Update on Diffractive Dijet Production Search Hardeep Bansil University of Birmingham 23/07/2012

Reconstructing ξ Proper way to calculate ξ can be done in Pomwig by looking at proton & pomeron Can calculate M X from invariant mass then convert to ξ (= M X 2 /s) Truth level: all final state particles excluding intact proton (if there is one in event) Reconstructed level: all caloClusters (not just above significance thresholds) Also calculate ξ using E±p z method (C=1 for truth, determine for data) Base choice on position of where forward gap starts using gap algorithm – Gap start at -4.9 use ξ- and gap start at +4.9 use ξ+ 2 Largest rapidity gap between truth particles MYMY MXMX ~

Reconstructing ξ Pomwig comparison (generator cut at ξ < 0.1) – all gap & jet (R=0.6) cuts applied Want to calculate C based on resolution of Truth log 10 (ξ) v Recon log 10 (ξ) See truth ξ > 0.1 meaning largest gap not always between intact proton and other particles in an event 3 Truth ξ v Reconstructed ξ using E+Pz method Truth ξ v Truth ξ using E+Pz method ~ ~~

Reconstructing z IP Can determine the actual value of z IP with Pomwig generator using pomeron and parton emitted by it (= p z[Parton] /p z[Pomeron] ) Notably found events in Pomwig at generator level where z IP was less than 0 (should be 0 < z IP < 1) – typically for jets generated between 8-17 GeV Use following approximations based on starting position of forward gap – Done with anti- k T jets R = 0.4 & M jj MxMx ξX ξX

Reconstructing z IP Pomwig studies - all gap & jet (R=0.6) cuts applied Actual truth z IP suggests that we can go between 0.01 < z IP < 1 with cuts applied Observe tail in truth z IP going out much further – Denominator (E±pz) X shows truth level events where (E±pz) X = 7 TeV due to gap algorithm picking out wrong side for gap start using particles in [-4.9,4.9] compared to intact proton direction Got similar behaviour in Pythia 8 5 Truth z IP v Reconstructed z IP using E+Pz method Truth z IP v Truth z IP using E+Pz method ~

MBTS Activity If we have gap size of 3.0, would expect little to zero activity in the MBTS counters on the same side of the detector that gap started in – Potentially more in outer ring of counters (2.09<|η|<2.82) – Much less in inner ring of counters (2.82<|η|<3.84) Means MBTS could help in selecting events with large gaps 6 Most events still have gap size > 3.0 after pt cuts loosened but around 100 do not Looking in η ranges of MBTS rings for tracks and caloClusters Can see some low pt tracks in region of outer MBTS ring In both rings, see caloClusters in LAr that are lower than pt cut or have low Esig or both

MBTS Activity Still get events where more than 4 counters are fired based on a gap of 3.0 Gap algorithm requires pt cuts on clusters and tracks so what happens to gap size when these cuts are removed (interesting as we do not require pt cuts for ξ & z IP ) Smaller statistics of events with no p T requirement but show fewer activity in MBTS counters 7 Standard gap algorithm Gap algorithm with low pt objects MBTS Counters Fired in Combined Rings – Pomwig with Gap & Jet cuts

Systematics Started putting systematics into analysis – Jet Energy Scale (for 2010 data) – Jet Energy Resolution (for 2010 data) – Gap Energy Scale (clusters) – Gap Threshold Cut Uncertainty – MC Unfolding Uncertainty – Trigger – Tracking – Luminosity – Pile-up – Additional Material Others still to be considered 8

Backgrounds Look at data sample (2010 Periods A & B) again using unpaired bunches e.g. for beam gas – Using MBTS_1_UNPAIRED & MBTS_2_UNPAIRED triggers rather than jet or regular MBTS triggers Found 3 events passing cuts with non-zero gap size Scale background based on unassociated Pixel hits between unpaired beams and paired beams as in Soft Diffractive analysis Or based on trigger rates for UNPAIRED to PAIRED triggers 9

New cross section definition Rather than looking mainly at, now want to focus on using diffractive variables and Make new definition, for SD & DD (M Y < “7 GeV”) Truth Level – Largest gap anywhere, Jets, ξ X < Recon Level – Forward gap > 3, Jets, (ξ X < ?) removing pt requirements 10

Next steps Continue to develop systematics & cross section calculation (now including backgrounds) Fine-tune ξ and z IP calculation for SD & ND samples Understand why Pomwig produces events with z IP < 0 and see if this occurs in Herwig++ Work more on proposed cuts for event selection/new cross section definition 11

Back up slides

Variables to add to Ntuples for LB, Peak etc. to keep track of pile-up for systematics Unassociated pixel hits for background studies Jets  rapidity for systematics Others (not as important) MBTS counters fired in separate rings Track author, track particle origin type 13