-- JuanCastillo - 09 Mar 2010

Papers tunings

If you want to se the result of analysis, see PythiaTunings

ALICE: Physics Performance Report, Volume I

Document: ALICE: Physics Performance Report, Volume I ALICE Collaboration. J. Phys. G: Nucl. Part. Phys. 30 (2004) 1517-1763 (19 October 2004)

pag.1736: PYTHIA models
The main parameter is $p_t$ min, a cut-off introduced to regularize the dominant 2:2 QCD cross sections, which diverge as pt approach 0 and drop rapidly at large pt.
Model 1: default
All other models assume a continuous turn-off of the cross section at pt min.
Models 3 and 4: varying impact parameter between the colliding hadrons.
Model 3: Gaussian hadronic matter distributions
Model 4: double-Gaussian hadronic matter distributions
To compare PYTHIA to data, pt min must be adjusted in each case to reproduce $<N>$.
The result depends strongly on $\sqrt{s}$, the multiple interaction model and the PDFs. These effects on $p_t$ min have been investigated. In each case, $p_t$ min appears to increase monotonically with $\sqrt{s}$. A power-law for $p_t$ min can be established. The same functional form of the energy dependence is implemented in PYTHIA, allowing users to select the parameter values. However, in PYTHIA 6.210 the default values of the parameters have been already tuned in order to reproduce all the available collider data. PYTHIA 6.150 (default in AliRoot), CTEQ4L PDF, Model 3 for multiple interactions with $p_t$ (0) = 3.47 GeV at the LHC energy $E_0$ = 14 TeV and $\epsilon$ = 0.087. PYTHIA 6.210 with CTEQ5L PDF, Model 4, with its default settings for multiple interactions, and with the default values for the parameters that regulate the cut-off energy dependence.

Pag. 1540 Fig. 1.7
Nch/(0.5*Nparticipants) = 5 $\sqrt{s} = 5.5$ TeV
(see text @ pag 1541)
y = 1
ALICE PPR I pag 1540 Nch predictions
mine: Nch = 4.64
$\sqrt{s} = 5500$ GeV
ptcut = 0.215 GeV
eta < 0.5
data file: e_5000_MB_E_055_pythia.root
(for the single value)
index file: production_MB_ALICE_PPR_plot.txt
(for the average charged particle multiplicities)
charged mine small

Pag. 1738, Fig. 4.34
Nch distribution
PYTHIA tunnings:
dashed: Model 1
dotted: Model 4
solid: HERWIG
$\sqrt{s} = 14$ TeV
ALICE PPR I pag 1741 Nch distribution
mine: visible the peak of SD/DD events. charged dist mine

Bottom production

Document: Bottom Production
P. Nason, G. Ridolfi, O. Schneider G.F. Tartarelli and P. Vikas. arXiv:hep-ph/0003142v2. (29 Aug 2001)

CDF-Pythia comparison

  • Pag 69. Fig 51, Nch = 13, Model 3 for multiple interactions, MB events, $\sqrt{s}$= 14 TeV. (mine: Nch= 13.45, shape OK (more statistics)
  • Pag 70, Fig 52. Nch = 13, CTEQ4L, Model 1 for multiple interactions, MB events, $\sqrt{s}$= 14 TeV.( mine: Nch OK, different model, shape OK with Non_MB)

Determining the inelastic p-p cross section at the LHC using MB events

Document: Determining the inelastic proton-proton cross section at the Large Hadron Collider using minimum bias events
I. Dawson, K. Prokofiev. arXiv:hep-ex/0702041v1 (27 Feb 2007)

Fig 2. paf 2. Nch distribution for $\sqrt{s}$= 14 TeV, different pt cuts, $|\eta|<2.5$ inelastic ND events.

$p_t$ cut Nch(text) Nch(mine)
500 15.4 16.7786
150 36.4 36.5204

Particle multiplicity in p–p collisions with ALICE

Document: Particle multiplicity in proton–proton collisions with ALICE
Marco Monteno for the ALICE Collaboration. Journal of Physics: Conference Series 5 (2005) 209-218 Presented: (18 June 2004)

sample $\sqrt{s}$ $p_t$ cut abs($\eta$) Ncn PYTHIA events
paper 14 TeV 0.1 GeV/c 0.9 50 6.150 5000 MB
mine "" "" "" 14.3204 "" ""

Measuring P(Nch) with the ALICE detector

Document: Measuring the charged particle multiplicity distribution with the ALICE detector
Jan Fiete Grosse-Oetringhaus. ALICE-INT-2008-002 version 2.0. last change : (9 July 2008)

Standart AliRoot software, $\sqrt{s}$ = 14 TeV

Pag. 16. Fig 9, PYTHIA with $|\eta|<2$. Mine: similar, Non_MB, cut on pt = 0.6 GeV/c (cut for B = 0.5 T, including SPD), cut on $|\eta|<2.0$ (not for only TPC)
Pag 46. Fig 31, 0.6 million MB events, $|\eta|<0.9$ (only TPC)

Multiplicity studies and effective energy in ALICE at the LHC

Document Multiplicity studies and effective energy in ALICE at the LHC
A. Akindinov et al . Eur. Phys. J. C 50, 341-352 (12 Feb 2007)

Pag. 342, Fig 1. Average charged particle multiplicity. Experimental data up to 1000 GeV. Mine: similar. Macro: AverMult.C, data file "production.txt".Cuts:
  • $|\eta|<2.44$ full rapidity (except 10 degrees)
  • no MB but all
  • pt = 0.215 GeV/c ("analysis" cut for MB)

Pag. 343, Table 1. PYTHIA tunning for MB (non-diffractive) pp events.

Parameter Our tuning Default
MSTP(51) 7 (CTEQ5L) 7 (CTEQ5L)
MSTP(81) 1 1
MSTP(82) 2 4
PARP(82) 2.15 GeV 1.80 GeV
PARP(89) 1000 GeV 1000 GeV
PARP(90) 0.215 0.160

Fig 3. Nch from PYTHIA, after the tunning. All primary charged particles considered, full rapidity, no pt cut. Mine: bigger in a factor 10% with the actual cuts.

Prediction for minimum bias and the underlying event at LHC energies

Document: Prediction for minimum bias and the underlying event at LHC energies
A. Moraes, C.Buttar, I. Dawson. Eur. Phys. J. C 50, 435-466 (23 January 2007)

Pag. 437. Table 1. Default PYTHIA parameters for ptmin as defined in PYTHIA 6.214.

PARP(81) = 1.9 simple scenario
PARP(82) = 1.9 complex scenario
PARP(89) = 1 TeV energy scale
PARP(90) = 0.16 power which regulates ptmin’s energy dependence

So, same energy scale and same default PARP(90), in comparison with ALICE.

General characteristics of h-h collisions

Document: General characteristics of hadron-hadron collisions
W. Kittel. PACS numbers: 12.38.Qk, 13.66.Bc, 13.85.Hd, 13.87.Fh (4 October 2004)

Pag 17, Fig 2.1. Average charged-particle multiplicity of the hadronic system. Low energy (up to 100 GeV). mine: full rapidity, cut on pt.

My cuts

  • On transverse momentum. Since $ p = (E,p_T,p_z)$ a cut on transverse momentum is done defining $p_T = {\sqrt{p_x^2 +p_y^2}}$. Particles below certain pt are lost of measured with a very low efficiency. This is due to magnetic field as well as to multiple scattering through small angles, that is proportional to $1/{\beta_{particle}}$(pag. 40. ALICE-INT-2008-002)

Original PYTHIA tunning

PYTHIA version 5.720 ("FORTRAN" version)

beam energy variable (from 1 to 14 TeV)
PYINIT 'CMS','p','p',pbeam
PYSTAT 4 : kinematical cuts CKIN(I) in the current run
COMMON/LUDAT2/KCHG(500,3),PMAS(500,4),PARF(2000),VCKM(4,4) block ludat2 (jetset):
KC code
PMAS for particle masses:
PMAS(lucomp(4),1) = 1.35 tuned: c-quark mass
PARF and VCKM default
COMMON/PYPARS/MSTP(200),PARP(200),MSTI(200),PARI(200) block pypars:
mstp(52)=2: PDFLIB one with PDFLIB MODE (set) mstp(51)
mstp(91) = 1: primordial k_T distribution in hadron gaussian
parp(91)=1.0 (gaussian width)
parp(93)=3.0 (upper cutoff)
COMMON/PYSUBS/MSEL,MSUB(200),KFIN(2,-40:40),CKIN(200) block pysubs:
msel not set
msub array default
kfin target side
ckin array default
COMMON/LUJETS/N,K(4000,5),P(4000,5),V(4000,5) block lujets:
default all: standart way of storing event info
Topic attachments
I Attachment Action Size Date Who Comment
charged_ALICE_small.pngpng charged_ALICE_small.png manage 19.2 K 2008-03-27 - 10:56 JuanCastillo ALICE PPR I pag 1540 Nch predictions
charged_distribution_ALICE_big_detail.pngpng charged_distribution_ALICE_big_detail.png manage 10.0 K 2008-03-27 - 13:50 JuanCastillo ALICE PPR I pag 1741 Nch distribution
nch_dist_ALICE_PPR_I.pngpng nch_dist_ALICE_PPR_I.png manage 4.2 K 2008-03-27 - 13:21 JuanCastillo charged mine small
nch_prob_ALICE_PPR_I.pngpng nch_prob_ALICE_PPR_I.png manage 6.1 K 2008-03-27 - 14:13 JuanCastillo charged dist mine
Topic revision: r2 - 2010-03-31, JuanCastillo
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