Preliminary analysis of p-pb data update n. 6

Transcription

1 LHCf Catania meeting 19 December 2013 Preliminary analysis of p-pb data update n. 6 Lorenzo Bonechi

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3 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) Normal 600 Events ATLAS filters for LHCf trigger Pilot run x x x x NoAlg x x x x NoAlg x x x x NoAlg + mbsptrk x x x x NoAlg p-pb (p-remnant) 4 TeV/n Pb-p (Pb-remnant) 4 TeV/n Nominal run Nominal run x x x x NoAlg x x x x NoAlg x x x x NoAlg + mbsptrk x x x x NoAlg + mbsptrk x x x x NoAlg + mbsptrk x x x x NoAlg + mbsptrk x x x x NoAlg + mbsptrk x x x x x NoAlg x x x x NoAlg + mbsptrk x x x x NoAlg + mbsptrk x x x x NoAlg + mbsptrk x x x x NoAlg + mbsptrk p-p TeV Nominal run x x x x NoAlg + 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 3

4 Main parts of the analysis Mitsuka: neutral pions 1 st presentation in the afternoon Menjo: Ultra Peripheral Collisions (UPC) 2 nd presentation in the afternoon Lorenzo: gamma rays + UPC now??? (few updates with respect to september ) 4

5 Description of this work Reduction of raw data performed by Menjo on a first set of data files for p-remnant side Files from 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 (10 7 ev) and EPOS1.99LHC (10 7 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 to Aaron and Brian on 23 July) 5

6 Impact point distribution and beam center 6

7 View from IP1 REAL DATA 7

8 View from IP1 REAL DATA 8

9 Hadron profiles in the small tower x B = 1.07 ± 0.09 mm REAL DATA y B = 1.87 ± 0.08 mm REAL DATA 9

10 A 2D gaussian fit confirm the position of the center of the beam 10

11 Comparison of the impact point distribution Photon - x Photon - y Neutron - x Neutron - y 11

12 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 12

13 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 p t 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) 13

14 Normalization: first estimation of dead time 98% of the events!? These peaks are placed at multiple values with respect to the first peak. How can we interpret them? 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).? t ACQ (1 ev) = (t i+1 -t i ) min = ms 14

15 2.5 s 3 s file change? 15

16 Normalization Fill Jan 2013: Start of fill at 14:12 (4h 26m = 4.433h), start of Stable Beam (SB) at 5:00; bunches, B1= p, B2= Pb, peak lumi = 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 , 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= , the total number of generated Shower-triggers N= and the total live time = 51.4 s Cross section DPMJET barn Measurement by LHCb: = ( ) b Luminosity (expected uncertainty about 20%) Started data taking after 43 min from beginning of the SB, for s. L t + dt = L t e dt τ t L t 1 dt dl t = L t τ t dt τ t assuming τ t = τ i + τ f τ i α t = α + βt L t = L t f t 0 i α + βt Our data taking lasted from t=2760 s until t= s; the mean luminosity, from the integration of the previous expression, is cm -2 s -1 Total inelastic interactions ΔN ine = σ L t = = interactions 1 β 4.2 b -1 16

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21 Dependency of spectrum from I have identified 5 possible regions in (reasonable?) A = 0.493, cm B = , cm C = , cm D = , cm r 1 = 0.49 cm r 2 = 1.00 cm r 3 = 1.50 cm r 4 = 3.00 cm r 5 = 4.00 cm r 6 = 5.00 cm E = 1.431, cm F = 3.183, cm G = 1.919, cm H = 3.873, cm 1) > ) < < ) 9.83 < < ) 8.85 < < ) 8.63 < < 8.85 θ < 35 μrad 35 μrad < θ < 71 μrad 71 μrad < θ < 107 μrad 214 μrad < θ < 286 μrad 286 μrad < θ < 357 μrad 21

22 Dependency of spectrum from ) > ) < < ) 9.83 < < ) 8.85 < < ) 8.63 < <

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25 large small 25

26 Neutral pions See Mitsuka presentation 26

27 5667 events between 120 MeV and 150 MeV 529 background events (9.3%) 27

28 Comparison with the models With the new normalization we are not in agreement with the simulations. Have I forgot some factor??? Energy scale is corrected to get the 0 peak at w=135mev 28

29 Approximately 3.2 Hz trigger rate for neutral pions 29

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33 Neutrons 33

34 Neutron production cross section (normalized by the area) as function of the scattering angle By Menjo 34

35 Neutron production cross section (normalized by the area) as function of the scattering angle Data: p-pb run (2013) dσ ds = ΔN ΔS L Δt 35

36 Data: p-pb run (2013) 36

37 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 37