Neutral particles energy spectra for 900 GeV and 7 TeV p-p collisions, measured by the LHCf experiment Physics at LHC – 2012, Vancouver (BC) Raffaello D'Alessandro* on behalf of the LHCf collaboration *Università di Firenze & INFN-Firenze Physics at LHC – 2012 R. D'Alessandro 1 Vancouver, BC Università di Firenze & INFN-Firenze
Outline ● Introduction and physics case ● The detector ● Photon and π0 analysis ● Status of LHCf and future prospects ● Conclusions Physics at LHC – 2012 R. D'Alessandro 2 Vancouver, BC Università di Firenze & INFN-Firenze
The physics case lies in cosmic ray energy spectrum and composition ● AGASA and HiRes showed a marked discrepancy in results 10 years ago ● Recent results Auger, HiRes (final), and TA indicate the presence of GZK cutoff ● Absolute values differ between experiments and between detection methods used. Physics at LHC – 2012 R. D'Alessandro 3 Vancouver, BC Università di Firenze & INFN-Firenze
● X max gives information of the Composition too ….. primary particle ● Results are different between experiments ● Interpretation relies on the MC prediction and has quite strong model dependence HiRes Outer atmosphere limit X max Auger Proton and nuclear showers of same total energy Physics at LHC – 2012 R. D'Alessandro 4 Vancouver, BC Università di Firenze & INFN-Firenze
LHCf : a bridge between cosmic ray physics and accelerators ● Use the colliding beams at LHC to study the interaction of UHE primary cosmic rays in the atmosphere. ● E CM ~ ( 2 × E lab × M p ) ½ ● √s =14TeV collision at LHC → 10 17 eV cosmic ray impacting on the atmosphere 1. Inelastic cross section (ex. by TOTEM) 2. Forward energy spectrum large model 3. Inelasticity dependence... Physics at LHC – 2012 R. D'Alessandro 5 Vancouver, BC Università di Firenze & INFN-Firenze
Where colliders stand on the cosmic ray spectrum ● Pioneering measurements performed by UA7 at the SppS collider at CERN in the 80s (E. Pare et al., Phys. Lett, B242 (1990), 531.) LHC 0.9TeV LHC 7 TeV LHC 14 TeV RHIC SppS ISR Physics at LHC – 2012 R. D'Alessandro 6 Vancouver, BC Università di Firenze & INFN-Firenze
Where does the energy flow ? ● Most of the energy flows in the very forward direction ● Particles with X F > 0.1 contribute to 50% of the air shower ● Very important to study what's happening at high eta Multiplicity Energy Flux All particles 8.4 < h < ∞ Neutral Physics at LHC – 2012 R. D'Alessandro 7 Vancouver, BC Università di Firenze & INFN-Firenze
The LHCf experiment Here the beam pipe splits in the two separate tubes that circle LHC ● Charged particles (and the proton beams) are channelled away by the magnets ● Unique configuration (better than SppS) that allows the LHCf calorimeters to ● extend their coverage to | h |> 8 TAN LHCf/ZDC Physics at LHC – 2012 R. D'Alessandro 8 Vancouver, BC Università di Firenze & INFN-Firenze
The LHCf detectors (1) ● Two “tiny” E.M. calorimeters with precise reconstruction of transverse and longitudinal shower profiles De te c to r II De te c to r I De te c to r II De te c to r I INTERACTION POINT INTERACTION POINT Tung s te n Tung s te n Tung s te n Tung s te n S c intilla to r S c intilla to r S c intilla to r S c intilla to r IP1 (ATLAS ) IP1 (ATLAS ) S ilic o n s trips S ilic o n s trips S c intilla ting f i be rs S c intilla ting f i be rs Front Counter Front Counter 140 m 140 m γ 8 cm 6 cm n γ π 0 44X 0 , 1.6 int 90mm 2 9 0 m m Arm#1 Physics at LHC – 2012 R. D'Alessandro 9 Vancouver, BC Università di Firenze & INFN-Firenze Arm#2
LHCf operations @900 GeV & 7 TeV ● With Stable Beam at 900 GeV Dec 6th – Dec 15th 2009 ● With Stable Beam at 900 GeV May 2nd – May 27th 2010 Shower Gamma Hadron Arm1 46,800 4,100 11,527 Arm2 66,700 6,158 26,094 ● With Stable Beam at 7 TeV March 30th - July 19th 2010 ● We took data with and without 100 μrad crossing angle for different vertical detector positions Shower Gamma Hadron π0 Arm1 172,263,255 56,846,874 111,971,115 344,526 Arm2 160,587,306 52,993,810 104,381,748 676,157 Physics at LHC – 2012 R. D'Alessandro 10 Vancouver, BC Università di Firenze & INFN-Firenze
Inclusive photon spectrum analysis ● Measurement of zero degree single photon energy spectra for √ s = 7 TeV proton–proton collisions at LHC. (Physics Letters B 703 (August 2011) 128–134) ● Measurement of zero degree inclusive photon energy spectra for √ s = 900GeV proton-proton collisions at LHC. (Submitted to Physics Letters B) ● Analysis Procedure – Energy Reconstruction from total energy deposition in a tower (corrections for shower leakage, light yield etc.) – Particle Identification by analysis of the longitudinal shower development – Remove multi-particle events by looking at transverse energy deposit – Two Pseudo-rapidity regions selections, η>10.94 and 8.81<η<8.9 – Combine spectra between the two detectors – Compare data with the expectations from the models Physics at LHC – 2012 R. D'Alessandro 11 Vancouver, BC Università di Firenze & INFN-Firenze
Energy and Particle ID ● Impact position from lateral distribution ● Position dependent corrections ● Light collection non-uniformity ● PID criteria based on transition curve ● L90% Arm1 Example L 90 is the longitudinal distance in radiation lengths measured from the entrance to a calorimeter to the position where 90% of the total shower energy has been deposited Physics at LHC – 2012 R. D'Alessandro 12 Vancouver, BC Università di Firenze & INFN-Firenze
Inclusive photon (continued) ● Reject events with multi-peaks – Identify peaks in one tower with position sensitive layers – Select only single peak events for spectra – Efficiency evaluated from MC and Data (artifical samples) ● Physics at LHC – 2012 R. D'Alessandro 13 Vancouver, BC Università di Firenze & INFN-Firenze
Acceptance and Energy scale R1 = 5mm, R2-1 = 35mm, R2-2 = 42mm, q = 20 o ● Small Tower → h > 10.94 ● Large Tower → 8.81 < h < 8.99 ● ● Energy scale checked by π 0 identification from two separate tower events. ● Mass shift observed both in Arm1 (+7.8%) and Arm2 (+3.7%) ● No energy scaling applied, but shifts assigned in the energy scale systematic error Arm2 Data Peak at 135.0 ± 0.2 MeV Peak at 140.0 ± 0.1 MeV Arm2 MC Physics at LHC – 2012 R. D'Alessandro 14 Vancouver, BC Università di Firenze & INFN-Firenze
Photon Spectra Physics at LHC – 2012 R. D'Alessandro 15 Vancouver, BC Università di Firenze & INFN-Firenze
7TeV single photon comparisons. DPMJET 3.04 SIBYLL 2.1 EPOS 1.99 PYTHIA 8.145 QGSJET II-03 Physics at LHC – 2012 R. D'Alessandro 16 Vancouver, BC Università di Firenze & INFN-Firenze
900 GeV results ● Data sets used in the analysis were taken on 2, 3 and 27 May 2010 during the LHC operations with proton-proton collisions at √s =900 GeV, (Fill ID = 1068, 1069 and 1128) ● Monte Carlo(MC) used the hadronic interaction models, QGSJET II-03, PYTHIA 8.145, SIBYLL 2.1, EPOS 1.99 and DPMJET 3.04 ● The detector response was calculated by using the EPICS 8.81/COSMOS 7.49 simulation package . Physics at LHC – 2012 R. D'Alessandro 17 Vancouver, BC Università di Firenze & INFN-Firenze
900 GeV single photon ● Same type of selection as in the previous case. ● Lower energy photons ● No p 0 mass . ● No reconstructed beam position. Because the f l ux of secondary particles produced by � s=900GeV proton-proton collisions is expected to be uniform over the acceptance Systematic uncertainty caused by the uncertainty of the of the LHCf detectors, the ‘beam center’ can not be determined template f i tting method for obtaining the photon spectra. directly from our measurements. In this analysis, we assumed that the beam center was at the center position determined by the alignment measurement of the detectors. Background levels were estimated as about 1 % and 2 % for the small and large towers, respectively, in both Arms. The estimated backgrounds were subtracted from the energy spectra. Systematic uncertainties of the absolute energy scale were evaluated from the reconstructed invariant mass of � 0 s from the 7 TeV data. These differences were compatible with uncorrelated energy scale errors (±3.5 %) for the SPS beam calibrations or long term time variation. Energy scale uncertainties were estimated to be [� 10.2%,+1.8%] and [� 6.6%,+2.2%] for Arm1 and Arm2. Physics at LHC – 2012 R. D'Alessandro 18 Vancouver, BC Università di Firenze & INFN-Firenze
900 GeV, Data vs MC ● Combined Arm1 and Arm2 photon energy spectra compared with MC predictions. All systematics included except luminosity. ● Similar behaviour to 7 TeV data. Physics at LHC – 2012 R. D'Alessandro 19 Vancouver, BC Università di Firenze & INFN-Firenze
900 GeV comparisons continued …... ● Ratio of MC spectra divided by data. Comparison 7 TeV vs 900 GeV spectra Physics at LHC – 2012 R. D'Alessandro 20 Vancouver, BC Università di Firenze & INFN-Firenze
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