
Au+Au √sNN=62 GeV
A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 12
Φ(1020) e+e- B.R. 0.000296 c = 44 fm
p+p √sNN=200 GeV d+Au √sNN=200 GeV
Au+Au √sNN=200 GeV
PHENIX
PHENIX
PHENIX
S. Huang DIS2007, Munich,Germany
A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 13
ρ0(770) π+ π- B.R. ~1 c = 1.3 fm
20-40% dAu0.6 ≤ pT < 0.8 GeV/c
STAR Preliminary
√sNN = 200 GeV
40-100% dAu0.6 ≤ pT < 0.8 GeV/c
STAR Preliminary
√sNN = 200 GeV
40-80% Au+Au0.6 ≤ pT < 0.8 GeV/c
STAR Preliminary
√sNN = 62 GeV
0-20% dAu0.6 ≤ pT < 0.8 GeV/c
STAR Preliminary
√sNN = 200 GeV
A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 14
Mass and widths of resonances
Even in the absence of the phase transition, temperature and density dependent modifications of the mass, width and shape of short-lived resonances are predicted. Possible explanations are:
•Dynamical interactions with the surrounding matter (M. Bleisher and H. Stocker, J. Phys. G30(2004)S111, E. V. Shuryak and G.E. Brown, Nucl. Phys. A717(2003)322)
•Phase-space distortions(S. Pratt and W. Bauer, Phys. Rev. C68(2003)064905, R. Rapp Nucl.Phys. A725(2003)254)
A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 15
K* Mass and Width
• K*0 pT < 1 GeV mass shift of ~10 MeV observed
• K*± and K*0 pT > 1 GeV mass agrees with PDG for all systems within errors
• Width agrees with PDG for all systems within errors
PDG K*0
PDG K*±
PDG
STAR Preliminary
STAR Preliminary
MC
A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 16
Φ Mass and WidthSTAR Preliminary
STAR Preliminary
PDG
PDG
• pT > 1 GeV mass and width agree with MC and PDG for all systems
• pT < 1 GeV mass agrees with MC for all systems within errors
• pT < 1 GeV width higher than MC for all systems real physics or detector effect?
A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 17
mass and widthmass and width
Mass and width of meson reconstructed by KK channel do not depend on centrality
Mass and width in agreement with PDG for all system
d+Au √sNN=200 GeVAu+Au √sNN=200 GeV
S. Huang , DIS2007, Munich Germany
Au+Au √sNN=62 GeV
A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 18
Particle production in pp collisions dominated by two mechanisms:
a) soft, thermal-like processes at low pT (exponential shape)
b) Hard, parton-parton processes at high pT (power-law shape)
STAR Coll, PRC71(2005)064902
A unique (Levy) function is used to parametrize the overall shape
Transverse spectra
A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 19
K*0 Transverse Momentum Spectra
Au+Au @62 GeV Cu+Cu @62 GeV Cu+Cu@ 200 GeV
STAR PRELIMINARY STAR PRELIMINARY
STAR PRELIMINARY
K*0 spectra fitted by an exponential function
S. Dash SQM07
A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 20
→K+K- Spectra
STAR PreliminarySTAR Preliminary
STAR Preliminary
•Change of Φ spectra from exponential in central Au+Au collisions to Levy function shape in peripheral Au+Au Matter formed in peripheral Au+Au collisions favors hard Φ production
A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 21
SPS puzzle NA49%NA50
NA45 - PRL 96 (2006) 152301]
NA50 reported a yield measured via dileptons larger than yield determined by NA49 in K+K- channel. Further, the mT spectra exhibit a different inverse slope parameter
NA45 has studied the leptonic and the kaon decay modes of the
meson.
Yield and inverse slope parameter agree in both decay modes
Results are in agreement with the
NA49 results
Pb+Au @E/A=158 GeV
A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 22
SPS results for →+- (NA60)NA60 In-In (pT < 1.6 GeV/c)NA49 Pb-Pb(pT<1.6 GeV/c)NA50 Pb-Pb(pT>1.2 GeV/c)
M. Floris, SQM07
NA60 In-In (pT > 1.1 GeV/c)NA49 Pb-Pb(pT<1.6 GeV/c)NA50 Pb-Pb(pT>1.2 GeV/c)
A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 23
Difference between NA50 and NA49 was not due to different
decay channel
Agreement with NA49 when the fit is performed in the same range. T value grows with the centrality of the collision
Lower T values and flatter distribution if the fit is performed in
the same pT range of NA50.
This hints for the presence of radial flow → blast wave analysis
Φ Production K+K- and e+e-
• The leptonic channel yield is a little higher than hadronic channel• More accurate measurement is required to confirm if there is
branching ratio modification
e+e-
K+K-
A. Kozlov (Phenix coll.),QM2005
A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 24
Φ K+K- STAR-PHENIX comparison
J. Rafelski et al.,Phys.Rev. C72 (2005) 024905
• Φ production there is a factor of ~2 difference between PHENIX and STAR
STAR
PHENIX
STAR + PHENIX
Au+Au @ √sNN = 200 GeV
A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 25
Suppression scales with dNch/dy ~ system size
STAR preliminary
Resonance suppression (system size dependence)
C. Markert, SQM07
A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 26
For K* seems less re-scattering at lower energies in peripheral collisions
Lower density smaller interactions cross section? Shorter hadronic lifetime less hadronic interactions ?
STAR preliminary
Resonance suppression (energy dependence)Life-time [fm/c]
K(892) = 4.0 (1020) = 45
S. Dash SQM2007
STAR preliminary
C. Markert, SQM07
A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 27
Elliptic flow
Baryons
Mesons
For KET >1 GeV, mesons and baryons scale separately
Universal scaling is observed for mesons and baryons when
quark number scaling is employed
S. Adare et al. (Phenix coll.) nucl-ex 0608033
A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 28
Elliptic flow for resonances
Measurement of flow for meson and baryon resonances is of great interest to further validate the picture sorting of this
scaling i.e. that partonic collectivity dominates the transverse expansion dynamics.
Mass meson ~ Mass proton
v2 of mesons confirms this
universal scalingS. Afanasiev et al. (PHENIX Coll. ) nucl-ex 0703024
Au-Au @200 GeV
A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 29
K*(892) elliptic flow
Au+Au @ 200 GeV
C. Nonaka, et al., Phys.Rev.C69:031902,2004
Partonic generation → resonances are produced in a hadronizing QGP → v2 scales with n=2
Hadronic generation → resonances are produced in the hadronic final state via hadron-hadron scattering →v2 scales with n=4 (K*=K+=2+2)
Most of K* are produced in partonic phase and only a
small quantity is originated in rigeneration (Need more precise measurements)
Using the deviations of the measured flow coefficient v2 from the scaling law
given by the quark recombination formalism to probe the amount of hadronic final state interactions
A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 30
Nuclear Modification Ratios (RCP) for resonances
RHIC results have shown as, in the intermediate pt
region, nuclear modification factors
depend on the constituent quarks rather than on
particle mass.
K*(892) and (1020), (mass ~ mass proton), have RCP values close
to the kaon ones.
A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 31
Nuclear Modification Ratios (RCP) for resonances
Recent suggestion by Maiani et al. to use this observable to solve the problem of the real quark composition of some resonances as the fo(980)
( or ?) ][ ss ]][[ qssq
L. Maiani et al., Phys. Lett. B645(2007)138
A two components recombination/fragmentation model
A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 32
ALICE performance on primary vertex reconstruction
Pb-Pb
p-p
Primary vertex in ALICE is reconstructed by means of
tracklets in the two innermost pixel layers and
by a Kalman vertex procedure for p-p events
< 40 m
~ 5 m
A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/0733
ALICE performance on track impact parameter
Pb-Pb
p-p
<60 m @ pt> 1GeV/c
A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 34
In ALICE Kalman filter strategy allows a good tracking performance down to very low momenta
ITS + TPC
Tracking efficiencyp
t/pt(%
)
pt(GeV/c)
Momentum resolution
pt/pt <0.7% for pt<2 GeV/c pt/pt ~ 3 % at 100 GeV/c
pt(GeV/c)
35
ALICE performance on particle identification
with ITS and TPC at low momenta…
and TOF at high momenta…
stable hadrons (, K, p): 100 MeV < p < 5 GeV (few 10 GeV)
dE/dx in silicon (ITS) and gas (TPC) + Time-of-Flight (TOF) + Cerenkov (RICH)
decay topology (K0, K+, K-, )
K and decays up to at least 10 GeV
leptons (e, ), photons, 0, electrons in TRD: p > 1 GeV, muons: p > 5 GeV, 0 in PHOS: 1 < p < 80 GeV
A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 36
Mass resolution
Mass resolution ~3 MeV/c2
0.6<pt<0.8 GeV/c 1.0<pt<1.1 GeV/c
1.6<pt<1.8 GeV/c 2.0<pt<2.1 GeV/c
K*(892)
(1020)
Mass resolution ~ 1.3 MeV/c2
A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 37
Invariant mass (GeV/c2) Invariant mass (GeV/c2)
K*(892)0
Invariant mass (GeV/c2)
Short-lived resonances in ALICE
Pb-Pb events studied for PPR
A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 38
Resonance K*(892) Φ(1020) *(1520) Decay channel (B.R.) K (~100%) K+K- (49%) N K (45%)
Width [MeV/c2] 50.8 4.5 15.6 Life time [fm/c] 3.9 44 13
Now several activities are going on in ALICE concerning the study of such resonances in pp collisions (using PDC06 events).
In particular, resonances reconstructed by their hadronic decay are studied in PWG2. Reconstruction of (1020) by its e+e- decay has also been probed. Catania people have expecially worked on reconstruction of:
•Software code development
•Test distributed analysis of events
•Optimization of reconstruction tools
•Background estimation
•Efficiency evaluation
Study of short-life resonances in ALICE
Started study of +- correlations
In next talk results obtained in p-p simulated
events at 900 GeV and 14 TeV
A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 39
Φ(1020): signal 5.00 Tp 15.0 Tp 5.11 Tp
25.1 Tp 5.22 Tp 35.2 Tp
5.33 Tp 45.3 Tp
Background estimation
35.2 Tp
For K*(892)0 BAD agreement between background
estimated by event-mixing technique and true
background
35.2 Tp
Jet-like azimuthal correlations in -K pairs generated in
PYTHIA events at 14 TeV.
A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 40
1
2
Summary
•Many interesting results on short-lived resonances from SPS and RHIC
•ALICE performances (tracking and PID) give us the possibility to do well this kind of physics
•We are working to be ready to analyze first data
EXTRA SLIDES
K*(892)0 pT-analysis with realistic PID
pT= 0 - 0.5 pT= 1.5 - 2
pT= 3.5 - 4
p-p@14 TeV
Overall number of particles + antiparticles generated by PYTHIA@900 GeV:
1.34 K*(892)/event0.08 (1520)/event0.23 Φ(1020)/event
Resonance yield
Exp.data
PYTHIA
K*(892) yield
A. Badalà- SQM07- Levoča – 24/06/-29/06/07
(780)
K*(892)0
1 GeV/c<pt<2 GeV/c2 GeV/c<pt<3 GeV/c
Inside same event, correlations between
K+ and π- candidates
K- and π+ candidates
Evaluate invariant mass spectrum
Combinatorial background:
Signal extraction (unlike-sign)
Mixed-event technique
Like-sign technique
Example: K*(892) Kπ (~100%)
)()(2)( mNmNmNKKSignLike
ALICE PID A common BAYESIAN approach is adopted by every ALICE detector
performing PID;The probability w(i|s) to be a particle of type i (i = e,, , K, p...) if a signal s
(dE/dx, TOF,...) is detected, is:
π...μ,e,kk
i
Ck|srCi|sr
s|iw
r(s|i)(Detector response function)conditional probability density functions to get a signal s in a
detector, if a particle of i-type hits the detector
Ci (particle concentration)a priori probability to find a
particle of type i in the detector
,...,,
)|()|(
)|(
ekk
i
iSRCiSRC
SiW
Probability to be a particle of i-type (i = e, , , K, p, … ), if we observe a vector S= {sITS, sTPC, sTOF, …} of PID signals in different detectors is:
)|()|(,...,
isriSR ddTPCITSd
Combinated response function
preliminary
Temperature and lifetime from (1520) / and K*/K
results between : T= 175 MeV => = 4-6 fm/c = 0 fm/c => T= 110-130 MeV
Dependence of the two ratios K*/K and (1520)/, on the chemical freeze-out temperature and time interval between chemical and kinetic freeze-out. Model: termally produced particle yields + rescattering phase. Then regeneration is not taken into account.
G. Torrieri and J. Rafelski, Phys. Lett. B509 (2001) 239
C. Market, J. Phys. G. Nucl. Part. Phys. 31 (2005) 1045.
(1520)/ = 0.034 0.011 0.013
K*(892)/K = 0.19 0.05
> 4 fm/c for T=160 MeV
0-20% most central Au+Au
Results for p-p collisions @14 TeV
Detailed analysis for K*(892)0 on PID
perfomances
1.5 x 106 PYTHIA events
Mass resolution ~ 3MeV
K*
A. Badalà- SQM07- Levoča – 24/06/-29/06/07
Found K*(±2)=89182
True K*(±2)=85360
(1020) and *(1520) with realistic PID p-p@14 TeV
(1020)
(1020)
(1520)
(1520)
Mass resolution 1.2 MeV
A. Badalà- SQM07- Levoča – 24/06/-29/06/07
True =4893
Found =4967
True *=3879
Found *=3649
• HIJING events with a realistic simulation of detector response
• Use ω and K*0 shape from HIJING to fit the data
• K*0 signal is fixed using STAR measurement
ρ0(770) π+ π-
STAR Preliminary
ρ0
sNN = 200 GeV
K0S
π+ π-
K0S
ω(782) (π+ π-) π0 and π+ π-
ω η (π+ π-) π0 and (π+ π-)
η’ (π+ π-) η and (π+ π-) ρ0η + η’K*(892)0 K π with K misidentified as πK*0 + K*0
misidentified
π+π- Invariant Mass Distribution from Monte Carlo
K*(892)0: like-sign / “true” background
5.00 Tp 15.0 Tp 5.11 Tp
25.1 Tp 5.22 Tp 35.2 Tp
5.33 Tp 45.3 TpGood agreement in all bins of pT
K*(892)0: event mixing / “true” background
5.00 Tp 15.0 Tp 5.11 Tp
25.1 Tp 5.22 Tp 35.2 Tp
5.33 Tp45.3 Tp
BAD agreement except for bins of very small pT
φ1φ2 correlations for πK pairs
25.1 Tp 5.22 Tp 35.2 Tp
ρ0 Mass
• Mass shift observed for all systems• Systematic errors shown for Minimum Bias d+Au 200
GeV
STAR Preliminary
Λ* signal
Formation of hadronic resonances (from jets)
in a chiral medium
side 1
side 2
near
away
Low pt High pt Near side No medium or
late hadronic medium
No medium
Away side Late hadronic medium Partonic or early hadronic medium (depend on formation time) CSR ?
Side 1 & 2 Late hadonic medium Early hadronic medium
Formation time arguments:a.) General pQCD:Formation time [fm/c] ~ pT [GeV]Formation time [fm/c] ~ 1/massb.) Specific string fragmentation (PYTHIA) formalism:Gallmeister, Falter, PLB630, 40 (2005)Intermediate pT resonances form earlyc.) Vitev et al. (hep-ph/0611109): High pT heavy particles and resonances form early
Need to determine the right momenta for trigger and resonance particle