dN/d  and dN/dp T analysis status Gabor Veres for the working group QCD meeting, Jan 12, 2010

Developments since preapproval Studies on Zero Bias data, trig. eff. measurements Changed trigger/event selection strategy Using 20 times more statistics for 900 GeV data Results at the world-record collision energy, 2.36TeV Decreasing systematic errors for the trigger-related uncertainty, looking at the SD fraction in data

BSC: MC simhits, new measurement. Inner segments: arc-shape is true Outer paddles: ~OK, only 2% loss Overall: (31*0.72+2*0.28)=~23% hit loss w.r.t CMSSW

Trigger efficiencies Without any other event selection, 900 GeV PYTHIA. Very little change NEWold / /

Crosstalk, conversions There is NO insulation between the two outer channels in one paddle. This can cause bit 41 fire more often, even on a single hit Al: inner: 2-4 mm, outer: 2 mm Scintillator thickness: 10 mm, also incorrect in CMSSW (13 mm) Photon conversion: 5-10% probability in the Al

Trigger: Zero Bias study Run Paired beam bunches: 151 || 2824 Pixel – vertex compatibility cut Valid vtx: 495 events Full collision definition: 402 events

Collision selection Select events with valid vertex as collision events Clean event selection Min bias Zero bias

‘Trigger’ rates Check “Trigger” rates relative to events with valid vertex to measure efficiency from data BSC: bits 34, 40, 41 HF Tower Count above threshold: One Hit OR, One Hit Coinc., Two Hit Coinc.

‘Trigger’ efficiencies Trigger Efficiency relative to events with valid vertex MC reference: Pythia D6T, default SD fraction HF Trigger is very well described by MC: Efficiency as well as Threshold ratios Efficiencies Ratios

New Trigger/online selection The BSC bit 34 efficiency is >98% (after requiring a vertex) Strategy: analyze Min Bias data (triggered by BSC bit34), and select on HF One Hit Coincidence [instead of bit 40] dNdEta results agree within 1% at when comparing the BSC and HF event selection

Changing from BSC to HF ● Open Blue circle: results from paper (BSC 40) ● Red circle: Use HF Tower coincidence (# of tower > 3 GeV) threshold >= 1. ● Results from both trigger are consistent in 1% level.

PYTHIA PHOJET Fits to data: total diffractive fraction (SD+DD) BSC bit 34 + Vertex comp. cut Run GeV % Truth: 20.1% % Truth: 22.7% [Using the HF]

Diffractive component from data

SD and DD fraction uncertainty The trigger efficiencies for SD, DD, ND are 0.165, 0.306, The pythia fractions of SD, DD, ND are 0.23, 0.12, The inel trigger eff therefore is: 0.165* * *0.65 = 0.65 The SD fractions are: phojet: 21%, pythia: 23%, UA5: 15.3% The DD fractions are: phojet: 8%, pythia: 12%, UA5: 8% I.e. taking the largest spread, we get +-4% for SD and +-2% for DD. How much change does this cause in dN/deta? SD: +-4% in the fraction means: 0.04*0.165/0.65 = 1.0% change in dN/deta DD: +-2% in the fraction means: 0.02*0.306/0.65 = 1.0% change in dN/deta Underestimated SD and DD both leads to too small dN/deta. We can be conservative and add them linearly to get the full error: = 2.0%

Pixel cluster charge distributions 900 GeV 2.36 TeV Good agreement with MC

Pixel cluster charge distributions 900 GeV 2.36 TeV Good agreement with MC

Angle corrected cluster charge Distribution of the pixel cluster charge corrected by η in layer 1 Apply common event selection on MC and data 900 GeV 2.36 TeV

Cluster size distributions 900 GeV 2.36 TeV

Cluster counting results 900 GeV 2.36 TeV

Tracklets: 900 GeV x-check Use Run Lumi section Applied the same event selection. 40K events passed our selection criteria. Use MC sample corresponds to Run with the correct beam spot. The results are consistent with Run

Tracklets: 2.36 TeV Use Run (2.36 TeV), applied the same event selection. ~11K events passed our selection criteria. Corrected by PYTHIA 2.36 TeV D6T sample with correct beam spot.

dN/deta vs root(s)

Tracking 900 GeV (other run + higher statistics) Run (the standard) Run , newly added (red colored points and lines) 2.36 TeV (new): Run Mean pT = 0.51 GeV/c with similar errors as 900 GeV

900 GeV: more statistics

Tracking: 900 GeV more statistics

Tracking: 2.36 TeV

2.36 TeV: comparison of methods

Mean p T vs root(s)

Summary Successful winter-break, active work Extension of the paper, 16 pages now Large part of comments addressed Approval session: tomorrow, CMS plenary