Signals from Δ ++ and f 0 in the AliRsn package

24.02.2009 PWG2/ALICE, CERN S.Kiselev 1

Signals from Δ++ and f0 in the AliRsn package

• Sergey Kiselev, ITEP Moscow for the TOF group

• Introduction

– Motivation, Data, Estimations

• Experience with the AliRsn package

– Input, output info

– ϕ K+K- , K*0 K+π-

– Δ++ pπ+ , Δ0 pπ- , f0 π+π-

– ρ0 , ω, K*0 π+π-

• Conclusions and recommendations


Introduction

a1(1260) π ~0.5 0.5

ρ0(770) π+ π- ~100 1.3 p+p/d+A/Au+Au -70 p+p/Au+Au

Δ++(1232) p π+ ~100 1.6 p+p/d+Au -40

f0(980) π+ π- 66 2.6 p+p/Au+Au

K*(892) π K ~100 4 p+p/d+Au/Au+Au -10 p+p/Au+Au

Σ*(1385) Λ π 88 5.5 p+p/d+Au/Au+A 0

Λ*(1520) p K 45 12.6 p+p/d+Au/Au+Au 0 p+p/Au+Au

Ξ*(1530) Ξ π ~100 21 p+p/d+Au/Au+Au 0

ω(782) π+ π- π0 89 23 p+p/d+Au 0

ω(782) π0 9 23 p+p/d+Au/Au+Au 0

ω(782) π+ π- 2 23

ω(782) e+e- 7 10-2 23 p+p/d+Au/Au+Au in prog.

Φ(1020) K+ K- 49 44 p+p/d+Au/Au+Au 0 p+p/Au+Au

Φ(1020) e+e- 3 10-2 44 p+p/d+Au/Au+Au in prog.

channel B.R.(%) c (fm) RHIC data Δm (MeV) ALICE studies

SQM’07: short-lived resonances, motivation + last resultsL

ife Tim

e


Δ++ Mass and Width• Δ++ mass shift observed in

both minimum bias p+p and d+Au at √sNN = 200 GeV

• Width agrees with PDG for both systems within errors

• possible explanations: π+ π- rescattering in p+p collisions, P. Fachini et.al., J.Phys.G33:431-440,2007 PDG

PDG

Introduction – Δ++ motivationP.Fachini SQM07


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.

Recent suggestion by Maiani et al. (Phys. Lett. B645(2007)138) to use

this observable to solve the problem of the real quark composition of some resonances as the fo(980)( or

?)

][ ss ]][[ qssq

A. Badalà- SQM07- Levoča – 24/06/-29/06/07

Introduction – f0 motivation


RHIC data: Δ++/p, f0 /π- ratiosnucl-ex/0305034nucl-ex/0403026

Δ++/p ~ 0.20 f0/ π- ~ 0.05

~107 min.bias pp events


Estimations, SHAKER + data ratios (31.03.08 PWG2/ALICE week)

AliRsn analysis: input infoTwo Alberto Pulvirenti’s macros: AliRsnAnalysis.C, AddRsnAnalysisTask.C for the PROOF analysis on CAF

Main input values:

277500 Pythia6 min.bias pp @ 10 TeV events: /COMMON/COMMON/LHC08c11_10TeV_0.5T

absolute value of the resonance code (e.g. 2224 for Δ++ and ant- Δ++, 10221 for f0). !!! Pythia6 code, mass, width, … could differ from PDG ones (e.g. 9010221 for f0). Look at the PYTHIA6 particle table in the file: AliRoot/PYTHIA6/AliDecayerPythia.cxx

The daughter pair of the resonance (p+pi+ for Δ++, p-pi- for anti-Δ++)

nMixedEvents = 5

other parameters for tracking, vertex, …


AliRsn analysis: output infoMain output:

3 types of the invariant mass distribution for particle pairs:

1. true event pairs, true signal, Strue, from Monte-Carlo (MC)

- will be fitted by the Breit-Wigner (BW) with parameters M0 , Γ0

2. event pairs, signals+backgrount (S+B)

3. mixed event pairs, background (Bmix)

- Bmix will be normalized to S+B in the region Minv.mass > Mb

- the extracted signal: (S+B) - Bmix

For each of the types:

reconstructed info

MC info24.02.2009 PWG2/ALICE, CERN S.Kiselev 8

AliRsn: ϕ K+K-


Mb = 1.1 GeV

Strue is in a good agreement with(S+B)-Bmix

Higher statisticsneeded

AliRsn: K*0 K+π-


Mb = 1.2 GeV

! (S+B)-Bmix ,besides Strue, has probably input from other resonances. Recommendation: to list all other mothers of the pairs.

? Large χ2 /ndf

Γ0 (fit)=Γ0 (PYTHIA6)

AliRsn: Δ+

+ pπ+


Mb = 1.4 GeV

? Ntrue (Δ++ ) = Ntrue (ϕ) Recommendation: to list primary multiplicities.

? Γ0 (fit)=80 MeV < Γ0 (PYTHIA6) =120 MeV

add anti- Δ++ to increase statistics

AliRsn: … +

anti-Δ++


! The larger pt the largerdiscrepancy between(S+B)-Bmix and Strue

Strue/Bmix (±2RMS) = 3, 8 and 12% for pt

=1-2, 2-3 and 3-4 GeV/crespectively (~2 times lower than estimations with SHAKER)

reconstructed MC

…with MC info


Results with MC are very close to oneswith reconstruction.All open questionsstill exist.

AliRsn: Δ0 pπ- + anti-Δ0


…

! discrepancy between(S+B)-Bmix and Strue

larger than for Δ++

Input from other resonances?

Additional source of “signals” in PYTHIA6: GEANT primaries can be decay products of resonances.

AliRsn: f0 π+π-


PDG

Only one true pair!PYTHIA6 multiplicity of f0 is too low !?

PYTHIA6 KF KC particle chg col anti mass width w-cut lifetime decay10221 259 f_0 0 0 0 1.00000 0.00000 0.00000 0.00000E+00 1 IDC on/off ME Br.rat. decay products 1574 1 0 0.520000 pi+ pi- 1575 1 0 0.260000 pi0 pi0 1576 1 0 0.110000 K+ K- 1577 1 0 0.055000 K_L0 K_L0 1578 1 0 0.055000 K_S0 K_S0

AliRsn: ρ0

π+π-


Mb = 1.2 CeV

…

~2 times discrepancy between (S+B)-Bmix

and Strue

Contributions of other resonances, ω, …

AliRsn: ω π+π-


AliRsn: K*0 π+π-

True pairs not from one channel: ω π+π- (Br=2.2%)ω π+π-π0 (Br=89%)AliRsn controls the pair, not thechannel

313 K*0 m= 0.896 width=0.050 Br.rat. decay products 0.665 K+ pi- 0.333 K0 pi0 0.002 K0 gamma

There is no such channel in PYTHIA6

It looks like we observe the π+ π- pairs from the chain K*0 K0π0 π+π-π0 Experts study the problem


Conclusions and recommendations• The AliRsn package works well. Takes ~10 min. on CAF for ~3 105 pp

@ 10 TeV events.

• Thanks a lot Alberto with colleagues.

• 1. The signal extracted with mixed events, (S+B)-Bmix , is higher than the true signal Strue , exception ϕ K+K-

• 2. Large χ2 of the BW fit. Γ0(fit)< Γ0(PYTHIA6), exception K*0 K+π-

• 3. PYTHIA6 multiplicity of f0 is too low! Only ONE π+π- pair from f0

• Recommendations for AliRsn:

– to test the package with a “cocktail” generator with random primary particles + resonances (PYTHIA6 primaries can be decay products of resonances)

– to list all mothers of the pair studied

– to list multiplicity of all primaries

Signals from Δ ++ and f 0 in the AliRsn package

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