Inelastic Cross Section and Forward Particles Multiplicity in TOTEM Giuseppe Latino (University of Siena & Pisa INFN) (on behalf of the TOTEM Collaboration) MPI 2012 CERN – December 3, 2012 1/20
TOTEM Physics Program Overview Stand-Alone - TOT pp with a precision ~ 1-2%, simultaneously measuring ( L ind. meth.): N el down to -t ~10 -3 GeV 2 and N inel with losses < 3% - Elastic pp scattering in the range 10 -3 < |t| ~ (p ) 2 < 10 GeV 2 - Soft diffraction (SD and DPE) - Particle flow in the forward region (cosmic ray MC validation/tuning) CMS-TOTEM (largest acceptance detector ever built at a hadron collider) (CMS/TOTEM Physics TDR, CERN/LHCC 2006-039/G-124) - Soft and hard diffraction in SD and DPE (production of jets, bosons, h.f.) - Central exclusive particle production - Low-x physics - Particle and energy flow in the forward region 2/20 G. Latino – TOTEM Inel. Xsec. and fwd Part. Multip MPI 2012 – Dec. 3, 2012
TOTEM Detector Setup @ IP5 of LHC ( Same of CMS ) Inelastic Telescopes: Detectors on both sides of IP5 reconstruction of tracks and interaction vertex; trigger capability with acceptance > 95 % T1: 3.1 < < 4.7 T1: 18 - 90 mrad CMS T2: 5.3 < < 6.5 T2: 3 - 10 mrad = - log(tg( /2)) HF HF T1 10.5 m T2 ~14 m Elastic Detectors (Roman Pots): reconstruction of elastically scattered and diff. p Active area up 1-1.5 mm from beam: 5-10 rad RP220 (RP147) ZDC 3/20 G. Latino – TOTEM Inel. Xsec. and fwd Part. Multip MPI 2012 – Dec. 3, 2012
TOTEM Detectors Package of 10 “edgeless” Si -detectors hit 10 µm RP 147 Vertical Vertical Horizontal Pot Pot Pots Vertical Vertical Pot Pot T2 (GEMs) T1 (CSCs) hit 100 µm hit 1 mm p. 4 4/20 G. Latino – TOTEM Inel. Xsec. and fwd Part. Multip MPI 2012 – Dec. 3, 2012
Inelastic Cross Section @ 7 TeV Direct T1 and T2 measurement: inel = N inel / L ( L from CMS) Data sample - Oct. 2011 run with β * = 90 m: same data subsets used for the L -independent total cross section measurement - T2 triggered events - Low pile-up: ( μ = 0.03) tracks T2 Inelastic events in T2: classification T2 - Tracks in both hemispheres: mainly non-Diffractive η minimum bias (ND) and Double Diffraction (DD) - Tracks in a single hemisphere: mainly single diffraction (SD) with M X > 3.4 GeV/c 2 η Optimized study of trigger efficiency and beam gas background corrections η 5/20 G. Latino – TOTEM Inel. Xsec. and fwd Part. Multip MPI 2012 – Dec. 3, 2012
Inelastic Cross Section @ 7 TeV: Corrections Corrections to the “T2 visible” events ( 95%) - Trigger Efficiency (from zero bias data, vs track multiplicity) : 2.3 0.7 % 1.0 0.5 % - Track reconstruction efficiency (based on MC tuned with data) : 0.6 0.4 % - Beam-gas background (from non colliding bunch data) : 1.5 0.4 % - Pile-up ( μ = 0.03) (from zero bias data) : Corrections for “m issing ” inelastic cross-section 1.6 0.4 % - Events visible in T1 but not in T2 (from zero bias data): 0.35 0.15 % - Rapidity gap in T2 (from T1 gap probability transferred to T2): 0.0 0.35 % - Central Diffraction: T1 & T2 empty (based on MC): 4.2 % 2.1 % - Low Mass Diffraction (based on QGSJET-II-03 MC): ( constrained by elastic scattering measurement, see later ) Uncertainty related to L (CMS): 4% Compatible with σ inelastic = 73.7 ± 0.1 stat ± 1.7 syst ± 3.0 lumi mb other similar meas. @ LHC CERN-PH-EP-2012-352 6/20 G. Latino – TOTEM Inel. Xsec. and fwd Part. Multip MPI 2012 – Dec. 3, 2012
Low-Mass Diffraction: T1+T2 Acceptance QGSJET-II-03: M X > 3.4 GeV/c 2 (T2 acceptance) dN/dM diff T1+T2 (3.1 < | | < 6.5) give an unique forward charged particle coverage @ LHC lower M diff reachable: minimal model dependence on required corrections for low mass diffraction Several models studied: correction for low mass single diffractive cross-section based on QGSJET-II-03 (well describing low mass diffraction at lower energies), imposing observed 2hemisphere/1hemisphere event ratio and the effect of “secondaries” Mx < 3.4 GeV = 3.1 ± 1.5 mb 7/20 G. Latino – TOTEM Inel. Xsec. and fwd Part. Multip MPI 2012 – Dec. 3, 2012
Low-Mass Diffraction: Constraint from N el Constraint on low mass diffraction cross-section: Use total cross-section determined from elastic observables (via the Optical Theorem) no assumption on low mass diffraction inel = tot – el = 73.2 1.3 mb and the measured “visible” inelastic cross -section for | | < 6.5 (T1, T2) inel, | | < 6.5 = 70.5 2.9 mb to obtain the low-mass diffractive cross-section (| | > 6.5 or M X < 3.4 GeV) inel, | | > 6.5 = inel - inel, | < 6.5 = 2.6 2.2 mb (or < 6.3 mb @ 95% CL) [MC: 3.1 1.5 mb] 8/20 G. Latino – TOTEM Inel. Xsec. and fwd Part. Multip MPI 2012 – Dec. 3, 2012
Inelastic Cross Section @ 7 TeV: Other Meas. inel = tot – el (see J. Kašpar talk for σ el and σ tot measurements) = 0.141 0.007 (I) CMS L + Elastic Scattering + Optical Theorem (Compete) depends on CMS luminosity , elastic efficiencies & ρ : no depenence on low mass diffraction (small L bunches, * = 90 m, |t| min 2 10 -2 GeV 2 ): σ inel = 73.5 1.6 mb EPL 96 (2011) 21002 (large L bunches, * = 90 m, |t| min 5 10 -3 GeV 2 ): σ inel = 73.2 1.3 mb CERN-PH-EP-2012-239 (II) ( L L -independent): Elastic Scattering + Inelastic Scattering + Optical Theorem eliminates dependence on luminosity, depends on & low mass diffraction models σ inel = 72.9 1.5 mb CERN-PH-EP-2012-353 using L- and -independent ratio: σ el / σ inel = N el / N inel = 0.354 0.009 9/20 G. Latino – TOTEM Inel. Xsec. and fwd Part. Multip MPI 2012 – Dec. 3, 2012
Inelastic Cross Section @ 7 TeV: Summary (CERN-PH-EP-2012-353) Excellent agreement among measurements: - with different methods (understanding of systematic uncertainties and corrections) - with other LHC experiments 10/20 G. Latino – TOTEM Inel. Xsec. and fwd Part. Multip MPI 2012 – Dec. 3, 2012
Inelastic Cross Section @ 8 TeV: Results July 2012: runs at * * = 90 m Same analysis strategy as for the measurement @ 7 TeV L – independent with the L “method II”: - tot = 101.7 2.9 mb - N el / N inel = 0.362 0.011 inel = 74.7 1.7 mb Paper draft approved for submission to journal 11/20 G. Latino – TOTEM Inel. Xsec. and fwd Part. Multip MPI 2012 – Dec. 3, 2012
Charged Particle Pseudo-Rapidity Density (dN ch /d ) @ 7 TeV May 2011 run, * * = 3.5 m, low pile-up ( 0.03) x T2 alignment IP - Internal alignment z two different track-based methods (HIP and Millepede) implemented in order to resolve misalignment (x-, y-shifts) among detectors in a quarter - Quarter-quarter alignment using tracks in the overlap region - Global alignment each arm aligned (tilts and shifts) respect to the nominal position by imposing the symmetry of the “beam pipe shadow” on each detector plane Final precision achieved: ~ 1 mm (x,y-shifts); ~ 0.4 mrad (plane tilts) 12/20 G. Latino – TOTEM Inel. Xsec. and fwd Part. Multip MPI 2012 – Dec. 3, 2012
dN ch /d in T2: Analysis Highlights Data sample: events at low luminosity and low pile-up, triggered with T2 ( 5.3 < | | < 6.5 ) Selection: at least one track reconstructed in T2 Primary particle definition: charged particle with > 0.3 10 -10 s, p T > 40 MeV/c Primary particle selection: -primary/secondary discrimination, data-driven based on reconstructed track parameters (Z Impact ) Primary track reconstruction efficiency: - evaluated as a function of the track and pad multiplicity, MC-based - efficiency of 80% - fraction of primary tracks within the cuts of 75% – 90% ( dependent) Un-folding of ( ) resolution effects: MC driven bin “migration” corrections Systematic uncertainties (< 10%): dominated by primary track efficiency and global alignment correction uncertainty 13/20 G. Latino – TOTEM Inel. Xsec. and fwd Part. Multip MPI 2012 – Dec. 3, 2012
Secondary Particles in T2 Track reconstruction in T2 is 90% (80% ) of the challenging because of the large amount of charged signal (tracks) in particles generated by the T2 is given by interaction with the material secondaries placed between the IP and T2 A detailed revision of the volumes and of the GEANT setting was necessary HF IP HF T2 telescope Effect of the BP on the hit didtribution Material contributing to secondary particle generation: Left: BP flange and ion-pumps. Right: BP cone at =5.53 and the lower edge of HF 14/20 G. Latino – TOTEM Inel. Xsec. and fwd Part. Multip MPI 2012 – Dec. 3, 2012
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