Neutral pion cross section and spin asymmetries at intermediate pseudorapidity in polarized proton collisions at root s=200 GeV

Adamczyk, L.; Adkins, J. K.; Agakishiev, G.; Aggarwal, M. M.; Ahammed, Z.; Alekseev, I.; Alford, J.; Anson, C. D.; Aparin, A.; Arkhipkin, D.; Aschenauer, E. C.; Averichev, G. S.; Balewski, J.; Banerjee, A.; Barber, B.; Barnovska, Z.; Beavis, D. R.; Bellwied, R.; Betancourt, M. J.; Bhasin, A.; Bhati, A. K.; Bhattarai, P.; Bichsel, H.; Bielcik, J.; Bielcikova, J.; Bland, L. C.; Bordyuzhin, I. G.; Borowski, W.; Bouchet, J.; Brandin, A. V.; Bridgeman, A.; Brovko, S. G.; Bultmann, S.; Bunzarov, I.; Burton, T. P.; Butterworth, J.; Caines, H.; Sanchez, M. C. D.; Cebra, D.; Cendejas, R.; Cervantes, M. C.; Chaloupka, P.; Chang, Z.; Chattopadhyay, S.; Chen, H. F.; Chen, J. H.; Chen, L.; Cheng, J.; Cherney, M.; Chikanian, A.; Christie, W.; Chwastowski, J.; Codrington, M. J. M.; Corliss, R.; Cramer, J. G.; Crawford, H. J.; Cui, X.; Das, S.; Leyva, A. D.; De Silva, L. C.; Debbe, R. R.; Dedovich, T. G.; Deng, J.; Derevschikov, A. A.; de Souza, R. D.; Dhamija, S.; di Ruzza, B.; Didenko, L.; Dilks, C.; Ding, F.; Dion, A.; Djawotho, P.; Dong, X.; Drachenberg, J. L.; Draper, J. E.; C. M., Du; Dunkelberger, L. E.; Dunlop, J. C.; Efimov, L. G.; Engelage, J.; Engle, K. S.; Eppley, G.; Eun, L.; Evdokimov, O.; Fatemi, R.; Fazio, S.; Fedorisin, J.; Fersch, R. G.; Filip, P.; Finch, E.; Fisyak, Y.; Flores, C. E.; Gagliardi, C. A.; Gangadharan, D. R.; Garand, D.; Geurts, F.; Gibson, A.; Girard, M.; Gliske, S.; Grosnick, D.; Guo, Y.; Gupta, A.; Gupta, S.; Guryn, W.; Haag, B.; Hajkova, O.; Hamed, A.; Han, L. X.; Haque, R.; Harris, J. W.; Hays-Wehle, J. P.; He, W.; Heppelmann, S.; Hirsch, A.; Hoffmann, G. W.; Hofman, D. J.; Horvat, S.; Huang, B.; Huang, H. Z.; Huck, P.; Humanic, T. J.; Igo, G.; Jacobs, W. W.; Jang, H.; Jena, C.; Judd, E. G.; Kabana, S.; Kalinkin, D.; Kang, K.; Kauder, K.; H. W., Ke; Keane, D.; Kechechyan, A.; Kesich, A.; Khan, Z. H.; Kikola, D. P.; Kisel, I.; Kisiel, A.; Koetke, D. D.; Kollegger, T.; Konzer, J.; Koralt, I.; Korsch, W.; Kotchenda, L.; Kravtsov, P.; Krueger, K.; Kulakov, I.; Kumar, L.; Kycia, R. A.; Lamont, M. A. C.; Landgraf, J. M.; Landry, K. D.; Lauret, J.; Lebedev, A.; Lednicky, R.; Lee, J. H.; Leight, W.; Levine, M. J.; Li, C.; Li, W.; Li, X.; Li, Y.; Z. M., Li; Lima, L. M.; Lisa, M. A.; Liu, F.; Ljubicic, T.; Llope, W. J.; Longacre, R. S.; Luo, X.; G. L., Ma; Y. G., Ma; Don, Dmmdm; Mahapatra, D. P.; Majka, R.; Manweiler, R.; Margetis, S.; Markert, C.; Masui, H.; Matis, H. S.; Mcdonald, D.; Mcshane, T. S.; Minaev, N. G.; Mioduszewski, S.; Mohanty, B.; Mondal, M. M.; Morozov, D. A.; Munhoz, M. G.; Mustafa, M. K.; Naglis, M.; Nandi, B. K.; Nasim, M.; Nayak, T. K.; Nelson, J. M.; Nogach, L. V.; Noh, S. Y.; Nord, P. M.; Novak, J.; Nurushev, S. B.; Odyniec, G.; Ogawa, A.; Oh, K.; Ohlson, A.; Okorokov, V.; Oldag, E. W.; Oliveira, R. A. N.; Olson, D.; Pachr, M.; Page, B. S.; Pal, S. K.; Pan, Y. X.; Pandit, Y.; Panebratsev, Y.; Pawlak, T.; Pawlik, B.; Pei, H.; Perkins, C.; Peryt, W.; Peterson, A.; Pile, P.; Planinic, M.; Pluta, J.; Plyku, D.; Pochron, W.; Poljak, N.; Porter, J.; Poskanzer, A. M.; Powell, C. B.; Pruneau, C.; Pruthi, N. K.; Przybycien, M.; Pujahari, P. R.; Putschke, J.; Qiu, H.; Ramachandran, S.; Raniwala, R.; Raniwala, S.; Ray, R. L.; Riley, C. K.; Ritter, H. G.; Roberts, J. B.; Rogachevskiy, O. V.; Romero, J. L.; Ross, J. F.; Roy, A.; Ruan, L.; Rusnak, J.; Sahoo, N. R.; Sahu, P. K.; Sakrejda, I.; Salur, S.; Sandacz, A.; Sandweiss, J.; Sangaline, E.; Sarkar, A.; Schambach, J.; Scharenberg, R. P.; Schaub, J.; Schmah, A. M.; Schmidke, W. B.; Schmitz, N.; Seger, J.; Selyuzhenkov, I.; Seyboth, P.; Shah, N.; Shahaliev, E.; Shanmuganathan, P. V.; Shao, M.; Sharma, B.; Shen, W. Q.; Shi, S. S.; Shou, Q. Y.

doi:10.1103/PhysRevD.89.012001

The differential cross section and spin asymmetries for neutral pions produced within the intermediate pseudorapidity range 0.8<2.0 in polarized proton-proton collisions at s=200 GeV are presented. Neutral pions were detected using the end cap electromagnetic calorimeter in the STAR detector at RHIC. The cross section was measured over a transverse momentum range of 5<16 GeV/c and is found to agree with a next-to-leading order perturbative QCD calculation. The longitudinal double-spin asymmetry ALL is measured in the same pseudorapidity range and spans a range of Bjorken- x down to x≈0.01 . The measured ALL is consistent with model predictions for varying degrees of gluon polarization. The parity-violating asymmetry AL is also measured and found to be consistent with zero. The transverse single-spin asymmetry AN is measured over a previously unexplored kinematic range in Feynman- x and pT . Such measurements may aid our understanding of the onset and kinematic dependence of the large asymmetries observed at more forward pseudorapidity ( η≈3 ) and their underlying mechanisms. The AN results presented are consistent with a twist-3 model prediction of a small asymmetry over the present kinematic range.