Preliminary analysisof p-Pb data

update n. 6

Lorenzo Bonechi

LHCf Catania meeting – 19 December 2013

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Data taking – preliminary summary table

LHCf - Summary table for data taking in 2013

Beam crossing angle (urad)

Detector vertical position (mm, 0=center) Thresholds (mV) PMT HV (V)

BPTX only (min bias) Events

ATLAS filters for LHCf

trigger290 170 0 -3 +5 +10 +15 +35 +40 -11 -13 -18 -24 -36 Normal 600

p-Pb (p-remnant)

4 TeV/n

Pilot run x x x x 5.4 ´ 105NoAlg

Nominal run

x x x x 2.4 ´ 106NoAlg

x x x x 1.3 ´ 108NoAlg + mbSpTrk

x x x x 2.4 ´ 106NoAlg

x x x x 2.4 ´ 106NoAlg

x x x x 2.4 ´ 106NoAlg

x x x x 9.4 ´ 106NoAlg + mbSpTrk

x x x x 9.2 ´ 106NoAlg + mbSpTrk

x x x x 8.7 ´ 106NoAlg + mbSpTrk

x x x x 6.9 ´ 106NoAlg + mbSpTrk

x x x x 5.9 ´ 106NoAlg + mbSpTrk

x x x x x 2.2 ´ 107NoAlg

Pb-p (Pb-remnant)

4 TeV/nNominal run

x x x x 1.4 ´ 106NoAlg + mbSpTrk

x x x x 4.8 ´ 105NoAlg + mbSpTrk

x x x x 6.3 ´ 105NoAlg + mbSpTrk

x x x x 3.2 ´ 106NoAlg + mbSpTrk

p-p 1.38+1.38 TeV Nominal run x x x x 9.7 ´ 106NoAlg + mbSpTrk

Atlas filters:– NoAlg = the LHCf trigger is only prescaled down– mbSpTrk = the LHCf trigger is prescaled and acquired only in case of tracks in Atlas

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Main parts of the analysis

• Mitsuka: neutral pions– 1st presentation in the afternoon

• Menjo: Ultra Peripheral Collisions (UPC)– 2nd presentation in the afternoon

• Lorenzo: gamma rays + UPC– now??? (few updates with respect to september…)

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Description of this work• Reduction of raw data performed by Menjo on a first set of data

files for p-remnant side– Files from 27400 to 27440, taken on 02 February 2013 between 05:45 and

06:15; 1.2 million triggers– Root files with reconstruction of physical data for these data set have been

copied to the INFN farm in Firenze

• Rough comparison with models– DPMJET-III (107 ev) and EPOS1.99LHC (107 ev) have been used– Models are analyzed at the level of generator (no detector and pipes)– After Christmas time also QGSJET-II model should be available

• No LHCf/Atlas combined analysis yet– Discussion was started between May and June with Aaron Angerami and

Brian Cole of the Atlas Heavy Ion Group– I have given them a table with some reconstructed variable from LHCf data;

no answer since June (my last email to Aaron and Brian on 23 July)

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Impact point distributionand

beam center

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View from IP1

REAL DATA

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View from IP1

REAL DATA

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𝑥𝐵=(1.07±0.09 )mm

𝑦𝐵=(−1.87 ±0.08 )mm

Hadron profiles in the small tower

REAL DATA

REAL DATA

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A 2D gaussian fit confirm the position of the center of the beam

Comparison of the impact point distribution

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Photon - yPhoton - x

Neutron - x Neutron - y

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Particle spectra- Real beam position is now included in the simulations

• For simplicity I moved the detector wrt the beam center- 2 mm margin from border is now considered

• For simplicity I moved the detector wrt the beam center- Energy scale is corrected on the basis of the 0 peak position in the

invariant mass distribution- Comparisons of photon spectra from data and DPMJET 3.05 and

EPOS1.99LHC models are shown for both towers • Now added some study in pseudo-rapidity regions

- Some results for neutrons- Study of the dependence of the neutron production cross section by the

scattering angle - Reconstruction of energy not yet implemented

- Applied the cut on energy (E > 100 GeV)- Several corrections implemented to the simulation code- Preliminary normalization of spectra applied

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Debug of simulation codes

• Long revision of my code• Several bugs have been corrected

– Wrong beam crossing angle read in the EPOS model– Wrong calculation of theta and phi angles– Wrong normalization of the pt distributions– Wrong normalization of the energy spectra– Slightly different selection criteria for data and simulations for pion

events– Wrong evaluation of the dead time– …

• Now the results should be more reliable… – Interpretation of disagreement between data and simulations not

due to some mistake (I hope), but to UPC (see Menjo’s presentation)

14tACQ(1 ev) = (ti+1-ti)min = 1.271 ms

?These peaks are placed at multiple values withrespect to the first peak.How can we interpret them?

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Normalization: first estimation of dead time

98% of the events!

Interpretation: some event is discarded during data reduction (pedestal and CRC error), but I evaluate the time difference between two good events (if one or two discarded events were in between, the dt is almost double or triple and so on).

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?

2.5 s – 3 s file change

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Normalization• Fill 3510 31 Jan 2013:

– Start of fill at 14:12 (4h 26m = 4.433h), start of Stable Beam (SB) at 5:00; 338+338 bunches, B1=5.871012 p , B2=3.73 1012 Pb, peak lumi = 98.7801027 cm-2 s-1, *=0.81, LUMI_LIFETIME_SSB=18761 s (lifetime at the beginning of the SB), LUMI_LIFETIME_EOF=24605 s (lifetime at the end of the SB)

• Analyzed data– File 27400-27440, start on 01 Feb 2013 at 05:46; thanks to some counters codified in

the data we estimated the total number of triggered events, n=1.205521 106, the total number of generated Shower-triggers N=38.857127 106 and the total live time = 51.4 s

• Cross section– DPMJET 3.05 2.165 barn– Measurement by LHCb: = (2.09 0.12) b

https://www.phenix.bnl.gov/WWW/publish/jjia/jqr2013/day1_2_constantin_loizides.pdf

• Luminosity (expected uncertainty about 20%)– Started data taking after 43 min from beginning of the SB, for 1784.6 s.

– Our data taking lasted from t=2760 s until t=4544.6 s; the mean luminosity, from the integration of the previous expression, is 8.1811028 cm-2 s-1

• Total inelastic interactions– interactions

4.2 b-1

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Dependency of spectrum from • I have identified 5 possible

regions in (reasonable?)

A B C D

E F G H

1)

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Dependency of spectrum from

1)

1

4

2 3

5

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large

small

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Neutral pions

See Mitsuka presentation

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5667 events between 120 MeV and 150 MeV529 background events (9.3%)

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Comparison with the models

With the new normalizationwe are not in agreementwith the simulations.Have I forgot some factor???

Energy scale is corrected to getthe 0 peak at w=135MeV

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Approximately 3.2 Hz triggerrate for neutral pions

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TO BE UPDATED

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Neutrons

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Neutron production cross section (normalized by the area) as function of the scattering angle

By Menjo

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Neutron production cross section (normalized by the area) as function of the scattering angle

Data: p-Pb run (2013)

𝑑𝜎𝑑𝑆

=

Δ𝑁Δ𝑆𝐿 ∙ Δ𝑡

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Data: p-Pb run (2013)

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To do• First priority: UPC (we will submit a letter)

– Define common criteria for theoretical analysis and data analysis– Reprocess raw data with the updated software with calibrations and

optimized cuts for the p-Pb case (Mitsuka)– Data set must be defined (same one that Mitsuka is using for pi0?)– Graph of neutron flux versus theta using the whole LHCf acceptance– Reconstruction of neutron energy distribution (measured energy, not

unfolded)– Plot of pi0 pt spectrum in one rapidity bin for the letter (Mitsuka)

• Then…– I am writing the contribution for the Crete conference (ICNFP 2013)– Improve the analysis for gamma rays and neutrons

• One point: for gamma rays pt vs eta