on behalf of the ALICE Collaboration Workshop Hadronic resonance production in heavy ion and elementary collisions University of Texas in Austin 57 March 2012 Hadronic resonances from ALICE ID: 696189
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Slide1
Enrico FragiacomoINFN – Triesteon behalf of the ALICE CollaborationWorkshop “Hadronic resonance production in heavy ion and elementary collisions” University of Texas in Austin5-7 March 2012
Hadronic resonances from ALICE in pp collisionsSlide2
Resonances at LHC with ALICEALICE is the LHC experiment mainly devoted to the study of hot and high energy density nuclear matter created in heavy-ion collisionsALICE has also developed a detailed proton-proton physics program
, aimed at:setting the baseline for the heavy-ion data (see Anders Knospe’s talk tomorrow)investigating the novel energy regime made available by LHC
The
study of resonances in pp contributes to a proper tuning of the QCD-inspired particle production models
and to a complete understanding of the underlying event.Analysis of f, K*, S*, X*, L* in pp collisions at s = 7 TeV (using ~150M events from 2010)
Hadronic
resonances from ALICE in pp collisions - Enrico Fragiacomo
200920102011pp@900 GeVpp@900 GeV, pp@2.36 TeV, pp@7 TeV, PbPb@2.76 TeV pp@2.76 TeV, pp@7 TeV, PbPb@2.76 TeV
3/5/2012
2Slide3
OutlineExperimental setup and resonance reconstructionInvariant mass spectra for
f, K*, S*,
X*, L
*
in pp collisions at
s = 7 TeV will be discussed together with the methods for raw yields extractionComparison of pT-spectra with QCD-based models (PYTHIA and PHOJET)Comparison of pT-spectra at different pp collision energies (
s = 900 GeV
and s = 7 TeV
) Particles ratios (f/p and f/K) will be shownHadronic resonances from ALICE in pp collisions - Enrico Fragiacomo 3/5/20123Slide4
Hadronic resonances from ALICE in pp collisions - Enrico Fragiacomo The ALICE detector
|
|
≤
0.9
K.
Aamodt
et al. (ALICE Collaboration) J. Instrum. 3 (2008) S08002K. Aamodt et al. (ALICE Collaboration) J. Instrum. 5 (2010) P03003Global tracking using ITS and TPCParticle ID with TPC and TOFSPD
3/5/20124Slide5
Tracking and PIDHadronic resonances from ALICE in pp collisions - Enrico Fragiacomo
TrackingTracking via Kalman
filter algorithmRequirement of at least 70
/159
TPC clusters
Requirement of one cluster in the innermost ITS detector (SPD) to reduce secondary particlesDCA to the primary vertex used to discriminate between primary and secondary particlesParticle Identification:TPCp and K up to p ~ 0.7 GeV/cp/anti p and p/K up to p ~ 1 GeV/cTOFK and p up to p ~ 2 GeV
/cp/anti p and p
/K up to p ~ 2.5 GeV/c
Time resolution ~100 psDifference between measured time of flight and the one expected by the mass hypothesis3/5/20125TPC dE/dx
resolution ~5.2%Difference between measured energy loss and the one expected by the mass hypothesisSlide6
Resonance reconstructionK+
p-
K*
f
(1020)
K + + K-K*(892)0
± + K
±
(1520) p + K-(1385)± + p±(1530)0 - + p+
Hadronic
resonances from ALICE in pp collisions - Enrico Fragiacomo
Short lifetimes
(few fm/c)!!
Decay products not distinguishable by primary particles!
(unlike
L
,
X,
W
)
->
no topological reconstruction is possible
Invariant mass analysis for signal extraction
Combinatorial background + correlated background from misidentified resonances!!
3/5/2012
6Slide7
Signal extraction: f and
S*
Fit
:
polynomial background + Voigtian Hadronic resonances from ALICE in pp collisions - Enrico Fragiacomo
Fit
:
negative power law + Gaussian |y| ≤ 0.8|y| ≤ 0.5
Alternative
methods
:
like-sign
and
event
mixing
implemented
!
Alternative
method
:
event
mixing
implemented
!
p
T
bin (
GeV
/c)
0.7 – 0.8
PDG Mass (
MeV
/c
2
)
1019.46
PDG
Γ
(M
eV
/c
2
)
4.26
Fit Mass (
MeV
/c
2
)
1019.30 ± 0.10
Fit
Γ
(
MeV
/c
2
)
4.52
Fit
σ
(
MeV
/c
2
)
Fixed to 1.2
p
T
bin (
GeV
/c)
1.6 – 1.8
PDG Mass (
MeV
/c
2
)
1382.8 (
Σ
*
+
)1387.2 (Σ*-)PDG Γ (MeV/c2)35.8 (Σ*+)39.4 (Σ*-)Fit Mass (MeV/c2)1383 ± 1Fit Γ (MeV/c2)33 ± 3
3/5/2012
7Slide8
Signal extraction: *and K*
Hadronic resonances from ALICE in pp collisions - Enrico Fragiacomo
Fit
: 5th order pol. background +
Voigtian
Alternative methods: like-sign and event mixing implemented!
Combinatorial
background (
estimated by like-sign) subtractedFit: Breit-Wigner
+ straight
line for the
residual
background
|y| ≤ 0.5
p
T
bin (
GeV
/c)
1.2 – 1.6
PDG Mass (
MeV
/c
2
)
1531.8
PDG
Γ
(M
eV
/c
2
)
9.1
Fit Mass (
MeV
/c
2
)
1531.5 ± 0.4
Fit
Γ
(
MeV
/c
2
)
Fixed to PDG
Fit
σ
(
MeV
/c
2
)
2.0 ± 0.5
p
T
bin (
GeV
/c)
2.0 – 2.5
PDG Mass (
MeV
/c
2
)
895.9
PDG
Γ
(M
eV
/c
2
)
48.7
Fit Mass (
MeV
/c
2
)
893.4 ± 0.5
Fit Γ (MeV/c2)54.0 ± 2.03/5/20128|y| ≤ 0.5Slide9
Signal extraction: *and L* Hadronic resonances from ALICE in pp collisions - Enrico Fragiacomo
Alternative method 1: like-sign
Alternative method 2: event mixing
3/5/2012
9Slide10
Yellow band:
data systematics
Comparison with models:
f
Hadronic resonances from ALICE in pp collisions - Enrico Fragiacomo pT ≥ 2 GeV/c: good agreement with PHOJET
p
T ≤ 2
GeV/c: good agreement with PYTHIA D6TRaw counts from the invariant mass spectra for all measured pt bins are corrected for the efficiency3/5/201210Slide11
Comparison with models : S*
Hadronic resonances from ALICE in pp collisions - Enrico Fragiacomo
p
T
≥ 2
GeV/c: good agreement with ATLAS-CSC3/5/201211Slide12
f spectra and <pt>Hadronic resonances from ALICE in pp collisions - Enrico Fragiacomo
S
pectra are fitted with a Levy function
A rise in the mean
p
T with collision energy is observed!ISR parameterization fails to describe the dataYields scales with the multiplicity of the collisionFor f@900 GeV see K.
Aamodt et al., Eur. Phys. J. C. (2011) 71
T (
MeV)nC2/NDF900 GeV164 ± 914.2 ± 2.50.6/17 TeV278 ± 157.0 ± 0.511.4/23
3/5/201212Slide13
f particle ratiosHadronic resonances from ALICE in pp collisions - Enrico Fragiacomo 3/5/2012
13
The
f
/K ratio does not increase with energy
The f/p ratio increases with energy both in heavy-ion and in pp collisions. This trend changes at the energy of ~1 TeV in pp collisions, for which a saturation is observedSlide14
ConclusionsResults for f, K*, S
*, X*, L*
in pp collisions at s = 7
TeV
(~150 M events collected in 2010 by ALICE) have been shownThe raw signals for all the resonances have been extracted in several pT-bin and good agreement observed for the masses and the widths wrt the PDG valuespT-spectra have been compared to QCD-based models (PYTHIA and PHOJET) indicating a not fully satisfactory description of the datap
T-spectra at
s = 900 GeV and
s = 7 TeV have been shown for the f, indicating a rise in the mean pT with collision energy The f/p ratio increases with energy both in heavy-ion and in pp collisions. This trend changes at the energy of ~1 TeV in pp collisions, for which a saturation is observed. The f/K ratio does not increase with energyStudy energy dependence of resonance production with
s in the future
Hadronic resonances from ALICE in pp collisions - Enrico Fragiacomo
3/5/2012
14Slide15
Backup slidesHadronic resonances from ALICE in pp collisions - Enrico Fragiacomo
3/5/201215Slide16
L* Hadronic resonances from ALICE in pp collisions - Enrico Fragiacomo Example of the invariant mass of bin (1.5 GeV/c<pt<1.75
GeV/c) fitted with a Breit-Wigner + 3th order polynomial (magenta) and the extracted background function (red)
3/5/2012
16