1. Validation for PythiaVPhoton10 Jiahang Zhong (Academia Sinica)

2. 2015-12-15DTY bi-weekly meeting, J. Zhong2 Motivation  W/Zinclusive (5104/5105/5144/5145) were chosen as background samples, in which Pt>25GeV Photons are rare. (110/500,000)  Have more phase space for cuts.  In Pythia, VPhoton processes are singular in the limit Pt->0, hence Pt should not be too small.

3. 2015-12-15DTY bi-weekly meeting, J. Zhong3 Z  Cross Section Table (Electron) unit [pb] Baur’s Generator PYTHIA Zinclusive PYTHIA ZGamma25 PYTHIA ZGamma10 Electron Channel s(FSR) [PT(g) > 5GeV & Mee > 40 GeV] 209193.3 s(FSR) [PT(g) > 10GeV & Mee > 40 GeV] 110.1104.4 s(FSR) [PT(g) > 15GeV & Mee > 40 GeV] 62.261.1 s(FSR) [PT(g) > 25GeV & Mee > 40 GeV] 17.220.7 s(ISR) [PT(g) > 5GeV & Mee > 40 GeV] 8.611.5 s(ISR) [PT(g) > 10GeV & Mee > 40 GeV] 4.236.343.90 s(ISR) [PT(g) > 15GeV & Mee > 40 GeV] 2.53.72.64 s(ISR) [PT(g) > 25GeV & Mee > 40 GeV] 1.141.541.011.28

4. 2015-12-15DTY bi-weekly meeting, J. Zhong4 Z  Plots (Electron) Normalized from 25~200 GeVNormalized from 10~200 GeV FSR ISR

5. 2015-12-15DTY bi-weekly meeting, J. Zhong5 W  Cross Section Table (Electron) unit [pb] Baur’s Generator (W + g) Baur’s Generator (W - g) PYTHIA Winclusive (W + g) PYTHIA Winclusive (W - g) PYTHIA WGamma25 (W + g) PYTHIA WGamma25 (W - g) PYTHIA WGamma10 (W + g) PYTHIA WGamma10 (W - g) Electron Channel s(FSR) PT(g)>5GeV600431585412 s(FSR) PT(g)>10GeV327.8235.8323.0225.2 s(FSR) PT(g)>15GeV194.0137.8196.4134.9 s(FSR) PT(g)>25GeV62.144.474.447.9 s(ISR) PT(g)>5GeV52376452 s(ISR) PT(g)>10GeV17.512.034.328.89.66.5 s(ISR) PT(g)>15GeV8.835.9720.716.96.294.37 s(ISR) PT(g)>25GeV3.182.178.796.912.101.362.922.06

6. 2015-12-15DTY bi-weekly meeting, J. Zhong6 W  Plots (Electron) Normalized from 25~200 GeVNormalized from 10~200 GeV ISR FSR

7. 2015-12-15DTY bi-weekly meeting, J. Zhong7 Control Tags for a new sample  In pythia, adjust PYSUBS-CKIN3 from 25 to 10. CKIN3: Pt lower limit in the rest frame of hard interaction.  In GeneratorFilter, adjust PhotonFilter.Ptcut from 25000 to 10000. PhotonFilter.Ptcut: (GenStat==1&&Pt>25GeV) photon in pythia output  In additional, PhotonFilter requests Photon Eta<2.7.  All 3 leptonic decay channels are turned on.

8. 2015-12-15DTY bi-weekly meeting, J. Zhong8 Cross Section Comparison applied selection cuts  Two cuts are used to select Pt>25GeV events from VPhoton10 samples.  #1 Lab frame Pt Cut (as Generator Filter)  Require Type==22 & GenStat==1 & Pt>25GeV  With-filter samples only  #2 W+Gamma Rest frame Pt cut (as CKIN3)  KOriVNt==4 & GenStat==3  Boost 2 particles to their CM frame  After boost, require Pt>25GeV  For samples with filter, both cuts are used For samples without filter, only cut #2 are applied

9. 2015-12-15DTY bi-weekly meeting, J. Zhong9 Cross Section Comparison WGamma  Both Filtered and Non- Filter samples are tested.  Non-100% selection for WPhoton25 samples indicates problem with CKIN3 definition  Similar discrepancy observed among the comparison between 10GeV/25GeV/40GeV no-filter samples with cut on 40GeV  Zgamma has same discrepancy WPhoton25WPhoton10 With Filter Cut #1 & #2 No Filter Cut #2 With Filter Cut #1 & #2 No Filter Cut #2 σ(total) 7.41pb11.5pb32.8pb52.3pb Cut efficiency 96.5%91.0%27.7%28.3% σ(output) 7.2pb10.5pb9.1pb14.7pb

10. 2015-12-15DTY bi-weekly meeting, J. Zhong10 Cross Section Comparison CKIN3 comparison  Log histogram for CKIN3 value (Photon Pt in rest frame) Tails below cuts imply distortion of original kinematics.  WPhoton25 histogram is normalized to WPhoton10’s scale Visible different slopes responsible for cross- section shift

11. 2015-12-15DTY bi-weekly meeting, J. Zhong11 Meaning of CKIN3 discussion in MC hyper news (1)  Inspiring discussion in the MC generators HN, still undergoing… https://hypernews.cern.ch/HyperNews/Atlas/get/Generators/60.html https://hypernews.cern.ch/HyperNews/Atlas/get/Generators/60.html  First suggestions to play with MSTP 61 & 91 tags. Correction as underlying events, rather than switch for our ISR hard process  MSTP 61: ISR switch. Default=2 as on. Switch to 0 as off. Correction as underlying events, rather than switch for our ISR hard process Gaussian distribution with peak around ~400MeV  MSTP 91: Primordial Kt distribution of parton in protons. Default=1 as Gaussian dist. Switch to 0 as no Kt correction. Gaussian distribution with peak around ~400MeV  These MSTP parameters are corrections happened after “hard process”. While CKIN3 is cut in the “hard process”

12. 2015-12-15DTY bi-weekly meeting, J. Zhong12 Meaning of CKIN3 discussion in MC hyper news (cont. 2)  Cross section not changed by these corrections.  The tail was eliminated mainly by switching off ISR  Less significant effect from Kt dist.  Even output file size will be reduced by stop ISR. MSTP61=0 & MSTP91=0 MSTP61=d & MSTP91=d MSTP61=0 & MSTP91=d MSTP61=d & MSTP91=0

13. 2015-12-15DTY bi-weekly meeting, J. Zhong13 Meaning of CKIN3 discussion in MC hyper news (cont. 3)  The four momentum of incoming and outgoing particles are not conserved.  KEndVNt==4 as incoming particles, 1 & 2  KOriVNt==4 as outgoing particles, 3 & 4  Boost particle 3&4 (Z+gamma) to the 1+2 (incoming quarks) rest frame.  Plot entries over ln[Pt(Z+gamma)]  A peak around 6, namely ~400MeV  Broad distribution up to hundreds GeV.

14. 2015-12-15DTY bi-weekly meeting, J. Zhong14 Meaning of CKIN3 discussion in MC hyper news (cont. 4)  In the rest frame of incoming quarks and gluons, Pt of W+gamma has a distribution, rather than flat zero if four momentum are conserved  The peak is at ~400MeV, which is around the peak of Kt distribution correction.  Indicates inconsistency of data documentation between incoming and outgoing particles, in different stages (before or after Kt dist. correction)  There was similar report earlier in generator HN.  This may be the reason of CKIN3 shift. Athena Generator group will investigate into it.

15. 2015-12-15DTY bi-weekly meeting, J. Zhong15 Further discussion ISR in hard/soft process  In our attempt, we turned off the ISR switch. And the cross- section didn’t have noticeable deviation.  Though in physics, this ISR as correction is the same Feynman diagram as our ISR process (t-channel of VPhoton), in Pythia they are two different conceptions.  Maybe it’s more exact to turn off the ISR switch for our ISR hard process  Is there some potential trouble by comparing the hard process ISR in VPhoton and the soft ISR correction in V- inclusive samples?

16. 2015-12-15DTY bi-weekly meeting, J. Zhong16 Validation in Version 13  No support in version12 for new sample validation anymore.  Need version 13, which use latest Pythia version  Test run with transformation is successful in a local installation  Joboption to convert EVNT into CBNT has failed. Need to find a solution

17. 2015-12-15DTY bi-weekly meeting, J. Zhong17 Conclusion  Lower Pt cut can give more phase space for study.  Comparison of the cross-section reveals discrepancy with cross- section, and further questions that we omitted before.  Pythia_i need to be investigated, especially data documentation needs some check.  Need more understanding of how generator works, rather than use everything as a black box.