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Hadronic resonances from ALICE in pp collisions

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1 Hadronic resonances from ALICE in pp collisions
Enrico Fragiacomo INFN – Trieste on behalf of the ALICE Collaboration Workshop “Hadronic resonance production in heavy ion and elementary collisions” University of Texas in Austin 5-7 March 2012

2 Resonances at LHC with ALICE
ALICE is the LHC experiment mainly devoted to the study of hot and high energy density nuclear matter created in heavy-ion collisions ALICE 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) 2009 2010 2011 GeV GeV, TeV, TeV, TeV TeV, TeV, TeV 11/10/2018 Hadronic resonances from ALICE in pp collisions - Enrico Fragiacomo

3 Hadronic resonances from ALICE in pp collisions - Enrico Fragiacomo
Outline Experimental setup and resonance reconstruction Invariant 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 extraction Comparison 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 shown 11/10/2018 Hadronic resonances from ALICE in pp collisions - Enrico Fragiacomo

4 Hadronic resonances from ALICE in pp collisions - Enrico Fragiacomo
The ALICE detector Global tracking using ITS and TPC Particle ID with TPC and TOF || ≤ 0.9 SPD K. Aamodt et al. (ALICE Collaboration) J. Instrum. 3 (2008) S08002 K. Aamodt et al. (ALICE Collaboration) J. Instrum. 5 (2010) P03003 11/10/2018 Hadronic resonances from ALICE in pp collisions - Enrico Fragiacomo

5 Hadronic resonances from ALICE in pp collisions - Enrico Fragiacomo
Tracking and PID Tracking Tracking via Kalman filter algorithm Requirement of at least 70/159 TPC clusters Requirement of one cluster in the innermost ITS detector (SPD) to reduce secondary particles DCA to the primary vertex used to discriminate between primary and secondary particles TPC dE/dx resolution ~5.2% Difference between measured energy loss and the one expected by the mass hypothesis Particle Identification: TPC p and K up to p ~ 0.7 GeV/c p/anti p and p/K up to p ~ 1 GeV/c TOF K and p up to p ~ 2 GeV/c p/anti p and p/K up to p ~ 2.5 GeV/c Time resolution ~100 ps Difference between measured time of flight and the one expected by the mass hypothesis 11/10/2018 Hadronic resonances from ALICE in pp collisions - Enrico Fragiacomo

6 Resonance reconstruction
f(1020)  K + + K- K*(892)0   ± + K ± (1520)  p + K- (1385)±   + p± (1530)0  - + p+ K+ K* 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!! p- 11/10/2018 Hadronic resonances from ALICE in pp collisions - Enrico Fragiacomo

7 Signal extraction: f and S*
|y| ≤ 0.5 |y| ≤ 0.8 Fit: polynomial background + Voigtian Fit: negative power law + Gaussian pT bin (GeV/c) 0.7 – 0.8 PDG Mass (MeV/c2) PDG Γ (MeV/c2) 4.26 Fit Mass (MeV/c2) ± 0.10 Fit Γ (MeV/c2) 4.52 Fit σ (MeV/c2) Fixed to 1.2 pT bin (GeV/c) 1.6 – 1.8 PDG Mass (MeV/c2) (Σ*+) (Σ*-) PDG Γ (MeV/c2) 35.8 (Σ*+) 39.4 (Σ*-) Fit Mass (MeV/c2) 1383 ± 1 Fit Γ (MeV/c2) 33 ± 3 Alternative methods: like-sign and event mixing implemented! Alternative method: event mixing implemented! 11/10/2018 Hadronic resonances from ALICE in pp collisions - Enrico Fragiacomo

8 Signal extraction: *and K*
|y| ≤ 0.5 |y| ≤ 0.5 Fit: 5th order pol. background + Voigtian Combinatorial background (estimated by like-sign) subtracted Fit: Breit-Wigner + straight line for the residual background pT bin (GeV/c) 1.2 – 1.6 PDG Mass (MeV/c2) 1531.8 PDG Γ (MeV/c2) 9.1 Fit Mass (MeV/c2) ± 0.4 Fit Γ (MeV/c2) Fixed to PDG Fit σ (MeV/c2) 2.0 ± 0.5 pT bin (GeV/c) 2.0 – 2.5 PDG Mass (MeV/c2) 895.9 PDG Γ (MeV/c2) 48.7 Fit Mass (MeV/c2) 893.4 ± 0.5 Fit Γ (MeV/c2) 54.0 ± 2.0 Alternative methods: like-sign and event mixing implemented! 11/10/2018 Hadronic resonances from ALICE in pp collisions - Enrico Fragiacomo

9 Signal extraction: *and L*
Alternative method 1: like-sign Alternative method 2: event mixing 11/10/2018 Hadronic resonances from ALICE in pp collisions - Enrico Fragiacomo

10 Comparison with models: f
Raw counts from the invariant mass spectra for all measured pt bins are corrected for the efficiency pT ≥ 2 GeV/c: good agreement with PHOJET pT ≤ 2 GeV/c: good agreement with PYTHIA D6T Yellow band: data systematics 11/10/2018 Hadronic resonances from ALICE in pp collisions - Enrico Fragiacomo

11 Comparison with models : S*
pT ≥ 2 GeV/c: good agreement with ATLAS-CSC 11/10/2018 Hadronic resonances from ALICE in pp collisions - Enrico Fragiacomo

12 f spectra and <pt>
For GeV see K. Aamodt et al., Eur. Phys. J. C. (2011) 71 Yields scales with the multiplicity of the collision ISR parameterization fails to describe the data Spectra are fitted with a Levy function T (MeV) n C2/NDF 900 GeV 164 ± 91 4.2 ± 2.5 0.6/1 7 TeV 278 ± 15 7.0 ± 0.5 11.4/23 A rise in the mean pT with collision energy is observed! 11/10/2018 Hadronic resonances from ALICE in pp collisions - Enrico Fragiacomo

13 Hadronic resonances from ALICE in pp collisions - Enrico Fragiacomo
f particle ratios 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 energy 11/10/2018 Hadronic resonances from ALICE in pp collisions - Enrico Fragiacomo

14 Hadronic resonances from ALICE in pp collisions - Enrico Fragiacomo
Conclusions Results for f, K*, S*, X*, L* in pp collisions at s = 7 TeV (~150 M events collected in 2010 by ALICE) have been shown The 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 values pT-spectra have been compared to QCD-based models (PYTHIA and PHOJET) indicating a not fully satisfactory description of the data pT-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 energy Study energy dependence of resonance production with s in the future 11/10/2018 Hadronic resonances from ALICE in pp collisions - Enrico Fragiacomo

15 Hadronic resonances from ALICE in pp collisions - Enrico Fragiacomo
Backup slides 11/10/2018 Hadronic resonances from ALICE in pp collisions - Enrico Fragiacomo

16 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) 11/10/2018 Hadronic resonances from ALICE in pp collisions - Enrico Fragiacomo

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